EPA has finalized its TSCA risk evaluation for 1,3-butadiene (CASRN 106-99-0), a high-volume colorless gas used primarily as a monomer in synthetic rubber and plastic manufacturing. Based on the weight of scientific evidence, EPA determined that 1,3-butadiene presents unreasonable risk to human health under 11 of 30 conditions of use, driven by inhalation exposure causing cancer and non-cancer effects in workers and occupational non-users. EPA will now initiate risk management rulemaking under TSCA section 6(a) to eliminate the unreasonable risk, with public comment to be solicited on any proposed rule.123