The U.S. Environmental Protection Agency was ordered by a federal appeals court on Friday to take a fresh look at whether glyphosate, the active ingredient in Bayer AG's Roundup weed killer, poses unreasonable risks to humans and the environment.

In a 3-0 decision, the 9th U.S. Circuit Court of Appeals agreed with several environmental, farmworker and food-safety advocacy groups that the EPA did not adequately consider whether glyphosate causes cancer and threatens endangered species.

The litigation began after the EPA reauthorized the use of glyphosate in January 2020.

Groups including the Natural Resources Defense Council, the Center for Food Safety and the Rural Coalition, which represents farmworkers, faulted the agency for rubber-stamping glyphosate despite its alleged harms to agriculture, farmers exposed during spraying, and wildlife such as the Monarch butterfly.

Circuit Judge Michelle Friedland wrote for the Pasadena, California-based appeals court that the EPA did not properly justify its findings that glyphosate did not threaten human health and was unlikely to be carcinogenic to humans. She also faulted aspects of the agency's approval process.

Bayer's Monsanto unit, which makes Roundup, opposed groups challenging the EPA reauthorization. Friday's decision does not prevent people from using Roundup or similar products.

An EPA spokeswoman said the agency will review the decision.

Bayer said the EPA conducted a "rigorous assessment" of more than 40 years of science, and believes that the agency will continue to conclude that glyphosate-based herbicides are safe and are not carcinogenic.

George Kimbrell, legal director of the Center for Food Safety, which represented the Rural Coalition, in an interview called the decision "a historic victory for farmworkers, the public and endangered species."

Bayer has faced tens of thousands of lawsuits claiming that Roundup causes cancer and other illnesses.

The U.S. Supreme Court is expected to decide soon whether to hear the German company's appeal of a $25 million damages award to Edwin Hardeman, a Roundup user who blamed his cancer on its weedkillers.

The cases are Natural Resources Defense Council et al v EPA, 9th U.S. Circuit Court of Appeals, No. 20-70787, and Rural Coalition et al v EPA et al in the same court, No. 20-70801.

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