Analysis of pesticides in water samples based on the combination of solid phase extraction and solid phase microextraction coupled to gas chromatography mass detection.

BONANSEA, ROCÍO; WUNDERLIN, DANIEL ALBERTO; AMÉ, MARÍA VALERIA

Congreso; SETAC World Congress / SETAC Europe 22nd Annual Meeting; 2012

The increase of the agricultural surface area in Argentina has triggered the generalized use of pesticides, which are spread across soils contaminating both surface and groundwaters.The aim of this study was: (a) develop a sensitive Gas Chromatography tandem Mass Spectrometry (GC-MS) method for the quantification of the most widely usedpesticides at environmentally relevant concentrations and (b) test this method with surface waters collected from the Suquía River basin, Córdoba, Argentina.Sample pretreatment involves a combination of Solid Phase Extraction (SPE) and Solid Phase Microextraction (SPME) affording highly effective enrichment of six pesticides,which can be analyzed at ppb levels. We tested the effect on SPE of cartridges and elution solvents as well as type of fiber, absorption-desorption temperature and time, headspaceor immersion for SPME. A fractional factorial design was applied to obtain optimal conditions. GC and MS operational issues were also optimized to afford LODs inthe same range that ECD detectors. The optimized method was validated in terms of linearity, precision, recovery and repeatability, showing that the proposed procedure issensitive (LODs ranging 0.2 to 3.5 ng L’1), precise and robust (recoveries ranged 61 - 104%, RSD varied from 4.0% to 22.6 %), with a linear analytical range from 0.1 to 10ug L-1.This method was successfully applied to natural water samples, collected at five monitoring sites along Suquía River, considering pre and post-application of agriculturalpesticides. Most studied pesticides were present throughout the entire period. Nevertheless, post-application period showed concentrations of atrazine, acetochlor, endosulfan,endosulfan sulfate and cypermethrine 1.5 to 5 fold higher than the corresponding to pre-application. As expected, highest levels of pesticides were observed in areas withintensive agricultural practices, being atrazine, cypermetrine and endosulfan sulfate predominant. In urban or recreational areas the prevalent pesticide was cypermethrine.Some values surpasse the National Guidelines for pesticides in freshwaters, pointing out the need of controls in addition to the evaluation of damage to aquatic biota.