Organic solvents and time-dependent sensitization.

The nervous system is main target of the toxic action of most of organic solvents. There is little doubt that occupational solvent exposure may result in persisting neurobehavioural disturbances--the organic solvent syndrome. Recently, the solvents are quoted among possible causes of the abnormal condition referred to as multiple chemical sensitivity (MCS), and which is characterized by a psychosomatic over-reactivity to a variety of chemicals present in food or ambient air. According to some authors, MCS is a manifestation of the time-dependent sensitization (TDS), a phenomenon of progressive increase in responsiveness to chemical agents following acute or intermittent exposure, and related to some functional aberrations within limbic structures. TDS is commonly induced by psychostimulant drugs. The purpose of the present paper was to show, based on the literature data, that under circumstances of acute and repeated exposure, some solvents (mainly toluene) exert effect on behaviour and on the functional state of some neurotransmitter systems similar to that exerted by drugs known to induce TDS. Of special importance is the fact that in case of solvents the behavioural and biochemical changes suggestive of sensitization appear after exposure at levels close to those admissible in the occupational exposure, and that the concentration-effect relationship is nonlinear (an inverted U curve). To date, however, only a few of the existing data may be regarded as a direct evidence of the solvent-induced TDS. It is mainly due to the fact that the experimental protocol of a TDS study does not match the experimental routine of neurotoxicity assessment. Some data suggest that some solvents are possibly unable to induce TDS. The necessity to assess the commonly used solvents for their ability to induce TDS has been emphasized.