Grass sprayed with glyphosate© Tim Scrivener

A large long-term study into the use of glyphosate by US agricultural workers has found no clear evidence linking glyphosate to cancer.

The study, published in the Journal of the National Cancer Institute on Thursday (9 November), found there was no association between glyphosate and “any solid tumours or lymphoid malignancies overall, including non-Hodgkin lymphoma and its subtypes”.

However, the research found there was “some evidence” of an increased risk of acute myeloid leukaemia [AML] among the highest exposed group, but this was “not statistically significant”.

See also: Video – farmers explain why glyphosate is vital

The work was part of the Agricultural Health Study (AHS), which analysed the effects of glyphosate on more than 50,000 farmers and their families in Iowa and North Carolina, since 1993.

It looked at 54,251 pesticide applicators, of which 44,932 (82.9%) used glyphosate.

The report is significant as the data is at the centre of the World Health Organization’s International Agency for Research on Cancer’s (IARC) decision in 2015 to brand glyphosate as a “probable carcinogen to humans”.

But over the summer, Reuters news agency revealed Aaron Blair, the chairman of the IARC’s glyphosate study, had seen the scientific data in the AHS report – but did not consider it as part of his evaluation.

IARC evaluation

Speaking under oath, Mr Blair admitted that had IARC considered the study, it likely would have changed its conclusion on glyphosate and said “[the] data would have altered IARC’s analysis”.

The AHS data on glyphosate was published on the same day EU member states voted on a European Commission proposal to reauthorise glyphosate for five years.

Although half of member states – 14 including the UK – voted in favour of the proposal, it was not enough to secure a licence renewal. It means the EU’s Appeal Committee will now decide the fate of glyphosate next month.

Environmental groups, including Greenpeace and Friends of the Earth (FoE), have relied on the conclusion of the IARC report as “evidence” to support their calls for a total ban on glyphosate.

This is despite the European Food Safety Authority (Efsa) and the European Chemicals Agency both concluding glyphosate, the key active ingredient in Monsanto’s Roundup herbicide, is safe.

Comprehensive study

David Spiegelhalter, a professor of public understanding at Cambridge University, who has no links to the AHS study, said it showed “no significant relationship between glyphosate use and any cancer”.

“The reported possible association with AML is no more than one would expect by chance when looking at 22 different cancer types,” said Prof Spiegelhalter.

“In fact, the association that comes closest to statistical significance is a negative link with testicular cancer – that is, higher glyphosate use was associated with lower risk – but again this is just the sort of chance result one would expect.”

In a statement, the American Chemistry Council (ACC) said the (AHS) study is highly regarded throughout the scientific community as the most comprehensive study on glyphosate exposure in humans to date.

ACC president Cal Dooley said the IARC had “misinformed and misguided” the public and policymakers with their glyphosate report.