Pesticide warning sign on a bright green lawn. (Bigstock)

A weedkiller sprayed widely on farms and used in a number of popular lawn-care products has been designated as "possibly" carcinogenic to humans by a World Health Organization research arm.

The analysis, published in Tuesday's the Lancet Oncology, showed that there is strong evidence that the herbicide, 2,4-D, causes an imbalance in the body called oxidative stress, and moderate evidence that it leads to immunosuppression, but the panel concluded that there was insufficient information to make a stronger link to cancers.

The WHO's International Agency for Research on Cancer also classified the insecticide lindane, which was once used for insect control in agriculture and as a treatment for lice but is now restricted as a moderately hazardous substance, as carcinogenic for non-Hodgkin lymphoma — its strongest classification — and the insecticide DDT, introduced in World War II and later banned in many parts of the world, as "probably" carcinogenic. In March, the group also gave the "probably" carcinogenic label to glyphosate, the active ingredient in Monsanto's flagship herbicide Roundup, which had been the No. 1 weedkiller in the United States.

[Startling link between mother's exposure to DDT and daughter's risk of breast cancer]

The addition of 2,4-D to the WHO group's cancer list is especially significant because it is so widespread in our environment today. The chemical, made by Dow AgroSciences and contained in products such as Ortho Weed B Gone Max and Bayer Advanced Lawn Weed & Crabgrass Killer, has been found on golf courses, in parks and other grassy areas and in waters used by recreational swimmers and treated for aquatic weeds. Low-level residue has also been documented in crops and drinking water.

[Md. Gov. Larry Hogan has non-Hodgkin’s lymphoma. Even in late stages, it’s often curable.]

In a 2012 article by a Natural Resources Defense Council (NRDC) researcher in the Atlantic, 2,4-D is referred to the "Agent Orange in Your Backyard:"

2,4-D was invented in the chemical boom during World War II, making it one of the oldest pesticides that's still legally on the market today. It was one of the two active ingredients in Agent Orange, the notorious Vietnam War defoliant. Despite decades of scientific studies showing links to non-Hodgkin's lymphoma in humans (and Canine Malignant Lymphoma in household dogs), this chemical survives and thrives as one of the top three pesticides sold in the United States today. Newer science shows that it's not just a cancer problem, but that this pesticide interferes with several essential hormones, thereby increasing the risks of birth defects and neurologic damage in children. Studies in Midwest wheat-growing areas (where 2,4-D is heavily used) have shown increased rates of certain birth defects, especially in male children, and lower sperm counts in adults.

Dow said in a statement obtained by Reuters that the new classification is "inconsistent with government findings in nearly 100 countries" that have affirmed the safety of 2,4-D when used as labeled.

The U.S. Department of Agriculture, in its most recent guidance on the chemical, notes that “'Agent Orange' was a mixture of herbicides 2,4,5-T and 2,4-D, kerosene and diesel fuel." However, the substance of concern is "high levels of dioxin, a contaminant found in 2,4,5-T that causes cancer and other health concerns in people."

The EPA stopped use of  2,4,5-T in 1985 because of these risk but considers 2,4-D "safe when used according to the EPA-approved labeling."

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