The neuroepidemiology of styrene: a critical review of representative literature

Abstract

Because exposure to styrene occurs commonly in some industries and styrene is highly lipid soluble, it is reasonable to be concerned about the possibility that styrene is neurotoxic. Styrene, like many other solvents, volatile anesthetics, and drugs, does, at certain concentrations, produce acute changes in consciousness with consequent alterations of feelings, cognition, and psychomotor functioning. Such acute actions do not imply that styrene also would produce reversible or irreversible damage to the nervous system; the evaluation of long-term exposures to styrene also is necessary to draw conclusions about the full range of neural effects that styrene might produce. To that end, several studies of workers exposed to styrene for up to 30 years have been undertaken in factories in many parts of the world. Epidemiologists have suggested that neuropsychological deficits such as slowing of reaction time, loss of color vision, and vestibulooculomotor dysfunction are reliably induced by styrene at levels near or below current exposure standards, which range from 20 to 50 ppm in most of the world. However, the workers so studied always were described as healthy, and the effects noted were considered to be subclinical. A detailed evaluation of much of the neuroepidemiological literature on styrene (38 papers and related literature), however, indicated that the findings were, almost universally, false positive outcomes due to (1) type I statistical error, (2) the action of some factor other than styrene, and (3) misinterpretation of data. Despite the study of workers exposed for many years, no indications of persisting damage to the nervous system were evident from this review. The conclusions of this review of the neuroepidemiology of styrene are consistent with those based on critical reviews of the solvent literature in general, with specific reference to the probable absence of such an entity as the "painter's syndrome" or "chronic toxic encephalopathy". Because the results on styrene neurotoxicity that provide an inclination to lower the current threshold limit values (TLVs) are false positive findings, there is no scientific basis for a reduction in the current TLV.