Page 2: Guidelines for Canadian Drinking Water Quality: Guideline Technical Document – 2-Methyl-4-chlorophenoxyacetic Acid (MCPA)
Part I. Overview and Application
1.0 Guideline
The maximum acceptable concentration (MAC) for 2-methyl-4-chlorophenoxyacetic acid (MCPA) in drinking water is 0.1 mg/L (100 µg/L).
2.0 Executive summary
2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a phenoxyacetic acid herbicide, registered in Canada for use on agricultural sites, fine turf and lawns, in forestry and at industrial sites. It is among the top 10 pesticides sold in Canada and is used across the country, most extensively in the Prairie provinces. Herbicide formulations can use various forms of MCPA, including the free acid, salts and esters, but all release the acid as the active ingredient.
This Guideline Technical Document reviews the health risks associated with MCPA in drinking water. It assesses all identified health risks, taking into account available studies and approaches, as well as the limitations of available treatment technology. It considers exposure to MCPA through drinking water only from ingestion, as exposure through inhalation and skin contact is not considered to be significant. From this review, a maximum acceptable concentration (MAC) of 0.1 mg/L (100 µg/L) for MCPA in drinking water is established, based on health effects.
2.1 Health effects
Some studies have been conducted on the impacts of chlorophenoxy herbicides, including MCPA, on human health. However, because the subjects were exposed to several pesticides, as well as to other organic compounds, these studies cannot be used to assess the toxicity of MCPA to humans. The MAC is established based on kidney effects observed in the rat.
Health Canada classifies MCPA as unclassifiable with respect to carcinogenicity in humans, based on inadequate data from human studies and a lack of adequate animal studies. This is consistent with the classification of the International Agency for Research on Cancer.
2.2 Exposure
There are limited data available on human exposure to MCPA. Based on these data, drinking water is not expected to be a significant route of exposure. Low levels of MCPA in sources of drinking water have been found in many Canadian provinces. In specific situations, MCPA can be found in water as a result of spills, deliberate dumping of tank residues or equipment washing operations.
2.3 Analysis and treatment
The establishment of a drinking water guideline must take into consideration the ability to both measure the contaminant and remove it from drinking water supplies. MCPA can be detected at levels well below the MAC of 0.1 mg/L.
MCPA can be effectively treated in municipal-scale treatment facilities to below the MAC through a number of well-documented methods. At the residential scale, no drinking water treatment devices available on the market are currently certified for the removal of MCPA; however, certified devices capable of reducing the concentration of organic compounds may be suitable for MCPA removal.
3.0 Application of the guideline
Note: Specific guidance related to the implementation of drinking water guidelines should be obtained from the appropriate drinking water authority in the affected jurisdiction.
The guideline for MCPA is based on a lifetime exposure to MCPA from drinking water and is protective against health effects from lifetime exposure. Short-term exceedances above the guideline value are unlikely to have an impact on health, unless these exceedances are due to massive contamination or spills. However, in the event that monitoring results show elevated levels on a regular basis, it is suggested that a plan be developed and implemented to address the situation.
MCPA, a phenoxyacetic acid herbicide registered for use in Canada, is not a concern for the majority of Canadians. Although MCPA is used everywhere in Canada, it is used most extensively in the Prairie provinces for agriculture, in the production of cereals, canary seeds, legumes and grasses, asparagus, field corn and sweet corn. Therefore, its application is limited to the growing season. As a result, in these high-use areas, MCPA can be introduced into surface water and possibly groundwater through runoff or as the result of spills, deliberate dumping of tank residues or equipment washing operations. MCPA is not persistent in water or soil because of its biological degradation (under aerobic conditions), an important degradation pathway. However, in oxygen-deprived environments such as groundwater or during periods of cold weather and low light, the degradation of MCPA via biological degradation or photodecomposition is rather limited.
3.1 Monitoring
MCPA is registered in Canada for various uses, with the major one being on agricultural sites, where it is used most extensively in the Prairie provinces during the growing season.
Frequent monitoring of treated surface water is recommended in areas of high use such as the Prairies and other agricultural areas during periods of peak use, which occur from May to early fall, and for treatment plants located downstream of these areas. This frequency will provide a complete picture of runoff contamination, especially after rainfall has occurred. Monitoring of groundwater from areas of high use is also recommended for MCPA, but at a reduced frequency.
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