Oxamyl
(endorsed 2011)
Guideline
Based on human health concerns, oxamyl in drinking water should not exceed 0.007 mg/L.
Related chemicals
Oxamyl (CAS 23135-22-0) belongs to the carbamate class of chemicals. There are many pesticides in this class including aldicarb, methomyl, carbaryl and methiocarb (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, oxamyl 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 effects on foetal bodyweight following short-term exposure.
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: Oxamyl is an insecticide for the control of weevil borers and nematodes in agricultural crops.
There is at least one registered product containing oxamyl in Australia. Oxamyl products are intended for professional use and are available as a liquid concentrate formulation applied by stem injection and hand spray to banana crops, and by irrigation to tomato and capsicum crops. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to oxamyl and its metabolites is residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of oxamyl 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 on occurrence of oxamyl in Australian waters could be found. The United States Environmental Protection Agency estimates environmental concentration of 0.001 mg/L in surface waters and 0.004 mg/L in groundwater in the USA (USEPA 2007).
Treatment of drinking water
No specific data on the treatment of oxamyl in drinking water have been identified.
Measurement
Oxamyl can be measured by routine high-performance liquid chromatography–mass spectrometry analysis, with a limit of reporting of 0.001 mg/L (Queensland Health 2007).
History of the health values
The current acceptable daily intake (ADI) for oxamyl 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 developmental study in rats. The NOEL is based on reduced foetal weights. The ADI incorporates a safety factor of 100 and was established in 1993.
The previous ADI for oxamyl was 0.03 mg/kg bw/day, based on NOELs of 2.5 mg/kg bw/day from long-term dietary studies in rats and dogs. The ADI was amended in 1993 following consideration of the developmental study in rats that demonstrated a lower overall NOEL.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Oxamyl is readily and extensively absorbed in rats. It is not extensively metabolised, and is excreted in the urine almost completely within 168 hours.
Acute effects: Oxamyl has high acute oral toxicity and low dermal toxicity. It is not a skin sensitiser in guinea pigs.
Short-term effects: Short-term (21-day) dermal studies in rabbits and short-term (29-day) dietary studies in rats reported decreases in cholinesterase in plasma, brain, and red blood cells, but no clinical signs of nervous system toxicity at 10 mg/kg bw/day.
Three-month dietary studies in rats and dogs reported decreased bodyweight gain at 15 mg/kg bw/day (rats), and increased serum alkaline phosphatase without associated organ histopathology (dogs), at doses of 15 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies in mice, rats and dogs reported decreased bodyweight gains (all species), hyperactivity and decreased plasma cholinesterase (rats and dogs), and tremors, decreased red blood cell counts, increased absolute brain weights, and inhibition of brain cholinesterase activity (dogs) at 1.3 mg/kg bw/day and above. The lowest overall NOEL was 0.9 mg/kg bw/day (dogs). No other effects were seen in rats and mice.
Carcinogenicity: Based on long-term studies in mice, rats and dogs, there is no evidence of carcinogenicity for oxamyl.
Genotoxicity: Oxamyl is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: In reproduction studies in rats, there was no evidence of effects on reproductive parameters. Developmental studies in rats reported reduced foetal bodyweight at 0.5 mg/kg bw/day and above, and maternotoxicity at 0.8 mg/kg bw/day. The NOEL was 0.2 mg/kg bw/day and is the basis for the current ADI.
Poisons Schedule: Oxamyl is included in Schedule 7 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 oxamyl was determined as follows:
where:
0.2 mg/kg bw/day is the NOEL based on a developmental study in rats using gavage administration.
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 oxamyl and it is excluded from the list of agricultural chemicals guideline value derivation because it is “unlikely to occur in drinking water” (WHO 2006).
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.
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.
USEPA (United States Environmental Protection Agency) (2007). Interim Reregistration Eligibility Decision. Oxamyl – List A, case 0253. USEPA.
WHO (World Health Organization) (2006). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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