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

Permissible levels of styrene exposure do not cause damage to hearing capacity.

Studies show that styrene is not ototoxic (i.e., causing hearing damage) at levels to which humans are exposed in the workplace or the environment.

Styrene was reported to be ototoxic in young rats exposed to extremely high styrene concentrations of 800 parts per million (ppm), but these levels are 16 times higher than federal workplace limits. Further, a study on the hearing ability of rats exposed to 200 ppm of styrene for prolonged periods showed no observable effect. Since this is four times higher than the styrene industry's voluntary workplace exposure limit endorsed by the Occupational Safety and Health Administration (OSHA), occupational exposure to styrene at or below the present voluntary standard of 50 ppm limit should not affect hearing ability.

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. Such effects are associated with higher styrene concentrations, and styrene-induced color vision deficiencies improve when exposure is decreased. The research shows that the level of styrene-induced color vision effect is likely not subjectively noticeable, translating to 0.35 transpositions on the D-15 test; a test commonly used for occupational vision screening. Such effects are roughly the same differences in color perception normally found in the general population in individuals between the ages of 35 and 65. Additionally, a D-15 test score of less than one (<1) transposition represents an acceptable color perception rating for most occupational settings.