Formation and Emission of Hexachlorobutadiene during Chlorinated Chemical Production and Its Impact on the Surrounding Environment
Hexachlorobutadiene (HCBD) is a persistent organic pollutant (POP) regulated under the Stockholm Convention. Chlorinated chemical production processes are major sources of unintentional HCBD emissions, posing potential threats to ecosystems and human health. This study systematically reviews the formation, emission, and environmental impact of HCBD from such processes. HCBD is widely generated as a by-product during chlorination stages of producing carbon tetrachloride, dichloroacetylene, tri-/tetrachloroethylene, and chlorobenzene, via free-radical mechanisms. It is released through waste gas, wastewater, and solid waste. In the environment, HCBD exhibits multimedia distribution, undergoing long-range atmospheric transport and adsorbing onto soil and sediments, thereby becoming secondary pollution sources. HCBD shows significant bioaccumulation and food-chain magnification; it is toxic to aquatic organisms and causes hepatic and renal damage with potential carcinogenicity in mammals. Effective pollution control requires combined process improvements and end-of-pipe treatments, supplemented by stringent emission standards and life-cycle management. Future research should focus on developing precise emission inventories, elucidating multi-media transport and transformation mechanisms, and assessing composite ecotoxicological effects, thereby providing scientific support for implementing international conventions and formulating effective prevention strategies.