The International Agency for Research on Cancer (IARC), the specialised cancer
agency of the World Health Organisation (WHO), has confirmed that a common
insecticide causes cancer.
The agency came to the conclusion after evaluating the
carcinogenicity of the insecticides gamma-hexachlorocyclohexane (lindane) and
dichlorodiphenyltrichloroethane (DDT) and the herbicide
2,4-dichlorophenoxyacetic acid (2,4-D).
In a statement yesterday, the WHO said after thoroughly reviewing
the latest available scientific literature, a working group of 26 experts from
13 countries convened by the IARC Monographs Programme classified the
insecticide lindane as carcinogenic to humans (Group 1).
According to the WHO, there was sufficient evidence in humans for
the carcinogenicity of lindane for non-Hodgkin lymphoma (NHL). The insecticide
DDT was classified as probably carcinogenic to humans (Group 2A), based on
sufficient evidence that it 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.
The herbicide 2,4-D was classified 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 immune suppression, 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.
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.
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