Evaluation of PFAS extraction and analysis methods for biosolids

Per- and polyfluoroalkyl substances (PFAS) in the environment is a growing concern leading to a focus on PFAS occurrence in biosolids, a byproduct of wastewater treatment processes, often applied to improve soil health. This led to the need for analytical method development for assessing PFAS in biosolids. This study compares three methods for PFAS quantitation, evaluating solvent extraction, clean-up techniques, and final injection solvents. Three biosolids examined included not stabilized, anaerobically digested, and activated sludge with long-term lagoon-stabilized solids, resulting in differing properties. One method is a methanolic extraction with ENVI-Carb clean-up (ME), modified by adding isopropanol (ME-P) to the injection vial to prevent emulsification that can occur with more complex biosolids matrices. The second method was the U.S. EPA 1633 method involving additional solid-phase extraction (SPE) and filtration while the third method was Quick Easy Cheap Effective Rugged and Safe (QuEChERS), yet to be tested on biosolids. Method performance was evaluated based on instrument precision, limit of quantitation (LOQ), and extraction recoveries. PFAS concentrations and recoveries were similar for Me-P and 1633 methods while QuEChERS performed poorly. Method 1633 exhibited better reproducibility with lower relative standard deviations but had higher LOQ values due to sample dilution. Most LOQs ranged between 0.06 and 0.3 μg/kg across methods, while recovery of spiked native PFAS ranged between 70 and 130 % in most cases. Methanol-based mobile phases resulted in better peak shape. ME-P excelled in overall cost-effectiveness showing superior extraction efficiency with fewer operational steps compared to other methods for PFAS quantitation in biosolids.