Disparate effects of DOM extracted from coastal seawaters and freshwaters on photodegradation of 2,4-Dihydroxybenzophenone

Abstract

Dissolved organic matter (DOM) plays an important role in degradation of organic pollutants by photochemically-produced reactive intermediates (RIs), such as excited triplet-states of DOM (³DOM*), singlet oxygen (¹O₂) and hydroxyl radical (·OH). However, it is not clear whether DOM extracted from coastal seawaters (CS-DOM) and DOM derived from freshwaters (FW-DOM) exhibit similar effects on photodegradation of organic micropollutants. Herein, 2,4-dihydroxybenzophenone (BP-1) was adopted as a model compound to probe the effects of different DOM on photodegradation kinetics of organic micropollutants. Results show that the CS-DOM promotes the photodegradation of BP-1 mainly via the pathway involving ³DOM*; while ³DOM*, ¹O₂ and ·OH are responsible for BP-1 photodegradation in the presence of the FW-DOM. Compared with the FW-DOM, the CS-DOM undergoes more photobleaching, and contains less aromatic C=C and C=O functional groups. Although ³DOM* formation quantum yields for the CS-DOM are relatively higher than those for the FW-DOM, the CS-DOM has lower rates of light absorption, leading to lower steady-state RI concentrations for the CS-DOM. BP-1 photodegradation in the presence of the CS-DOM is faster than in the presence of the FW-DOM, due to higher second-order reaction rate constants between BP-1 and CS-³DOM* and fewer antioxidants contained in the CS-DOM.

Keywords: 2,4-Dihydroxybenzophenone; Dissolved organic matter; Excited triplet-state dissolved organic matter; Hydroxyl radical; Photodegradation; Singlet oxygen.