The pesticide glyphosate, sold by Monsanto in its Roundup weed killer product and widely used in agriculture and by gardeners, is unlikely to cause cancer in people, according to a new safety review by United Nations health, agriculture and food experts.
In a statement likely to intensify a row over its potential health impact, experts from the U.N.'s Food and Agriculture Organization and World Health Organization said glyphosate is "unlikely to pose a carcinogenic risk to humans" exposed to it through food. It is mostly used on crops.
Having reviewed the scientific evidence, the joint WHO/FAO committee also said glyphosate is unlikely to be genotoxic in humans. In other words, it is not likely to have a destructive effect on cells' genetic material.
Diazinon and malathion, two other pesticides reviewed by the committee, which met last week and published its conclusions on Monday, were also found to be unlikely to be carcinogenic.
"In view of the absence of carcinogenic potential in rodents at human-relevant doses and the absence of genotoxicity by the oral route in mammals, and considering the epidemiological evidence from occupational exposures, the meeting concluded that glyphosate is unlikely to pose a carcinogenic risk to humans from exposure through the diet," the committee said.
Glyphosate is also "unlikely to be genotoxic at anticipated dietary exposures", it added.
The group reaffirmed an acceptable daily intake (ADI) of up to 1 milligram of glyphosate for every kilogram of body weight.
The conclusions appear to contradict a finding by the WHO's Lyon-based International Agency for Research on Cancer (IARC), which in March 2015 said glyphosate is "probably" able to cause cancer in humans and classified it as a 'Group 2A' carcinogen.
Seven months after the IARC review, the European Food Safety Authority (EFSA), an independent agency funded by the European Union, published a different assessment, saying glyphosate is "unlikely to pose a carcinogenic hazard to humans".
The United States' Environmental Protection Agency (EPA), which first assessed glyphosate in 1986 and has reviewed it several times since then, had also previously concluded it has "low toxicity for humans".
The differing findings thrust glyphosate into the centre of a row involving EU and U.S. politicians and regulators, the IARC experts, the WHO and environmental and agricultural scientists.
The EU's pesticides committee is due to meet later this week to decide whether to re-license glyphosate. The U.S. EPA is being investigated for withdrawing a report saying the chemical is probably not carcinogenic.
In a question-and-answer document issued alongside the joint FAO/WHO statement, the WHO denied that the conclusions by the joint group and by IARC were contradictory. It said they were "different, yet complementary", with the IARC assessment focussed on hazard while the other looked at risk.
"IARC reviews published studies to identify potential cancer hazards," the WHO said. "It does not estimate the level of risk to the population associated with exposure to the hazard."
In contrast, it said, the joint FAO/WHO committee looks at published and unpublished studies to assess the health risk to consumers from dietary exposure to pesticide residues in food.