Intermediates and Reaction Pathways from the Degradation of Microcystin-LR with Sulfate Radicals

Abstract

Degradation of the cyanotoxin microcystin-LR (m/z 995.5) using sulfate radical-based advanced oxidation technologies (AOTs) and identification of reaction intermediates formed during treatment were investigated in this study. To the best of our knowledge this is the first study on the degradation and identification of reaction intermediates for any cyanotoxin with SO(4)(•-). Tandem mass spectrometry designated the formation of nine (as m/z) reaction intermediates with four of them (m/z 1011.5, 1027.5, 1029.5, and 1045.5) having multiple peaks in the TIC chromatogram. New peaks that were not observed with hydroxyl radical formed during photocatalytic oxidation (PCO) have been detected such as m/z 1045.5. The initially formed intermediates involved the oxidation of the unsaturated bonds of MC-LR especially the diene bonds located on the chain of the Adda amino acid. Subsequent intermediates implicated the oxidative cleavage of small functional groups (i.e., -COOH), up to the complete removal of the Adda chain. The electrophilic character of SO(4)(•-) is proven by the multihydroxylation of the aromatic ring. Toward the end of treatment, simultaneous oxidation of the Adda chain and the cyclic structure occurred without the formation of linear products.

Physiological and Proteomic Responses of Continuous Cultures of Microcystis aeruginosa PCC 7806 to Changes in Iron Bioavailability and Growth Rate

“…Also, MCYST is capable of effectively scavenging ·OH (28,29), though little is known of the impact that the resultant degradation products might have on cell growth or viability.…”

Comparison of UVC/S2O82− with UVC/H2O2 in terms of efficiency and cost for the removal of micropollutants from groundwater

“…•-) are currently being investigated because they have higher selectivity for oxidation and higher standard redox potentials than HO  for the abstraction of electrons (Anipsitakis and Dionysiou, 2004;Antoniou et al, 2010a;Antoniou et al, 2010b).…”

“…Atrazine, methyl tert-butyl ether (MTBE), 1,4-dioxane, cis-dichlorethene (DCE) and 1,1,1-trichlorethane) (Table A1) were chosen as model compounds because they exhibit different susceptibilities to photolysis and AOPs. Atrazine and cis-DCE can both be photolysed and they are targets for selective oxidation by sulfate radicals, due to their π-electrons in their double bonds (Antoniou et al, 2008;Antoniou et al, 2010b;Waldemer et al, 2007). MTBE and 1,4 dioxane are typically difficult treatment targets for most conventional water treatment methods and therefore are typically mentioned as target chemicals for UVC/H 2 O 2 (Burbano et al, 2002;Stefan and Bolton, 1998), while 1,1,1-trichlorethane is known to be resilient to chemical oxidation (Li et al, 2013;Nelson et al, 1990).…”

“…The obtained orders can also be explained in terms of the contaminants' structures. The double carbon bonds of DCE can undergo attack by both sulfate and hydroxyl radicals through mechanisms of hydroxyl addition or substitution (Antoniou et al, 2010b;Waldemer et al, 2007). Atrazine is susceptible to hydroxyl substitution and bond cleavage (Balci et al, 2009;Bandala et al, 2007) but heteroatoms in the aromatic ring reduce the second order rate constants for reaction with the radicals (Antoniou et al, 2009).…”

“…Free radicals are atoms or molecules that have unpaired valance electrons (odd number of electrons), which makes them particularly reactive. They can be stabilized by taking electrons from nearby compounds through e -abstraction, and reactions of addition, substitution, oxidation, and bond cleavage (Antoniou et al, 2008;Antoniou et al, 2010b;Li et al, 2013;Stefan and Bolton, 1998). Hydroxyl radicals (HO • ) are the most commonly used radicals in drinking water treatment because of their low selectivity and high reactivity with organic compounds (Buxton et al, 1988).…”