There is a weed-killer called Roundup. It is manufactured by Monsanto, which is now owned by Bayer.

Roundup contains a chemical called glyphosate, which may or may not be carcinogenic. That, at least, is the question that juries around the country are being asked to answer. The evidence on the question is split, with Monsanto, Bayer and the Environmental Protection Agency asserting that Roundup does not cause cancer.

But several juries have disagreed, based upon evidence from World Health Organization’s International Agency for Research on Cancer. There, studies in rats, mice and humans, have led the Organization to conclude that the chemical probably does cause cancer.

So far, several cases have gone to trial, and Bayer and Monsanto have lost.
And the verdicts have been enormous.

Moreover, there are still over 13,000 lawsuits against Bayer pending, arising out of claims that Roundup has caused cancer.

So, why this dispute? What is the answer? Does Roundup cause cancer, or not? A thoughtful article in Business Insider takes a close look at this issue, and concludes that “the EPA and Bayer (the company that now owns Monsanto) both maintain that glyphosate does not cause cancer in humans. But Bayer and the US government may not be considering all types of exposure in their analyses.” Brueck, H., “The EPA Says A Chemical In Monsanto’s Weed-Killer Doesn’t Cause Cancer — But There’s Compelling Evidence The Agency Is Wrong.” Business Insider, June 1, 2019.

Specifically the difference is this: Bayer and EPA base the conclusion that Roundup and glyphosate do not cause cancer upon studies of industrial agricultural use, where the chemical is applied by “farmers out in the field with their large, modern spray rigs, where the operator is inside a steel and glass cab with a sophisticated air filtration system that essentially eliminates exposure.” But Roundup contains Glyphosate and surfactants which lets the chemical be absorbed through the skin. So many users, workers are golf courses, for example, who apply Roundup by hand, may be exposed to high levels of the chemical through spray drift.

The studies that Monsanto and EPA looked at (and that Monsanto funded) looked at the farmers, insulated from exposure in their cabs. The WHO studies looked at direct exposure.

The entire article is well worth reading, since it highlights not only the risks of Roundup and exposure to glyphosate, but also the differing lenses of scientific studies and how to assess them for reliability, credibility, and truth.