Associations between airborne crude oil chemicals and symptom-based asthma

Abstract

Rationale: The 2010 Deepwater Horizon (DWH) oil spill response and cleanup (OSRC) workers were exposed to airborne total hydrocarbons (THC), benzene, toluene, ethylbenzene, o-, m-, and p-xylenes and n-hexane (BTEX-H) from crude oil and PM_2.5 from burning/flaring oil and natural gas. Little is known about asthma risk among oil spill cleanup workers.

Objectives: We assessed the relationship between asthma and several oil spill-related exposures including job classes, THC, individual BTEX-H chemicals, the BTEX-H mixture, and PM_2.5 using data from the Gulf Long-Term Follow-up (GuLF) Study, a prospective cohort of 24,937 cleanup workers and 7,671 nonworkers following the DWH disaster.

Methods: Our analysis largely focused on the 19,018 workers without asthma before the spill who had complete exposure, outcome, and covariate information. We defined incident asthma 1-3 years following exposure using both self-reported wheeze and self-reported physician diagnosis of asthma. THC and BTEX-H were assigned to participants based on measurement data and work histories, while PM_2.5 used modeled estimates. We used modified Poisson regression to estimate risk ratios (RR) and 95% confidence intervals (CIs) for associations between spill-related exposures and asthma and a quantile-based g-computation approach to explore the joint effect of the BTEX-H mixture on asthma risk.

Results: OSRC workers had greater asthma risk than nonworkers (RR: 1.60, 95% CI: 1.38, 1.85). Higher estimated THC exposure levels were associated with increased risk in an exposure-dependent manner (linear trend test p < 0.0001). Asthma risk also increased with increasing exposure to individual BTEX-H chemicals and the chemical mixture: A simultaneous quartile increase in the BTEX-H mixture was associated with an increased asthma risk of 1.45 (95% CI: 1.35,1.55). With fewer cases, associations were less apparent for physician-diagnosed asthma alone.

Conclusions: THC and BTEX-H were associated with increased asthma risk defined using wheeze symptoms as well as a physician diagnosis.

Keywords: Asthma; BTEX-H; Mixtures; Oil spills; Total hydrocarbons; Volatile organic compounds.

FIGURE 1.. Results from quantile g-computational BTEX-H mixture analysis with asthma risk.

a) Shows the marginal structural model (MSM) fit (dark gray) for the association between increasing mixture exposure quartiles and asthma risk. The x-axis represents quartiles of the BTEX-H mixture and the y-axis represents the log odds of asthma. b) Weight representing contribution to the mixture effect of each chemical component. When all components are considered together, the relative contribution of toluene, xylene, and n-hexane have the greatest contribution to the mixture effect. Coefficients for each chemical component from the underlying model are as follows: Benzene (Beta:−0.07, SE:0.08, p-value:0.36), Toluene (Beta:0.34, SE:0.08, p-value:1.60 × 10⁻⁵), Ethylbenzene (Beta:−0.11, SE:0.09, p-value: 0.23), Xylene (Beta:0.19, SE:0.08, p-value:0.02), n-Hexane (Beta:0.08, SE:0.06, p-value:0.20).