Benomyl
(endorsed 2011)
Guideline
Based on human health concerns, benomyl in drinking water should not exceed 0.09 mg/L.
Related chemicals
Benomyl (CAS 17804-35-2) belongs to the benzimidazole class of carbamate compounds. Other pesticides in this class include carbendazim, dicamba and diflubenzuron (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, benomyl would not be a health concern unless the concentration exceeded 0.09 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: Benomyl is a systemic, broad-spectrum fungicide for use on fruit trees, nuts, vegetables, cereals, ornamentals and turf.
There are no registered products containing benomyl in Australia, as the active was suspended and subsequently withdrawn due to health concerns in December 2006. However, de-registered compounds may still be detected in water.
Exposure sources: The main source of public exposure to benomyl and its metabolites if used in the future would be residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of benomyl in the future 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 reports of benomyl detected in Australian drinking water supplies have been identified.
Treatment of drinking water
No definitive literature regarding the removal of benomyl from drinking water has been identified. Some field trials have been undertaken regarding the removal of benomyl from water using activated carbon and other adsorbents (Massey et al. 1992, Giry et al. 2001). Biodegredation (Matsumura et al. 1991) and ultraviolet irradiation (Grechko et al. 1982) in wastewater have been reported.
Measurement
No standard methods for the analysis of benomyl in drinking water have been identified. However, benomyl can be analysed by high–performance liquid chromatography with detection by ultraviolet absorbance (Marvin et al. 1991). The reported detection limit for this method is 0.009 mg.L⁻¹.
History of the health values
The current acceptable daily intake (ADI) for benomyl is 0.02 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 2.5 mg/kg bw/day from a 2-year dog study. The NOEL is based on an increase in testicular degeneration. The ADI incorporates a safety factor of 100 and was established in 2003.
The acute reference dose (ARfD) of 0.06 mg/kg bw/day for benomyl was established in 2003, based on a NOEL of 6.25mg/kg bw/day from three developmental studies, which showed an increase in micro-/anophthalmia. The ARfD incorporates a safety factor of 100.
The previous health value was 0.1 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Benomyl is rapidly and extensively absorbed via the gastrointestinal tract and distributed widely throughout the body. It is metabolised to carbendazim (70% within 1 hour). Excretion is via the urine and, to lesser extent, faeces, and is essentially complete within 72 hours.
Acute effects: Benomyl has a very low acute oral toxicity; there are no data on acute dermal toxicity. There are reported cases of skin sensitisation in humans.
Short-term effects: In 70/90 day dietary studies in rats and dogs, there was reduced sperm count in rats at the highest dose tested of 20 mg/kg bw/day and increased liver weights at 125 mg/kg bw/day. In dogs, there were increased liver enzymes at 125 mg/kg bw/day.
Long-term effects: Long-term (2-year) dietary studies in mice and rats did not demonstrate any toxicity. In a 2-year study in dogs, there was testicular atrophy at doses of 12.5 mg/kg bw/day and above, and increased levels of liver enzymes in serum were seen at the highest dose tested of 62.5 mg/kg bw/day. The lowest overall NOEL was 2.5 mg/kg bw/day in dogs, which was used as the basis for the ADI.
Carcinogenicity: Based on long-term studies in mice, rats and dogs, there was evidence of carcinogenicity only in the mouse, where liver tumours were observed. These were considered to be species-specific, possibly as a result of liver toxicity. Based on the available data, benomyl was not considered to be a carcinogenic risk to humans.
Reproduction and developmental effects: Reproduction studies in rats and dogs reported decreased sperm production at 45 mg/kg bw/day. Testicular degeneration and atrophy was also reported at doses of 45 mg/kg bw/day (rats) and 12.5 mg/kg bw/day (dogs). Developmental studies in mice and rats (but not rabbits) reported teratogenic effects in the foetuses in the absence of any maternal toxicity at doses of 10 mg/kg bw/day.
Poisons Schedule: Benomyl 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 value of 0.09 mg/L for benomyl was determined as follows:
where:
2.5 mg/kg bw/day is the NOEL based on a long-term (2-year) study in dogs.
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 the safety factor applied to the NOEL derived from the acute human study. The safety factor of 100 incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variations.
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.
Giry G, Ayele J, Gauthier C (2001). Removal of carbendazim from fruit conditioning waters by adsorption on different materials. Environmental Technology, 22(7):803-811.
Grechko AV, Marchenko PV, Shevchenko MA (1982). Removal of pesticides from greenhouse drainage wastewater. Khimiya i Tekhnologiya Vody, 4(1):56-58.
Marvin CH, Brindle ID, Hall CD, Chiba M (1991). Rapid on-line precolumn high-performance liquid chromatographic method for the determination of benomyl, carbendazim and aldicarb species in drinking water. Journal of Chromatography, 555(1-2):147-154.
Massey JH, Lavy TL, Skulman BW (1992). Field and laboratory evaluations of an activated charcoal filtration unit. In: Proceedings of International Workshop on Research in Pesticide Treatment/Disposal/Waste Minimization, Department of Agronomy,University of Arkansas, Fayetteville, AR, USA, pp. 85-94.
Matsumura F, Katayama A (1991). Photochemical and microbial degradation technologies to remove toxic chemicals. In: Pesticide Waste Management: Technology and Regulation. From a symposium sponsored by the Division of Agrochemicals at the Fourth Chemical Congress of North America, New York, New York 1992, pp 201-209.
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.
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