2,2-DPA
(endorsed 2011)
Guideline
Based on human health concerns, 2,2-DPA in drinking water should not exceed 0.5 mg/L.
Related chemicals
2,2-DPA (2,2-dichloropropionic acid)(CAS 127-20-8) belongs to the class of halogenated aliphatic chemicals. Another pesticide in this class is iodomethane (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, 2,2-DPA would not be a health concern unless the concentration exceeded 0.5 mg/L. Excursions above this level would need to occur over a significant period to be of 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: 2,2-DPA is a herbicide for the control of grasses and broad-leaf weeds in industrial sites, footpaths, domestic and public areas.
There are registered products that contain 2,2-DPA as its sodium salt in Australia. These products are intended for professional and home garden use. All are soluble powder formulations intended to be diluted and applied by hand spray or backpack spray. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to 2,2-DPA and its metabolites are the use of home garden products, and exposure from treated public places such as footpaths.
Use of 2,2-DPA in public spaces 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 reported occurrences of 2,2-DPA in Australian drinking waters have been identified.
Treatment of drinking water
No information regarding the effective treatment of 2,2-DPA in drinking water has been identified.
Measurement
2,2-DPA can be measured in drinking waters by liquid–liquid microextraction, acidic methanol derivatization, and gas chromatography–mass spectrometry. The reported method detection limit is 0.13 mg/L (Xie 2001).
History of the health values
The current acceptable daily intake (ADI) for 2,2-DPA is 0.2 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 15 mg/kg bw/day from a long-term (2-year dietary) study. The NOEL is based on increased kidney weight in rats. The ADI incorporates a safety factor of 100 and it was established in 1989.
The previous health value was 0.5 mg/L (NHMRC and NRMMC 2004).
Health considerations
Metabolism: 2,2-DPA is rapidly absorbed from the gastrointestinal tract in humans. Peak levels in blood are reached by 2 to 3 hours, and decrease with a half life of 2-3 days. Metabolism is limited, with the majority of the 2,2-DPA excreted unchanged in urine.
Acute effects: 2,2-DPA has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: Three-month dietary studies were conducted in rats and dogs. In rats, kidney weights were increased at doses of 50 mg/kg bw/day, and at higher doses there were effects on the liver. In dogs, there was no evidence of toxicity at doses up to 1000 mg/kg bw/day, however the study was of a poor quality.
Long-term effects: Long-term dietary studies in mice, rats and dogs reported increased kidney weights at 50 mg/kg bw/day and above. The lowest overall NOEL was 15 mg/kg bw/day in the rat study.
Carcinogenicity: Benign adenomas in lacrimal glands were noted in mice at 200 mg/kg bw/day, however, these tumours were not considered relevant to low-dose human exposure.
Reproductive and developmental effects: A 3-generation reproduction study in rats and a developmental study in rabbits did not produce any evidence of reproductive effects, delayed development or teratogenicity.
Genotoxicity: 2,2-DPA is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Poisons Schedule: 2,2-DPA is considered not to require control by scheduling due to its low toxicity and is therefore 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 health-based guideline
The health-based guideline of 0.5 mg/L for 2,2-DPA was determined as follows:
where:
15 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 derived from animal studies. This safety factor incorporates a factor of 10 for interspecies extrapolation and 10 for intraspecies variation. An additional safety factor is unnecessary.
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.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th Edition, British Crop Production Council, UK.
Xie Y (2001). Analyzing haloacetic acids using gas chromatography/mass spectrometry. Water Research, 35(6):1599-1602.
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