Ethoprophos
(endorsed 2011)
Guideline
Based on human health concerns, ethoprophos in drinking water should not exceed 0.001 mg/L.
Related chemicals
Ethoprophos (CAS 13194-48-1) belongs to the organothiophosphate class of chemicals. Other pesticides in this class include terbufos, chlorpyrifos, dimethoate, and ethion (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, ethoprophos would not be a health concern unless the concentration exceeded 0.001 mg/L. 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: Ethoprophos is a nematocide and insecticide for the control of root nematodes in agricultural crops including bananas, cereals and tobacco, and for the control of certain grubs in sugar cane and maize.
There are currently no products registered in Australia that contain ethoprophos, but de-registered compounds may still be detected in water. Previously registered products containing ethoprophos were intended for professional use only. These products were granular formulations applied directly to the soil to control root nematodes or were diluted and applied by hand spray for the control of grubs.
Exposure sources: The main sources of public exposure to ethoprophos and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of ethoprophos in the future may potentially lead to contamination of source waters through processes such as run-off or entry into groundwater.
Typical values in Australian drinking water
No reports of ethoprophos in Australian drinking waters have been identified. It is rarely detected in drinking or environmental waters in overseas countries. When it has occasionally been reported, levels are extremely low; for example, a time-weighted annual concentration in source waters in several USA states of 0.002 ppb and a maximum concentration of 0.012 ppb.
Treatment of drinking water
No specific data on the treatment of ethoprophos in drinking water have been identified.
Measurement
Residue determination of ethoprophos is amenable to multiresidue procedures using solvent extraction with dichloromethane followed by gas chromatography with nitrogen-phosphorous detection. Limits of detection are as low as 0.01 µg/L using this technique.
History of the health values
The current acceptable daily intake (ADI) for ethoprophos is 0.0003 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.025 mg/kg bw/day from a long term study. The NOEL is based on decreased erythrocyte cholinesterase activity in a 1-year dietary toxicity study in dogs. The ADI incorporates a safety factor of 100 and was established in 1988.
The previous ADI for ethoprophos was 0.0001 mg/kg bw/day, based on the same NOEL but with a safety factor of 200, due to reporting deficiencies. The ADI was amended after submission of additional information on the study.
The previous health value was 0.001 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Ethoprophos is rapidly absorbed via the gastrointestinal tract and and widely distributed in the tissues of rats. Metabolism is extensive and excretion of phosphorothioic acid and related esters is mainly through urine, but is incomplete by 7 days, with 1.7–3.5% of total dose remaining in tissues
Acute effects: Ethoprophos has high acute oral toxicity and moderate to high acute dermal toxicity. It is a skin sensitiser in guinea-pig tests.
Short-term effects: In both oral and dermal short-term studies from 3 to 6 weeks in rats, rabbits and dogs, the major effect reported was a decrease in chlolinesterase activity at 0.05 mg/kg bw/day and above. In dietary studies from 3-5 months in the rat and dog, there was a decrease in brain, plasma and erythrocyte cholinesterase levels and elevation of adrenal weights (rat) at 0.025 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies in mice, rats, and dogs reported decreases in erythrocyte cholinesterase activity in all species; the lowest dose was 1 mg/kg bw/day in the dog. Decreased brain and plasma cholinesterase activity and reduced haemoglobin levels were seen at higher doses in all species. The lowest overall NOEL was 0.025 mg/kg/day, based on a decrease in erythrocyte cholinesterase activity in dogs. This NOEL is the basis for the current ADI.
Carcinogenicity: Based on an 18-month study in mice and a 2-year study in rats, there is no evidence of carcinogenicity for ethoprophos.
Genotoxicity: Ethoprophos is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 3-generation reproduction study in rats and developmental studies in rabbits did not produce any evidence of reproductive effects, delayed development or teratogenicity.
Poisons Schedule: Ethoprophos is included in Schedule 6 and 7 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline value of 0.001 mg/L for ethoprophos was determined as follows:
where:
0.025 mg/kg bw/day is the NOEL based on a long-term (1-year) dietary study in 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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