Unveiling the Differential Impacts of S-nZVI and nZVI on Microbial Dechlorination of Trichloroethene by Dehalococcoides.

Sulfidated nanoscale zerovalent iron (S-nZVI) is a promising material for the remediation of chlorinated hydrocarbons (CHCs) in groundwater, offering enhanced reactivity and selectivity over unmodified nanoscale zerovalent iron (nZVI). However, integrating S-nZVI with bioremediation using organohalide-respiring bacteria (OHRB) poses potential cytotoxicity challenges. This study investigated the differential impacts of S-nZVI and nZVI on the dechlorination activity of Dehalococcoides mccartyi strain 195 (Dhc 195), a representative OHRB. Key factors, including hydrogen evolution reaction (HER), pH, Fe2+ concentration, and nanoparticle-cell interactions, were assessed. S-nZVI exhibited significantly lower cytotoxicity compared to nZVI, primarily due to the reduced nanoparticle adhesion to Dhc 195 cell membranes, attributed to its negative surface charge rather than to the milder physicochemical disturbances in the culture medium. S-nZVI minimally disrupted extracellular polymeric substances (EPS), preserving cell integrity, and provided a more sustained hydrogen supply under hydrogen-limited conditions. Limited contact experiments confirmed that the reduced cytotoxicity of S-nZVI stemmed from lower contact toxicity rather than its intrinsic chemical reactivity. This study unveils the mechanisms underlying the interaction between S-nZVI and OHRB, highlighting S-nZVI's potential for safer and more effective abiotic-biotic remediation strategies. The findings provide a scientific basis for optimizing combined remediation approaches for comprehensive CHCs cleanup.