Enhancing anaerobic dehalogenation of γ-hexachlorocyclohexane with cyclodextrins: Evaluating roles as bioavailability promoter and microbial carbon source.

γ-Hexachlorocyclohexane (γ-HCH), a typical persistent organic pollutant, exhibits strong soil adsorption and low bioaccessibility, which limit its microbial degradation efficiency. Cyclodextrins (CDs) are environmentally friendly, biodegradable compounds with hydrophobic cavities that show potential for pollution remediation; however, their multiple roles in anaerobic γ-HCH degradation remain unclear. This study investigated the effects of α-CD and β-CD as solubilizers, carbon sources, and potential electron donors on the anaerobic biodegradation of γ-HCH in liquid and soil-liquid mixed culture systems. Results indicated that in soil-containing system, CDs, especially β-CD, significantly enhanced the bioaccessibility of γ-HCH through inclusion complexation, promoting the accumulation of benzene and chlorobenzene during early degradation stages. Simultaneously, CDs served as utilizable carbon sources, supporting the growth and metabolism of dechlorinating functional bacteria (e.g., Clostridium). However, CDs could not replace direct electron donors such as hydrogen in driving reductive dechlorination. Structural differences between CDs influenced their efficacy: β-CD, with its larger cavity, showed superior solubilization of γ-HCH, while α-CD exhibited stronger inclusion affinity for degradation intermediates (benzene and chlorobenzene), altering their accumulation profiles. This study systematically clarifies the dual mechanisms and structure-dependent effects of CDs in anaerobic bioremediation of γ-HCH, providing a theoretical basis for developing targeted and green CD-based remediation strategies.