An arm of the World Health Organization has determined that several different types of popular weedkillers and pesticides are likely cancer-causing agents. 

The International Agency for Research on Cancer (IARC) released a statement (PDF) on June 23, declaring that it has categorized the insecticide lindane as carcinogenic to humans, specifically causing non-Hodgkin lymphoma. In addition, the IARC determined that the insecticide DDT is probably a cancer-causing agent, and the herbicide 2,4-D is possibly carcinogenic. The group’s scientific data was published in the medical journal The Lancet Oncology on June 22.

Lindane is a neurotoxin used as a pesticide since 1942 and was originally used to treat crops. It is also used to treat lice and scabies, but has been banned in other countries around the world and by even some parts of the U.S. due to potentially lethal side effects.

Lindane has long been linked to toxic health side effects, particularly for the elderly and children, the latter of whom are most likely to be subjected to treatment by lindane-based lice shampoos and lotions.

Because of risks to the liver and kidneys and the environment, Lindane was banned from international agricultural use by the Stockholm Convention on Persisten Organic Pollutants in 2009. The treaty also called for the phase-out of Lindane as a second-line treatment for lice by 2014.

Dichlorodiphenyltrichloroethane (DDT) was first used in the U.S. in 1945 to fight mosquitoes that carried diseases like malaria. It became heavily used in the 50s and 60s; but was phased out when it began to affect wildlife, causing declines in the populations of bald eagles and ospreys. DDT use continues in Africa and Asia.

The IARC’s findings come on the heels of a recent report which linked the chemical to an increased risk of breast cancer from DDT among daughters of women who were exposed to the pesticide during pregnancy.

2,4-D Classification Sparks Industry Pushback

The most controversial of the group’s cancer determinations is its ruling on 2,4-D, which has been used as an herbicide since 1945. The group said there is inadequate evidence in humans and limited evidence in experimental animals to call the chemical safe.

“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,” the IARC statement notes. “However, epidemiological studies did not find strong or consistent increases in risk of NHL or other cancers in relation to 2,4-D.”

The 2,4-D classification has sparked immediate pushback from industry, including its manufacturer, Dow Chemical.

In a statement released on Monday, Dow called the IARC’s findings inconsistent with the determinations of nearly 100 countries who have deemed the drug safe.

In October 2014, the U.S. Environmental Protection Agency (EPA) determined that 2,4-D was not a carcinogen.

“No herbicide has been more thoroughly studied and no national regulatory body in the world considers 2,4-D a carcinogen,” John Cuffe, Global Regulatory Sciences and Regulatory Affairs Leader of Dow AgroSciences, said in the press release. “In fact, IARC stated that there is ‘inadequate evidence’ for human carcinogenicity.”

Officials from the National Corn Growers Association and the American Soybean Association also attacked the IARC, saying that the group’s classifications would promote fear and confusion among consumers.

Tags: Cancer, DDT, Dow, Herbicide, Lindane, Pesticide