Permethrin
(endorsed 2011)
Guideline
Based on human health concerns, permethrin in drinking water should not exceed 0.2 mg/L.
Related chemicals
Permethrin (CAS 52645-53-1) is in the pyrethroid class of chemicals. Other pesticides in this class include cyfluthrin, cypermethrin, alpha-cypermethrin and deltamethrin (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, permethrin would not be a health concern unless the concentration exceeded 0.2 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: Permethrin is an insecticide used for the control of mosquitoes and flies in domestic and agricultural settings, seed infestation in food industry settings, and fleas on dogs.
There are many registered products containing permethrin in Australia. The products are intended for both professional and home garden use. Use patterns include sprays and drenches for livestock in agricultural settings, paint formulations on timber as a preservative in industrial settings, shampoos for dogs, sprays for insects in domestic settings, and sprays for application directly to clothing. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to permethrin are home garden use as an insecticide, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use 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 data are available on the concentrations of permethrin in Australian drinking waters or in drinking water overseas.
Treatment of drinking water
There are no identified reports of the treatment of permethrin in drinking water.
Measurement
Several methods have been reported for the analysis of permethrin in water, including gas chromatography with micro-electron capture detection (limit of detection [LOD] 2.18 ng/L, Casas et al. 2006; LOD 3 ng/L, Mekebri et al. 2008), liquid chromatography with electrospray ionisation mass spectrometry (LOD 0.4 ng/L in groundwater and 0.7 ng/L in sea water) (Gil-Garcia et al, 2006), and gas chromatography–high resolution mass spectrometry (LOD 0.15ng/L) (Woudneh and Oras 2006).
History of the health values
The current acceptable daily intake (ADI) for permethrin is 0.05 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 5 mg/kg bw/day from a 2-year dietary study in rats and a 1-year oral dosing study in dogs. This NOEL is based on neurotoxic effects including tremors, incoordination and convulsions. The ADI incorporates a safety factor of 100 and was established in 1986.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Permethrin is rapidly absorbed from the gastrointestinal tract and widely distributed in the body. It is rapidly eliminated, mainly in the urine and faeces as polar metabolites in the form of glucuronide conjugates, benzyl alcohols, and weak acids. Permethrin has a low potential for bioaccumulation. The primary metabolites are m-phenoxybenzyl alcohol and m-phenyxybenzoic acids.
Acute effects: Permethrin has low acute oral and dermal toxicity. Symptoms of acute poisoning were indicative of nervous system poisoning and included tremors, hyperexcitability, salivation and paralysis. It is not a skin sensitiser.
Short-term effects: A 10-day dietary study in rats produced clinical symptoms indicative of an effect on the nervous system (impaired muscle relaxation) at 30 mg/kg bw/day. Recovery from these effects was observed one week after dosing. Medium-term studies were conducted in rats and dogs. Rats were most sensitive to permethrin, with liver centrilobular hypertrophy observed in males at 7.5 mg/kg bw/day. Dogs reported increased liver weight from 50 mg/kg bw/day and decreased bodyweight at 500 mg/kg bw/day.
Long-term effects: A long-term (2-year) dietary study with permethrin in rats, and a 1-year oral dosing study in dogs showed the main effects to be on the liver, and central and peripheral nervous systems. Symptoms included increased serum glucose levels and absolute liver weight at the highest dose tested of 25 mg/kg bw/day (rats), and tremors, incoordination and convulsions at doses of 100 mg/kg bw/day and above (dogs). The NOEL in both studies was the next lowest dose levels tested, 5 mg/kg bw/day, and this is the basis for the current ADI.
Carcinogenicity: Based on long-term studies in rats, there is no evidence of carcinogenicity for permethrin.
Genotoxicity: Permethrin is not considered to be genotoxic, based on in vitro or in vivo short-term studies.
Reproductive and developmental effects: In a 3-generation reproduction study in rats and developmental toxicity studies in rats and rabbits, there was no evidence of effects on reproductive parameters or on foetal development.
Poisons Schedule: Permethrin is either exempt from scheduling or in Schedule 4, 5 or 6 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on the 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 0.2 mg/L for permethrin was determined as follows:
where:
5.0 mg/kg bw/day is the NOEL based on a long-term (1-year) oral dosing study in dogs and a long-term (2-year) dietary 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 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.
The World Health Organization has established a guideline value of 0.3 mg/L for permethrin (WHO 2006).
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.
Casas V, Llompart M, Garcia-Jares C, Cela R, Dagnac T (2006). Multivariate optimisation of the factors influencing the solid-phase microextraction of pyrethroid pesticides in water. Journal of Chromatography A, 1124:148-156.
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.
Gil-Garcia MD, Barranco-Martinez D, Martinez-Galera M, Parrilla-Vazquez P (2006). Simple, rapid solid-phase extraction procedure for the determination of ultra-trace levels of pyrethroids in ground and sea water by liquid chromatography/electrospray ionisation mass spectrometry. Rapid Communications in Mass Spectrometry, 20:2395-2403.
Mekebri A, Crane DB, Blondina GJ, Oros DR, Rocca JL (2008). Extraction and analysis methods for the determination of pyrethroid insecticides in surface water, sediments and biological tissues at environmentally relevant concentrations. Bulletin of Environmnetal Contamination and Toxicology, 80:455-460.
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) (2006). Guidelines for Drinking-water Quality. 3rd Edition, First addendum WHO, Geneva, Switzerland.
Woudneh MB, Oros DR (2006). Quantitative determination of pyrethroids, pyrethrins and piperonyl butoxide in surface water by high-resolution gas chromatography/high resolution mass spectrometry. Journal of Agricultural and Food Chemistry, 54(19):6957-6962.
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