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Environmental Medicine: Integrating a Missing Element into Medical Education
Short exposures to methylene chloride result in formation of carboxyhemoglobin (COHb) that continues to increase after exposure before slowly returning to normal levels. The presence of methanol further prolongs period of COHb elevation and cardiovascular stress.
with the air pollution in his section of Milwaukee. This nonsmoker was discovered to have a COHb saturation of 6%, and of 8% on each of the two mornings following a two-hour exposure the previous evening to paint-and-varnish-remover vapors. After a fruitless search to discover the exogenous source of CO, the cardiologist was exposed for one hour to a low concentration of methylene chloride vapor in a controlled-environment chamber.2 The subject’s COHb level rose from a preexposure level of 0.4% to 2.4%. Because there was no evidence of a hemolytic process, it was presumed that the CO was a metabolite of CH2Cl2. To confirm this isolated observation, a series of experiments were conducted in which 21 male and nine female volunteers were exposed to CH2Cl2 vapor concentrations of 50, 100, 250, 500, and 1,000 ppm for varying periods of time. A prompt elevation of COHb was observed in each subject exposed to CH2Cl2.2,7
Paint Remover Exposure.—To investigate the potential of paint and varnish removers that contain CH2Cl2 to elevate COHb to toxic levels, four three-hour paint stripping operations were carried out in a controlled-environment chamber where the ventilation rate could be regulated, the CH2Cl2 vapor concentration accurately monitored, and careful medical surveillance of the four volunteer participants was possible. Two individuals participated in each experiment. One actively applied the paint remover and did the stripping while the second subject remained sedentary, making it possible to assess the effect of alveolar ventilation on absorption. Three room-ventilation rates were studied. The first simulated the air turnover commonly encountered in home basements, while the other two simulated the higher rates of air turnover that could be encountered in industrial settings. In each three-hour experiment, one quart of a liquid gel paint remover was applied to a baby crib with a paint brush and later, scraped off. The volatile components of the paint remover were 80% CH2Cl2 and 20% methanol by weight.
Subjects.—Four healthy men ranging in age from 19 to 47 years volunteered for the study after the purpose, procedure, and risks of the investigation had been fully explained. None of the subjects used drugs or consumed alcohol during the 24-hour periods preceding and following each experiment. One subject, who was a smoker, abstained for 12 hours prior to the experiment and was not permitted to smoke until a final COHb determination had been made.
Exposure Chamber.—The four experiments were conducted in an 817-cu m (2,680-cu ft) controlled-environment chamber.2,7 Air flow was adjusted so that the half-life of the CH2Cl2 vapor would range from 33 to 11 minutes. Air temperature was 22.3 to 23.3 C and the relative humidity was 55%.
Analysis of Exposure Chamber Atmosphere.—The CH2Cl2 vapor concentration in the breathing zone of the subjects was continuously recorded by an infrared spectrometer equipped with a 10-meter path-length gas cell. This gas cell was continuously supplied with air drawn from the subject’s breathing zone through a polyethylene tubing that measured 0.635 cm in diameter.2,7 The absorbance of 13.3µ