Matrix effect challenges to quantify 2,4-D and fipronil in aquatic systems.

Fipronil and 2,4-D are two main pesticides of sugarcane cultivation in Brazil. While pesticides have helped to improve food quality and quantity, the continuous increase in usage has raised concerns over the unintended negative environmental impacts they introduce. Mesocosm systems are used as surrogate ecosystems to evaluate the fate, transport, and transformation of pesticides. Controlled experimental manipulations on mesocosms simulate the effects of stressors on the environment, in which the studies to evaluate effects on the living organisms and assess pesticide dynamics produce more realistic data than those obtained in the laboratory. However, analytical methods that follow mesocosm studies shall be robust enough towards sensitive variations in analyte concentration and matrix-induced effects of suppression or enhancement of analytical response. An analytical method using solid-phase extraction (SPE) along with liquid chromatography tandem mass spectrometry (LC-MS/MS) was developed for simultaneous determination of fipronil, 2,4-D, and their respective transformation products in aquatic systems. The method presented instrument quantification limits from 0.1 to 10.0 ng mL-1 and recovery values from 14 to 101%, with a maximum relative standard deviation (RSD) value of 12%. In the matrix effect assessment, the majority of matrix proportions showed a statistically relevant matrix effect for all compounds (p < 0.05). The method was further applied to over 500 different samples from mesocosm systems during controlled pesticide application and conversion of pastureland into sugarcane cropland. 2,4-D and fipronil mesocosm concentrations varied from 5 ng L-1 to 1.6 mg L-1 and 0.3 ng L-1 to 56 μg L-1, respectively.