Trichlorfon
(endorsed 2011)
Guideline
Based on human health concerns, trichlorfon in drinking water should not exceed 0.007 mg/L.
Related chemicals
Trichlorfon (CAS 52-68-6) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, which includes dichlorvos, diazinon, and phorate (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, trichlorfon 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: Trichlorfon is used as an insecticide for the control of insect pests in home garden lawns, sports fields and agricultural crops, and as an acaricide for the control of parasites in livestock, and household and commercial aquariums.
There are registered products that contain trichlorfon in Australia. The products are intended for professional and home garden use. They are available as concentrated solutions to be diluted and applied by aerial and ground sprays to crops as an insecticide. When used as an acaricide, trichlorfon is supplied as pellets for addition to aquarium water, and as pellets or paste for oral drenching of livestock. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The potential sources of public exposure to trichlorfon and its metabolites are the use of home garden and aquarium products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of chemical may potentially lead to contamination of source waters through processes such as run-off, spray drift or entry into groundwater. When trichlorfon is added to water, it degrades to dichlorvos.
Typical values in Australian drinking water
No reports of trichlorfon in Australian drinking waters have been identified.
Treatment of drinking water
There is insufficient information on the treatment of trichlorfon in drinking water, but it is expected that advanced treatment methodologies such as ozonation and advanced oxidation would be effective.
Measurement
Several methods have been reported for the analysis of trichlorfon in water, including high performance liquid chromatography with ultraviolet detection, with a limit of detection (LOD) of 2.0 µg/L (Zhu et al. 2008); liquid chromatography with mass spectrometry-mass spectrometry, LOD 10 µg/L (Geiss et al. 2006); liquid chromatography with ionspray mass spectrometry, LOD 0.2 µg/L (Molina et al. 1996); and gas chromatography with mass spectrometry, LOD 0.73 µg/L (Molto et al. 1991).
History of the health values
The current acceptable daily intake (ADI) for trichlorfon 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 long-term (10-year) dietary study in monkeys. The NOEL is based on inhibition of cholinesterase. The ADI incorporates a safety factor of 100, and was established in 1986.
The previous health value was 0.005 mg/L (NHMRC and NRMMC, 2004).
Health considerations
Metabolism: Triclorfon is extensively and rapidly absorbed from the gastrointestinal tract and distributed widely in the body. Under normal alkaline physiological conditions, it is converted to dichlorvos by a non-enzymatic process. Following metabolism, excretion is rapid, primarily via the urine, with a half-life of about 80 minutes.
Acute effects: Triclorfon has moderate acute oral toxicity and low acute dermal toxicity. It is a skin sensitiser in guinea pigs. Clinical symptoms of toxicity were typical of cholinesterase inhibition and included tremors, prostration, coma, piloerection, ataxia, and salivation.
Short-term effects: In short-term oral studies (12-26 weeks) in rats, dogs and monkeys, the most significant effect was on the nervous system, with cholinesterase depression reported at 10 mg/kg bw/day in rats and 1.25 mg/kg bw/day in dogs. A 12-week oral study in humans reported clinical signs of toxicity and cholinesterase depression at 0.2 mg/kg bw/day.
Long-term effects: In long-term dietary studies in rats, dogs and monkeys, the most significant effect was on the nervous system, with monkeys the most sensitive to cholinesterase depression, at 1 mg/kg bw/day. The NOEL was 0.2 mg/kg bw/day, and this is the basis of the ADI.
Carcinogenicity: Based on long-term studies in rats, there is no evidence of carcinogenicity for trichlorfon.
Genotoxicity: While positive in in vitro assays, the weight of evidence indicates that trichlorfon is not genotoxic in vivo.
Reproductive and developmental effects: Reproduction studies in rats and developmental studies in mice and rats did not show any evidence of effects on reproductive parameters or foetal development.
Neurotoxicity: There was no evidence of delayed neuropathy in chickens. Short-term neurotoxicity studies in rats, hens and monkeys, conducted with oral doses up to 200 mg/kg bw/day, confirmed that trichlorfon has an effect on the nervous system, with effects such as increased locomotor activity and decreased learning ability and nerve conduction velocity, impaired nerve conduction, demyelination of nerves and axonal degeneration observed at high doses.
Poisons Schedule: Trichlorfon is included in Schedule 6 and in Schedule 4 (as metrifonate, for human therapeutic use) 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 0.007 mg/L for trichlorfon was determined as follows:
where:
0.2 mg/kg bw/day is the NOEL based on a long-term (10-year) dietary study in monkeys.
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 a safety factor derived from a long-term study in monkeys. The safety factor of 100 incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variations.
The World Health Organization has not established a health-based guideline value for trichlorfon and it is excluded from the list of agricultural chemicals 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.
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.
Geiss S, Gebert S (2006). Extraction of highly polar organophosphorus pesticides from water. Acta Hydrochimica et Hydrobiologica, 34:464-473.
Molina C, Grasso P, Benfenati E, Barcelo D (1996). Automated sample preparation with extraction columns followed by liquid chromatography-ionspray mass spectrometry. Interferences, determination and degradation of polar organophosphorus pesticides in water samples. Journal of Chromatography A, 737:47-58.
Molto JC, Pico Y, Font G, Manes J (1991). Determination of triazines and organophosphorus pesticides in waters amples using solid-phase extraction, Journal of Chromatography, 555:137-145.
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.
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.
Zhu H-Z, Liu W, Mao J-W, Yang MM (2008). Cloud point extraction and determination of trace trichlorfon by high performance liquid chromatography with ultraviolet-detection based on its catalytic effect on benzidine oxidising. Analytica Chimica Acta, 614:58-62.
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