Despite two decades of cleaning up carcinogenic fumes from cars and factories, Californians are breathing some of the most toxic air in the nation, with residents of Los Angeles and Orange counties exposed to a cancer risk about twice the national average.
A nationwide, county-by-county snapshot of the cancer threat posed by air pollution provides a troubling portrait of California, revealing that many potent chemicals still pose an excessive risk.
New York tops the U.S. Environmental Protection Agency's list, followed closely by California, while rural residents of Wyoming, South Dakota and Montana have the least chance of contracting cancer from breathing the air.
One in every 15,000 Californians -- or 66 per million -- is at risk of contracting cancer from breathing the air over his or her lifetime, according to the EPA's National-Scale Air Toxics Assessment, which was released in February and based on emissions of 177 chemicals in 1999, the most recent data available.
In the Los Angeles area, the cancer threat is much higher, 93 per million in Los Angeles County -- or one person in every 10,700 -- and 79 per million in Orange County. The national average is 41.5 per million: one in every 24,000 Americans. Riverside and San Bernardino counties are near the U.S. average.
Although a tiny fraction of all cancers in the United States are caused by chemicals, an array of air pollutants has been shown to cause lung cancer or leukemia in both human and animal studies. Some have been classified as known human carcinogens for 20 years or longer.
The biggest contributors, by far, are cars, trucks and other mobile sources that burn gasoline or diesel fuel.
"One of the most significant environmental exposures" to cancer-causing chemicals for Californians comes from breathing them, said Melanie Marty, chief of air toxicology and epidemiology at the California Office of Environmental Health Hazard Assessment. "People should understand that mobile sources have very large impacts on health. It's not just asthma and heart disease. It's cancer too."
A Times review of the national assessment as well as other, more up-to-date federal and state databases shows that the levels of most carcinogenic chemicals have declined substantially in California in recent years.
Nevertheless, for at least 10 chemicals, Californians are still exposed to higher cancer risks than the levels considered acceptable under government guidelines.
