Dichlorine radicals (Cl2•—) promote the photodegradation of propranolol in estuarine and coastal waters

Propranolol (PRO) is frequently detected in estuarine and coastal waters, which has adverse effects on estuarine and coastal ecosystems. In this study, the effects of halide ions and DOM from estuarine and coastal waters on the photochemical transformation of PRO were investigated. The results demonstrated that the presence of Br- alone exhibited slight effect on photochemical transformation of PRO, while photodegradation rates of PRO increased with the addition of 0.1–0.54 M Cl-. The quenching experiments and the laser flash photolysis experiments together demonstrated the generation of Cl2•— in the photolytic systems. Cl2•— is possibly produced through the charge separation of exciplex of 3PRO* and Cl- rather than via direct oxidation of Cl-. Additional experiments indicated that addition of seawater DOM inhibited the halide ions-sensitized photodegradation rates of PRO, which may be due to the quenching of Cl2•— by phenolic substances in DOM molecules. Compared with pure water, three new photochemical intermediates were identified in the presence of DOM or Cl-. The direct photolysis of PRO mainly reacted by hydroxyl additions, hydroxyl elimination and de-propylation, whereas electron transfer coupled with H-abstraction by Cl2•— and 3DOM* was proposed as the primary role for PRO degradation in the presence of Cl- or DOM.