Potential of a laccase-1-hydroxybenzotriazole system from Trametes versicolor to degrade per- and polyfluoroalkyl substances

Abstract

Per- and polyfluoroalkyl substances (PFAS) are a group of chemicals used for consumer and industrial applications due to their favourable properties to provide resistance to oil, grease, and water. PFAS are persistent organic pollutants being found globally in environmental matrices at increasing concentrations due to their recalcitrance. Current degradation based treatments for PFAS in groundwater or soil have seen some, but limited success. Due to the toxic effects related to PFAS exposure, finding a successful option to degrade PFAS in the environment is a pressing area of research. In the current study the biodegradation potential of five PFAS in a laccase and laccase-1-hydroxybenzotriazole system with either copper (II) sulfate or citrate-phosphate buffer was evaluated. The laccase evaluated in this work originated from a white rot fungi Trametes versicolor (TV) which had not previously been evaluated for PFAS degradation potential. The five PFAS evaluated were perfluorooctanoic acid, perfluorooctane sulfonic acid, 6:2 fluorotelomer carboxylic acid, 6:2 fluorotelomer sulfonic acid, and the ammonium salt of hexafluoropropylene oxide dimer acid (GenX). 7:3 fluorotelomer carboxylic acid was evaluated as an additional PFAS in the citrate-phosphate buffer experiments. Aqueous PFAS concentrations of 0.75 parts per million (ppm) were evaluated, along with a study for 6:2 fluorotelomer sulfonic acid biodegradation at 2 parts per billion (ppb). It was shown in the citrate-phosphate buffer that the two fluorotelomers with a 6:2 structure were degradable in the laccaseTV system and the fluorotelomer with the 7:3 structure was degradable in the laccaseTV-1-hydrobenzotriazole system illustrating the likely preference for different degradation pathways based on chain length. At the lowered concentration (2 ppb) the 6:2 fluorotelomer sulfonic acid was able to degrade at a faster rate than 0.75 ppm, likely a result of a higher ratio of enzyme to PFAS. The perfluorooctanoic acid and perfluorooctane sulfonic acid were not transformed in the laccaseTV system, yet were previously demonstrated to degrade with laccase originating from Pleurotus ostreatus, showing that the source of laccase influences the system. GenX was shown to be resistant to degradation in all tested systems indicating that perfluoroether chains cannot undergo biological degradation by laccaseTV under the tested conditions.