The Poison We Breathe

Great numbers of Americans are inhaling carbon monoxide, a notoriously poisonous gas, in quantities far above levels normally considered safe. That fact, reported in the A.M.A. Journal last week by a team of researchers from the Medical College of Wisconsin, is not surprising in itself. It has long been known that cigarette smokers, workers in certain industries and people in the dense traffic areas of major cities breathe in abnormally large amounts of carbon monoxide. But the Wisconsin study reveals that surprisingly many nonsmokers, office workers and residents of rural communities are also exposed to high concentrations of the gas.

Carbon monoxide (CO) produces its poisonous effect by crowding out oxygen molecules that normally attach themselves, in the lungs, to the hemoglobin molecules in red blood cells. By a malign quirk of nature, CO has an affinity for hemoglobin more than 200 times as great as that of oxygen. Thus too much carbon monoxide starves the body of oxygen, causing illness and sometimes death--as in the case of the suicide who runs a hose from the engine exhaust to the inside of his car. But how many Americans are inhaling an excessive amount of CO?

This was the question that the Wisconsin team, headed by Dr. Richard Stewart, attempted to answer during a massive three-year study. Concluding that air-monitoring systems are almost useless as a guide, the researchers decided to measure the concentrations of CO in the blood of 29,000 donors at blood centers in 18 areas of the U.S. They accepted as the danger threshold the one laid down by the Environmental Protection Agency under the Clean Air Act: a 1.5% concentration of car boxy hemoglobin (COHb)--the proportion of the body's oxygen-transport system that has been usurped by CO. Nonsmokers breathing pure air, they found, had a natural concentration of .45%.

In ten of the study areas--Honolulu, Houston, Miami, Milwaukee, Phoenix, St. Louis, Salt Lake City, Vermont, New Hampshire and Washington, D.C. --nonsmoking donors had COHb levels just below the threshold: from 1.2% to 1.4%. The New York metropolitan area scored an average of 1.2% for 15 stations, mostly suburban (but Brooklyn rated 2.1% and a Manhattan blood center 2%). Three areas were on the 1.5% mark: Anchorage, San Francisco and Seattle. Five were over: Chicago 1.7%, Denver 2%, Detroit 1.6%, Los Angeles 1.8% and New Orleans 1.6%.

Potential Risk. In every area, cigarette smokers averaged concentrations three to four times as high as those of nonsmokers, with gradations according to the number of packs smoked. The major factors pushing up the COHb levels in both nonsmokers and smokers were the type of work, where it was performed, and the CO in the ambient air. Even nonsmoking taxi drivers in New York City had levels as high as 5.8% after a bumper-to-bumper day; workers at Chicago's O'Hare field registered 2.5%, at New York's Kennedy Airport 2.1%. Other CO-laden occupations: printing, welding and processing metals, chemicals, stone or glass.

To the Milwaukee investigators, the most "astounding observation" was that no fewer than 45% of all nonsmoking donors had COHb levels above 1.5%, and in Denver the proportion reached a still more astounding 76%. Moreover, they say, there is potential risk in giving a transfusion of smoker's blood with a high CO concentration to a heart patient whose blood oxygenating system is already impaired.

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