Styrene exposure and neurologic effects in residents of the US Gulf States

Abstract

Styrene is an established neurotoxicant at occupational levels, but epidemiologic studies to date have focused on highly exposed workers. We examine whether neurologic effects are associated with styrene at environmental levels, and attempt to identify underlying sources of uniquely elevated exposure levels among Gulf coast residents. In Aims 1 and 2, we utilized data from the Gulf Long-term Follow-up Study and the nested Chemical Biomonitoring Study (CBS) to assess predictors of blood styrene levels (N = 667). In Aim 3, we estimated cross-sectional associations between ambient styrene exposure and neurologic symptoms (N = 21,962), as well as peripheral neurologic function (N = 2,956). Among CBS participants, we assessed blood styrene in relation to neurologic symptoms (N = 874) and peripheral neurologic function (N = 310). Ambient exposures were modeled as quartiles, and blood exposures were divided at the median or 90th percentile. We estimated prevalence ratios using log-binomial regression, and differences in continuous outcomes using linear regression. Blood styrene levels are 2-3 times higher in CBS compared to the U.S. general population. Smoking, housing characteristics, and recent behaviors were predictors of blood styrene levels. Neither ambient styrene concentrations nor industrial styrene emissions were determinants of blood styrene levels. The highest quartile of ambient styrene was associated with increased central (PR = 1.20, 95% CI: 1.09, 1.32) and peripheral (PR = 1.12, 95% CI: 1.02, 1.23) nervous system symptoms, as well as impairments in vision (mean difference = -0.15, 95% CI: -0.25, -0.04), vestibular (β = -4.65 mm/s, 95% CI: -8.20, -1.10), and sensory function (β = -0.12 log microns, 95% CI: -0.22, -0.01). We observed statistically significant monotonic exposure-response relationships between ambient styrene concentration and many neurologic endpoints. The relationship was less clear for blood styrene exposure, with some suggestive effects. Personal predictors of increasing blood styrene levels were largely consistent with previous literature. Our measures of increased regional exposure opportunity do not fully explain these elevated blood styrene levels. Increasing ambient styrene exposures elicited consistent neurotoxic effects, as well as some notable associations with measured blood styrene. Environmental styrene exposure levels may be sufficient to elicit subclinical neurotoxic effects.Doctor of Philosoph