Trends in NHANES Biomonitored Exposures in California and the United States following Enactment of California's Proposition 65

Abstract

Background: The prevalence of toxic chemicals in US commerce has prompted some states to adopt laws to reduce exposure. One with broad reach is California's Proposition 65 (Prop 65), which established a list of chemicals that cause cancer, developmental harm, or reproductive toxicity. The law is intended to discourage businesses from using these chemicals and to minimize consumer exposure. However, a key question remains unanswered: Has Prop 65 reduced population-level exposure to the listed chemicals?

Objective: We used national biomonitoring data from the Centers for Disease Control and Prevention (CDC) to evaluate the impact of Prop 65 on population-level exposures.

Methods: We evaluated changes in blood and urine concentrations of 37 chemicals (including phthalates, phenols, VOCs, metals, PAHs, and PFAS), among US National Health and Nutrition Examination Survey (NHANES) participants in relation to the time of chemicals' Prop 65 listing. Of these, 11 were listed prior to, 11 during, and 4 after the biomonitoring period. The remaining 11 were not listed but were closely related to a Prop 65-listed chemical. Where biomonitoring data were available from before and after the date of Prop 65 listing, we estimated the change in concentrations over time for Californians compared with non-Californians, using a difference-in-differences model. We used quantile regression to estimate changes in exposure over time, as well as differences between Californians and non-Californians at the 25th, 75th, and 95th percentiles.

Results: We found that concentrations of biomonitored chemicals generally declined nationwide over time irrespective of their inclusion on the Prop 65 list. Median bisphenol A (BPA) concentrations decreased 15% after BPA's listing on Prop 65, whereas concentrations of the nonlisted but closely related bisphenol S (BPS) increased 20% over this same period, suggesting chemical substitution. Californians generally had lower levels of biomonitored chemicals than the rest of the US population.

Discussion: Our findings suggest that increased scientific and regulatory attention, as well as public awareness of the harms of Prop 65-listed chemicals, prompted changes in product formulations that reduced exposure to those chemicals nationwide. Trends in bisphenols and several phthalates suggest that manufacturers replaced some listed chemicals with closely related but unlisted chemicals, increasing exposure to the substitutes. Our findings have implications for the design of policies to reduce toxic exposures, biomonitoring programs to inform policy interventions, and future research into the regulatory and market forces that affect chemical exposure. https://doi.org/10.1289/EHP13956.

Figure 1.

Estimated change (range shows 95% confidence interval) in natural-logged chemical concentrations from pre- to post-Prop 65–listing, for Californians and non-Californians, for the 25th, 75th, and 95th percentiles of the distribution, based on quantile regression models, controlling for demographics, creatinine for chemicals measured in urine, and cotinine for chemicals associated with smoking. Chemicals are those listed on Prop 65 during the biomonitoring period. Underlying data for the figure is contained in Excel Table S2, “Figure 1 Supporting Data” tab. Note: AAMA, $n$-acetyl-$S$-(2-carbamoylethyl)-l-cysteine; ATCA, 2-aminothiazoline-4-carboxylic acid; BBP, benzylbutyl phthalate; BPA, bisphenol A; CA, Californian; DEHP, di(2ethylhexyl) phthalate; DIDP, diisodecyl phthalate; DINP, diisononyl phthalate; DnBP, di-$n$-butyl phthalate; MBzP, monobenzyl phthalate; MCNP, mono(carboxynonyl) phthalate; MCOP, mono(carboxyoctyl) phthalate; MEHHP, mono-(2-ethyl-5-hydroxyhexyl) phthalate; MnBP, mono-$n$-butyl phthalate; Non, non-Californian; Prop 65, Proposition 65.

Figure 2.

Biomonitored concentrations, for the United States as a whole, for chemicals listed on Prop 65 during the biomonitoring period. NHANES cycle is listed along the x-axis. Box plots represent 5th (lower whisker), 25th (bottom of box), 50th (dark center line), 75th (top of box), and 95th (upper whisker) percentiles of the nationally representative, publicly available data. For chemicals measured in urine, concentrations shown are creatinine-adjusted. Dashed pink line corresponds to the Prop 65 listing date. Underlying data for the figure is contained in Excel Table S3, “Figure 2 Supporting Data” tab. Note: AAMA, $n$-acetyl-$S$-(2-carbamoylethyl)-l-cysteine; ATCA, 2-aminothiazoline-4-carboxylic acid; BBP, benzylbutyl phthalate; BPA, bisphenol A; DEHP, di(2ethylhexyl) phthalate; DiDP, diisodecyl phthalate; DINP, diisononyl phthalate; DnBP, di-$n$-butyl phthalate; MBzP, monobenzyl phthalate; MCNP, mono(carboxynonyl) phthalate; MCOP, mono(carboxyoctyl) phthalate; MEHHP, mono-(2-ethyl-5-hydroxyhexyl) phthalate; MnBP, mono-$n$-butyl phthalate; NHANES, National Health and Nutrition Examination Survey; Prop 65, Proposition 65.

Figure 3.

Biomonitored concentrations, for the United States as a whole, for chemicals listed before 1999 (start of NHANES data). NHANES cycle is listed along the x-axis. Box plots represent 5th (lower whisker), 25th (bottom of box), 50th (dark center line), 75th (top of box), and 95th (upper whisker) percentiles of the nationally representative, publicly available data for (A) non–diesel-related and (B) diesel-related chemicals. For chemicals measured in urine, concentrations shown are creatinine-adjusted. Underlying data for the figure is contained in Excel Tables S4 and S5, “Figure 3a Supporting Data” and “Figure 3b Supporting Data” tabs. Note: 2HPMA, n-acetyl-S-(2-hydroxypropyl)-L-cysteine; 3MHA, 3-methylhippuric acid; 4MHA, 4-methylhippuric acid; CYMA, $n$-acetyl-$S$-(2-cyanoethyl)-l-cysteine; DHBMA, $n$-acetyl-$S$-(3,4-dihidroxybutyl)-l-cysteine; MHBMA3, $n$-acetyl-$S$-(4-hydroxy-2-butenyl)-l-cysteine; NHANES, National Health and Nutrition Examination Survey; p-DCB, $p$-dichlorobenzene.

Figure 3.

Biomonitored concentrations, for the United States as a whole, for chemicals listed before 1999 (start of NHANES data). NHANES cycle is listed along the x-axis. Box plots represent 5th (lower whisker), 25th (bottom of box), 50th (dark center line), 75th (top of box), and 95th (upper whisker) percentiles of the nationally representative, publicly available data for (A) non–diesel-related and (B) diesel-related chemicals. For chemicals measured in urine, concentrations shown are creatinine-adjusted. Underlying data for the figure is contained in Excel Tables S4 and S5, “Figure 3a Supporting Data” and “Figure 3b Supporting Data” tabs. Note: 2HPMA, n-acetyl-S-(2-hydroxypropyl)-L-cysteine; 3MHA, 3-methylhippuric acid; 4MHA, 4-methylhippuric acid; CYMA, $n$-acetyl-$S$-(2-cyanoethyl)-l-cysteine; DHBMA, $n$-acetyl-$S$-(3,4-dihidroxybutyl)-l-cysteine; MHBMA3, $n$-acetyl-$S$-(4-hydroxy-2-butenyl)-l-cysteine; NHANES, National Health and Nutrition Examination Survey; p-DCB, $p$-dichlorobenzene.

Figure 4.

Biomonitored concentrations, for the United States as a whole, for chemicals not listed on Prop 65 as of the end of the biomonitoring period. NHANES cycle is listed along the x-axis. Box plots represent 5th (lower whisker), 25th (bottom of box), 50th (dark center line), 75th (top of box), and 95th (upper whisker) percentiles of the nationally representative, publicly available data. For chemicals measured in urine, concentrations shown are creatinine-adjusted. Underlying data for the figure is contained in Excel Table S6, “Figure 4 Supporting Data” tab. Note: BPS, bisphenol S; DEP, diethyl phthalate; DiBP, diisobutyl phthalate; MEP, monoethyl phthalate; MiBP, monoisobutyl phthalate; NHANES, National Health and Nutrition Examination Survey; N-MeFOSAA, 2-($N$-methyl-perfluorooctane sulfonamido)acetic acid; PFDA, pefluorodecanoic acid; PFHxS, perfluorohexane sulfonic acid; PFNA, perfluorononanoic acid; PFOA, perfluorooctanoic acid; PFOS, perfluorooctane sulfonic acid; Prop 65, Proposition 65.