Mechanism studies on chlorine and potassium permanganate degradation of microcystin-LR in water using high-performance liquid chromatography tandem mass spectrometry

Abstract

The presence of microystins (MCs) in water has the potential to harm people's health. In the MCs various isomers, MC-LR has the strongest toxicity and is the most harmful one. At present, several kinds of pre-oxidants, which are commonly used in water treatment process, are effective to remove MC-LR. However, it is still not clear about their degeneration mechanisms. Chlorine and potassium permanganate were selected in the present work since they are used worldwide for preoxidation treatment. Using the testing method of HPLC-MS, studies on the degeneration of MC-LR were conducted. The results indicate that HPLC-MS is creditable and sensitive. It was also found that linear relationship between concentration of MC-LR and peak area holds in the range of 5-500 microg.L(-1) on the calibration curves, the correlation coefficient (R2) is 0.9993. Under the general condition of oxidant dose and reaction time, MC-LR was degraded rapidly. With active chlorine and potassium permanganate the degradation reaction followed the mode of first-order kinetics. The molecular weight of the degradation product was determined through analyzing the full-scan mass spectrum of MC-LR. And the oxidative degradation mechanism of MC-LR was discussed as well.

Oxidation of Microcystins by Permanganate: pH and Temperature-Dependent Kinetics, Effect of DOM Characteristics, and Oxidation Mechanism Revisited

“…Permanganate (MnO 4 – ; Mn­(VII)) is an oxidant used for the removal of organic contaminants, and offers advantages that include wide available pH conditions, ease of handling, relatively low oxidant demand, low cost, and absence of production of harmful byproducts (unlike ozone and chlorines). − The oxidation of MCs by Mn­(VII) has been studied from various aspects, including the kinetics and mechanism of MC oxidation, effects of treatment conditions and water quality parameters, and toxicity changes. The literature has reported second-order rate constants for the reactions of representative MCs with Mn­(VII) ( k Mn(VII),MC ). − Oxidation mechanisms have also been studied: dihydroxylation of alkene groups in Adda and Mdha moieties of MCs (refer to Figure ) was postulated as a primary oxidation mechanism, ,, which was further supported by mass spectrometry. , In addition, it has been demonstrated that the hepatotoxicity of MCs is effectively removed by Mn­(VII) oxidation . The effects of water quality parameters, such as pH, temperature, and organic and inorganic substances, have also been examined, showing that dissolved organic matter (DOM) is an important factor that affects the MC-LR oxidation rate by Mn­(VII). ,, …”

Physico-chemical treatment for the degradation of cyanotoxins with emphasis on drinking water treatment—How far have we come?

“…Although chlorination treatment forms product due to the nucleophilic substitution reaction, still it might be believed that the formation rate of these hydroxylated products (linked to reduced toxicity) is accelerated using UV/chlorination treatment. Hence, Hybridized oxidation methods not only have potential to eliminate the toxicity level of the final solution but also promises to reduce the treatment period which is equally important for the drinking water plant (operational) perspective.A different perspective of reducing the microcystin toxicity apart from hydroxylation is the ability of MCs to form ketone by-products (keto-MCs)[117]. A DWTP which employs permanganate addition before chlorination (for disinfection), might change the requirement of chlorine dose demanded in excess to remove the cyanotoxins (or MCs).…”

Fast removal of cyanobacterial toxin microcystin-LR by a low-cytotoxic microgel-Fe(Ⅲ) complex

“…The pH value may play a decisive role during MC-LR removal because the structure and characteristics of both microgel-Fe(Ⅲ) and MC-LR were very dependent on it. Also, initial and final concentration of MC-LR treated by microgel-Fe(Ⅲ) or the isotherm study was also a key factor which should be considered first for different MC-LR removal methods (Feitz and Waite, 2003;Huang et al, 2008).…”