Neurobehavioural changes and persistence of complaints in workers exposed to styrene in a polyester boat building plant: Influence of exposure characteristics and microsomal epoxide hydrolase phenotype

Abstract

Objectives - To investigate neurobehavioural effects and the persistence of complaints in workers exposed to styrene relative to exposure characteristics and the enzyme microsomal epoxide hydrolase (mEH) activity. Methods - A cross sectional study was performed in a retrospective cohort of workers of a polyester boat building plant 3 years after the main activity shut down in 1989. Workers still currently exposed to a much lower concentration of styrene in air than before (n=27) and formerly exposed workers (n=90) were compared with matched control workers (n=64). Currently and formerly exposed workers laminated 4700 and 3610 hours on average at mean exposure to styrene concentrations of 148 and 157 mg/m3 respectively. A structured neurological anamnesis into former and present complaints, the NSC-60 questionnaire, and computer assisted neurobehavioural tests (NES) were administered. The mEH phenotype activity was measured in lymphocytes with a novel gas chromatography-mass spectroscopy (GC-MS) method. Results - For the period before 1989, currently and formerly exposed workers reported more complaints than control workers which related well with the mean exposure to airborn styrene concentration (p=0.03). Most complaints disappeared after the end of exposure, although the chest, equilibrium, and somatic category scores of NSC-60 and the number of workeres reporting diminished sense of smell remained increased in formerly exposed workers (p≤0.05). Symbol-digit substitution and digit span forwards test results were worse in currently and formerly exposed workers (p≤0.01). In the combined group of currently and formerly exposed workers, the symbol-digit substitution and colour-word vigilance results related well to duration of exposure (p<0.01 and p=0.03) and mEH phenotype activity (p=0.01 and p=0.05), whereas the digit span forwards results only showed associations of borderline significance (duration of exposure (p=0.08) and mEH phenotype activity (p=0.08)). Conclusion - Most subjective symptoms were reversible but some persisted after the end of exposure to styrene, whereas dysfunction of visuomotor performance and perceptual speed seemed to persist. Duration of exposure at lamination tasks and the interaction, duration of exposurexconcentration of exposure, were found to be the best predictors of worsening visuomotor and perceptual speed performances. Activity of the mEH phenotype may play a modulating parr in styrene neurotoxicity. The results suggested that less than 10 years of exposure to atmospheric styrene at an average concentration of 155 mg/m3 may result in persistent neurotoxic effects.