Sulprofos
(endorsed 2011)
Guideline
Based on human health concerns, sulprofos in drinking water should not exceed 0.01 mg/L.
Related chemicals
Sulprofos (CAS 35400-43-2) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, which includes fenthion, parathion, profenofos, and ethoprofos (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, sulprofos would not be a health concern unless the concentration exceeded 0.01 mg/L. Excursions above this level even for a short period are of concern, as sulprofos causes cholinesterase inhibition even after relatively short periods of exposure.
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: Sulprofos is an insecticide for the control of whiteflies and other small plant-sucking pests on cotton, tomato and pepper crops.
There are no registered products containing sulprofos in Australia, but de-registered compounds may still be detected in water. Previously registered products were intended for professional use and were available as concentrated solutions to be applied in diluted form using ground or aerial sprays directly onto cotton or tomato foliage.
Exposure sources: The main source of public exposure to sulprofos and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of sulprofos in the future may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
No reports of sulprofos in Australian drinking waters have been identified.
Treatment of drinking water
No specific data on the treatment of sulprofos in drinking water have been identified.
Measurement
No suitable techniques for the analysis of sulprofos in drinking water have been identified. However, it is expected that a suitable method using high performance liquid chromatography with tandem mass spectrometry could be developed if required.
History of the health values
The current acceptable daily intake (ADI) for sulprofos is 0.003 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.3 mg/kg bw/day from long-term (2-year) dietary studies in rats and rabbits. The NOEL is based on decreased cholinesterase activity in plasma and red blood cells at doses of 3 mg/kg bw/day (dogs) and 4 mg/kg bw/day (rats) in dietary studies conducted over 2 years. The ADI incorporates a safety factor of 100, and was first established in 1979.
The previous health value was 0.01 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Sulprofos is readily and extensively absorbed via the gastrointestinal tract in rats. It is extensively metabolised via the organothiophosphate groups to form an organophosphate, and via sulfoxidation to form sulfoxides and sulfones. Excretion is mainly via urine and is complete within 72 hours.
Acute effects: Sulprofos has moderate acute oral and dermal toxicity. It is not a skin sensitiser. Clinical signs of acute poisoning were typical of cholinesterase inhibition and included hyperexcitability, salivation, bronchoconstriction, headache, vomiting and other behavioural changes.
Short-term effects: A 4-week oral study in rats reported decreased plasma and brain cholinesterase activity at doses of 1 mg/kg bw/day and above. No other effects were reported in this study.
Three-month dietary studies were conducted in rats and dogs. In rats, there was plasma cholinesterase inhibition and decreased bodyweight gain at doses of 0.6 mg/kg bw/day and above. In dogs, plasma cholinesterase was inhibited at doses of 0.7 mg/kg bw/day and clinical signs of cholinesterase inhibition were seen at higher doses. The NOEL in both studies was 0.3 mg/kg bw/day.
Long-term effects: Two-year dietary studies were conducted in mice, rats and dogs. There was cholinesterase inhibition in plasma and erythrocytes at doses of 4 mg/kg bw/day (mice and rats) and 3 mg/kg bw/day (dogs). Brain cholinesterase inhibition occurred in all three species at higher doses. The lowest overall NOEL was 0.3 mg/kg bw/day (rat, dog), and this is the basis for the current ADI.
Carcinogenicity: Based on 2-year studies in mice and rats, there is no evidence of carcinogenicity for sulprofos.
Genotoxicity: Sulprofos is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 3-generation study in rats and developmental studies in rats and rabbits did not identify any adverse effects on reproductive parameters or foetal development.
Neurotoxicity: A 3-week dietary studies in hens using doses up to 50 mg/kg bw did not identify any clinical or histological signs of neurotoxicity.
Poisons Schedule: Sulprofos is included in Schedule 6 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 the health-based guideline
The health-based guideline of 0.01 mg/L for sulprofos was determined as follows:
where:
0.3 mg/kg bw/day is the NOEL based on long-term (2-year) studies in rats and dogs.
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.
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.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
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