Acute effects of low doses of methyl parathion on human EEG.

Biological monitoring of workers exposed to organophosphates consists mainly of measuring serum or erythrocyte cholinesterase activity. However, animal experiments and a field study suggest that quantitative analysis of EEG may be more sensitive. In a parallel group design, 25 farmers were investigated, spraying methyl parathion or water for 50min. EEG was recorded before and after spraying. Serum and erythrocyte cholinesterase activity was compared with intraindividual pre-exposure values. Plasma methyl parathion concentrations ranged up to 12.1µg/l, methyl paraoxon was not detectable. Based on plasma concentrations, two exposed subgroups were defined. In EEG recorded with closed eyes, α(1)-power increased insignificantly (Kruskal-Wallis test) in both subgroups. ß(1)-power was enhanced in both exposed subgroups, reaching significance (p≤0.05) at five of 17 electrodes. Spearman's rank correlation showed a significant association between methyl parathion plasma concentration and the median of ß(1)-band power of the 17 electrodes (rho=0.48, p=0.015). Cholinesterase activity did not decrease. On a group basis, EEG is possibly more sensitive than cholinesterase. EEG changes suggest brain cholinesterase inhibition following low exposure to methyl parathion.

Acute exposure to 50ppm toluene does not increase sleepiness.

The Pupillographic Sleepiness Test (PST) is a new neurophysiological method to assess sleepiness. In an exposure study to a constant exposure level of 50ppm toluene on 20 healthy men, our aim was to find out, if increased sleepiness could be seen with PST. PST was performed before and after 4.5h of exposure. General complaints were assessed with the Swedish Performance Evaluation System (SPES) self-assessment questionnaire, once before and during exposure. Values obtained during exposure were related to pre-exposure values. Parametric cross-over analysis of logarithmic Pupillary Unrest Index (PUI) values did not show an effect of toluene exposure. In a nonparametric cross-over analysis of SPES-scores a significant increase of the scores of unpleasant smell and irritation to the throat, but not of tiredness was found. In conclusion, acute exposure to 50ppm toluene, corresponding to the German threshold limit value, did not increase sleepiness.