The ruling overturned a November 2020 decision by Alameda County Superior Court Judge Brad Seligman upholding the department’s continued approval of diphacinone without a new evaluation.

“If you have rodent traps around your yard, there’s a good chance you’re using it,” said Stephanie Safdi, a Stanford Law School teacher and attorney for Raptors Are the Solution, or RATS, the group that sued the state for a re-evaluation of the chemical. It is part of the environmental advocacy group Earth Island Institute.

Safdi said diphacinone’s anticoagulant ingredients, which kill rodents by preventing their blood from clotting, have the same effect on bobcats, coyotes, owls and other predators, and can affect humans who eat contaminated meats. “There are safe alternatives” that the state agency should evaluate, she said.

Safdi said the department could restrict the use of diphacinone, require warning labels and impose restrictions to protect children — or, if those measures are inadequate, prohibit its use in California.