PFAS in plant-biosolids-soil systems: Distribution, fractionation, and effects on soil microbial communities

This study examined the behavior of six U.S. Environmental Protection Agency (EPA) regulated per- and polyfluoroalkyl substances (PFAS) compounds in vegetated soils amended with Class A and Class B biosolids. Short-chain PFAS were evenly distributed throughout the 8-cm soil column, while long-chain PFAS accumulated in the lower layers. Sequential extraction showed that short-chain PFAS dominated the water-leachable fraction, while long-chain PFAS were more concentrated in the methanol-extractable fraction. Plant cultivation appeared to promote the redistribution of long-chain PFAS from the water-leachable to the methanol-extractable fraction, potentially reducing their soil mobility. Elevated perfluorobutane sulfonate (PFBS) levels were detected in the alkaline hydrolysable fraction, likely due to the release of strongly bound PFBS from soil organic matter and the transformation of PFAS precursors, both of which may have contributed to its increased plant uptake. Both the class of biosolids and PFAS exposure had significant impacts on soil microbial diversity. The observed microbial stratification appeared to be associated with the vertical distribution of PFAS: microbiomes in the top soil layer were determined by hexafluoropropylene oxide dimer acid (HFPO-DA, also known as GenX) and PFBS, while those in the bottom layer were determined by perfluorooctanoic acid (PFOA), perfluorooctane sulfonate (PFOS), and perfluorohexanesulfonic acid (PFHxS). Overall, our findings highlight the complex behavior of PFAS in plant-biosolids-soil systems and emphasize the need for mitigation addressing both regulated PFAS and PFAS precursors.