Environmental Photodegradation Of A Representative Benzotriazole UV Stabilizer (UV-P) In Coastal Seawaters

Photodegradation is a major elimination pathway for many trace organic contaminants?TOrCs?in the aquatic environments.Benzotriazole UV stabilizers?BT-UVs?are added to a variety of plastic products due to photo-stability,which have been detected in environments frequently.As far as we know,there are no available data about the photochemical behaviour of BT-UVs.It is of significance to investigate whether BT-UVs would show remarkable photo-stability and pontential persistence in the aquatic environments.Aquatic factors are important in regulating photodegradation of TOrCs.Dissolved organic matter?DOM?from freshwaters has been proved to influence photodegradation of many TOrCs,and the effects depend on sources of DOM and structures of contaminants.DOM from coastal seawaters are in high concentration and have specific DOM input,due to anthropogenic discharges,such as mariculture activities.Previous studies showed marine DOM can promote photodegradation of sulfonamide antibiotics.But little is known about the role of marine DOM in photodegradation of TOrCs?e.g.,BT-UVs?.In this study,the photodegradation of a representative molecular structure of BT-UVs,2-?2-hydroxy-5-methylphenyl?benzotriazole?UV-P?,was investigated in coastal seawaters,especially the effects of coastal seawater DOM and halide ions on photodegradation of UV-P.Major content and results of this research are as follows:?1?Simulated sunlight experiments were performed,and the photodegradation kinetics of UV-P in phosphate buffer solution?PBS?,freshwater and coastal seawaters were measured.Results show that observed photodegradation rate constants and quantum yields of UV-P are smaller under neutral conditions?neutral form?than that under acidic or alkaline conditions?ionic forms?.The rates in natural waters are one order larger than that in PBS,which can attribute to the high reactivity between UV-P and reactive intermediates?RIs?.The second-order rate constants of UV-P with singlet oxygen?¹O₂?,hydroxyl radical?HO??and triplet excited state of DOM?³DOM^*?are higher than that of some of antibiotics,medicine,sunscreen and flame retardant.Based on the foregoing data,photodegradation half-lives(t_1/2)of UV-P in seawater,freshwater and estuarine water bodies in the Yellow River estuary were predicted as a function of water depth?0-2 m?and time?0-24 h?,and the corresponding average t_1/2 values were 41.93 h,49.66 h and 24.38 h,respectively.?2?The effects of DOM and halide ions on photodegradation of UV-P were studied.Results show that both three types of seawater DOM?DOM-S1,DOM-S2,DOM-S3?impacted less or more by mariculture and Suwannee River Natural Organic Matter?SRNOM?can promote photodegradation of UV-P.DOM accelerate the photodegradation rates mainly via ³DOM^*,and the contribution of 4 types of DOM to indirect photodegradation of UV-P are measured to be in the range of 98.361%-99.278%.The roles of ¹O₂ and HO?are negligible in the matrixes.The photodegradation rates of UV-P are positively correlated with the concentrations of DOM.DOM affect the photodegradation of UV-P mainly via forming reactive intermediates,not antioxidation.Both Cl??0.54 M?and Br??0.8 mM?can promote photodegradation of UV-P at a concentration of seawater level.Seawater DOM and halide ions are antagonists to photodegradation of UV-P with decreased steady-state concentration of ³DOM^*under coexistence conditions.