International Agency for Research on Cancer (IARC) on 23 June 2015 classified lindane, DDT and 2,4-D as carcinogenic to humans. IARC is the specialized cancer agency of the World Health Organisation (WHO).

The decision was taken in this regard after the conclusion of mandatory eight day meeting by a working group of 26 experts from 13 countries in Lyon (France). The group was set up by the IARC, as part of Monographs Programme, to evaluate the carcinogenicity of the three agents.

Gamma-hexachlorocyclohexane (Lindane): IARC classified the pesticide as carcinogenic to humans (Group 1) based on sufficient evidence in humans for the carcinogenicity for non-Hodgkin lymphoma (NHL).

It 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 it is now banned or restricted in most countries.

Large epidemiological studies of agricultural exposures in the USA and Canada showed a 60 percent increased risk of NHL in those exposed to lindane.

Dichlorodiphenyltrichloroethane (DDT): IARC classified the pesticide as probably carcinogenic to humans (Group 2A) based on sufficient evidence 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.

Although most uses of DDT were banned (under the Stockholm Convention) from the 1970s, DDT and its breakdown products are highly persistent and can be found in the environment and in animal and human tissues throughout the world. Exposure to DDT still occurs, mainly through diet.

2,4-dichlorophenoxyacetic acid (2,4-D): IARC classified the herbicide as possibly carcinogenic to humans (Group 2B), based on inadequate evidence in humans and limited evidence in experimental animals. There is 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.

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.

About IARC Monographs Programme

• It identifies and evaluates environmental causes of cancer in humans.

• It evaluates chemicals (e.g. formaldehyde), complex mixtures (e.g. air pollution), occupational exposures (e.g. work in coke production), physical agents (e.g. solar radiation), biological agents (e.g. hepatitis B virus), and personal habits (e.g. tobacco smoking).

• After evaluation, IARC classifies carcinogens in five categories ranging from carcinogenic to humans (Group 1) to probably not carcinogenic to humans (Group 4).

• Since 1971, more than 900 agents have been evaluated, of which more than 400 have been identified as carcinogenic, probably carcinogenic, or possibly carcinogenic to humans.

• IARC only classify the agents and does not recommend regulations, legislation, or public health interventions, which remain the responsibility of individual governments and other international organizations.

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