Urinary t,t-muconic acid as a proxy-biomarker of car exhaust and neurobehavioral performance in 15-year olds

Abstract

Introduction: Traffic-related air pollution has been shown to induce neurotoxicity in rodents. Several recent epidemiological studies reported negative associations between residential outdoor air pollution and neurobehavioral performance. We investigated in a population of non-smoker adolescents the associations between the urinary concentration of trans,trans-muconic acid (t,t-MA-U), a metabolite of benzene and used as proxy-biomarker of traffic exposure, and two neurobehavioral domains: sustained attention and short-term memory. Methods: In the framework of an environmental health surveillance study in Flanders (Belgium), we examined between 2008 and 2014 grade nine high school students (n = 895). We used reaction time and number of omission errors in the Continuous Performance Test to evaluate sustained attention, and for the evaluation of short-term memory we used digit span forward and backward of the Digit Span Test. All estimates were adjusted for gender, age, passive smoking, the education level of the parents, time of the day, day of the week, and study period. The models for t,t-MA-U were additionally adjusted for blood lead and vice versa. Results: A ten-fold increase in t,t-MA-U was associated with a 0.22 SD lower sustained attention (95% CI: -0.36 to -0.07) and a 0.17 SD diminished short-term memory (95% CI: -0.32 to -0.03). For the same increment in t,t-MA-U, the Continuous Performance Test showed a 12.2 msec higher mean reaction time (95% CI: 4.85 to 19.5) and 0.51 more numbers of errors of omission (95% CI: 0.055 to 0.97), while for the Digit Span Test the digit span forward decreased by 0.20 digits (95% CI: -0.38 to -0.027) and digit span backward by 0.15 digits (95% CI: -0.32 to 0.022). We found no evidence of effect-modification by education level of the parents. Conclusions: The concentration of t,t-MA-U, used as a proxy for traffic exposure, was associated with a decreased sustained attention and short-term memory in adolescents.