Roundup weedkiller contains a carcinogenic chemical that could be dangerous for humans, according to a new study.

The International Agency for Research on Cancer (IARC) brought together 17 experts from 11 nations, between March 3 and 10, in order to study the health effects of five insecticides and pesticides: parathion, diazinon, malathion, glyphosate, and tetrachlorvinphos.

The international group, working under the auspices of the United Nations and the World Health Organization (WHO), concluded that Roundup, produced by food and chemical giant Monsanto, is probably carcinogenic, due to the presence of glyphosate.

"The general population is exposed (to glyphosate) primarily through residence near sprayed areas, home use and diet, and the level that has been observed is generally low," IARC officials declared.

The group also stated that a pair of other weedkillers, which are already severely restricted or illegal, are also possible causes of cancer. Tetrachlorvinphos and parathion were the two chemicals which caused concern in those products.

Glyphosate was first produced in mass quantities in Roundup, during the 1970s. Today, the chemical is available in a generic form, and is the most popular weedkiller in the world. Crops are now genetically engineered to be resistant to the chemical. These "Roundup ready" plants can, therefore, be dosed with large quantities of the chemical in a single application.

Non-Hodgkin lymphoma, a form of cancer that begins in the immune system, has become more common in farmers and other agricultural workers since 2001, IARC officials said. Glyphosate was classified as possibly carcinogenic for humans by the Environmental Protection Agency (EPA) in 1985, following a series of tests on lab rats. However, that classification was changed in 1991, and the EPA reported the substance is non-carcinogenic in human beings.

Parathion was the subject of several legal restrictions beginning in the 1980s, and its use was banned in the United States and Europe in 2003. Tetrachlorvinphos is forbidden in Europe, but is still used in the United States, in products including flea collars. Restrictions were placed on the use of diazinon by governments in Europe and America, but malathion is still in common use around the world.

Monsanto officials quickly released a statement, saying the IARC findings did not utilize new research, and that the group excluded scientific data that would have confirmed the safety of the herbicide.

"We take great pride in the science behind, and safety of, our products... And, we are reaching out to the World Health Organization (WHO) to understand how, despite the wealth of existing science on glyphosate, the IARC panel could make a classification that disagrees with scientific and regulatory reviews," Monsanto officials declared.

Investigation of potential carcinogens in Roundup was published in The Lancet Oncology.

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