Observed versus predicted carboxyhemoglobin levels in cellulose triacetateworkers exposed to methylene chloride

Background Occupational exposure to methylene chloride, together with carbo xyhemoglobin concentrations, has not been studied previously. Methods Carboxyhemoglobin levels were measured in non-smoking employee expo sed to varying concentrations of methylene chloride during the manufacture of cellulose triacetate fibers. The observed carboxyhemoglobin levels were com ared o redicted concentrations using a pharmacokinetic model. Results The presence of carboxyhemoglobin in non-smokers exposed to methyle ne chloride results primarily from the metabolism of methylene chloride, in the liver and exhibits a linear dose-response relationship. The observed l evels of carboxyhemoglobin in non-smokers at the end of an 8-hour shift dep end upon exposures to methylene chloride that day but are independent of oc cupational exposures on previous days. The observed daily concentrations of carboxyhemoglobin are consistent with predicted concentrations using a pha rmacokinetic model, While varying exposure patterns were shown to change th e rate of metabolite formation at the end of shift, these same exposure pat terns had almost no effect on the total amount of carbon monoxide in the bl ood. Conclusion While the present study addresses the relationship between methy lene chloride, carbon monoxide, carboxyhemoglobin and ischemic heart diseas e, it does not address the issue of tumorigenicity, which is also the basis for the current U.S. Occupational Health and Safety workplace exposure lim it of 25 ppm. This study provides support for the conclusion that the curre nt American Conference of Governmental Industrial Hygienists 8-hour Thresho ld Limit Value of 50 ppm adequately protects human health with regard to is chemic heart disease and carboxyhemoglobin formation among non-smokers. (C) 2001 Wiley-Liss, Inc.