NEUROTOXICITY RESEARCH

The data do not demonstrate that styrene is neurotoxic at occupational exposure levels.

A critical review of representative literature on the neuroepidemiology of styrene, by Drs. Charles Rebert and Thomas Hall, was published in Critical Reviews in Toxicology in 1994. They noted that styrene, like many solvents, at certain concentrations could be expected to produce acute changes in consciousness; although they point out that such acute effects do not mean that styrene would produce reversible or irreversible damage to the nervous system. Drs. Rebert and Hall reviewed studies of workers in reinforced plastics and related industries, with emphasis on the value of those studies for setting safe exposure limits in the work place. They reported that the "results concerning styrene workplace neurotoxicity are not actually as they are represented in the literature, where results are often interpreted to show that styrene is neurotoxic in workers exposed to levels typically encountered in the reinforced plastics industry." They concluded that the literature does not demonstrate that styrene is neurotoxic at levels of worker exposure, because the literature fails to meet well-recognized criteria for establishing causal relationships.

Ototoxicity Research

Studies have been conducted in workers and in laboratory animals to investigate the potential for exposure to styrene to have an adverse effect on hearing. In studies before 2009 limited evidence was obtained for styrene-induced hearing loss in workers due to co-exposure to noise and other solvents. In the study of Triebig et al (2009) no hearing deficits were found in workers exposed to styrene for 10 years to 12.5 ppm and 50 ppm. However there was an indication for styrene-induced hearing losses in workers exposed to styrene concentration of 25-33 ppm from 15 to 26 years. Higher exposures of 80-100 ppm existed for a time more than 10 years before this study was initiated therefore these effects are considered to stem from the former high exposure.

Color Vision Research

Dr. James Sheedy completed a review of literature investigating reports of color vision deficiencies associated with occupational exposure to styrene (The SIRC Review, August 1997). Although some of the studies are inconclusive, evidence of slight decreases in color perception was noted. However, in all studies when slight changes were detected in tests, the effects were reversible, and individuals concerned were not aware of any deficit and there was no indication that performance was affected in jobs requiring good color discrimination. The effect is associated with higher styrene concentrations, and styrene-induced color vision deficiencies improve when exposure is decreased. Similar differences in color perception is normally found in the general population in individuals between the ages of 35 and 65. These results were confirmed by Seeber et al.(2009) who did not find color deficiencies at exposures up to 50-100 ppm.

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