A large long-term study on the use of the weedkiller glyphosate by agricultural workers has found no firm link between exposure to the pesticide and cancer, scientists said last week.
Published in the Journal of the National Cancer Institute (JNCI), the study found no association between glyphosate, the main ingredient in the herbicide Roundup, "and any solid tumors or lymphoid malignancies overall, including non-Hodgkin Lymphoma . . . and its subtypes."
It said there was "some evidence of increased risk of acute myeloid leukemia . . . among the highest exposed group," but added that this association was "not statistically significant."
The findings are likely to affect legal proceedings in the United States against Monsanto, the maker of Roundup, in which more than 180 plaintiffs are claiming that exposure to the pesticide gave them cancer — allegations that Monsanto denies.
The findings may also influence a crucial decision due by the end of the year on whether glyphosate should be relicensed for sale across the European Union. EU countries had been due to vote on the issue last week but again failed to agree to a proposal for a five-year extension.
The EU decision has been delayed for more than a year after the World Health Organization's International Agency for Research on Cancer reviewed glyphosate in 2015 and concluded it was "probably carcinogenic" to humans. Other bodies, such as the European Food Safety Authority, have concluded that glyphosate is safe to use.
The new research is part of the Agricultural Health Study, which has been tracking the health of tens of thousands of agricultural workers, farmers and their families in Iowa and North Carolina.
Since the early 1990s, it has gathered and analyzed detailed information on the health of participants and their families, and their use of pesticides, including glyphosate.
David Spiegelhalter, a professor at Britain's Cambridge University who has no link to the research, said the findings were from a "large and careful study" and showed "no significant relationship between glyphosate use and any cancer."
In a summary of the results, the researchers, led by Laura Beane Freeman, principal investigator of the study at the National Cancer Institute, said that among 54,251 pesticide applicators studied, 44,932, or 82.9 percent, used glyphosate.
"Glyphosate was not statistically significantly associated with cancer at any site," the summary said.