Assessing cadmium-based quantum dots effects on the gonads of the marine Mussel Mytilus galloprovincialis

Gonçalves, Joanna Melissa Ribeiro

http://hdl.handle.net/10400.1/12266

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Authors

Gonçalves, Joanna Melissa Ribeiro

Advisor(s)

Bebianno, Maria João

Mestre, Nélia C. Costa

Abstract(s)

Nanotechnology is found in many aspects of modern life, and its applications are continuously increasing. Engineered nanomaterials (ENMs) have helped improve the quality of life as well as economic growth. Quantum dots (QDs) are ENMs with unique optical and biofunctional properties, known to be useful in nanomedicine, biology and electronics. Of emerging concern is the fate of these ENMs, as they can enter the marine environment and prompt short-term and long-term effects on marine organisms. Tissue-specific responses in mussels have been studied, however knowledge on the effect of these ENMs in the gonads and possible effects on gametogenesis is scarce. The aim of this study was to assess the ecotoxicity of CdTe QDs (2 – 7 nm) in the gonads of the marine mussel Mytilus galloprovincialis, in comparison with its dissolved counterpart. Mussels were exposed to CdTe QDs and dissolved Cd for 14 days at 10μgCd.L-1. Cd accumulation, oxidative stress (superoxide dismutase - SOD, catalase - CAT, glutathione peroxidase - GPx, glutathione S-transferase - GST) and oxidative damage (Lipid peroxidation – LPO), were analysed in the gonads looking for a distinction between male and female responses. Results show that both Cd forms caused antioxidant responses to change in both male and female gonads, wherein QDs are more pro-oxidant when compared to dissolved Cd. In male mussels, QDs induced higher Cd accumulation than its dissolved counterpart, whilst both Cd forms showed high Cd accumulation in females. SOD, CAT, GPx and GST activities, in both male and female mussels, decreased after exposure to QDs, wherein females are the main sex affected. Females undergo oxidative damage after three days of exposure to QDs, shown by an 18.6-fold increase in LPO levels. Males also undergo oxidative damage due to exposure to QDs, with a gradual increase in LPO levels throughout exposure period. Overall, QDs mediated toxicity is time and sex-dependent, wherein QDs effect on females is prominent after a short period of exposure, whilst in males, QDs toxicity is more noticeable after a longer time of exposure. Results predominately show that females are the sex most affected by CdTe QDs. Female gonads have twice as much lipid content compared to males, and these lipid contents are important sources of energy iii during gametogenesis and for embryo and larval development. Therefore, there is a rising concern on how gametes are affected and the potential changes at the cellular level that they may undergo, making it crucial to understand the effects of ENMs on gametogenesis, fertilization success, embryogenesis and larval development, as these may have serious impacts to population sustainability and ecosystem health.

A nanotecnologia trata da manipulação da matéria a nível atómico e molecular sendo que, atualmente as suas aplicações são diversas e contribuem para o melhoramento da qualidade de vida e a tendência para o aparecimento de novas aplicações revela ser promissor. Os nanomateriais manufaturados (ENMs) são componentes utilizados em produtos consumíveis, em tecnologia informática, equipamentos químicos e em medicina. Dentro dos ENMs existem os pontos quânticos (“quantum dots” – QDs) que são nanocristais semicondutores com propriedades óticas e biofuncionais, úteis para as mais variadas áreas como a medicina, a biologia ou a eletrónica. A nível da estrutura geral, um ponto quântico é constituído por um núcleo inorgânico com um material semicondutor (e.g. CdS ou CdTe), um invólucro inorgânico com um material semicondutor (e.g. ZnS) e com um gap de energia distante, à superfície é constituído por um revestimento orgânico aquoso (e.g. -ROOH). O invólucro dos QDs protege o núcleo de fenómenos como a oxidação ou a degradação, enquanto os ligandos à superfície aumentam a solubilidade e compatibilidade na água. As características abióticas do ambiente aquático tais como o pH, a força iónica, as radiações eletromagnéticas e UV, promovem diferentes transformações físico-químicas na superfície dos QDs, alterando o seu comportamento e o seu destino no meio aquático. Contudo, tem havido uma maior preocupação sobre o destino desses ENMs uma vez que poderão acabar no oceano e provocar efeitos, a curto e longo prazo, indesejáveis para os organismos marinhos sendo importante garantir que o potencial efeito tóxico seja adequadamente estudado e compreendido.