People’s exposure to toxic chemicals declined in the U.S. following listing under California law

With growing concern about the ubiquity of toxic chemicals in consumer products, many states have passed laws aimed at protecting people from harmful substances in everyday items like cosmetics, cleaning supplies, plastics, and food packaging. California’s Proposition 65, for instance, is considered one of the most extensive toxics laws in the country.

But does the law work? According to a new study published in the journal Environmental Health Perspectives, it does.

“Not only have people’s exposures to specific toxic chemicals gone down in California, but we also see exposures going down across the country driven in part by Proposition 65,” says lead author Kristin Knox, a research scientist at Silent Spring Institute.

The study’s findings could help inform policies and programs to further curb the use of toxic chemicals in products as well as new research on how regulations and the marketplace influence people’s exposures.

Under Proposition 65, or Prop 65, the state of California maintains a list of more than 850 chemicals known to cause cancer, birth defects, or reproductive harm. Companies that sell products in California are required to warn consumers if their products expose them to harmful amounts of the chemicals.

“We know Prop 65 has helped increase public awareness of risky chemicals and encouraged businesses to reformulate their products with safer ingredients,” says Knox. “But have exposures to toxic chemicals decreased as a result? That’s been a key question.”

Working in collaboration with researchers at the University of California, Berkeley, Knox pulled data from the U.S. National Health and Nutrition Examination Survey (NHANES). Every year, the federal program collects health data from adults and children around the country. The program also collects people’s blood and urine samples and tests them for synthetic chemicals and pollutants.

The researchers analyzed data for 37 biomonitored chemicals through NHANES, including 26 listed under Prop 65 (the remaining 11 were not listed). The analysis showed that, for the majority of the chemicals, levels in people’s bodies went down both in California and nationwide in the years following the chemicals’ listing.

“This aligns with what we’ve learned by interviewing companies,” says Knox. “When companies reformulate their products to avoid Prop 65 chemicals, they end up doing that for all their products, not just those sold in California.”

Exposures to several unlisted chemicals also went down, suggesting other factors at play, the researchers note. For instance, chemicals included in NHANES’ biomonitoring program are chosen because they raise health concerns and therefore may already be subject to pressure from federal regulations, policies, or consumer campaigns that target specific chemicals.

Overall, people in California had a lower body burden than the general population. Levels of 18 of the 37 biomonitored chemicals were lower in California compared with the rest of the U.S. These included diesel-related chemicals, as well as several phthalates, BPA, and PFAS.

The lower levels may reflect increased local press coverage around Prop 65 enforcement and litigation, leading more people in the state to avoid products with harmful ingredients. California’s strict diesel emissions standards likely accounted for the lower exposures to chemicals from diesel exhaust, the researchers note.

“Our finding that Californians are generally less exposed to toxic chemicals than are other Americans has potentially far-reaching implications. It suggests a tangible public health payoff from the state's more stringent environmental regulations,” says co-author Claudia Polsky, Director of the Environmental Law Clinic at UC Berkeley School of Law. “We hope other researchers will probe this issue further so we can better understand which regulations work, and why.”

The study found evidence of companies swapping out one toxic chemical, after its listing under Prop 65, for another problematic chemical with similar chemical structure and health effects. For instance, levels of BPA, which has been used in some plastic bottles, thermal receipt paper, and food can linings, decreased after the chemical was listed in 2013. Meanwhile, levels increased of its unlisted chemical cousin BPS.

Similarly, levels of the phthalate DEHP, used in vinyl and other plastic products, went down after it was listed in 2003. At the same time, exposures to a closely related unlisted phthalate called DiNP went up. Levels of DiNP then dropped after it was also listed in 2013.

The researchers say their findings highlight the need to increase investment in biomonitoring programs to track changes in people’s exposures to toxic chemicals in response to environmental policies. “We have relatively good national-level biomonitoring data, but NHANES isn’t designed to detect changes in chemical exposures driven by local or state-level policy,” says co-author Meg Schwarzman, a physician and environmental health scientist at the UC Berkeley School of Public Health.

“Policymakers could change this picture by better supporting both NHANES and state-level biomonitoring programs, as well as creating chemicals policies that require before-and-after testing to measure the policy’s effectiveness. This could really help identify interventions that actually reduce toxic exposures,” says Schwarzman.

Funding for this project was provided by the California Breast Cancer Research Program (Grant #23QB-1881) and payments that private litigants directed to Silent Spring Institute in lieu of civil penalties in Prop 65 enforcement cases to further the cause of toxics reduction and charitable contributions to Silent Spring Institute.

Reference: Knox, K.E., M.R. Schwarzman, R.A. Rudel, C. Polsky, and R.E. Dodson. 2024. “Trends in NHANES biomonitored exposures in California and the U.S. following enactment of California’s Proposition 65.” Environmental Health Perspectives. 132(10). DOI: 10.1289/EHP13956

About Silent Spring Institute: Silent Spring Institute, located in Newton, Mass., is the leading scientific research organization dedicated to uncovering the link between chemicals in our everyday environments and women's health, with a focus on breast cancer prevention. Founded in 1994, the institute is developing innovative tools to accelerate the transition to safer chemicals, while translating its science into policies that protect health. Visit us at www.silentspring.org.