DIRECT IN SITU MEASUREMENT OF PFAS LEACHING AT A LONG-TERM LAND-APPLIED BIOSOLIDS SITE

Per- and polyfluoroalkyl substances (PFAS) are a group of synthetic chemicals known for their persistence in the environment and potential health risks. PFAS are linked to several adverse effects in human and wildlife health. The detection of PFAS in biosolids has raised concerns about their use in agricultural and land application practices. This is because some PFAS are known to enter the food system through plant uptake and some leach into groundwater. The purpose of this study was to examine the PFAS profile in soils and porewater with depth at an agricultural site with historical biosolids applications. The site selected has received biosolids at agronomic rates for corn for approximately four decades. This study utilized a total of six lysimeters, three “shallow” at 60 cm and three “deep” at 120 cm, to monitor PFAS leaching in soil. Porewater samples were collected within 1-3 days after rain events based on rainfall amount and response of the moisture sensor installed at the site. For each of five porewater sampling events, PFAS and supplemental water parameters like total organic carbon (TOC) and pH were measured. Soil cores, taken in one-foot increments before and after the 3-month study, were analyzed for PFAS, soil OC, moisture, and grain size. All samples were analyzed using high resolution mass spectrometry for 54 PFAS and in line with EPA 1633 method. Soil characteristics such as texture, moisture, and soil OC significantly influence PFAS transport and sorption capacity within the soil profile, impacting PFAS distribution across soil depths. PFAS in the soil profile decreased with increasing depth and directly correlated with soil OC. Long chain PFAS were strongly retained in the top 60 cm and minimally distributed to the porewater. Short-chain PFAS proportionally dominated porewater samples, with elevated concentrations observed in shallow porewater driven by increased saturation (perched water) from a low permeability clay layer. Unsaturated conditions enhance PFAS retardation through air-water interface partitioning in addition to soil particle sorption mechanisms. In this study, less than 0.1% of PFAS leach from the vadose zone of a biosolid impacted plot annually, underscoring the longevity of PFAS in the soil profile and importance of understanding PFAS transport dynamics for effective environmental management.