Underrecognized three-carbon chlorinated aliphatic hydrocarbons: Occurrence, regulation, and treatment strategies

Three-carbon chlorinated aliphatic hydrocarbons (3C-CAHs) are a group of contaminants widely used in various industrial processes. Despite their frequent occurrence in diverse environmental matrices and established toxicity, these compounds receive much less attention compared to their shorter-chain counterparts such as trichloroethylene and dichloroethylene, leading to significant gaps in regulations and knowledge about their contamination levels and treatment approaches. This review aims to address these notable research gaps on 3C-CAHs, exploring their use, discharge, occurrence, fate, and transport across environmental matrices. By comparing them with one- and two-carbon CAHs, we highlight the unique properties and toxicity profiles of 3C-CAHs. Furthermore, we discuss state-of-the-art treatment techniques for 3C-CAHs, focusing on adsorption, chemical treatment, and biodegradation, and identify respective advantages and limitations. We also summarize regulations at state and federal levels in the U.S. and globally, underscoring the inadequacy of existing regulations for many 3C-CAH compounds. Lastly, we propose future research needs to further advance our understanding of the current contamination status of 3C-CAHs and to promote the development of sustainable and effective treatment methods for mitigating their environmental impacts. Overall, through this review, we aim to raise awareness and stimulate discussion on the importance of addressing 3C-CAHs in environmental management strategies.