Quantifying interactions between propranolol and dissolved organic matter (DOM) from different sources using fluorescence spectroscopy

Beta blockers are widely used pharmaceuticals that have been detected in the environment. Interactions between beta blockers and dissolved organic matter (DOM) may mutually alter their environmental behaviors. To assess this potential, propranolol (PRO) was used as a model beta blocker to quantify the complexation with DOM from different sources using the fluorescence quenching titration method. The sources of studied DOM samples were identified by excitation-emission matrix spectroscopy (EEMs) combined with fluorescence regional integration analysis. The results show that PRO intrinsic fluorescence was statically quenched by DOM addition. The resulting binding constants (log K (oc)) ranged from 3.90 to 5.20, with the surface-water-filtered DOM samples claiming the lower log K (oc) and HA having the highest log K (oc). Log K (oc) is negatively correlated with the fluorescence index, biological index, and the percent fluorescence response (P (i,n)) of protein-like region (P (I,n)) and the P (i,n) of microbial byproduct-like region (P (II,n)) of DOM EEMs, while it is correlated positively with humification index and the P (i,n) of UVC humic-like region (P (III,n)). These results indicate that DOM samples from allochthonous materials rich in aromatic and humic-like components would strongly bind PRO in aquatic systems, and autochthonous DOM containing high protein-like components would bind PRO more weakly.