Uptake of individual and mixed per- and polyfluoroalkyl substances (PFAS) by soybean and their effects on functional genes related to nitrification, denitrification, and nitrogen fixation

In this study, we set up a soil-microbe-soybean system spiked with PFOA, PFOS, or a PFAS mixture of eight PFAS and investigated the distribution of PFAS in the system and impacts on the abundance and expression level of genes involved in the nitrogen (N) cycle. When soybean was exposed to the PFAS mixtures, synergistic uptake by shoots was detected. PFAS exhibited remarkable impacts on abundance of nitrification and denitrification genes in both bulk soil and rhizosphere as well as expression of N fixation gene in soybean nodules. The abundance of nitrification genes AOA and AOB amoA and denitrification gene nirK was significantly reduced (p < 0.05) in almost all treatments in bulk soil, except PFOA at 10 μg/kg. The abundance of other functional genes, such as nirS and norZ was affected differently depending on PFAS concentrations and sample location, either bulk soil or the rhizosphere. Interestingly, the N fixation gene nifH in soybean nodules was overexpressed by a PFAS mixture at 100 μg/kg. Hence, this work provided in-depth knowledge regarding the distribution of PFAS and their impacts on the N cycle for the studied system. Results from this study provide insights on assessing risks posed by individual or mixed PFAS to soybean.