Asulam
(endorsed 2011)
Guideline
Based on human health concerns, asulam in drinking water should not exceed 0.07 mg/L.
Related chemicals
Asulam (CAS 3337-71-1) belongs to the carbamate class of chemicals. Other pesticides in this class include 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, asulam would not be a health concern unless the concentration exceeded 0.07 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
Users: Asulam (methyl sulfanilylcarbamate) is a selective, post-emergent systemic herbicide. It is used to control weeds in crops and pastures.
There are registered products containing asulam in Australia. These products are intended for professional use and all are aqueous concentrate liquids. Application methods include boom spray, aircraft and knapsack. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to asulam is residues in food. Residue levels in crops produced according to good agricultural practice are generally low.
Agricultural use of asulam 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
Although asulam is considered to be amongst the most significant herbicides in use (Radcliffe 2002), it is not widely tested in drinking water. Where it has been tested, it has not generally been detected above guideline values.
Treatment of drinking water
Asulam is a highly water soluble compound and therefore the effectiveness of its removal by activated carbon processes is limited (Matsui et al. 2003).
Partial removal of asulam may be achieved by ozonation (Abe and Tanaka 1996). However, advanced oxidation techniques have been shown to remove asulam much more effectively than ozone treatment.
Measurement
Asulam may be detected in drinking waters by liquid chromatography–tandem mass spectrometry, with a practical limit of detection of 0.001 mg/L (1µg/L) (Honing 2000).
History of the health values
The current acceptable daily intake (ADI) for asulam is 0.02 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 40 mg/kg bw/day from a 2-year rat study. The NOEL is based on effects on the thyroid and adrenal medulla. The ADI incorporates a safety factor of 2000 and was established in 1985.
The previous health value was 0.05 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: There is no information available on the absorption or metabolism of asulam.
Acute effects: Asulam has a low oral and dermal toxicity. Its skin sensitisation potential has not been determined, although it is structurally similarity to sulfonamide, which is a sensitiser. There was no evidence of neurotoxic symptoms normally associated with carbamates.
Short-term effects: A 6-month dietary study in dogs reported haematological changes at dose levels above 60 mg/kg bw/day and thyroid hypertrophy at 1500 mg/kg bw/day.
Long-term effects: Long-term studies were conducted in mice, rats and dogs. In all species, effects were noted on haematological parameters and on the thyroid gland. Thryoid hypertrophy was reported in mice at 180 mg/kg bw/day and reductions in white blood cells in dogs at 60 mg/kg bw/day. In rats, there were effects on the adrenals in both sexes and on the thyroid of males. The NOEL in the rat was 40 mg/kg/day, which was used as the basis for the ADI.
Carcinogenicity: Long-term studies in rats indicated an increased incidence of phaeochromocytomas in the adrenal medulla at the highest dose level only. This was not considered relevant at the dose levels to which humans are exposed.
Genotoxicity: Asulam is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: Reproduction studies in rats and developmental toxicity studies in rats and rabbits did not produce any evidence of effects on reproductive parameters or on foetal development.
Poisons Schedule: Asulam is considered not to require control by scheduling due to its low toxicity and is therefore included in Appendix B 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 0.07 mg/L for asulam was determined as follows:
where:
40 mg/kg bodyweight/day is the NOEL based on a long-term (2-year) 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.
2000 is the safety factor applied to the NOEL from the long-term study in rats. It incorporates a safety factor of 10 for interspecies extrapolation, 10 for intraspecies variation, and an additional 20 for the failure of some studies to demonstrate NOELs.
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.
Abe K, Tanaka K (1996). Degradation of phenol, asulam and lignin in aqueous solution by ozonation. Toxicological and Environmental Chemistry, 54(1):187-193.
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.
Honing M (2000). Carbamate and carbamoyloxime insecticides: single-class, multiresidue analysis of. In: Encyclopedia of Analytical Chemistry, John Wiley & Sons.
Matsui Y, Fukuda Y, Inoue T, Matsushita T (2003). Effect of natural organic matter on powdered activated carbon adsorption of trace contaminants: characteristics and mechanism of competitive adsorption. Water Research, 37:4413-4424.
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.
Radcliffe JC (2002). Pesticide use in Australia: a review undertaken by the Australian Academy of Technological Sciences and Engineering. Australian Academy of Technological Sciences and Engineering, Victoria, Australia.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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