Bioavailability and Desorption Kinetics of Sulfonamide Antibiotics in Soil Assessed by Diffusive Gradients in Thin-Films
The diffusive gradients in thin-films (DGT) technique has emerged as a promising tool for assessing the desorption kinetics and bioavailability of organic contaminants in soil. This study compared DGT, soil solution, and organic solvent extraction methods for evaluating the bioavailability of four sulfonamide antibiotics (SAs) in soil using pot experiments with Brassica rapa subsp. chinensis and Lactuca sativa. Results demonstrated that plant uptake of SAs depended on compound properties and plant species, with roots as the primary accumulation site. DGT-measured concentrations (CDGT) showed significant linear correlations with SA concentrations in both roots and leaves, and effective concentrations (CE) were positively correlated with plant tissue levels (P < 0.05). The soil solution method also showed predictive ability but with lower stability. The mass of SAs adsorbed by DGT increased non-linearly with deployment time, indicating that solid-phase resupply sustained long-term DGT uptake. DIFS model-derived soil-water partition coefficients (Kdl) ranged from 0.23 to 1.25 mL·g−1, with higher Kdl values corresponding to greater bioavailability. Response times (Tc) ranged from 2307 to 7523 seconds, with sulfamethoxazole (SMZ) exhibiting the highest Tc, indicating its release was most constrained. Meta-analysis of desorption parameters for other organic contaminants revealed that soil pH and particle size were key determinants of Kdl, while molecular volume and hydrophobicity influenced resupply rates. This study confirms the reliability of DGT for assessing antibiotic bioavailability in soil and provides fundamental data on their migration and fate.