World Health Organization cancer agency releases 2,4-D herbicide evaluation

The International Agency for Research on Cancer (IARC), the specialist cancer agency of the World Health Organization, has evaluated the carcinogenicity of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) as well as insecticides gamma-hexachlorocyclohexane (lindane) and dichlorodiphenyltrichloroethane (DDT).

After reviewing the latest available scientific literature, a working group of 26 experts from 13 countries convened by the IARC Monographs Programme has classified the herbicide 2,4-D "as possibly carcinogenic to humans (Group 2B), based on inadequate evidence in humans and limited evidence in experimental animals".

It said there was "strong evidence" that 2,4-D induces oxidative stress, a mechanism that can operate in humans, and "moderate evidence" that 2,4-D causes immunosuppression, based on in vivo and in vitro studies. However, epidemiological studies did not find strong or consistent increases in risk of NHL or other cancers in relation to 2,4-D exposure.

An industry task force on the chemical found it meets modern safety standards. See

The Common Sense Gardening Group of the Crop Protection Association has issued the following statement in response.

"Many independent experts disagree with these classifications on the basis that no new research or data was used, the most relevant, scientific data was excluded from review, and the conclusion did not appear to be supported by the scientific data.

"IARC’s reviews are limited and the process is designed to result in ‘possible’ and ‘probable’ classifications. IARC’s assessment of 2,4-D is similar to their assessment of other everyday items such as coffee, mobile phones, aloe vera (whole leaf extract), pickled vegetables and occupations including hairdresser, carpenter and chip shop worker, all of which fell into these categories.

"IARC reviews seek to identify cancer hazards, meaning the potential for the exposure to cause cancer. However, it does not indicate the level of risk associated with exposure. The cancer risk associated with substances or agents assigned the same classification may be very different, depending on factors such as the type and extent of exposure and the strength of the effect of the agent.  This distinction between hazard and risk is important. An agent is considered a cancer hazard if it is capable of causing cancer under some circumstances. Risk measures the probability that cancer will occur, taking into account the level of exposure to the agent."

"Claims that 2,4-D is ‘possibly’ carcinogenic also contradict conclusions reached by the IARC’s own parent body the WHO and the Food and Agriculture Organisation (FAO) through their Joint Meeting on Pesticide Residues (JMPR), which has reviewed 2,4-D five times, most recently concluding that there is no evidence of carcinogenicity.

"IARC itself has admitted it decided on the ‘possibly’ carcinogenic classification because there was "inadequate evidence in humans and limited evidence in experimental animals" of ties between 2,4-D and cancer.

Gary Philpotts, chair of the Common Sense Gardening Group said:

"It’s important to note that 2,4-D is amongst the most thoroughly tested and evaluated herbicide products on the market. Numerous health assessments conducted by public authorities over 70 years have consistently concluded that 2,4-D does not pose an unacceptable risk to public health.

"Human health and responsible use of garden care chemicals is and must always be our highest priority. As an industry we take pride in the detailed submissions we provide to regulators and the extreme rigor with which our products are assessed. Gardeners and the general public should rest assured that these products are safe and effective when used according to the instructions on the label."

In the same report, IARC classified the insecticide lindane as carcinogenic to humans.

The insecticide DDT was classified as probably carcinogenic to humans, based on what it described as sufficient evidence that DDT causes cancer in experimental animals and limited evidence of its carcinogenicity in humans. Epidemiological studies found positive associations between exposure to DDT and NHL, testicular cancer, and liver cancer.

There was also strong experimental evidence that DDT can suppress the immune system and disrupt sex hormones. However, overall there was no association between breast cancer and DDT levels measured in samples of blood or fat.

A summary of the final evaluations is available online in The Lancet Oncology, and the detailed assessments will be published as Volume 113 of the IARC Monographs.

Lindane has been used extensively for insect control, including in agriculture and for treatment of human lice and scabies. High exposures have occurred among agricultural workers and pesticide applicators; however, the use of lindane is now banned or restricted in most countries.

Most uses of DDT were banned from the 1970s. The remaining and essential use of DDT is for disease vector control, mainly for malaria. This use is strictly restricted under the Stockholm Convention.

Since its introduction in 1945, 2,4-D has been widely used to control weeds in agriculture, forestry, and urban and residential settings. Occupational exposures to 2,4-D can occur during manufacturing and application, and the general population can be exposed through food, water, dust, or residential application, and during spraying.

2,4 D is widely available in garden lawn weed killer producers. See

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