Effects of styrene exposure on vibration perception threshold.

We aimed to investigate whether styrene can affect the vibration perception threshold (VPT) and to examine the dose-effect relationship at current and past styrene exposure levels. VPT was examined using a Vibrometer (TM-31A) for 67 subjects exposed to styrene in a fiberglass reinforced plastic boat plant and 151 non-exposed subjects. We selected 67 age-matched controls out of the non-exposed subjects for the analyses. End shift urinary metabolites of styrene were measured for evaluation of the dose-effect relationship for the past eight years and at the time of VPT measurement. The current exposure level was expressed by the end shift urinary mandelic acid (MA) and phenylglyoxylic acid (PGA) levels. Cumulative exposure index (CEI) were calculated based on the exposure frequency and urinary MA concentrations measured for the past eight years. The VPT of the exposed group was higher than that of non-exposed group. Multiple regression analysis revealed that past maximum exposure level and age were significant factors explaining the variation of VPT. Dose-effect relationship was recognized in upper limbs but not in lower limbs among exposure groups. When the exposed group was divided into high- and low-level groups for the past maximum exposure level by the cutoff point of MA 0.83 g/g cr (equivalent to 50 ppm in air) and compared to the control group, we found significant differences in the VPT in upper limbs, between the high-level exposed group and control group, and in lower limbs, between both of the high- and low-level exposed groups and the control group. If the maximum concentration of styrene exposure exceeded 50ppm in the past, effects of exposure to styrene on the VPT are likely to persist.