Towards a sustainable rice husk ash-derived solid-phase extraction: Perfluoroalkyl substances as probe contaminants of waters

Abstract

Rice husk ash is an important waste of agricultural industry that, within the framework of the circular economy, has been easily converted into a sustainable sorbent material. This was tested in this work for the pre-concentration of perfluorooctanoic acid (PFOA) and perfluorooctane sulfonic acid (PFOS), representative perfluoroalkyl substances as probe environmental pollutants of waters, with HPLC-MS/MS quantification. The preparation involves a rapid microwave-assisted oxidation followed by a hydrothermal treatment, which was studied using a 2² design of experiments. The final material was thoroughly characterized and tested for its affinity to the target analytes by solid-phase extraction in environmental waters and wastewaters. Recoveries in the range 67–113 % (RSD < 11 %, n = 3) were achieved at environmentally relevant concentrations (10, 50, and 100 ng L^-1) and the sorbent was reusable for at least ten consecutive extractions. Good linearity (R² = 0.9997) was observed, with a method quantification limit in the water sample of 10 ng L^-1 that allows the analysis of PFOA and PFOS below the established limits. The method was evaluated for greenness using AGREEprep and SPMS metrics, and it was then applied to the analysis of actual water samples from Northern Italy.