California officials have long touted their pesticide regulations as the toughest in the nation. But a new report from the University of California, Los Angeles, reveals a major flaw in the state’s approach to evaluating safety, one that has broad implications for the way pesticides are regulated nationally: Regulators assess pesticide safety one product at a time, but growers often apply pesticides as mixtures. That’s a serious problem, the authors argue, because pesticide interactions can ratchet up toxic effects, greatly enhancing the risk of cancer and other serious health conditions.
“The federal EPA and California Department of Pesticide Regulation (DPR) have not adequately dealt with interactive effects,” says John Froines, a report coauthor and a chemist with decades of experience assessing health risks of toxic chemicals as a scientist and regulator. “People are exposed to a large number of chemicals. You can’t simply look chemical by chemical to adequately address the toxicity of these compounds.”
Fumigants, used to combat a range of pests and diseases, are among the most toxic chemicals used in agriculture. They are a staple of high-value crops like tomatoes and strawberries. Studies in humans and animals have linked them to acute respiratory and skin damage and serious chronic health problems, including cancer and neurological and reproductive disorders.
To get around the state’s failure to collect data on cumulative exposures to these fumigants, Froines and his colleagues drew on what’s known about the chemical and biological properties of three of the most heavily used fumigants in California: chloropicrin, Telone (the trade name for 1,3-dichloropropene), and metam sodium.
Individual fumigants are highly reactive chemicals that damage DNA and interfere with proteins that perform critical cell functions. Acting together, these effects multiply. So even pesticides that don’t cause cancer on their own might do so together by interfering with or overwhelming the body’s ability to clear toxic substances, or harming DNA and then blocking mechanisms to repair it.
These interactive effects would not be detected in studies of individual pesticides.
Pesticide regulators are aware of the report, says California DPR spokesperson Charlotte Fadipe, but adds that the agency rarely comments on such studies because “the information often lacks the extensive rigorous science for a regulatory department to make regulations.” What’s more, she notes, “DPR has the most protective and robust pesticide program in the country.”
Froines, who served as director of the Office of Toxic Substances at the Occupational Safety and Health Administration under President Jimmy Carter and has led several scientific review panels at the state’s request to assess chemical toxicity, has revealed flaws in pesticide regulations before. In 2010, he headed a California scientific review panel that deemed chloropicrin—one of the fumigants studied in the current report—a “potent carcinogen.” State officials ignored the panel’s advice and decided the evidence was ambiguous. The same year, he chaired another review panel that called the fumigant methyl iodide a “highly toxic chemical” that poses a serious threat to public health. This time, manufacturers withdrew the product from the market.