Soil enzyme dynamics under PFAS contamination in arid and Mediterranean soils

Abstract Per- and polyfluoroalkyl substances (PFAS) are persistent contaminants increasingly detected in agricultural soils, yet their effects on extracellular enzyme activities remain poorly resolved. This study examined the short- and long-term effects of perfluorooctanoic acid (PFOA) and 6:2 fluorotelomer sulfonic acid (6:2 FTSA) on the biochemical functioning of Mediterranean and arid agricultural soils. Soils were spiked with environmentally relevant concentrations (10, 50, and 250 ng g⁻¹ dry soil) and incubated for 210 days. The tested PFAS concentrations were selected to span literature-reported levels, ranging from typical to highly contaminated conditions. In the arid soil, both PFAS markedly impaired biochemical functioning, with Treated-Soil Quality Index values declining below 70% of control levels. In particular, 6:2 FTSA strongly inhibited β-glucosidase and alkaline phosphomonoesterase activities (up to 81.7%). The Mediterranean soil showed little enzymatic response to PFAS exposure. Eco-enzymatic stoichiometric modeling revealed PFAS-induced shifts in microbial enzyme allocation, particularly in the arid soil after prolonged exposure. PFOA remained stable throughout incubation, whereas 6:2 FTSA dissipated with the formation of perfluoroheptanoic acid. Overall, the arid soil was more biochemically sensitive to both PFAS compounds, suggesting that repeated applications of PFAS-contaminated biosolids or composts pose a greater biochemical risk in dryland agricultural systems.