The Cumulative Exposure Project (CEP)
and Hazardous Air Pollutants (HAPs)

Read a precautionary note, issued by EPA, on the interpretation of CEP data.

EPA Addendum: Accuracy and Underestimation of the Model.

The questions most often asked about human exposure to toxic chemicals are 'How do these chemicals affect our health?' and 'Which groups in society face the greatest health risks from toxic exposures?' Until now, scientists and regulators have tried to answer these questions one source at a time. For example, recent studies have focused on Toxic Release Inventory (TRI) facilities or Transfer, Storage and Disposal (TSD) facilities. For each chemical pollutant, risks have been calculated and expressed in terms of how many additional cancers would appear in a million members of the exposed population. The Federal Clean Air Act sets a goal for the air we breathe as not to exceed a 1-in-a-million threshold, meaning that breathing the air in our communities should not cause more than one additional cancer per million members of the exposed population. But this method of addressing one source at a time ignores the fact that people in America are exposed to many hazardous chemicals from multiple sources simultaneously. And these exposures do not fall evenly across the population. Current methods fail to inform us about how great are the risks and which communities are most likely to be harmed by chemical exposures in the environment.

For the first time, US EPA's new Cumulative Exposure Project goes beyond the current, oversimplified source by source approach to human health risk assessment by recognizing that the human population is simultaneously exposed to multiple environmental pollutants from multiple sources. It does this in two ways: first, by summing up the combination of chemicals in a community's environment (expressed for the San Francisco Bay Area above as a sum of 118 Hazardous Air Pollutants, or HAPS, in the region). And second, by translating this information into a cumulative risk to human health - against the 1-in-a-million standard - from all chemical pollutants measured in the air we breathe. The ultimate goal of the Cumulative Exposure Project (CEP) is to learn how human health is affected by multiple exposures in air, water and food from multiple pollutants and sources, and then to identify communities or demographic groups most at risk.

Silicon Valley Toxics Coalition, through our new series of 16 chemical exposure and demographic CEP Eco-Maps, hopes to contribute to understanding cumulative health impacts on San Francisco Bay Area communities. The data from Silicon Valley Toxics Coalition series of CEP maps are taken from US EPA's Cumulative Exposure Project. The US EPA's Science Advisory Board has reviewed the Project and called its framework "scientifically sound" with the caveat that much more work needs to be done in data collection, modeling and interpretation. It is a powerful beginning.

Visit EPA's Cumulative Exposure Project website to learn more.

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