Presence and effects of micro- (< 5mm) and nanomaterials (<100 nm, NM) in the environment are a current issue of concern. Aquatic ecosystems with high pollution pressure already present a cocktail of chemicals, where micro- ...
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Presence and effects of micro- (< 5mm) and nanomaterials (<100 nm, NM) in the environment are a current issue of concern. Aquatic ecosystems with high pollution pressure already present a cocktail of chemicals, where micro- and NMs can act as sponges for these pollutants due to their high surface to volume ratio and hydrophobic surface. This phenomenon can alter the bioavailability of the pollutants present in the aquatic ecosystem, especially for hydrophobic compounds and, therefore, modulate their toxicity to aquatic organisms. Therefore, in the present Thesis the following objectives were established: (1) To assess the potential bioavailability and toxicity of polystyrene nanoplastics (NPs), and of microplastics (MPs) alone and with sorbed polycyclic aromatic hydrocarbons (PAHs) to brine shrimp larvae and zebrafish; (2) To determine sorption capacity of PAHs to MPs and graphene oxide NMs (GNMs); (3) To assess the potential bioavailability and toxicity of GNMs alone and with sorbed PAHs to zebrafish.Exposure to pristine MPs did not cause any significant impact on brine shrimp larvae and zebrafish embryo survival, while some treatments containing elevated concentrations (mg/L) of MPs with sorbed benzo(a)pyrene (B(a)P) and B(a)P alone resulted in acute toxicity. In addition, both sizes of MPs were successful vectors of B(a)P to brine shrimp and zebrafish embryos. Results indicated that small MPs (0.5 µm) showed higher maximum sorption capacity for B(a)P than larger MPs (4.5 µm). In the case of a complex and environmentally relevant PAH mixture, as that formed in the water accommodated fraction (WAF) of a crude oil, a relatively limited sorption to 4.5 µm MPs, driven by the hydrophobicity and initial concentration of each PAH, was observed. In adult zebrafish, MPs did not act as PAH vehicle after 21-day exposure to MPs with sorbed PAHs. Only fish exposed to MPs for 21 days presented changes in the transcription level of biotransformation metabolism-related gene cyp1a in the liver, along with a significant increase in the prevalence of liver vacuolisation. 21 days of exposure to NPs, but not to MPs, caused oxidative stress in adult zebrafish. Ingestion of NPs was observed in the developing organisms (brine shrimp and zebrafish). In embryos, fluorescent NPs were specially localised in the eyes, yolk sac and tail, showing their capacity to translocate and spread into the embryo body.For GNMs, graphene oxide (GO) showed a higher sorption capacity for B(a)P than MPs. For the PAH mixture of the WAF, sorption to GO was also higher than to MPs. In embryos exposed to different GNMs alone and with PAHs, no significant mortality was recorded for any treatment. Nevertheless, malformation rate increased significantly in embryos exposed to the highest concentrations (5 or 10 mg/L) of GO, reduced GO alone and with sorbed B(a)P. According to chemical analysis of adult fish tissues, bioavailability of PAH sorbed to GO for fish was lower than in the case of PAHs alone. Only biochemical responses and genes related to biotransformation metabolism were altered in the liver of fish exposed to B(a)P for 3 days. Transcription level of genes related to oxidative stress were not altered. On the contrary, the gills of fish exposed to GO with sorbed B(a)P and to B(a)P for 3 days and co-exposed to GO and WAF for 21 days showed significantly higher oxidative stress than control fish. A common neurotoxic effect was caused in all fish treated for 21 days. Finally, adult fish exposed to GO presented GO ingestion and liver vacuolisation, but absence of GO translocation to the adult tissue was reported. The present work shows evidences of the capacity of MPs with sorbed PAHs to cause sublethal effects (1) and to carry PAHs (2) in brine shrimp and zebrafish. Finally, GO was greater carrier of PAHs to zebrafish than MPs (3) due to its higher sorption capacity (2), exerting oxidative stress and neurotoxicity as the main sublethal effects in adult zebrafish.
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