Epidemiological bases for the current ambient carbon monoxide standards.

Carbon monoxide is widely distributed in the environment, and acute or chronic toxic effects may be of considerable public health significance. A review of the basis for current ambient standards is given. Mortality and morbidity studies have been negative or equivocal in relating carbon monoxide levels to health effects, but studies in human subjects with compromised coronary or peripheral circulation support an effect of acute exposure to CO at blood levels equivalent to about 20 ppm over several hours. It is possible that some of the cardiovascular effects of smoking may be related to the high levels of CO in cigarette smoke, but it has been difficult to isolate the contribution of CO independent of the effects of other smoke constituents.