The ecotoxicology of different forms of copper (nano, micro and salt) in marine mussels
Alnashiri, Hassien Mausa
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Copper oxide nanoparticles (CuO NPs) are one example of NPs that are used in many applications, such as batteries, semiconductors and inks. The growing usage of CuO NPs will likely result in an increased release into the environment, especially the marine environment. Furthermore, there is a lack of understanding of the toxicity of CuO NPs on environmental species and humans, particularly marine benthic filter feeders where data are particularly lacking. Therefore, the focus of the current study was to assess the cytotoxicity (cell viability) and genotoxicity (DNA damage and oxidative stress) of different forms of Cu in relevant biomarker organisms, the blue mussels Mytilus edulis and the horse mussel Modiolus modiolus. Both mussels were exposed to different concentrations (5, 10, 15 and 20 μgL-1) of different forms of particulate CuO (NPs, microparticles, MPs) and copper salt (CuSO4), for 72 hours. Flow cytometry and trypan blue techniques were used to assess the viability of the haemocytes of the mussels and the Comet assay was used to assess DNA damage in the haemocytes and gill cells of the mussels. Superoxide dismutase (SOD assay) and the thiobarbituric acid reactive substances (TBARS assay) were used to assess oxidative stress measuring SOD enzyme activity and lipid peroxidation level in gill cells of the mussels after the exposure period (72 hours). Results indicated that all three forms of Cu (NPs, MPs and salt) have the potential to decrease the cell viability in haemolymph cells for both type of mussels, M. edulis and M. modiolus in a concentration response manner. Similarly, NPs, MPs and salt forms of Cu caused DNA damage in both types of cells (haemolymph and gill) for M. edulis and M. modiolus mussels even at low concentrations (5μgL-1), which is consistent with the cell viability results. Moreover, SOD activity and lipid peroxidation were observed to have increased in the cells of mussels exposed to all forms of Cu, indicating oxidative stress. Overall, the nano form of Cu appears to be more toxic to both mussel species, more than the micro and salt forms. These effects are primarily influenced by the special features of NPs, particularly their small size and large surface area, which affect the amount of Cu ions released into the exposure medium and inside the exposed cells. Furthermore, M. edulis mussels were more sensitive to Cu forms than M. modiolus, especially when exposed to nano forms of CuO. Furthermore, the use of both mussel species (M. edulis and M. modiolus) as bioindicator organisms is useful in the determination of the toxicity of the different Cu forms (nano, micro and salt).