Fenthion
(endorsed 2011)
Guideline
Based on human health concerns, fenthion in drinking water should not exceed 0.007 mg/L.
Related chemicals
Fenthion (CAS 55-38-9) is in the organophosphate chemical class. There are many pesticides in this group, including chlorpyrifos, diazinon, dichlorvos, ethion, parathion and profenofos (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, fenthion would not be a health concern unless the concentration exceeded 0.007 mg/L. Excursions above this level even for a short period are of concern as the health-based guideline is based on short-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: Fenthion is an insecticide used for pre- and post-harvest treatment of various fruits and vegetables. It is also used as a commercial and domestic insecticide and as an ectoparasiticide in cattle and dogs.
There are registered products containing fenthion in Australia. These products include a spot-on treatment for cattle, an insecticide dust and spray, as well as paint, paste and gels for control of pest birds. Some products are available for use in the home garden and as household insecticides. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to fenthion and its metabolites are use of household insecticide products, and residues in food. Residue levels in crops grown according to good agricultural practice are generally low.
Agricultural use 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 data for fenthion in Australian drinking water are available. The highest predicted surface water concentration in the USA was 1.3 μg/L (USEPA 2001). The highest concentration reported in surface water in Japan was 0.27 μg/L (Tsuda et al. 1998). Fenthion concentration in Australian treated sewage was less than 2.4 μg/L (supporting data, NRMMC/EPHC/NHMRC, 2008).
Treatment of drinking water
Although no empirical data is currently available, it is likely that activated carbon would provide efficient removal for this chemical based on its chemical structure.
Measurement
Fenthion residues in water can be analaysed by solid-phase extraction–liquid chromatography with electrospray tandem mass spectrometry, with a detection limit of 0.021 μg/L (Hernandez et al, 2001); or by solid-phase extraction–gas chromatography–mass spectrometry, with a detection limit of 0.13 μg/L (Psathaki et al, 1994).
History of the health values
The current acceptable daily intake (ADI) for fenthion is 0.002 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 28-day human study showing cholinesterase inhibition. The ADI incorporates a safety factor of 10 and was established in 2004.
The acute reference dose (ARfD) of 0.007 mg/kg bw/day for fenthion was established in 2000, based on a NOEL of 0.07 mg/kg bw/day from a 28-day oral study in human volunteers. The ARfD incorporates a safety factor of 10. This NOEL is further supported by a NOEL of 0.07 mg/kg bw from an acute neurotoxicity study in rats.
A health value has not been previously established by NHMRC for fenthion.
Health considerations
Metabolism: Fenthion is rapidly absorbed from the gastrointestinal tract and broadly distributed in tissues, particularly in lipid stores. Metabolism is extensive and elimination is almost complete after 48 hours (90% in the urine). There are 3 major urinary metabolites – the oxygen analogue of fenthion and its sulfoxide and sulfone derivatives.
Acute effects: Fenthion has moderate acute oral and dermal toxicity. Symptoms of acute poisoning were indicative of central and peripheral nervous system poisoning and included hyperexcitability, salivation, broncoconstriction, headache, vomiting and other behavioural changes. It is not a skin sensitiser.
Short-term and long-term effects: In short-term and long-term studies in rodents, monkeys and dogs, the main effect was the inhibition of cholinesterase (plasma, brain and red blood cell) at dose levels of 0.04 mg/kg bw/day (mouse) 0.07mg/kg bw/day (monkey), 0.32 mg/kg bw/day (dog) and above.
In a 4-week human volunteer study, there was a dose-related inhibition of plasma cholinesterase at 0.07 mg/kg bw/day. There was no inhibition of red blood cell cholinesterase. The NOEL of 0.02 mg/kg bw/day is the basis for the ADI.
Carcinogenicity: Based on long-term studies in rodents, there is no evidence of carcinogenicity for fenthion.
Genotoxicity: Fenthion is not considered to be genotoxic, based on in vitro or in vivo short-term studies.
Reproductive and developmental effects: In a reproduction study in rats, there was decreased fertility, decreased litter sizes and increased neonatal deaths at high doses. Similarly, developmental studies in rats and rabbits showed increased resorptions and delayed skeletal development as a result of high dose maternotoxicity. In both cases, this was the result of central nervous system effects and well above the likely levels of human exposure.
Neurotoxicity: There was no evidence of delayed neurotoxicity in hen, rat and dog studies.
Poisons Schedule: Fenthion is included in Schedule 5, 6 or 7 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on the concentration and the use of the product. 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 fenthion was determined as follows:
where:
0.02 mg/kg bw/day is the NOEL based on a short-term (28-day) study in human volunteers.
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.
10 is a safety factor applied to the NOEL derived a human study to account for variation within the human population (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.
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.
Hernandez F, Sancho JV, Pozo O, Lara A, Pitarch E (2001). Rapid direct determination of pesticides and metabolites in environmental water samples at sub-ug/l level by on-line solid-phase extraction–liquid chromatography–electrospray tandem mass spectrometry. Journal of Chromatography, A 939(1-2): 1-11.
NRMMC (Natural Resource Management Ministerial Council), EPHC (Environment Protection and Heritage Council), NHMRC (National Health and Medical Research Council) (2008). Australian Guidelines for Water Recycling: Managing health and environmental risks (Phase 2) - Augmentation of drinking water supplies. NRMMC, EPHC, NHMRC.
Psathaki M, Manoussaridou E, Stephanou EG (1994). Determination of organophosphorus and triazine pesticides in ground- and drinking water by solid-phase extraction and gas chromatography with nitrogen-phosphorus or mass spectrometric detection. Journal of Chromatography A, 667(1-2): 241-248.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
Tsuda T, Kojima M, Harada H, Nakajima A, Aoki S (1998). Pesticides and their oxidation products in water and fish from rivers flowing into Lake Biwa. Bulletin of Environmental Contamination and Toxicology, 60: 151-158.
USEPA (United States Environmental Protection Agency) (2001). Interim Reregistration Eligibility Decision for Fenthion. EPA 738-R-00-013. USEPA.
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