SAN FRANCISCO (CBS SF) — California added a controversial chemical found in the world’s most popular weedkiller to the list of chemicals known to the state to cause cancer, and the FDA is now testing U.S. crops for residues from that same chemical.

Glyphosate, a key ingredient in hundreds of products including Monsanto’s best-selling herbicide Roundup, was added to the state’s Prop 65 list on Friday. The list was created by The Safe Drinking Water and Toxic Enforcement Act of 1986 and includes hundreds of chemicals known to the state to cause cancer or reproductive toxicity.

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Whether or not glyphosate should have been added to the list remains a contentious issue.

Monsanto is currently being sued in California by nearly 200 individual plaintiffs claiming exposure to Roundup gave them cancer and that the company failed to warn them of its risks.

Monsanto says its product is not carcinogenic and is fighting the lawsuits as well as California’s decision to add the chemical to the Prop 65 list.

Many Dow Chemical products also contain glyphosate.

The U.S. Food and Drug Administration is currently testing four crops for glyphosate and several other acid herbicide chemical residues.

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An FDA spokeswoman told CBS San Francisco on Friday that a special assignment testing for glyphosate residues in soybeans, corn, milk, and eggs began in 2016, and after a months-long hiatus, resumed last month.

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In California, companies aren’t yet required to label products containing the chemical as carcinogenic, as a lawsuit filed by Monsanto against the state’s Office of Environmental Health Hazard Assessment is still pending.

For now, products containing glyphosate remains on store shelves and in homes across California, without warning labels.

Californians who no longer wish to use the product or store it in their homes can return the product to the store where they bought it.

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ScottsMiracle-Gro, the distributor of Monsanto’s Roundup, says consumers can return their products, no questions asked, and receive a refund.