Short duration exposures to organic solvents: the relationship between neurobehavioral test results and other...

Short duration exposure to solvents at even low concentrations can induce signs of mild toxicity such as mucous membrane irritation, tearing, nasal irritation, headache, and nausea. These irritant effects are often used as warning properties for potential solvent toxicities and have frequently been classified in the literature as pre-narcotic effects. With higher exposures the toxic effects are more pronounced and can include intoxication, incoordination, exhilaration, sleepiness, stupor, and the beginning stages of anesthesia. Collectively these effects are taken as indicators of narcosis. Offering recommendations for safe exposure limits for these shorter term exposures is made difficult because, (1) the mild toxic effects are often reported subjectively and tolerance usually develops, (2) the solvent concentration(s) cannot be documented in all cases, and (3) the effects are reversible when individuals are removed from exposure. Laboratory experiments involving controlled exposures to solvents using neurobehavioral performance tests represent one form of investigation that can provide meaningful information in this instance. The results can be viewed in two ways with reference to issues of safe exposure limits. One is to ensure that performance functions that can compromise safety are not affected by the exposure limits prescribed. The second is to consider performance changes due to short-term exposures as possible precursors of similar but more severe effects given longer term exposures. Thus, setting exposure limits to protect against these performance changes could possibly prevent the development of more serious cases of chronic solvent neurotoxicity. This paper compares solvent concentrations from short-duration exposure studies using neurobehavioral tests with the concentrations producing irritant and narcotic effects, as documented by the two main standards recommending bodies, the National Institute for Occupational Safety and Health and the American Conference of Governmental Industrial Hygienists. Comparisons are also made with the regulatory exposure limits established by the Occupational Safety and Health Administration. In general, the neurobehavioral changes which occur following short-duration exposures are reported at concentrations between those which produce irritant effects and narcosis. For the chemicals which have been tested, the performance changes measured by the present day neurobehavioral tests in use rarely occur at or below those limits recommended by the standards recommending bodies.