Effects of cadmium and cobalt mixtures on growth and photosynthesis of Raphidocelis subcapitata (Chlorophyceae)

• Published in: Aquatic toxicology Vol. 244; p. 106077
• Main Authors: dos Reis, Larissa Luiza, Alho, Lays de Oliveira Gonçalves, de Abreu, Cínthia Bruno, Gebara, Renan Castelhano, Mansano, Adrislaine da Silva, Melão, Maria da Graça Gama
• Format: Journal Article
• Language: English
• Published: Netherlands Elsevier B.V 01-03-2022
• Subjects: Cadmium - toxicity; Chlorophyceae; Chlorophyll A; Cobalt - toxicity; Combined effects; Ecotoxicology; Metal toxicity; Photosynthesis; Species sensitivity distribution; Synergism; Water Pollutants, Chemical - toxicity; Species sensitivity distribution; Combined effects; Ecotoxicology; Synergism; Metal toxicity
• ISSN: 0166-445X; 1879-1514
• DOI: 10.1016/j.aquatox.2022.106077

•IC50–96h values of growth inhibition of R. subcapitata were 0.08mg L−1 Cd and 0.11 mg L−1 Co•CA model and DR deviation best fitted to our data in mixture tests.•In mixtures, synergic effects occurred above 0.1 mg Co L−1 and below 0.05 mg Cd L−1.•In mixtures, antagonism occurred above 0.05 mg Cd L−1 and below 0.1 Co mg L−1.•We found antagonism effects on maximum quantum yield (ΦM) and oxygen evolving complex (OEC).
Metals occur simultaneously in the environment, and therefore it is important to know their toxicity and mechanism of action when associated with another metal. Furthermore, anthropogenic actions increase their concentrations in the environment where they can interact and undergo transformations that can even increase their toxicity. This study aimed to evaluate the effects of cadmium (Cd) and cobalt (Co), isolated and combined, on the microalgae Raphidocelis subcapitata. Regarding the toxicity of isolated metals, the IC5096 h was 0.08 mg L−1 of Cd and 0.16 mg L−1 of Co. Cell density decreased at all concentrations of the Cd tested. The parameters related to cell size, cell complexity and mean cell chlorophyll a (Chl a) fluorescence were significantly affected by both metals. According to species sensitivity curves (SSD), the microalgae R. subcapitata was the second most sensitive organism to Co exposure and the tenth concerning Cd. Metal mixture data were best fitted to the concentration addition (CA) model and dose-ratio dependence (DR) deviation, showing synergism at high concentrations of Co and low concentrations of Cd. Besides that, antagonism was observed at low concentrations of Co and high concentrations of Cd. Photosynthetic performance, assessed by maximum quantum yield (ΦM) and oxygen evolving complex (OEC), presented antagonism effects for both analyzed parameters. Thus, the mixture of Cd and Co showed synergistic and antagonistic interactions for the parameters analyzed in R. Subcapitata, indicating the importance of understanding the mechanisms of toxicity of metal mixtures in phytoplankton.