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Serosurveillance provides a unique opportunity to quantify the proportion of the population that has been exposed to pathogens. Here, we developed and piloted Serosurveillance for Continuous, ActionabLe Epidemiologic Intelligence of Transmission (SCALE-IT), a platform through which we systematically tested remnant samples from routine blood draws in two major hospital networks in San Francisco for SARS-CoV-2 antibodies during the early months of the pandemic. Importantly, SCALE-IT allows for algorithmic sample selection and rich data on covariates by leveraging electronic medical record data. We estimated overall seroprevalence at 4.2%, corresponding to a case ascertainment rate of only 4.9%, and identified important heterogeneities by neighborhood, homelessness status, and race/ethnicity. Neighborhood seroprevalence estimates from SCALE-IT were comparable to local community-based surveys, while providing results encompassing the entire city that have been previously unavailable. Leveraging this hybrid serosurveillance approach has strong potential for application beyond this local context and for diseases other than SARS-CoV-2.

The unexpectedly high affinity of microplastics (MPs) for heavy metals has attracted increasing attention in recent years. However, there is a scarcity of information on the effects of coexisting constituents on plastic–metal interactions, especially in terms of metal speciation. This study aimed to explore the role of benzophenone-type UV filters on the sorption, oxidation state, and toxicity of chromium (Cr) by pristine and UV-irradiated polystyrene MPs (PSMPs). Results showed that Cr uptake by PSMPs was remarkably higher when UV filters were present. This enhanced affinity was attributed to the formation of Cr–UV filter complexes together with multilayer sorption on PSMPs’ surfaces. Subsequent chemical state measurements indicated alteration of the oxidation state of MP-bound metals as a higher Cr­(VI) abundance was identified on the PSMPs with coexisting UV filters. More importantly, our toxicity assessments found that PSMP-bound Cr with a higher oxidation state displayed more severely inhibited microalgae growth. It is noteworthy that toxicological effects of Cr–UV filter complexes were observed only with PSMPs, which thus reaffirms the unique role of MPs in accumulating and transforming contaminants in natural environments. Overall, this study provides the first evidence into the effects of coexisting constituents on the oxidation states and toxicities of MP-bound heavy metals.