A diffusive gradients in thin-films (DGT) methodology for in situ measurement of imazamox and imazapyr herbicide residues

Imidazolinones (IMIs) are a group of commonly used chiral herbicides. However, because of their persistence and mobility, IMI herbicides pose a toxicity risk to non-target aquatic organisms and sensitive crop varieties. Conventional grab sampling and the subsequent solvent extraction of IMI herbicides from environmental samples do not provide information on their bioavailability. The current study focuses on the development of an in situ passive sampling technique based on the diffusive gradients in thin-films (DGT), to measure labile imazamox (IMX) and imazapyr (IMPy) herbicide residues in soil and water systems. Eleven different materials were tested to select an efficient binding phase for the DGT. Of them, SepraZT-WAX and bioactive carbon (BAC) showed high adsorption and elution efficiency when incorporated into a polyacrylamide binding gel after extensive testing of the gel incorporation and elution procedures. The SepraZT-WAX binding gels yielded a stable elution efficiency (∼85 %) at different preloaded herbicide concentrations (0.01-5.0 μM), whereas the elution efficiency increased with increased preloaded herbicide concentration in BAC binding gels. This highlights the need to investigate a concentration-dependent elution factor when testing novel DGTs. Compared to SepraZT-WAX DGT, BAC-DGT showed a higher binding capacity and faster adsorption rate, and its performance was independent of the solution pH (4.0-9.1), electrical conductivity (1-50 mS cm^-1), and bicarbonate (0-1800 mg HCO₃^- L^-1) and sulfate (0-600 mg SO₄^2- L^-1) concentrations for both herbicides. This study demonstrates the reliability and accuracy of this DGT device for measuring IMI herbicides and other anionic contaminants frequently detected in water and soil systems.