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

Abstract

Manganese (Mn), an essential metal in trace amounts, and chromium (Cr), a nonessential metal to algae, are often found in effluent discharges and may co‐occur in contaminated aquatic environments. Therefore, we investigated the effects of Mn and Cr, and their mixtures, on a freshwater Chlorophyceae, Raphidocelis subcapitata, using a multiple endpoint approach. Regarding the single exposure of metals, Mn was 4 times more toxic (median inhibitory concentration at 72 h [IC5072 h] = 4.02 ± 0.45 µM Mn) than Cr (IC5072 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 curve. Overall, the tested metals did not lead to significant changes in reactive oxygen species 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 and independent action were used to analyze the data, and the independent action model was the best fit to describe our results. Therefore, the Mn and Cr mixture was noninteractive, showing additive effects. This is the first study to address the combined toxicity of Mn and Cr regarding freshwater Chlorophyceae. Environ Toxicol Chem 2022;41:1004–1015. © 2022 SETAC

Effects of Cadmium and Nickel Mixtures on Multiple Endpoints of the Microalga Raphidocelis subcapitata

“…Decreased Chl a fluorescence (FL3‐H) may indicate damage to photosynthetic processes (Alho et al, 2022). Studies have indicated that Ni can interfere with photosynthesis, inhibiting electron transport and decreasing Φ M , because it can replace Mg in the chlorophyll molecule and compete with Ca 2+ at its binding site (Baumann et al, 2009; Boisvert et al, 2007).…”

“…Furthermore, high levels of oxidative radicals can lead to failures in cell volume regulation (Jamers et al, 2013), and the cell cycle can be interrupted before the division step (Machado & Soares, 2014). Previous studies with the microalgae R. subcapitata also observed increased cell size after exposure to environmental concentrations of Zn, Al (Gebara et al, 2020), Mn, and Cr (Alho et al, 2022). Jamers et al (2009) exposed Chlamydomonas reinhardtii to Cd and observed an increase in cell size at 0.56 mg L −1 .…”

“…Asterisks represent significant differences from the control group (p < 0.05). exposure), and by Alho et al (2022) at 0.4 and 1.0 mg Cr L −1 (after 48h of exposure). These results suggest that the decrease may be due to the antioxidant mechanisms that algae have, such as low-molecular-weight compounds and enzymes (ascorbate, GSH, ascorbate peroxidase, catalase, glutathione peroxide, and superoxide dismutase) that allow algae to decrease their intracellular content of ROS (Pinto et al, 2003).…”

“…Franklin et al (2002) studied Cd, Cu, and Zn mixtures and observed synergistic effects in Cu–Cd mixtures and antagonistic effects in Cu–Zn, Cd–Zn, and Cu–Cd–Zn combinations, on the microalga Chlorella pyrenoidosa . Alho et al (2022) explored the effects of chromium (Cr) and manganese (Mn) on R. subcapitata and found that the metals did not interact according to reference models (CA and IA), indicating an additive effect in the mixture. Moreover, Qian et al (2009) exposed Chlorella vulgaris to a Cu and Cd mixture, observing a synergistic increase in ROS production and a simultaneous decrease in chlorophyll content.…”

Key Properties for the Toxicity Classification of Chemicals: A Comparison of the REACH Regulation and Scientific Studies Trends

“…The most widespread tests are growth inhibition test, measurement of chlorophyll values, or evaluation of several biomarkers that can be used to determine if chemicals can affect the algae community. Some species used are Chlorella pyrenoidosa [96] and Raphidocelis subcapitata [93,94,97,98].…”