Chlorsulfuron
(endorsed 2011)
Guideline
Based on human health concerns, chlorsulfuron in drinking water should not exceed 0.2 mg/L.
Related chemicals
Chlorsulfuron (CAS 64902-72-3) belongs to the sulfonylurea herbicide class of chemicals. Other pesticides in this class include azimsulfuron, etametsulfuron-methyl, ethoxysulfuron, metsulfuron-methyl, halosulfuron-methyl, iodosulfuron methyl-sodium salt, sulfometuron methyl, sulfosulfuron, triasulfuron, tribenuron methyl and trifloxysulfuron (Tomlin 2006).
Human risk statement
With good water quality management practices, the exposure of the general population is expected to be well below levels that may cause health concerns.
If present in drinking water as a result of a spillage or through misuse, chlorsulfuron would not be a health concern unless the concentration exceeded 0.2 mg/L. Excursions above this level would need to occur over a significant period to be of health concern, as the health-based guideline is based on long-term effects.
With good water quality management practices, pesticides should not be detected in source waters used for drinking water supplies. Persistent detection of pesticides may indicate inappropriate use or accidental spillage, and investigation is required in line with established procedures in the risk management plan for the particular water source.
General description
Uses: Chlorsulfuron is a selective post-emergence herbicide used for control of broad-leaf weeds in cereal crops.
There are currently products containing chlorsulfuron registered in Australia. These products are intended for professional use and are available in wettable powder and granular formulations. Product labels indicate products are to be diluted and applied directly to crops and soil by ground and aerial spray application methods. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to chlorsulfuron and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of chlorsulfuron may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Reported values in Australian waters
No data were found on chlorsulfuron in Australian waters. In the USA, modelling by the United States Environmental Protection Agency suggests maximum concentrations of 41.3 µg/L and 3.5 µg/L in surface water and groundwater, respectively (USEPA, 2005).
Treatment of drinking water
No specific data on the treatment of chlorsulfuron in drinking water have been identified.
Measurement
Chlorsulfuron in water can be measured by high performance liquid chromatography with ultraviolet detector, with a limit of detection of 1 µg/L (Sarmah and Kookana 1999).
History of the health values
The current acceptable daily intake (ADI) for chlorsulfuron is 0.05 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 5 mg/kg bw/day from a long-term (2-year dietary) study. This NOEL is based on haematological changes observed in rats. The ADI incorporates a safety factor of 100 and was established in 1982.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Chlorsulfuron is not extensively metabolised, and is rapidly excreted mostly unchanged in the urine. A small portion is metabolised to a sulfonamide and a triazine residue.
Acute effects: Chlorsulfuron has low acute oral and dermal toxicity and is not a skin sensitiser. The minor amounts of sulfonamide and triazine metabolites formed also have low acute oral toxicity and are not skin sensitisers.
Short-term effects: Medium-term dietary studies in mice and rats reported haematological changes and decreased urine pH at doses above 8 mg/kg bw/day.
Short-term dietary studies in rats indicated that chlorsulfuron metabolites are less toxic than their parent compound.
Long-term effects: Long-term dietary studies in mice and rats reported reduced bodyweight as the major effect, occurring markedly at 120 mg/kg bw/day in rats, with the only effect noted in mice at 750 mg/kg bw/day. In addition, male rats had minor changes in haematological parameters (increased red blood cell volume, mean cell haemoglobin and haematocrit) in addition to reduced bodyweight from 25 mg/kg bw/day, but only at the 1-year interim. The NOEL for the rat study was 5 mg/kg bw/day, and this is the basis for the current ADI.
Carcinogenicity: Based on long-term studies in rats, there is no evidence of carcinogenicity for chlorsulfoton
Genotoxicity: Chlorsulfuron and its metabolites are not considered genotoxic, based on a variety of in vitro and in vivo short-term tests.
Reproductive and developmental effects: Three-generation reproductive studies in rats and developmental studies in rats and rabbits did not produce any evidence of reproductive effects, delayed development or teratogenicity.
Poisons Schedule: Chlorsulfuron is included in Schedule 5 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010). Current versions of the Poisons Standard should be consulted for further information.
Derivation of health-based guideline
The health-based guideline of 0.2 mg/L for chlorsulfuron was determined as follows:
where:
5 mg/kg bw/day is the NOEL based on a long-term (2-year) dietary study in rats.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the assumption that 10% of the ADI will arise from the consumption of drinking water.
2 L/day is the estimated maximum amount of water consumed by an adult.
100 is the safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation. No additional safety was considered necessary.
References
NOTE: The toxicological information used in developing this fact sheet is from reports and data held by the Department of Health, Office of Chemical Safety. This includes the NDPSC and PACC references below.
DoHA (2010) The Poisons Standard; Schedule 1-Standard for the Uniform Scheduling of Medicines and Poisons, Department of Health and Ageing, Commonwealth of Australia, Canberra.
NHMRC (National Health and Medical Research Council), NRMMC (Natural Resources Management Ministerial Council) (2004). Australian Drinking Water Guidelines. National Water Quality Management Strategy, Paper 6. NHMRC and NRMMC.
Sarmah AK, Kookana RS (1999). Simultaneous analysis of triasulfuron, metsulfuron-methyl and chlorsulfuron in water and alkaline soils by high-performance liquid chromatography. Journal of Environmental Science and Health Part B, 34(3):363-380.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
USEPA (2005). Reregistration eligibility decision for chlorsulfuron, case no. 0631. 20 May 2005. United States Environmental Protection Agency.
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