Individual and Combined Effects of Manganese and Chromium on a Freshwater Chlorophyceae

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Abstract
Manganese (Mn), an essential metal in trace amounts, and Chromium (Cr), a non-essential metal to algae, are often found in effluent discharges and may co-occur in contaminated aquatic environments. Therefore, we aimed to investigate the effects of Mn and Cr, and their mixtures, on freshwater Chlorophyceae Raphidocelis subcapitata using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (IC50-72 h = 4.02 ± 0.45 µM Mn) than Cr (IC50-72 h = 16.42 ± 4.94 µM Cr) for microalgae, considering the effects on the relative growth rate. Moreover, this species was the most sensitive to Mn, according to the Species Sensitivity Distribution (SSD) curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species (ROS)production, cellular complexity and cell relative size, but significantly decreased the algal growth and the mean cell chlorophyll a (Chl a) fluorescence at the highest concentrations (3.64 - 14.56 µM of Mn, and 15.36 - 19.2 µM of Cr). The decreased mean cell Chl a fluorescence indicates an impact on pigment synthesis, which may be related to the observed growth inhibition. In the mixture tests, the reference models Concentration Addition (CA) and Independent Action (IA) were used to analyze the data, and the IA model was the best fit to describe our results. Therefore, Mn and Cr mixture is non-interactive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. This article is protected by copyright. All rights reserved. © 2022 SETAC.
Funding Information
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (1422758)
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (141126/2017-5, 305229/2016-8)
  • Fundação de Amparo à Pesquisa do Estado de São Paulo (2016/00753-7, 2018/07988-5)
  • Coordenação de Aperfeiçoamento de Pessoal de Nível Superior (1422758)
  • Conselho Nacional de Desenvolvimento Científico e Tecnológico (141126/2017‐5, 305229/2016‐8)

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