Approved Abstracts

in vivo exposure effects of polystyrene nanoplastics in the marine mussel Mytilus galloprovincialis



Author(s): Gonçalves, JM; Bebianno, MJ;
Presenter: Joanna Melissa Gonçalves

Nanoplastics (NPs) (1 – 100 nm) are an emerging concern, and there is still a scarcity of information on the effects that nanoplastics pursue on marine biota. NPs stability and feasibility to form aggregates are highly dependent for the fate, mobility and resistance of NPs. Also, regarding their nano-size properties, the biological reactivity increases as plastic particle size decreases, and with cellular boundaries being susceptible to the entry of these NPs, understanding the burden of NPs availability and its biological impact on marine biota is crucial. This study aimed to comprehend the effects on 50 nm polystyrene nanoplastics (nPS, 10 µg/L) in an in vivo (21 days) exposure in the marine mussel Mytilus galloprovincialis. Seawater quality was analysed daily by measuring salinity (36.5 ± 0.75), temperature (24.5 ± 1.5°C), pH (7.9 ± 0.2) and oxygen saturation (100 ± 1.7%). Mussels were only fed with the plankton existing in the natural seawater. A multibiomarker approach namely the antioxidant defence system (superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), glutathione – S – transferase (GST)), and oxidative damage (LPO) were the chosen biomarkers analysed in digestive glands of mussels. Aggregation/agglomeration of nanoplastics was favoured in seawater compared to ultrapure water. Results showed that nPS indicates that there is no aggregation, whereas in seawater aggregation does occur. The first line of defence, the antioxidant enzyme superoxide dismutase (SOD), increased in activity after 3- and 7-d of exposure to nPS (p < 0.05) following a decrease after 14-d, being this decrease significant after 21-d exposure (p < 0.05). On the other hand, a decrease in activity was observed in catalase (CAT) and glutathione peroxidase (GPx) (p < 0.05), whereby an inhibition pattern is observed as the time of exposure increases. Furthermore, no alterations in the biotransformation enzyme glutathione-s-transferase (GST) compared to controls were encountered (p > 0.05), although a decrease at 21-d of GST activity is significant compared to the beginning of the experiment (p < 0.05). Antioxidant enzymes were overwhelmed by nPS exposure and led to lipid peroxidation (LPO). An increase by 5-fold in LPO is encountered at 7-d of exposure to nPS (p < 0.05). Accordingly, PCA indicates that both SOD and LPO are the main loadings affecting the principal component whilst all other enzymatic responses vary in the opposite direction. The IBRv2 results also confirms that 7 days of exposure is the most crucial for mussel digestive glands. Abiotic and biotic characteristics of seawater lead to an increase in hydrodynamic diameter and aggregation of polystyrene nanoplastics. In M. galloprovincialis, 10 µg/L of 50 nm polystyrene nanoplastics overwhelmed antioxidant defences and led to oxidative damage in digestive gland of mussels. It is understood that once nanoparticles enter the internal structure of mussels, that larger NPs and aggregates are redirected to the digestive gland where they either accumulate and/or partially translocate to the haemolymph to be re-distributed to other tissues. Overall, the inhibition and induction of antioxidant defences may be a result of reactive oxygen species generated by the physical and chemical damage produced by the ingestion of NPs, and thus further analysis on a longer exposure period is essential to comprehend how mussels respond to nanoplastic exposure post 21 – days.

Keywords: digestive gland; oxidative stress; oxidative damage

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