Does weedkiller cause cancer? According to a ruling by a Californian court last week, yes. Monsanto, the agricultural chemicals company, has been ordered to pay $289 million to Dewayne Johnson, a groundskeeper who says his terminal cancer was caused by their products Roundup and RangerPro, which contain the chemical glyphosate.
The ruling has led to Greenpeace for sales of the weedkiller to be restricted and in Monsanto’s parent company Bayer to drop. Meanwhile, Thérèse Coffey, an environment minister in the UK government, is for her tacit support, having that she was about to “deploy the amazing Roundup!”.
But while the jury ruled that Johnson’s cancer, a non-Hodgkin’s lymphoma, was probably caused by glyphosate, the evidence for a link is extremely thin.
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“I don’t think there’s any good scientific evidence,” says , who studies cancer epidemiology at the University of Cambridge. We simply don’t know if glyphosate was a relevant cause of cancer in this case or any other, he says.
In 2015, the International Agency for Research on Cancer (IARC), a branch of the World Health Organization, that glyphosate is “probably carcinogenic”, having reviewed the evidence.
No evidence
But Pharoah says this decision is controversial. The IARC found no evidence at all from human studies, and its evidence from animal studies is unconvincing: some studies in rats and mice found evidence of a raised risk of certain tumours at very high doses, while other studies found no association.
In particular, there was no evidence of a raised risk of the non-Hodgkin’s lymphoma that Johnson developed. “It’s bizarre,” says Pharoah. Ěý“You can’t tell a coherent story.”
The IARC’s finding stands out further because separate reviews of glyphosate’s safety by the , the and the US found no increased Ěýrisk of cancer.
Another by a different branch of the WHO also found that it wasn’t carcinogenic in rats, although it couldn’t rule out that it might be in mice, in very high doses. Cancer Research UK there is a “small amount of evidence” that people exposed to very high doses might have increased risk, but no evidence of risk at normal levels.
There’s also a problem in that there’s no plausible mechanism. Cancer is usually the result of DNA damage, which glyphosate does not cause.
Pharoah adds that the jury’s wariness is understandable. Major corporations have a long and inglorious history of obfuscating evidence that would make their product seem harmful – the manufactured doubt over the links between tobacco and cancer, or fossil fuels and global warming, are obvious examples.
But there’s no evidence that that is what has happened here. There have been Ěý finding no link. It’s OK to be cautious about big companies selling chemicals and claiming that they’re harmless, but in the specific case of glyphosate, the likelihood of it causing cancer is somewhere between zero and negligible.
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