Data on onsite emissions for the facilities displayed on MapEcos come from the most recent publication (2005) of the Environmental Protection Agency's Toxic Release Inventory (TRI). Facilities with ten or more employees who store, transfer, or process any one of more than 600 chemicals fall under TRI requirements, and must report to the EPA information about the waste they generate, where and how it is processed, and the amount emitted to various environmental media (air, water, land).

More than 23,000 facilities reported to the TRI in 2005. Approximately another 25,000 reported emissions for at least one year between 1987 and 2005, but did not report in 2005.  This may be because they have reduced their emissions so much that they no longer need to report, or that they have gone out of business. More information on TRI data can be found at the EPA.

Although the TRI also includes information on the chemicals facilities treat, recycle, burn for energy, or transfer to others for processing, we have chosen to report only the onsite emissions from each facility In future versions of MapEcos, we may include information on the extent to which facilities process chemicals onsite or transfer chemicals to others for processing.

In recent years, other nations have begun to adopt legislation that resembles that for the TRI. In future versions of MapEcos, we hope to include information about both Mexican and Canadian facilities. We also hope to continue to be able to include updated data about the United States. The TRI remains a contentious political issue, and there have been numerous proposals to change TRI reporting requirements The 109th congress passed legislation to weaken reporting requirements, but both houses of the present congress have introduced bills to undue some of these changes.  More information about legislation that might effect the TRI can be found at OMB Watch.