Occurrence of pesticides and some of their degradation products in waters in a Spanish wine region

A multi-residual analytical method based on solid phase extraction (SPE) followed by liquid chromatography–electrospray ionisation–mass spectrometry (LC–MS) was developed to monitor pesticides in natural waters. Fifty-eight compounds, including herbicides, fungicides, insecticides and some of their degradation products, were surveyed to evaluate the quality of natural waters throughout the wine-growing region of La Rioja (Rioja DOCa). Ninety-two sampling points were selected, including surface and ground waters that could be affected by agricultural activities covering the region’s three sub-areas. Different parameters that may affect the efficiency of the SPE procedure were optimised (sorbent type, elution solvent and sample volume), and matrix-matched standards were used to eliminate the variable matrix effect and ensure good quantification. The developed method allows the determination of target compounds below the level established by the European Union for waters for human use with suitable precision (relative standard deviations lower than 18%) and accuracy (with recoveries over 61%). Forty compounds included in this study (six insecticides, 12 herbicides, 16 fungicides and six degradation products) were detected in one or more samples. The herbicides terbuthylazine, its metabolite desethyl terbuthylazine, fluometuron and ethofumesate and the fungicides pyrimethanil and tebuconazole were the compounds most frequently detected in water samples (present in more than 60% of the samples). Concentrations above 0.1μgL−1 were detected for 37 of the compounds studied, and in several cases recorded values of over 18μgL−1. The results reveal the presence of pesticides in most of the samples investigated. In 64% of groundwaters and 62% of surface waters, the sum of compounds detected was higher than 0.5μgL−1 (the limit established by EU legislation for the sum of all pesticides detected in waters for human use).