Insecticides lindane and DDT linked to cancer, WHO

The insecticide lindane, once widely used in agriculture and to treat human lice and scabies, causes cancer and has been specifically linked to non-Hodgkin lymphoma, the World Health Organisation has warned.

The WHO’s International Agency for Research on Cancer (IARC) also said DDT, or dichlorodiphenyltrichloroethane, probably causes cancer, with scientific evidence linking it to non-Hodgkin lymphoma, testicular cancer and liver cancer.

In a review of various agricultural chemicals, IARC’s specialist panel said it had decided to classify lindane as “carcinogenic to humans” in its Group 1 category, DDT as “probably carcinogenic to humans” in its Group 2A class, and the herbicide 2,4-D as “possibly carcinogenic to humans” in its Group 2B.

Lindane, which since 2009 has been banned or restricted in most countries under the Stockholm Convention on Persistent Organic Pollutants, was previously used extensively for insect control in agriculture. An exemption to the ban allows it to be used as a second-line treatment for lice and scabies. IARC said high exposures to lindane have previously been reported among agricultural workers and pesticide applicators.

“Large epidemiological studies of agricultural exposures in the United States and Canada showed a 60 per cent increased risk of non-Hodgkin lymphoma in those exposed to lindane,” it said. DDT was introduced for control of insect-borne diseases during World War Two and was later applied widely to eradicate malaria and in agriculture.

Although most uses of it were banned from the 1970s, IARC cautioned that 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,” it said, adding that DDT is still used, mainly for malaria control in parts of Africa, although under very strict conditions. Since it was introduced in 1945, 2,4-D has been widely used to control weeds in agriculture, forestry and urban and residential settings. IARC said occupational exposure to 2,4-D can occur during manufacturing and application, and people in the general population can be exposed through food, water, dust, or residential application, and during spraying.

Elsewhere, WHO, animal health and national defence officers called for wider international cooperation to avoid the spread of animal diseases that could be used as biological weapons.

Sixty per cent of human diseases come from animal agents and 80 per cent of the agents that could be used for bio terrorism are of animal origin, said Bernard Vallat, director general of the World Organisation for Animal Health.

“History has shown that animal diseases have often been used as weapons before. Advances in genetics can now make them even more harmful. So we are calling for further investment to be made at national level on bio security,” Vallat told reporters at a conference on biological threat reduction. Diseases have spread from animals to humans for millennia, with latest examples including the bird flu virus that has killed hundreds of people around the globe.

The OIE and the WHO warned that animal disease agents could escape naturally, accidentally but also intentionally from laboratories, to be used as bio weapons. Earlier during the conference Kenneth Myers, Director of the US Defense Threat Reduction Agency (DTRA), part of the Department of Defense, stressed the need for international collaboration to avoid the loss of biological material.

“Terrorists have clearly shown they will use any weapons at their disposal,” Myers said.

Security breaches involving animal diseases are not rare. The Pentagon said in May and earlier this month the US military had sent live samples of anthrax, which can be used as biological weapon, to five countries outside the United States and to dozens of US labs.