Used widely for domestic and agricultural purposes, 2,4-dichlorophenoxyacetic acid (2,4-D) has been well known commercial herbicide since the 1940s. According to Statistics Canada (2006), almost half of Canadian farms reported use of herbicides, including 2,4-D, on over 24 million hectares of land in addition to its domestic use for aesthetic purposes in yards and gardens. Used to control broadleaf plants, 2,4-D is found commercially in three main forms: alkali salts, amine salts and esters (HC 1993). As a herbicide, 2,4-D is applied directly for weed control but has the potential to enter the environment through many pathways including accidental spills, excessive application, runoff and aerial drift (HC 1993).
For humans, potential pathways to 2,4-D exposure include: ingestion of residuals on food or in water, direct accidental ingestion, dermal exposure most often through the workplace or application, and inhalation by volatilization (HC 1993, EPA 2005). The US Environmental Protection Agency (2005) identifies sensitive populations including toddlers and pregnant women; however, individuals producing or using the chemical have potential for exposure. Toxicological research on 2,4-D often focuses on its potential association with cancer; however, in a recent review of the literature, Burns and Swaen (2012) summarized historical research into four additional human health endpoints including reproductive toxicology, genotoxicity, neurotxicity, and general toxicity.
The effects of 2,4-D on human health have been a long standing public controversy, likely partly due to its historical association with the war-time chemical Agent Orange and 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) (ACS 2013), and the lack of evidence linking human health effects when used according to guidelines (Burns and Swaen 2012, HC 2008). As a result, both Health Canada and the US Environmental Protection Agency have conducted re-evaluations of 2,4-D in an effort to determine, using scientifically defensible research, the potential risk posed by 2,4-D and the subsequent regulations or management required to minimize that risk (EPA 2005, HC 2008).
Despite the large number of studies looking at the toxicity of 2,4-D, the lack of conclusive evidence that 2,4-D is cancer causing (HC 2008) may be contributing to international, national and public perceptions regarding 2,4-D to differ. The limited epidemiological evidence on which to base guidelines (WHO 2003) and history of public perceptions of 2,4-D has perhaps led to extreme viewpoints on the use of 2,4-D. For example, the Sierra Club, an environmental activist organization, is opposed to the use of 2,4-D (2005). Despite reviews of 2,4-D by Health Canada and other world national health organizations to determine the safety of 2,4-D under proper use conditions, there currently exists uncertainty with regard its potential risk to human health.
The purpose of this article is to further discuss the potential human health risks posed by exposure to 2,4-D, and is 2,4-D really ‘bad’ for humans under normal use conditions. In addition, discussion will explore how the past research has informed the guidelines and reference values used by relevant health organizations. Due to the relevance of public perception associated with acceptance of risk (Siegrist and Cvetkovich 2000), the current perspectives on the use of 2,4-D by the public and national/international governments will be discussed. Lastly, a short summary of current research and comment on future direction of 2,4-D research or use will be provided.
American Cancer Society. 2013. Agent Orange and cancer. Website http://www.cancer.org/cancer/cancercauses/othercarcinogens/intheworkplace/agent-orange-and-cancer
Burns, C.J. and G.M.H. Swaen. 2012. Review of 2,4-dichlorophenozyacetic acid (2,4-D) biomonitoring and epidemiology. Critical Reviews in Toxicology. 42(9):768-786
Health Canada. 1993. Fact sheet on the chemical/physical parameters of 2,4-dichlorophenoxyacetic acid. Health Canada.
Health Canada. 2008. Information note: Health Canada releases final re-evaluation decision on 2,4-D. Health Canada.
Siegrist, M. and Cvetkovich, G. 2000. Perception of Hazards: The Role of Social Trust and Knowledge. Risk Analysis. 20: 713–720.
Sierra Club. 2005. Overview of the toxic effects of 2,4-D. Sierra Club of Canada.
Statistics Canada. 2006. Area of commercial fertilizer, herbicides, insecticides and fungicides applied, in Canada from 1996-2006. Statistics Canada.
United States Environmental Protection Agency. 2005. Reregistration eligibility decision for 2,4-D. Prevention, Pesticides and Toxic Substances. EPA 738-R-05-002.
World Health Organization. 2003. 2,4-D in drinking-water: background document for the development of WHO guidelines for drinking-water quality. World Health Organization.