Glyphosate weed killer
Glyphosate is the herbicide active in Monsanto Co.’s Roundup weedkiller.

SACRAMENTO, CALIF. — The California Environmental Protection Agency’s Office of Environmental Health Hazard Assessment (OEHHA) said glyphosate, the herbicide active in Monsanto Co.’s Roundup weedkiller, was being added to California’s Proposition 65 list of chemicals the state says are known to cause cancer.

The OEHHA said the effective date of the listing will depend on the outcome of a request for a stay in the case Monsanto v OEHHA in Fresno County Superior Court that challenges OEHHA’s ability to list the chemical on California’s Proposition 65 list. OEHHA said the trial court ruled in its favor, but Monsanto is appealing the decision and asking the court to issue a stay that would block the listing while the appeal is pending. OEHHA said it continued to oppose Monsanto’s efforts to delay the listing of glyphosate on the Proposition 65 list.

OEHHA said glyphosate was being added to the list of carcinogens because the World Health Organization’s International Agency for Research on Cancer (IARC) identified the herbicide as causing cancer in animals. Proposition 65 requires that certain chemicals identified as cancer-causing by IARC be added to the list.

Monsanto has consistently maintained that glyphosate is not a carcinogen and has typically hit back at efforts to define it as such. The company’s patent protection of its Roundup product expired in 2000, and other manufacturers have developed their own products using glyphosate as an herbicide. China now is the largest producer of glyphosate worldwide.

OEHHA said Proposition 65 is a “right-to-know” law initially approved by California voters in 1986. The state maintains a list of chemicals known to cause cancer, birth defects or other reproductive harm. While not banning or restricting the listed chemicals outright, Proposition 65 requires businesses to provide warnings of risk from the listed chemicals as well as barring discharges of any of the chemicals into drinking water.