Combined exposure of methylene chloride and carbon monoxide in smoking and nonsmoking paint strippers.

Carbosyhemoglobin (COHb) is formed when carbon monoxide (CO) combines reversibly with the oxygen carrying sites on the hemoglobin molecule. COHb levels above 5% increase the risk of angina pectoris and coronary infarctions by decreasing the oxygen supply in the blood and also the myoglobin of the heart muscle. Cigarette smoke contains 4% carbon monoxide and a one-pack-per-day smoker exhibits COHb levels of about 5.9%. Methylene chloride exposure also results in increased COHb levels. Therefore, the combined effect of smoking and methylene chloride exposure may increase the risk of disease to dangerous levels. This thesis tests the null hypothesis that smokers do not have statistically differences in COHb levels following days of exposure to methylene chloride when compared to days of non-exposure. Subjects were drawn from businesses which strip and refinish future in northern Utah. Furniture strippers were solicited as study subjects because methylene chloride is commonly found as a major constituent in paint and varnish stripping products. The study population contained eight smoking males, eight nonsmoking males and tow nonsmoking females. Daily smoking ranged from six cigarettes to a pack and a half. Blood samples from study subjects were drawn before and after the work shift and at corresponding times during a non-exposure day. Therefore, controls were self-paired where possible. Four subjects (two smokers and two nonsmokers) did not provide blood samples for the non-exposure period. Controls were selected fro these individual and matched for age, sex and smoking habits. Ages were matched within four years for nonsmokers and smoking habit was matched to within five cigarettes per day for smokers. Exposures of subjects to methylene chloride were measured with passive organic vapor monitors and charcoal sorbent tubes. Carbon monoxide concentrations in work areas were measured with direct reading instrumentation to ensure that sources of CO other than cigarette smoking were absent. The data were analyzed for significant differences in COHb levels between periods of exposure and periods of non-exposure. Smokers and nonsmokers demonstrated statistically significant increase in COHb levels during periods of exposure when compared to periods of non-exposure (p<0.05). Dose response curves for smokers and nonsmokers were estimated. The curve for nonsmokers reached a plateau of about 7% COHb following an eight-hour time-weighted-average (TWA) exposure to approximately 1800 mg/m3. The smokers dose response curve did not plateau but methylene chloride exposures were lower than those experienced by nonsmokers.