Photodegradation Of Sulfachloropyridazine In Presence Of Seawater Dissolved Organic Matter

Due to riverine input,mariculture activities and so on,coastal waters in many regions are threatened by organic micropollutants?OMPs?.It is necessary to investigate their environmental fates in coastal waters for their ecological risk assessments.Photodegradation is one of the most important degradation pathways for OMPs and dissolved organic matter?DOM?can influence this process significantly.Due to challenging in extraction of coastal seawater DOM?S-DOM?,previous studies mainly focused on freshwater DOM.As S-DOM is different from freshwater DOM in composition,their effects on photodegradation of OMPs are different.Thus,the current study employed solar irradiation experiments to investigate the effects of extracted S-DOM and commercialized freshwater DOM on photodegradation of sulfachlorpyridazine?SCP?which was frequently detected in coastal waters.The major contents and results of the current research are as follows:?1?Effects of SDOM-1?extracted from sweater influenced by mariculture?,SDOM-2?extracted from seawater witn little influence of mariculture?and Nordic lake natural organic matter?NRNOM?on photodegradation kinetics of SCP were investigated.Both two S-DOMs accelerated the photodegradation of SCP significantly with SDOM-1 more conspicuous while NRNOM showed slightly inhibition effects.Stronger light screening effect of NRNOM on direct photolysis of SCP was observed than two S-DOMs.Excited triplet-state DOM?³DOM*?are the most important photochemically produced reactive intermediate in indirect photodegradation of SCP among three DOMs.Based on the data determined above,photodegradation half-lives(t_1/2)of SCP in freshwater,estuarine water and seawater bodies in the Yellow River estuary were predicted as a function of water depth and time,and the corresponding t_1/2 are 929,849 and 479 h.?2?The reactivities of SCP with ³DOM*formed by S-DOMs and freshwater DOM were studied.With chemical probes and Folin-Ciocalteu methods,content of high-energy ³DOM*?Hi-³DOM*?and phenolic antioxidants that are highly related to reactivity of ³DOM*,were determined to explain different ³DOM*reactivities.The second-order reaction rate constant between ³DOM*and SCP(k_SCP,3DOM*)were determined as 6.05×10⁸ M^-1 s^-1>2.81×10⁸ M^-1s^-1>4.94×10⁷ M^-1 s^-1 for SDOM-1,SDOM-2 and NRNOM,respectively.Lower steady-state concentration of Hi-³DOM*in S-DOMs indicated Hi-³DOM*played trivial roles in high excited triplet-state seawater ³DOM*?³S-DOM*?reactivity.Lower phenolic antioxidants in S-DOM show low inhibition effects during reaction between ³S-DOM*and SCP,and play the pivotal role in high ³S-DOM*reactivity.For two S-DOMs,as their phenolic contents are comparable,high reactivity of ³SDOM-1*was attributed to its high content of Hi-³DOM*.