Exposure to Unconventional Oil and Gas Development and All-cause Mortality in Medicare Beneficiaries

Abstract

BACKGROUND AND AIM: Wide-scale adoption of Unconventional Oil and Gas Development (UOGD) has changed the domestic and global energy landscape. However, little is known about whether and how UOGD impact all-cause mortality. METHODS: We used an open cohort design and Cox Proportional Hazard model to estimate the relative risk of mortality associated with living proximity and downwind to UOGD. The study region of this population-based research includes all counties within major UOGD production areas in the conterminous United States. We studied 15,198,496 Medicare beneficiaries (N=136,215,059 person-years) in the study region from 2001 to 2015. We obtained records for more than 2.5 million oil and gas wells from Enverus™. For each person-year, we calculated proximity-based exposure (PE) to UOGD and categorized PE into four levels from high to low. To isolate the impact contributed by UOGD-related air pollutants, we calculated the proportion of PE contributed by upwind wells, defined as downwind exposure (DE) to UOGD. Each PE level was dichotomized into downwind and upwind sub-levels (DE+ and DE-) accordingly. Due to the independence of wind direction on potential confounders, the estimated associations are less vulnerable to unobserved confounding bias. RESULTS:High PE level was associated with a statistically significant increase in mortality risk compared to the unexposed group (hazard ratio [HR], 1.025; 95% confidence interval [CI], 1.021 to 1.029). Within high PE, the HR associated with DE+ is 1.031 (95% CI 1.025 to 1.037), significantly higher than that associated with DE- (HR 1.022, 95% CI, 1.016 to 1.027), when both are compared to the same unexposed group. CONCLUSIONS:Exposure to UOGD, characterized by PE and DE, is statistically significantly associated with an increased mortality risk in Medicare beneficiaries. The wind-dependent difference in the health effects indicates that air pollution sourced from UOGD is one of the exposure pathways. KEYWORDS: Long-term exposure, Mixtures, Multi-pollutant/Multi-media, Mortality.