Ethion
(endorsed 2011)
Guideline
Based on human health concerns, ethion in drinking water should not exceed 0.004 mg/L.
Related chemicals
Ethion (CAS 563-12-2) is in the organophosphate class of chemicals. There are many other pesticides in this class, including diazinon, dichlorvos, fenthion, parathion and profenofos (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, ethion would not be a health concern unless the concentration exceeded 0.004 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: Ethion is an insecticide used for the control of cotton worm in agricultural settings, and for controlling mites and fleas in cattle.
There are registered products containing ethion in Australia. These include an emulsifiable concentrate to be diluted and sprayed on cotton, used as ground and aerial sprays; and topical solutions/suspensions used as cattle dips/sprays. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to ethion is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use may potentially lead to contamination of sources waters through processes such as run-off, spray-drift or entry into groundwater.
Typical values in Australian drinking water
No reports of ethion in Australian drinking waters have been identified.
Treatment of drinking water
No specific data on the treatment of ethion in drinking water have been identified.
Measurement
Ethion can be measured in natural waters using headspace solid-phase microextraction followed by gas chromatography with flame thermionic or mass spectrometric detection. The practical limit of quantitation for this technique is 0.04 µg/L (Lambropoulou and Albanis 2001, Wang et al. 2007).
History of the health values
The current acceptable daily intake (ADI) for ethion is 0.0013 mg per kg of bodyweight (mg/kg bw), based on no-observed-effect levels (NOEL) of 0.13 mg/kg bw/day from a 2-year rat dietary study and 0.1 mg/kg bw/day from a 3-generation rat study. In both cases, the NOEL was based on decreased cholinesterase activity. The current ADI incorporates a safety factor of 100 and was established in 1987.
The previous health value was 0.003 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Ethion is rapidly absorbed from the gastrointestinal tract and widely distributed in the body. It is rapidly metabolised to monoxons, dioxons, conjugates and numerous polar compounds, and has low potential for bioaccumulation. It is rapidly eliminated, mainly in the urine and to a minor extent in faeces.
Acute effects: Ethion has high acute oral and dermal toxicity. Symptoms of acute poisoning are indicative of central and peripheral nervous system poisoning and included hyperexcitability, salivation, broncoconstriction, headache, vomiting and other behavioural changes. The effects are dose-related and reversible. Ethion is not a skin sensitiser.
Short-term effects: Short-term and long-term dietary studies in rodents and dogs resulted in symptoms indicative of nervous system toxicity. Decreased cholinesterase activity was observed in serum and brain at dose levels above 0.46 mg/kg bw/day in mice and 1.8 mg/kg bw/day in rats.
Long-term effects: A long-term (2-year) dietary study in rats reported decreased serum cholinesterase. The NOEL was 0.13 mg/kg bw/day, and is the basis for the current ADI.
Carcinogenicity: Based on long-term studies in mice and rats, there is no evidence of carcinogenicity for ethion.
Genotoxicity: Ethion showed no evidence of genotoxicity in in vitro and in vivo short-term studies.
Reproductive and developmental effects: In reproduction studies in rats and developmental studies in rats and rabbits, there was no evidence of effects on reproductive parameters or on foetal development, but serum cholinesterase was decreased at dose levels above 0.l mg/kg bw/day.
Poisons Schedule: Ethion is included in Schedule 7 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 0.004 mg/L for ethion was determined as follows:
where:
0.1 mg/kg bw/day is the NOEL based on decreased serum cholinesterase levels in a 3-generation 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 a safety factor applied to the NOEL derived from animal studies. This safety factor incorporates a factor of 10 for interspecies variation and 10 for intraspecies extrapolation.
References
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.
Lambropoulou DA, Albanis TA (2001). Optimization of headspace solid-phase microextraction conditions for the determination of organophosphorus insecticides in natural waters. Journal of Chromatography A, 922(1-2):243-255.
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.
Wang S, Zhao P, Min G, Fang GZ (2007). Multi-residue determination of pesticides in water using multi-walled carbon nanotubes solid-phase extraction and gas chromatography-mass spectrometry. Journal of Chromatography A, 1165(1-2):166-171.
Last updated
