EPA is amending the significant new use rules (SNURs) under section 5(a)(2) of the Toxic Substances Control Act (TSCA) for 21 chemical substances which were the subject of premanufacture notices (PMNs). This action amends the SNURs to allow certain uses without requiring a significant new use notice (SNUN), and extends SNUN requirements to certain additional uses. EPA is amending these SNURs based on review of new data for each chemical substance. This action requires persons who intend to manufacture (including import) or process any of these 21 chemical substances for an activity that is designated as a significant new use by this proposed rule to notify EPA at least 90 days before commencing that activity. The required notification would provide EPA with the opportunity to evaluate the intended use and, if necessary, to prohibit or limit that activity before it occurs.