Bentazone
(endorsed 2011)
Guideline
Based on human health concerns, bentazone in drinking water should not exceed 0.4 mg/L.
Related chemicals
Bentazone (CAS 25057-89-0) belongs to the benzimidazole class of chemicals. Other pesticides in this class include benomyl, carbendazim and dicamba (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, bentazone would not be a health concern unless the concentration exceeded 0.4 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: Bentazone is a herbicide for the control of broad-leaf weeds in home garden lawns, turf and agricultural crops.
There are registered products containing bentazone or its sodium salt in Australia. These products are intended for professional and home garden use and are available as concentrated solutions to be applied using ground, aerial or hand-held spray methods. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to bentazone are the use of home garden products, and residues in food. Residue levels in food produced according to good agricultural practice are generally low.
Agricultural use of bentazone 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 values for concentrations of bentazone in Australian waters were found. Bentazone has been used for a considerable period of time and has been detected in surface waters overseas at levels of 0.1 to 6 µg/L (WHO/SDE/WSH 2004).
Treatment of drinking water
Bentazone has been shown to be completely removed by ozonation (Bozkaya-Schrotter et al. 2008). Moderate removal can be achieved using powdered activated carbon adsorption. Advanced oxidation using ultraviolet irradiation and peroxide has been demonstrated to achieve a moderate level of bentazone removal (Kruithof et al. 2002).
Measurement
Measurement of bentazone can readily be achieved to detection limits of 0.05 µg/L using dichloromethane extraction and gas chromatography with electron capture detection (FAO/WHO, 1991). Enhancement of sensitivity for analysis of bentazone in water can be achieved by use of solid phase extraction and gas-chromatography–mass spectrometry, achieving a detection limit of 0.02 µg/L (Thortensen et al. 2000).
History of the health values
The current acceptable daily intake (ADI) for bentazone is 0.1 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 10 mg/kg bw/day. This NOEL is based on decreased bodyweight and significant changes in organ weights observed in a 2-year rat study. The ADI incorporates a safety factor of 100 and was established in 1988.
The previous health value was 0.03 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: Bentazone is readily and extensively absorbed via the gastrointestinal tract. It is not extensively metabolised, and is rapidly excreted in the urine, almost completely within 24 hours.
Acute effects: Bentazone has low acute oral toxicity and moderate acute dermal toxicity.
Short-term effects: Three-month dietary studies in rats and dogs reported clinical signs of neurotoxicity, as well as changes in biochemical and haematological parameters and organ weight changes at 120 mg/kg bw/day.
Long-term effects: Long-term dietary studies in mice and rats reported decreased food consumption and bodyweight gain as well as significant changes in relative organ weights at 45.7 mg/kg bw/day.
Carcinogenicity: Based on long-term studies in mice and rats, there is no evidence of carcinogenicity for bentazone.
Genotoxicity: Based on in vitro and in vivo short-term studies, bentazone is not considered to be genotoxic.
Reproductive and developmental effects: A 3-generation reproduction study in rats and a developmental study in rabbits did not produce any evidence of effects on reproductive parameters or on foetal development.
Poisons Schedule: Bentazone 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 0.4 mg/L for bentazone was determined as follows:
where:
10 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 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 from animal studies. The safety factor of 100 incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation.
The World Health Organization has established a health-based guideline value of 0.3 mg/L for bentazone in 1998 (WHO 2004).
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 Technology: Water Supply, 8(2):223-230.
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.
FAO/WHO (World Health Organization/Food and Agriculture Organization) (1991). Pesticide residues in food – 1991 evaluations. Part I – Residues. Rome, Food and Agriculture Organization of the United Nations, Joint FAO/WHO Meeting on Pesticide Residues (FAO Plant Production and Protection Paper 113/1).
Kruithof J, Kamp P, Belosevic M (2002). UV/H2O2 treatment: the ultimate solution for pesticide control and disinfection. Water Science Technology: Water Supply, 2(1):113-122.
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.
Thorstensen CW, Lode O, Christiansen AL (2000). Development of a solid-phase extraction method for phenoxy acids and bentazone in water and comparison to a liquid−liquid extraction method. Journal of Agricultural and Food Chemistry, 48(12):5829-5833.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
WHO/SDE/WSH (2004). Bentazone in Drinking Water. Background Document for Development of WHO Guidelines for Drinking Water Quality. World Health Organization, Geneva, WHO/SDE/WSH/03.04/77.
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