Studies of the liposolubility and the ecotoxicity of MC-LR degradation by-products using computational molecular modeling and in-vivo tests with Chlorella vulgaris and Daphnia magna
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Section snippets
Introdution
The rapid growth of cyanobacteria in surface waters has attracted considerable attention due to the damage these organisms are causing to the ecological environment and human health (Wang et al., 2017; Su et al., 2020; Liang et al., 2020). These blooms may be associated with the formation of toxic metabolites in which cyanotoxins are commonly present (Liang et al., 2020). Among these toxins, Microcystine-Leucine Arginine (MC-LR) is one of the most common congeners and also one of the variants
Microcystin-LR and study water
The microcystin-LR used in this study was obtained from a strain of the cyanobacterium Microcystis aeruginosa (Word Data Center Microorganisms 835). The total MC-LR was considered: the sum of extracellular and intracellular fractions. For this, the cyanobacterial culture samples were subjected to three freeze/thaw cycles, with the objective of causing cell lysis and consequent release of the intracellular toxin to the extracellular medium (Brooke et al., 2006; Wang and Bai, 2017).
In the
Advanced oxidation process
Regarding the characterization of the study water, alkalinity of 53 mg.L−1 CaCO3 was obtained, hardness 40 mg.L−1 CaCO3 and pH around 7.6. Also observed were true color, turbidity and MC-LR in concentrations of, respectively, 105 Hz, 23 NTU and 5 µg.L−1. These physical-chemical characteristics are similar to those found in natural waters with high levels of contamination by cyanotoxins (Thees et al., 2018). Percent of color removal, turbidity and MC-LR concentration data at the end of the T1-T5
Conclusion
It was found that coagulation, decantation and filtration steps did not contribute to the removal of MC-LR, after oxidation by the action of OH• radicals coming from the Fenton process. Toxin oxidation triggered the formation of oxidation by-products, of which the m/z 445 fragment was the most abundant and resistant to degradation, maintaining the molecular structure of diene bonds, which confer Adda toxicity. The surface charge intensity of the by-product molecule of m/z 445 (tPSA = 132.88 Ų)
CRediT authorship contribution statement
Maria Virgínia da Conceição Albuquerque: Methodology, Formal analysis, Investigation, Writing – original draft. Railson de Oliveira Ramos: Data curation, Software, Writing – review & editing. Valderi Duarte Leite: Conceptualization, Supervision, Resources. José Tavares de Sousa: Supervision, Resources, Writing – review & editing. Mário César Ugulino de Araújo: Software, Resources, Writing – review & editing. Beatriz Susana Ovruski de Ceballos: Methodology, Investigation, Supervision, Writing –
Declaration of Competing Interest
The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper.
Acknowledgments
The authors wish to thank Conselho Nacional de Desenvolvimento Científico e Tecnológico (CNPq), Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (CAPES), and Fundação de Apoio à Pesquisa do Estado da Paraíba (FAPESQ-PB). The English text of this paper has been revised by Sidney Pratt, Canadian, MAT (The Johns Hopkins University), RSAdip - TESL (Cambridge University).
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