Washington ? At least two-thirds of Americans live in areas where toxic chemicals pose an elevated cancer risk, an Environmental Protection Agency analysis concluded Friday.

The findings are contained in a long-awaited EPA assessment of health risks from 32 toxic chemicals. The study is based on 1996 emissions data subjected to several years of internal analysis.

The assessment concludes that the accumulated exposure to the various toxic chemicals could be expected to cause 10 additional cancers over a lifetime of exposure for every 1 million people, or a 10 in 1 million cancer risk. These risks can be found across virtually the entire country, said the study, which was reviewed by outside scientists.

“More than 200 million people live in census tracts where the combined upper-bound lifetime cancer risk from these (chemical) compounds exceeded 10 in 1 million risk,” said the study. It added that 20 million people lived in areas where the risks were even higher a risk of 100 additional lifetime cancers for every 1 million people.

“The risks are very much in line with what we expected all along,” said Jeffrey Holmstead, head of the EPA’s air office. He said in an interview the risks of cancer from toxic chemical exposure “are very, very small,” compared with overall cancer risks from all sources.

The EPA considers a cancer risk of 1 in a million or greater as a matter of concern, although those levels do not always trigger regulatory actions.

Holmstead said the report was “designed to be a baseline” for further studies on risks posed by air toxins. He also emphasized the findings are based on 1996 data. “Since that time, the risks already have been reduced significantly,” Holmstead said.

But environmentalists said the study’s findings provided clear evidences that tougher measures were needed to reduce releases of toxic chemicals such as benzene, mercury, formaldehyde and other carcinogens from automobiles, power plants and industrial sources.

They show “a lifetime cancer risk at least 10 times greater than the level considered acceptable by the EPA,” said Emily Figdor of the U.S. Public Interest Research Group.

“These findings are a wake-up call that EPA should take action to reduce this long overlooked public health threat” from toxic air releases, argued Figdor.

Among the study’s conclusions is that automobiles and trucks contribute substantially to the public’s exposure to cancer-causing air toxins.

It estimated that 100 million people live in areas where motor vehicles both on and off-road account for an additional lifetime cancer risk of at least 10 in a million.