Determination of organic microcontaminants in agricultural soils irrigated with reclaimed wastewater: Target and suspect approaches.

Water scarcity is a problem worldwide, affecting specially countries with desert/semi-desert areas and low/irregular rainfall. In this context, reuse of reclaimed wastewater (RWW) for agricultural irrigation is undoubtedly a key strategy to reduce fresh water consumption. It is well-known that current wastewater treatments do not effectively remove organic microcontaminants (OMCs), and research in water analysis of OMCs is extensive. However, the focus on agricultural soils irrigated with RWW as potential recipients of OMCs and potential sources of OMCs to crops is still in their beginnings. This study aims to apply a target and a suspect approach for the multi-residue monitoring of OMCs in agricultural soils and a soilless subtract, both irrigated with RWW for more than ten years. The study involved, firstly, the development and validation of an extraction method for target analysis of 73 OMCs using a QuEChERS-based method and liquid chromatography coupled to quadrupole-linear ion trap mass spectrometry (LC-QqLIT-MS/MS); and secondly, the application of a suspect workflow for the screening of a list of 1300 potential contaminants using LC coupled to quadrupole-time-of-flight MS (LC-QTOF-MS). The results demonstrated the occurrence of 11 OMCs in the agricultural soil samples and 26 in the soilless subtract (0.1-100 ng g-1, dry weight, d.w.). The suspect analysis leaded to the confirmation of 28 OMCs analytes from the list of candidates. The subsequent combination of both strategies (suspect and target) revealed the presence of 11 new OMCs which were not previously reported. Furthermore, this study presents the first application of a OMCs suspect screening to agricultural soils irrigated with RWW for a long period. These results highlight the importance of monitoring soils with RWW-based irrigation and the application of wide-scope approaches for environmental analysis.