IRONTON — Individuals living in both Lawrence and Scioto counties are breathing concentrations of air so polluted with dangerous toxins that it puts them at a greater risk of contracting cancer compared to any other area of the state, the Environmental Protection Agency said Wednesday.

The announcement by the EPA signifies the most detailed analysis of Ohio’s total air quality when it comes to cancer. The figures are based on emissions of 80 cancer-causing substances released by automobiles and factories from 2002, the latest year for which the EPA had detailed estimates of pollution from across the nation.

Called the National-Scale Air Toxics Assessment, the study is used to identify areas of the country where residents could face the greatest health threats from air pollution. The EPA study is not a general cancer risk study, but more of an excess cancer risk from air pollution study.

As a state, Ohio did not rank among the states that showed the highest risk of developing cancer from breathing toxic chemicals. Those dubious honors went to New York, California and Oregon.

But, in a nationwide county-by-county breakdown, the Lawrence and Scioto county region ranked seventh worst in the entire country in terms of risk. Los Angeles County in California was ranked to be the worst.

In its report, the EPA says most U.S. residents will have a 36 in one million risk of cancer in their lifetime based on emissions levels of the most recent test. However, some two million Americans are said to have an increased cancer risk of greater than 100 in one million because of exposure to toxins in air.

Benzene was the largest contributor to the increased cancer risks.

Regulators consider an excess of 100 cancers per one million “unacceptably high.” An excess cancer risk of 100 in one million means the air pollution within that area would cause an additional 100 cases of cancer for every million exposed throughout their lives.

Lawrence and Scioto counties’ risk was a whopping 612 in one million people, nearly 18 times the national average.

“Air toxic risks are local. They are a function of the sources nearest to you,” said Dave Guinnup, of the EPA. “If you are out in the Rocky Mountains, you are going to be closer to two in a million. If you are in an industrial area with a lot of traffic, you are going to be closer to 1,100 in 1 million.”

Wednesday’s announcement follows a string of unfavorable air quality reports Lawrence County has received in recent months.

In April, the EPA selected Whitwell Elementary School as one of only seven schools in the state to monitor the air quality outside of the building.

The selection came following a University of Maryland and Johns Hopkins University study that showed the air quality outside of Whitwell to be some of the worst in the United States.

Also named in the study as to having terrible air was both Dawson Bryant High and Middle schools.

Neither school was selected by the EPA for monitoring.

The EPA was scheduled to install air monitoring equipment at Whitwell in April however that plan has been delayed until late July to get Ohio’s schedule on track with monitoring being conducted at three schools in Ashland, Ky., according to Ohio EPA spokesperson Erin Strouse.

Monitoring should take approximately 60 days.

In addition, last month the American Lung Association awarded Lawrence County a grade of “F” in its annual “State of the Air” report. The county received the lowest marks possible in ozone and the second lowest mark possible in both annual and short-term particle pollution.

The failing grade came after two years of passing marks for the county.

The Associated Press contributed to this story.