Section 6(h) of the Toxic Substances Control Act (TSCA) directs EPA to issue regulations under section 6(a) for certain persistent, bioaccumulative, and toxic chemical substances that were identified in the 2014 update of the TSCA Work Plan. EPA is selecting among the available prohibitions and other restrictions in TSCA section 6(a), in order to address risks of injury to health or the environment that the Administrator determines are presented by the chemical substances and reduce exposure to the chemical substances to the extent practicable. Since the statute states that a risk evaluation is not required for these chemical substances under TSCA section 6(h), EPA developed an exposure and use assessment. EPA intends to take final action on all of the chemicals that were addressed in the proposed rule that published on July 29, 2019 (i.e., the following persistent, bioaccumulative, and toxic chemicals identified pursuant to TSCA section 6(h): decabromodiphenyl ether; phenol, isopropylated phosphate (3:1), also known as tris(4-isopropylphenyl) phosphate; 2,4,6-tris(tert-butyl)phenol; pentachlorothiophenol; and hexachlorobutadiene). Although addressed in a single proposed rule, EPA intends to issue final separate actions. As such, the original Regulatory Agenda entry (RIN 2070-AK34) was split into five separate Regulatory Agenda entries. This particular entry is for hexachlorobutadiene (HCBD). HCBD is produced as a byproduct in the production of chlorinated solvents and has also been used as an absorbent for gas impurity removal and as an intermediate in the manufacture of rubber compounds. For information about the other chemical substances, see the Regulatory Agenda entries identified as RIN 2070-AK34 (decabromodiphenyl ether); RIN 2070-AK58 (tris(4-isopropylphenyl) phosphate. PIP (3:1)); RIN 2070-AK59 (2,4,6-tris(tert-butyl)phenol); and RIN 2070-AK60 (pentachlorothiophenol).