title: Oxidation of microcystin-LR by ferrate(VI): kinetics, degradation pathways, and toxicity assessments.
abstract: The presence of the potent cyanotoxin, microcystin-LR (MC-LR), in drinking water sources poses a serious risk to public health. The kinetics of the reactivity of ferrate(VI) (Fe(VI)O4(2-), Fe(VI)) with MC-LR and model compounds (sorbic acid, sorbic alcohol, and glycine anhydride) are reported over a range of solution pH. The degradation of MC-LR followed second-order kinetics with the bimolecular rate constant (kMCLR+Fe(VI)) decreasing from 1.3 ± 0.1 × 10(2) M(-1) s(-1) at pH 7.5 to 8.1 ± 0.08 M(-1) s(-1) at pH 10.0. The specific rate constants for the individual ferrate species were determined and compared with a number of common chemical oxidants employed for water treatment. Detailed product studies using liquid chromatography-mass spectrometry/mass spectrometry (LC-MS/MS) indicated the oxidized products (OPs) were primarily the result of hydroxylation of the aromatic ring, double bond of the methyldehydroalanine (Mdha) amino acid residue, and diene functionality. Products studies also indicate fragmentation of the cyclic MC-LR structure occurs under the reaction conditions. The analysis of protein phosphatase (PP1) activity suggested that the degradation byproducts of MC-LR did not possess significant biological toxicity. Fe(VI) was effective for the degradation MC-LR in water containing carbonate ions and fulvic acid (FA) and in lake water samples, but higher Fe(VI) dosages would be needed to completely remove MC-LR in lake water compared to deionized water.
authors.affiliation: Department of Chemistry and Biochemistry, Florida International University , 11200 SW Eighth Street, Miami, Florida 33199, United States.
authors.forename: Wenjun
authors.initials: W
authors.lastname: Jiang
authors.forename: Long
authors.initials: L
authors.lastname: Chen
authors.forename: Sudha Rani
authors.initials: SR
authors.lastname: Batchu
authors.forename: Piero R
authors.initials: PR
authors.lastname: Gardinali
authors.forename: Libor
authors.initials: L
authors.lastname: Jasa
authors.forename: Blahoslav
authors.initials: B
authors.lastname: Marsalek
authors.forename: Radek
authors.initials: R
authors.lastname: Zboril
authors.forename: Dionysios D
authors.initials: DD
authors.lastname: Dionysiou
authors.forename: Kevin E
authors.initials: KE
authors.lastname: O'Shea
authors.forename: Virender K
authors.initials: VK
authors.lastname: Sharma
mesh_terms: D000812:Anhydrides / Q000737:chemistry; D002853:Chromatography, Liquid; D005618:Fresh Water / Q000737:chemistry; D005998:Glycine / Q000031:analogs & derivatives / Q000737:chemistry; D000441:Hexanols / Q000737:chemistry; D007501:Iron / Q000737:chemistry*; D007700:Kinetics; D008387:Marine Toxins; D052998:Microcystins / Q000737:chemistry* / Q000633:toxicity; D016877:Oxidants / Q000737:chemistry; D010084:Oxidation-Reduction; D054645:Protein Phosphatase 1 / Q000037:antagonists & inhibitors; D013011:Sorbic Acid / Q000737:chemistry; D053719:Tandem Mass Spectrometry; D014867:Water
chemical_list: D000812:Anhydrides; D000441:Hexanols; D008387:Marine Toxins; D052998:Microcystins; D016877:Oxidants; D014867:Water; C065785:sorbyl alcohol; C017311:ferrate ion; D007501:Iron; D054645:Protein Phosphatase 1; C057862:cyanoginosin LR; D005998:Glycine; D013011:Sorbic Acid