<p>Some of the most common, extensively tested chemicals — radon, lead, particulate matter, asbestos, tobacco and benzene — appear to be proportionally more harmful to a person's health at the lower levels of exposure, according to a <a href="http://journals.plos.org/plosbiology/article?id=10.1371/journal.pbio.2003066" target="_blank">new review</a> of decades of research. </p><p>"Not only is there no apparent safe levels or thresholds, but at the lowest levels of exposure, there is a steeper increase in the risk," said author Dr. Bruce Lanphear, a professor and researcher at Simon Fraser University.</p><p>The key word here is <em>proportionally</em>—smoking three packs of cigarettes a day for 40 years is obviously worse for your lungs than a little secondhand smoke from time to time. However, the point is that for the nonsmoker exposed to secondhand smoke, the risk is "extraordinarily large," Lanphear said.</p><p>Lanphear, a renowned environmental health expert, has for years been a leading voice on how low levels of lead can have big impacts on kids' health. In a commentary published in today's PLOS Biology journal he summarizes key research on low levels of exposure to lead and other toxics and argues, in largely ignoring such exposures, most health and regulatory agencies are not fully protecting public health. </p><p>"For toxic chemicals without a threshold … we will inevitably fail to prevent most deaths, diseases, and disabilities, like obesity, heart disease, diabetes, and cancer, until we expand our focus to include population strategies that target people who have low-to-moderate exposures," he wrote. </p><p>Lanphear acknowledges it's a tough concept to wrap your head around—most people, including health professionals, think of safe levels or thresholds for toxics. </p><p>"If we took this research seriously, we could prevent a lot of death and disease and disability," Lanphear said. "And that makes me hopeful."</p><p>Take this example: In Scotland, a smoking ban in public places led to a 20 percent reduction in heart attacks among <em>nonsmoking</em> adults. It also led to a 15 percent reduction in preterm births among <em>nonsmoking </em>pregnant women. </p><p>"We can prevent about 15 percent of preterm births just by environmental regulation," Lanphear said. </p><p>Kirk Smith, a professor of Global Environmental Health at University of California, Berkeley, said Lanphear raises an "intriguing and potentially profound set of issues" that many in the scientific community have been talking about for years.</p><p>He cautioned, however, that measuring people's exposure to various pollutants is a complex and sometimes inconsistent science. "Certainly the idea of thresholds are going by the wayside," he said. "But having the EPA change all the regulations around air pollution or other pollutants? Not yet."</p><p>Smith quoted the late scientist Carl Sagan: "Extraordinary claims require extraordinary evidence."</p><p><span></span>"It is an extraordinary claim, and I don't think we have extraordinary evidence yet, but it's nevertheless an intriguing hypothesis," Smith said of Lanphear's paper.</p>
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