QuEChERS extraction followed by liquid chromatography coupled with tandem mass spectrometry for perfluoroalkyl acid determination in strawberries irrigated with treated wastewater

Agriculture is typically characterized by a high-water demand, since about 70% of worldwide freshwater (FW) withdrawals is used for agricultural irrigation. On the other hand, limited FW availability is a problem of increasing concern and the reuse of treated wastewater (TWW) for irrigation could be an efficient tool of reducing water shortage. However, the TWW reuse is currently far to be fully realized, due to several barriers, such as potential risks for the environment and the human health in the reuse of wastewater improperly treated, due to residual concentrations of priority and/or emerging (e.g. perfluorinated compounds) organic micropollutants. In this regard, this work focused on the development of an analytical method for the identification and determination of selected linear perfluoroalkyl acids (PFAAs) in strawberries irrigated with TWWs. The method is based on the QuEChERS approach, which include the liquid/liquid partition of analytes between salty water and acetonitrile, combined with dispersive solid phase extraction (d-SPE) as clean-up step, followed by liquid chromatography coupled with tandem mass spectrometry (LC-MS/MS) analysis. Different d-SPE sorbent phases and their mixtures (e.g. C18/PSA 90/10 w/w) were tested in order to evaluate the best compromise between matrix effect (ME%) and analyte recoveries. Satisfactory recovery values were obtained for all selected PFAAs using C18 sorbent (92% - 108%). ME% and apparent recoveries (AR%) of the adopted extraction and clean-up procedure were evaluated through the fortification of sample extracts at the following concentration levels of target analytes: 50, 100, 250 and 500 ng L-1. For the majority of the investigated analytes |ME%| decreased adopting d-SPE procedure, confirming the importance of this step; among the selected analytes, only perfluorodecanoic acid showed a higher absolute value of matrix effect (|ME%|=34%) in cleaned-up extracts, compared to untreated ones. The proposed analytical method exhibited better analytical performances than those published in the literature until now, in terms of analysis time and/or sensitivity, achieving method quantification limits in the range of 7.4-184 pg g-1 level, with a whole analysis time of about 35 min per sample. Based on the results obtained, this method could represent a valid and effective tool to be used for monitoring also other micropollutants in strawberry and, more in general, other water-rich food matrices. Future studies are necessary for the evaluation of the method applicability to non-aqueous food matrices (e.g. olive) and soil in order to allow the monitoring of the whole agricultural production chain linked to TWW reuse.