Extraction of Polycyclic Aromatic Hydrocarbons and Polychlorinated Biphenyls from Urban and Olive Mill Wastewaters Intended for Reuse in Agricultural Irrigation

Background: Domestic and industrial wastewater can be introduced in a reuse chain for irrigation purposes. Objective: In this paper, we developed analytical procedures for the extraction of polycyclic aromatic hydrocarbons (PAHs) and polychlorinated biphenyls (PCBs) along a wastewater reuse chain for irrigation purposes. Besides urban wastewaters, olive mill wastewater (OMWW) was considered as a potential water source. Wastewaters were purified by different treatments (urban wastewater plants, pilot-activated sludge, and constructed wetland) and used for the irrigation of olive trees. Suitable extraction procedures were used to analyze treated and untreated wastewaters, soils, and postirrigation leachates. Results: For wastewater and leachate samples, the optimized reverse-phase solid-phase extraction (SPE) provided recoveries up to 79%. For OMWW, the SPE procedure was preceded by a normal-phase purification stage with silica gel for the removal of polyphenols, which were as high as 8.7 g/L. After optimization, extraction recoveries in blank solutions were in the range 20-67% and moderately reduced (10-38%) in OMWW as a result of the matrix effect (ME; -10/-60%) ascribed to the very high value of chemical oxygen demand (264 g/L). LODs of the method were below 1.1 µg/L (PAHs) and 3.2 µg/L (PCBs) using GC-MS analysis. For soil samples of different compositions, microwave-assisted extraction (MAE) provided better extraction recoveries and reproducibility than the more common quick, easy, cheap, effective, rugged, and safe approach, which was affected by a high ME. The LODs of the MAE/GC-MS method were below 4.9 µg/kg (PAHs) and 12.3 µg/kg (PCBs). Conclusions: The analytical procedures developed are a valuable tool to quantify the possible propagation of residual contamination from PAHs/PCBs with irrigation along the wastewater reuse chain.