The Risk-Screening Environmental Indicators (RSEI) model estimates toxicity-weighted concentrations based on human health risks from modelled exposures to Toxic Release Inventory (TRI) chemicals. Numerous studies have reported on the inequitable distribution of TRI sites and pollutant exposures among minority and low-income populations, which may be leading to poorer health outcomes and contribute to health disparities. Population groups who are most susceptible to the untoward effects of pollutants are pregnant women and infants, with minority and poorer women at greatest risk. The goal of this research is to investigate maternal and infant health outcomes associated with TRI chemical exposures in Michigan from 2008-2017 from an environmental justice perspective using an ecosyndemic theoretical approach. The objectives of this research are: 1) To outline the ecosyndemic theoretical approach as a holistic lens by which to conceptualize maternal exposures to multiple toxic chemicals. 2) To investigate the spatial and temporal patterns and clusters of RSEI toxicity-weighted concentrations and the degree to which these human health risks are more elevated in minority and low-income communities. 3) Estimate the impact(s) of maternal exposure to RSEI toxicity-weighted concentrations on adverse birth outcomes, including lethal congenital anomalies, controlling for potential maternal level confounding variables. U.S. Census data was used to measure racial composition and poverty at the census tract level. The annual RSEI toxicity-weighted concentrations across census tracts were sub-divided into exposure quartiles and these were spatially and temporally assigned to each mother's pregnancy. The analyses were conducted using geographic information systems (GIS) and spatial epidemiological methods including cluster detection techniques. This study found that building upon the ecosyndemic framework the urban areas of Detroit and Grand Rapids were found to contain 80% of the census tracts with the highest RSEI toxicity-weighted concentrations. African Americans, Hispanics and residents living near and below poverty were most likely to live in these census tracts. These inequities persisted over time for African Americans living in Detroit and Grand Rapids and more recently for Hispanics living in Detroit, demonstrating on-going and emerging environmental injustices. Mothers exposed to the highest RSEI quartiles were at higher odds of low birth weight and preterm birth controlling for other known risk factors. The interactions between exposures to highest RSEI quartile and other behavioral and medical risks exacerbated the likelihood of these adverse birth outcomes. Finally, space-time analysis revealed several areas in Michigan with persistent clusters of lethal congenital anomalies. Clusters in Detroit and Muskegon that were in part explained by proximity to RSEI toxicity-weighted concentration values requires further investigation. Based on the study findings, recommendations include increased monitoring of TRI sites, incentivize companies to reduce their use of highly toxic chemicals and add additional environmental justice evaluations when approving new industrial facilities and targeting areas for pollution reduction, particularly census tracts in the highest RSEI quartile where mothers are at greatest risk of adverse birth outcomes. Future research should investigate possible interaction and mediating effects between chemical exposures and maternal behavioral and medical factors, further investigate the clusters of lethal birth defects in Michigan and investigate the upstream forces that contribute to environmental injustices and adverse birth outcomes in Michigan.
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