Acephate
(endorsed 2011)
Guideline
Based on human health concerns, acephate in drinking water should not exceed 0.008 mg/L.
Related chemicals
Acephate (CAS 30560-19-1) belongs to the organophosphate class of chemicals. There are many other pesticides in this class, including chlorpyrifos, diazinon, dichlorvos, ethion and temephos (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, acephate would not be a health concern unless the concentration exceeded 0.008 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: Acephate (O,S-dimethyl acetylphosphoramidothionate) is used for the control insects on fruit, vegetable and nut crops. Acephate breaks down and is metabolised to methamidophos, another insecticide.
There are registered products containing acephate in Australia. These products are intended for professional use and are available as soluble concentrates intended to be diluted and applied by ground or aerial spray application. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to acephate and its metabolites is residues in food. Residue levels in crops grown according to good agricultural practice are generally low.
Agricultural use of acephate 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
There are few data on concentrations of acephate in drinking water in Australia. Acephate has been detected in mains water in Poland with concentrations generally in the range of 0.0001 to 0.0015 mg/L (0.1 to 1.5 µg/L), and up to a maximum of 0.0106 mg/L (10.6 µg/L) (Badach et al. 2007). Acephate has also been reported in river water in Spain, with a mean concentration of 0.00047 mg/L (0.47 µg/L) and a maximum of 0.00217 mg/L (2.17 µg/L) over 20 sampling sites (Espigares et al. 1997).
Treatment of drinking water
No reported instances of reliable removal of acephate from drinking water at typical activated carbon doses and contact times have been identified. Some case studies on activated carbon have been reported with very high carbon doses; for example, on the treatment of wastewater from a pesticide manufacturing plant (Banerjee 2002) or in benchscale tests (Suzuki 2002). Although acephate has a relatively short soil half-life of between 3 and 6 days, the hydolysis half life is much longer, at 169 days, rendering reservoir detention an unreliable treatment method for the removal of acephate from water.
Measurement
Residues of acephate and methamidophos are traditionally determined by gas chromatography–electrodialysis (Espigares et al. 1997, Badach et al. 2007). The detection limit by this method is 0.00005 mg/L (0.05 μg/L) (Badach et al. 2007). Analysis of highly polar, water-soluble organophosphates, including acephate and methamidophos, using hydrophilic interaction liquid chromatography with tandem mass spectrometry has produced much lower limits of detection (Hayama et al. 2008).
History of the health values
The current acceptable daily intake (ADI) for acephate is 0.003 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.22 mg/kg bw/day from a 2-year dietary rat study. The NOEL was based on inhibition of cholinesterase. The ADI incorporates a safety factor of 100 and it was established in 1998.
The previous health value was 0.01 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Acephate is rapidly absorbed from the gastrointestinal tract and widely distributed in the body. It is rapidly eliminated, mainly in the urine, as unchanged acephate. It has a low potential for bioaccumulation. The primary metabolite is methamidophos.
Acute effects: Acephate has low to moderate oral acute toxicity, and low dermal toxicity. It is not a skin sensitiser. Clinical symptoms of toxicity were typical of cholinesterase inhibition and included tremors, prostration, coma, piloerection, ataxia, and salivation.
Short-term effects: Decreased erythrocyte cholinesterase activity was seen at the lowest dose tested of 0.5 mg/kg bw/day and above in a 21-day repeat-dose dermal study in rabbits. No other effects were seen.
Decreased plasma, erythrocyte, and brain cholinesterase activity was seen at a dose of 2.5 mg/kg bw/day (monkey) and 3.75 mg/kg bw/day (rat) in 1-month repeat dose dietary studies. Both studies used a single dose level and no other effects were seen. A NOEL was not established in either study.
Long-term effects: Long-term toxicity studies were performed in mice (2 years), rats (28 months), and dogs (2 years). Decreased brain, plasma and erythrocyte cholinesterase activity was seen at doses of 2 mg/kg bw/day (rats). The sole effect in dogs was decreased erythrocyte cholinesterase activity at the highest dose tested of 2.5 mg/kg bw/day. Histopathological changes in the liver (non-neoplastic lesions) at doses of 15 mg/kg bw/day and above were the only effect observed in mice. The lowest overall NOEL was 0.22 mg/kg bw/day in rats, and this is the basis for the current ADI.
Carcinogenicity: Based on a 2-year study in mice, there is no evidence of carcinogenicity for acephate.
Genotoxicity: Acephate is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A reproduction study in rats and developmental studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or foetal developmental.
Poisons Schedule: Acephate 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 guideline
The health-based guideline value of 0.008 mg/L for acephate was determined as follows:
where:
0.22 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 a 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.
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.
Badach H, Nazimek T, Kaminska IA (2007). Pesticide content in drinking water samples collected from orchard areas in central Poland. Annals of Agricultural and Environmental Medicine, 14(1):109-114.
Banerjee G, Kumar B (2002). Pesticide (acephate) removal by GAC: A case study. Indian Journal of Environmental Health, 44(2):92 – 101.
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.
Espigares M, Coca C, Fernandez-Crehuet M, Moreno O, Bueno A, Galvez R (1997). Pesticide concentrations in the waters from a section of the Guadalquivir River basin, Spain. Environmental Toxicology and Water Quality, 12(3): 249-256.
Hayama T, Yoshida H, Todoroki K, Nohta H, Yamaguchi M (2008). Determination of polar organophosphorus pesticides in water samples by hydrophilic interaction liquid chromatography with tandem mass spectrometry. Rapid Communications in Mass Spectrometry, 22(14):2203-2210.
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.
Suzuki S, Numajiri S, Misawa K, Toyooka K (2002). Appropriate management of granular activated carbon with adsorption amount of organic compounds. Yosui to Haisui, 44(11):994-1000.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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