HUMAN EXPOSURE TO m -XYLENE. KINETICS AND ACUTE EFFECTS ON THE CENTRAL NERVOUS SYSTEM

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Abstract
Inhalation exposure to m -xylene at 100–400 ppm caused some changes of psychophysiological performance of volunteer subjects, e.g. impairment of body balance and increase of reaction times. With repetitive exposure, tolerance developed within a few days with regard to most of these effects. At steady-state and under conditions of increased xylene absorption, blood xylene concentration was directly related to the rate of xylene uptake. Acute xylene effects on the central nervous system were correlated with blood xylene concentrations and their occurrence also seemed to depend on a rapid rise of blood xylene level. Thus, exposure to a fluctuating xylene concentration with high uptake rates during the peak concentration caused more pronounced effects than a corresponding exposure to a constant concentration. Physical exercise may also greatly raise the uptake rates and enhance the effects. Kinetic data showed that well perfused tissues such as the brain will reach xylene equilibrium within some minutes and brain xylene concentration probably closely follows blood xylene levels. A very brief period of increased xylene absorption, not exceeding a few minutes, is not likely to bring about effective brain levels of xylene, however. Post-exposure excretion of xylene from most tissues takes place rapidly (elimination half-time about 0.5–1.0 h within the first hours). Consequently, acute xylene effects are probably short-lived. Xylene stored in adipose tissue is eliminated slowly but its mobilization results in only low blood levels. Compared to effects by moderate doses of alcohol (blood alcohol concentration 6.5–15.2 mmol l . −l ) xylene effects were clearly weaker, suggesting the practical inference that exposure to xylene may not be as serious an occupational and motoring hazard as social drinking.

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