Compound Events and Exposure Science: Characterizing Mixtures and Assessing Cumulative Risks Using Participatory Research Methods

Abstract

Environmental justice (EJ) communities face disproportionate contaminant exposure due to systemic inequities, industrial proximity, and inadequate regulatory protections, with climate change further exacerbating these risks. This work explored environmental exposure in a diverse range of environmental justice communities, including border, mining and urban communities. This dissertation employed a transdisciplinary, multi-contaminant, and multi-media approach to assess environmental exposures, integrating environmental monitoring, chemical mixture analysis, climate-driven exposure pathways, and community-based research. Rather than focusing on a single pollutant, it examined metal(loid)s, per- and polyfluoroalkyl substances (PFAS), polycyclic aromatic hydrocarbons (PAHs), and dioxins across soil, rooftop-harvested rainwater, settled dust, and drinking water, providing a comprehensive understanding of contaminant distribution, transport, and human exposure pathways. Therefore, this work utilized a systems thinking approach to understand the interconnectedness between contaminants, communities, climate change and the environment. The first study applied a community-engaged research approach to assess metal(loid) contamination in drinking water sources along the Arizona-Mexico border, a region experiencing severe climate change impacts, including prolonged droughts, extreme heat, reduced groundwater recharge, and intensified monsoon flooding. These challenges are further compounded by the complexities of binational environmental management, affecting water quality, availability, and long-term sustainability. Therefore, residents rely on pipas (water trucks), private wells, and public water systems. This study used the Social Determinants of Health (SDOH) framework to examine the relationships between measured contaminant levels, water source types, and public perceptions of water quality. Although most drinking water samples met regulatory limits in this study, arsenic and lead concentrations exceeded the maximum contaminants level goals. Additionally, the study finds that perceptions of water quality often do not align with measured contamination levels, indicating a need for improved risk communication strategies and increased public health interventions. The second study employed a co-created community science approach to examine PFAS contamination in a mining-impacted EJ community affected by wildfires and post-fire flooding. This study evaluates potential PFAS release from mining operations, while assessing the role of extreme climate events in contaminant redistribution. Soil samples from flood-affected residential areas had significantly elevated PFAS concentrations, suggesting that wildfire and flood events facilitate contaminant transport. These findings highlight the importance of long-term monitoring and the need for regulatory strategies that account for climate-driven remobilization of persistent pollutants. The third study continued the work from the previous co-created community science study and applies cumulative risk assessment methodologies to evaluate co-exposure to PAHs, dioxins, and PFAS in post-wildfire and flood-affected soils and indoor dust. Using Monte Carlo-based probabilistic risk modeling, this study quantifies both carcinogenic and non-carcinogenic risks associated with chemical mixtures in an EJ community. The results show that PAHs contribute the most to estimated cancer risks, largely due to their release from wildfires, which generate combustion byproducts that accumulate in soils and dust, and flooding, which remobilizes PAHs from contaminated industrial sites, roadways, and degraded infrastructure. Meanwhile, PFAS contributed the most to the non-carcinogenic hazard indices. This study highlights the limitations of single-chemical risk assessments and demonstrates the necessity of mixture-based exposure models to better characterize environmental health risks. Given the complex interactions between contaminants, the use of Toxic Equivalency Factors (TEFs) is essential for evaluating the combined toxicity of as different compounds within the same chemical class exhibit varying degrees of toxicity. The fourth study used co-created community science data to investigates metal(loid)s contamination in rooftop-harvested rainwater (RHRW) in four Arizona EJ communities using the Pollution Load Index (PLI) to quantify cumulative contamination. Results indicate that mining-impacted communities had the highest contamination levels, with monsoon season contributing to increased metal(loid) deposition through atmospheric transport and surface runoff. The findings emphasize the need for enhanced regulatory oversight and public health guidance to ensure the safe use of harvested rainwater in water-insecure regions. This dissertation advances environmental exposure science by integrating cumulative risk assessment, climate-responsive exposure models, and community-based participatory research. By characterizing the distribution and health risks of complex contaminant mixtures in EJ communities, this work provides critical data for improving environmental health assessments and policy decisions. The findings support the development of adaptive regulatory frameworks that incorporate climate change considerations and emphasize the importance of community-engaged research in shaping public health interventions. Future research should build on these findings to refine exposure models, improve mixture-based risk assessment methodologies, and develop targeted mitigation strategies that reduce environmental health disparities in vulnerable populations.