Glyphosate Use: Important Update for Weed Control

Background

In the first of many pending lawsuits to go to trial, a jury in San Francisco, California concluded on Aug. 10, 2018 that the plaintiff had developed a form of cancer known as non-Hodgkin lymphoma from exposure to Roundup, Monsanto’s widely used herbicide. The plaintiff was a former school groundskeeper who had applied Roundup as part of his job. The jury found that Monsanto should pay $289 million in damages and the judge ordered the company to do so; Monsanto plans to appeal.

This news has resulted in questions to UF/IFAS Extension offices and faculty regarding the safety of glyphosate, the active ingredient in Roundup. Glyphosate is the most commonly used herbicide worldwide, found in hundreds of products and important for numerous residential, industrial and agricultural applications.

Reports on Glyphosate

Much of the current discussion about glyphosate involves a 2015 monograph issued by the World Health Organization’s International Agency for Research on Cancer, which classified glyphosate as “probably carcinogenic to humans.” (http://www.iarc.fr/en/media-centre/iarcnews/pdf/MonographVolume112.pdf)

This assessment has been challenged by scientists and journalists, notably in a Reuters article dated Oct. 19, 2017, “In glyphosate review, WHO cancer agency edited out ‘non-carcinogenic’ findings.” (https://www.reuters.com/article/us-who-iarc-glyphosate-specialreport/in-glyphosate-review-who-cancer-agency-edited-out-non-carcinogenic-findings-idUSKBN1CO251)

It must be understood that the 2015 assessment by the International Agency for Research on Cancer focused on a single question – is glyphosate capable of promoting cancer development in people? The agency did not address follow-up questions such as, what amount of glyphosate exposure would increase someone’s cancer risk to a medically significant degree?

A research paper involving licensed pesticide applicators published Nov. 9, 2017 in the Journal of the National Cancer Institute, “Glyphosate Use and Cancer Incidence in the Agricultural Health Study,” provided additional information. (https://academic.oup.com/jnci/article/110/5/509/4590280)

This investigation involved 54,251 participants, who were recruited in the mid-1990s for a multifaceted federal initiative known as the Agricultural Health Study and had been tracked up through 2005. These participants had no history of cancer when they enrolled in the Agricultural Health Study, and more than 80 percent of them reported that they had used glyphosate. The researchers estimated the probable glyphosate exposure for each participant, using self-reported data as well as information imputed to participants based upon factors such as location and workplace characteristics.

In the final paragraph of the article’s Discussion section, the researchers concluded that, “we found no evidence of an association between glyphosate use and risk of any solid tumors or lymphoid malignancies, including (non-Hodgkin lymphoma) and its subtypes.”

Also, the researchers indicated that they “found some evidence of a possible association” between glyphosate use and another form of cancer, acute myeloid leukemia. The researchers stated that the association was not statistically significant and was only found among participants with the highest levels of glyphosate exposure, but they recommended further investigation nonetheless.

On Dec. 12, 2017 the U.S. Environmental Protection Agency issued draft risk assessments concerning the potential effects of glyphosate on human health and the environment. These assessments were publicized by EPA, which noted in a Dec. 18, 2017 news release that the draft human health risk assessment “concludes that glyphosate is not likely to be carcinogenic to humans.” (https://www.epa.gov/pesticides/epa-releases-draft-risk-assessments-glyphosate)

According to the Dec. 18 news release, EPA is scheduled to publish its proposed interim registration review decision for glyphosate in 2019. The proposed decision will outline any proposed measures to reduce the risk of glyphosate use, if such measures are needed.

A package of risk-assessment material relevant to EPA’s review of glyphosate is available online. (https://www.epa.gov/ingredients-used-pesticide-products/draft-human-health-and-ecological-risk-assessments-glyphosate.) Within the package, one section relevant to job-related glyphosate exposure is, “Glyphosate Draft Human Health Risk Assessment in Support of Registration Review.” This section is 41 pages long and includes numerous references to past studies concerning glyphosate; it contains findings issued subsequent to the most recent EPA human health risk assessment, which was completed in November 2012. In that assessment, EPA officials conducted an open literature review and concluded that glyphosate should be classified as “not likely to be carcinogenic to humans.”

Readers should be aware that EPA is not merely assessing whether glyphosate is capable of promoting cancer development in people. Instead, EPA is concerned with the question, are people who use glyphosate on the job likely to experience a medically significant increase in cancer risk?

Recommendation

For years, UF/IFAS weed scientists have been aware of controversies associated with glyphosate. Consequently, these scientists have made it a point to monitor both the scientific press and the popular media for new developments concerning glyphosate and its use.

Given the lack of any new evidence that would steer us otherwise, we continue to recommend glyphosate as a weed control tool. Users of products containing glyphosate, or any pesticide, should carefully read and follow all label directions. The label will provide guidance regarding the clothing and/or personal protective equipment that should be worn to reduce exposure and, thus, reduce the overall hazard associated with use of the product.

UF/IFAS is committed to safety and supports integrated pest management as the first line of defense against weeds and other pests, including the use of glyphosate and other pesticides. If credible science proves otherwise, we will appropriately revise our recommendations. However, the ultimate decision to select a particular herbicide for a particular purpose rests with the individual producer, as do all management decisions.

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