Available online at www.sciencedirect.com
Waste Management 28 (2008) 1518–1527
www.elsevier.com/locate/wasman
Organometals of tin, lead and mercury compounds in landfill gases
and leachates from Bavaria, Germany
G. Ilgen a, D. Glindemann
a,1
, R. Herrmann
b,z
, F. Hertel
a,2
, J.-H. Huang
c,*
a
c
Central Analytic, Bayreuth Institute of Terrestrial Ecosystem Research (BITÖK), University of Bayreuth, D-95440 Bayreuth, Germany
b
Department of Hydrology, University of Bayreuth, D-95448 Bayreuth, Germany
Department of Soil Ecology, Bayreuth Institute of Terrestrial Ecosystem Research (BITÖK), University of Bayreuth, D-95440 Bayreuth, Germany
Accepted 4 June 2007
Available online 11 September 2007
Abstract
Organo-Sn, -Pb and -Hg compounds were monitored in gases and leachates of 11 municipal waste landfills and one hazardous waste
landfill from Bavaria, Germany, with the objectives to estimate the methylation of Sn, Pb and Hg and to assess the risk of their release
into the adjacent environment. In the gases, tetramethyl Sn predominated (>80% of total gaseous Sn) with concentrations up to 160 lg
Sn m3. Dimethyl-Hg and tetramethyl-Pb were only occasionally detected with concentrations up to 2.9 and 2.1 lg m3 as Hg or Pb,
respectively. In all leachates, trimethyl-Sn dominated with a maximum concentration of 2100 ng Sn L1. No organo-Pb compounds were
found, and monomethyl-Hg was detected in only one leachate. The concentrations of trimethyl-Sn were up to 100-fold higher in the
condensate water than in leachates, and the concentrations of organo-Sn compounds were lower in the adjacent groundwater than in
the corresponding leachates. The high abundance of methylated Sn species in the gases and leachates indicates Sn methylation, suggesting the landfill as a source for organo-Sn compounds. In comparison, methylation of Hg and Pb was of little importance, probably due to
low Hg concentrations and low rates of Pb methylation in the landfill. The risks of organo-Sn compounds release to the adjacent air is
low due to flaring of landfill gases. However, there is probable release of organo-Sn compounds, especially trimethyl-Sn, to the adjacent
groundwater.
Ó 2007 Elsevier Ltd. All rights reserved.
1. Introduction
Organo-Sn, organo-Hg and organo-Pb compounds play
an important role in the geochemical cycle due to their
higher toxicity, volatility and/or lipophilicity as compared
to their inorganic forms (Thayer, 1995).
Tin has a larger number of organometallic derivatives in
commercial use than any other element. This gave rise to a
*
Corresponding author. Present address: Institute of Biogeochemistry
and Pollutant Dynamics, Swiss Federal Institute of Technology Zurich
(ETHZ), ETH Zentrum, CHN, CH-8092 Zürich, Switzerland. Tel.: +41
44 632 88 19; fax: +41 44 63 11 18.
E-mail address: [email protected] (J.-H. Huang).
1
Present address: Goettinger Bogen 15, D-06126 Halle, Germany.
z
Deceased.
2
Present address: Alnylam Europe AG/Chemische Synthese, FritzHornschuch-Str. 9, D-95326 Kulmbach, Germany.
0956-053X/$ - see front matter Ó 2007 Elsevier Ltd. All rights reserved.
doi:10.1016/j.wasman.2007.06.020
dramatic increase in the worldwide production of organoSn compounds from less than 5000 tons in 1955 up to
50,000 tons in 1992 (Hoch, 2001). Organo-Sn compounds
are common industrial products which are used as biocides,
as stabilizing additives in polyvinylchloride (PVC) and as
antifouling agents. Peralkylated organo-Pb compounds
like tetramethyl Pb and tetraethyl Pb have been used as
antiknock additives in gasoline products for several decades (Łobiñski et al., 1994). Lead-containing antiknock
additives have been terminated for several years in Northern and Central Europe but are still used in many countries
of Eastern Europe. In addition to anthropogenic sources,
organo-Sn and organo-Pb compounds can be formed or
transformed by chemical and biological processes in the
environment such as biomethylation and transalkylation
(Hamasaki et al., 1995; Hempel et al., 2000). Unlike organo-Sn and organo-Pb compounds, organo-Hg com-
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
pounds in the environment are generally considered to
originate from natural processes instead of anthropogenic
emission, e.g., in situ Hg methylation in wetland soils
and aquatic ecosystem (St. Louis et al., 1996) and in vivo
methylation by organisms (Jereb et al., 2003).
Landfills are waste disposal sites for the deposit of waste
onto or into land, including domestic and industrial waste.
The major environmental impact to the landfill is emission
of pollutants via the leachate and gas pathway. The commercial use of Sn, Pb and Hg compounds reflects their
occurrence in the landfill body (Kjeldsen et al., 2002).
The anoxic conditions in the landfill may benefit the methylation of inorganic Sn, Pb and Hg (Lindberg et al., 2005).
Nevertheless, the occurrence and fate of organo-Sn, organo-Pb and organo-Hg compounds in landfills has not
been widely studied. Feldmann and Hirner (1995) identified tetramethyl-Sn, organo-Sn hydrides and five tetramethylethyl-Pb in landfill gases from central Germany.
Neither Hg0 nor methylated Hg species could be identified.
The concentrations of total gaseous Sn, Hg and Pb ranged
over the intervals 8.6–35, 0.05–0.13 and 0.01–0.03 lg m3,
respectively. However, much higher total gaseous Hg concentrations were observed in gases from the landfills in
USA with concentrations up to 12 lg m3 (Lindberg
et al., 2005). Furthermore, dimethyl Hg was the dominant
organo-Hg compound in the landfill gases. Mersiowsky
et al. (2001) found methyl-Sn, butyl-Sn and octyl-Sn species in the landfill leachates from eight European landfills.
Monobutyl-Sn predominated with a maximum concentration of 4.1 lg L1. Recently, ethylated and propylated Sn
species were found in landfill gases in Scotland and Germany (Mitra et al., 2005). In comparison with organo-Sn
compounds, there is still very little knowledge about organo-Pb and organo-Hg in the landfill leachates.
Therefore, the objectives of this study are: (1) to monitor
gaseous and ionic organo-Sn, -Pb and -Hg compounds in a
number of landfills from Bavarian, Germany; (2) to estimate the methylation of Sn, Hg and Pb in the landfills;
and (3) to estimate the risks of release of organo-Sn, -Pb
and -Hg compounds from the landfills to the adjacent
environment.
1519
(Table 1). In comparison, the air in the vicinity of the landfill contains lower percentages of CO2 and CH4 (up to 3.6%
and 1.2%, respectively). With the age of about 30 years old,
the investigated landfills were in the stable methanogenic
phase (CH4 concentrations higher than those of CO2 concentrations) (Barlaz et al., 1989; Kjeldsen et al., 2002). A
raised waste temperature (up to 28 °C related to ambient
air temperature <10 °C in February 2000) was due to
microbial activity at all sites (Table 2). Leachates and condensates from most landfills were neutral or slightly alkaline as a consequence of microbial methane production
(Barlaz et al., 1989). The conductivities (up to
17,000 lS cm1) and total organic and inorganic C and
total N concentrations (up to 2200 mg L1) in leachates
and condensates were much higher than in the groundwater. The various chemical parameters in the gases and
leachates indicate different phases of decomposition and
varying microbial activity at different landfills investigated.
2.2. Materials
All ionic organometallic species in the form of chlorides
and peralkylated organometallic species analyzed were purchased with purities between 95% and 99%. Sodium tetra(n-propyl)borate, 98%, was purchased from GALAB,
Geesthacht, Germany. Individual stock solutions
(10 lg mL1 as Sn, Pb or Hg) of ionic organometallic species (monomethyl Sn, monobutyl-Sn, monomethyl-Hg,
monooctyl-Sn, dimethyl-Sn, dibutyl-Sn, dioctyl-Sn, trimethyl-Sn, tributyl-Sn, and trimethyl-Pb) and peralkylated
organometallic species (dimethyl-Hg, tetramethyl-Pb, tetraethyl-Pb, tetramethyl-Sn and tetraethyl-Sn) were prepared in methanol and cyclopentane, respectively, and
stored at 40 °C in the dark. Working solutions with a
concentration of 0.1 lg mL1 as Sn, Pb and Hg were prepared before each use by dilution of the stock solutions
with methanol or cyclopentane.
All glassware and sampling bottles used were cleaned by
rinsing with tap water followed by Milli-Q water and subsequently stored in a 10% nitric acid bath for at least 48 h.
Before use, glassware was thoroughly rinsed with Milli-Q
water.
2. Materials and methods
2.3. Instrumentation
2.1. Site descriptions for the investigated landfills
The 12 investigated landfills (D1–D12) are located in
Bavaria, Germany. All landfills are municipal sanitation
facilities containing liners and leachate collection systems
with two exceptions. The one denominated D12, which is
used for deposition of hazardous waste, does not have a
polyethylene liner but is instead sealed with clay. Landfill
D2 is an old landfill still without a liner at the bottom.
At all investigated landfills, deposition began in the period
1972–1976.
The percentage of CO2 and CH4 in the landfill gases ranged between 5.9% and 39% and 12% and 71%, respectively
A double GC–ICP–MS coupling consists of two gas
chromatographs (HP Model 5890 and 6890) and an ICP–
MS (ELAN 5000, Perkin–Elmer SCIEX, Thornhill, ON,
Canada). This design allows us to analyze gaseous species
with the cryogenic trap method and to perform spitless
injection with large volumes of solvent in order to analyze
analytes with both low and high boiling points. The thin
and flexible transfer line (1.5 m length, 1/1600 od, 0.0400 id,
‘‘Silcosteel’’ deactive stainless steel tubing, Restek) is
heated by a combination of hot argon mixed with the
GC effluent before passing the transfer line using a T-joint
in the GC oven, and by electrical resistance heating. The
21–57
38–71
50
n.a.
39–59
32–61
48–56
57–64
12–44
49–69
25–43
0.23–1.2
5.9–30
25–37
32
n.a.
19–28
27–37
23–31
34–39
17–32
31–34
13–24
0.97–3.6
0.2–5.3
<DL–0.01
Range
Range
Range
2.4. Sampling of landfill gas and analysis of gaseous
organometallic compounds
0.07–2.1
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
1.5
<DL–3.0
<DL–0.21
<DL–0.22
22–66
11–44
23–52
15–56
32–160
7.0–34
38–40
16–25
22–96
<DL–2.9
<DL–0.18
<DL–0.18
19–42
10–36
20–50
14–19
29–160
5.6–28
31–32
14–22
20–79
n.a., not analyzed.
n, number of samples.
Absolute detection limits (DL: pg): tetramethyl-Sn = 1.8,dimethyl-Hg = 45, tetramethyl-Pb = 1.7.
a
Air samples in the vicinity of the landfill.
Median
Range
Median
flow through the transferline can be reversed to eliminate
the solvent peak and to prevent graphite deposition onto
the ICP–MS cones after large volume splitless injection.
Operation parameters of this system and further details
of the coupling were described by Glindemann et al. (2002).
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
0.98
<DL–0.34
Range
<DL–0.14
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
1.3
4.7–48
8.0–39
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
1.3
Median
Range
Median
Range
10
23
20
57
24
30
17
69
20
38
18
54
Median
Range
4.3–43
6.4–34
9.3
19
19
41
20
28
16
64
16
32
15
47
D1 (n = 9)
D2 (n = 3)
D3 (n = 1)
D4 (n = 3)
D5 (n = 4)
D6 (n = 4)
D7 (n = 4)
D8 (n = 5)
D9 (n = 4)
D10 (n = 3)
D11 (n = 3)
D12 (n = 3)a
Median
Total gaseous Hg
(lg Hg m3)
Dimethyl Hg
(lg Hg m3)
Total gaseous Sn
(lg Sn m3)
Tetramethyl Sn
(lg Sn m3)
Landfill
Table 1
Concentrations of carbon dioxide, methane, organometals of tin, mercury and lead compounds in the landfill gases
Tetramethyl Pb
(lg Pb m3)
Total gaseous Pb
(lg Pb m3)
CH4 (%)
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
CO2 (%)
1520
Sampling of landfill gases, leachates, condensates and
groundwater was conducted in February 2000. Landfill
gases were sampled at different places in each landfill using
1–10 L Tedlar bags (MKC/ANALYT) by pumping. To
prevent organometallic compounds from photolytic degradation, the Tedlar bags were shielded by aluminium foil
against UV radiation. Before each sampling, about 200 L
of fresh air was pumped through the pump for cleaning.
Clean-up of the Tedlar bag was conducted by evacuation
and argon purging in turns at least three times.
For speciation of gaseous organometallic species,
250 mL gas from the samples kept in the Tedler bags was
transferred using a gas-tight syringe, and passed through
a Pasteur pipette (150 mm length) filled with 2.0 g NaOH(s)
to remove CO2 and water vapor. Samples were then twice
trapped (ultimate tubing ID 0.53 mm and fused silica tubing ID 0.32 mm, both uncoated and methyl deactivated) at
approximately 186 °C (cooled in liquid argon) and further measured by GC (HP 5890)–ICP–MS. This method
allows analysis of analytes out of a boiling point ranging
from 40 to 200 °C. Quantification was conducted with
external standard mixture of 3.3 lg Sn, Hg and Pb m3
as dimethyl-Hg, tetramethyl-Sn and tetramethyl-Pb in
nitrogen gas (Fig. 1a). Total gaseous Sn, Hg or Pb was
defined as the sum of all identified and unknown gaseous
Sn, Hg or Pb species in the GC–ICP–MS chromatogram.
Using a similar analytical design, Feldmann et al. (2001)
demonstrated >90% recoveries of gaseous Sn compounds
from CO2-rich samples.
2.5. Sampling of aqueous samples and analysis of ionic
organometallic compounds
Landfill leachates were taken from wells, basins or pipes
and then filled in 1 L evacuated glass flasks with a glass
stopper and a hermetic polytetrafluoroethylene sealing
ring. Groundwater samples were taken in the vicinity of
the landfills. Condensate water was collected from the
landfill gas flair station. The groundwater was sampled
by pumping from the depth of 6–25 m at a distance of
50–600 m from the center of the landfills. The aqueous
samples were filtered through 0.45 lm filter of cellulose
acetate membrane for further analysis. All aqueous samples were then stored at 4 °C for no more than 2 weeks
until analysis.
Derivatization of the samples was done by 10 mg
sodium tetra(n-propyl)borate in acetate buffer (pH was
adjusted to 4), and extracted with 2 mL cyclopentane
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
1521
Table 2
Chemical parameters of landfill leachates, condensates and groundwater
Landfill
Range
Temperature (°C)
pH
Conductivity (lS cm1)
Total organic C (mg L1)
Total inorganic C (mg L1)
Total N (mg L1)
Leachate
D1 (n = 5)
D2 (n = 2)
D3
D4
D5
D6
D7 (n = 2)
D8
D9
D10 (n = 3)
D11 (n = 4)
D12
7.1–28
10–16
24
n.a.
6.2
12–18
5.2–18
7.1
18
6–11
7.7–15
12
7.1–8.5
7.2–7.3
7.4
n.a.
n.a.
7.1–8.0
7.6–7.8
7.1
7.7
7.0–8.2
7.3–7.9
9.0
3500–10,000
3000–8500
13,000
n.a.
4200
2510–17,000
4800–5500
5000
3200
2620–5500
6200–8000
60,000
99–350
20–61
430
n.a.
127
18–760
210–260
120
160
220–550
230–280
1300
84–500
98–670
900
n.a.
210
1300–2200
130–160
160
110
380–490
600–730
840
83–480
64–210
550
n.a.
55
210–640
170–220
240
160
220–380
250–380
520
Condensate
D9
D10
8.8
21
5.9
7.1
500
5600
230
180
65
580
100
580
Groundwater
D2
D6
D12
9.2
12
12
6.6
7.1
6.5
2200
2500
1000
5.0
18
<DL
220
2200
27
58
210
10
n.a., not analyzed.
n, number of samples; n = 1, if not otherwise mentioned.
containing tetraethyl-Sn in 10 ng Sn as internal standard by
vigorous shaking for 10 min. The cyclopentane extract was
cleaned-up with a Pasteur pipette (150 mm length) filled
with 0.15 g Al2O3 (3% deactived with Milli-Q water) and
was then analyzed with a coupling of a gas chromatograph
(HP 6890) to an ELAN 5000 ICP–MS (Perkin–Elmer
SCIEX, Thornhill, ON, Canada). A GC–ICP–MS chromatogram with propyl derivates of ionic organo-Sn standards is shown in Fig. 2a.
2.6. Further analysis
Analysis of CO2 and CH4 in the landfill gas was carried
out with GC (HP-6890)-TCD. Total inorganic and organic
carbon was determined as CO2 after acidification of the
sample with HCl and then combustion at 800 °C (Elementar, High TOC). Total N was detected as N2 after combustion. For analysis of total Sn, Hg and Pb in leachates,
15 mL samples were filtered to 0.45 lm. Total Sn and Pb
were then directly determined by ICP–MS (PlasmaQuad
II+ Turbo, VG Elemental) and total Hg by AAS (AAS
4100, FIAS 400, Perkin–Elmer).
3. Results
3.1. Organotin, organomercury and organolead compounds
in landfill gases
In all investigated landfills, gaseous Sn species were
detected in the gas phase with the highest total gaseous
Sn concentration up to 160 lg Sn m3 (Table 1). Tetramethyl-Sn was the dominant Sn species and occupied at
least 80% of the total concentrations of gaseous Sn
(Fig. 1b). Additionally, several unidentified gaseous Sn species were detected in the landfill gases. Gaseous Hg and Pb
species were only found in the landfill gases at three of the
12 investigated sites (D1, D4 and D12). Their concentrations were at least one order of magnitude lower than the
concentrations of Sn species. The concentrations of
dimethyl-Hg were up to 0.18 lg Hg m3 in landfill gases
at sites D1 and D4, whereas the dimethyl-Hg concentrations reached a value of 2.9 lg Hg m3 in the landfill gases
at site D12. Tetramethyl-Pb and some unidentified Pb species were detected in the landfill gases at site D12 with concentrations up to 2.1 lg Pb m3 for tetramethyl-Pb and
5.3 lg Pb m3 for total gaseous Pb. Unknown gaseous
Pb species were also found in the landfill gases at site
D04, however, with much lower concentrations (0.01 lg
Pb m3) compared to those at site D12.
3.2. Organotin, organomercury and organolead compounds
in landfill leachates, landfill condensates and adjacent
groundwater
Methyl-Sn (mono-, di- and trimethyl-Sn), butyl-Sn
(mono-, di- and tributyl-Sn) and octyl-Sn species (monoand dioctyl-Sn) were identified in the landfill leachates
(Fig. 2, Table 3). Among all organo-Sn compounds, trimethyl-Sn predominated with concentrations between 22–
480 ng Sn L1 in most cases. Dimethyl-Sn was the second
abundant organo-Sn compound in the landfill leachates.
The concentrations of dimethyl Sn ranged up to 430 ng
Sn L1. At site D12, the concentrations of trimethyl-Sn
and dimethyl-Sn in the leachates (2100 and 980 ng Sn
1522
a
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
a
50000
50000
Tetramethyl Sn
TTET
Tetramethyl Pb
40000
Intensity (cps)
Intensity (cps)
40000
30000
20000
Dimethyl Hg
30000
20000
TBT
TMT
DBT
TTPrT
10000
10000
DMT
0
0
50
100
150
200
DOT
MMT
0
250
200
300
400
Retention time (s)
b
MOT
MBT
120
Sn
202
Hg
208
Pb
500
600
700
Retention time (s )
b
1600000
Tetramethyl Sn
120000
TTET
MBT
1200000
Intensity (cps)
Intensity (cps)
DBT
80000
800000
Dimethyl Hg
400000
Tetramethyl Pb
40000
TMT
120
TTPrT
Sn
202
Hg
208
Pb
0
0
200
400
600
800
Retention time (s)
Fig. 1. (a) GC/ICP–MS chromatograms of gaseous organometals of Sn,
Pb and Hg compounds standards with 0.1 lg as Sn, Hg and Pb. (b) GC/
ICP–MS chromatograms of gaseous organometals of Sn, Pb and Hg
compounds from D12 landfill gas.
L1, respectively) were extraordinarily high compared to
those from the other sites. The concentrations of monomethyl-Sn in the landfill leachates (up to 83 ng Sn L1) were
much lower than trimethyl-Sn and dimethyl-Sn, so that the
abundance of methyl-Sn species in the landfill lechates was
in the order tri- > di- monomethyl-Sn. The buthyl-Sn
and octyl-Sn species were much less abundant than methyl
Sn species in the landfill leachates. The concentrations of
butyl-Sn and octyl-Sn species never exceeded 570 and
17 ng Sn L1, respectively. In contrast to methyl Sn species,
the abundance of butyl Sn species in the landfill leachates
was in the order mono- > di- > tri-butyl Sn. Organo-Hg
compounds was detected only in one leachate (D1) as
monomethyl-Hg with concentrations of 21 ng Hg L1.
No organo-Pb compounds were detected in any of the
investigated leachates.
The concentrations of total Sn were generally higher
than total Pb in the landfill leachates and were much higher
than those of total Hg (Table 3). At site D12, the total Sn
and Hg concentrations in the leachates (210 lg Sn L1 and
1.9 lg Hg L1) were much higher than those from the other
sites. However, the concentration of total Pb in leachates at
DMT
TBT
MMT
MOT
DOT
0
200
300
400
500
600
700
Retention time (s)
Fig. 2. (a) GC/ICP–MS Sn120 chromatograms of (a) organo-Sn standards
with 5 ng Sn of each species and (b) organo-Sn compounds in D06 landfill
leachate. (Abbreviations used are TMT (propyl derivates of trimethyl-Sn),
MMT (monomethyl-Sn), TTPrT (tetrapropyl-Sn), MBT (monobutyl-Sn),
(DBT) dibutyl-Sn, (TBT) tributyl-Sn, (MOT) monooctyl-Sn, (DOT)
dioctyl-Sn.)
site D12 was only slightly higher than those from the other
sites.
In condensate water, the concentrations of trimethyl-Sn
(610 ng Sn L1 at site D9 and 2300 ng Sn L1 at D10) were
much higher compared to those in the corresponding landfill leachates (29 and 28–98 ng Sn L1, respectively) (Table
2). In comparison, the concentrations of other organo-Sn
compounds in the condensates were at a quite similar level
to those in the leachates. No organo-Pb and organo-Hg
compounds were found in the condensates.
In the investigated groundwater, the concentrations of
organo-Sn compounds were all below 60 ng Sn L1. The
concentrations of methyl-Sn species in the investigated
groundwater were much lower than those in the landfill
leachates. Especially at site D12, the concentrations of trimethyl-Sn and dimethyl-Sn decreased largely from 2,100
and 980 ng Sn L1, respectively, in the landfill leachates
to 0.7 ng Sn L1 respective below the detection limit in
Table 3
Concentrations of organo-Sn compounds (ng Sn L1) in landfill leachates, condensates and groundwater
Landfill
Dimethyl Sn
Monomethyl Sn
Tributyl Sn
Dibutyl Sn
Monobutyl Sn
Dioctyl Sn
Monooctyl Sn
Total Organo-Sn
Median Range
Median Range
Median Range
Median Range
Median Range
Median Range
Median Range
Median Range
Range
Leachte
D1 (n = 5)
D2 (n = 2)
D3
D4
D5
D6
D7 (n = 2)
D8
D9
D10 (n = 3)
D11 (n = 4)
D12
41
245
220
140
130
68
27
65
29
58
170
2100
28–88
18
160–330 228
36
150
170
25
22–31
<DL
14
20
28–98
1.0
56–480 122
980
Condensate
D9
D10
2300
610
<DL
11
4.4
<DL
<DL
Groundwater
D2
54
D6
13
D12
0.7
<DL–28 7.3
25–430
14
<DL
9.4
<DL
10
<DL
<DL
3.5
<DL–16 3.6
20–410
12.4
24
<DL–8.0 <DL
3.3–25
1.3
5.2
<DL
<DL
15
<DL
2.4
<DL
1–3.8
0.3
<DL–83 <DL
<DL
9.0
<DL–2.6 2.1
51
14
14
210
<DL
38
0.6
<DL–2.4 3.7
6.9
<DL
<DL–14
1.1–3.0
8.4–110
19
33
<DL
31
570
9.8
40
11
<DL–5.5 9.2
4.6–11
33
<DL
<DL
0.2
10
<DL
<DL
<DL
8.6–11 <DL
<DL
2.8
5.4–9.3 <DL
12–44 <DL
<DL
3.1
0.9
<DL
<DL
<DL
0.9
95
25
7.0
1.8
120
6.3
2500
650
0.7
<DL
1.5
0.1
<DL
1.5
0.4
<DL
27
1.8
12
19
0.6
<DL
12
1.5
2.1
21
64
27
83
10–27
<DL–6.8 <DL
<DL–0.3 <DL
<DL
<DL
<DL
45
<DL
<DL
12
<DL–3.6 <DL
<DL
<DL
<DL–17
48–200
400–620
350
320
340
940
31–41
160
80
<DL–0.9 59–120
140–1000
3100
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
Trimethyl Sn
n, number of samples; n = 1, if not otherwise mentioned.
Detection limits (ng Sn L1): trimethyl Sn = 0.01, dimethyl Sn = 0.08, monomethyl Sn = 0.02, tributyl Sn= 0.08, dibutyl Sn = 0.3, monobutyl Sn = 0.8, dioctyl Sn = 0.2, monooctyl Sn= 0.4.
1523
1524
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
the groundwater. Conversely, butyl-Sn and octyl-Sn species, which were not found in the leachates, were detected
in the groundwater at site D12. No organo-Pb or organo-Hg was observed in the investigated groundwater.
The concentrations of total Sn, Hg and Pb in the groundwater were apparently lower than those in the leachtes at
both sites and were mostly below detection limits.
4. Discussion
The high percentages of CO2 and CH4 in the landfill
gases indicate the anoxic conditions in the landfills. The
generation of CH4 by anaerobic microorganisms suggests
that landfills may act as a bioreactor for methylated heavy
metals compounds (Lindberg et al., 2001, 2005). The high
abundance and dominance of tetramethyl-Sn and trimethyl-Sn in the investigated landfill gases and leachates,
respectively, compared to the other organo-Sn compounds
support the methylation of inorganic Sn in the landfills. To
our knowledge, there is no industrial use of trimethyl-Sn,
and the anthropogenic organo-Sn compounds are mostly
butyl-Sn species (Hoch, 2001). This is reflected by the much
more abundance of butyl-Sn species than methyl-, octyland phenyl-Sn species in different environments where organo-Sn compounds are found, e.g., soils, sediments and
natural waters (Wilken et al., 1994; Hoch, 2001; Jiang
et al., 2001; Huang et al., 2004). Methyl-Sn species found
in the environment may be partly originated from in situ
methylation processes (Pecheyran et al., 1998; Tessier
et al., 2002). In the environmental compartments without
Sn methylation processes, methyl-Sn species will degrade
and no tetramethyl-Sn will be emitted (Huang and Matzner, 2004a). There are no significant correlations between
concentrations of methyl Sn species and CH4 in gases
and total Sn in leachates for the entire data set. This may
be due to the different chemical and biological reactivity
at each site and because the methylation of Sn and CH4
formation is controlled by different processes in landfills.
In simulated landfills, the CH4 production started at 20
days and reached its maximum at 70 days after incubation
(Barlaz et al., 1989). In comparison, the concentrations of
methyl Sn species bloomed at the first 30 days and
decreased dramatically after 56 days (Michalzik et al.,
2007).
In comparison with methylated Sn, methylated Hg and
Pb species were only occasionally found in our landfill
gases and leachates. Lindberg et al. (2001, 2005) have demonstrated the formation of dimethyl-Hg and monomethylHg in the landfills with highest concentrations of
100 ng m3. In contrast, methylated Hg could not be found
in the landfill gases in central Germany (Feldmann and
Hirner, 1995). The methylated Hg detected at sites D1,
D4, D8 and D12 suggest a potential for methylation of
Hg in these landfills. The Hg methylation process occurring
in the landfills appears to be dependent on the Hg concentrations in the landfills. This is suggested by the very low
total Hg concentrations in the leachates at the sites with
methylated Hg below the detection limit (Table 4). The
concentrations of Hg compounds in the landfill leachates
may range up to 160 lg L1 (Christensen et al., 2001).
Table 4
Concentrations of total Sn, Hg and Pb in the landfill leachates, condensates and groundwater
Landfills
Total Sn (lg Sn L1)
Total Hg (lg Hg L1)
Total Pb (lg Pb L1)
Median
Range
Median
Range
Median
Range
Leachate
D1 (n = 5)
D2 (n = 2)
D3
D4
D5
D6
D7 (n = 2)
D8
D9
D10 (n = 3)
D11 (n = 4)
D12
12
2.9
35
n.a.
<DL
100
17
110
<DL
3.4
20
210
1.8–53
<DL–5.8
0.09
<DL
<DL
n.a.
<DL
0.04
0.12
0.21
<DL
<DL
<DL
1.9
<DL–0.23
8.2
7.7
11
n.a.
9.1
18
18
21
<DL
11
4.5
25
2.0–12.0
3.2–12
Condensate
D9
D10
n.a.
<DL
n.a.
<DL
n.a.
<DL
Groundwater
D2
D6
D12
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
4.6
16–17
<DL–22.2
13–28
n = 1, if not otherwise mentioned.
n.a., not analyzed.
Detection limits: 1 lg L1 for Sn and Pb, 0.04 lg L1 for Hg.
0.11–0.14
16–20
<DL–74
3.8–5.2
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
The low concentrations of total Hg in our landfill leachates
may be explained by strictly enforced limitation on Hg
deposition on landfills in Germany. Subsequently, the concentrations of bioavailable Hg for methylation is low. Further explanation is the immobilization of Hg by
precipitation with biogenic sulfide in the landfill body
(Kjeldsen et al., 2002). Craig and Moreton (1986) postulated that S2 prevented methylation of Hg2+ by precipitation of very insoluble HgS. In addition, the presence of S2
aided the conversion of monomethyl-Hg into dimethyl-Hg
(Weber et al., 1998). This may explain why dimethyl-Hg
was more frequently found in our landfills than monomethyl Hg.
The landfill deposition of Pb and Sn is not as strictly regulated as Hg in Germany. Lead and Sn may have been buried in a landfill as part of domestic waste in the form of
metallic ingredients of common goods or as incineration
ash. These deposited metals and ashes could undergo corrosion under landfill conditions and subsequently generate
high concentrations of dissolved metals in leachates. The
much higher concentrations of methylated Sn than methylated Pb might be explained by a higher rate of methylation
of Sn compared to Pb. This may due to fact that the Pb–C
linkage is more labile than Sn–C, which enhances the rates
of dealkylation, and the extreme instability of monoalkylPb, which favors formation of inorganic Pb (Thayer, 1995).
Several gaseous Sn species in our landfill gases could not
be identified due to the lack of available standards. The
chromatogram indicates higher boiling points for these
unknown Sn species than for tetramethyl-Sn. Thus, they
may be methylbutyl-Sn, butyl-Sn hydrides and methylbutyl-Sn hydrides instead of methyl-Sn hydrides. Feldmann
and Hirner (1995) indicate higher boiling points for
monobutyl Sn and dibutyl Sn hydrides with 98 and
204 °C, respectively, than for tetramethyl Sn (82 °C). The
occurrence of methylbutyl-Sn and butyl-Sn hydrides has
already been reported for the other landfills (Feldmann
and Hirner, 1995; Mailefer et al., 2001).
Leaching of organo-Sn compounds from the polyvinyl
chloride (PVC) pipes into drinking water has been demonstrated (Sadiki et al., 1996, 1999). Nevertheless, Mersiowsky et al. (1999) indicated that leaching of organo-Sn
compounds from PVC products under landfill conditions
was found to be generally low. The occurrence of monoand dioctyl-Sn in the landfill leachates indicates PVC products as a source of organo-Sn compounds, since octyl-Sn
species are employed solely as PVC stabilizers (Mersiowsky
et al., 2001). For butyl-Sn species, there may be some additional sources. Butyl-Sn species are also applied for wood
preservation, used in glass treatment, used in agrochemicals and used for material protection (Hoch, 2001). The
apparent dominance of monobutyl-Sn among butyl-Sn
species in the landfill leachates points out the dealkylation
of butyl-Sn in the landfill.
Interestingly, the concentrations of trimethyl-Sn in the
condensates were up to 100-fold higher than in the corresponding leachates. To explain these high levels in the con-
1525
densates, we suggest that the gaseous tetramethyl-Sn is
demethylated to trimethyl-Sn in the landfill gas pipes and
adsorbed by the relatively small amount of condensed
water to produce a high concentration of trimethyl-Sn in
the condensate. Di- and monomethyl-Sn in the condensates
may be the products of further demethylation of trimethylSn. Beside methyl-Sn species, monobutyl-Sn and monooctyl-Sn were found in the condensates, but less enriched.
The occurrence of butyl-Sn and octyl-Sn species point
out the probable release of ionic organo-Sn compounds
to the gas phase as halides (Mester and Sturgeon, 2002;
Saint-Louis and Pelletier, 2004). This can be true because
the concentrations of chloride are usually very high in the
landfill leachates (150–4500 mg L1, Kjeldsen et al.,
2002). Also, the butyl-Sn and octyl-Sn may travel as their
peralkylated or hydride derivates and did undergo subsequent degradation and condensation. It is not easy to evaluate the relevance of both pathways for the occurrence of
ionic organo-Sn compounds in the condensates due to
the limited knowledge. However, the low concentrations
of gaseous butyl- and octyl-Sn derivates in the landfill gases
suggest that the pathway of halide formation seems to be
more important for butyl- and octyl-Sn species. Although
the tetramethyl-Sn concentrations were at the same level
in D9 and D10 gases, the concentration of trimethyl-Sn
in the condensate of D9 (2300 ng Sn L1) was much higher
than in that of D10 (610 ng Sn L1). Probably, the rate of
demethylation differed among sites, which should be
addressed in the further investigation.
The organo-Sn compounds in the landfill leachates may
have an impact on the adjacent groundwater, especially at
the landfills without a liner system. For example, a high
concentration of trimethyl-Sn was observed in the adjacent
groundwater at site D2. Still, the concentration of trimethyl-Sn was high in the adjacent groundwater at a site
with a liner system (D06). However, we do not know
how the organo-Sn compounds penetrate the liner. Here,
the soils play a role as filter reducing concentrations of organo-Sn compounds in the adjacent groundwater. There is a
lowest decrease of concentrations from the landfill leachates to groundwater for trimethyl-Sn among all organoSn compounds, coinciding with the lowest affinity of trimethyl-Sn to organic and mineral soil materials (Huang
and Matzner, 2004b). The concentrations of all organoSn compounds in groundwater at site D12 is low; probably
the sealed clay is a more effective adsorbent than soils and
polyethylene liner (Hermosin et al., 1993).
There is little knowledge about the ecotoxicological
effects of trimethyl-Sn in the environment. However, tributyl-Sn with a similar structure to trimethyl-Sn cases chronic
and acute poisoning of the most sensitive aquatic organisms, such as algae, zooplankton, mollusks and the larval
stage of some fish even at low nanomolar aqueous concentrations (1–2 ng L1) (Gibbs and Bryan, 1996). Lethal concentrations are in the range of 40–1600 ng L1 for short
term exposure, depending on the aquatic species (Hoch,
2001). Generally, the toxicity of trimethyl-Sn seems to be
1526
G. Ilgen et al. / Waste Management 28 (2008) 1518–1527
higher than that of tributyl-Sn (Hoch, 2001). Therefore, the
elevated concentrations of trimethyl-Sn in the groundwater
indicate an increasing risk to the aquatic ecosystem in the
vicinity of the landfill. Since June 2005, waste in Germany
must be treated in such a way that it cannot degrade further or release pollutant (BMU, 2007). Much lower concentrations of organo-Sn compounds in gases and
leachates may be thus expected from the future landfills.
5. Conclusion
Landfills may serve as bioreactors for methylation of Sn
species. The high concentrations of gaseous Sn species suggest the landfills as a possible anthropogenic source of organo-Sn compounds emission to air. However, generated
landfill gases are generally flared in Germany, leading to
decomposition of organo-Sn compounds to its less toxic
inorganic form. Emissions of organo-Hg and organo-Pb
compounds from the investigated landfills are low, probably due to the low Hg concentrations and low rates of Pb
methylation in the landfills. The elevated trimethyl-Sn concentrations in the adjacent groundwater indicate a contamination potential of organo-Sn compounds from the
landfills to adjacent groundwater from the landfills.
Acknowledgements
The authors thank the members of Central Analytic,
Bettina Popp, Petra Dietrich and Yvonne Hoffmann, for
their analytical support and help with sampling. We particularly acknowledge the GALAB, Geesthacht, for their
assistance concerning this research. We appreciate also
the help of the municipal authorities during the sampling
events at the investigated landfills. Financial support of this
study came from Bayerischer Forschungsverband Abfallforschung und Reststoffverwertung. Thanks also due to
Dr. Björn Berg for his comments on this manuscript and
language editing.
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