RESUMO
Contrarily to the general opinion about the harmlessness of dichloromethane, clear functional disturbances of the central nervous system could be recorded by means of effect investigations as well in humans as in animals. The depressive effect on the REM-sleep of albino rats was especially well recognisable, similarly as with carbon monoxide exposure. Surprisingly the analytical investigations of the blood of these animals showed a clearly elevated blood-CO-content after exposure to dichloromethane. Further experiments during which albino rats were exposed three hours along to a dichloromethane-concentration equal to the TLV (1750 mg/m3!!) resulted in a blood-COHb-level of about 13%, corresponding to over 30 mug CO/ml blood. So high blood-COHb-levels are obtained after a three-hour-exposure to 120 ppm CO. Following these findings, a number of halogenated and oxygenated hydrocarbon compounds of the methane and ethane series were investigated relatively to their CO-forming capacity. Only the di- and trihalogenated methane derivatives were found leading to an increased blood-COHb-level. After a three hours-exposure to 1000 ppm respectively the jodoalkanes yielding about 23% COHb were strongestly, the bromoalkanes with about 20% COHb more strongly and the chloroalkanes with about 12% COHb strongly implicated in the endogenous CO-formation. By means of detailed experiments with human volunteers (non-smokers) it resulted that after eight-hours-exposure to 500 ppm dichloromethane (TLV) a mean value for CO-content in blood of about 30 mug/ml corresponding to 12% COHb was obtained, in one case raising as high as 60 mug CO/1 ml blood or 24% COHb. After an eight-hours-exposure to 100 ppm of the halocarbon, the blood-COHb-level reached 5%. The elimination was very slow, so that 24 to 26 hours were necessary to reestablish the original blood-COHb-level. These results show that the actually TLV for dichloromethane e.g. 1750 mg/m3 has to be revised, because a fifth of this value already leads to a blood-COHb-content equal to that produced by the TLV for carbon monoxide and that also eventually arising problems due to gas mixtures have to be considered and thoroughly investigated.
