Association between exposure to PM2.5 components and disease aggravation in amyotrophic lateral sclerosis: an analysis in New York State

Abstract

BACKGROUND AND AIM: In a previous study we found that long-term exposure to fine particle matter (PM2.5) may contribute to disease aggravation in amyotrophic lateral sclerosis (ALS). However, PM2.5 is a heterogeneous mixture of particles whose composition changes over time and space. In this study, we examined the association between ALS disease aggravation and long-term exposure to specific PM2.5 components. Our study brings insight into whether PM2.5 composition influences its toxicity and shed light into potentially relevant pollution sources. METHODS: We used data from the New York Department of Health Statewide Planning and Research Cooperative System (2000–2014) to construct annual county counts of first hospitalizations with an ALS diagnosis. We used well-validated prediction models at 1km2 resolution to estimate county-level population-weighted annual concentrations of six PM2.5 components: black carbon, organic matter, nitrate, sulfate, sea salt, and soil. Exposure was assigned based on county of residence. We used mixed quasi-Poisson models with county-specific random intercepts to estimate rate ratios (RRs) and 95% confidence intervals (CI) for a 1-year exposure to each PM2.5 component. We allowed for nonlinear exposure–outcome relationships using penalized splines and accounted for potential geospatial and temporal confounders. RESULTS:On average, nitrate and organic matter constituted most of the total PM2.5 mass, 35 and 31% respectively. Sulfate had the strongest correlation with PM2.5 with a Spearman correlation coefficient of 0.88. We found a linear positive association between one-year exposure to organic matter and disease aggravation in ALS (RR=1.20, 95%CI: 1.13, 1.27 per one standard deviation increase). We found no association between the outcome and nitrate, sulfate, sea salt, or soil exposure. CONCLUSIONS:Our results suggest that PM2.5 adverse effects on ALS may vary by particle composition, and we identified organic matter as a potentially relevant PM2.5 component. KEYWORDS: Neurodegenerative diseases, air pollution, particle components, long-term exposures, disease aggravation, ALS