Environmental styrene exposure and neurologic symptoms in U.S. Gulf coast residents

Abstract

Background: Styrene is an established neurotoxicant at occupational levels, but effects at levels relevant to the general population have not been studied. We examined the neurologic effects of environmental styrene exposure among U.S. Gulf coast residents.

Methods: We used National Air Toxics Assessment (NATA) 2011 estimates of ambient styrene concentrations to assign exposure levels for 21,962 non-diabetic Gulf state residents, and additionally measured blood styrene concentration in a subset of participants (n = 874). Neurologic symptoms, as well as detailed covariate information, were ascertained via telephone interview. We used log-binomial regression to estimate prevalence ratios (PR) and 95% confidence intervals (95% CI) for cross-sectional associations between both ambient and blood styrene levels and self-reported neurologic symptoms. We estimated associations independently for ten unique symptoms, as well as for the presence of any neurologic, central nervous system (CNS), or peripheral nervous system (PNS) symptoms. We also examined heterogeneity of associations with estimated ambient styrene levels by race and sex.

Results: One-third of participants reported at least one neurologic symptom. The highest quartile of estimated ambient styrene was associated with one or more neurologic (PR, 1.12; 95% CI: 1.07,1.18), CNS (PR, 1.17; 95% CI: 1.11,1.25), and PNS (PR, 1.16; 95% CI: 1.09,1.25) symptom. Results were less consistent for biomarker analyses, but blood styrene level was suggestively associated with nausea (PR, 1.78; 95% CI: 1.04, 3.03). In stratified analyses, we observed the strongest effects among non-White participants.

Conclusions: Increasing estimated ambient styrene concentration was consistently associated with increased prevalence of neurologic symptoms. Associations between blood styrene levels and some neurologic symptoms were suggestive. Environmental styrene exposure levels may be sufficient to elicit symptomatic neurotoxic effects.

Keywords: Air pollution; Biomarker; Nervous system; Neurologic; Styrene.

Figure 1.

Probability density of styrene concentrations in air (N=21,962) and blood (N=874). Ambient styrene concentrations are National Air Toxics Assessment (NATA) 2011 modeled estimates of annual average concentrations (µg/m³) at the census tract level. Blood styrene exposure concentrations (ng/mL) are measured from a single blood draw obtained in the participant’s home. Values at the top of reference lines indicate exposure concentrations; labels at the bottom of reference lines indicate locations in the exposure distribution: P25, 25^th percentile; P50, 50^th percentile; P75, 75^th percentile; P90, 90^th percentile; P95, 95^th percentile; Max, maximum value.

Figure 2.

Associations between estimated ambient styrene concentration and neurologic symptom clusters (N=21,962). Models adjusted for sex, age, season, race, education, employment status at enrollment, alcohol drinking status at enrollment, and smoking status at enrollment. Estimated ambient styrene quartiles are based on National Air Toxics Assessment (NATA) 2011 estimates of annual average concentrations at the census tract level; referent group is the lowest quartile (not shown on figure). Q2, second quartile; Q3, third quartile; Q4 fourth (highest) quartile. CNS symptoms include: dizziness, headache, nausea, sweating, and palpitations. PNS symptoms include: tingling/numbness, blurred vision, and stumbling.

Figure 3.

Associations between estimated ambient styrene concentration and neurologic symptom clusters, stratified by race (N=21,962). Models adjusted for sex, age, season, education, employment status at enrollment, alcohol drinking status at enrollment, and smoking status at enrollment. Estimated ambient styrene quartiles are based on National Air Toxics Assessment (NATA) 2011 estimates of annual average concentrations at the census tract level; referent group is the lowest quartile (not shown on figure). Q2, second quartile; Q3, third quartile; Q4 fourth (highest) quartile. CNS symptoms include: dizziness, headache, nausea, sweating, and palpitations. PNS symptoms include: tingling/numbness, blurred vision, and stumbling.