Ecotoxicological effects of neodymium on Mytilus galloprovincialis subjected to environmental changes

• Autor(a) principal: Cunha, Marta Barros
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/40789
• topic: Multiple stressors; Rare earth elements; Bioremediation; Bivalves; Paralytic shelfish toxins; Macroalgae; Biochemical parameters

Rare earth elements (REEs), particularly neodymium (Nd), are receiving growing attention due to their significant economic value, widespread applications, and their consequent increase in environmental concentrations. In addition, the environmental contamination resulting from the discharge of waste from the electrical and electronic equipment and fluorescent lamps industries is also attributed to mercury (Hg). These pollutants persist in ecosystems and accumulate in marine organisms, which has led to the development of water remediation techniques, like sorption methods, using biomass such as live marine macroalgae. The macroalga Ulva lactuca has already shown potential for removing potentially toxic elements from water. In parallel, the effects of climate change are fostering conditions conducive to harmful algal blooms (HABs), with rising temperatures and nutrient levels playing a pivotal role in their occurrence. Notably, dinoflagellate species responsible for producing paralytic shellfish toxins (PSTs) are the primary drivers of HABs events worldwide. In Portuguese coastal waters, Gymnodinum catenatum, a specific phytoplankton species, is commonly linked to the contamination of bivalves with PSTs. Thus, the first aim of this study was to assess the toxicity of the emerging pollutant Nd (70 μg Lˉ¹), induced after twenty-eight days exposure period to the mussel Mytilus galloprovincialis, and compare the effects observed with the ones caused by Hg (50 μg Lˉ¹) as a representative of a classical pollutant. Furthermore, the impacts caused by Nd (acting alone) were compared with the ones induced in mussels exposed to Nd in the presence of the macroalgae Ulva lactuca. Considering that the environment is a dynamic ecosystem with several variables acting at the same time, the present study also aimed to assess the biological effects of Nd (20 μg Lˉ¹) on the mussel M. galloprovincialis when exposed to G. catenatum for fourteen days, followed by a recovery period in uncontaminated seawater for another fourteen days. Assessing the biochemical alterations in the mussels, the results confirmed that Hg was more toxic to mussels than Nd. In addition, these studies also showed the good capability of U. lactuca in preventing the onset of cellular disturbance and homeostasis disruption in M. galloprovincialis by reducing bioavailable Hg levels. In particular, the biochemical parameters evaluated related to metabolism, antioxidant and biotransformation defences, redox balance and cellular damage, showed that algae were able to prevent biological effects in mussels exposed to Hg compared to those exposed to Nd. In the exposure of M. galloprovincialis to Nd and G. catenatum cells, after fourteen days, mussels showed similar toxin accumulation in the mix treatment (Nd and G. catenatum) in comparison with the G. catenatum treatment alone. The present study also highlighted that the toxins dcSTX and GTX5 were the contributors to toxin profile in the G. catenatum supplied to the mussels, inducing an increase in metabolism and enzyme production in the organisms exposed to the G. catenatum cells, while Nd inhibited enzyme production and caused cell damage in the mussels. In general, this study revealed that the combined presence of G. catenatum cells and Nd, produced positive synergistic effects on M. galloprovincialis biochemical responses compared to G. catenatum alone, indicating that organisms performance may be significantly modulated by the presence of multiple co-occurring stressors. In final remarks, this study showed that Hg is more toxic than Nd, inducing more biochemical changes in the organisms. With regard to the two concentrations of Nd tested (70 and 20 μg Lˉ¹), it was found that, for this metal, a longer exposure period allowed a better response from the organisms, with less cellular damage being observed in organisms exposed to a higher concentration and for a longer time. Exposure to G. catenatum cells proved to be less harmful to the M. galloprovincialis than exposure to Nd alone, since in the presence of the toxins the organisms were able to avoid cellular damage. The fourteen days of recovery period proved sufficient for M. galloprovincialis to recover its biochemical performance after exposure to G. catenatum, but the same was not observed after exposure to Nd. The present study highlights the importance of examining the ecosystem as a complex interplay of several variables acting simultaneously, encompassing abiotic and biotic stressors. Consequently, future research efforts should be directed toward addressing the anticipated impacts of climate change and the escalating contamination of aquatic ecosystems by emerging pollutants.