Bioresmethrin
(endorsed 2011)
Guideline
Based on human health concerns, bioresmethrin in drinking water should not exceed 0.1 mg/L.
Related chemicals
Bioresmethrin (CAS 28434-01-7) belongs to the pyrethroid class of chemicals. This is one of the largest groups of insecticides, and includes cyfluthrin, esfenvalerate, fenvalerate, permethrin, and flucythrinate (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, bioresmethrin would not be a health concern unless the concentration exceeded 0.1 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: Bioresmethrin is a household insecticide used for the control of flies, mosquitoes, spiders, ants, cockroaches, fleas, silverfish, and moths.
There are registered products that contain bioresmethrin in Australia. These products are intended for domestic use and are applied by spray directly onto insects or laid as baits in areas of infestation. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to bioresmethrin and its metabolites is the use of household insecticide products. Levels of exposure from these uses are low.
The domestic use of this chemical provides only limited potential for contamination of drinking water.
Typical values in Australian drinking water
No data on occurrence of bioresmethrin in Australian waters could be found.
Treatment of drinking water
No specific data on the treatment of bioresmethrin in drinking water have been identified.
Measurement
Bioresmethrin can be measured by routine gas chromatrography–mass spectrometry analysis, with a limit of reporting of 0.1 µg/L (Queensland Health 2007).
History of the health values
The current acceptable daily intake (ADI) for bioresmethrin is 0.03 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 3 mg/kg bw/day from a 2-year dietary rat study. The NOEL is based on evidence of mild liver toxicity in the form of increased relative liver weight, discolouration, hepatocellular hypertrophy, and fatty vacuolisation (steatosis) at doses of 15 mg/kg bw/day and above. The ADI incorporates a safety factor of 100 and was established in 1991.
The previous ADI for bioresmethrin was set in 1975 at 0.3 mg/kg bw, based on a NOEL of 30 mg/kg bw/day from a medium-term dietary study in rats, which showed evidence of mild liver toxicity. The ADI was amended after submission of a long-term dietary study in rats showing a lower NOEL for liver toxicity.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Bioresmethrin is rapidly absorbed via the gastrointestinal tract and extensively metabolised. It has wide, uniform distribution including the brain and testes in mammals. The primary metabolic pathway is hydrolysis and oxidation to 5-benzyl-3-furan carboxylic acid (BFCA). Bioresmethrin is slowly eliminated in the urine and to a lessor extent in faeces, almost completely within 6 days.
Acute effects: Bioresmethrin has low acute oral and acute dermal toxicity. It is not a skin sensitiser.
Short-term effects: Two-week studies in rats and dogs did not demonstrate any toxicity at low dose levels. Effects in rats were confined to decreased liver and thymus weights, and decreased haemoglobin levels at doses of 1000 mg/kg bw/day. No toxicity was seen in dogs at this dose level. Three-month studies in rats and dogs reported increased liver weight, fatty deposits in the liver, increased liver enzyme activity, and decreased red blood cells at doses of 100 mg/kg bw/day in rats and at 250 mg/kg bw/day in dogs.
Long-term effects: A long-term dietary study in rats reported evidence of mild liver toxicity (increased weight, hepatocellular hypertrophy, fatty deposits, and increased serum enzyme activity) at doses of 15 mg/kg bw/day. The NOEL was 3 mg/kg bw/day and this is the basis for the current ADI.
Carcinogenicity: Based on a 2-year study in rats, there is no evidence of carcinogenicity for bioresmethrin.
Genotoxicity: Bioresmethrin is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 2-generation reproduction study in rats and developmental studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal development.
Neurotoxicity: Short-term dietary studies in rats reported evidence suggestive of nervous system toxicity but only at extremely high dose levels, which are well in excess of the likely level of human exposure. The metabolite 5-benzyl-3-furancarboxylic acid (BFCA) is responsible for most of the nervous system toxicity from bioresmethrin in mammals.
Poisons Schedule: Bioresmethrin is included in Schedule 5 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 0.1 mg/L for bioresmethrin was determined as follows:
where:
3.0 mg/kg bw/day is the NOEL based on 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 (WHO) has not established a health-based guideline value for bioresmethrin. This relates to the WHO’s policy to exclude the use of pyrethroids for direct addition to drinking water as mosquito larvicides. This is based on concern over the developing of resistance to synthetic pyrethroids, which interferes with the global anti-malaria strategy (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.
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.
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.
Queensland Health (2007). Organochlorine, organophosphorous and synthetic pyrethroid pesticide, urea and triazine herbicides and PCBs in water. QHFSS SOP 16315.
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.
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