The role of dissolved organic matters in the aquatic photodegradation of atenolol.

Atenolol (ATL) is a photostable and hydrolysis resistant beta-blocker and has been frequently detected in natural water. In this study, mechanism on aquatic photodegradation of ATL was investigated with an emphasis on the role of dissolved organic matters (DOMs) as well as other natural water compositions (nitrate, bicarbonate and ferric ions). Significant acceleration of photodegradtion of ATL was observed in the presence of each DOMs added, namely Suwannee River Fulvic Acid (SRFA), Suwannee River Humic Acid (SRHA), Nordic Lake Fulvic Acid (NOFA) and Nordic Lake Humic Acid (NOHA). Hydroxyl radical (•OH) was determined as the main reactive species in this process, instead of singlet oxygen or excited triplet of DOM. Addition of these four DOMs all inhibited photodegradation of ATL in nitrate solutions through reducing nitrated-derived •OH and screening photons absorbed by nitrate. No loss of ATL was detected in bicarbonate solution with or without DOMs. Bicarbonate exhibited a scavenger of •OH derived from DOMs. However, in the presence of iron species, photodegradation of ATL was significantly enhanced by the addition of each DOM, due to the high yield of •OH in the photoprocess of Fe(III)-DOM complex. The photoproducts distribution of ATL demonstrated that SRFA promote the hydroxylation on aromatic ring in the presence of nitrate and reduce the ketone moiety to alcohol in the system of ferric ions. Our findings indicate that DOMs should be considered in aquatic photoprocesses of organic pollutants induced by themselves as well as other coexisting photoactive water compositions.