Per- and Polyfluoroalkyl Substances (PFASs) and Soil Quality: Effects on the Chemical, Physical and Biological Properties of Soils, with Emphasis on Mediterranean Agroecosystems

Per- and polyfluoroalkyl substances (PFASs) are persistent, surface-active contaminants for which soil represents the largest terrestrial reservoir. This review synthesizes a rapidly expanding but fragmented body of literature in order to reframe PFAS not merely as a groundwater transport problem but as a systemic stressor of soil health, drawing together their reported effects on the chemical, physical and biological properties of soils and giving particular attention to the calcareous, alkaline, carbon-poor and seasonally dry soils of the Mediterranean. The reviewed evidence suggests that, chemically, PFASs perturb the coupled carbon and nitrogen cycles rather than the bulk soil reaction, transiently stimulating and then depressing organic carbon turnover, drawing down the dissolved organic carbon pool and disturbing nitrification, while their retention and bioavailability are governed chiefly by organic carbon, chain length and pH. Physically, the surfactant character that defines these molecules lowers the surface tension of soil water and concentrates PFASs at the air–water interface, so that in unsaturated and drought-prone soils much of the burden is retained and then released episodically, most clearly on rewetting after dry periods. Biologically, the literature consistently reports dose-dependent declines in microbial viability, diversity and enzyme activity, alongside toxicity to earthworms and other soil fauna, with sensitivity strongly modulated by soil texture and organic matter. Across all three domains, the Mediterranean emerges as both potentially vulnerable and conspicuously understudied, the available data being clustered in a few western countries and effectively absent for much of the eastern and southern basin, so that the regional assessment offered here rests largely on mechanistic inference rather than on direct observation. The review argues that these coupled mechanistic and geographic gaps define an urgent, region-specific research agenda for the protection of soil health.