California's Office of Environmental Health Hazard Assessment filed a Notice of Intent on October 9, 2026, to add atrazine to the state's Proposition 65 list of chemicals known to cause cancer. A 30-day public comment period runs through November 9, 2026.
The filing is a Notice of Intent to List Chemicals by the Labor Code Mechanism, published on the OEHHA Proposition 65 website. California's Labor Code mechanism requires the state to list any chemical that the International Agency for Research on Cancer has classified as a known or probable human carcinogen. IARC placed atrazine in Group 2A, meaning probable evidence of carcinogenicity in humans. That classification is the sole basis for the California action; the state is not conducting an independent hazard review.
Atrazine is one of the most widely used herbicides in the United States, applied primarily to corn, sorghum, and sugarcane fields. A Prop 65 listing will require businesses to warn California consumers when exposure to atrazine may exceed a safe harbor threshold. It does not ban atrazine. The federal EPA maximum contaminant level for atrazine in drinking water remains 3 parts per billion.
A note on the underlying science: the EPA's most recent dietary and drinking water assessment for atrazine found no risks of concern at regulated exposure levels. The difference between IARC's finding and EPA's reflects methodology, not a factual disagreement. IARC asks whether a chemical can cause cancer under any exposure conditions. The EPA asks whether realistic exposures produce measurable harm. Proposition 65's Labor Code mechanism follows IARC, not EPA's dose-based analysis. Both positions are worth knowing when you read news coverage of this action.
Atrazine is the second most commonly detected pesticide in U.S. drinking water. The exposure picture is geographically specific: agricultural runoff carries the herbicide from farm fields into rivers, reservoirs, and aquifers that supply municipal systems in Illinois, Iowa, Nebraska, Kansas, and Missouri. Rural well owners in the corn and sorghum belt face the most direct route of exposure. Households served by systems fed by mountain snowpack or non-agricultural groundwater are unlikely to be affected.
Your water utility is required to publish an annual Consumer Confidence Report listing detected contaminants and their measured levels. The Environmental Working Group's Tap Water Database maps detections nationally, often including data that utilities report even when readings fall below the federal limit. For households in agricultural regions that want additional reduction: filters certified to NSF/ANSI 53 are independently verified to reduce atrazine. If you are shopping right now, the product directory is filtered against the criteria this action calls out; our water filter guide covers pitcher, under-sink, and whole-home options.
Cover image: RDNE Stock project via Pexels (Pexels License). Source.
