We have used data from the US EPA Cumulative Exposure Project <http://ehp.niehs.nih.gov/members/1998/106p245-251woodruff/woodruff-full.html> to estimate exposure to toxic air pollutants in Cuyahoga County.

The Cumulative Exposure Project developed a computer model to estimate outdoor exposure to 148 air toxics, by census tract, for the continental U.S. The model is based on 1990 emission source inventories, including background, point, area and mobile sources. An air dispersion model estimated how far the pollutants travel after emission, based on wind speed and direction, breakdown of chemicals and secondary formation of pollutants.

In addition to the exposure estimates, the Cumulative Exposure Project developed health effects benchmarks for those chemicals for which sufficient health data was available. For cancer, the benchmark is based on one-in-a-million excess cancer deaths from lifetime exposure.

The results of the CEP modeling are startling and disturbing. Nationally, seven air toxics exceeded the cancer benchmark in all 60,000 U.S. census tracts. Estimated exposure for benzene, formaldehyde and 1,3-butadiene -- mobile source air toxics -- exceed the cancer benchmark in over 90% of U.S. census tracts.

Some census tracts in the U.S. had as many as 32 pollutants that exceeded the cancer benchmark. The average was 14 per census tract.

Our analysis of the Cumulative Exposure Project data for Cuyahoga County found 14 air toxics estimated to exceed the cancer benchmark. Four of these derived primarily from mobile sources. Mobile air toxics had the highest exceedences of the cancer benchmarks, by far. The estimated exposures for benzene, formaldehyde and 1,3-butadiene exceeded the cancer benchmarks by 23 times, 36 times and 86 times, respectively.

It is important to note that there are many limitations to this kind of study. Its estimates have been criticized as being too high because they are based on out-dated 1990 source data, prior to recent improvement in air quality. However, our comparison of model estimates with the Ohio EPA 1996 monitoring data from Cleveland and Cincinnati found generally good correspondence between the two.

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