The Toxic 100 index identifies the top U.S. air polluters among the world's largest corporations. The index relies on the U.S. Environmental Protection Agency's Risk Screening Environmental Indicators (RSEI) project. The starting point for the RSEI is the EPA's Toxics Release Inventory (TRI), which reports on releases of toxic chemicals at facilities across the United States. TRI data are widely cited in press stories on "top polluters," but they have limitations that the Toxic 100 addresses:
- TRI data are reported simply in terms of total pounds of chemicals. The RSEI data factors in relative toxicities of TRI chemicals. Pound-for-pound, some chemicals are up to ten million times more hazardous than others.
- The RSEI data account for exposures and numbers of people impacted by the release of toxic chemicals based on modeling designed by the EPA.
- The PERI research team matches RSEI data, reported on a facility-by-facility basis, with information on corporate ownership of these facilities. PERI develops a picture of overall corporate performance that is essential to engaging corporate leaders in finding ways to reduce toxic pollution.