MCPA
(endorsed 2011)
Guideline
Based on human health concerns, MCPA in drinking water should not exceed 0.04 mg/L.
Related chemicals
2-methyl-4-chlorophenoxyacetic acid (MCPA)(CAS 94-74-6) belongs to the phenoxycarboxylic acid class of chemicals. Other pesticides in this class include 2,4-D, 2,4-DB, dichlorprop, dichlorprop-P, MCPB and mecoprop (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, MCPA would not be a health concern unless the concentration exceeded 0.04 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: MCPA is a herbicide for the control of various broad-leaf weeds in crops, pastures and turf.
There are many registered products that contain MCPA or its salt/variants in Australia. The products are intended for professional and home garden use and are generally available as emulsifiable concentrates, aqueous concentrates and liquids to be applied using ground boom, aerial or hand-held sprays. Data on currently registered products are available from the Australian Pesticides and Veterinary Medicines Authority.
Exposure sources: The main sources of public exposure to MCPA 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 MCPA 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 occurrence data for MCPA in Australian waters could be found, however it has occasionally been measured in some Australian drinking-water supplies at concentrations generally less than 1 mg/L. In the USA, MCPA was detected up to 0.54 µg/L in surface waters and up to 5.5 µg/L in groundwater (WHO 2003).
Treatment of drinking water
No data on drinking water treatment removal efficacy could be found for MCPA, although activated carbon is expected to be quite effective, based on its structure.
Measurement
MCPA can be measured by routine gas chromatography–mass spectrometry analysis, with a limit of reporting of 0.01 µg/L (Queensland Health 2007).
History of the health values
The current acceptable daily intake (ADI) for MCPA is 0.01 mg per kg of bodyweight (mg/kg bw), based on a no-observed-effect level (NOEL) of 1.1 mg/kg bw/day from a 2-year dietary rat study. The NOEL is based on evidence of mild liver effects (changes in clinical chemical parameters). The ADI incorporates a safety factor of 100, and was established in 1994.
A health value has not been previously established by NHMRC.
Health considerations
Metabolism: MCPA is readily absorbed via the gastrointestinal tract. It is not extensively metabolised, and is rapidly excreted, mainly unchanged, in the urine.
Acute effects: MCPA has low acute oral and dermal toxicity. It is not a skin sensitiser.
Short-term effects: In 13-week dietary studies in rats and dogs, there was evidence of kidney and liver damage. In rats, increased kidney weights were reported at 7.5 mg/kg bw/day and increased creatinine and decreased calcium at 22.5 mg/kg bw/day. In dogs, increased serum glutamic pyruvic transaminase, blood urea nitrogen and creatinine levels were reported at 3 mg/kg bw/day. Decreased bodyweight gain and bile duct proliferation were reported at 12 mg/kg bw/day, and gross pathological changes in the liver and microscopic changes in both the liver and kidney at 48 mg/kg bw/day.
Long-term effects: Long-term dietary studies were conducted in mice and rats. A 2-year mouse study reported pathological changes in the kidney at 71.4 mg/kg bw/day. A 2-year rat study reported an increase in serum glutamic pyruvic transaminase levels at 4 mg/kg bw/day. At 16 mg/kg bw/day there was a slight decrease in bodyweight gain, haemosiderosis in the spleen, and an increase in absolute kidney weight in males, accompanied by evidence of chronic nephropathy. The NOEL of 1.1 mg/kg bw/day in the rat study is the basis for the current ADI.
Carcinogenicity: Based on 2-year studies in mice and rats, there is no evidence of carcinogenicity for MCPA.
Genotoxicity: MCPA is not considered to be genotoxic, based on in vitro and in vivo short-term studies.
Reproductive and developmental effects: A 2-generation reproduction study in rats reported reduced pup bodyweight gain at 15 mg/kg bw/day and above. Developmental studies in rats and rabbits reported decreased bodyweight gain and increased post-implantation loss at 75 mg/kg bw/day. There were no effects at lower dose levels on reproductive parameters or foetal development.
Poisons Schedule: MCPA is included in Schedule 5 and 6 of the Standard for the Uniform Scheduling of Medicines and Poisons No.1, 2010 (the Poisons Standard)(DoHA 2010), depending on its concentration and use. Current versions of the Poisons Standard should be consulted for further information.
Derivation of the health-based guideline
The health-based guideline of 0.04 mg/L for MCPA was determined as follows:
where:
1.1 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.
The World Health Organization has a health-based guideline value of 0.002 mg/L for MCPA (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.
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.
Queensland Health (2007). Organochlorine, organophosphorous and synthetic pyrethroid pesticide, urea and triazine herbicides and PCBs in water. QHFSS SOP 16315.
Tomlin CD (ed) (2006). The Pesticide Manual: a world compendium, 14th edition, British Crop Production Council, UK.
WHO (World Health Organization) (2003). MCPA in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality. WHO.
WHO (World Health Organization) (2004). Guidelines for Drinking-water Quality. 3rd Edition, WHO, Geneva, Switzerland.
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