Pyroxsulam
(endorsed 2011)
Guideline
Based on human health concerns, pyroxsulam in drinking water should not exceed 4 mg/L.
Related chemicals
Pyroxsulam (CAS 422556-08-9) is in the triazolopyrimidine 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, pyroxsulam would not be a health concern unless the concentration exceeded 4 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: Pyroxsulam is a post-emergence herbicide used to control a wide range of grass and broad-leaf weeds in wheat.
There is at least one registered product containing pyroxsulam in Australia. Pyroxsulam products are for professional use and are available as an oil-dispersible liquid to be applied by ground boom spray for one post-emergent (early season) application to wheat. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to pyroxsulam is residues in food. Residue levels in food produced according to good agricultural practice are generally low
Agricultural use may potentially lead to residues in source waters through processes such as run-off, spray drift or entry into groundwater.
Typical values in Australian drinking water
No reports of pyroxsulam in Australian drinking waters have been identified.
Treatment of drinking water
There is insufficient information on the treatment of pyroxsulam in drinking water, but it is expected that advanced treatment methodologies such as ozonation and advanced oxidation would be effective.
Measurement
No suitable analytical techniques have been identified, but the use of high performance liquid chromatography–tandem mass spectrometry is expected to be suitable for residue levels of this pesticide in water.
History of the health values
The current acceptable daily intake (ADI) for pyroxsulam is 1.0 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 100 mg/kg bw/day from an 18-month dietary study in mice. The NOEL is based on effects on the liver. The ADI incorporates a safety factor of 100, and was established in 2008.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Pyroxsulam is rapidly absorbed from the gastrointestinal tract. It is rapidly eliminated, mainly in the urine, largely unchanged. It has low potential for bioaccumulation. The primary metabolite of pyroxsulam is 2’-demethyl-pyroxsulam.
Acute effects: Pyroxsulam has low to moderate oral acute toxicity, and low dermal toxicity. It is a skin sensitiser in guinea pigs.
Short-term effects: Medium-term dietary studies were conducted in mice, rats and dogs. The only effect observed was an increase in serum cholesterol levels at 1000 mg/kg bw/day; however, these returned to normal after cessation of treatment and were likely be adaptive and non-adverse.
Long-term effects: Long-term dietary studies were conducted in mice, rats and dogs. In mice, there was an increase in liver weight at the highest dose, 1000 mg/kg bw/day. No adverse effects were observed in rat and dog studies.
Carcinogenicity: Based on long-term studies in mice and rats, there is no evidence of carcinogenicity for pyroxsulam.
Genotoxicity: Pyroxsulam is not considered to be genotoxic, based on in vitro or in vivo short-term studies.
Reproductive and developmental effects: In a 2-generation reproduction study in rats and developmental studies in rats and rabbits, there was no evidence of effects on reproductive parameters or on foetal development.
Poisons Schedule: Pyroxsulam 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 4 mg/L for pyroxsulam was determined as follows:
where:
100 mg/kg bw/day is the NOEL based on a long-term (2-year) dietary study in mice.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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