Cypermethrin isomers
(endorsed 2011)
Guideline
Based on human health concerns, cypermethrin in drinking water should not exceed 0.2 mg/L.
Related chemicals
Cypermethrin (CAS 52315-07-8) belongs to the pyrethroid class of chemicals. Cypermethrin is a mixture of 8 isomers, comprising 4 diastereoisomeric pairs. Alpha-, beta- or zeta-cypermethrin each contain different amounts of the isomers. There are many other pesticides in this class including allethrin, bifenthrin, deltamethrin, permethrin, phenothrin and tetramethrin (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, cypermethrin would not be a health concern unless the concentration exceeded 0.2 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 medium- to 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: Cypermethrin is an insecticide used to control a broad range of insect and rodent pests in domestic, commercial and industrial areas, and in crops. It is also used as an ectoparasiticide in cattle and domestic pets, and as a fungicide in crop seeds.
There are many registered products containing cypermethrin in Australia; some contain alpha-cypermethrin, and a small number contain beta-cyperemethrin or zeta-cypermethrin. Cypermethrin products are intended for professional and home garden use, and include insecticide dusts, sprays and bait, rodent pellets, sheep drenches, cattle ear tags and pet shampoos. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to cypermethrin are the use of household products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of cypermethrin may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
The veterinary use of cypermethrin provides some potential for contamination of drinking water through the washing of equipment near dams, streams or watercourses.
Typical values in Australian drinking water
No reports of cypermethrin in Australian drinking waters have been identified.
Treatment of drinking water
No reports of the treatment of cypermethrin in drinking water have been identified.
Measurement
Several methods have been reported for the analysis of cypermethrin in water, including gas chromatography with micro-electron capture detection (limit of detection [LOD] 1 ng/L, Casas et al. 2006; LOD 2 ng/L, Mekebri et al, 2008) and gas chromatography with high resolution mass spectrometry (LOD 0.1 ng/L, Woudneh and Oras 2006).
History of the health values
The acceptable daily intake (ADI) for cypermethrin, alpha-cypermethrin, and beta-cypermethrin is 0.05 mg per kg of bodyweight (mg/kg bw). For cypermethrin, the ADI is based on a no-observed-effect level (NOEL) of 5 mg/kg bw/day from a 2-year rat study. This NOEL is based on increased liver weights, and haematological and biochemical effects. For alpha-cypermethrin, the ADI is based on a NOEL of 4.7 mg/kg bw/day from a 13-week dog study. This NOEL is based on neurological effects. The ADIs for both cypermethrin and alpha-cypermethrin incorporate a safety factor of 100 and were established in 1988 and 1994, respectively.
For beta-cypermethrin, the 2-year rat study used for establishing the cypermethrin ADI was considered appropriate to use for the beta-cypermethrin ADI.
For zeta-cypermethrin, the ADI is 0.07 mg/kg bw, based on a NOEL of 7 mg/kg bw/day from a multigeneration reproduction study in rats. The NOEL is based on clinical signs of toxicity and evidence of neurotoxicity. The ADI incorporates a safety factor of 100 and was established in 1996.
An acute reference dose (ARfD) of 0.05 mg/kg bw/day for beta-cypermethrin was established in 2002, based on a NOEL of 4.7 mg/kg bw/day from a 3-month dog study. The NOEL was based on neurological effects. The ARfD incorporates a safety factor of 100.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Cypermethrin and alpha-cypermethrin are both well absorbed via the gastrointestinal tract and readily metabolised in rats and humans. Excretion is rapid and mainly via the urine. In humans, cyclopropane carboxylic acid is the major urinary metabolite.
Acute effects: Cypermethrin has moderate acute oral toxicity and low acute dermal toxicity. There is some evidence of skin sensitisation. Alpha-cypermethrin has moderate to high acute oral toxicity. Beta-cypermethrin has low acute oral and dermal toxicity. Zeta-cypermethrin has moderate acute oral toxicity and low dermal toxicity.
Short-term effects: In 13-week dietary studies in rats and dogs with cypermethrin, there was nervous system toxicity in both species at doses above 7.5 mg/kg bw/day. Changes indicative of kidney and liver toxicity were also observed in rats at higher dose levels.
In 5- and 13-week dietary studies in rats and dogs with alpha-cypermethrin, there were clinical signs indicative of neurotoxicity (hypersensitivity to noise and abnormal gait) as well as increased organ weights for brain, liver and kidney at 21.9 mg/kg bw/day and above in rats and at 14 mg/kg bw/day in dogs. The NOEL of 4.7 mg/kg bw/day in this dog study is the basis for the current alpha-cypermethrin ADI.
Long-term effects: Long-term (2-year) studies in mice, rats and dogs with cypermethrin reported increased organ weights and haematological and biochemical changes in all species. The rat was the most sensitive species, with effects observed at 50 mg/kg bw/day and above. The NOEL of 5 mg/kg bw/day in this rat study is the basis for the current cypermethrin ADI.
There were no long-term studies conducted on alpha-cypermethrin or other isomers; however, the data for cypermethrin are considered representative of other isomers in relation to potential long-term effects.
Carcinogenicity: On the basis of long-term studies in mice and rats, there is no evidence of carcinogenicity for cypermethrin.
Genotoxicity: Cypermethrin and alpha-cypermethrin are not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A multigenerational reproduction study in rats and developmental studies in rats and rabbits with cypermethrin reported no evidence of effects on reproductive parameters or on foetal development. There are no reproduction or developmental studies available for the other cypermethrin isomers; however, the data for cypermethrin are considered representative of other isomers for these endpoints.
Neurotoxicity/immunotoxicity: Studies in rats and hamsters with cypermethrin reported no evidence of delayed neurotoxicity or toxicity to the immune system.
Poisons Schedule: Cypermethrin and alpha-, beta- and zeta-cypermethrin are in Schedules 5, 6 and 7 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 cypermethrin was determined as follows:
where:
5 mg/kg bw/day is the NOEL for cypermethrin and alpha-cypermethrin based on a long-term (2-year) study in rats and a medium-term (13-week) study in dogs, respectively. This NOEL is considered to be protective for other cypermethrin isomers.
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. The safety factor of 100 incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
The World Health Organization has included cypermethrin in the list of chemicals from agricultural activities excluded from guideline value derivation because it is “unlikely to occur in drinking water” (WHO 2004).
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.
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.
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, Switzerland.
Woudneh MB, Oros DR (2008). 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.
Last updated
