Assessment of two extraction methods to determine pesticides in soils, sediments and sludges. Application to the Túria River Basin.

Pressurized liquid extraction (PLE) and Quick, Easy, Cheap, Effective, Rugged and Safe (QuEChERS) extraction methods were optimized for the simultaneous determination of 50 pesticides in sediment, soils and sewage sludge. For QuEChERS development, several buffers and dispersive solid-phase extraction clean-up (dSPE) sorbents were tested. In the PLE method, several parameters affecting the extraction efficiency, such as organic solvent, amount of sample, cell size, temperature, pressure, static time, number of cycles and % of flush, as well as sorbent used for the on-line clean up, were also evaluated. PLE and QuEChERS were assessed and compared in obtained recoveries (33-89% versus 25-120%), number of pesticides for which recoveries are in the range of 80-100% (up to 13 versus up to 35) and cost of the approach. QuEChERS procedure was faster, cheaper and easier to perform. Recoveries were around 80% (at 50ngg(-1) d.w.) and the matrix effect was less than -20% using matrix-matched standard calibration curve for most of the analytes. The limits of quantification were between 0.1 and 10ngg(-1) (d.w.) except for alachlor and acetochlor. Repeatability and reproducibility were lower than 28% (%RSD, n=5). Soil, sediment and sludge samples, taken from the Túria River Basin, were analyzed by QuEChERS to determine pesticides. Chlorpyrifos (up to 65.3ngg(-1) d.w.) was the most frequent and at higher concentrations. Thiabendazole, imazalil, diazinon, pyriproxyfen, hexythiazox, carbofuran, isoproturon, terbuthylazine and terbumeton were also found in some samples.