title: Halogen Radicals Promote the Photodegradation of Microcystins in Estuarine Systems.
abstract: The transport of microcystin, a hepatotoxin produced by cyanobacteria (e.g., Microcystis aeruginosa), to estuaries can adversely affect estuarine and coastal ecosystems. We evaluated whether halogen radicals (i.e., reactive halogen species (RHS)) could significantly contribute to microcystin photodegradation during transport within estuaries. Experiments in synthetic and natural water samples demonstrated that the presence of seawater halides increased quantum yields for microcystin indirect photodegradation by factors of 3-6. Additional experiments indicated that photoproduced RHS were responsible for this effect. Despite the fact that dissolved organic matter (DOM) concentrations decreased in more saline waters, the calculated photochemical half-life of microcystin decreased 6-fold with increasing salinity along a freshwater-estuarine transect due to the halide-associated increase in quantum yield. Modeling of microcystin photodegradation along this transect indicated that the time scale for RHS-mediated microcystin photodegradation is comparable to the time scale of transport. Microcystin concentrations decline by ∼98% along the transect when considering photodegradation by RHS, but only by ∼54% if this pathway were ignored. These results suggest the importance of considering RHS-mediated photodegradation in future models of microcystin fate in freshwater-estuarine systems.
authors.affiliation: Department of Civil and Environmental Engineering, Stanford University , 473 Via Ortega, Stanford, California 94305, United States.
authors.forename: Kimberly M
authors.initials: KM
authors.lastname: Parker
authors.affiliation: Aquatic Ecology and Ecosystem Studies, School of Civil, Environmental and Mining Engineering, The University of Western Australia , 35, Stirling Highway M015, Crawley, Western Australia 6009, Australia.
authors.forename: Elke S
authors.initials: ES
authors.lastname: Reichwaldt
authors.affiliation: Aquatic Ecology and Ecosystem Studies, School of Civil, Environmental and Mining Engineering, The University of Western Australia , 35, Stirling Highway M015, Crawley, Western Australia 6009, Australia.
authors.forename: Anas
authors.initials: A
authors.lastname: Ghadouani
authors.affiliation: Department of Civil and Environmental Engineering, Stanford University , 473 Via Ortega, Stanford, California 94305, United States.
authors.forename: William A
authors.initials: WA
authors.lastname: Mitch
mesh_terms: D063366:Estuaries; D006207:Half-Life; D006219:Halogens / Q000737:chemistry*; D052998:Microcystins / Q000737:chemistry*; D010782:Photolysis
chemical_list: D006219:Halogens; D052998:Microcystins