The contribution of 2,4-D Dichlorophenoxyacetic acid (2,4-D) in helping farmers to feed the world has been revolutionary. In 2004, the Henry Ford Foundation, a non-profit organization dedicated to supporting visionary leaders and organizations on the frontlines of social change, listed 2,4-D as one of the 75 most important innovations of modern times. The combination of its effectiveness in controlling yield-destroying weeds, along with favorable human health and environmental profiles, has made this one of the most trusted and effective tools for modern agriculture.
2,4-D is a member of the phenoxy family of herbicides originally introduced in 1946. It provides broad-spectrum control of many annual, biennial and perennial broadleaf weeds which compete with crops and threaten yields. Since its introduction, it has become an important tool controlling these weeds in key crops ranging from corn and wheat to asparagus and stone fruits.
2,4-D is perhaps the most extensively researched and studied crop protection tool used in agriculture. Today, the product is authorized for use by regulators charged with the protection of public health and our environment in about 70 countries worldwide, including the United States, Canada, the United Kingdom, Australia, New Zealand, Germany, France and Japan. In the last 20 years, 2,4-D has undergone as many as 26 major regulatory and expert scientific panel reviews worldwide, all concluding that 2,4-D does not present an unacceptable risk to human health or the environment when used properly.
In 2012, the EPA upheld past approvals of 2,4-D by rejecting a petition from the Natural Resource Defense Council (NRDC) seeking to revoke registrations.
The following is intended to provide a general overview of the mammalian and environmental toxicology profiles of 2,4-D based on the wealth of reviews and scientific studies which have been conducted.
Based on reviews from regulatory agencies (including extensive reviews conducted by the U.S. EPA and Canada’s Pest Management Regulatory Agency as recently as 2005 and 2008, respectively) and the scientific literature, potential exposure from labeled uses of 2,4-D are thousands of times less than levels that would pose a risk to human health.
Toxicity testing indicates 2,4-D:
- Does not result in genetic damage that might cause cancer.
- Is not an endocrine disruptor; it does not mimic or block hormones which disrupt the body’s normal functions.
- Is not a developmental toxicant; it does not cause adverse effects on a developing child.
- Does not adversely affect reproduction.
- Has only a low to moderate acute toxicity when exposed to the concentrated material.
New study: A qualitative review of the extensive literature since 2001 on 2,4-D and health by CJ Burns and GHM Swaen (2012) has been published. The review concludes that in the context of biomonitoring, the epidemiology data give no convincing or consistent evidence for any chronic effect of 2,4-D in humans.
Research has consistently shown exposures to 2,4-D are low, even for those working directly with 2,4-D. The exposures are well below those identified by regulatory agencies as posing any risk to human health.
New study: A new study on 2,4-D and human exposure has been published, “2,4-D Exposure and risk assessment: Comparison of external dose and biomonitoring based approaches.” Findings from the case study indicate external dose-based assessments result in estimates of exposure and resulting hazard quotients that are consistently several-fold higher than those based on biomonitoring data. The comparisons support a conclusion that exposure assessments conducted as part of the registration process for 2,4-D incorporate sufficiently conservative assumptions.
2,4-D does not persist in the environment. 2,4-D has a favorable environmental profile, and its exposures are expected to be minimal in both terrestrial and aquatic environments. It is rapidly broken down by microbial action in the soil and does not persist, accumulate or leach to groundwater under conditions of proper use.
- In field studies conducted across the U.S. under actual use conditions, 2,4-D:
- Had an average soil half-life of only five days with a range of less than two to about 13 days.
- Although not strongly absorbed by soil, 95 percent or more of the residues were limited to only the top six inches of soil, and the maximum depth any residues were found was only 24 inches.
- In grass and thatch, the average half-lives were less than seven days.
- In natural water, the half-life is one to two weeks, and in treated rice paddy conditions, the half-life is as short as one day.
Exposures of wildlife to 2,4-D, whether through direct contact or consumption of treated vegetation, has been shown to be of low toxicological concern. Studies have shown 2,4-D is:
- Practically non-toxic to both freshwater and estuarine/marine fish, amphibians (frogs).
- Only slightly toxic to aquatic invertebrates.
- Practically non-toxic to honeybees and earthworms.
The use of 2,4-D to control undesirable vegetation and invasive plants has a positive contribution to wildlife by allowing growth of native plants and restoring the naturalhabitat. In aquatic systems, 2,4-D has been used to counter the intrusion by invasive vegetation which can choke off aquatic habitats and degrade water quality.
Want more information? A list of scientific resources can be found at "Studies and Reports on 2,4-D".
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