Is 2,4-D Safe for my Landscape?

On Friday, May 16, 2008, Health Canada's Pest Management Regulatory Agency (PEMA) released its final reevaluation of 2,4-D, the leading pesticide in use in Canada. It was one of the most comprehensive science reviews in Canadian history, carried out exclusively by Health Canada scientists.

After a thorough reevaluation of the herbicide 2,4-dichlorophenoxy acetic acid (2,4-D), Health Canada's Pest Management Regulatory Agency (PMRA) has decided to allow continued registration for the sale and use in Canada of certain products containing 2,4-D.

Products containing 2,4-D do not pose unacceptable risks to human health or the environment. They also have value for lawn and turf, agriculture, forestry and industrial uses when used according to the label directions proposed in previous consultation documents.

The key objective of the Pest Control Products Act is to prevent unacceptable risks to people and the environment from the use of pest control products. Health or environmental risk is considered acceptable if there is reasonable certainty that no harm to human health, future generations or the environment will result from use or exposure to the product under its conditions or proposed conditions of registration. The act also requires that products have value when used according to the label directions.

What is 2,4-D?
2,4-D is a selective systemic phenoxy herbicide that mimics the plant growth regulator indole-3-acetic acid (also known as auxin). It is registered for the control of broadleaf weeds, weedy trees and brush and aquatic weeds after they emerge. Use is permitted on fine turf, aquaculture (oyster farms), aquatic non-food sites, forests and woodlots (conifer release and forest site preparation), terrestrial feed and feed crops and industrial non-food sites (non-cropland).

When assessing health risks, two key factors are considered: The levels at which no health effects occur and the levels to which people may be exposed. The dose levels used to assess risks are established to protect the most sensitive human population (e. g., children and nursing mothers). Only those uses for which the exposure is well below levels that cause no effects in animal testing are considered acceptable for registration. 2,4-D is unlikely to affect health when used according to the revised label directions.

Reference doses define levels to which an individual can be exposed over a single day (acute) or lifetime (chronic) and expect no adverse health effects. Generally, dietary exposure from food and water is acceptable if it is less than 100% of the acute reference dose or chronic reference dose (acceptable daily intake). An acceptable daily intake is an estimate of the level of daily exposure to a pesticide residue that, over a lifetime, is believed to have no significant harmful effects. Human exposure to 2,4-D was estimated from residues in treated crops and drinking water, including the most highly exposed sub-population (e. g., children 1-6 years old).

Today, 2,4-D is the third most widely used herbicide in Canada based on the amount of active ingredient applied. The use of 2,4-D reduces a portion of the economic losses incurred annually by weeds across Canada. Over the past 40 years, 2,4-D has played an important role in maintaining turf. Without it, the number of broadleaf weed control products presently available to homeowners would be severely limited.

Most of the domestic class products used to control broadleaf weeds on lawns contain 2,4-D; there are few registered alternatives in Canada. 2,4-D also controls a wide variety of broadleaf weeds in non-turf sites. It has long been recognized as being a superior tank mixing partner with other herbicides. These tank mixes control a broader range of weeds compared to products containing only a single active ingredient, resulting in fewer applications, less soil compaction and reduced costs for growers.

Connections between 2,4-D and certain cancers?
A number of epidemiology studies (both independent and industry-funded) from the U. S., New Zealand and Australia report no association between 2,4-D and soft-tissue sarcoma, non-Hodgkin's lymphoma or Hodgkin's lymphoma, and more recent studies have not shown an association between 2,4-D and non-Hodgkin's lymphoma or other cancers. Several major scientific panels have evaluated this body of research and have described the evidence for cancer effect in humans as limited, inconclusive, inconsistent and weak.

The PMRA examined relevant health-related studies during its evaluation of 2,4-D and reviewed the references provided. Study results indicate there is no associated increase in breast cancer incidence when all potential chemical exposures were combined. In fact, an increase in chemical uses was actually associated with a decreased incidence of breast cancer. Also, confounding factors such as smoking, previous residence, drinking, diet and family history were not taken into consideration.

There is no indication of widespread neurological effects in the extensive 2,4-D toxicology database. While certain pesticides, such as specific carbamate and organophosphate insecticides, inhibit acetylcholinesterase (AChE), this is not a typical endpoint of concern associated with herbicides such as 2,4-D.

Renu Ghandi, with Cornell University’s Breast Cancer and Environmental Rick Factors Program states, "There are no reports that indicate a direct link between 2,4-D exposure and cancer in humans." While there is concern with respect to non-Hodgkin's lymphoma, "results from different studies are not consistent. While one half of the studies indicated higher rates of non-Hodgkin's lymphoma among populations exposed to 2,4-D, the other half did not."

Risks to homeowners and their children from contact with treated lawns and turf are not of concern. Products containing 2,4-D do not pose unacceptable risks to human health or the environment. They also have value for lawn and turf, agriculture, forestry and industrial uses when used according to the label directions. Click here for more information.