The EPA is finalizing the designation of five chemical substances as High-Priority Substances for risk evaluation under TSCA section 6(b): Acetaldehyde, Acrylonitrile, Benzenamine, Vinyl Chloride, and MBOCA (4,4'-Methylene bis(2-chloroaniline)). This designation, effective December 18, 2024, initiates a three-year risk evaluation process for each substance. It is not a finding of unreasonable risk. EPA received 977 unique public comment submissions across two 90-day comment periods before finalizing the designations. Separately, EPA is also initiating a new prioritization round for five additional candidate chemicals, with comments due March 18, 2025.1