Analysis and study of the distribution of polar and non-polar pesticides in wastewater effluents from modern and conventional treatments

The analysis of a wide range of pesticides in wastewaters (WWs) undergoing different treatments (both modern and conventional) has been studied. The need for optimizing specific extraction methods for each WW effluent based on their physico-chemical characteristics has been considered. A distribution study was performed to establish if the filtration step before extraction is a correct procedure since pesticides can be more prone to be in the aqueous or the solid phase, depending on their hydrophobicity. This evaluation demonstrated that pesticides are distributed between the aqueous phase and the suspended particulate matter (SPM; e.g. pyrethroids are only found in the SPM). The proposed methodologies involved the determination of 39 polar and 139 non-polar pesticides using solid-phase extraction (SPE) and pressurized-liquid extraction (PLE) for the extraction of the aqueous phase and the SPM, respectively. Ultra high pressure liquid chromatography and gas chromatography coupled to tandem mass spectrometry (UHPLC–MS/MS, GC–MS/MS) were used in the determination stage. WW samples from four different technologies were evaluated: membrane bioreactor, extended aeration, maturation pond and anaerobic pond. Validation data for the four effluents studied were generated, obtaining adequate precision values (estimated as % relative standard deviation, RSD) in almost all cases (<25%). The methods showed limits of detection at 0.01–0.20 μg L−1 and limits of quantification from 0.02 to 0.50 μg L−1. The proposed methods were applied to the analysis of real samples collected from an experimental WW treatment plant, detecting non-polar and polar pesticides at concentrations in the range 0.02–1.94 μg L−1 and 0.02–0.33 μg L−1, respectively.