PRESS RELEASE N° 236 23
June
2015
IARC
Monographs evaluate DDT, lindane, and 2,4-D
Lyon,
France, 23 June 2015
The International Agency
for Research on Cancer (IARC), the specialized cancer agency of the World
Health Organization, has evaluated the carcinogenicity of the insecticides
gamma-hexachlorocyclohexane (lindane) and dichlorodiphenyltrichloroethane (DDT)
and the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D).
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).
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 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.
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 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.
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.
Large epidemiological
studies of agricultural exposures in the USA and Canada showed a 60% increased
risk of NHL in those exposed to lindane.
DDT was introduced for
the control of insect-borne diseases during the Second World War and was later
applied widely to eradicate malaria and in agriculture.
Although most uses of
DDT were banned 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. 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.
