PESTICIDES – POSSIBLE CARCINOGEN (IARC 2B)
- A pesticide used in agricultural, forest, and industrial sites and on fine turf and lawns
- Associated cancers: Non-Hodgkin lymphoma, soft-tissue sarcoma (limited evidence)
- Most important route of exposure: Inhalation, skin contact
- Primary use or primary source: Weed control in agriculture (on cereals such as barley and oats, canary seeds, legumes and grasses, asparagus, and corn)
- Occupational exposures: Via manufacturing, applying, and disposing of MCPA
- Environmental exposures: Via contaminated drinking water, air and food; MCPA has been detected in Canadian lakes, rivers, and drinking water
- Fast fact: MCPA is often mixed with other herbicides (such as 2,4-D or MCPB) to increase its effectiveness.
2-Methyl-4-chlorophenoxyacetic acid (MCPA) is a chlorophenoxy herbicide. The parent compound, MCPA-acid, is a colourless and crystalline solid. It can also appear as white to light brown solid flakes, crystalline powder, or dissolved in water. MCPA can be formulated into a number of esters, salts, and amine derivatives which are primarily sold as liquid herbicide. There are 90 products registered with the Canadian Pest Management Regulatory Agency (PMRA) that list MCPA as an active ingredient. Of these, none are registered for domestic use. Trade names that MCPA is sold under include Buctril® and Herbatox®.
Chlorophenoxy herbicides, which include MCPA, have been classified by the International Agency for Research on Cancer (IARC) as Group 2B, possibly carcinogenic to humans. This classification is based on limited evidence of carcinogenicity in humans and insufficient evidence in experimental animals. While the epidemiological studies reviewed by IARC suggested associations between exposure to the chlorophenoxy herbicides and non-Hodgkin lymphoma (NHL), as well as soft-tissue sarcoma, the studies had several limitations and results were inconsistent. MCPA has not been evaluated by IARC in nearly 20 years. More recent studies and reviews show that MCPA (or chlorophenoxy herbicides) may be associated with increased risk of NHL and soft-tissue sarcoma, but the association remains unclear. Toxicological studies in rodents still do not support MCPA’s carcinogenicity, and regulatory agencies consider MCPA not likely to be carcinogenic.[6,7,8,9]
Other health effects of high, acute exposure to MCPA include nervous system problems and liver and kidney damage. Paternal exposure to phenoxy herbicides, including MCPA, before conception may also be associated with an increased risk of early spontaneous abortion.
Regulations and Guidelines
Canadian environmental guidelines and standards*
|Canadian Drinking Water Guidelines||100 µg/L||2010|
|Saskatchewan’s Drinking Water Standards||100 µg/L||2020|
|Quebec’s Drinking Water Standards||30 µg/L||2012|
|Maximum Residue Limits||Dry field peas, edible podded peas, succulent shelled peas: 0.1 ppm;
Animal meat and fat products: 0.05 ppm;
Wheat bran: 0.04 ppm;
Various cereals (barley, oats, rye): 0.03 ppm;
Milk: 0.01 ppm
|BC’s Contaminated Sites Regulation, BC Reg 375/96||Sets soil standards for the protection of human health:
Agricultural and low density residential sites: 8 μg/g
Urban park and high density residential sites: 15 μg/g
Commercial and industrial sites: 100 μg/g
Drinking water standards: 100 μg/L
*Standards are legislated and legally enforceable, while guidelines (including Ontario ambient air quality criteria) describe concentrations of contaminants in the environment (e.g. air, water) that are protective against adverse health, environmental, or aesthetic (e.g. odour) effects
µg/L = micrograms per litre
ppm = parts per million
μg/g = micrograms per gram
|Health and Environment Canada||NDSL*||2009|
*The Non-Domestic Substances List is an inventory of substances included in the EPA’s Toxic Substances Control Act (TSCA), but not on Canada’s DSL. The substances are accepted for international use, but requirements for information are less than those on the DSL.
MCPA was not included in other Canadian government guidelines, standards, or chemical listings reviewed.
MCPA is a herbicide used to selectively control broadleaf weeds in agriculture and to act as a defoliant. Its formulations can occur as the free acid or as salts and esters, but all release the acid as the active ingredient.
MCPA is primarily used in agriculture and is often mixed with other chlorophenoxy herbicides (e.g. 2,4-D or MCPP) to increase its effectiveness.[2,34] It is used on a number of different crops, including barley, oats, rye, wheat, flax, canary seeds, legumes and grasses, asparagus, field corn, and sweet corn. MCPA was produced extensively during the 1950s but production and use are now decreasing in many countries.
Canadian Production and Trade
MCPA production ceased in Canada when Uniroyal Chemicals in Edmonton and Dow Chemical in Fort Saskatchewan, Alberta closed their plants in the 1980s. During their operation these companies provided Western Canada, the largest national market, with phenoxy herbicides. Production stopped primarily because of market conditions.
Although Canada engages in international trade of herbicides, MCPA was not listed in TradeMap for trade commerce for Canada.
Environmental Exposures Overview
The general Canadian population may be exposed to MCPA through contaminated drinking water, air, and food. MCPA has been detected in Canadian lakes, rivers, and drinking water sources. It enters bodies of water via aerial or ground spraying, deposition from rain, and soil erosion by wind, runoff, or leaching. Other sources of MCPA are accidental spills, equipment washing operations, and intentional dumping of tank residue. Although more research is needed on MCPA exposure via drinking water, the limited Canadian data available suggests that concentrations are very low.
MCPA is not persistent in water or soil. The speed that MCPA breaks down in the environment depends on sunlight, soil composition, pH, moisture, the presence of organic matter, and the concentration of MCPA. MCPA can be introduced to the atmosphere through application drift, evaporation, sublimation, or erosion of treated soil. MCPA can be redistributed through wind or degraded and returned to the soil by the rain.
Release of MCPA is not reportable to the National Pollutant Release Inventory (NPRI). A search in the Household Products Database in 2010 returned five consumer products containing MCPA, all weed killers.
A summary of environmental concentration data is available here [PDF].
Occupational Exposures Overview
Inhalation and dermal absorption are the most important routes of occupational exposure to MCPA.
Occupational exposure can occur during production, formulation, application, and disposal of MCPA. High level exposures in the workplace can occur as a result of accidents, such as spills. Particular tasks where exposure to MCPA may occur include ground spraying and manual application of herbicides containing MCPA, as well as handling raw materials, intermediates, and finished products during pesticide manufacture. Waste processing is another task where exposure to MCPA may take place.
In a study of Ontario herbicide applicators, the use of personal protective equipment (e.g. goggles, face shield) when handling herbicides was associated with lower MCPA and 2,4-D exposure as measured in urine samples. However, many workers in this study did not follow personal protection recommendations.
CAREX Canada has not prioritized MCPA for exposure estimate development. This is because a lack of exposure data precluded it in the past. However, the team is investigating new sources of data and methods in order to potentially address this exposure in the future.
- BC Ministry of the Environment. Survey of Pesticide Use in BC (1999) (PDF)
- Dreiher J, Kordysh E. “Non-Hodgkin Lymphoma and pesticide exposure: 25 years of research.” Acta Haematologica2006;116(3):153-164.
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