Section 8 (b) of the Toxic Substances Control Act (TSCA) requires EPA to compile, keep current, and publish a list of each chemical substance that is manufactured or processed in the United States.

Under TSCA, the term 'chemical substance' means any organic or inorganic substance of a particular molecular identity, including any combination of these substances occurring in whole or in part as a result of a chemical reaction or occurring in nature, and any element or uncombined radical. Chemical substances on the Inventory include: organics, inorganics, polymers, and UVCBs (chemical substances of unknown or variable composition, complex reaction products, and biological materials)...

As new chemicals enter commerce, the number of chemicals on the Inventory changes. Today more than 84,000 chemical substances are on the Inventory.