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Cancer warning over weedkiller – consumers should take care

Gardeners should look more closely at the products they use following a cancer warning by the World Health Organisation (WHO) about commonly-used weedkiller glyphosate.

The chemical is widely used in agriculture, forestry and domestic gardening. It is found in 750 products, including market-leading weedkiller Roundup.

Yet a panel of 17 experts assembled by the WHO’s International Agency for Research on Cancer (IARC) declared the herbicide to be “a probable carcinogen”, along with insecticides malathion and diazinon.

The IARC's findings were welcomed by Professor Andreas Kortenkamp, an expert in human toxicology at Brunel University London. Professor Kortenkamp has long called for a more critical look at chemicals used in every day household products, and for harmful substances to be banned.

He said: “The authorities in the EU must now consider whether existing measures are sufficient to protect consumers and pesticide applicators from cancer risks. This will be particularly important for the widely used weedkiller glyphosate, now classified as probably carcinogenic to humans. Home gardeners, especially, should exercise the utmost care when they use weedkillers that contain glyphosate.”

Explaining its “probable carcinogen” grading, the IARC cited studies from America, Canada and Sweden. These found glyphosate in water, food and in air during spraying. There was evidence it could cause cancer in laboratory animals and limited evidence of a link to non-Hodgkin lymphoma in humans.

The IARC is not a regulatory body and as such its decisions do not necessarily lead to bans or marketing restrictions. However, the grading will bolster campaigners’ efforts and put pressure on regulators.

The classification provoked a strong reaction in the agrochemical industry. Monsanto, Roundup’s manufacturers, robustly contested the IARC stance on glyphosate pointing to the conflict with other official assessments of its safety.

In its declaration, the IARC categorised insecticides tetrachlorvinphos and parathion as “possibly carcinogenic to humans”, a grading lower than that of glyphosate. A summary of the assessment is published in the Lancet Oncology journal here: