Fenitrothion
(endorsed 2011)
Guideline
Based on human health concerns, fenitrothion in drinking water should not exceed 0.007 mg/L.
Related chemicals
Fenitrothion (CAS 122-14-5) belongs to the organophosphate class of chemicals. There are many other pesticides in this class including fenthion, parathion, profenofos and ethoprophos (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, fenitrothion would not be a health concern unless the concentration exceeded 0.007 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: Fenitrothion is an insecticide for the control of a variety of pests (grasshoppers, locusts, beetles, weevils) on crops, fruits, vegetables and pastures. It is also used to treat flour mills, grain storage facilities (prior to storage) and broiler poultry houses (before restocking).
There are registered products containing fenitrothion in Australia, all of which are intended for professional use. All products are liquid concentrates which are diluted and then sprayed. Ground spraying can be done using air-assisted, misting, electrostatic and boom sprayers. Aerial applications are also used, particularly for large scale locust control, where ultra-low volume (ULV) application is common. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to fenitrothion is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of fenitrothion may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater.
Reported values in Australian waters
No data were found on fenitrothion in Australian drinking waters. In the 1981 spruce budworm spray program in Canada, the concentrations of fenitrothion residues detected in water were low (maximum 1.30 μg/L), and post-spray samples did not contain detectable concentrations (<0.01 μg/L) (Mallett and Cassista 1984, cited in WHO 2004a).
Treatment of drinking water
There is insufficient information on the treatment of fenitrothion in drinking water, but it is expected that advanced treatment methodologies such as ozonation and advanced oxidation would be effective.
Measurement
Fenitrothion can be measured by routine gas chromatography with 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 fenitrothion is 0.002 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.2 mg/kg bw/day from a 1-year dietary study in dogs. This NOEL is based on plasma cholinesterase inhibition. The ADI incorporates a safety factor of 100 and was established in 1997. The previous ADI was 0.003 mg/kg bw/day based on a NOEL of 0.3 mg/kg bw/day from a 92-week rat study.
The acute reference dose (ARfD) of 0.03 mg/kg bw/day for fenitrothion was established in 2000, based on a NOEL of 0.33 mg/kg bw/day from a single dose study in humans for plasma and red blood cell cholinesterase inhibition. The ARfD incorporates a safety factor of 10 (for intraspecies variation).
The previous health value was 0.01 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Following oral administration, fenitrothion is readily absorbed from the gastrointestinal tract in all species. It is initially metabolised in the liver to fenitrooxon, then to other metabolites, which are excreted mainly via the urine. The main metabolites are desmethylfenitrothion, desmethylfenitrooxon and 3-methyl-4-nitrophenol (both free and conjugated with sulfate or βglucuronic acid).
Acute effects: Fenitrothion has low to moderate acute oral and dermal toxicity. It does not cause skin sensitisation.
Short-term effects: Short-term studies in rats reported decreased plasma, brain and red blood cell (RBC) cholinesterase activity and symptoms indicative of nervous system toxicity. A decrease in RBC cholinesterase was observed in a 4-week study at dose levels above 1 mg/kg bw/day.
Long-term effects: Long-term dietary studies in rodents, dogs and monkeys also showed the main effect to be on the nervous system, measured as inhibition of cholinesterase activity. A 1-year dietary study in dogs reported a decrease in plasma cholinesterase inhibition at 0.3 mg/kg bw/day and above. The NOEL of 0.2 mg/kg bw/day in this study is the basis for the current ADI.
Carcinogenicity: Based on long-term dietary studies, there is no evidence of carcinogenicity for fenitrothion.
Genotoxicity: Fenitrothion is not considered to be genotoxic, based on short-term in vitro and in vivo studies (JMPR 2000).
Reproductive and developmental effects: Reproduction studies in rats and developmental studies in rats, rabbits and mice reported no evidence of effects on reproduction, no developmental delays and no evidence of teratogenicity due to fenitrothion.
Neurotoxicity: There was no evidence of delayed neurotoxicity in hens.
Poisons Schedule: Fenitrothion is included in Schedule 6 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 0.007 mg/L for fenitrothion was determined as follows:
where:
0.2 mg/kg bw/day is the NOEL based on a long-term (1-year) dietary 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 the safety factor applied to the NOEL derived from animal studies. The safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
The World Health Organization has not established a health-based guideline value for fenitrothion and it is included in the list of agricultural chemicals for which a guideline value has not been established because it “occurs in drinking water at concentrations well below those at which toxic effects may occur” (WHO 2004b).
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.
JMPR (Joint Meeting on Pesticide Residues) (2000). Pesticide residues in food: Fenitrothion.
Mallett VN, Cassista A (1984). Fenitrothion residue survey in relation to the 1981 spruce budworm spray program in New Brunswick. Canada. Bulletin of Environmental Contamination and Toxicology, 32:65–74.
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) (2004a). Fenitrothion in Drinking-water. Background document for development of WHO Guidelines for Drinking-water Quality. The World Health Organization.
WHO (World Health Organization) (2004b). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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