- A pesticide used in agriculture, forestry, and industrial sites
- Associated cancer: Non-Hodgkin lymphoma (inadequate evidence)
- Most important route of exposure: Skin contact, diet
- Uses: Kills annual and perennial weeds, weedy trees and brush, and aquatic weeds
- Occupational exposures: Handling 2,4-D leads to greatest exposures, but secondary exposures can occur through drift and contact with residues
- Environmental exposures: Via residues in food products, pesticide drift, or direct contact with dust
- Fast fact: The mutagenic effects of Agent Orange were originally attributed to 2,4-D, but have since been credited to TCDD, a contaminant of Agent Orange.
2,4-dichlorophenoxyacetic acid (2,4-D) is a colourless or white crystalline powder. It is used as an herbicide, defoliant, and regulator of plant growth. As an herbicide, 2,4-D controls broadleaf weeds and is used in a variety of settings. 2,4-D is often formulated with other herbicides, including dicamba, mecoprop, mecoprop-p, MCPA, and clopyralid.
2,4-D is an acid and is sold commercially in the form of a salt, amine, or ester. These chemical forms have slightly different properties and consequently behave differently in the environment. The ester form is the most commonly used form in Canada. Commercial names for products containing 2,4-D include Weedex®, Tektamer®, and Killex®. Many other synonyms and product names exist; see the Hazardous Substances Data Bank (HSBD) for more information.
Many concerns exist about the carcinogenicity of 2,4-D due to the mutagenic and teratogenic effects of Agent Orange, an herbicide used during the Vietnam War that contains 2,4-D. These effects have since been attributed to the presence of the contaminant 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). In its recent assessment of carcinogenicity, the International Agency for Research on Cancer (IARC) classified 2,4-D as Group 2B, possibly carcinogenic to humans. There was inadequate evidence of carcinogenicity in humans for non-Hodgkin lymphoma in the meta-analysis of 11 studies. There was limited evidence that 2,4-D can cause cancer in laboratory animals. Lastly, there was strong evidence of 2,4-D’s ability to induce oxidative stress, and moderate evidence of its ability to suppress the immune system.
Other health effects resulting from acute exposures to 2,4-D may include headaches, aggression, diarrhea, kidney failure, skeletal muscle damage, and skin irritation.
Regulations and Guidelines
Occupational Exposure Limits (OEL)
|Canadian Jurisdictions||OEL (mg/m3)||Notes|
|Canada Labour Code||10||[TWA, inhalable]|
|MB, NL, NS, PE||10||[TWA; inhalable]|
|NU, NT, SK, YT||10
|ON||10||[TWA; i; skin]|
|Other Jurisdiction||OEL (mg/m3)||Notes|
|ACGIH 2018 TLV ||10||[TWA; inhalable]|
i = inhalable fraction
skin = substances that contribute significantly to the overall exposure by the skin route
TWA = time weighted average (8 hours)
stel = short term exposure limit (15 min. maximum)
ACGIH = American Conference of Governmental Industrial Hygienists
TLV = threshold limit value
Canadian Environmental Guidelines
|Health Canada’s Maximum Residue Limits for Foods||Food type:
Cranberries: 0.5 ppm
Citrus fruits: 2 ppm
Asparagus: 5 ppm
Potatoes: 0.4 ppm
Other berries, fruits and vegetables: 0.01 – 0.05 ppm
Kidney (goats, horses, sheep, cattle): 3 ppm
All other meats and animal fat: 0.05-0.3 ppm
Milk: 0.03 ppm
Eggs: 0.01 ppm
|Canadian and Ontario Drinking Water Guidelines||100 µg/L (MAC)||2017
|Quebec’s Regulation Respecting the Quality of Drinking Water||70 µg/L (MAC)||2015|
|Water Quality Guidelines for AB, MB, and SK||4 µg/L||2015[30,31,32]|
|BC’s Contaminated Sites Regulation, BC Reg 375/96||Sets soil standards for the protection of human health:
Agricultural and low density residential sites: 150 μg/g
Urban park and high density residential sites: 300 μg/g
Commercial and industrial sites: 2,500 μg/gDrinking water: 100 μg/L
|WHO Drinking Water Guideline||0.03 mg/L (applies to free acid)||2011|
|Agreement Respecting the Great Lakes Basin Ecosystem||Listed as “Hazardous polluting substance” but no guidelines developed||1987|
|Health Canada’s Domestic Substances List||Listed as a high priority substance with lowest potential for exposure, but no guidelines developed||2006|
ppm = parts per million
MAC = maximum allowable concentration
Canadian Legal Status
|Federal||Multiple titles||Not included|
|AB||Environmental Code of Practice for Pesticides under the Environmental Protection and Enhancement Act, RSA 2000, cE-12||Restricts 2,4-D application to specific methods, target weeds, distance from bodies of water, amount of area treated, and a maximum application rate of 1.4 kg active ingredients (ai) per hectare|
|BC||Contaminated Sites Regulation, BC Reg 375/96, Schedule 6||Sets a limit for 2,4-D concentrations in drinking water of 0.1 mg/L|
|MB||Non-Essential Pesticide Use Regulation, Man Reg 285/2014||Prohibits domestic/cosmetic use of 2,4-D|
|NB||Pesticides Control Act, RSNB 2011, c 203 (replaced: Pesticides Control Act, RSNB 1973, c P-8)||Prohibits domestic/cosmetic use of 2,4-D|
|NL||Pesticides Control Regulations, 2012||Prohibits domestic/cosmetic use of 2,4-D except for on golf courses, forestry activities, and agricultural activities; the minister has the authority to allow a 2,4-D pesticide to be applied to sports turf or other highly managed turf areas|
|NS||List of Allowable Pesticides Regulations, NS Reg 181/2010||Prohibits domestic/cosmetic use of 2,4-D|
|NT, NU, SK, YK||Multiple titles||Not included|
Pesticides Act Ontario Regulation 63/09 General
Pesticides Act, RSO 1990, c P. 11
A permit is required for the aerial application of a Class 3 pesticide that contains 2,4-D
Prohibits domestic/cosmetic use of 2,4-D
|PE||Pesticides Control Act, RSPEI 1988, c P-4
General Regulations, PEI Reg EC761/05
|Prohibits domestic/cosmetic use and sale of 2,4-D except for commercial golf courses under set criteria|
|QC||Pesticides Management Code, CQLR c P-9.3, r 1||Prohibits cosmetic/domestic use of 2,4-D in a number of different settings not including golf courses, nurseries/seed orchards, and lawns used by children greater than 14 years of age, or lawns that are fenced in or equipped with a watering system|
Several Provincial, Territorial, and Municipal governments have passed laws to reduce risk to human health and the environment from pesticide products, including 2,4-D. These laws may include a restriction on sales, production, or trade.[42,43] Although seven provinces and one territory have implemented some form of cosmetic pesticide policy (QC, 2003; NB, 2009; ON, 2009; AB, 2010; PEI, 2010; NS, 2010; NL, 2012; YK 1994), only the Ontario and Nova Scotia legislation is considered strong enough to significantly reduce cosmetic pesticide exposure. Ontario’s Cosmetic Pesticide Ban Act, the most comprehensive restrictions on lawn and garden pesticides in North America, prohibits the use of over 250 pesticide products and over 95 pesticide ingredients, including 2,4-D, for cosmetic use.
2,4-D was developed and introduced in 1946 as the first successful selective herbicide able to control weeds without damaging the crop. It is a systemic herbicide used to control annual and perennial broad-leaved weeds, weedy trees and brush, and aquatic weeds after they emerge. 2,4-D is essential to managing weeds that are resistant to other pesticides.
In Canada, 2,4-D is the fourth most widely used pesticide, the most commonly used pesticide in the non-agricultural sector, and one of the top ten most commonly used pesticides in the agricultural sector. It is used on fine turf, aquaculture (oyster farms), aquatic non-food sites, forests and woodlots (for conifer release and forest site preparation), terrestrial feed and feed crops, and industrial non-food sites (non-cropland). The use of 2,4-D in aquatic and domestic settings has been restricted.
Examples of 2,4-D use in Canada include:
- Agriculture: to control weed growth in croplands – including sorghum, millet, strawberries, raspberries, barley, rye, wheat, and corn, as well as in pastures, fallow land, and hay lands
- Forestry: to preserve trails, manage wildlife habitats, clear campgrounds, control weeds near outbuildings, treat stumps and inject trunks of invasive species to discourage growth, and to selectively control brush in conifer forests
- Industrial/Commercial: to control weed growth in drainage ditches, roadsides, rights-of-way, power lines, railways, hydro installations, pipelines and highways, highway interchanges, airports, industrial parks, wasteland, vacant lots, fencerows and woody growths in all these areas, golf courses, zoos, botanical gardens, athletic playing fields, schools, and cemeteries
- Residential: to eradicate weeds, including dandelion, clover, chickweed and plantain, in or around residences
There are 78 products containing 2,4-D as an active ingredient registered with the Canadian Pest Management Regulatory Agency (PMRA), of which 23 are registered for domestic use.
Canadian Production and Trade
There is no domestic production of 2,4-D in Canada. Instead, parent companies in foreign countries sell active ingredients or refined products to Canadian distributors to refine and/or sell at the retail level. Import data specific to 2,4-D is not available in TradeMap after 2006 due to a change in coding systems.
In terms of sales, 2,4-D is on the list of top 10 active ingredients sold in Canada from 2007 to 2013, with greater than one million kilograms of active ingredients sold in the five years combined. Sales vary greatly across provinces. In Alberta, there was a decrease in commercial and domestic sales, with an overall reduction of 32.7% from 2008 to 2013 (from 680 tonnes ai to 570 tonnes ai). BC saw a 44% increase in sales from 2003 to 2010 (from 20 tonnes ai to 28 tonnes ai). In 2008, Ontario used 93 tonnes ai of 2,4-D esters and amines in the agricultural sector alone.
Environmental Exposures Overview
The general population is exposed to 2,4-D by ingesting residues in food products, inhaling as a result of volatilization and drift from application by spraying, and directly contacting dust.[56,57,58]
The spouses and children of pesticide applicators are more likely to be exposed (termed para-occupational exposure) compared to the general population. This is because 2,4-D may be brought into homes on the bottom of shoes, increasing potential for exposure especially in young children through dermal means and hand to mouth transfer. This is an important exposure route for young children because they spend the majority of their time indoors, and because 2,4-D persists longer indoors than outdoors. In children younger than 3 years of age, non-dietary exposure to 2,4-D accounted for 15% of total exposure.
One study that examined herbicide exposure for families on Ontario farms found that 2,4-D residues were detected on surfaces in farm homes even though 2,4-D was not being used at the time. This suggests that 2,4-D may be tracked into homes from neighbouring farms, or from previous seasons. When detected by urine analysis, para-occupational exposures in these individuals were 1/3 of the acceptable daily intake used by Canada.
Exposure to 2,4-D through diet and water consumption are considered low. When detected, residues of 2,4-D in surface water, groundwater, and treated drinking water were generally low. On Alberta farms, less than 1% of well water samples tested positive for 2,4-D. Dietary exposures are highest in children aged 1-2 years.
The commercial form of 2,4-D and its derivatives are classified as non-persistent to slightly persistent in soil and water. In terrestrial and aquatic environments, 2,4-D has a half-life of less than two weeks; however, in anaerobic environments, 2,4-D is more persistent with half-lives ranging up to several years, depending on the chemical form. 2,4-D is highly mobile and is known to leach and run-off from soils in treated areas. 2,4-D acid and amine forms have low vapour pressure, indicating that they are not volatile. However, the esters, the most commonly used form in Canada, have higher vapour pressures and do become volatile in small amounts. Bioaccumulation of 2,4-D acid and amines is unlikely to occur, while bioaccumulation of the ester forms is more likely.
In the Canadian prairies, 2,4-D is the most frequently detected herbicide in rainfall; it is present in up to 93% of samples collected. 2,4-D may enter the atmosphere when it volatilizes during and after spray applications, when drops of 2,4-D are transported by wind currents after spraying, and when 2,4-D adheres to dust and is incorporated in clouds during the cloud forming process.
A summary of environmental concentration data is available here [PDF].
Occupational Exposures Overview
In occupational settings, 2,4-D can be absorbed via inhalation, oral, and dermal routes. Skin absorption, however, is the dominant source of occupational exposure, accounting for more than 90% of the total amount entering the body.
Exposure to 2,4-D among workers is highly variable depending whether they have an opportunity for direct exposure. Those who produce, handle, or apply 2,4-D tend to have greater direct exposures than other workers, which include farmers, foresters, and municipal, public utilities, parks, and garden workers. Those who work on a farm but are not responsible for applying 2,4-D can be exposed via secondary exposure to treated fields, farm machinery, and the drift of herbicide during application, as well as subsequent contact with residues on farm and home surfaces.
CAREX Canada has not prioritized 2,4-D 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.
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