A large long-term study on the use of the big-selling weedkiller glyphosate by agricultural workers in the United States has found no firm link between exposure to the pesticide and cancer, scientists said on Thursday.
Published in the Journal of the National Cancer Institute, the study found there was "no association between glyphosate", the main ingredient in Monsanto's popular herbicide RoundUp, "and any solid tumours or lymphoid malignancies overall, including non-Hogkin Lymphoma (NHL) and its subtypes".
It said there was "some evidence of increased risk of acute myeloid leukemia (AML) among the highest exposed group", but added "this association was not statistically significant" and would require more research to be confirmed.
The findings are likely to impact legal proceedings taking place in the United States against Monsanto, in which more than 180 plaintiffs are claiming exposure to RoundUp gave them cancer - allegations that Monsanto denies.
The findings may also influence a crucial decision due in Europe this week on whether glyphosate should be re-licensed for sale across the European Union.
That EU decision has been delayed for several years after the World Health Organization's International Agency for Research on Cancer (IARC) reviewed glyphosate in 2015 and concluded it was "probably carcinogenic" to humans.
The research is part of a large project known as the Agricultural Health Study (AHS), 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 analysed detailed information on the health of participants and their families, and their use of pesticides, including glyphosate.