Environmental Styrene Exposure and Sensory and Motor Function in Gulf Coast Residents

Abstract

Background: Although styrene is an established neurotoxicant at occupational exposure levels, its neurotoxicity has not been characterized in relation to general population exposures. Further, occupational research to date has focused on central nervous system impairment.

Objective: We assessed styrene-associated differences in sensory and motor function among Gulf coast residents.

Methods: We used 2011 National Air Toxics Assessment estimates of ambient styrene to determine exposure levels for 2,956 nondiabetic Gulf state residents enrolled in the Gulf Long-term Follow-up Study, and additionally measured blood styrene concentration in a subset of participants 1 to 2 y after enrollment ([Formula: see text]). Participants completed an enrollment telephone interview and a comprehensive test battery to assess sensory and motor function during a clinical follow-up exam 2 to 4 y later. Detailed covariate information was ascertained at enrollment via telephone interview. We used multivariate linear regression to estimate continuous differences in sensory and motor function, and log-binomial regression to estimate prevalence ratios for dichotomous outcomes. We estimated associations of both ambient and blood styrene exposures with sensory and motor function, independently for five unique tests.

Results: Those participants in the highest 25% vs. lowest 75% of ambient exposure and those in the highest 10% vs. lowest 90% of blood styrene had slightly diminished visual contrast sensitivity. Mean vibrotactile thresholds were lower among those in the highest vs. lowest quartile of ambient styrene and the highest 10% vs. lowest 90% of blood styrene ([Formula: see text] log microns; 95% CI: [Formula: see text], [Formula: see text] and [Formula: see text] log microns; 95% CI: [Formula: see text], [Formula: see text], respectively). The highest vs. lowest quartile of ambient styrene was associated with significantly poorer postural stability, and (unexpectedly) with significantly greater grip strength.

Discussion: We observed associations between higher styrene exposure and poorer visual, sensory, and vestibular function, though we did not detect associations with reduced voluntary motor system performance. Associations were more consistent for ambient exposures, but we also found notable associations with measured blood styrene. https://doi.org/10.1289/EHP3954.

Figure 1.

Probability density of styrene concentrations in air ($N=\mathrm{2,956}$) and blood ($n=310$). Note: Ambient styrene exposure is 2011 National Air Toxics Assessment (NATA) modeled estimates of annual average concentrations ($\mathrm{\mu }\mathrm{g}/\mathrm{m}3$) at the census-tract level. Blood styrene concentrations (ng/mL) are measured from a single blood draw obtained in the participant’s home; limit of $\text{detection}=0.03\text{ng}/\mathrm{mL}$. Values at the top of reference lines indicate exposure concentrations; labels at the bottom of reference lines indicate locations in the exposure distribution: P25, 25th percentile; P50, 50th percentile; P75, 75th percentile; P90, 90th percentile; P95, 95th percentile. Max, maximum value.

Figure 2.

Ambient ($n=\mathrm{2,888}$) and blood ($n=307$) styrene concentrations and differences in vibrotactile threshold. Note: Symbol markers and labels indicate change in vibrotactile threshold multiplied by $-1$ (log microns); negative values reflect sensory deficits; error bars indicate 95% confidence intervals (CI). Models adjusted for gender, age, height, race, education, enrollment employment status, enrollment drinking status, and enrollment smoking status. Ambient styrene exposure is 2011 National Air Toxics Assessment (NATA) estimates of annual average concentrations (${\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$) at the census-tract level. Q1, first quartile (referent exposure group); Q2, second quartile; Q3, third quartile; Q4, fourth quartile. Blood styrene concentration (ng/mL): Top 10% vs. Lower 90%, compares measurements in the highest decile to the rest of the distribution; Q4 vs. Q1–Q3, compares measurements in the highest quartile to the rest of the distribution. Numeric data provided in Table S3.

Figure 3.

Ambient ($n=\mathrm{2,855}$) and blood ($n=299$) styrene concentrations and differences in standing steadiness. Symbol markers and labels indicate change in sway speed (mm/s) multiplied by $-1$; negative values reflect sensory deficits; error bars indicate 95% confidence intervals (CI). Models adjusted for gender, age, race, education, enrollment employment status, enrollment drinking status, and enrollment smoking status. Ambient styrene exposure is 2011 National Air Toxics Assessment (NATA) estimates of annual average concentrations (${\mathrm{\mu }\mathrm{g}/\mathrm{m}}^3$) at the census-tract level. Q1, first quartile; Q2, second quartile; Q3, third quartile; Q4, fourth quartile. Blood styrene concentration (ng/mL): Top 10% vs. Lower 90%, compares measurements in the highest decile to the rest of the distribution; Q4 vs. Q1-Q3, compares measurements in the highest quartile to the rest of the distribution. Numeric data provided in Table S3.