Anaerobic Biotransformation and Biodefluorination of 6:2 Fluorotelomer Carboxylic Acid by Biosolids under the Nitrate-Reducing Condition

Abstract

The prevalence of per- and polyfluoroalkyl substances and their precursors, specifically 6:2 fluorotelomer carboxylic acid (6:2 FTCA), in the environment attests to their importance as contaminants of regulatory concern. This study compared three redox conditions (i.e., nitrate reduction, sulfate reduction, and methanogenesis) on biotransformation and biodefluorination of 6:2 FTCA using biosolids mixed from three wastewater treatment plants. Expected redox conditions were achieved in nitrate-reducing and methanogenic microcosms, but not in sulfate-amended treatments. Over 5 months of incubation, significant 6:2 FTCA removal (0.265 μM/day) was depleted under the nitrate-reducing condition, while minimal or no biotransformation was observed under the sulfate-amended or methanogenic conditions. This observed decline in 6:2 FTCA was accompanied by a decrease in nitrate (∼28 mM) and an increase in inorganic fluoride (∼28 μM), correlating to a loss of ∼0.70 fluoride per removed 6:2 FTCA molecule. Less fluorinated compounds 5:3 fluorotelomer carboxylic acid (5:3 FTCA) and perfluorohexanoic acid (PFHxA) were also detected under the nitrate-reducing condition. Microbial community analysis revealed the increase of Anaerolineae, which could be accountable for 6:2 FTCA biotransformation under nitrate-reducing conditions. Results indicate anaerobic biotransformation is dependent on the availability of specific election acceptors, informing future strategies to enhance the biotransformation rate and biodefluorination extent.