Pesticides and degradation products in groundwaters from a vineyard region: optimization of a multiresidue method based on SPE and GC-MS.

A reliable multiresidue method based on solid phase extraction was developed using GC-MS to determine and quantify 34 pesticides, including herbicides, fungicides, insecticides, and some of their degradation products, in groundwater in a vineyard region of La Rioja (northern Spain). Different parameters were optimized and good recoveries (65-108% range) and precisions (12-19% range) were achieved with spiked water samples for a concentration of 0.1 µg/L. The experimental results showed an excellent linearity (r(2) > 0.99) over the 0.1-1.5 µg/L range. The detection limits of the proposed method were 1-37 ng/L for most of the compounds studied. The methodology has been successfully applied to the analysis of groundwater samples from vineyard areas in La Rioja and the presence of pesticides, especially fungicides and herbicides, at several concentration levels was revealed. Terbuthylazine, its metabolite desethyl-terbuthylazine, and fluometuron were the pesticides most frequently detected in higher concentrations. Overall and taking into consideration the European Union maximum residue limit of pesticides in groundwater, 16 of the 34 compounds included in this study were detected in concentrations over that limit in at least one of the samples analyzed.