Amitraz
(endorsed 2011)
Guideline
Based on human health concerns, amitraz in drinking water should not exceed 0.009 mg/L.
Related chemicals
Amitraz (CAS 33089-61-1) is in the amidine class of chemicals. There are no other pesticides in this class (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, amitraz would not be a health concern unless the concentration exceeded 0.009 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: Amitraz is an acaricide (miticide) and insecticide used for the control of heliothis and aphids on cotton; for the control ticks on cattle, deer, sheep, goats, circus animals and dogs; and for the control of mange in pigs.
There are registered products containing amitraz in Australia. These are intended for both professional and home veterinary use. The products are applied by ground spray or aircraft when used on cotton. They are used as a spray or in a pour-on formulation when used on livestock. Amitraz is also incorporated into a collar or a shampoo for use on dogs. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure are use of the home veterinary products, and residues in the food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of amitraz may potentially lead to contamination of source waters through processes such as run-off, spray-drift or entry into groundwater. The veterinary use of amitraz 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 amitraz in Australian drinking waters have been identified.
Treatment of drinking water
No specific data on the treatment of amitraz in drinking water have been identified.
Measurement
No suitable analytical methods for amitraz in drinking water have been identified. If there is an identified need to monitor amitraz in drinking water, it is expected that gas-chromatography–mass spectrometry and high performance liquid chromatography–mass spectrometry would be suitable techniques. Both of these approaches have previously been used for monitoring amitraz in food products such as fruit and honey.
History of the health values
The acceptable daily intake (ADI) for amitraz is 0.002 mg per kg of bodyweight (mg/kg bw) based on a no-observed-effect level (NOEL) of 0.25 mg/kg bw/day from a 2-year study in dogs. The ADI incorporates a safety factor of 100 and was established in 1986.
A health-based guideline value has not been previously established by NHMRC.
Health considerations
Metabolism: Amitraz is absorbed rapidly from the gastrointestinal tract of humans, and is metabolised and excreted mainly in the urine within 72 hours. The main metabolites are 4-formamido-3-methyl benzoic acid and 4-acetamido-3-methyl benzoic acid. In dogs, peak blood levels were seen at 8 hours and 80% of the dose was excreted within 24 hours.
Acute effects: Amitraz has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: Short-term dietary studies in mice indicated liver toxicity at 3 mg/kg bw/day and above.
Long-term effects: A 2-year dietary study in rats showed an increase in nervous and aggressive behaviour at 10 mg/kg bw/day. A 2-year study in dogs showed central nervous system depression on days 1 and 2 of treatment. There was also an increase in the blood glucose levels at doses above 0.25 mg/kg bw/day. The NOEL of 0.25 mg/kg bw/day is the basis for the ADI.
Carcinogenicity: An increase in hepatocellular adenomas and carcinomas was observed in female B6C3F1 mice at 60 mg/kg bw/day. This is considered to be a species-specific effect and not relevant to humans.
Genotoxicity: Amitraz is not considered genotoxic, based on in vitro or in vivo short-term studies.
Reproductive and developmental effects: A reproduction study in rats showed decreased bodyweight gain and reduced fertility in the dams together with decreased pup survival at 21 days in all generations treated at 50 mg/kg bw/day. A 28-week study in mice reported hormonal changes and effects on the oestrus cycle at 14.3 mg/kg bw/day. In developmental studies in rats and rabbits, there was evidence of foetal toxicity at dose levels of 12 and 25 mg/kg bw/day, respectively, but no evidence of teratogenicity.
Poisons Schedule: Amitraz is included in Schedule 6 of the 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 value of 0.009 mg/L for amitraz was determined as follows:
where:
0.25 mg/kg bw/day is the NOEL based on a long-term (2-year) 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 a 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 variations.
Amitraz is included in the World Health Organization guidelines for drinking water quality list of chemicals from agricultural activities excluded from guideline value derivation because it “degrades rapidly in the environment and is not expected to occur at measurable concentrations in drinking-water supplies” (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.
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.
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.
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