Phytoremediation of soil contaminated with per- and polyfluoroalkyl substances (PFAS)

Abstract: Per- and polyfluoroalkyl substances (PFAS) are anthropogenic compounds recognised for their persistence, mobility and potential toxicity. This thesis examines the efficacy of phytoremediation as a potential technique for managing PFAS-contaminated soil and groundwater. First, an extraction and clean-up method was developed to measure PFAS in different plant tissues. A solid-liquid extraction method using methanol and ENVICarb cartridge as clean-up showed satisfactory performance and was selected for validation and application. PFAS were then analysed in plants, soil and groundwater at one landfill and three former fire training sites. The aim was to investigate the phytoextraction potential of trees growing at these sites. Plant tissue concentration and composition profiles highly depended on the soil and groundwater fingerprints. Birch and willow showed the highest PFAS concentrations in the field. Furthermore, the phytoextraction potential of five plants (i.e. sunflower, mustard, hemp, willow and poplar) was also investigated in pot experiments. Parameters such as species-specific uptake, bioaccumulation in different plant tissues, duration of PFAS exposure and effects of supplements were assessed. The supplements i.e. fertilizer, microbes and hormones had limited influence on plant concentration in some cases increased plant biomass, which in turn increased total mass PFAS removal by the plants. Willow and sunflower showed the highest PFAS removal efficiency of all investigated plants. The highest PFAS removal obtained was for short chain PFAS (C3 – C6), with up 34% removal by the plants after 90 days of exposure. These results can be useful for field application of phytoremediation. Further work is required to improve the efficiency of the method and to study the fate of PFAS in plant biomass following remediation.