EPA has made chemical list changes through the chemical petitions process and EPA-initiated review, therefore, the TRI list of reportable toxic chemicals can vary from year to year. To account for variation in the chemical list between years, TRI Explorer provides you the option of selecting a core chemical list which includes chemicals that have been reported in every year since the year denoted on the list. For example, when you select 1988 Core Chemicals, TRI Explorer will generate a report limited to chemicals that have been reportable to TRI in every year between 1988 and the most current reporting year. For trend reports, the earliest year TRI Explorer will display is the first year that chemical group was reportable to TRI.
For a list of changes made to the TRI chemical list, see EPA’s TRI program website: https://www.epa.gov/tri/chemical/list%20changes/ChemListChanges05.pdf