"Smoke," the lyrics of the old Hoagy Carmichael song lament, "gets in your eyes." But that's not the only place it ends up.

Research shows it also gets in your lungs and bloodstream - even if you don't smoke yourself. Secondhand tobacco smoke so permeates society that one federal study found traces of nicotine in the blood of nine out of 10 nonsmokers among 10,000 people tested. As Philadelphia City Council prepares to take testimony today on a proposed ordinance to limit smoking in restaurants and other public places, the search to precisely define the risk posed by this ubiquitous vapor goes on. But the weight of the evidence over the last 14 years points to the growing likelihood that environmental tobacco smoke contributes to cancer, heart disease and respiratory ailments. "There is lots of information now suggesting that secondhand smoke is a significant public-health issue," said Mary Smith, director of the U.S. Environmental Protection Agency's Indoor Environment Division. The data come from about 40 epidemiological studies on secondhand smoke and lung cancer and 20 studies on cardiovascular disease. "They have been pretty consistent," said Jonathan Samet, a Johns Hopkins University School of Public Health epidemiologist and an expert on secondhand smoke. While Philadelphia is only the second municipality in the region to take up the issue - Glassboro prohibited smoking in restaurants last year - the debate over limiting smoking in public places is widespread. Nationally, the number of ordinances on public smoking has swelled six-fold during the last 15 years. Today, 845 municipalities and 28 states have laws limiting smoking in public places, according to the American Non-Smokers Rights Foundation and the federal Centers for Disease Control and Prevention. "Boston, New York, Los Angeles, San Francisco, San Diego all have controls on smoking in public places," said Edward Sweda Jr., a senior attorney with the Tobacco Control Resource Center at Northeastern University in Boston. "Controlling smoking in public places has become an established municipal activity." The Philadelphia ordinance, proposed by Councilman Michael Nutter, would ban smoking in all enclosed public places. Outside areas within 20 feet of a restaurant entrance - such as a sidewalk cafe - would also fall under the ban, as would restaurant bars. Private clubs, union halls, taverns and bars that make 60 percent of their gross revenues from selling drinks would be exempt. Critics of the push to limit public smoking, including the industry-funded Tobacco Institute, have pointed out that the link between casual exposure to tobacco smoke and disease is not well understood. Nevertheless, the CDC last week added environmental tobacco smoke to its list of known carcinogens, although experts concede even that link is not conclusive. "Part of the issue has been quantifying the risk of environmental tobacco smoke," Samet explained. "Is it a carcinogen? Yes. How much of a carcinogen? That is a more complicated question." So what precisely is known about secondhand smoke and the risks it poses? The content of the fumes - a mixture of the smoke exhaled by the smoker and smoke from the burning tobacco - has been analyzed, and it contains 4,000 chemicals, including 45 known or suspected carcinogens. Present in tobacco smoke are cancer-linked substances such as benzene, formaldehyde and benzopyrene. Other toxic agents include carbon monoxide, acetone, acrolein and nicotine. How much of these chemicals find their way into the lungs of a nonsmoker dining in a restaurant or bending an elbow at a local pub is not clear. One study, however, found that in a smoky bar a person could inhale as much as 98 parts per billion of benzene in an hour. There is no EPA ambient air standard for benzene; the health standard for drinking water is 5 parts per billion. That hour in a smoky bar can also give a nonsmoker the same dose of nitrosamine - another carcinogen - as smoking 35 cigarettes, according to Health Canada, that country's national health agency. Perhaps the most dramatic study on the pervasiveness of secondhand smoke was the CDC's Third National Health and Nutrition Examination Survey, conducted between 1988 and 1991. Analyzing blood samples from 10,000 participants, the CDC discovered measurable levels of cotinine - a metabolized form of nicotine - in 88 percent of the nonsmokers. Cotinine was a sign that the subject had been exposed to tobacco smoke within the previous three days. The CDC study, published in 1996, documented "for the first time the widespread exposure of people in the U.S. to environmental tobacco smoke," according to David Satcher, then head of the CDC and now the U.S. surgeon general. But the study also highlighted one of the issues raised by opponents of ordinances to limit public smoking - the question of where people receive the greatest exposure to tobacco smoke. To date, most of the studies have involved secondhand smoke in the home. Within the surveyed group, people living with smokers or exposed to smoke in the workplace had "significantly higher serum cotinine levels," the CDC reported. Indeed, most of the epidemiological studies have focused on nonsmokers - mainly women and children - living with smokers. The weight of these studies led the EPA, in 1992, to classify environmental tobacco smoke as a Class A, or "known human," carcinogen. The EPA estimated that 3,000 lung cancer deaths a year in nonsmokers can be attributed to secondhand smoke. The move was challenged by the tobacco industry in a North Carolina federal district court. The federal court ruled that the EPA had improperly set that risk and ordered the agency not to use it in developing policy. The EPA has appealed the decision. Several recent studies have calculated that environmental tobacco smoke may be an even more serious threat for heart disease and could be responsible for as many as 62,000 heart disease-related deaths a year - 20 times the number of lung-cancer deaths. "The studies continue to show that this is a significant public-health issue," said Johns Hopkins' Samet. A recent study by Health Canada also indicated that long-term exposure to secondhand smoke might be linked to a significant increase in breast cancer. Published in March in Cancer Cause and Control, the study evaluated 1,420 women and found that premenopausal women with long-term exposure to secondhand smoke had a 100 percent greater chance of contracting breast cancer. In postmenopausal women the risk was 30 percent greater. The impact of environmental smoke on children is even clearer, with studies showing decreased lung function, higher risk of respiratory infections, and worsened asthma in up to a million American children each year. For both children and adults, the research has consistently pointed in one direction, experts contend."EPA's 1992 risk assessment created some controversy," the agency's Smith said, "but the research over the last eight years, I think, tends to bear out the agency. Environmental tobacco smoke is a key public-health issue."

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