Temephos
(endorsed 2011)
Guideline
Based on human health concerns, temephos in drinking water should not exceed 0.4 mg/L.
Related chemicals
Temephos (CAS 3383-96-8) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, including fenthion, parathion, profenofos and ethoprophos (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, temephos would not be a health concern unless the concentration exceeded 0.4 mg/L. Excursions above this level even for a short period are of concern, as the health-based guideline is based on short-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: Temephos is an insecticide for the control of skin parasites on farm and non-farm animals, and for the control of mosquito and midge larvae in breeding areas.
There are registered products containing temephos in Australia. The products are intended for professional use only. Use patterns include hand-held sprays, shower sprays, dip solution, and shampoo for control of fleas on farm and non-farm animals, and as a liquid concentrate for application to surface water for control of mosquito and midge larvae in public health settings. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to temephos and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
The application of temephos to surface water in mosquito breeding areas may potentially lead to the contamination of drinking water.
Typical values in Australian drinking water
No reports of temephos in Australian drinking waters have been identified.
Treatment of drinking water
There is insufficient information on the treatment of temephos in drinking water, but it is expected that advanced treatment methodologies such as ozonation and advanced oxidation would be effective.
Measurement
Temephos can be measured in water by solvent extraction followed by high performance liquid chromatography (WHO 2008) or by on-line solid-phase extraction followed by thermospray liquid chromatography with mass spectrometry (Lacorte and Barcel 1995). The practical limit of quantitation is 0.04 mg/L.
History of the health values
The current acceptable daily intake (ADI) for temephos is 0.1 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1 mg/kg bw/day from a 4-week dietary study in humans. This NOEL is based on serum cholinesterase inhibition. The ADI incorporates a safety factor of 10, and was first established in 1988.
The previous health value was 0.3 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Temephos is only partially absorbed from the gastrointestinal tract, with wide, uniform tissue distribution in mammals. It is rapidly eliminated unchanged in the faeces or as temephos sulfoxide in urine. It has a low potential for bioaccumulation.
Acute effects: Temephos has low to moderate oral acute toxicity, and low dermal toxicity. It is not a skin sensitiser.
Short-term effects: Short-term dietary studies in rats and dogs reported symptoms indicative of nervous system toxicity. In a 5-day dietary study in humans, temephos had no effects on blood cholinesterase activity at 256 mg/kg bw/day. In a 4-week dietary study in humans, temephos had no effect on cholinesterase activity at 1 mg/kg bw/day. In medium-term dietary studies in rats and dogs, effects included red blood cell cholinesterase inhibition and increased liver weight at dose levels above 0.1 mg/kg bw/day in rats and above 0.45 mg/kg bw/day in dogs.
Long-term effects: Long-term dietary studies in rats and dogs reported symptoms indicative of nervous system toxicity. No toxicity was noted up to 15 mg/kg bw/day, but cholinesterase was not measured in these studies.
Carcinogenicity: Based on long-term toxicity studies in rats, there is no evidence of carcinogenicity for temephos.
Genotoxicity: Temephos is not considered to be genotoxic, based on 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 foetal development.
Poisons Schedule: Temephos is included in Schedule 5 and 6 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 of 0.4 mg/L for temephos was determined as follows:
where:
1.0 mg/kg bw/day is the NOEL based on a short-term (4-week) dietary study in humans.
70 kg is taken as the average weight of an adult.
0.1 is a proportionality factor based on the conservative 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.
10 is the safety factor applied to the NOEL derived from studies conducted in humans in order to take into account human variation.
Temephos is included in the WHO Guidelines for Drinking Water Quality list of pesticides excluded from guideline value derivation, as it is added to water supplies for control of mosquitoes and larvae (WHO 2006). The philosophy is that these pesticides play an important role in the control of disease, and guidelines that are unnecessarily stringent as to impede their use should be avoided if possible.
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.
Lacorte S, Barcel D (1995). Determination of organophosphorus pesticides and their transformation products in river waters by automated on-line solid-phase extraction followed by thermospray liquid chromatography-mass spectrometry. Journal of Chromatography A, 712:103-112.
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.
WHO (World Health Organization) (2004) Guidelines for Drinking-water Quality 3rd Edition, WHO, Geneva, Swizterland.
WHO (World Health Organization (2008)) WHO Specifications and Evaluation for Public Health Pesticides – Temephos. WHO, Geneva, Switzerland.
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