2,4-D Profile
Contents
2,4-D Profile
QUICK SUMMARY
- 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: An estimated 31,000 to 44,000 workers are exposed to 2,4-D in the agricultural sector
- Environmental exposures: Over 2 million people in Canada live in areas with higher potential for 2,4-D exposure
- 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.
General Information
2,4-dichlorophenoxyacetic acid (2,4-D) is a colourless or white crystalline powder.[1] It is used as an herbicide, defoliant, and regulator of plant growth.[2] As an herbicide, 2,4-D controls broadleaf weeds and is used in a variety of settings.[3] 2,4-D is often formulated with other herbicides, including dicamba, mecoprop, mecoprop-p, MCPA, and clopyralid.[4]
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.[5] The ester form is the most commonly used form in Canada.[6] Commercial names for products containing 2,4-D include Weedex®, Tektamer®, and Killex®.[7] Many other synonyms and product names exist; see the Hazardous Substances Data Bank (HSBD) for more information.[5]
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).[8] 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.[9] 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.[9]
Other health effects resulting from acute exposures to 2,4-D may include headaches, aggression, diarrhea, kidney failure, skeletal muscle damage, and skin irritation.[10]
Regulations and Guidelines
Occupational exposure limits (OEL) [11,12,13,14,15,16,17,18,19,20,21,22,23,24,25]
| Canadian Jurisdictions | OEL (mg/m3) | Notes |
|---|---|---|
| Canada Labour Code | 10 | [TWA, inhalable] |
| AB | 10 | [TWA] |
| BC | 10 20 | [TWA; i] [stel; I] |
| NB | 10 | [TWA] |
| MB, NL, NS, PE | 10 | [TWA; inhalable] |
| NU, NT, SK, YT | 10 20 | [TWA] [stel] |
| ON | 10 | [TWA; i; skin] |
| QC | 10 | [TWA] |
| Other Jurisdiction | OEL (mg/m3) | Notes |
| ACGIH 2020 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 and standards*
| Jurisdiction | Limit | Year |
|---|---|---|
| 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 ppmRange: 0.01-0.5 | 2015[26] |
| Drinking Water Guidelines (Canada, MB) and Standards (ON, SK**) | 100 µg/L (MAC) | 1991-2020[27,28,29,30] |
| Quebec’s Regulation Respecting the Quality of Drinking Water | 70 µg/L (MAC) | 2012[31] |
| 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 | 2017[32] |
| WHO Drinking Water Guideline | 0.03 mg/L (applies to free acid) | 2011[33] |
| Health Canada’s Domestic Substances List | Listed as a high priority substance with lowest potential for exposure, but no guidelines developed | 2006[34] |
*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
**IMAC = interim maximum allowable concentration
ppm = parts per million
MAC = maximum allowable concentration
2,4-D was not included in other Canadian government guidelines, standards, or chemical listings reviewed.
Canadian legal status[35]
| Jurisdiction | Legislation | Notes |
|---|---|---|
| Federal | Multiple titles | Not included |
| Provincial/Territorial | ||
| 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 |
| ON | 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.[36,37] 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.[37] 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.[38]
Main Uses
2,4-D was developed and introduced in 1946 as the first successful selective herbicide able to control weeds without damaging the crop.[39] 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.[40]
In Canada, 2,4-D is the fourth most widely used pesticide,[41] the most commonly used pesticide in the non-agricultural sector, and one of the top ten most commonly used pesticides in the agricultural sector.[4] 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).[40] The use of 2,4-D in aquatic and domestic settings has been restricted.[42]
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[38]
- 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[43]
- 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[38]
- Residential: to eradicate weeds, including dandelion, clover, chickweed and plantain, in or around residences[43]
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.[39]
Canadian Production and Trade
There is no domestic production of 2,4-D in Canada.[44] Instead, parent companies in foreign countries sell active ingredients or refined products to Canadian distributors to refine and/or sell at the retail level.[45] Import data specific to 2,4-D is not available in TradeMap after 2006 due to a change in coding systems.[46]
In terms of sales, 2,4-D is on the list of top 10 active ingredients sold in Canada from 2007 to 2019; in 2019, greater than one million kilograms of active ingredients was sold in Canada.[47] Sales vary greatly across provinces. In Alberta, there was an increase in commercial and domestic sales, with an overall increase of 4.3 % from 2013 to 2018 (from 641 tonnes ai to 720tonnes ai).[48] BC saw a 27% decrease in sales from 2010 to 2015 (from 27 tonnes ai to 20 tonnes ai).[49] In 2008, Ontario used 93 tonnes ai of 2,4-D esters and amines in the agricultural sector alone.[50]
Environmental Exposures Overview
The general population is exposed to 2,4-D by ingesting residues in food products or water, inhaling the product during application or drift, and directly contacting dust.[51,52,53]
CAREX Canada estimates that over 2 million people in Canada live in areas where the potential for exposure to 2,4-D is higher than other areas in the country, which amounts to about 6% of the Canadian population. Since people residing near agricultural land may have higher pesticide exposures than those who live in non-agricultural areas due to the geographical proximity to areas with high pesticide usage, these estimates focus on community exposure related to agricultural pesticide use.[54,55] In addition, data availability for other routes of exposure (e.g. diet, domestic application) are limited.
As expected, exposure varies based on agricultural activity and the types of crops grown. Potential exposure to 2,4-D is much higher in areas where cereal crops, potatoes, and fruit are more commonly grown due to the higher application rates for these crops. The prairie provinces (Alberta, Saskatchewan, Manitoba), Prince Edward Island and Southern Quebec all had higher potential for exposure to 2,4-D than other areas. These estimates primarily consider exposure through inhalation, which is a more immediate form of exposure, but pesticides can also seep into ground water and soil and lead to subsequent exposure. The CAREX Canada estimates do not account for dietary ingestion, which is a major route of pesticide exposure, especially for young children.[56]
In addition to those living near agricultural areas, the spouses and children of pesticide applicators are more likely to be exposed (termed para-occupational exposure) compared to the general population.[57] 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.[58] 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.[58] In children younger than 3 years of age, non-dietary exposure to 2,4-D accounted for 15% of total exposure.[59]
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.[60] 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.[61]
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.[62]
CAREX Canada estimates that between 31,000 and 44,000 Canadian workers are exposed to 2,4-D in the agricultural sector. The majority of pesticides sold in Canada are used in agricultural (70% of active ingredients sold, by weight). For this reason, these exposure estimates focus on workers in the agricultural industry. Exposure among these workers occurs during the mixing, loading, and application of 2,4-D, but many more may be exposed during other, farm-related activities through dermal contact with treated crops. Farm types with the largest number of exposed workers are other grain farming, dairy cattle and milk production (where 2,4-D is applied on crops that are grown to feed livestock), and fruit farming.
For more information, see the occupational exposure estimate for 2,4-D.
Workers in industries other than agriculture, including forestry, public utilities, and landscaping, may be at risk of exposure to 2,4-D.[63]
Sources
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