A potentially cancer-causing chemical found in weed killer is being sprayed on produce across the country, but data obtained by NBC News found that the some of the highest levels are recorded in parts of Illinois and the Midwest.

That chemical is glyphosate — a key ingredient in Roundup. Non Selective Post Emergence Herbicide

The herbicide came under increasing scrutiny after the France-based International Agency for Research on Cancer, which is part of the World Health Organization, classified it as a “probable human carcinogen” in 2015. Since then, thousands of lawsuits have been filed over cancer claims involving the chemical, with Bayer saying in 2020 that it would pay up to $10.9 billion to settle litigation.

Monsanto first developed glyphosate in the 1970s. The weed killer has been sold in more than 160 countries and widely used in the U.S.

Bayer, which bought St. Louis-based Monsanto in 2018, said previously that all government regulators that have looked at the issue have rejected a link between cancer and glyphosate. Monsanto has attacked the international research agency’s opinion as an outlier. The U.S. Environmental Protection Agency says glyphosate is safe for people when used in accordance with label directions.

NBC News analyzed data from the U.S. Geological Survey surrounding the use of glyphosate in agriculture, with the weed killer being used on everything from corn to soy beans to fruits and more. In fact, the data showed nearly half of all produce in the U.S. are sprayed with weed killer containing the chemical.

According to the report, data showed Iowa and Illinois, known for growing corn and soy bean products, accounted for 15% of the national usage. And several counties in the Chicago area had levels among the highest in the country.

That included counties like LaSalle, DeKalb and Grundy, along with several other central and northern Illinois counties. Other counties in the Chicago area that also had higher levels included Kankakee, Kendall and McHenry.

Selective Herbicide To Kill Grass Other key findings in the report included that more than 55 million people live in counties with above-average use of the chemical. Lake County, Colorado, had the highest usage rate of U.S. counties, with almost 2,000 pounds sprayed per square mile.