Glyphosate to join Proposition 65 list

By Elaine Watson

- Last updated on GMT

Glyphosate to join Proposition 65 list

Related tags Roundup

The herbicide glyphosate is to be added to the list of chemicals known to cause cancer under California's Proposition 65 legislation, which means companies producing products containing residues of the popular herbicide may in future have to feature warning labels.

The effective date of the listing will depend on whether Monsanto - which uses glyphosate in its RoundUp herbicides - is able to block the Prop 65 listing while it awaits the outcome of a legal challenge. (Monsanto sued the OEHHA in 2016 - Monsanto v OEHHA​ -​ after it announced its intention to add glyphosate to the Prop 65 list in 2015, and lost the case​, but is currently appealing the decision.)

If Monsanto cannot block the move, its impact will depend on how low the safe harbor level for glyphosate is set (ie. if levels are below the safe harbor, firms will not have to issue Prop 65 warnings), so all eyes are now on the Office of Environmental Health Hazard Assessment (OEHHA), which says it will finalize the safe harbor level "prior to the effective date of the warning requirement for exposures to glyphosate."

Prop 65 requires manufacturers selling products in California to give clear warnings if their products expose consumers to any detectable amount of 800+ chemicals linked to cancer or reproductive toxicity.

Despite its laudable aims, however, Prop 65 has proved controversial given that the vast majority of firms sued over alleged violations opt to settle - even if they are supremely confident in the safety of their products - because the burden of proof is on defendants to prove exposure levels are zero (or in the case of substances where safe harbor levels have been set, below a set threshold).

While this might seem eminently reasonable, critics of the law say many Prop 65 chemicals are present at trace levels in scores of foods without presenting a threat to human health, while safe harbor levels enshrined in Prop 65 are unrealistically low.

The primary frustration for manufacturers, however, is that even if they can​ prove they are under Prop 65 safe harbor levels, the costs associated with defending yourself (hiring a toxicology expert, legal fees etc) will likely exceed whatever amount plaintiffs demand in settlement, prompting some lawyers to argue that Prop 65 has turned into a form of “legalized blackmail​”.

Glyphosate and safety

A 2015 statement from the International Agency for Research on Cancer​ (part of the World Health Organization) that glyphosate was ‘probably carcinogenic to humans’ was the trigger behind the OEHHA action.

The IARC statement was also cited in a wave of lawsuits​ against General Mills, Post Foods and Quaker (PepsiCo), who were sued last year on the grounds that no reasonable consumer would expect ready-to-eat cereals, bars and snacks labeled as '100% natural' to contain even trace amounts of synthetic pesticide residues, regardless of the legal limits.


Monsanto, however, said it was baffled​ ​by the IARC’s statement as “there is no new research or data that was used; the most relevant, scientific data was excluded from review; the conclusion is not supported by scientific data; and there is no link between glyphosate and an increase in cancer when the full data set is included in a rigorous review”.

It also noted that the IARC's findings were inconsistent with those of two other WHO programs – the Core Assessment Group and the International Program on Chemical Safety – which have both concluded glyphosate is not​ carcinogenic.

A November 2015 report​ from the European Food Safety Authority (EFSA) also found that "glyphosate is unlikely to pose a carcinogenic hazard to humans and the evidence does not support classification with regard to its carcinogenic potential."

On April 29, 2016, the EPA posted a report concluding that glyphosate is “not likely to be carcinogenic,​” but later took down the report and said it would publish a full assessment at a later date.

Meanwhile, a May 16, 2016 report​ by the Food and Agriculture Organization of the United Nations' (FAO's) Panel of Experts on Pesticide Residues in Food and the Environment, and the World Health Organization (WHO) Core Assessment Group on Pesticide Residues found that "glyphosate is unlikely to be genotoxic at anticipated dietary exposures."

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