Investigation and application of diffusive gradients in thin films for in situ monitoring of pharmaceuticals in surface water during rainfall events.

Pharmaceutically active compounds have garnered increased attention as emerging contaminants due to their widespread presence and potential ecological impacts. This study conducted a field evaluation under varied rainfall conditions, assessing the effects of rainfall intensity and duration on pharmaceutical concentrations. Grab sampling was complemented by the deployment of diffusive gradients in thin films (DGT) passive samplers along two urban rivers in Beijing, China. Twenty-four target pharmaceuticals were detected, with concentrations ranging from 370 to 686 ng/L in the Beixiao River and 376 to 610 ng/L in the Qing River. Rainfall influenced pharmaceutical concentrations through either dilution or enhancement, depending on local factors. Rainfall had a minimal impact on DGT performance, while biofouling showed compound-specific effects. For about 70 % of the pharmaceuticals, hydrophilic poly tetrafluoroethylene (PTFE) membranes used over 9-15 days effectively minimized biofouling influence (Mbiofouled/Mclean > 0.8). The effectiveness of DGT for long-term monitoring depended on the biofilm formation time. Overall, DGT proved to be a reliable tool for accurately characterizing pharmaceutical concentrations in dynamic water systems. This study represents the first attempt to evaluate DGT performance for pharmaceuticals under fluctuating concentration scenarios in the field, providing valuable insights into the occurrence and environmental behavior of these contaminants.