Physical-chemical transformations for the remediation and valorization of hexachlorocyclohexanes (HCHs) including lindane: A review.

The production of the former insecticide lindane (γ-HCH) resulted in the generation of vast quantities of hexachlorocyclohexanes (HCH) residues, creating one of the most significant environmental challenges related to persistent organic pollutants in the world. This contamination is present today in different scenarios, including stockpiles and highly concentrated mixed waste, contaminated surface soils, subsoil, and waters. In particular, Dense Non-Aqueous Phase Liquids (DNAPLs) represent challenging subsurface and groundwater contamination. This review provides a comprehensive and critical overview of the physical-chemical methodologies and remediation projects reported in the literature for addressing lindane contamination through separation, transformation, disposal, and valorization approaches. The available physicochemical techniques include dehydrochlorination, oxidation, reduction, substitution, isomerization, as well as electrochemical, photochemical, sonochemical, plasma, and other high energy treatments. Key aspects, such as advantages and limitations, remediation effectiveness, technological maturity, scalability, estimated costs, and applicability to different contamination scenarios are thoroughly analyzed for each method. The review culminates in a detailed comparison of these methodologies for various contamination contexts, providing valuable insights for the identification of optimal solutions to this global environmental challenge. In addition, the review assesses, for the first time, the potential for valorization of the products formed during HCH treatment or remediation. This aspect highlights the opportunity to transform HCH residues into higher value-added chemicals, thereby enhancing the circular economy of the remediation process. Finally, the integration of physicochemical methods with separation and biological tools offers a holistic perspective that underscores the importance of comprehensive strategies for addressing HCH contamination effectively and sustainably.