SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
IDENTIFICATION OF PBT AND vPvB SUBSTANCE
RESULTS OF EVALUATION OF PBT / vPvB PROPERTIES
This dossier covers three substances manufactured and supplied as detailed below.
Substance name:
Dioctyltin dichloride
EINECS number: 222-583-2
EINECS name:
Dichlorodioctylstannane
CAS number:
3542-36-7
Registration number(s): 05-2114350016-61
Molecular formula: C16H34Cl2Sn
Structural formula:
Composition:
mono-constituent product 94.5 – 100 per cent dioctyltin dichloride;
(typically 96.04 per cent dioctyltin dichloride; impurities 3.05 per cent octyltin
trichloride, 0.68 per cent trioctyltin chloride, 0.23 per cent hexadecane) (JS Organotin
Consortium REACH registration, 2010).
Substance name:
EINECS number:
EINECS name:
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
239-622-4
2-Ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia-4stannatetradecanoate
CAS number:
15571-58-1
Registration number(s): 05-2114362069-46
Molecular formula: C36H72O4S2Sn
Structural formula:
1
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Composition:
multi-constituent product 67 – 76 per cent dioctyltin bis(2ethylhexyl mercaptoacetate); 24 – 33 per cent octyltin tris(2ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl
mercaptoacetate, 0 – 0.3 per cent 2-ethylhexan-1-ol (Organotin
Consortium REACH registration, 2010)
Substance name:
Octyltin tris(2-ethylhexyl mercaptoacetate)
EINECS number: 248-227-6
EINECS name:
2-Ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4octyl-7-oxo-8-oxa-3,5-dithia-4-stannatetradecanoate
CAS number:
27107-89-7
Registration number(s): 05-2114085657-35
Molecular formula: C38H74O6S3Sn
Structural formula:
Composition: marketed mono-constituent product 99.7 – 100 per cent octyltin tris(2ethylhexyl mercaptoacetate); impurities 0 – 0.3 per cent dioctyltin bis(2-ethylhexyl
mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1-ol; 0 – 1 per cent 2-ethylhexyl
mercaptoacetate
marketed multi-constituent products 60 – 68 per cent octyltin tris(2-ethylhexyl
mercaptoacetate); 30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate);
impurities 0 – 2 per cent 2,2-dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2ethylhexyl mercaptoacetate, 0 – 1 per cent 2-ethylhexan-1-ol (Joint REACH
registration, 2010).
Summary of how the substances meet the CMR (Cat 1 or 2), PBT or vPvB criteria, or
are considered to be substances of an equivalent level of concern
In line with REACH Article 13.1 and Annex XI this evaluation is made taking into account
the data available for dioctyl tin and monooctyl tin derivatives using a grouping and readacross approach. This evaluation considers bioaccumulation and other data submitted by
2
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Industry in response to Commission Regulation 465/2008. The grouping and read-across
approach is justified on the basis that dioctyltin dichloride, dioctyltin bis(2-ethylhexyl
mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are rapidly hydrolysed to
common or structurally similar intermediate products (either dioctyltin hydroxide/oxide or
octyltin hydroxide/oxide) and that these hydrolysis products are the environmentally relevant
form of the substance. Furthermore, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin
tris(2-ethylhexyl mercaptoacetate) are generally supplied as multi-constituent products that
can contain a high concentration of both substances.
Overall it is concluded that the three substances considered, dioctyltin dichloride, dioctyltin
bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) do not meet
the PBT or vPvB criteria. Although they are considered to be potentially persistent (in that
they do not biodegrade rapidly but rather hydrolyse rapidly to either dioctyltin
hydroxide/oxide or octyltin hydroxide/oxide that are themselves potentially persistent) and
toxic, the available evidence suggests that the substances and hydrolysis products do not meet
the Annex XIII criteria for bioaccumulation.
Carrying out aquatic testing in general for these substances is difficult owing to their poor
solubility, rapid hydrolysis, and difficulties with their analysis. In particular, conducting a
fish bioconcentration test for these substances is technically challenging owing to the rapid
hydrolysis and the lack of analytical methodology to allow determination of the individual
substances present to which organisms are exposed. This results in the following
uncertainties in the B-assessment:
•
The individual substances actually present in solution are not known; it was possible
only to measure concentrations on the basis of total tin or total mono- and dioctyltin
species. This would be important if the observed uptake was the result of exposure to
a minor component in water (for example if the accumulative component made up
only a small fraction of the total mono- or dioctyltin compounds present in the test
medium). In such a case, the actual BCF for the individual substance may be higher
than that determined based on the total tin, total mono- or total dioctyltin compounds.
The analytical difficulties mean that it is not technically possible to investigate further
whether or not this is the case.
•
The available data do not provide any information on the accumulation of the
monooctyltin compound or its degradation products. Based on read-across, it can be
expected that the bioaccumulation potential of the octyltin hydroxide/oxide
hydrolysis products would be similar to (or possibly even lower than) that of the
dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty
in the overall evaluation.
•
The lack of a definitive hydrolysis rate for the test substance is important in relation
to the bioconcentration test, if hydrolysis had actually been much slower than has
been concluded from the available data. In this case, conclusions about the
bioaccumulation potential of the hydrolysis products could not be drawn from this
study. Again, the analytical difficulties mean that it is not technically possible
currently to investigate further whether or not this is the case. Further evaluation of
the oxide could be warranted if, in the future, more definitive hydrolysis data
suggested that the test substance was more stable than concluded here.
3
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Hydrolysis of both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl
mercaptoacetate) would also result in formation of 2-ethylhexyl mercaptoacetate. This
substance is not considered to meet the PBT criteria as it has a low predicted BCF.
4
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Contents
1
Identification of the Substance and physical and chemical properties ..............................7
1.1
Name and other identifier of the substance.................................................................7
1.2
Composition of the substances..................................................................................10
1.3
Physico-chemical properties .....................................................................................14
2
Manufacture and uses ......................................................................................................17
3
Classification and labelling..............................................................................................17
4
Environmental fate properties..........................................................................................20
4.1
Degradation ...............................................................................................................21
4.1.1
Abiotic degradation............................................................................................21
4.1.2
Biotic degradation..............................................................................................24
4.1.3
Summary and discussion of persistence ............................................................26
4.2
Environmental distribution........................................................................................27
4.2.1
Adsorption..........................................................................................................27
4.2.2
Distribution modelling .......................................................................................27
4.2.3
Other information...............................................................................................28
4.2.4
Summary of environmental distribution ............................................................28
4.3
Bioaccumulation........................................................................................................28
4.3.1
Screening data....................................................................................................28
4.3.2
Measured bioaccumulation data ........................................................................30
4.3.3
Other supporting information ............................................................................35
4.3.4
Summary and discussion of bioaccumulation....................................................35
4.4
Secondary poisoning .................................................................................................37
5
Human health hazard assessment.....................................................................................38
6
Human health hazard assessment of physicochemical properties ...................................39
7
Environmental hazard assessment ...................................................................................39
7.1
Aquatic compartment (including sediment)..............................................................39
7.1.1
Toxicity test results ............................................................................................39
7.1.2
Fish.....................................................................................................................39
7.1.3
Aquatic invertebrates .........................................................................................41
5
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
8
7.1.4
Algae and aquatic plants ....................................................................................43
7.1.5
Quantitative structure-activity relationships (QSARs) ......................................45
7.1.6
Sediment organisms ...........................................................................................45
7.1.7
Other aquatic organisms ....................................................................................45
7.1.8
Summary of aquatic toxicity data ......................................................................45
PBT and VPVB .................................................................................................................49
8.1
Comparison with criteria from Annex XIII...............................................................49
8.2
Assessment of substances of an equivalent level of concern ....................................51
8.3
Emission characterisation..........................................................................................51
8.4
Conclusion of PBT and vPvB or equivalent level of concern assessment................51
6
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
JUSTIFICATION
Note: Most of the data for dioctyltin and monooctyltin compounds have been reviewed and
internationally agreed previously under the OECD HPV programme (OECD, 2006a and
2006b). The three substances subject to this assessment have been registered under REACH
and non-confidential information not found in the OECD assessment from these registration
dossiers has been used in this assessment. Where information has been found to conflict, that
presented in the REACH registration has been used as it is understood this is more relevant
for the EU.
1
IDENTIFICATION OF THE SUBSTANCE AND PHYSICAL AND
CHEMICAL PROPERTIES
1.1
Name and other identifier of the substance
Name:
EC Number:
CAS Number:
IUPAC Name:
Molecular Formula:
Structural Formula:
Dioctyltin dichloride
222-583-2
3542-36-7
Stannane, dichlorodioctylC16H34Cl2Sn
Molecular Weight:
Synonyms (and
registered trade names):
416.04 g/mol
Dichlorodioctylstannane
Name:
EC Number:
CAS Number:
IUPAC Name:
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
239-622-4
15571-58-1
8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4-4dioctyl-7-oxo-, 2-ethylhexyl ester
C36H72O4S2Sn
Molecular Formula:
Structural Formula:
7
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Molecular Weight:
Synonyms (and
registered trade names):
751.8
Dioctyltin bis(2-ethylhexyl thioglycolate)
2-Ethylhexyl 10-ethyl-4,4-dioctyl-7-oxo-8-oxa-3,5-dithia4-stannatetradecanoate
Name:
EC Number:
CAS Number:
IUPAC Name:
Octyltin tris(2-ethylhexyl mercaptoacetate)
248-227-6
27107-89-7
8-Oxa-3,5-dithia-4-stannatetradecanoic acid, 10-ethyl-4[[2-[(2-ethylhexyl)oxy]-2-oxoethyl]thio]-4-octyl-7-oxo, 2ethylhexyl ester
C38H74O6S3Sn
Molecular Formula:
Structural Formula:
Molecular Weight:
Synonyms (and
registered trade names):
841.9 g/mol
Octyltin tris(2-ethylhexyl thioglycolate)
2-Ethylhexyl 10-ethyl-4-[[2-[(2-ethylhexyl)oxy]-2oxoethyl]thio]-4-octyl-7-oxo-8-oxa-3,5-dithia-4stannatetradecanoate
8
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
The report draws on information for these three substances, and information for the following
three related substances as appropriate.
•
Diisooctyl 2,2’-[(octylstannylidyne)bis(thio)]diacetate, also known as dioctyltin
bis(isooctyl mercaptoacetate) or dioctyl tin bis(isooctyl thioglycolate); CAS No
26401-97-8. This is a dioctyltin structural isomer of dioctyltin bis(2-ethylhexyl
mercaptoacetate).
•
Trichlorooctylstannane, also known as octyltin trichloride; CAS No 3091-25-6. This
is a monooctyl tin derivative.
•
Triisooctyl 2,2’2’’-[(octylstannylidyne)tris(thio)]triacetate, also known as octyltin
tri(isooctyl mercaptoacetate) or octyltin tri(isooctyl thioglycolate); CAS No 2640186-5. This is a monooctyl tin structural isomer of octyltin tris(2-ethylhexyl
mercaptoacetate)
9
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
As discussed in Section 1.2 the substance octyltin trichloride is particularly relevant for this
assessment as: a) it is present in substantial quantities in some commercially supplied
dioctyltin dichloride products and b) the commercially supplied octyltin trichloride products
will contain substantial amounts of dioctyltin dichloride. Therefore information on octyltin
trichloride in particular is included in the evaluation where relevant.
The two isooctyl thioglycolate derivatives are structural isomers of either dioctyltin bis(2ethylhexyl mercaptoacetate) or octyltin tris(2-ethylhexyl mercaptoacetate). The OECD
(2006a and 2006b) evaluations indicate that there is little actual experimental information
available relevant to the PBT assessment for these two isooctyl thioglycolate derivatives and
concludes that the information for either dioctyltin bis(2-ethylhexyl mercaptoacetate) or
octyltin tris(2-ethylhexyl mercaptoacetate) can be used interchangeably for these two isooctyl
thioglycolate derivatives, as the compounds produce the same dioctyl- or octyltin hydrolysis
products.
In line with REACH Article 13.1 and Annex XI this evaluation is made taking account of the
data available for dioctyltin and monooctyl tin derivatives using a grouping and read-across
approach. This grouping and read-across approach is justified on the basis that dioctyl tin
dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl
mercaptoacetate) are rapidly hydrolysed to common or structurally similar intermediate
products (either dioctyltin hydroxide/oxide or octyltin hydroxide/oxide) and these hydrolysis
products are the environmentally relevant form of the substance. Furthermore, dioctyltin
bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are
generally supplied as multi-constituent products that can contain a high concentration of both
substances.
1.2
Composition of the substances
The following information is taken from the respective OECD evaluations of the substances
(OECD, 2006a and 2006b) and the relevant REACH registrations. The information from the
two sources differs somewhat. The OECD assessment describes the substances as multiconstituent and gives a wide concentration range for the main component in each product.
The REACH registrations list the mono-constituent material and then possible marketed
multi-constituent products (that are covered by the registration of the mono-constituent
material) and give more information on impurities. For this assessment, the information from
the REACH registrations is more relevant as the latter should more accurately describe the
forms marketed in the EU.
Dioctyltin compounds
Dioctyltin dichloride
Commercially supplied dioctyltin dichloride always contains octyltin trichloride. According
to the REACH registration, the purity of the substance is 94.5 – 100 per cent. The
registrations include a composition containing 96.04 per cent dioctyltin dichloride, 3.05 per
cent octyltin trichloride, 0.68 per cent trioctyltin chloride and 0.23 per cent hexadecane, the
latter three substances listed as impurities (JS Organotin Consortium REACH registration,
2010).
10
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
According to the OECD assessment, the dioctyltin dichloride content of the commercially
supplied products varied between 10 per cent by weight to 99 per cent by weight, however
only the commercially supplied products with dioctyltin dichloride contents of 50 per cent or
more are considered to be dioctyltin dichloride products (products containing less than 50 per
cent of dioctyltin dichloride are considered to be octyltin trichloride products). In all products
the sum of dioctyltin dichloride, octyltin trichloride and other minor impurities (trioctyltin
chloride and tin tetrachloride) account for approximately 99.5 per cent of the manufactured
product by weight.
According to both sources, the commercially supplied products do not contain chemical
additives.
In summary, the composition of dioctyltin dichloride products in the EU is typically as
follows:
94.5 – 100 per cent dioctyltin dichloride; (e.g. 96.04 per cent dioctyltin dichloride; 3.05
per cent octyltin trichloride; 0.68 per cent trioctyltin chloride; 0.23 per cent
hexadecane).
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Dioctyltin bis(2-ethylhexyl mercaptoacetate) products always contain octyltin tris(2ethylhexyl mercaptoacetate). According to the REACH registration, they are only marketed
as multi-constituent products. Dioctyltin bis(2-ethylhexyl mercaptoacetate) is registered as a
(not marketed) mono-constituent material described as having a purity of ≥ 80 percent. Two
marketed products are included in the registration, containing
•
67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 24 – 33 per cent
octyltin tris(2-ethylhexyl mercaptoacetate), with impurities of 2.5 – 5.5 per cent 2,2dioctyl-1,3,2-oxathiastannolan-5-one (CAS 15535-79-2), 0 – 2 per cent 2ethylhexyl mercaptoacetate (CAS 7659-86-1) and 0 – 0.3 percent 2-ethylhexan-1-ol
(CAS 104-76-7);
•
30 – 35 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 60 – 68 per cent
octyltin tris(2-ethylhexyl mercaptoacetate), with impurities of 0 – 2 per cent 2,2dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate
and 0 – 1 per cent 2-ethylhexan-1-ol (Organotin Consortium REACH registration,
2010).
In this assessment, the latter is considered to be an octyltin tris(2-ethylhexyl mercaptoacetate)
product.
According to the OECD (2006a) assessment, the dioctyltin bis(2-ethylhexyl mercaptoacetate)
content of commercial products typically ranges from 20 per cent to 95 per cent. Only the
products with dioctyltin bis(2-ethylhexyl mercaptoacetate) contents of 50 per cent or more
are considered to be dioctyltin bis(2-ethylhexyl mercaptoacetate) products (those with
contents less than 50 per cent are considered octyltin tris(2-ethylhexyl mercaptoacetate)
products). Other trace impurities that may be present in the commercial products include
trioctyltin compounds (typically <0.2% calculated as tin), residual amounts of 2-ethylhexyl
mercaptoacetate, mono- and di-octyltin mercaptoacetate chlorides, or alkyl isomers such as
11
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
isooctyl or iso-hexadecyl groups bonded to tin (typically <0.5% calculated as tin (OECD,
2006a).
According to both sources, the commercially supplied products generally do not contain
chemical additives.
In summary, the composition of dioctyltin bis(2-ethylhexyl mercaptoacetate) products in the
EU is typically as follows:
67 – 76 per cent dioctyltin bis(2-ethylhexyl mercaptoacetate); 24 – 33 per cent octyltin
tris(2-ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2-dioctyl-1,3,2oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 0.3 percent 2ethylhexan-1-ol.
Monooctyltin compounds
Octyltin tris(2-ethylhexyl mercaptoacetate)
Octyltin tris(2-ethylhexyl mercaptoacetate) products always contain dioctyltin bis(2ethylhexyl mercaptoacetate), either as part of their composition or as an impurity; according
to the REACH registration, they are marketed as mono- and multi-constituent products. The
following compositions are included in the registration.
Marketed mono-constituent product:
• 99.7 – 100 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 0 – 0.3
per cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1ol, 0 -1 per cent 2-ethylhexyl mercaptoacetate;
Marketed as multi-constituent products; composition covered by registration of individual
constituents:
• 60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 30 – 35 per cent
dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 0 – 2 per cent 2,2-dioctyl1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 1 per
cent 2-ethylhexan-1-ol.
•
24 – 33 per cent octyltin tris(2-ethylhexyl mercaptoacetate); 67 – 76 per cent
dioctyltin bis(2-ethylhexyl mercaptoacetate); impurities 2.5 – 5.5 per cent 2,2dioctyl-1,3,2-oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate,
0 – 0.3 per cent 2-ethylhexan-1-ol1.
No description, but listed in the registration:
• >97 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurity 1 - 3 per cent
dioctyltin bis(2-ethylhexyl mercaptoacetate).
•
1
>90 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurity 3 - 10 per cent
dioctyltin bis(2-ethylhexyl mercaptoacetate).
In this assessment, this is considered a dioctyltin bis(2-ethylhexyl mercaptoacetate) product
12
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
•
>70 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurity 10 - 30 per cent
dioctyltin bis(2-ethylhexyl mercaptoacetate).
According to the OECD (2006b) assessment, the commercially supplied octyltin tris(2ethylhexyl mercaptoacetate) products contain between 5 per cent and 80 per cent octyltin
tris(2-ethylhexyl mercaptoacetate) with the remainder consisting of dioctyltin bis(2ethylhexyl mercaptoacetate) and other minor impurities. However, only the products with
octyltin tris(2-ethylhexyl mercaptoacetate) contents of 50 per cent or more are considered to
be octyltin tris(2-ethylhexyl mercaptoacetate) products.
In summary, the composition of octyltin tris(2-ethylhexyl mercaptoacetate) products is
typically as follows.
Marketed mono-constituent product:
99.7 – 100 per cent octyltin tris(2-ethylhexyl mercaptoacetate); impurities 0 – 0.3 per
cent dioctyltin bis(2-ethylhexyl mercaptoacetate), 0 – 1 per cent 2-ethylhexan-1-ol, 0 -1
per cent 2-ethylhexyl mercaptoacetate;
Marketed as multi-constituent products; composition covered by registration of
individual constituents:
60 – 68 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 30 – 35 per cent dioctyltin
bis(2-ethylhexyl mercaptoacetate); impurities 0 – 2 per cent 2,2-dioctyl-1,3,2oxathiastannolan-5-one, 0 – 2 per cent 2-ethylhexyl mercaptoacetate, 0 – 1 per cent 2ethylhexan-1-ol.
Octyltin trichloride (supporting information)
Based on the above discussion (OECD, 2006b), the composition of octyltin trichloride
products is typically as follows:
≥50 to ~90 per cent octyltin trichloride
~10 to <50 per cent dioctyltin dichloride
The REACH registrations for dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2ethylhexyl mercaptoacetate) both indicate that 2,2-dioctyl-1,3,2-oxathiastannolan-5-one
(CAS 15535-79-2; EC number 239-581-2) is present in multi-constituent products as an
impurity in the range 0 – 5.5%, depending on the product. This substance has the following
structure:
13
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
No information on this substance has been located.
1.3
Physico-chemical properties
The physico-chemical property data are summarised in Tables 1 - 3. The data are taken from
the OECD assessments (OECD, 2006a and 2006b) unless otherwise indicated.
Table 1 Summary of relevant physico-chemical properties: Dioctyltin Dichloride
REACH ref
Annex, §
Property
V, 5.1
Physical state
at 20°C and
101.3 kPa
White powder
OECD (2006a)
White/off white solid block
Harlan (2010)
Melting /
freezing point
45°C - 47°C
OECD (2006a) (4)
45.8°C
Harlan (2010) (2)
Boiling point
175°C at 130 Pa
OECD (2006a) (4)
230°C (decomp.)
Harlan (2010) (2)
V, 5.2
V, 5.3
Value
-4
Comments/ Klimisch code
V, 5.5
Vapour
pressure at
25°C
5.2×10 Pa
OECD (2006a) (2)
V, 5.7
Water
solubility at
20°C
0.24-0.28 mg/l
OECD (2006a). Values
estimated from water
accommodated fraction
(WAF) data (4)
Partition
coefficient noctanol/water
(Kow, log
value) at 25°C
5.8
Dissociation
constant (pKa)
Not applicable.
V, 5.8
VII, 5.19
(data waiver submitted under REACH
owing to hydrolytic instability)
(data waiver submitted under REACH
owing to hydrolytic instability)
14
OECD (2006a). QSAR
estimated value (EPISUITE
KOWWIN v1.67). It is not
clear whether the substance
falls within the model’s
applicability domain (4)
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 2 Summary of relevant physico-chemical properties: Dioctyltin Bis(2-ethylhexyl
mercaptoacetate)a
REACH ref
Annex, §
Property
V, 5.1
Physical state
at 20°C and
101.3 kPa
Yellowish liquid
OECD (2006a)
Clear, colourless to slightly yellow
liquid
NOTOX (2010)
Melting /
freezing point
-90 to -70°C
OECD (2006a) (2)
-39°C
Arkema (2007) (4)
Boiling point
≥260°C (decomposition)
OECD (2006a) (2)
≥275°C (decomposition)
NOTOX (2010) (1)
V, 5.2
V, 5.3
Value
-4
Comments/ Klimisch code
V, 5.5
Vapour
pressure at
20°C
≤2.50×10 Pa
Baltussen (2010a) (2)
V, 5.7
Water
solubility at
20°C
<0.1 mg/l
OECD (2006a). QSAR estimated
value. (EPISUITE, WSKOW v1.41).
It is not clear whether the substance
falls within the model’s applicability
domain (4)
Partition
coefficient noctanol/water
(Kow, log
value) at 25°C
15
Dissociation
constant (pKa)
Not applicable
V, 5.8
VII, 5.19
Note: a)
(data waiver submitted under
REACH owing to hydrolytic
instability)b
(data waiver submitted under
REACH owing to hydrolytic
instability)b
OECD (2006a). QSAR estimated
value. (EPISUITE KOWWIN
v1.67). It is not clear whether the
substance falls within the model’s
applicability domain (4)
OECD (2006a) indicates that as dioctyltin bis(2-ethylhexyl mercaptoacetate) and dioctyltin
bis(isooctyl mercaptoacetate) are isomers the physico-chemical data can be used interchangeably for
these two substances.
b) See discussion under Table 3 below.
15
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 3 Summary of relevant physico-chemical properties: Octyltin Tris(2-ethylhexyl
mercaptoacetate)a
REACH ref
Annex, §
Property
V, 5.1
Physical state
at 20°C and
101.3 kPa
Colourless liquid
OECD (2006b)
V, 5.2
Melting /
freezing point
-80 to -70°C
OECD (2006b) (2)
V, 5.3
Boiling point
≥250°C (decomposition)
OECD (2006b) (2)
V, 5.5
V, 5.7
V, 5.8
VII, 5.19
Note: a)
Value
-3
Comments/ Klimisch code
2.87×10 Pa
Baltussen (2010b) (1)
[4 Pa at 25°C]
[QSAR estimated value from OECD
(2006b)] (4)
Water
solubility at
20°C
0.51-2.71 mg/l
OECD (2006b). Values estimated
from water accommodated fraction
(WAF) data (4)
Partition
coefficient noctanol/water
(Kow, log
value) at 25°C
14.4
Dissociation
constant (pKa)
Not relevant.
Vapour
pressure at
20°C
(data waiver submitted under
REACH owing to hydrolytic
instability)b
(data waiver submitted under
REACH owing to hydrolytic
instability)b
OECD (2006b). QSAR estimated
value. (EPISUITE KOWWIN v1.67).
It is not clear whether the substance
falls within the model’s applicability
domain. (4)
OECD (2006b) indicates that as octyltin tris(2-ethylhexyl mercaptoacetate) and octyltin tris(isooctyl
mercaptoacetate) are isomers the physico-chemical data can be used interchangeably for these two
substances. The log Kow value for octyltin tris(isooctyl mercaptoacetate) is calculated to be 14.1.
b) See discussion below.
OECD (2006a and 2006b) notes that the determined water solubility of the substances (using
a WAF method) may overestimate the actual solubility of the substance as there may be
contributions from more water soluble impurities and the substance may decompose in water
(analyses were generally based on total tin or were not species-specific in the case of monoor dioctyl tin analysis).
Following the OECD assessments, a further attempt was made to investigate the vapour
pressure, water solubility and octanol-water partition coefficient of dioctyltin bis(2ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate). It was reported
for both substances that it was not technically feasible to carry out the water solubility or
octanol-water partition coefficient studies owing to the instability of the substances in water
and the lack of substance-specific analytical methods (Baltussen, 2010a and 2010b).
However, no definitive information is available on the rate at which hydrolysis proceeds as a
function of pH (see Section 4.1.1.2). This uncertainty is discussed further in relation to the
bioconcentration study (section 4.3.2), in which test media preparation and exposure occurred
in reasonably quick succession (unlike in the ecotoxicity studies; see section 7.1.1).
The results for the vapour pressure studies are briefly reported below.
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
16
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
The test was carried out using the isothermal thermogravimetric effusion method based on
the OECD TG 104 (Baltussen, 2010a). The method is valid for vapour pressures in the range
10-8 to 10-3 Pa. In brief, the method involved applying the substance to a roughened glass
plate and measuring the weight loss of the substance as a function of time over a defined
temperature programme. The data were then used to derive the evaporation rates (VT) at
defined temperatures (T) of 150°C, 160°C and 170°C and the evaporation rate at 20°C was
obtained by regression analysis of a plot of log VT against 1/T and the log VT value at 20°C
was obtained by extrapolation of this curve to 20°C. The vapour pressure at 20°C was
obtained by calibration of the method using standards of known vapour pressure. Three sets
of measurements were carried out on the samples (two using a temperature programme
starting at 30°C and one using a temperature programme starting at 100°C). The vapour
pressure at 20°C estimated using the method was 1.30×10-4 Pa in the first experiment,
2.50×10-4 Pa in the second experiment and 1.18×10-5 Pa in the third experiment. Baltussen
(2010a) commented that the significant differences between the individual measurements
may result from reaction/degradation of the substance during the measurement. However, as
the substance tested had a purity of 95.9%, another possible explanation for the variability
seen that was not considered by Baltussen (2010a) may be that the presence of significant
impurities could have affected the results in different ways under the different temperature
programmes used (no information was given on possible impurities). Overall the results can
be taken to show that the vapour pressure of the test substance is ≤2.5×10-4 Pa at 20°C.
Octyltin tris(2-ethylhexyl mercaptoacetate)
The test with octyltin tis(2-ethylhexyl mercaptoacetate) was carried out using essentially the
same isothermal thermogravimetric effusion method as above (Baltussen, 2010b). In this case
the substance tested had a purity of 98% and two determinations of the log VT versus 1/T
were carried out (at 140°C, 150°C and 160°C). In this case the agreement between the two
determinations was very good, and the vapour pressure was determined to be 2.87×10-3 Pa at
20°C.
As supporting information, the key physico-chemical properties of octyltin trichloride are a
vapour pressure of 0.5 Pa at 25°C, a water solubility of 0.33 mg/l and a log Kow of 2.1
(OECD, 2006b).
2
MANUFACTURE AND USES
Not relevant for this type of dossier.
3
CLASSIFICATION AND LABELLING
The following classifications are given in Annex VI to Regulation (EC) No 1272/2008. Selfclassification by the REACH registrants is included.
17
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Dioctyltin compounds
Dioctyltin dichloride
Entry in Table 3.1 of Annex VI.
Acute Tox. 3
H331
Toxic if inhaled
STOT RE 1
H372
Causes damage to organs through prolonged or
repeated exposure
Aquatic Chronic 3
H412
Harmful to aquatic life with long lasting effects
Entry in Table 3.1 of Annex VI.
T; R23-48/25
Toxic by inhalation.
Toxic: danger of serious damage to health by
prolonged exposure if swallowed.
R53*
May cause long-term adverse effects in the
aquatic environment.
* GHS Aquatic Chronic 3 classification is equivalent to R52/53. There is no indication why this disparity exists.
Self-classification in REACH registration (according to Regulations 67/548/EEC and (EC)
No 1272/2008):
GHS
DSD
Acute Tox. 2 H330
R48/25-43-62-63
Skin sens 1B H317
R53*
Repr. Cat. 2 H361
STOT RE 1 H372
Aquatic Chronic 3 H412
* GHS Aquatic Chronic 3 classification is equivalent to R52/53, while R53 is equivalent to Aquatic Chronic 4.
There is no indication why this disparity exists.
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
No classification listed in Annex VI to Regulation (EC) No 1272/2008.
Self-classification in REACH registration (according to Regulations 67/548/EEC and (EC)
No 1272/2008):
GHS
DSD
Acute Tox. 4 H302
R48/25 R43 R63; Xi: R38; Xn: R22; N: R50/53
Skin sens 1B H317
18
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Repr. Cat. 2 H361
STOT RE 1 H372
Aquatic Chronic 1 H410
Monooctyltin compounds
Octyltin tris(2-ethylhexyl mercaptoacetate)
No classification listed in Annex VI to Regulation (EC) No 1272/2008.
Self-classification in REACH registration (according to Regulation (EC) No 1272/2008)*.
>99 per cent octyltin tris(2-ethylhexyl mercaptoacetate), <1 per cent dioctyltin bis(2ethylhexyl mercaptoacetate):
Aquatic Chronic 1 (M
factor 10)
H410
Very toxic to aquatic life with long lasting effects
>97 per cent octyltin tris(2-ethylhexyl mercaptoacetate), <3 per cent dioctyltin bis(2ethylhexyl mercaptoacetate):
STOT rep. exp. 2
H373
May cause damage to the thymus through
prolonged or repeated exposure
Aquatic Chronic 1 (M
factor 10)
H410
Very toxic to aquatic life with long lasting effects
>90 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 3 - 10 per cent dioctyltin
bis(2-ethylhexyl mercaptoacetate):
Repr. Cat 2
H361
Suspected of damaging fertility or the unborn
child
STOT rep. exp. 2
H373
May cause damage to organs through prolonged
or repeated exposure
Aquatic Chronic 1 (M
factor 10)
H410
Very toxic to aquatic life with long lasting effects
>70 per cent octyltin tris(2-ethylhexyl mercaptoacetate), 10 – 30 per cent dioctyltin
bis(2-ethylhexyl mercaptoacetate):
Repr. Cat 2
H361
Suspected of damaging fertility or the unborn
child
STOT rep. exp. 1
H372
Causes damage to organs through prolonged or
repeated exposure
Aquatic Chronic 1 (M
factor 10)
H410
Very toxic to aquatic life with long lasting effects
19
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
<70 per cent octyltin tris(2-ethylhexyl mercaptoacetate), >30 per cent dioctyltin bis(2ethylhexyl mercaptoacetate):
Skin sens. 1
H317
May cause an allergic skin reaction.
Repr. Cat 2
H361
Suspected of damaging fertility or the unborn
child
STOT rep. exp. 1
H372
Causes damage to organs through prolonged or
repeated exposure
Aquatic Chronic 1 (M
factor 10)
H410
Very toxic to aquatic life with long lasting effects
Note: *Several self-classifications according to relative quantities of octyl- and
dioctylstannane are presented in the registration.
Self-classification in REACH registration (according to Regulation 67/548/EEC):
>99 per cent octyltin tris(2-ethylhexyl mercaptoacetate):
DSD
Xi:R38
Irritating to skin,
N: R50/53
Dangerous for the environment; very toxic to aquatic
organisms, may cause long-term adverse effects in the
aquatic environment
Octyltin trichloride (supporting information)
No classification listed in Annex VI to Regulation (EC) No 1272/2008.
4
ENVIRONMENTAL FATE PROPERTIES
Most of the information for this section has been taken from the OECD assessments for the
dioctyltin dichloride and selected esters category (OECD, 2006a) and the monooctyltin
chloride and selected esters category (OECD, 2006b). This is supplemented by information
reported in the earlier PBT Factsheets for the three substances produced under the Existing
Substances Regulation (ECB, 2004a, 2004b and 2004c).
As these data sources have been agreed internationally or in the EU, only the key findings are
reported. Where new data have become available since the OECD assessments were
completed a more detailed description of the study has been included.
In order to facilitate the PBT and vPvB assessment the available data have been separated, as
far as possible, into data for the dioctyl tin compounds and data for the monooctyl tin
compounds. In addition, a further distinction is made between data obtained for the three
20
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
substances that are the subject of this evaluation and data for other similar substances that are
used for read-across.
4.1
Degradation
4.1.1
Abiotic degradation
4.1.1.1 Atmospheric degradation
The reaction of the substances with atmospheric hydroxyl radicals has been reviewed in
OECD (2006a) and OECD (2006b). The rate constant for reaction with hydroxyl radicals,
and the estimated atmospheric half-lives were estimated using the AOPWIN v1.91 program.
The results are summarised in Table 4. For all three substances the estimated atmospheric
half-life is low (of the order of 4-7 hours). As for the other predictions, it is not clear if the
substances were within the applicability domain of the model.
Table 4 Summary of atmospheric half-lives for dioctyltin and monooctyltin
compounds (taken from OECD (2006a and 2006b))
Substance
Hydroxyl radical rate
constant (cm3 molecule-1 s-1)
Estimated atmospheric halflive (hours)
40×10-12
6.5
-12
3.9
Octyltin tris(2-ethylhexyl
mercaptoacetate)
59×10-12
4.3
Octyltin trichloride (supporting
information)
20×10-12
12.9
Dioctyltin compounds
Dioctyltin dichloride
Dioctyltin bis(2-ethylhexyl
mercaptoacetate)
66×10
Monooctyltin compounds)
4.1.1.2 Hydrolysis
The hydrolysis of the substances has been considered in OECD (2006a) and OECD (2006b),
and the main findings of these assessments are summarised below. Further details of the main
study used in these assessments have been obtained; these are also discussed below.
Dioctyltin compounds
OECD (2006a) concluded that both dioctyltin dichloride and dioctyltin bis(2-ethylhexyl
mercaptoacetate) undergo rapid hydrolysis to form, in both cases, dioctyltin
hydroxide/dioctyltin oxide. The hydrolysis of both substances was studied using electrospray
ionization mass spectrometry (ESI/MS) and, in both cases, it was found that the hydrolysis
reaction was rapid (occurring in 10 minutes or less; the exact conditions (pH, temperature,
etc.) of these measurements are not stated in OECD (2006a)). Further details of this study are
available and are given below.
21
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
The ESI/MS study was conducted to determine whether dioctyltin compounds in water
behave like dibutyltin compounds and form oxides relatively quickly (Yoder, 2003).
Dioctyltin oxide was also of interest to the study’s authors but no detectable amount could be
dissolved in any solvent (however, no information is provided on the solvents that were
used). The sensitivity of the method for detecting dioctyltin species was about 100 ng/ml (all
concentrations quoted relative to tin). Two sample preparation methods were used: 1) test
substances were first dissolved in acetonitrile and water was added (to give a ratio of 1:1
acteonitrile to water) immediately prior to analysis, or 2) test substances were dissolved in
acetonitrile, which was subsequently removed under nitrogen, then water was added to the
resulting powder; solutions were then shaken for 24 hours before analysis (these were called
“water contact experiments”).
In the acetonitrile/water solutions, as analysis was conducted immediately after addition of
water to test substance solutions in acetonitrile, the author concluded that the results should
give some indication of the rapidity of hydrolysis (ion intensities were normalized relative to
the highest intensity peak for tin in the initial analysis to indicate concentrations). For both
substances, at lower sample concentrations (e.g. 125 ng/ml (as tin)), almost all of the parent
compound was converted to the oxide in less than 10 minutes (analysis took about 10
minutes, and in that time the parent dioctyltin material had virtually disappeared). An
apparent relationship was found between the relative quantities of the parent substance and
the oxide hydrolysis product measured in solution, depending on the concentration at which
the parent substance sample had been prepared; at 1000 ng/ml, the parent compound
dominated but the oxide was apparent, whereas at 125 ng/ml the oxides became predominant.
It was noted, however, that this may be an artefact of the relative solubilities of the
substances in solution and that the oxide might have been at its saturation concentration; in an
experiment in which the 1000 ng/ml loading was analysed against time, the tin parent
concentration decreased eight-fold while the oxide ion intensities hardly changed. It must be
borne in mind that all of the concentrations tested appear to be above the solubility limits of
the dichloride and mercaptoacetate dioctyltins, so the interpretation can be taken further to
suggest that the dissolution kinetics of the parent will be the limiting factor for the rate of
hydrolysis in this study.
In the water contact experiments (sampled shaken with water for 24 hours prior to analysis)
only the oxide was visible in the dioctyltin bis(2-ethylhexyl mercaptoacetate) spectrum,
whereas both the oxide and the parent chloride were present in the dioctyltin dichloride
spectrum. Given the duration over which the samples were shaken with water prior to
analysis, the result with dioctyltin dichloride may seem surprising. The study report does not
indicate the concentration at which the water contact samples were prepared, but it is possible
that the test concentration was above water solubility so that dissolution kinetics would limit
the rate of hydrolysis. The concentration of oxide in the water contact samples was estimated
from the dioctyltin bis(2-ethylhexyl mercaptoacetate) and dioctyltin dichloride standards. The
oxide concentration was estimated as 10 – 40 ng/ml for the dioctyltin bis(2-ethylhexyl
mercaptoacetate) sample and 30 – 120 ng/ml for the dioctyltin dichloride sample.
Overall, it is not possible to conclude definitively on the hydrolysis rate of the dioctyl
compounds from this study, although it does indicate that it is rapid (half lives of minutes to
hours). This is important in the interpretation of the bioaccumulation test data for the 2ethylhexyl mercaptoacetate substituted substance (see section 4.3.2).
The hydrolysis reaction of dioctyltin dichloride liberates hydrogen chloride. The reaction of
dioctyltin bis(2-ethylhexyl mercaptoacetate) liberates the corresponding thioester group. For
22
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
dioctyltin dichloride it was found that reaction is an equilibrium, but reformation of the
dioctyltin dichloride from the dioctyltin hydroxide/dioctyltin oxide would only be significant
if an excess of chloride is present. Equation 1 below shows a possible pathway for hydrolysis,
with postulated sequential nucleophilic substitution of labile ligands followed by
rearrangement and loss of water to give the tin oxide from the hydroxide. Alternatively, the
second ligand could leave through rearrangement without the nucleophilic attack of a second
water molecule, depending on how good a leaving group R is (equation 2).
→ (octyl)2 Sn = O (↓ ppt)
(octyl)2 SnR 2 ←-→ (octyl)2 Sn(R)OH ←-→ (octyl)2 Sn (OH)2  
-R
-R
-H 2O
Eqn 1
→ (octyl)2 Sn = O (↓ ppt)
(octyl)2 SnR 2 ←-→ (octyl)2 Sn(R)OH  
-R
- RH
Eqn 2
where R = Cl or (2-ethylhexyl mercaptoacetate)*
*substitutions of 2-ethylhexyl mercaptoacetate ligand unlikely to be reversible
In the case of dioctyltin bis(2-ethylhexyl mercaptoacetate), the thioester group itself
undergoes further hydrolysis to form thioglycolic acid and 2-ethylhexanol (hydrolysis of the
ester linkage).
Based on the OECD (2006a) evaluation and information in the REACH registrations it can be
concluded that in the environment, both dioctyltin dichloride and dioctyltin bis(2-ethylhexyl
mercaptoacetate) will hydrolyse rapidly to the same tin species (dioctyltin
hydroxide/dioctyltin oxide). The dioctyltin oxide formed is less soluble than either of the two
parent substances and may precipitate out of solution. OECD (2006a) concluded that the
octyl groups in these hydrolysis products would be reasonably stable to further hydrolysis.
Monooctyltin compounds
OECD (2006b) notes that there are no experimental data available for octyltin tris(2ethylhexyl mercaptoacetate) (nor for either of the two similar substances octyltin trichloride
or octyltin tris(isooctyl thioglycolate)). However, using a read-across approach from the data
for the above dioctyltin compounds and other similar dibutyltin compounds it was concluded
that octyltin tris(2-ethylhexyl mercaptoacetate) would be expected to hydrolyse rapidly
(within minutes to hours) in solution to form octyltin hydroxide which would eventually
precipitate out of solution as the oxide.
Based on the OECD (2006b) evaluation and the information above it can be concluded that in
the environment, octyltin tris(2-ethylhexyl mercaptoacetate) will hydrolyse rapidly to the
corresponding octyltin hydroxide/octyl tin oxide species. OECD (2006b) concluded that the
octyl group in these hydrolysis products would be reasonably stable to further hydrolysis.
Similarly for the supporting substance, octyltin trichloride, OECD (2006b) concluded that,
although there are no specific studies with octytin trichloride, by read-across, rapid hydrolysis
to the octyl tin hydroxide/oxide species would be expected in an equilibrium reaction. It was
also concluded that reformation of the octyltin trichloride would not be significant in the
absence of an excess of chloride.
23
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
New data
New studies have been considered to investigate the hydrolysis as a function of pH of
dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate).
However for both substances it was reported that it was not technically feasible to carry out
such studies owing to the instability of the substances in water and the lack of specific
analytical methods for the test substances (Baltussen, 2010a and 2010b).
Other work done in relation to the analytical method development for the bioconcentration
tests (see Section 4.3.2) explored the stability of the derivatised and extracted diocyltin
species (DOT) (Baltusssen, 2009b), which is relevant here when considering the stability of
the tin – carbon bond in the parent substances and hydroxide/oxide hydrolysis products. As
part of this study, the substance was dissolved in ISO-medium at a nominal concentration of
1 µg/l and the concentration of all dioctyltin species (DOT) in the medium was determined
over 18 days (see Section 4.3.2 for further details of the analytical method). The
concentration of DOT was found to decrease over time, declining to around 0.2 µg/l after 18
days. The decline in concentration was found to follow first order kinetics and the half-life
was calculated to be 5.5 days. The temperature of the experiment was 15°C. The pH of the
medium used was not given. The method used by Baltusssen (2009b) would have detected all
DOT present, and does not give any information on any initial hydrolysis of the parent.
Furthermore, the study does not necessarily indicate that the DOT (and by inference the
hydroxide/oxide hydrolysis products) is unstable in ISO medium; adsorption or precipitation
may have been occurring over time causing the observed decrease in concentrations. This
interpretation is consistent with the conclusion of the OECD assessments (OECD 2006a and
b) and the discussion above.
4.1.2
Biotic degradation
The available biodegradation data are summarised in OECD (2006a and 2006b) and are
outlined below.
Dioctyltin compounds
The results of biodegradation screening tests for dioctyltin dichloride and dioctyltin bis(2ethylhexyl mercaptoacetate) are summarised in
Table 5.
24
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 5 Summary of biodegradation screening tests for dioctyltin compounds
(taken from OECD (2006a))
Method
Result (%
biodegradation)
Conclusion
Comment/ Klimisch code
Dioctyltin dichloride
OECD TG 301F – Manometric
Respirometry Test
0% after 28 days
Not readily
biodegradable
Purity of substance tested
was 99.9%. Test
concentration 27.3 mg/l.
Study extended to 39 days
(no biodegradation noted)
(1)
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Directive 92/69/EEC, C.4-D –
Manometric Respirometry Test
(test
29-43% after 28
days
Not readily
biodegradable
Purity of substance tested
was 99.4%. Test
concentration 50 mg/l. Test
prolonged to 74 days (40 –
50% biodegradation) (1)
Directive 84/449/EEC, C.5 –
Modified Sturm Test
11-19% after 28
days
Not readily
biodegradable
Purity of substance tested
was 90%. (1)
Directive 84/449/EEC, C.5 –
Modified Sturm Test
23% after 28 days
Not readily
biodegradable
Purity of substance was
70%. (1)
Based on these test results it is concluded that both dioctyltin dichloride and dioctyltin bis(2ethylhexyl mercaptoacetate) are not readily biodegradable. OECD (2006a) concluded that the
degradation seen in the experiments with dioctyltin bis(2-ethylhexyl mercaptoacetate)
probably results from the (partial) degradation of the 2-ethylhexyl mercaptoacetate ligands
once they have been liberated from the tin by hydrolysis.
Monooctyltin compounds
The results of biodegradation screening tests for octyltin tris(2-ethylhexyl mercaptoacetate)
are summarised in Table 6.
25
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 6 Summary of biodegradation screening tests for monooctyltin compounds
(taken from OECD (2006b))
Method
Conclusion
Result (%
biodegradation)
Comment/ Klimisch
code
Octyltin tris(2-ethylhexyl mercaptoacetate)
Directive 92/69/EEC, C.4-D –
Manometric Respirometry Test
32-44% after 28
days
(concentration
50mg/l)
Not readily
biodegradable
Purity of substance was
99.63%. test extended to
39 days (50 – 60%) (1)
Directive 84/449/EEC, C.5 –
Modified Sturm Test
40% after 28 days
(concentration
11.7 mg/l);
Not readily
biodegradable
Purity of substance was
70% (30 % DOTC). (1)
Not readily
biodegradable
Purity of substance tested
was 100%
28% after 28 days
(concentration
22.7 mg/l)
Octyltin trichloride (supporting information)
OECD TG 301F – Manometric
Respirometry Test
0.9% after 28
days
Based on these results it can be concluded that neither octyltin tris(2-ethyl mercaptoacetate),
nor the supporting substance octyltin trichloride is readily biodegradable.
The OECD (2006a and 2006b) evaluations also reported the results of a ready biodegradation
test using 2-ethylhexyl mercaptoacetate itself. This was not readily biodegradable (15%
degradation after 29 days in an OECD TG 301B study).
4.1.3
Summary and discussion of persistence
Based on the available information, the dioctyltin and monoctyl tin compounds considered
are not readily biodegradable.
Degradation in the atmosphere is predicted to occur rapidly by reaction with hydroxyl
radicals, with a half-life of the order of a few hours, although this is unlikely to be an
important pathway given the substances’ low vapour pressure.
Hydrolysis of the substances is expected to occur rapidly in aquatic systems. The initial
hydrolysis products formed are dependent on whether the substance is a dioctyltin substance
or a monooctyltin substance as the octyl groups attached to the tin atom appear to be more
resistant to hydrolysis than the other groups in the substances considered. Thus both
dioctyltin dichloride and dioctyltin bis(2-ethylhexylmercaptoacetate) will form essentially the
same hydrolysis product in the environment, dioctyltin hydroxide/oxide. Similarly both
octyltin trichloride (supporting substance) and octyltin tris(2-ethylhexylmercaptoacetate) will
form octyltin hydroxide/oxide.
As the hydrolysis reaction appears to be rapid (half-lives of a few minutes to hours) it can be
expected that, on release to the environment, the substances considered will be rapidly
converted to the corresponding dioctyltin hydroxide/oxide or octyltin hydroxide/oxide and so
26
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
it is the properties of these hydroxide/oxide products that are most relevant to the PBT
assessment.
As such hydrolysis would also occur under the conditions of the ready biodegradation tests,
the results of these tests will reflect the biodegradability of the dioctyltin hydroxide/oxide or
octytin hydroxide/oxide and the released organic ligand. As none of the substances tested
were readily biodegradable it can therefore be concluded that the dioctyltin hydroxide/oxide
and octytin hydroxide/oxide are also not readily biodegradable and so potentially persistent.
The hydrolysis reaction of dioctyltin dichloride and the supporting substance octyltin
trichloride is to some extent reversible. Although significant reformation of the dioctyltin
dichloride or octytin trichloride from the dioctyltin hydroxide/oxide and octytin
hydroxide/oxide would not be expected to occur in freshwater environments the same may
not necessarily be true in marine environments where higher chloride concentrations are
present. However there is no information available about whether or not the reverse reaction
can occur under the pH conditions prevalent in the marine environment (i.e. pH around 7.5 8).
The hydrolysis of both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2ethylhexyl mercaptacetate) will result in the release of 2-ethylhexyl mercaptoacetate itself.
This substance is not readily biodegradable but can undergo hydrolysis to form thioglycolic
acid and 2-ethylhexanol.
4.2
Environmental distribution
4.2.1
Adsorption
The three substances under consideration all have high log Kow values (5.8-15) and so would
be expected to adsorb strongly onto sediment and soil. The supporting substance, octyltin
trichloride, has a much lower log Kow of 2.1 and so will adsorb less strongly to sediment and
soil than the other three substances.
Given that an important degradation mechanism for these substances appears to be
hydrolysis, adsorption may be a very important property in determining the overall fate in the
environment. For example, if adsorption to suspended material is significant, then this may
result in a longer overall environmental half-life in sediment (or the aquatic compartment)
than may be suggested based on rapid hydrolysis alone. However, there are no data available
to demonstrate that this may be the case.
No information on the adsorption of the hydrolysis products octyl or dioctyl tin
hydroxide/oxide was located. The study summarized in section 4.1.1.2 by Baltusssen (2009b)
does suggest that dioctyltin oxide would be adsorptive, which is also indicated by its
predicted log Kow value (9.26).
4.2.2
Distribution modelling
Distribution modelling using a Level III fugacity model has been carried out for the three
substances as part of the OECD (2006a) and (2006b) evaluations. The results of this
modelling indicate that the three substances are predicted to partition primarily to sediment
27
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
(45%-74%) and soil (22%-38%). For the supporting substance, octyltin trichloride, the
modelling indicated that this substance would partition primarily to water (69%), soil (20%)
and air (11%) rather than sediment, presumably owing to the lower log Kow value for this
substance. However, the relevance of this modelling is questionable given the hydrolytic
instability of the substances and the lack of information on adsorption, as stated above.
4.2.3
Other information
No other relevant information.
4.2.4
Summary of environmental distribution
The available information suggests that the substances dioctyltin dichloride, dioctyltin bis(2ethylhexylmercaptoacetate) and octyltin tris(2-ethylhexylmercaptoacetate) will partition
preferentially to the soil and sediment compartments. The effect of adsorption to sediment on
the hydrolysis of the substances in the environment is not known.
The environmental distribution behaviour of the supporting substance octyltin trichloride is
different to the above three substances, with the substance predicted to partition primarily to
the water, soil and air compartments.
4.3
Bioaccumulation
4.3.1
Screening data
The log Kow values for the three substances are as follows (see Section 1.3):
Dioctyltin compounds
Dioctyltin dichloride
Log Kow = 5.8
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Log Kow = 15
Monooctyltin compounds
Octyltin tris(2-ethylhexyl mercaptoacetate)
Log Kow = 14.4
Octyltin trichloride (supporting substance)
Log Kow = 2.1
All log Kow values are estimated values and so are uncertain. Based on these, dioctyltin
dichloride, dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl
mercaptoacetate) would meet the screening criteria for bioaccumulative (B) and very
bioaccumulative (vB). However the predicted log Kow for the supporting substance octyltin
trichloride is below the screening criteria cut-off of 4.5 for B or vB.
The estimated log Kow value for dioctyltin oxide is 9.26 (KOWWIN v1.67). For dioctyltin
dihydroxide the estimate is 6.00, and for a potential hydrolysis product of octyltin tris(2ethylhexyl mercaptoacetate) (the octyltin hydroxy oxide) the estimated log Kow is 2.16. As
28
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
for the parent substances, these values are also uncertain but the first two estimates suggest
the dioctyl hydrolysis products meet the screening criteria.
In addition to these log Kow values, OECD (2006a) and OECD (2006b) contain estimates for
fish bioconcentration factors (BCFs) obtained using the USEPA BCFWIN software. These
estimates are summarised below.
Dioctyltin compounds
Dioctyltin dichloride
BCF = 630
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
BCF = 100
29
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Monooctyltin compounds
Octyltin tris(2-ethylhexyl mercaptoacetate)
BCF = 100
Octyltin trichloride (supporting substance)
BCF = 8.9
Based on these data, OECD (2006a and 2006b) concluded that although dioctyltin dichloride,
dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate)
have high log Kow values, the substances would be expected to have only a low potential for
bioaccumulation. Again, the log Kow values used to estimate these BCFs are predicted using a
model which may not be validated for these types of substance.
OECD (2006a and 2006b) also estimated the fish bioconcentration factors for 2-ethylhexyl
mercaptoacetate (which is likely to be released on hydrolysis of both dioctyltin bis(2ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate). The log BCF
was estimated to be 0.8 (i.e. BCF = 6.3).
4.3.2
Measured bioaccumulation data
No measured bioaccumulation data are reported in OECD (2006a and 2006b) for any of the
dioctyltin and monooctyl tin compounds considered. Since the OECD evaluations were
completed, further experimental data on bioconcentration have become available. These are
summarised below.
Dioctyltin compounds
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Preliminary Study
A preliminary bioconcentration study was conducted with a 14C-radiolabelled test substance
in rainbow trout (Oncorhynchus mykiss), originally to investigate the duration of the uptake
phase required in the definitive test (Bogers, 2006). The report for the study indicates that the
14
C radiolabel was present at the 1-position in one of the octyl chains in the test substance.
Information on radiopurity and other substance information is not available. Two test
concentrations were run with nominal concentrations of 1 µg/l and 10 µg/l in a flow-through
system, with the radiolabelled test substance present at a concentration of 0.2 µg/l in both
tested substances (the radiolabelled material was mixed with “cold” test substance). The
uptake phase lasted for 5 days and the depuration phase for 10 days. Liquid Scintillation
Counting was used to analyse the amount of radioactivity associated with the water and fish
tissue during the uptake phase and depuration phase. Exposure concentrations varied by less
than 20% of nominal values. Four analyses for radioactivity during the exposure period
indicated that the radiolabelled substance was steadily taken up by the fish in both test
groups, achieving concentrations of about 0.16 µg/g whole fish wet weight and 0.44 µg/g
whole fish wet weight in the 1 µg/l and 10 µg/l treatments, respectively, at the end of 5 days’
uptake. Information from the laboratory indicates that whole fish were sampled, without
removal of skin. Steady state was not reached in either group. Concentrations appeared still to
be increasing exponentially after 5 days. The report includes plots of (concentration ratio
based) BCF for both test concentrations; the highest value is for the low dose group at the end
of exposure, where a BCF of about 170 was reached. The results indicated that the higher
dose concentration exceeded the water solubility of the test substance (based on relative
30
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
uptake of the substance into fish tissue). During the 10 day depuration phase fish tissue
concentrations in the low dose test group hardly decreased, and decreased from about 0.44 to
0.29 µg/g whole fish wet weight in the high dose group (two measurements were taken in
each group, at the start and end of depuration). Neither a steady state nor a kinetic BCF can
be derived from these results with any degree of certainty. Further details on the study are not
available. The results showed that a definitive study needed to be conducted, which is
described below.
Definitive Study
A definitive bioconcentration test has been carried out for dioctyltin bis(2-ethylhexyl
mercaptoacetate) with rainbow trout (Oncorhynchus mykiss) (Bouwman, 2010d). Owing to
problems with the radiolabelled test substance2 and the realization of an analytical technique
for the “cold” test substance, the study was run using the “cold” substance (purity 97.5%). No
information is available on impurities present in the test substance. The methodology used
was OECD TG 305 and details of the test are as follows.
The fish used in the test had an initial mean weight of 1.74 g. The test was carried out using a
flow-though system with a flow-rate of 10 l/hour (giving approximately 4 volume
replacements in each tank per day). Stock solutions of the test substance were prepared in
acetone (two concentrations were prepared, 2.5 and 25 mg/l) and these were dosed into the
dilution water in the mixing chamber at a dilution of 1:10,000 in order to give nominal test
concentrations of 0.25 µg/l and 2.5 µg/l in the tank. At this dilution, the concentration of
acetone in the tank would be 0.1 ml/l. A control was run containing acetone alone at this
concentration. The dilution water used had a mean pH of 7.6 (range 7.4-7.8) and a hardness
of 180 mg/l as CaCO3. The mean temperature during the test was 14 °C (range 13.0 to
15.3 °C) and the dissolved oxygen concentration ranged from 8.5 mg/l to 9.8 mg/l.
The flow-through system was operated for 12 days prior to the start of the test in order for the
concentration of the test substance to stabilise. After this time the fish were added to the tanks
(maximum fish loading 0.42 g fish/l per day) and the uptake of the substance was monitored
at various time points for up to 30 days. The fish were fed pelleted fish food at a rate of 2% of
body weight per day during the uptake. Fish (one replicate for the control and two replicates
for each treatment group, each replicate consisting of 2 fish) were sampled on days 1, 3, 7,
14, 21, 28 and 30 of the uptake. Water samples (one sample per control and each treatment
group) were sampled on days -1, 0, 1, 3, 7, 14, 21, 28 and 30 of the uptake phase.
Mortalities or other adverse effects were <10% in the control group and the two treatment
groups. The mean measured exposure concentrations (±standard deviation) were
0.19±0.05 µg/l and 2.6±0.4 µg/l in the two treatment groups. The variation of the water
concentration over the course of experiment was within 20% of the mean concentration for
the higher concentration but the variation was slightly higher at the lower concentration
owing to the low concentrations measured (close to the detection limit of the analytical
method used). A more detailed discussion of the measured concentrations and analytical
method used is given below.
Analysis of the fish revealed that the concentrations of the test substance were below the limit
of quantification in all samples (<0.25 mg/kg). Assuming that the limit of quantification
2 Analysis of the radiolabel showed that its purity was very low; however it was not clear if this was the same
substance as used in the preliminary BCF test, and this analysis appeared to have been carried out a number of
years after the preliminary BCF study.
31
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
represents the maximum concentration of the substance in fish, the equivalent BCF factor can
be estimated as <1,300 l/kg for the group exposed to a concentration of 0.19 µg/l and <100
for the group exposed to 2.6 µg/l. As no detectable concentrations of the test substance were
evident in the fish at day 30 it was decided that no depuration phase was needed in this study.
Given that these BCF values are based on the limit of quantification in fish and that no test
substance was measured in the fish at either test concentration these data suggest that the
BCF for the test substance is <<2000.
In order to provide more evidence that the BCF is relatively low, Bouwman (2010d) also
analysed the fish from day 30 for the presence of total tin. The concentration of total tin
present in the fish was found to be 0.027 mg Sn/kg for the 0.19 µg/l exposure group and
0.054 mg Sn/kg for the 0.26 µg/l treatment group. In order to calculate the BCF, Bouwman
(2010d) corrected the measured water concentrations to take account of the percentage tin,
giving corrected water concentrations of 0.15 µg Sn/l and 0.92 µg Sn/l. Using these
concentrations the BCF based on total tin were 178 at the lower treatment group and 58 at the
higher treatment group. These analytical data, in particular the correction applied to the water
concentrations, are considered further below.
The lipid contents of the fish used in the test was reported to be around 4% at the start of the
test and reached around 6% at the end of the test3. Thus the lipid content of the fish were
close to the default lipid content of 5% recommended in the REACH Guidance Document
and so normalization to 5% is not considered necessary in this case.
Interpretation of the data
A key factor in interpreting the results of the definitive test is the analytical method used and
so this is considered in detail. Firstly, it is important to note that there is no substance-specific
method available that can currently analyse dioctyltin bis(2-ethylhexyl mercaptoacetate) with
sufficient sensitivity and so an indirect method has to be used. The method was designed to
detect both monooctyltin compounds and dioctyltin compounds. The method used for water
and fish is similar and is summarised in a number of reports (Appendix VI of Bouwman
(2010d) and Baltussen (2009a, 2009b and 2009c). The method involves simultaneous
derivatization and extraction of monooctyltin and dioctyltin compounds using sodium
tetraethyl borate solution and subsequent analysis of the diethyl derivative using gas
chromatography mass spectrometry (GCMS). Monoheptyltin trichloride and/or diheptyltin
dichloride were used as internal standards and octyltin trichloride was used as an analytical
standard. The method will detect all monooctyltin (the term MOT will be used here) and
dioctyltin (DOT) compounds present in the samples (provided these undergo the
derivitisation step) and so does not, in this case, distinguish between dioctyltin bis(2ethylhexyl mercaptoacetate) itself or any degradation products or impurities that contain the
dioctyltin group.
Using this method the following limits of quantification were determined for MOT and DOT
for water and fish.
3
The lipid contents are given in Appendix 1 of the test report (Bouwman, 2010d). Here the lipid content of the
fish at day 30 in the control and two treatment groups are all given as 6%. However the weight data for the two
treatment groups appears to suggest that the lipid contents were closer to 4.4% for these two groups (for
example for the 0.25 µg/l (nominal) group the lipid weight is given as 0.58 g for a sample weight of 13.09 g (i.e.
4.4% lipid) and for the 2.5 µg/l (nominal) group the lipid weight is given as 0.58 g for a sample weight of
13.25 g (i.e. 4.4% lipid).
32
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Limit of quantification
Water
Fish
MOT
0.25 µg/l
0.25 mg/kg
DOT
0.25 µg/l
0.25 mg/kg
For the water analysis the mean recoveries from procedural recovery samples were generally
between 86% and 105% for DOT and 78%-139% for MOT, except on one day when very
low recoveries were evident for both DOT and MOT (recovery 1.8-6.3%; the results on this
day were considered inaccurate) and one further day for MOT (recovery 44%).
The measured concentrations of MOT in the test water samples were generally below the
limit of quantification in both exposure groups (MOT was occasionally detected at
concentrations close to the limit of quantification in samples from the high treatment group).
DOT was detectable in all water samples from both treatment groups. The mean level of
DOT measured in the water samples was 0.19 µg/l in the low exposure group and 2.6 µg/l in
the high exposure group. These concentrations are used above in the estimation of the BCF
from the experiment. The concentration measured in the low exposure group is close to, but
just below, the limit of quantification and this may explain the higher variability in the
measured concentration in this treatment group compared with the higher exposure group.
For the fish samples, the mean recoveries from procedural recovery samples were between
87% and 134% for MOT and 88% and 119% for DOT. The concentration of both MOT and
DOT was below the limit of quantification in all of the fish samples from the treatment
groups in the study.
Overall the analytical methodology used appears to be robust for MOT and DOT. The
method should detect any mono- or dioctyltin substances (including dioctyltin bis(ethylhexyl
mercaptoacetate) and any transformation products containing the dioctyltin group) but will
represent the sum of mono- or dioctyltin substances rather identifying specific mono- or
dioctyltin substances. Furthermore, the inherent difficulties in analyzing for these types of
substances means that the limit of quantification in fish was high at 0.25 mg/kg in
comparison to that in water and this was not sufficiently sensitive to allow determination of
the actual concentration present in the fish (both MOT and DOT were below the limit of
quantification). However the detection limit for water was sufficiently low (0.25 µg/l) to
allow analytical verification of the exposure concentrations for DOT. When these exposure
concentrations for DOT are considered in relation to the limit of quantification for fish, it
appears that the BCF would be <1,300 for the low exposure group and <100 for the high
exposure group.
The method used for analyzing total tin concentrations in the fish is outlined in Baltussen
(2009d) and Appendix VI of Bouwman (2010d). The method essentially involved digestion
of a sample of fish using nitric and hydrochloric acid in a microwave and analysing the
concentration of tin present using inductively coupled plasma mass spectrometry (ICPMS).
The limit of quantification of the method was 0.025 mg/kg and the mean recoveries from
procedural recovery samples were in the range 98% to 104%. The total tin concentration in
the exposed fish samples on day 30 were 0.027 mg Sn/kg for the low exposure group and
0.054 mg Sn/kg for the high exposure group. As this method is not specific for any given
organotin compound these values will represent the total tin concentration for all tincontaining substances present in the samples.
33
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
No total tin analysis was carried out on the water concentration and so the measured
concentrations of DOT and MOT were converted to the equivalent level of tin. When
carrying out this conversion, Bouwman (2010d) assumed that the percentage tin in DOT was
29.5% and the percentage tin in MOT was 37%, by mass. The total tin concentration in water
was then estimated from the measured concentration of DOT and MOT by applying these
percentages; the total tin concentration was the sum of tin from these two sources. In the case
of MOT, as it was not quantifiable in water, the limit of quantification was used in the
calculation. This led to total tin concentration of 0.15 µg/l at the low exposure concentration
and 0.92 µg/l at the high exposure concentration. This correction as applied in Bouwman
(2010d) can be questioned in two respects.
1. The use of the limit of quantification for MOT may result in an overestimate of
the total tin concentration in water (and hence an underestimate of the resulting
BCF). This is particularly relevant at the lower test concentration where the
concentration of DOT is itself close to the limit of quantification. It may be more
appropriate to ignore here any contribution from MOT (particularly as the dioctyl
tin substance tested had a purity of ~97.5%).
2. Although the analytical method measures DOT and MOT in water, the method is
calibrated such that if the test substance does not degrade in the test the
concentration of the substance itself will be the same as indicated for DOT.
Therefore, it may be more relevant to use the percentage tin in dioctyltin bis(2ethylhexyl mercaptoacetate) than the percentage tin in DOT. The percentage tin in
dioctyltin bis(2-ethylhexyl mercaptoacetate) is 15.8%, by mass.
Taking into account these two factors, the revised total tin concentrations in test media can be
estimated to be around 0.030 µg Sn/l at the low exposure concentration and 0.41 µg Sn/l at
the high exposure concentration, compared to the concentrations of 0.15 µg/l and 0.92 µg/l
as derived by Bouman (2010d). Comparing these concentrations with the measured total tin
concentration in the fish (0.027 mg Sn/kg and 0.054 mg Sn/kg respectively) would lead to
revised estimates for the BCFs based on total tin of around 900 l/kg at the low exposure
concentration and 130 l/kg at the high exposure concentration. Again it should be stressed
that these values represent the total tin concentration in the fish from all sources (i.e.
including any transformation products) and not just exposure to parent dioctyltin bis(2ethylhexyl mercaptoacetate).
One final factor to consider with this study is that, as no time trend data on the actual
concentration of the substance in the fish are available (i.e. for analysis of total tin), it is not
possible to ascertain whether or not steady state was reached during the test.
A key consideration for this study is that the analytical method used, based on MOT and
DOT, would determine all monooctyltin and dioctyltin substances present in solution and the
fish (i.e. the parent substance and hydrolysis products). Therefore the rate at which the parent
substance hydrolyses in the test system is very important, given the method used to prepare
exposure solutions. If hydrolysis was much slower than might be expected for the substance
(see section 4.1.1.2), then the study results will be relevant for the parent substance but give
little information on the hydrolysis product dioctyltin oxide. Conversely, if hydrolysis in the
test system was very rapid, then the uptake seen would represent, at least in part, that of the
hydrolysis products rather than the parent compound. If the latter situation predominated,
then the basis for this category assessment holds and a conclusion for bioaccumulation
potential of the substance based on the hydrolysis products is reasonably straightforward.
34
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
However if this is not the case (and hydrolysis did not predominate), then it is difficult to use
this study to conclude on the bioaccumulation potential of the common hydrolysis product(s).
Overall, although the results of this study do not lead to the determination of a definitive
value for the BCF of dioctyltin bis(2-ethylhexyl mercaptoacetate) or its hydrolysis products,
they nevertheless provide strong evidence that the BCF is well below the 2,000 l/kg cut-off
for a bioaccumulative substance in relation to the Annex XIII criteria. The available data
suggest that the BCF is perhaps around 1,000 l/kg as a maximum.
Monooctyltin compounds
No new data are available. Although the above study does include the analysis of MOT, as
MOT was not detectable in either the water phase or the fish nothing can be inferred from the
study as to the actual accumulation potential of MOT. The DOT study may be acceptable for
read across to MOT for the reasons given in the introduction to this document and section
1.1. The REACH registration of octyltin tris(2-ethylhexyl mercaptoacetate) includes the DOT
study.
4.3.3
Other supporting information
Although full details have not been seen for this evaluation, the PBT factsheets produced
under the Existing Substances Regulation for dioctyltin dichloride (ECB, 2004a) and
dioctyltin bis(2-ethylhexyl mercaptoacetate) (ECB, 2004b) refer to a BCF test carried out on
dioctyltin maleate (CAS 16091-18-2, EC 240-253-6) (a more soluble substance than the
dioctyl tins assessed here) which showed a low BCF. This would support the limited
bioconcentration seen in the new study with dioctyltin bis(2-ethylhexyl mercaptoacetate)
reported in Section 4.3.2.
The hydrolysis product dioctyltin hydroxide is predicted to have a reasonably high log Koa
(10.3; KOAWIN v1.10) based on a predicted Henry’s Law constant of 1.27 10-6 atm.m3/mol
(HenryWin bond estimate) and log Kow of 6 (KOWWIN v1.67), which means there may be
the potential for it to bioaccumulate in air breathing organisms. The available human health
toxicokinetic and repeated dose toxicity dataset in the REACH registrations do not allow an
assessment of this; no organ-specific analysis seems to have been conducted for dioctyltin
dichloride or dioctyltin bis(2-ethylhexyl mercaptoacetate). The key repeated dose toxicity
study for dioctyltin dichloride (read across to the mercaptoacetate) shows weight effects on
the thymus.
4.3.4
Summary and discussion of bioaccumulation
Experimental fish bioconcentration data are available only for dioctyltin bis(2-ethylhexyl
mercaptoacetate). Carrying out a fish bioconcentration test for these substances is technically
challenging owing to the rapid hydrolysis of the substance and the lack of analytical
methodology to allow determination of the individual substances present. On first inspection
there is an apparent disparity between the results of the preliminary bioconcentration study
and the definitive study, in that uptake was noted in the former. The concentrations measured
in the preliminary study after 5 days’ uptake (based on radioanalysis) were around the
detection limit possible in the definitive study for DOT or MOT (about 0.16 and 0.44 µg/g
35
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
against a LOQ of 0.25 µg/g). The author of the preliminary study stated that if the increase in
concentration was extrapolated to 30 days for the low dose preliminary study (based on the
curve of the uptake), the BCF would have been about 1000 (this assumes first order uptake
kinetics based on four uptake data points). This is not out of line with the results of the
definitive study considering the lower exposure concentrations (0.19 and 0.26 µg/l as
opposed to about 1 and 10 µg/l) and the fact that measurements of total tin at the end of
exposure in the definitive study showed the presence of tin (at concentrations of 0.027 and
0.054 µg/g for the low and high doses, respectively). However, it is difficult to take
interpretation of the preliminary study further given the sparse details available on the test
substance, and the fact that measurement of radioactivity is even less-substance specific than
the analytical technique used in the definitive study.
Nevertheless the available definitive study can be taken to show that accumulation from
water of the tin-species, in whatever form it was present (if rapid hydrolysis occurred in the
test it is likely to be as the hydrolysis products dioctyltin hydroxide/oxide), results in a BCF
that is perhaps around 1,000 l/kg as a maximum.
The main uncertainty in this evaluation stems from the fact that the actual individual
substances present in solution are not known (only the total tin or total mono- and dioctyltin
compounds were determined), and that definitive hydrolysis data are not available. If the
uptake seen resulted from exposure of a minor component in water (for example if the
accumulative component made up only a small fraction of the total mono- or dioctyltin
compounds present) as, in this case, the actual BCF for the individual substance may be
higher than that determined based on the total tin, total mono- or total dioctyltin compounds.
If hydrolysis was actually much slower than expected (see section 4.1.1.2), then conclusions
about the bioaccumulation potential of the hydrolysis products would be difficult to draw
from this study. The analytical difficulties mean that it is not technically possible to
investigate further whether or not either of these situations is the case.
The measured accumulation in the fish bioconcentration study is consistent with the findings
of the OECD (2006a and 2006b) evaluations, which concluded that the bioaccumulation
potential of these substances was low. However the OECD (2006a and 2006b)
bioaccumulation evaluation was based on QSAR estimates, and did warn that the methods
used for estimation the BCF had not been validated for chemicals containing metals in their
molecular structure so that the estimated BCFs should be used with caution.
The available test does not provide any information on the accumulation of the monooctyltin
compounds as the concentration of these species in both the water and fish were below
detectable concentrations. Based on read-across from the dioctyltin compounds it can be
expected that the bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis
products would be similar to or possibly lower than (based on their lower lipophilicity), that
of the dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty
in the overall evaluation.
The available information suggests that 2-ethylhexyl mercaptoacetate released from
hydrolysis of dioctyltin bis(2-ethylhexyl mercaptoacetate) or octyltin tris(2-ethylhexyl
mercaptoacetate) will have a low potential for bioaccumulation.
Overall, the available fish bioconcentration results are strongly suggestive that the BCF of the
dioctyltin substances is perhaps around 1,000 l/kg as a maximum but more probably much
lower than this (around 100 l/kg or less).
36
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
4.4
Secondary poisoning
Not relevant for this dossier.
37
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
5
HUMAN HEALTH HAZARD ASSESSMENT
Of the substances considered only dioctyltin dichloride is currently included in Annex VI to
Regulation (EC) No 1272/2008 and classified for human health effects. The current
classification for this substance is as follows.
Entry in Table 3.1 of Annex VI.
Acute Tox. 3
H331
Toxic if inhaled.
STOT RE 1
H372
Causes damage to organs through prolonged or
repeated exposure.
Entry in Table 3.2 of Annex VI.
T; R23-48/25
Toxic by inhalation.
Toxic: danger of serious damage to health by
prolonged exposure if swallowed.
Based on the classification of R48, dioctlytin dichloride would meet the Annex XIII criteria
for T.
According to the REACH registrants, dioctyltin bis((2-ethylhexyl mercaptoacetate) products
are self-classified as STOT re 1 (H372) and multi-constituent octyltin tris(2-ethylhexyl
mercaptoacetate) products that contain 10 per cent or more dioctyltin bis((2-ethylhexyl
mercaptoacetate) are self-classified STOT re 1 (H372), equivalent to R48 under the old
system.
The toxicity of the dioctyltin compounds is reviewed in detail in OECD (2006a). A category
approach was used whereby read-across from oral data for dioctyltin dichloride to dioctyltin
bis(2-ethylhexyl mercaptoacetate) was justified on the basis of rapid conversion of the
thioesters to dioctytin dichloride under the physiological conditions present in mammalian
gastric contents (0.07 M HCl). Therefore on this basis, as the R48 classification for dioctyltin
dichloride is relevant to oral exposure, it can be assumed that dioctyl tin bis(2-ethylhexyl
mercaptoacetate) would also meet the Annex XIII criteria for toxic (T). On a similar basis
(i.e. that under the conditions prevalent in gastric contents chlorination can occur to form
dioctyltin dichloride) it can also be assumed that the hydrolysis product dioctyltin
hydroxide/oxide would also meet the Annex XIII criteria for T.
The toxicity of monooctyltin compounds is reviewed in detail in OECD (2006b). Using
similar arguments as above, the OECD (2006b) review concluded that the oral toxicity data
for octyltin trichloride was an appropriate surrogate for octyltin tris(2-ethylhexyl
mercaptoacetate) (and by extension for dioctyltin hydroxide/oxide). OECD (2006b)
concluded that the NOAEL from the key 90-day oral study with octytin trichloride was
approximately 7 mg/kg bw/day with another 90-day oral study giving a LOAEL of
1.4-4.8 mg/kg bw/day based on decreased thymus weights.
38
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
No classifications for mammalian toxicity for the monooctyltin compounds considered are
reported in Annex VI to Regulation (EC) No 1272/2008. The REACH registration of octyltin
tris(2-ethylhexyl mercaptoacetate) includes a proposal for self-classification of the substance
both as a mono-constituent product and a multi-constituent product (where the substance is
present with dioctyltin bis(2-ethylhexyl mercaptoacetate); see section 3). For multiconstituent products with 10 per cent or greater of the dioctyl, STOT rep. exp. 1 (H372) is
proposed.
6
HUMAN HEALTH HAZARD ASSESSMENT OF PHYSICOCHEMICAL
PROPERTIES
Not relevant for this dossier.
7
ENVIRONMENTAL HAZARD ASSESSMENT
7.1
Aquatic compartment (including sediment)
7.1.1
Toxicity test results
7.1.2
Fish
The available toxicity data to fish for the dioctyltin and monoctyltin compounds considered
have been reviewed in OECD (2006a and 2006b) and these data are summarised in Table 7
(dioctyltin compounds) and Table 8 (monooctyltin compounds).
Table 7 Summary of fish toxicity test for dioctyltin compounds (taken from OECD
(2006a) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Dioctyltin dichloride
Brachydanio rerio
99.91%
96 h
LC50 >0.24 mg/l
NOEC ≥0.24 mg/l
Semi-static test using dilutions
of a WAF. Analysis as DOT.
(2)
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Brachydanio rerio
87.2%
96 h
LC50 >25 mg/l
NOEC ≥25 mg/l
Brachydanio rerio
70%
96 h
LC50 >20 mg/l
NOEC ≥20 mg/l
39
Semi-static test using dilutions
of a WAF. Analysis as total Sn.
(2)
Static test using a cosolvent/emulsifier. Analysis as
DOT. (2)
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 8 Summary of fish toxicity test for monooctyltin compounds (taken from OECD
(2006b) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Octyltin tris(2-ethylhexyl mercaptoacetate)
Brachydanio rerio
54.0%
96 h
LC50 >2.3 mg/l
NOEC ≥2.3 mg/l
Brachydanio rerio
70%
48 h
LC50 = 2.3 mg/l
NOEC = 0.36 mg/l
Cyrpinus carpio
98%
95 h
LC50 >0.95 mg/l
NOEC ≥0.95 mg/l
Semi-static test using dilutions
of a WAF. Analysis as total Sn.
(2)
Static test. Analysis as MOT.
(2)
Static test using dilutions of a
WAF. Analysis as MOT.
Bouwan (2010a). See below
for details. (2)
Octyltin trichloride (supporting information)
Brachydanio rerio
98.9%
96 h
LC50 >0.33 mg/l
NOEC ≥0.33 mg/l
Static test using dilutions of a
WAF. Analysis as Total
Organic Carbon.
In summary, acute effects in fish were observed in one test with octyltin tris(2-ethylhexyl
mercaptoacetate) only. Since the OECD (2006a and 2006b) evaluations were completed a
further acute toxicity study has become available. The results are summarised below.
Octyltin tris(2-ethylhexyl mercaptoacetate)
A 96-hour toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate)
with carp (Cyrpinus carpio) (Bouwman, 2010a). The method used was a static procedure
following OECD TG 203. The substance tested had a purity of 98%. The test was carried out
using dilutions of a water accommodated fraction (WAF) obtained from a 100 mg/l loading.
The WAF was prepared by stirring the test substance with the test medium for one day
followed by a one day stabilisation period. The WAF was filtered through glass wool prior to
use. The WAF dilutions used were 1.0, 10 and 100%. The 100% WAF solution was reported
to be “slightly hazy” indicating that undissolved test material (or hydrolysis products) was
present. The non-specific concentration of octyltin tris(2-ethylhexyl mercaptoacetate) present
in the 100% WAF solution was determined as total monooctyltin compounds (MOT) using
the method discussed in 4.3.2. Two determinations revealed the initial concentration to be
1,805 µg/l and 849 µg/l; the variability in the values was thought to reflect the fact that not all
of the substance (or its hydrolysis products) was dissolved. The concentration in the 100%
WAF solution determined at 24 hours was 466-511 µg/l and the concentration determined at
96 hours was 997-1,044 µg/l. A precipitate was observed to be formed with time in the 100%
WAF solution. The mean concentration measured over the entire 96-hour exposure period
was determined to be 945 µg/l.
The water used in the test was ISO medium and had a pH of 7.5—7.7 and a hardness of
180 mg/l as CaCO3. The dissolved oxygen concentration was in the range 5.5 mg/l to 9.1
mg/l and the temperature was 21°C over the duration of the test.
No mortalities or visible effects were evident in any of the exposed carp when compared with
the control carp. Although there is some uncertainty over whether or not all of the test
40
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
substance was dissolved in the 100% WAF solution, the results can be taken to show that no
adverse effects occurred over 96 hours at the solubility limit of the test substance.
7.1.3
Aquatic invertebrates
The available toxicity data to aquatic invertebrates for the dioctyltin and monoctyltin
compounds considered have been reviewed in OECD (2006a and 2006b) and these data are
summarised in Table 9 (dioctyltin compounds) and Table 10 (monooctyltin compounds).
Table 9 Summary of invertebrate toxicity test for dioctyltin compounds (taken from
OECD (2006a) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Dioctyltin dichloride
Daphnia magna
99.9%
48 h
EC50 >0.28 mg/l
NOEC ≥0.28 mg/l
Daphnia magna
98.8%
48 h
EC50 >0.005 mg/l
NOEC ≥0.005 mg/l
Daphnia magna
99.8%
21 d
EC50 >0.87 mg/l
LOEC = 0.87 mg/l
Semi-static test using dilutions
of a WAF. Analysis as DOT.
(Key study in REACH
registration) (2)
Semi-static test using dilutions
of a WAF. Analysis as total Sn.
(2)
Semi-static using cosolvent/emulsifier. Analysis as
DOT. (2)
NOEC = 0.41 mg/l
(parental survival)
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Daphnia magna
95%
48 h
EC50 = 0.17 mg/l
NOEC = 0.07 mg/l
Daphnia magna
No data
24 h
EC50 > 0.06 mg/l
NOEC ≥0.06 mg/l
Daphnia magna
87.2%
21 d
EC50 >3.2 mg/l
LOEC = 1.4 mg/l
NOEC = 0.29 mg/l
(reproduction and
parental survival)
41
Static using cosolvent/emulsifier. Analysis as
DOT. (2)
Static test using dilutions of a
WAF. Analysis as total Sn. (2)
Semi-static using dilutions of a
WAF. Analysis as total Sn. (2)
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 10 Summary of invertebrate toxicity test for monooctyltin compounds (taken
from OECD (2006b) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Octyltin tris(2-ethylhexyl mercaptoacetate)
Daphnia magna
70%
48 h
EC50= 1 mg/l
NOEC = 0.1 mg/l
Daphnia magna
98%
48 h
EC50 = 0.039 mg/l
NOEC = 0.029 mg/l
Daphnia magna
60.9%
21 d
LOEC = 0.16 mg/l
NOEC = 0.036 mg/l
Static test. Nominal
concentrations. (2)
Static test using dilutions of
a WAF. Analysis as MOT.
Bouwman (2010b). See
below for further details. (2)
Semi-static test using
dilutions of a WAF. Analysis
as total Sn. (2)
Octyltin trichloride (supporting information)
Daphnia magna
98.9%
48 h
EC50 >0.33 mg/l
NOEC ≥0.33 mg/l
Static test using dilutions of
a WAF. Analysis as Total
Organic Carbon.
Since the OECD (2006a and 2006b) evaluations were completed a further acute toxicity
study has become available. The results are summarised below.
Octyltin tris(2-ethylhexyl mercaptoacetate)
A 48-hour toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate)
with Daphnia magna (Bouwman, 2010b). The method used was a static procedure following
OECD TG 202. The substance tested had a purity of 98%. The test was carried out using
dilutions of a water soluble fraction (WAF) obtained from a 100 mg/l loading. The WAF was
prepared by stirring the test substance with the test medium for one day followed by a one
day stabilisation period. The WAF was filtered through glass wool prior to use. The WAF
dilutions used were 10, 18, 32, 56 and 100%. The non-specific concentration of octyltin
tris(2-ethylhexyl mercaptoacetate) present in the WAF solutions was determined as total
monooctyltin compounds (MOT) using the method discussed in 4.3.2. The concentrations
were determined both at the start of the test and at the end of the test. The measured
concentrations were found to be relatively stable over the 48 hour test period at the three
highest concentrations (89-114% of the initial value after 48 hours) but the measured
concentration was found to decrease slightly over the 48 hour period for the two lowest
concentrations (62-70% of the initial value after 48 hours). The average measured
concentration present in the solutions over the entire test period were determined to be 19, 29,
49, 75 and 124 µg/l for the 10, 18, 32, 56 and 100% WAF dilutions respectively (two
measurements were taken for each dilution at each sampling time and the results of the two
measurements were generally consistent).
The water used in the test was medium M7 and had a pH of 7.7-7.9 and a hardness of
180 mg/l as CaCO3. The dissolved oxygen concentration was in the range 9.1-9.3 mg/l and
the temperature was 19.1-19.7°C over the duration of the test.
42
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
No immobilisation or visible effects were evident in the 19 µg/l and 29 µg/l treatment groups
when compared with the control group. The percentage immobilised daphnia at higher
concentrations was 95% at 49 µg/l, 100% at 75 µg and 100% at 124 µg/l compared with 0%
in the control group. The 48-hour EC50 was determined to be 39 µg/l (95%-confidence
interval 36-43 µg/l) and the 48-hour NOEC was 29 µg/l.
At the higher test concentrations a large number of the Daphnia were observed to be trapped
at the surface (particularly after 24 hours). These organisms were re-immersed into the
solution prior to recording the mobility. It is not clear if this reflects the presence of a surface
film of undissolved test substance or not.
7.1.4
Algae and aquatic plants
The available toxicity data to aquatic invertebrates for the dioctyltin and monoctyltin
compounds considered have been reviewed in OECD (2006a and 2006b) and these data are
summarised in Table 11 (dioctyltin compounds) and Table 12 (monooctyltin compounds).
Table 11 Summary of algal toxicity test for dioctyltin compounds (taken from OECD
(2006a) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Dioctyltin dichloride
Scenedesmus
subspicatus
98.8
72 h
EC50 >0.002 mg/l
NOEC ≥0.002 mg/l
Test using dilutions of a WAF.
Analysis as total Sn. (2)
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
Scenedesmus
subspicatus
95%
Scenedesmus
subspicatus
No data
72 h
EC50 = 0.17 mg/l
NOEC = 0.04 mg/l
72 h
EC50 >0.06 mg/l
NOEC ≥0.06 mg/l
43
Test using co-solvent/emulsifier.
Analysis as DOT. (2)
Test using dilutions of a WAF.
Analysis as total Sn. (2)
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Table 12 Summary of algal toxicity test for monooctyltin compounds (taken from
OECD (2006b) unless otherwise indicated)
Species
Test
substance
purity
Duration
Result
Comment/ Klimisch code
Octyltin tris(2-ethylhexyl mercaptoacetate)
Pseudokirchneriella
subcapitata
98%
Pseudokirchneriella
subcapitata
54%
48 h
LOEC = 0.009 mg/l
NOEC = 0.0009
mg/la
72 h
EC50> 0.44 mg/l
(growth)
Test using dilutions of a WAF.
Analysis as MOT. Bouwman
(2010c). See below for further
details. (2)
Test using dilutions of a WAF.
Analysis as MOT. (2)
EC50 = 0.18 mg/l
(biomass)
NOEC = 0.007 mg/l
Octyltin trichloride (supporting information)
Pseudokirchneriella
subcapitata
100%
72 h
EC50= 0.22 mg/l
(growth)
Test using dilutions of a WAF.
Analysis as MOT.
EC50 = 0.13 mg/l
(biomass)
NOEC = 0.045 mg/l
Note: a) The large step in concentrations tested precludes a reliable estimate of the NOEC in this study.
Since the OECD (2006a and 2006b) evaluations were completed a further acute toxicity
study has become available. The results are summarised below.
Octyltin tris(2-ethylhexyl mercaptoacetate)
A toxicity test has been carried out using octyltin tris(2-ethylhexyl mercaptoacetate) with the
freshwater algal species Pseudokirchneriella subcapitata (Bouwman, 2010c). The method
used followed OECD TG 201. The substance tested had a purity of 98%. The test was carried
out using dilutions of a water soluble fraction (WAF) obtained from a 100 mg/l loading. The
WAF was prepared by stirring the test substance with the test medium for one day followed
by a one day stabilisation period. The WAF was filtered through glass wool prior to use. The
WAF dilutions used were 1, 10 and 100%. The non-specific concentration of octyltin tris(2ethylhexyl mercaptoacetate) present in the WAF solutions was determined as total
monooctyltin compounds (MOT) using the method discussed in 4.3.2. The initial
concentration determined in the 100% WAF solution was 18 and 27 µg/l. The concentration
was found to decrease to 37% of the initial value after 24 hours and 23% of the initial value
after 72 hours. The time weighted average concentration over the entire test period in the
100% WAF solution was 8.8 µg/l.
The water used in the test was medium M2 and had a pH of 8.2-8.3 at the start of the test and
a pH of 8.2 at the end of the test. The water harness was of 24 mg/l as CaCO3. The test
temperature was between 22.7-23.1°C over the duration of the test.
44
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
The inoculum concentration used was 1×104 cells/ml. After 72 hours incubation the cell
density was 151.4×104 cells/ml in the control group, 156.2×104 cells/ml in the 1% WAF
dilution group, 155.5×104 cells/ml in the 10% WAF dilution group and 126.4×104 cells/ml in
the 100% WAF group. The cell yield was statistically significantly reduced (by around
16.5%) compared to the control group for the 100% WAF group(α=0.05 level).
The mean growth rate over 0-72 hours was 0.0698 d-1 in the control group, 0.0702 d-1 in the
1% WAF dilution group, 0.0701 d-1 in the 10% WAF dilution group and 0.0673 d-1 in the
100% WAF dilution group. The reduction in growth rate over 72 hours for the 100% WAF
group was 3.6%. These data were not analysed statistically by Bouwman (2010c) as the
reduction in growth rate was <10%. When the growth rate over specific time periods was
considered it was evident that most of the reduction in growth rate occurred over the first
24-hour period.
Overall these data show that the effects on biomass but not growth rate occurred in the 100%
WAF group (~8.8 µg/l). No significant effects are evident at the next lowest treatment level
of a 10% WAF (no analytical verification of the level of substance present was undertaken
but presumably this would be around 0.9 µg/l). However, the large step in concentrations
tested precludes a reliable estimate of the NOEC.
7.1.5
Quantitative structure-activity relationships (QSARs)
No QSAR estimates of the toxicity of the substances are reported as no reliable QSARs are
available for organometallic compounds containing tin.
7.1.6
Sediment organisms
No data are available.
7.1.7
Other aquatic organisms
No data are available.
7.1.8
Summary of aquatic toxicity data
A number of aquatic toxicity data are available for the substances of interest. For fish, only
the results of acute toxicity tests are available. These data show no effects at the solubility
limit of the substances, except in one case with an LC50 above 1 mg/l where sufficiently high
concentrations could be maintained.
Long-term NOEC data are available for some substances for both aquatic invertebrates and
algae. These data are more relevant for the PBT analysis as the Annex XIII criteria are based
on long-term NOEC values. The relevant lowest long-term NOECs (excluding the limit
values) are summarised below.
45
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Dioctyltin compounds
Daphnia magna
Dioctyltin dichloride
21-d NOEC = 0.41 mg/l
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
21-d NOEC = 0.29 mg/l
Dioctyltin dichloride
No NOEC established
Dioctyltin bis(2-ethylhexyl mercaptoacetate)
72-h NOEC = 0.04 mg/l
Alga
Monooctyltin compounds
Daphnia magna
Octyltin tris(2-ethylhexyl mercaptoacetate)
21-d NOEC = 0.036 mg/l
Octyltin trichloride (supporting information)
No NOEC available
Octyltin tris(2-ethylhexyl mercaptoacetate)
72-h NOEC = 0.007 mg/l
Octyltin trichloride (supporting information)
72-h NOEC = 0.045 mg/l
Alga
The quoted (no) effect concentrations are given in terms of the equivalent concentration of
parent compound; in most tests the concentration present was verified by an indirect
measurement (usually total Sn or MOT or DOT) and the (no) effect concentrations were
back-calculated from this assuming all of the tin, MOT or DOT present was the parent
substance. However, as discussed in Section 4.1.1.2 all of the substances tested are likely to
be rapidly hydrolysed under the conditions used in the tests and so the organisms in the test
would be exposed to the hydrolysis products in addition to, or rather than, the parent
compound. To investigate this further the above NOECs must be converted from mg/l of
parent compound to mmol/l. The NOECs on a molar basis can then be converted to the
equivalent concentration of the main likely hydrolysis products, dioctyl tin hydroxide/oxide
for the dioctyl tin compounds and octyl tin hydroxide/oxide from the monooctyl tin
compounds4. The effect of carrying out this transformation is shown below.
Dioctyltin compounds
Daphnia magna
4
The actual identities of the respective hydroxide/oxide compounds is unclear from OECD (2006a and 2006b)
but may possibly include oligomeric/polymeric structures. For the conversion here it is assumed that, at least
initially, the substances are dioctyltin dihydroxide (molecular weight 378.7 g/mol) or octyltin trihydroxide
(molecular weight 282.7 g/mole).
46
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Dioctyltin dichloride
21-d NOEC = 9.9×10-4
mmol/l
~0.37 mg/l as dioctyltin
hydroxide
Dioctyltin bis(2-ethylhexyl
mercaptoacetate)
21-d NOEC = 3.9×10-4
mmol/l
~0.15 mg/l as dioctyltin
hydroxide
Dioctyltin dichloride
No NOEC established
Dioctyltin bis(2-ethylhexyl
mercaptoacetate)
72-h NOEC = 5.3×10-5
mmol/l
~0.020 mg/l as
dioctyltin hydroxide
Octyltin tris(2-ethylhexyl
mercaptoacetate)
21-d NOEC = 4.3×10-5
mmol/l
~0.012 mg/l as octyltin
hydroxide
Octyltin trichloride
(supporting information)
No NOEC available
Octyltin tris(2-ethylhexyl
mercaptoacetate)
72-h NOEC = 8.3×10-6
mmol/l
~0.0023 mg/l as octyltin
hydroxide
Octyltin trichloride
(supporting information)
72-h NOEC = 1.3×10-4
mg/l
~0.037 mg/l as octyltin
hydroxide
Alga
Monooctyltin compounds
Daphnia magna
Alga
When compared on this basis essentially the same conclusions are reached as those based on
the parent compounds.
The hydrolysis products from the 2-ethylhexyl mercaptoacetate derivatives will include the 2ethylhexyl mercaptoacetate ligand. The OECD (2006a and 2006b) evaluations report the
following toxicity data for 2-ethylhexyl mercaptoacetate itself: 48-h LC50 for fish = 9 mg/l,
48-h LC50 for Daphnia magna = 0.38 mg/l, 72-h EC50 for algal growth = 0.91 mg/l, 72-h
EC50 for algal biomass = 0.41 mg/l and 72-h NOEC for alga <0.5 mg/l. These results show
that the acute toxicity of the 2-ethylhexyl mercaptoacetate itself is generally of a similar order
to that seen in some of the tests with the tin derivatives, suggesting that at least some of the
toxicity seen may have been a result of release of the 2-ethylhexyl mercaptoacetate ligand
from hydrolysis of the substance. This may be particularly relevant to the octyltin tris(2ethylhexyl mercaptoacetate) substance as this, on hydrolysis, will release three molecules of
2-ethylhexyl mercaptoacetate) into solution for every one molecule of octyltin
hydroxide/oxide.
Overall the available ecotoxicity test results suggest that only octytin tris(2-ethylhexyl
mercaptoacetate) would meet the T criterion based on the ecotoxicity results. It is possible
that some of the toxicity seen with this substance could result from release of 2-ethylhexyl
mercaptoacetate into solution.
47
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
Assuming that hydrolysis does occur in these tests, then the best estimates for the toxicity of
the dioctyltin hydroxide/oxide or octyltin hydroxide/oxide hydrolysis products probably
come from the experiments with dioctyltin dichloride or octyltin trichloride, where the
chloride released would be unlikely to complicate the interpretation of the results. Note that
no true NOEC was established with alga in the test with dioctyltin dichloride.
48
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
8
PBT AND VPVB
8.1
Comparison with criteria from Annex XIII
Persistence
A substance is considered to be persistent (P) if it has a half-life >60 days in marine water or
>40 days in fresh or estuarine water, or >180 days in marine sediment or >120 days in
freshwater or estuarine sediment or soil. A substance is considered to be very persistent (vP)
if it has a half-life >60 days in marine, fresh or estuarine water, or >180 days in marine,
freshwater or estuarine sediment, or soil.
The available biodegradation screening studies suggest that dioctyltin dichloride, dioctytin
bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) are
potentially persistent based on lack of ready biodegradability.
Hydrolysis of the substances is likely to occur rapidly in aquatic systems. The initial
hydrolysis products formed are dependent on whether the substance is a dioctyltin substance
or a monooctyltin substance as the octyl groups attached to the tin atom appear to be more
resistant to hydrolysis than the other groups in the substances considered. Thus both
dioctyltin dichloride and dioctyltin bis(2-ethylhexylmercaptoacetate) will form essentially the
same hydrolysis product in the environment, dioctyltin hydroxide/oxide. Similarly both
octyltin trichloride (supporting substance) and octyltin tris(2-ethylhexylmercaptoacetate) will
form octyltin hydroxide/oxide.
As the hydrolysis reaction appears to be very rapid (half-lives of a few minutes to hours) it
can be expected that, on release to the environment, the substances considered will be rapidly
converted to the corresponding dioctyltin hydroxide/oxide or octyltin hydroxide/oxide and so
it is the properties of these hydroxide/oxide products that are most relevant to the PBT
assessment.
As such hydrolysis would also occur under the conditions of the ready biodegradation tests,
the results of these tests will reflect the biodegradability of the dioctyltin hydroxide/oxide or
octytin hydroxide/oxide and the released organic ligand. As none of the substances tested
were readily biodegradable it can therefore be concluded that the dioctyltin hydroxide/oxide
and octytin hydroxide/oxide are also not readily biodegradable and so potentially persistent.
Bioaccumulation
According to Annex XIII of REACH, a substance is considered to be bioaccumulative (B) if
it has a bioconcentration factor (BCF) >2,000 l/kg or very bioaccumulative (vB) if it has a
BCF >5,000 l/kg. However, the REACH Annex XIII criteria has recently been revised in
terms of using a weight of evidence approach in the assessment of B and vB in addition to the
numerical criteria.
Bioconcentration data are available for only one of the three substances considered in this
evaluation (dioctyltin bis(2-ethylhexyl mercaptoacetate)).
Carrying out a fish bioconcentration test for these substances is technically challenging owing
to the rapid hydrolysis of the substance and the lack of a suitable analytical methodology to
allow determination of the individual substances present. The main uncertainty in this
49
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
evaluation stems from the fact that the actual individual substances present in solution are not
know, only the total tin or total mono- and dioctyltin compounds. This would be important if
the uptake seen resulted from exposure of a minor component in water (for example if the
accumulative component made up only a small fraction of the total mono- or dioctyltin
compounds present) as, in this case, the actual BCF for the individual substance may be
higher than that determined based on the total tin, total mono- or total dioctyltin compounds.
Furthermore, if hydrolysis was actually slower than concluded, then the available test would
only give limited information on the bioaccumulation potential of the common hydrolysis
product. The analytical difficulties mean that it is not technically possible to investigate
further whether or not either of these situations is the case.
Overall, the available fish bioconcentration results are strongly suggestive that the BCF of
these substances is perhaps around 1,000 l/kg as a maximum (but more probably lower than
this (around 100 l/kg or less)). Therefore, based on the currently available information the
substances are considered not to meet the B criterion.
The available test does not provide any information on the accumulation of the monooctyltin
compounds. Based on read-across from the dioctyltin compounds it can be expected that the
bioaccumulation potential of the octyltin hydroxide/oxide hydrolysis products would similar
to, or possibly even lower than (based on its lower lipophilicity), that of the dioctyltin
hydroxide/oxide. However this read-across is another source of uncertainty in the overall
evaluation.
Toxicity
A substance fulfils the toxicity criterion (T) when:
- the long term no observed effect concentration (NOEC) for marine or
freshwater organisms is less than 0.01 mg/l; or
- the substance is classified as carcinogenic (category 1 or 2), mutagenic
(category 1 or 2) or toxic for reproduction (category 1, 2 or 3)5; or
- there is other evidence of chronic toxicity, as identified by the classifications
T, R48, or Xn, R48, according to Directive 67/548/EEC6.
Based on the classification of R48, dioctlytin dichloride would meet the Annex XIII criteria
for T.
The toxicity of the dioctyltin compounds is reviewed in detail in OECD (2006a). A category
approach was used whereby read-across from oral data for dioctyltin dichloride to dioctyltin
bis(2-ethylhexyl mercaptoacetate) was justified on the basis of rapid conversion of the
thioesters to dioctytin dichloride under the physiological conditions present in mammalian
gastric contents (0.07 M HCl). Therefore on this basis, as the R48 classification for dioctyltin
dichloride is relevant to oral exposure, it can be assumed that dioctyl tin bis(2-ethylhexyl
mercaptoacetate) would also meet the Annex XIII criteria for toxic (T). On a similar basis
5
The CLP Regulation (EC) No 1272/2008 will amend this to be substances classified as carcinogenic (category
1A or 1B), germ cell mutagenic (category 1A or 1B), or toxic for reproduction (category 1A, 1B or 2).
6 The CLP Regulation (EC) No 1272/2008 will amend this to be “there is evidence of chronic toxicity, as
defined by the classifications STOT (repeated exposure), category 1 (oral, dermal, inhalation of gases/vapours,
inhalation of dust/mist/fume) or category 2 (oral, dermal, inhalation of gases/vapours, inhalation of
dust/mist/fume, according to Regulation (EC) No 1272/2008”.
50
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
(i.e. that under the conditions prevalent in gastric contents chlorination can occur to form
dioctyltin dichloride) it can also be assumed that the hydrolysis product dioctyltin
hydroxide/oxide would also meet the Annex XIII criteria for T.
No classifications for mammalian toxicity for the monooctyltin compounds considered are
reported in Annex VI to Regulation (EC) No 1272/2008. The REACH registration of octyltin
tris(2-ethylhexyl mercaptoacetate) includes a proposal for self-classification of the substance
both as a mono-constituent product and a multi-constituent product (where the substance is
present with dioctyltin bis(2-ethylhexyl mercaptoacetate); see section 3). For multiconstituent products with 10 per cent or greater of the dioctyl, STOT rep. exp. 1 (H372) is
proposed.
Octyltin tris(2-ethylhexyl mercaptoacetate) does however meet the Annex XIII criteria for Tbased on the toxicity to algae. The situation as to whether the hydrolysis product, octyltin
hydroxide/oxide would meet the Annex XIII criteria based on the ecotoxicity data is less
certain as, on hydrolysis, octytin tris(2-ethylhexyl mercaptoacetate) would release
2-ethylhexyl mercaptoacetate into solution and this could contribute to some of the toxicity
seen.
8.2
Assessment of substances of an equivalent level of concern
Not relevant for this dossier.
8.3
Emission characterisation
Since this dossier relates to evaluation of the data in the context of whether the PBT criteria
are met, emission characterisation is not relevant.
8.4
Conclusion of PBT and vPvB or equivalent level of concern assessment
Overall it is concluded that the three substances considered, dioctyltin dichloride, dioctyltin
bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl mercaptoacetate) do not meet
the PBT or vPvB criteria. Although they are considered to be potentially persistent (in that
they do not biodegrade rapidly but rather hydrolyse rapidly to either dioctyltin
hydroxide/oxide or octyltin hydroxide/oxide that are themselves potentially persistent) and
toxic, the available evidence suggests that the substance/hydrolysis products do not meet the
Annex XIII criteria for bioaccumulation.
Carrying out aquatic testing in general for these substances is difficult owing to their poor
solubility, rapid hydrolysis, and difficulties with their analysis. In particular, conducting a
fish bioconcentration test for these substances is technically challenging owing to the rapid
hydrolysis and the lack of analytical methodology to allow determination of the individual
substances present to which organisms are exposed. This results in the following
uncertainties in the B-assessment:
•
The individual substances actually present in solution are not known; it was possible
only to measure concentrations on the basis of total tin or total mono- and dioctyltin
species. This would be important if the observed uptake was the result of exposure to
a minor component in water (for example if the accumulative component made up
51
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
only a small fraction of the total mono- or dioctyltin compounds present in the test
medium). In such a case, the actual BCF for the individual substance may be higher
than that determined based on the total tin, total mono- or total dioctyltin compounds.
The analytical difficulties mean that it is not technically possible to investigate further
whether or not this is the case.
•
The available data do not provide any information on the accumulation of the
monooctyltin compound or its degradation products. Based on read-across, it can be
expected that the bioaccumulation potential of the octyltin hydroxide/oxide
hydrolysis products would be similar to (or possibly even lower than) that of the
dioctyltin hydroxide/oxide. However this read-across is another source of uncertainty
in the overall evaluation.
•
The lack of a definitive hydrolysis rate for the test substance is important in relation
to the bioconcentration test, if hydrolysis had actually been much slower than has
been concluded from the available data. In this case, conclusions about the
bioaccumulation potential of the hydrolysis products could not be drawn from this
study. Again, the analytical difficulties mean that it is not technically possible
currently to investigate further whether or not this is the case.
Given the inherent difficulties in carrying out a BCF test for these substances, the fact that the
available data suggests that the B criterion is not met, and the need to minimise vertebrate
testing, it would be difficult to justify further testing in relation to the B criterion. Further
information on the level of hydrolysis that occurred under the exposure test conditions of the
definitive BCF study for dioctyltin (2-ethylhexyl mercaptoacetate) would greatly help in the
interpretation of this test data, however current analytical techniques mean this is not
possible. If such information showed that the level of hydrolysis was lower than concluded
here because of the study’s dosing system, such that exposure to the parent substance
predominated, then there may be grounds for evaluating further the bioaccumulation potential
of the common hydrolysis product dioctyltin oxide. However given its very low solubility, it
would appear this would not be possible following OECD Test Guideline 305 methodology.
For both dioctyltin bis(2-ethylhexyl mercaptoacetate) and octyltin tris(2-ethylhexyl
mercaptoacetate) hydrolysis would also result in formation of 2-ethylhexyl mercaptoacetate.
This substance is not considered to meet the PBT criteria as it has a low predicted BCF.
52
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
INFORMATION ON USE, EXPOSURE, ALTERNATIVES AND
RISKS
No information has been sought on alternatives.
OTHER INFORMATION
53
SUBSTITUTED MONO- AND DIOCTYLTIN COMPOUNDS - PBT/vPvB EVALUATION
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