Highlights  Mytilus galloprovincialis bioaccumulated lanthanum  Mussels exposed to Lanthanum decreased their metabolic capacity  Contaminated mussels activated their antioxidant and biotransformation defences  Contaminated mussels showed increased lipid peroxidation and lower GSH/GSSG ratio  Neurotoxicity was induced in contaminated mussels  Histopathological alterations were induced by lanthanum Summary Inappropriate processing and disposal of electronic waste contributes to the contamination of aquatic systems by various types of pollutants such as the rare-earth elements (REE) in which lanthanum (La) is included. Knowledge on the toxicity of these elements in marine organisms is still scarce when compared to other metals such as mercury (Hg) and arsenic (As).

Recently, anthropogenic enrichment of rare earth elements (REE) have been reported in natural environments, due to increasing use and discharges of hospital/industrial wastewaters. Gadolinium (Gd), which is mainly used as contrast agent for magnetic resonance imaging in medical exams, may reach concentrations in water up to two orders of magnitude larger than baseline levels. Nevertheless, in marine systems scarce information is available concerning the toxicity of REE towards inhabiting organisms. This study aimed to evaluate the biochemical impact of anthropogenic Gd in the Mediterranean mussel Mytilus galloprovincialis, which is a species of commercial interest and one of the most accepted pollution bioindicator. Organisms were exposed to different concentrations of Gd (0, 15, 30, 60, 120 µg/L) for 28 days. At the end of the experiments, biomarkers related to mussels' metabolic (electron transport system activity and energy reserves content), oxidative stress status (cellular damage and the activity of antioxidant and biotransformation enzymes) and neurotoxic effects (activity of the enzyme Acetylcholinesterase) were measured, as well as Gd bioconcentration in organisms. Results showed a high content of Gd (2.5±0.50 µg/g) in mussels exposed to the highest concentration, contrary to those at control condition and at 15 and 30 μg/L of Gd (levels below 0.38 µg/g). Although no mortality was observed during the experimental period, exposure to Gd strongly affected the biochemical performance of M. galloprovincialis, including the decrease on mussels' metabolism, induction of oxidative stress and neurotoxicity, particularly evidenced at intermediate concentrations. These results may indicate that up to certain stressful levels, although lowering their metabolism, organisms may be able to activate defense strategies to avoid cellular injuries which, on the other hand, may compromise mussels physiological performance such as growth and reproduction success. Nevertheless, our findings support that the widespread utilization of Gd may represent an environmental risk in the future.

Mussels, such as the marine bivalve Mytilus galloprovincialis are sentinels for marine pollution but they are also excellent bioindicators under laboratory conditions. For that, in this study we tested the modulation of biochemical responses under realistic concentrations of the toxic metal Lead (Pb) in water for 28 days under different conditions of salinity and temperature, including control condition (temperature 17±1.0 ºC and salinity 30±1.0) as well as those within the range expected to occur due to climate change predictions (±5 in salinity and +4ºC in temperature). A comprehensive set of biomarkers was applied to search on modulation of biochemical responses in terms of energy metabolism, energy reserves, oxidative stress and damage occurrence in lipids, proteins as well as neurotoxicity signs. The application of an integrative Principal Coordinates Ordination (PCO) tool was successful and demonstrated that Pb caused an increased in the detoxification activity mainly evidenced by glutathione Stransferases and that the salinities 25 and 35 were, even in un-exposed mussels, responsible for cell damage seen as increased levels of lipid peroxidation (at salinity 25) and oxidised proteins (at salinity 35).

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