Pyrasulfotole
(endorsed 2011)
Guideline
Based on human health concerns, pyrasulfotole in drinking water should not exceed 0.04 mg/L.
Related chemicals
Pyrasulfotole (CAS 365400-11-9) belongs to the benzoylpyrazole class of chemicals. There are no other pesticides in this class (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, pyrasulfotole would not be a health concern unless the concentration exceeded 0.04 mg/L. Minor excursions above this level would need to occur over a significant period to be a 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: Pyrasulfotole is a herbicide used on cereal grains including wheat, barley, oats, rye and triticale.
There is at least one registered product containing pyrasulfotole in Australia. Pyrasulfotole products are intended for professional use only and is applied using ground boom apparatus. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to pyrasulfotole is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of pyrasulfotole 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 pyrasulfotole in Australian drinking waters have been identified.
Treatment of drinking water
No specific data on the treatment of pyrasulfotole in drinking water have been identified.
Measurement
No methods have been identified for the analysis of pyrasulfotole in drinking water.
History of the health values
The current acceptable daily intake (ADI) for pyrasulfotole is 0.01 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1 mg/kg bw/day from a long-term (2-year) study in rats. This NOEL is based on corneal and retinal lesions, and centrilobular hepatocellular hypertrophy at 10 mg/kg bw/day. The ADI incorporates a safety factor of 100, and was established in 2007.
The acute reference dose (ARfD) of 0.2 mg/kg bw/day was established in 2007, based on a LOEL of 200 mg/kg bw/day for clinical signs of toxicity. The ARfD incorporates a safety factor of 1000.
A health value has not been previously established by NHMRC for pyrasulfotole.
Health considerations
Metabolism: Pyrasulfotole is readily absorbed via the gastrointestinal tract, and approximately 60% is excreted in the urine within 6 hours, mainly unchanged. There is also excretion in the faeces, partially via the bile. By 48 hours, there is <2% remaining in the body, indicating a low potential for bioaccumulation. The main metabolite is a desmethyl derivative.
Acute effects: Pyrasulfotole has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: In 28-day studies, there were histopathological changes in the urinary bladder at 961 mg/kg bw/day in mice, and increased serum triglyceride levels and elevated liver weights at 171 mg/kg bw/day in dogs. In a 90-day study in rats, increased liver weight, corneal effects and microscopic renal abnormalities were reported at 77 mg/kg bw/day.
Long-term effects: Long-term dietary studies were conducted in mice, rats and dogs. In mice, an increased incidence of gallstones was observed at 14 mg/kg bw/day. A 2-year study in rats reported corneal and retinal lesions, increased liver weight, centrilobular hepatocellular hypertrophy and elevated plasma cholesterol at 10 mg/kg bw/day. In dogs, tubular dilatation of the kidneys was seen at 101 mg/kg bw/day. The NOEL of 1 mg/kg bw/day in the rat study is the basis for the current ADI.
Carcinogenicity: Pyrasulfotole caused an increased incidence of neoplasms in the urinary tract of mice and in the eye of rats at high dose levels only. These dose levels were considered to be well in excess of the normal levels of human exposure.
Genotoxicity: Pyrasulfotole is not considered genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: In multigeneration reproduction studies in rats, there was no evidence of effects on reproductive parameters. In developmental studies in rabbits, there was evidence of foetotoxicity in the absence of maternal toxicity at 10 mg/kg bw/day.
Poisons Schedule: Pyrasulfotole 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 the health-based guideline
The health-based guideline of 0.04 mg/L for pyrasulfotole was determined as follows:
where:
1 mg/kg bw/day is the NOEL from a long-term (2-year) rat study.
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. The safety factor of 100 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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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