2024 Theses Doctoral

Particulate air pollution and effects on cardiovascular health in American Indian communities

Li, Mengyuan

Fine particulate matter (PM2.5) exposure is associated with increased risk of adverse cardiovascular health outcomes. Prior research shows that PM2.5 is disproportionately concentrated in communities of low socioeconomic status and with higher proportions of underrepresented ethnic and racial groups. However, little is known about the levels and trends in PM2.5 in American Indian (AI) communities. Prior work has estimated the risk of CVD outcomes from exposure to total PM2.5 and PM2.5 constituents in white, Black, Asian, and Hispanic populations; however, AI populations have been historically excluded from many of these studies. While certain behavioral and environmental CVD risk factors have been extensively studied in AI populations, the CVD health impacts of air pollution have not been previously characterized.

In Chapter 2, we aimed to compare PM2.5 concentrations in AI- vs. non-AI-populated counties over time (2000 – 2018) in the contiguous US. We used a multi-criteria approach to classify counties as AI- or non-AI-populated. We ran linear mixed-effects models to estimate the difference in county-wide annual PM2.5 concentrations from monitoring sites and well-validated prediction models (measured and modeled PM2.5, respectively) in AI- vs. non-AI-populated counties, adjusting for population density and median household income. We estimated whether differences in AI- vs. non-AI-populated counties varied over time using interaction terms with calendar year. On average, adjusted measured PM2.5 concentrations in AI-populated counties were 0.79 μg/m3 (95%CI: 0.33, 1.26) lower than in non-AI-populated counties. However, this association was not constant over time; while in 2000, adjusted concentrations in AI-populated counties were 1.83 μg/m3 (95%CI: 1.53, 2.13) lower, by 2018, they were 0.84 μg/m3 (95%CI: 0.53, 1.15) higher than in non-AI-populated counties. Over the study period, measured PM2.5 mean concentrations in AI-populated counties decreased by 2.49 vs. 5.18 μg/m3 in non-AI-populated counties. Results were similar for satellite-based, modeled PM2.5. This study highlights disparities in PM2.5 trends between AI- and non-AI-populated counties over time, underscoring the need to strengthen air pollution regulations in tribal territories and areas where AI populations live.

In Chapter 3, we further interrogate what components of PM2.5 could be contributing to the trends in total PM2.5. We estimated that adjusted concentrations of all six PM2.5 components in AI-populated counties were significantly lower than in non-AI-populated counties. However, component-specific trends varied over time. Sulfate and ammonium levels were significantly lower in AI- vs. non-AI-populated counties in 2000 but higher after 2011. Nitrate levels were consistently lower in AI- counties, while black carbon, organic matter, and soil levels showed inconsistent differences in AI- vs. non-AI-populated counties. This study highlights how differences in time trends of certain components by AI-populated county type, namely sulfate and ammonium, are driving steeper declines in total PM2.5 in non-AI vs. AI-populated counties, providing potential directives for air pollution regulations of key emissions sources on tribal and AI-populated lands.

In Chapter 4, we estimated the effects of long-term PM2.5 exposure on CVD incidence, CVD mortality, and all-cause mortality in the Strong Heart Study (SHS), a longitudinal cohort of American Indian adults enrolled from centers in Arizona, Oklahoma, and North Dakota and South Dakota. We followed 2,115 participants from 2000–2019. Adjusted hazard ratios (95%CI) per 1μg/m3 increase in PM2.5 with CVD incidence, CVD mortality, and all-cause mortality were 1.09 (0.91, 1.30), 1.11 (0.91, 1.36), and 1.10 (0.96, 1.25), respectively. Center-specific models identified positive associations between PM2.5 and incident CHD (2.24 (1.40, 3.56)) and CVD (1.55 (1.05, 2.31)) in Arizona, marginally positive association between PM2.5 and CVD mortality in Oklahoma (1.29 (0.99, 1.68)), and null associations in North Dakota and South Dakota. This study assesses PM2.5 exposure and cardiovascular health effects in American Indian communities—addressing a critical gap in the representation of evidence in air pollution regulation. Further research on underlying mechanisms driving the unique associations observed across regions is needed.