Acute effects on the human EEG after an external exposure to 200 ppm methanol

Objectives: Even low concentrations of organic solvents may cause acute eff ects on the human central nervous system. The German MAK (threshold limit v alue) of methanol is 200 ppm. The aim of this study was to investigate whet her acute exposure to 200 ppm methanol causes adverse effects, measured by EEG, and moreover, whether it is possible to differentiate between sedative and excitatory effects with this method. Methods: Twelve healthy subjects were exposed for 4 h to 200 ppm and to 20 ppm (control) in an exposure cham ber in a cross-over design. The EEG was recorded before (reference) and at the end of each exposure with, the subject's eyes closed and opened and dur ing a choice reaction test (color word stress test). Spectral power was cal culated by fast Fourier transformation. Subjective symptoms and effects of blinding with 20 ppm methanol were assessed by questionnaires. Results: The study was a single-blind one. During subjects' exposure to 200 ppm, their scores for prenarcotic and irritating symptoms were not different from cont rols. In the closed-eye condition of subjects, the spectral power of the th eta -band and of some electrodes of the delta -band was significantly less at the end of exposure to 200 ppm, than that of controls. In the open-eye c ondition and during the color word stress test no significant changes were found. Conclusion: The changes in the theta -band suggest a slight excitato ry effect of 200 ppm methanol. The effect was weak, as scores of acute symp toms did not change. With respect to our results, it is not necessary for t he MAK value to be decreased.