Cholesterol: up in smoke: cooking meat dirties the air more than most people realize - charbroiling as a source of pollution - Cover Story

Science News, July 27, 1991 by Janet Raloff

Careful chemical analysis revealed more than 75 discrete compounds in the hamburger smoke. When the researchers compared meat smoke's organic-particulates profile against air samples collected in west Los Angeles during 1982, they discovered the marker they needed for tracing hamburger emissions: cholesterol.

Though dozens of chemical ingredients exist in both meat smoke and the fine organic aerosols in Los Angeles, cholesterol was "one of the more unusual," the researchers note. Unlike many of the others, cholesterol had few other major, identifiable sources.

The group also identified a supplemental set of six tracer compounds in meat smoke: myristic acid, palmitic acid, stearic acid and oleic acid (all fatty acids), together with nonanal (an aldehyde) and 2-decanone (a ketone). Though each of these air pollutants can arise from several different sources, meat smoke combines them in a distinctive ratio.

Quarter-pound hamburgers fried until medium to well done spewed into the air roughly 7 milligrams of cholesterol per kilogram of meat. Extra-lean burgers charbroiled on the gas grill to the same doneness emitted roughly four times more cholesterol, and broiling the fattier meat released 72.7 mg/kg of airborne cholesterol--10 times more than the fried hamburgers.

To arrive at a ballpark estimate of how this might translate into urban air pollution, the investigators went back to the 1979 EPA report. At that time, an estimated 9 percent of restaurant meats were charbroiled. Cass' group assumed that this percentage would also apply to Los Angeles restaurants and home cooks in 1982, when a Caltech student had collected the air samples they were studying. To keep things simple, the researchers assumed that all meat cooked in the Los Angeles area was ground beef.

By marrying their meat-smoke emissions data with published estimates of meat consumption in the metropolitan area, the team projected that fried and broiled meat released 25.6 to 30.4 kilograms of tiny cholesterol aerosols into the atmosphere daily over a highly urban 6,400-square-kilometer region centered on Los Angeles. When they went on to assay the cholesterol in their October 1982 air samples, they found concentrations of 14.6 nanograms per meter cubed--or about double their ballpark prediction of what should be there.

That's actually a remarkably small difference, says Cass, especially when one considers that the October air sample was chosen for the comparison because it featured the biggest, clearest cholesterol "signature."

Cass, currently on sabbatical at the Massachusetts Institute of Technology, is studying the meat smoke's effects on bacteria as an initial rough gauge of its potential toxicity and mutagenicity in humans. While he has no findings yet, studies reported earlier this year by EPA epidemiologist Joel Schwartz indicate that fine particulates can play an important role in aggravating respiratory disease (SN: 4/6/91, p.212). Schwartz' analyses of data from five U.S. cities show that nonaccidental death rates in each of these cities tended to rise and fall in near lockstep with daily levels of fine particulates -- but not with other pollutants.