In Situ Time-Weighted Average Monitoring of 11 Antiviral Drugs in Natural Waters Using Diffusive Gradients in Thin-Films with Graphitized Carbon Black and Mixed-Mode Resin Binding Gels

Abstract The widespread occurrence of antiviral drugs in aquatic systems has raised concerns on their potential ecological risks, necessitating reliable monitoring techniques. This study introduces the first application of the diffusive gradients in thin-films (DGT) technique for the in situ measurement of 11 commonly used antiviral drugs from six therapeutic categories. Two complementary DGT configurations were developed, employing graphitized carbon black (ENVI-CARB) and a mixed-mode resin (MCX + HLB at a 6:4 mass ratio) embedded in agarose as the binding phases. Diffusion coefficients of all target compounds in the diffusive gel were determined for the first time using a diffusion cell, and stable elution efficiencies were obtained with acetonitrile/formic acid for ENVI-CARB and acetonitrile/ammonia for MCX + HLB. Both DGT devices performed robustly across wide environmental gradients: pH 3.16−9.74, ionic strength 0.1−500 mmol L−1 and dissolved organic matter up to 20 mg L−1. The total binding capacities exceeded 230 μg per disc, supporting deployments over several months in natural waters. Laboratory evaluations of diffusive layer thickness (0.515−2.015 mm), deployment time (10−168 h), storage stability (≥148 days) and competitive adsorption confirmed the reliability of the method. Field deployments at five river sites in Nanjing, China, during a 14 day period detected ribavirin (9−29 ng L−1) and lamivudine (12−29 ng L−1) as the predominant antivirals. The DGT-derived time-weighted average concentrations closely matched those from repeated grab sampling while effectively capturing episodic pollution events that individual grab samples missed. The developed DGT samplers thus provide a robust, cost-effective and sensitive tool for source tracking and long-term monitoring of antiviral drugs, overcoming the inherent limitations of conventional grab sampling in dynamic aquatic environments.