Traces of chemicals known to cause human cancer lurk everywhere. But after decades of research, figuring out how many people might contract cancer because of them remains an elusive goal.
More than 60 percent of U.S. cancer deaths are caused by smoking and diet. But what about the rest?
A report by the President's Cancer Panel, released earlier this month, reignited a 30-year-old controversy among cancer experts and environmental epidemiologists about how large a role environmental factors play in the No. 2 killer of Americans.
Some experts, including the President’s panel, say a decades-old estimate that six percent of cancer deaths are due to environmental and occupational exposures is outdated and far too low.
But scientists most likely will never be able to tease out the true role of environmental contaminants because environmental exposures, genetics and lifestyle seem to all intertwine.
“It’s like looking at strands of a spider web and deciding which one is important,” said Dr. Ted Schettler, director of the Science and Environmental Health Network, a nonprofit group that advocates use of science in setting environmental policy.
From the womb to old age, people around the world are exposed to countless carcinogens in their food, air, water and consumer goods.
The National Institutes of Health has classified 54 compounds as known human carcinogens based on studies indicating they cause at least one type of cancer in people, according to the nation’s 11th Report on Carcinogens. The highest exposures occur in an occupational setting, but there are environmental exposures as well.
For example, benzene, a known cause of human leukemia, is a common pollutant in vehicle exhaust. Radon, a natural radioactive gas found in many homes, raises the risk of lung cancer. Arsenic, linked to skin, liver, bladder and lung cancer, contaminates some drinking water supplies. Other known human carcinogens include asbestos, hexavalent chromium, aflatoxins and vinyl chloride.
Since 1981, agencies and institutes have cited the same estimate when regulating carcinogens in the workplace, air, water and consumer products. Roughly four percent of cancer deaths – or 20,000 deaths per year - may be attributable to occupational exposures, and two percent – or 10,000 deaths per year – to environmental exposures.
In its new report, the panel, appointed by former President Bush, called that estimate “woefully out of date,” reporting that “the true burden of environmentally induced cancers has been grossly underestimated.”
But the American Cancer Society took issue with that statement, saying there was no scientific consensus.Please read By Brett Israel at:
http://www.scientificamerican.com/article.cfm?id=how-many-cancers-are-caused-by-the-environment
