Fenamiphos
(endorsed 2011)
Guideline
Based on human health concerns, fenamiphos in drinking water should not exceed 0.0005 mg/L.
Related chemicals
Fenamiphos (CAS 22224-92-6) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, which includes terbufos, chlorpyrifos, ethion, diazinon, fenitrothion, profenofos, trichlorfon, methidathion and acephate (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, fenamiphos would not be a health concern unless the concentration exceeded 0.0005 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: Fenamiphos is an insecticide used for the control of nematodes and sucking insects (e.g. aphids and thrips) on food and non-food producing crops, and for the control of nematodes in turf.
There are registered products containing fenamiphos in Australia. These products are intended for professional use and are available as concentrated solutions to be applied in diluted form using ground, aerial or hand-held sprays. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to fenamiphos is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of fenamiphos 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
Fenamiphos has been found at varying rates in soil (Kookana et al. 1997) and in groundwater (Di et al. 1995). Point-source fenamiphos pesticide contamination of groundwater from effluent from pest control operators was reported in Perth (Davis et al. 1996). Fenamiphos is routinely sampled by drinking water providers but no detections were reported in the literature searched.
Treatment of drinking water
Reverse osmosis challenger data reduced by more than 99% the initial fenamiphos concentration of 930 μg/L (USEPA 2005). Granular activated carbon is also very efficient in removing trace organic substance including fenamiphos.
Measurement
Fenamiphos can be extracted from water by liquid/liquid extraction or solid phase extraction. The extract is concentrated and analysed by gas chromatography (GC) coupled with a nitrogen phosphorus detector (NPD) and flame photometric detector. The method can achieve a limit of quantitation (LOQ) of 0.05 μg/L (López-Blanco et al. 2006). Solid-phase extraction (SPE) and GC with NPD or mass spectrometry in the selected-ion monitoring mode detection can achieve a LOQ of 0.08–0.60 μg/L, and 0.03–0.13 μg/L, repectively (Psathaki et al. 1994). SPE followed by thermospray liquid chromatography–mass spectrometry can achieve a LOQ of 0.012 μg/L (Lacorte et al. 1995).
History of the health values
The current acceptable daily intake (ADI) for fenamiphos is 0.0001 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.014 mg/kg bw/day from a 2-year dietary study in dogs. The NOEL is based on inhibition of plasma cholinesterase activity. The ADI incorporates a safety factor of 100 and it was established in 2005. This ADI is supported by a NOEL of 0.011 mg/kg bw/day based on plasma cholinesterase inhibition in a 6-month dietary dog study.
The acute reference dose (ARfD) of 0.003 mg/kg bw/day for fenamiphos was established in 2005, based on a NOEL of 0.25 mg/kg bw/day from an acute oral toxicity study in dogs. The ARfD incorporates a safety factor of 100.
The previous health value was 0.0003 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Fenamiphos is extensively and readily absorbed from the gastrointestinal tract, with wide distribution in tissues. Metabolism is extensive, and proceeds via sulfoxidation and phenylation pathways. Excretion is predominantly via the urine and to a lesser extent via the faeces, and is complete within 48 hours.
Acute effects: Fenamiphos has very high acute oral toxicity and high acute dermal toxicity. It is not a skin sensitiser.
Short-term effects: In 15-22 day dermal toxicity studies in rats and rabbits, plasma cholinesterase activity was decreased at 2.5 mg/kg bw/day in rabbits and at 40 mg/kg bw/day in rats.
In three-month oral toxicity studies in rats and dogs, plasma cholinesterase activity was decreased at 0.8 mg/kg bw/day in rats and at 0.05 mg/kg bw/day in dogs. Red blood cell cholinesterase activity was decreased at 1.6 mg/kg bw/day in rats and at 0.125 mg/kg bw/day in dogs. Clinical symptoms of cholinesterase inhibition were observed at 3.2 mg/kg bw/day in rats and at 0.45 mg/kg bw/day in dogs.
Long-term effects: In long-term dietary studies in mice, rats and dogs, plasma, red blood cell cholinesterase activity was decreased at 0.09 mg/kg bw/day in rats and dogs. In rats, brain cholinesterase activity was decreased and clinical symptoms of cholinesterase inhibition were observed at 2.45 mg/kg bw/day. In dogs, other signs of general toxicity were observed at 0.308 mg/kg bw/day. In mice, bodyweight decrease only was observed at 7.4 mg/kg bw/day. The lowest overall NOEL was 0.014 mg/kg bw/day in dogs. This NOEL is the basis for the current ADI.
Carcinogenicity: Based on a 2-year study in mice and rats, there is no evidence of carcinogenicity for fenamiphos.
Genotoxicity: Fenamiphos 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 a developmental toxicity study in rabbits found no evidence of effects on reproductive parameters or foetal development.
Neurotoxicity: A 21-day neurotoxicity study in hens found no evidence for delayed neurotoxicity for fenamiphos.
Poisons Schedule: Fenamiphos is included in Schedule 6 or 7 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on its 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 of 0.0005 mg/L for fenamiphos was determined as follows:
where:
0.014 mg/kg bw/day is the NOEL based on a long-term (2-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. This 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 fenamiphos 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.
Davis GB, Appleyard S (1996). Organic pollutants from urban developments over the unconfined groundwater system in Perth WA, Groundwater and Land-use Planning, Fremantle, Western Australia. Perth, Centre for Groundwater Studies, pp 56-65.
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.
Di HJ, Kookana R, Aylmore LAG (1995). Application of a simple model to assess the groundwater contamination potential of pesticides. Australian Journal of Soil Research, 33:1031–1040.
Kookana RS, Phang C, Aylmore LAG (1997). Transformation and degradation of fenamiphos nematicide and its metabolites in soils. Australian Journal of Soil Research, 35(4):753-762.
Lacorte S, Barcelo D (1995). Determination of organophosphorus pesticides and their transformation products in river waters by automated on-line solid-phase extraction followed by thermospray liquid chromatography-mass spectrometry. Journal of Chromatogr A, 712(1):103-12
López-Blanco C, Gómez-Álvarez S, Rey-Garrote M, Cancho-Grande B, Simal-Gándara J (2006). Determination of pesticides by solid phase extraction followed by gas chromatography with nitrogen-phosphorous detection in natural water and comparison with solvent drop microextraction. Analytical and Bioanalytical Chemistry, 384(4):1002-1006.
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.
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):241-8.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
USEPA (United States Environmental Protection Agency) (2005). Point of use drinking water treatment system application: Removal of chemical contaminants in drinking water: Reverse osmosis. The Environmental Technology Verification Program, USEPA.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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