Fipronil
(endorsed 2011)
Guideline
Based on human health concerns, fipronil in drinking water should not exceed 0.0007 mg/L.
Related chemicals
Fipronil (CAS 120068-37-3) belongs to the phenylpyrazole class of chemicals. Another pesticide in this class is ethiprole (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, fipronil would not be a health concern unless the concentration exceeded 0.0007 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: Fipronil is a broad-spectrum insecticide that has a range of agricultural uses, including seed dressings, control of pests in bananas, cotton, sorghum, vegetables and turf. Fipronil is also included in insect baits for household and commercial uses, and in home veterinary products for cats and dogs.
There are registered products containing fipronil in Australia. The products are intended for agricultural, professional, home garden, and household pet use. They are available as sprays, baits, dusts, and gels for control of cockroaches, fruit flies, ants and termites; as concentrated granular formulations for control of insect pests in turf; spot on and spray insecticide treatments for pets; and as liquid concentrates and/or wettable granules for application to seeds, and vegetable and other crops, to be applied in diluted form by ground and aerial sprays. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to fipronil and its metabolites are residues in food.
Agricultural and veterinary use of fipronil 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 reports of fipronil in Australian drinking waters have been identified.
Treatment of drinking water
No specific literature on the removal of fipronil has been identified. Jar testing to identify the effectiveness of various removal methods in specific waters is recommended if fipronil is detected.
Measurement
The practical limit of quantification (LOQ) for fipronil in water is 0.001 mg/L using liquid chromatography with tandem mass spectrometry (Alder et al. 2006). This LOQ is slightly above the guideline value.
History of the health values
The current acceptable daily intake (ADI) for fipronil is 0.0002 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.02 mg/kg bw/day from a 2-year rat dietary study for effects on the nervous system, thyroids and kidneys. The ADI includes a safety factor of 100 and it was initially established in 1994 and reconfirmed in 2006.
The current acute reference dose (ARfD) is 0.02 mg/kg bw, set in 2006 and based on a NOEL of 2.5 mg/kg bw for effects on the nervous system in an acute dietary study in rats. This incorporates a safety factor of 100. The previous ARfD was 0.003 mg/kg bw.
The ADI and ARfD values are a group value covering the parent compound and its main metabolites.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: Fipronil is completely absorbed via the gastrointestinal tract and extensively metabolised. Excretion is slow (more than 8 days) via the faeces. Dermal absorption is low.
Acute effects: Fipronil has moderate oral toxicity and low to moderate dermal toxicity. It is not a skin sensitiser in guinea pigs.
Short-term effects: In 4-6 week studies in mice, rats and dogs, effects were observed on the nervous system (muscular incoordination, convulsions and hyperactivity in mice at 6.5 mg/kg bw/day and head nodding in dogs at 10 mg/kg bw/day), and on the liver (at 2.4 mg/kg bw/day and above in mice, and 3.4 mg/kg bw/day in rats) and thyroid (at 3.4 mg/kg bw/day in rats).
In 3-month dietary studies in rats and dogs, there was increased liver and thyroid weight, and associated follicular cell hypertrophy and hyperplasia in rats, and decreased body weight gain in dogs at doses of 2 mg/kg bw/day. Symptoms of nervous system toxicity in dogs (convulsions, tremors, in-coordination) were seen at higher doses.
Long-term effects: In long-term studies in mice, rats and dogs, effects on the nervous system (irritability, hyperactivity and vocalisation) were observed in rats at 0.06 mg/kg bw/day and in dogs (convulsions, facial twitching, and disorientation) at 2 mg/kg bw/day. Nephropathy and increased liver and thyroid weight associated with hypertrophy and hyperplasia were observed in all species. The lowest NOEL was 0.02 mg/kg bw/day in the 2-year rat study, and is the basis for the current ADI.
Carcinogenicity: Based on a 2-year study in rats, there is no evidence of carcinogenicity for fipronil.
Genotoxicity: Fipronil is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproduction and developmental effects: Reproduction studies in rats and developmental studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal development.
Neurotoxicity: In a single oral dosing study in rats, there was decreased hind leg splay at 5 mg/kg bw/day. In a 6-day oral dosing study in rats, there was decreased levels of serotonin in the brain at 5 mg/kg bw/day. In a 13-week dietary study in rats, there was an increased incidence in “startled” responses and decreased forelimb strength at 7.2 mg/kg bw/day.
Poisons Schedule: Fipronil is either exempt from scheduling or is included in Schedule 5 or 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 value of 0.0007 mg/L for fipronil was determined as follows:
where:
0.02 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 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.
100 is the safety factor applied to the NOEL derived from a study conducted in rats. The safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
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.
Alder L, Greulich K, Kempe G, Vieth B (2006). Residue analysis of 500 high priority pesticides: better by GC-MS or LC-MS/MS? Mass Spectrometry Reviews, 25(6):838-65.
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.
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