UC Santa Barbara

The broad question examined in this dissertation is how environmental exposures shape the risk of Alzheimer’s disease and related dementias (ADRD). More specifically, this dissertation investigates socio-environmental inequalities, phthalate exposure, and air pollution as determinants of cognitive aging across multiple geographic and biological scales, drawing on methods from spatial epidemiology, environmental health, biomarker development, and population health research. Chapter 1 uses linked Panel Study of Income Dynamics (PSID), EPA Toxic Release Inventory (TRI), and U.S. Census data to examine whether long-term exposure to emissions from plastics and rubber manufacturing facilities is associated with ADRD risk in the United States. Using longitudinal modeling and logistic regression, this chapter finds that higher emissions intensity from plastics and rubber-related facilities is associated with increased ADRD risk, independent of individual socioeconomic characteristics and neighborhood disadvantage. Neighborhood disadvantage also emerges as a strong independent predictor of ADRD risk, underscoring the importance of structural and environmental determinants of cognitive aging. Chapter 2 develops a laboratory method for detecting phthalates in human fecal samples (n=10) using ultra-high-performance liquid chromatography-mass spectrometry (UPLC-MS), with data from the Microbiome in Alzheimer's Risk Study (MARS). This chapter demonstrates that phthalates are detectable in human fecal samples and establishes a proof-of-concept for using fecal biomarkers in environmental exposure research, laying the groundwork for future studies examining relationships among phthalate exposure, gut microbiome function, and cognitive health outcomes. Chapter 3 investigates air pollution and cognitive health within an under-resourced population in Lima, Peru using secondary door-to-door survey data (n=1,066) paired with PurpleAir and OpenStreetMap data. This chapter examines the feasibility of integrating citizen-science air pollution monitoring with community-based cognitive health research in a region with limited environmental monitoring infrastructure. While no significant associations were observed between PM2.5 and cognitive outcomes, uniformly high exposure levels and limited within-population exposure variation likely complicate detection of exposure-response gradients. Secondary findings suggest that roadway proximity may reflect both pollution exposure and improved access to transportation, healthcare, social engagement, and socio-economic status, highlighting the complexity of disentangling environmental risks in urban, low-and-middle-income contexts. This chapter also underscores persistent data gaps in cognitive health and environmental research in LMICs. Together these chapters demonstrate that environmental exposures, from industrial emissions to chemical pollutants to air quality, are unequally distributed and may contribute to disparate ADRD risk across populations and geographies. This dissertation advances interdisciplinary methods for studying environmental contributors to cognitive aging and points to the need for more equitable environmental and public health policy.