The weedkiller 2,4-D is “possibly carcinogenic to humans,” says the International Agency for Research of Cancer, the same WHO agency that classified glyphosate, the most widely used weedkiller in the world, as probably carcinogenic. The listing for 2,4-D, which follows a meeting of experts convened by IARC, is a step below the rating given to glyphosate. IARC chose the “possibly” listing because there was inadequate evidence of carcinogenicity in humans and limited evidence in animal tests, said Reuters, which was the first to report the decision.
Dow Chemical, which has genetically engineered crop varieties to tolerate 2,4-D, said the IARC listing “is inconsistent with government findings in nearly 100 countries,” including the United States. “IARC’s findings on 2,4-D are not the last word even within the WHO.” The weedkiller was brought into use after World War II.
“IARC’s findings on 2,4-D have been awaited by environmental and consumer groups that are lobbying U.S. regulators to tightly restrict the use of 2,4-D, as well as by farm groups and others that defend 2,4-D as an important agent in food production that does not need more restrictions,” said Reuters.
At the same meeting in which it considered 2,4-D, the panel of 26 experts classified lindane, an insecticide, as “carcinogenic to humans,” and DDT as “probably carcinogenic to humans,” said IARC. Lindane is banned or restricted in most countries. Studies show a 60 percent increased risk of one type of cancer among people exposed to lindane. DDT, first used as an insecticide during World War II, has been banned for most uses since the 1970s. “Exposure to DDT still occurs, mainly through diet,” said IARC. DDT is used to kill insects that would spread malaria.
The IARC classification system “indicates the weight of the evidence as to whether an agent is capable of causing cancer (technically called ‘hazard’), but it does not measure the likelihood that cancer will occur (technically called ‘risk’) as a result of exposure to the agent.”
A summary of the evaluations of the three pesticides will be posted online in The Lancet Oncology.
A question-and-answer sheet on IARC’s classification system is available here.