Hypochlorite – breakdown products and reaction-products relevant to the BPR
October 2016
Background & purpose of the document
The Biocidal Products Regulation states that residues, including breakdown and reaction products, should be
considered when assessing the effects of the biocide on health and the environment.
This document summarises relevant data for hypochlorite solutions sold for domestic or professional
cleaning and hygiene uses, drawing extensively on the EU Risk Assessment Report (EU RAR) compiled under
the Existing Chemicals Regulation.
The sections highlighted in yellow are notes for the companies about items they will need to add when
using the document as support for specific product dossiers.
Sodium hypochlorite solutions slowly disproportionate during storage into other inorganics, principally the
ions chlorate and chloride. During use, when in contact with organic matter and similar material,
hypochlorite is rapidly broken down primarily into chloride ion and water, neither of which pose a risk to
health or the environment. Like all reactive biocides sodium hypochlorite will yield some reaction byproducts. These two groups of substances are discussed in turn below.
Breakdown products
The slow disproportionation during storage into chlorate and chloride is summarised by the following
equation1:
3 NaClO→ 2 NaCl + NaClO3
Keq = 1027
The process depends on time, temperature and concentration of the solution, being faster in more
concentrated solutions and at elevated temperatures, and also pH. A 15% solution of hypochlorite as
commonly purchased by formulators will lose one sixth of its initial concentration within 3 months at room
temperature. Dilute solutions ready for use show only minor concentration losses. In bleach solutions
formulated at 3-5% hypochlorite there is a slow conversion of hypochlorite to chlorate and chloride: 10 to
20% hypochlorite is broken down in domestic products after storage for 1 year at 20°C2.
Disproportionation can also be accelerated by light. Metal impurities can also catalyse an alternative
decomposition to chloride with the release of oxygen:
2 NaClO → 2 NaCl + O2
Consequently, steps are taken during production to exclude trace metal impurities.
Products should be formulated with sufficient initial hypochlorite concentration to maintain efficacy until
the use by date bearing in mind the storage conditions normally likely to be encountered.
Stabilizers and impurities in the concentrated solution (15% w/w) are typically of the following order3:
•
Sodium hydroxide: 2-6 g/kg (up to 10 g/kg)
•
Sodium chloride 100-140 g/kg
•
Sodium carbonate 3-20 g/kg
•
Sodium chlorate 0.4-1.5 g/kg (up to 7 g/kg)
•
Sodium bromate 3-45 mg/kg (up to 90 mg/kg)
•
Iron 0.5-3 mg/kg
•
Mercury 0.10-0.25 mg/kg (up to 1.2 mg/kg)
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For chlorate a TDI (Tolerable Daily Intake) of 3ug/kg body weight has recently been proposed by the
European Food Standards Agency (EFSA). The EFSA report4 indicates that the major source of exposure for
much of the population is drinking water, with use of active chlorine biocides to disinfect food and food
contact surfaces also an important source.
[NOTE - The submitted risk assessment will need to include a calculation of potential exposure to chlorate
residues on surfaces etc. This will depend on the chlorate level in the product.]
As regards environmental safety, a freshwater PNEC of 1mg/l for sodium chlorate is available from the
consortium submitted ECHA dossier for this substance5. A worst-case calculation of the local environmental
concentration predicted to arise is set out in Appendix 1. This yields an RCR (PEC/PNEC) of 0.029, well below
1 which indicates no likely risk to the environment.
[NOTE – the submitted risk assessment would need a parallel calculation for hypochlorite used in I&I
cleaning where the chlorate levels may be different because of different concentrations and storage
parameters.]
The EU RAR concluded that in the household scenario mercury doesn’t represent a problem as only a
minimal percentage deposits as residues on washed surfaces, from which it cannot evaporate as it is the
form of ionised inorganic soluble mercury6.
Products of reaction and decomposition during cleaning and hygiene use
All reactive biocides de facto produce reaction by-products on contact with substrates during use. Peroxides
for example will produce a range of oxidised reaction products depending on the substrate. Hypochlorite
similarly produces a range of oxidised by-products but has attracted particular attention because it also gives
rise to minor quantities of halogenated by-products which historically have been a focus of concern. The
reactions taking place have been summarised schematically as follows7:
The principal reaction product accounting for most of the chlorine content is chloride ion and this rapid
mineralisation of the active biocide to an innocuous, environmentally ubiquitous species is an advantage of
hypochlorite and indeed of some similar oxidising biocides.
The oxidation of organic substrates would be expected to reduce hazard and improve their environmental
compatibility. Reduced inorganics such as sulphide and ammonia will also be oxidised to e.g. sulphate and
nitrate which reduces their ecotoxicity by orders of magnitude.
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A minor reaction pathway, consuming typically of the order of 1% of the applied active chlorine dose, is
chlorination of some organic substrates to yield certain organohalogen compounds2,8. Established cleaning
and hygiene uses take place at neutral to alkaline pH. Consequently:



The range of species formed closely parallels the range of ‘disinfection by-products’ (DBPs) formed
during disinfection of potable water before distribution, and during disinfection of swimming pools.
The main species formed are trihalomethanes (THMs) particularly chloroform and haloacetic acids
(HAAs). A second tier of DBPs formed at an order of magnitude lower concentrations includes
haloaldehydes, haloketones and haloacetonitriles2,9,10.
In total, several hundred halogenated organics have been identified as DBPs in treated drinking
water and a similar range may well be formed in cleaning and hygiene uses2. A substantial
proportion of the total organohalogens formed, often around 50%, typically comprises sparsely
chlorinated natural organic macromolecules, notably proteins, carbohydrates, fats and, especially in
raw water treatment, humic and fulvic substances2,11,12. Because of their size such molecules are
generally biologically inactive and otherwise have properties similar to those of the parent
substances.
Because use takes place at neutral to alkaline pH, no detectable quantities of dioxins or other highhazard molecules are formed.2
Risk Assessment
Human Health
The EU RAR on Hypochlorite did not undertake a specific health risk assessment in respect of by-products.
However, based on the information contained in the RAR, and literature describing the potential for
exposure to and uptake of DBPs, it is evident as explained below that exposure to by-products from cleaning
and hygiene uses will be a fraction of the exposure from drinking tap water that has been adjudged safe in
setting the EU Drinking Water Directive limits.
Direct ingestion of DBPs in cleaning solutions should be negligible other than by accident or deliberate
abuse. Indirect ingestion via transfer from cleaned/ disinfected surfaces and equipment to food can be
calculated. [The submitted risk assessment will need a parallel calculation to the one for chlorate above for
e.g. HAAs and THMs]
Human exposure to different DBPs from cleaning uses of active chlorine may also occur by inhalation or
dermal penetration. THMs are the most important volatile class of DBPs with significant potential for
inhalation exposure. Several studies have shown that showering and bathing are important routes of
exposure to THMs in tap water. Studies by Xu and Weisel13 showed exposure by inhalation could contribute
25 – 70% of the standard ingested dose.
The EU RAR identifies machine laundry to be the domestic cleaning activity in which there is the greatest
percentage conversion of applied chlorine to DBPs (typically 2.6%) because of the organic matter loads and
elevated temperatures involved14. Studies reported by Smith et al9 reported peak levels of THMs in air of
1.2 µg/m3 in an unventilated 7.7 m3 room, and similar peak levels in an unventilated shower room of similar
size after cleaning the shower walls with a hypochlorite-based mould and mildew remover. These represent
worst-case scenarios for THM evolution from domestic cleaning tasks.
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A study in homes in the USA15 examined a range of household water-using activities, including machine
laundry with and without use of bleach, and recorded THM levels in air and exhaled breath as summarised in
the table below. The levels are normalised per µg/l of THM measured in the domestic tap water during the
study.
Activity
Hot shower
Hot bath
Preparing hot drink
Washing hands
Machine clothes washing
Machine clothes washing with bleach
After auto dishwashing
Hand dishwashing
Relative concentration (µg/m3 per µg/l in water)
Air
Exhaled breath
2.3
0.19
0.7
0.25
0.1
0.04 (after drinking)
0.2
0.03
0.15
0.06
0.3
0.12
0.3
0.075
0.25
0.13
The table shows that although use of bleach in machine laundry doubles THM levels in air and exhaled
breath, the exposures involved are of the same order as that from other common domestic activities simply
using tap water (i.e. without bleach) such as hand dishwashing, and are substantially lower than the
exposures from showering and bathing which are themselves a fraction of the exposures from ingesting tap
water.
Xu et al16 showed that dermal penetration during showering and bathing could give rise to an exposure to
THMs of 40-70% of that received from ingesting the standard 2l per day used as the basis of risk assessment
of tap water. The EU RAR indicates that floor and surface cleaning solutions contain DBPs at similar levels to
those that may be found in tap water. As only the hands are immersed even if gloves are not used, the
dermal uptake is likely to be substantially less than that from showering and bathing and thus also from
drinking tap water.
The second most prevalent class of DBPs after the THMs is the haloacetic acids which are polar in nature and
not volatile. Both inhalation and dermal uptake will be low, and a fraction of the <0.5% and <0.1%
respectively of the ingestion dose which Xu & Weisel17 and Xu et al16 determined for showering and bathing.
Dermal and inhalation uptake of other significant DBPs is expected to lie between the extremes of the
volatile THMs and the polar, non-volatile HAAs. For example, dermal and inhalation uptake of volatile
haloketones was shown by Xu and Weisel17 to be a lower fraction of the daily ingested dose than for
chloroform.
In summary, available evidence shows that uptake of DBPs from domestic cleaning tasks will be much lower
than that from ingesting the standard risk assessment dose of tap water meeting the EU Drinking Water
Directive limits.
[Suitable equivalent statements will need to be added for I&I in dossiers for I&I products. This might include
that rinsing of surfaces is recommended after cleaning, and that tap water will bring some residues e.g.
chlorate]
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Environmental
The environmental risks of halogenated organics were evaluated in detail by the EU hypochlorite RAR and
conclusions of no significant risk (Conclusion ii) were reached in respect of all cleaning and hygiene uses18.
[The applicant should confirm that the conditions of use of hypochlorite in their cleaning and hygiene
applications have not changed since the EU RAR was completed in any way likely to affect by-product
formation in a way that would invalidate the RAR conclusions.]
To summarise key conclusions of the environmental part of the EU RAR:



The major by-product families, the THMs and HAAs were assessed using a conventional PEC/PNEC
approach. RCRs for both household and I&I uses were below 1.
Since it is impossible to speciate and individually risk assess all by-products, the EU RAR addressed the
question of minor, unidentified, halogenated by-products through ‘whole effluent’ tests on complex
substrate mixtures using raw, settled sewage as a worst case for several uses including both household
and I&I cleaning and hygiene19. These tests established that:
o formation of minor quantities of halogenated by-products does not increase the ecotoxicity of
the mixture
o biodegradability of the mixture is not diminished
o although some additional quantities of highly lipophilic substances are formed, these are
eliminated by biodegradation in conditions typical of sewage treatment.
Since cleaning and hygiene uses of hypochlorite are conducted at neutral or alkaline pH, no formation of
high-hazard molecules such as dioxins is expected.
In conclusion, from the information assembled in the EU RAR it is clear that the local environmental load of
halogenated organics arising from cleaning and hygiene use of hypochlorite will in total be a fraction of the
load of similar substances which will arise from normal daily domestic consumption (including bathing,
showering and cleaning tasks) of potable water at the EU Drinking Water Directive limits.
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Appendix 1
PEC/PNEC Calculation for chlorate from domestic bleach products
Assumptions





PNEC chlorate = 1mg/l (ECHA dossier5)
Domestic bleach consumption 11.8 kg/cap/yr (Spain, EU worst case, taken from EU Hypo RAR1)
Chlorate in bleach 1.8 g/l (per FIFE - AIS “Chlorate and bromate in relation to domestic use of
hypochlorite” dossier, version 1.4 - Dec. 1995)
Zero removal of chlorate in STW (conservative)
Standard TGD parameters for discharge – 200L/cap day water usage, 10-fold dilution into receiving
waters
Calculation
Concentration ClO3 in raw sewage = 11.8/365 * 1.8/200 = 0.29 mg/l
Concentration in receiving waters = 0.029mg/l
PEC/PNEC = 0.029
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References
1
EU Risk Assessment Report on Sodium Hypochlorite (RAR), Section 2.4.2. Available from:
https://www.echa.europa.eu/documents/10162/6434698/orats_final_rar_sodiumhypochlorite_en.pdf
2
RAR Section 3.1.1.2
3
RAR Section 1.2
4
Scientific Opinion on risks for public health related to the presence of chlorate in food. EFSA CONTAM Panel (EFSA
Panel on Contaminants in the Food Chain), 2015. EFSA Journal 2015;13(6):4135, 103 pp. doi:10.2903/j.efsa.2015.4135.
5
Consortium submitted ECHA dossier for sodium chlorate. https://www.echa.europa.eu/web/guest/registrationdossier/-/registered-dossier/14688
6
RAR Section 4.1.1.4.1.
7
Environmental safety of halogenated by-products from use of active chlorine. Euro Chlor Science Dossier 15 May 2010
8
Quantitative in situ monitoring of organohalogen compounds in domestic sewage resulting from the use of
hypochlorite bleach, Schowanek D; Racioppi F; Matthijs E; Bayko R; Gobba M; Buschini A and Garnidini G. Water
Research 30, 2193-2205 (1996)
9
Human and Environmental Safety of hypochlorite. Smith W L, In: Proc. Third World conference on Detergents, Global
Perspectives, A Cakn ed. AOCS Press, Champaign, II 183- 192 (1994)
10
De vorming van organochloor verbindingen ten gevolge van het huishoudelijk gebruik van actief-chloor bevattende
producten. Peeters 1991 - Peters, R.J.B. TNO Delft, The Netherlands, report 92/063 (1991)
11
Benefits and safety aspects of hypochlorite formulated in domestic products. A.I.S.E. Scientific Dossier March 1997
12
Characterization of Total Organic Halogen Produced During Disinfection Processes Prepared by: David A. Reckhow,
Guanghui Hua, and Junsung Kim University of Massachusetts and Patrick G. Hatcher, Sarah A.L. Caccamise, and Rakesh
Sachdeva Ohio State University. AWWA2007
13
Human respiratory uptake of chloroform and haloketones during showering. Xu X, Weisel CP. J Expo Anal Environ
Epidemiol. 2005 Jan;15(1):6-16
14
RAR Section 3.1.2.2
15
Changes in Breath Trihalomethane Levels Resulting from Household Water-Use Activities. Gordon SM, Brinkman MC,
Ashley DL, Blount BC, Lyu C, Masters J, Singer PC. Environmental Health Perspectives 2006 114(4) 514
16
Percutaneous absorption of trihalomethanes, haloacetic acids, and haloketones. Xu X, Mariano TM, Laskin JD, Weisel
CP. Toxicol Appl Pharmacol. 2002, Oct 1; 184(1):19-26
17
Exposure to Haloacetic Acids and Haloketones during Showering. Xu X, Weisel CP. Inhalation Environ. Sci. Technol.
2003, 37, 569-576
18
RAR Section 3.3.1.2.2
19
RAR Section 3.2.1.6.2 and Annex 7.
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