Evaluation of two extraction approaches for pesticide residue determination in biobeds using GC-MS/MS

Abstract

The development of reliable and accurate analytical methods is a requirement to ensure biobed bioremediation capacity. In this study two extraction approaches were evaluated for the determination of captan (and its degradation product, tetrahydrophthalimide), chlorothalonil, chlorpyrifos-ethyl, fenitrothion, methidathion, phosmet and tebuconazole in biobeds. These pesticides were selected because of their importance for apple plantations and the biobeds were used for bioremediation of pesticide wastes sprayed on plantations. After some preliminary experiments, the best extraction approach was selected and subjected to a complete validation study as advised by the SANTE Guidance Document. The validated approach consists of an optimized version of the Dutch mini-Luke method and is performed in only 4 steps (extraction, phase partitioning, centrifugation and filtration), which makes it very convenient and attractive. Linearity of analytical curves (r²), residuals, limits of detection (LODs) and quantification (LOQs), matrix effects (%), accuracy (in recovery%) and precision (as repeatability and reproducibility – relative standard deviation, RSD_r and RSD_wR, respectively) were assessed. Two internal standards were used for quality control. Validation studies were performed by analyzing blank biobed samples spiked at 50, 100 and 200 μg kg⁻¹ (n = 7) which yielded average recoveries from 75 to 117% and RSD_r ≤ 14%. The analytical curves obtained from matrix-matched standards were linear (r² ≥ 0.987) in the concentration range of 10 (or 20) to 300 μg L⁻¹ for all compounds, except for captan which was not detected in the validation study. LOQs were equal to 50 μg kg⁻¹. The calculated matrix effects were ≥±20%.