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). Therefore, this study aims to assess the toxicity of La on the mussel Mytilus galloprovincialis, considered a good bioindicator of aquatic pollution, through the analysis of metabolic, oxidative stress, neurotoxicity and histopathological markers. Organisms were exposed to different concentrations of La for a period of 28 days (0, 0.1, 1, 10 mg/L) under controlled temperature (18 °C ± 1.0) and salinity (30 ± 1) conditions. La concentrations in mussels increased in higher exposure concentrations. La exposure demonstrated a biochemical response in mussels, evidenced by lowered metabolism and accumulation of energy reserves, activation of the antioxidant defences SOD and GPx as well as the biotransformation enzymes GSTs, especially at intermediate concentrations. Despite oxidative stress being shown by a decrease in GSH/GSSG, oxidative damage was avoided as evidenced by lower LPO and PC levels. Inhibition of the enzyme AChE demonstrated the neurotoxicity of La in this species. Histopathological indices were significantly different from the control group, indicating impacts in gonads, gills and digestive glands of mussels due to La. These results show that La can be considered a risk for marine organisms and thus its discharge into the environment should be monitored.

Recently, anthropogenic enrichment of rare earth elements (REEs) 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 defence 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.

As a consequence of their unique characteristics, the use of Engineered Nanomaterials (ENMs) is rapidly increasing in industrial, agricultural products, as well as in environmental technology. However, this fast expansion and use make likely their release into the environment with particular concerns for the aquatic ecosystems, which tend to be the ultimate sink for this type of contaminants. Considering the settling behaviour of particulates, benthic organisms are more likely to be exposed to these compounds. In this way, the present review aims to summarise the most recent data available from the literature on ENMs behaviour and fate in aquatic ecosystems, focusing on their ecotoxicological impacts towards marine and estuarine bivalves. The selection of ENMs presented here was based on the OECD's Working Party on Manufactured Nanomaterials (WPMN), which involves the safety testing and risk assessment of ENMs. Physical-chemical characteristics and properties, applications, environmental relevant concentrations and behaviour in aquatic environment, as well as their toxic impacts towards marine bivalves are discussed. Moreover, it is also identified the impacts derived from the simultaneous exposure of marine organisms to ENMs and climate changes as an ecologically relevant scenario.