Amitrole
(endorsed 2011)
Guideline
Based on human health concerns, amitrole in drinking water should not exceed 0.0009 mg/L.
Related chemicals
Amitrole (CAS 61-82-5) belongs to the triazole class of chemicals. There are no other pesticides in this class (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, amitrole would not be a health concern unless the concentration exceeded 0.0009 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: Amitrole is a herbicide used to kill weeds in public places and home gardens.
There are registered products containing amitrole in Australia. These are for professional and home garden use. Amitrole is used alone or in combination with other herbicides as concentrated solutions or as wettable powders, and these are generally applied as a spray. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main source of public exposure to amitrole is direct exposure following home garden use. Amitrole is not currently registered for use on food crops and the maximum residue limits are set at the level of detection.
Use of amitole in public places and in the home garden 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 waters
Amitrole is a persistent herbicide that can easily pollute ground and surface waters used in drinking water production. No Australian data was found but concentrations in ground and surface water of up to 1.1 μg/L have been reported (Bobeldijk et al. 2001).
Treatment of drinking water
Amitrole has been shown to be effectively removed by ozonation (Bozkaya-Schrotter et al. 2008). Moderate removal can also be achieved using powdered activated carbon adsorption (Lopez-Ramon et al. 2007).
Measurement
Numerous analytical methods have been described for the detection of amitrole. Gas chromatography can achieve a limit of detection of 0.1 μg/L in drinking water (Pachinger et al. 1992). High-performance liquid chromatographic (HPLC) methods are currently the analytical techniques of choice for amitrole and other polar compounds. Different HPLC methods for the determination of amitrole after derivatisation have been described. HPLC with electrochemical detection can achieve limits of detection of 0.1 Arial g/L. Solid-phase extraction followed by HPLC with atmospheric pressure chemical ionisation–tandem mass spectrometry can achieve a limit of detection of 0.025 Arial g/L in drinking water (Bobeldijk et al. 2001).
History of the health values
The current acceptable daily intake (ADI) for amitrole is 0.0003 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 0.025 mg/kg bw/day from a 1-year rat study. The ADI incorporates a safety factor of 100 and was established in 1984.
An acute reference dose has not been established for amitrole.
The previous health value was 0.01 mg/L (NHMRC and NRMMC, 2004).
Health considerations
Metabolism: Amitrole is readily absorbed through the gastrointestinal tract. It undergoes minimal metabolism and is excreted largely unchanged in the urine.
Acute effects: Amitrole has a low acute oral and dermal toxicity. Its potential for skin sensitisation is unknown.
Short-term effects: Short-term oral toxicity studies in rats reported histopathological changes in the thyroid and changes to the uptake of iodine by the thyroid at 20 mg/kg bw/day and above.
Long-term effects: Long-term dietary studies were conducted in mice and rats. In mice, there were effects on thyroid weight and uptake of iodine at 15 mg/kg bw/day. In rats, there was a decrease in thyroid hormone levels, an increased incidence of thyroid hyperplasia and an increase in thyroid tumours at 2.5 mg/kg bw/day. The NOEL in the 1-year rat study was 0.025 mg/kg bw/day, and this is the basis of the ADI.
Carcinogenicity: In long-term studies in rats, amitole caused an increase in thyroid tumours, which is likely to be a consequence of an increased incidence of thyroid hyperplasia.
Genotoxcity: Amitole gave equivocal results in some in vitro studies, but negative results in in vivo studies. Based on the weight of evidence, amitole was not considered genotoxic.
Reproductive and developmental effects: In a reproduction study in rats and development studies in mice and rats, there was no evidence of effects on reproductive parameters or on foetal development.
Poisons Schedule: Amitrole is included in Schedule 5 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 0.0009 mg/L for amitole was determined as follows:
where:
0.025 mg/kg bw/day is the NOEL based on a long-term (1-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 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.
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.
Bozkaya-Schrotter B, Daines C, Lescourret A, Bignon A, Breant P, Schrotter J (2008). Treatment of trace organics in membrane concentrates I: pesticide elimination. Water Science and Technology: Water Supply, 8(2):223-230.
Bobeldijk I, Broess K, Speksnijder P, van Leerdam T (2001). Determination of the herbicide amitrole in water with pre-column derivatisation, liquid chromatography and tandem mass spectrometry. Journal of Chromatography A, 938(1-2):15-22.
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.
Lopez-Ramon MV, Fontecha-Camara MA, Alvarez-Merino MA, Moreno-Castilla C (2007). Removal of diuron and amitrole from water under static and dynamic conditions using activated carbons in form of fibers, cloth, and grains. Water Research, 41(13):2865-70.
Pachinger A, Eisner E, Begutter H, Klus H (1992). A simple method for the determination of amitrole in drinking and ground water. Fresenius’ Journal of Analytical Chemistry, 342:413-415.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
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