Styrene and Ototoxicity: Studies in volunteers and laminators

Introduction
The ototoxicity of styrene in high concentrations has been demonstrated in animal studies. Up to now it is unclear, whether common exposure at the workplace can cause hearing impairment. The objective of our experimental study was to examine, if a defined styrene exposure alone or in addition with noise is associated with hearing loss. The objective of this study was to examine if an exposure to styrene over several years is associated with hearing loss and if there are signs of reversibility of possible effects during holidays.

Methods
A group of workers from a boat building plant, some of whom were laminators, were examined in subgroups of current low (n=99, mean mandelic acid (MA)+phenylglyoxylic acid (PGA)=51mg/g creatinine), medium (n=118, mean 229 mg/g creat.) exposure to styrene. Hearing thresholds and transient evoked otoacoustic emissions (TEOAE) were measured. Examinations were carried out during normal work days and during company holidays.

Results
The analysis of all participants demonstrated no clear exposure effects. Particularly no sufficient proof of dose-response relationship measured against parameters of current as well as of chronic exposure was found. Significantly elevated odds ratio for cases of hearing loss (more than 25 dB(A) in one ear, 3.000-6.000 Hz) was found among the group exposed to high levels (above 30 ppm as average) for a longer period of time (more than 10-26 years). The measurements of TEOAE did not exhibit significant results related to exposure.

Discussion
Chronic and intensive styrene exposure increases the hearing thresholds. At levels of about 30-50 ppm as average inhaled styrene per work day over a period of about 15 years with higher exposure levels above 50 ppm in the past, an elevated risk for impaired hearing thresholds can be expected.