Influence of humic acids on the passive sampling of pharmaceutical compounds by POCIS and DGT

POCIS (Polar Organic Chemical Integrative Samplers) and DGT (Diffusive Gradients in Thin Films) are increasingly used for monitoring trace organic contaminants in aquatic environments. However, the influence of dissolved organic matter (DOM) on these samplers has remained poorly explored. This study investigates the potential influence of humic acids (HA) on the DGT and POCIS sampling performance for selected pharmaceuticals with different physicochemical properties. The sampling of six pharmaceuticals - atenolol (ATE), sulfadiazine (SDZ), trimethoprim (TMP), sulfamethoxazole (SMZ), carbamazepine (CBZ) and diclofenac (DCF) - was compared in the presence and the absence of humic acids at 5, 20 and 50 mgC.L^-1 under controlled laboratory conditions. For SMZ and SDZ, HA had no impact on POCIS and DGT sampling. In contrast, sampling of TMP was significantly influenced by the presence of HA, with a concentration-dependent impact in both POCIS and DGT experiments, and a sampling rate decrease of up to 92%. Finally, the sampling of ATE and CBZ was affected only at the highest HA concentration and just for DGT experiments. These findings highlight the importance of accounting for DOM effects when interpreting passive sampler data.