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Background Differential risks for adverse pregnancy outcomes may be influenced by prenatal chemical exposures, but current exposure methods may not fully capture data to identify harms and differences. Methods We collected maternal and cord sera from pregnant people in Fresno and San Francisco, and screened for over 2420 chemicals using LC-QTOF/MS. We matched San Francisco participants to Fresno participants (N = 150) and compared detection frequencies. Twenty-six Fresno participants wore silicone wristbands evaluated for over 1500 chemicals using quantitative chemical analysis. We assessed whether living in tracts with higher levels of pollution according to CalEnviroScreen correlated with higher numbers of chemicals detected in sera. Results We detected 2167 suspect chemical features across maternal and cord sera. The number of suspect chemical features was not different by city, but a higher number of suspect chemicals in cosmetics or fragrances was detected in the Fresno versus San Francisco participants’ sera. We also found high levels of chemicals used in fragrances measured in the silicone wristbands. Fresno participants living in tracts with higher pesticide scores had higher numbers of suspect pesticides in their sera. Conclusions Multiple exposure-assessment approaches can identify exposure to many chemicals during pregnancy that have not been well-studied for health effects.

BACKGROUND While research has shown that small community water systems in the San Joaquin Valley, an agricultural region in California, experience a disproportionate amount of drinking water contamination, little is known about the extent of contamination in other California regions. Additionally, state-wide research on drinking water contamination in areas not served by community water systems (mostly private domestic well users) and research comparing contamination across system size are also limited.METHODS Using a novel method to assign drinking water and groundwater contaminant data to community water system service areas and areas outside of service area boundaries, we conducted a spatial analysis to estimate concentrations of thirteen contaminants and two drinking water standard violations by system size and California region. We developed a cumulative ranking method to evaluate which regions or system size category are most burdened by multiple drinking water pollutants. A trend test was also used to evaluate the influence of system size on contaminant concentrations.RESULTS The San Joaquin Valley, areas not served by community water systems, and small water systems had the highest cumulative rank for multiple high contaminant concentrations, most notably arsenic and nitrate. Large systems and the South Coast region, which includes Los Angeles, had the highest levels of disinfection byproducts and industrial contaminants like tetrachloroethylene. Violations, arsenic, lead, and cadmium had negative trends as system size increased (p