| Author: | Yuen, Lai Shan |
| Title: | Cellular and physiological impacts of nanoplastics on the green-lipped mussel perna viridis under ocean acidification |
| Advisors: | Fang, Kar-hei James (ABCT) |
| Degree: | M.Phil. |
| Year: | 2024 |
| Subject: | Plastics -- Environmental aspects Ocean acidification Perna Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Applied Biology and Chemical Technology |
| Pages: | x, 101 pages : color illustrations |
| Language: | English |
| Abstract: | Plastics serve as an essential component of modern daily life worldwide, but a notable portion of these plastics eventually turn into waste and find their way into the ocean. Plastic waste breaks down into microplastics (1–5,000 µm) and nanoplastics (NPs; 1–1,000 nm) through processes like ultraviolet degradation. NPs, in comparison to larger-sized plastics, pose a greater biological threat as they can more easily enter cells, leading to immunological stress and oxidative damage that can hinder growth. Among marine organisms, bivalves are particularly susceptible to the impact of NPs due to their filter-feeding nature, which makes ingestion and bioaccumulation of NPs seemingly inevitable. Given the indispensable role of plastics in human society, it is expected that the environmental abundance of NPs will increase in the future. This escalation coincides with the occurrence of ocean acidification (OA), often referred to as the "evil twin" of climate change, which arises from anthropogenic carbon dioxide (CO2) emissions. OA is associated with reduced seawater pH and decreased calcium carbonate saturation, posing a significant risk to marine life, especially calcifying organisms that rely on calcium carbonate for their growth. When OA intersects with NPs, it presents an unresolved understanding of the nature of their interaction and the subsequent biological and ecological consequences. In light of this, the aim of this thesis is to investigate the combined effects of OA and NPs, using the green-lipped mussel Perna viridis as the model species, a calcifying filter-feeder which is vulnerable to both OA and NPs. A factorial-design experiment of OA and NPs was performed for P. viridis over 30 days. Mussels were exposed to four OA scenarios at pH 8.1, 8.0, 7.8 and 7.7, with the partial pressure of CO2 validated to be approximately 470 µatm, 590 µatm, 830 µatm and 1140 µatm, respectively. There were two treatments for each scenario, one without and one dosed with NPs. This experimental design led to eight treatments (4 levels of pH × 2 levels of NPs). The exposure level of NPs was environmentally realistic at 4 × 106 particles mL-1, for 2 h daily. At the end of the experiment, a total of 12 biological endpoints were examined in P. viridis to evaluate the individual and combined effects of OA and NPs. Four out of the 12 endpoints served as immunological biomarkers measured in haemocytes: Two of them, namely oxidative activity and apoptosis, exhibited significant increases in response to reduced pH, while the other two, lysosomal content and phagocytosis, decreased and increased significantly upon exposure to NPs, respectively. Another set of four endpoints focused on oxidative stress biomarkers assessed in soft tissue: Significantly higher activities of superoxide dismutase (SOD) and catalase (CAT), accompanied by decreased glutathione (GSH) content, were observed under the OA scenarios. Nevertheless, the levels of the four biomarkers related to oxidative stress, i.e. SOD, CAT, GSH and lipid peroxidation, all significantly increased in the presence of NPs. The remaining four endpoints centered around physiological changes at the individual level: The values of shell index, condition index and hepatosomatic index remained relatively consistent across all treatments. However, a significant increase was determined in the energy reserves of P. viridis under one of the OA scenarios. Among the 12 endpoints examined, there were no statistically significant interaction effects detected between pH and NPs in eight of them. In the remaining four endpoints (lysosomal content, phagocytosis, SOD and energy reserves), the obtained data trends across treatments did not support the presence of any synergistic or antagonistic interaction. Thus, it is likely that an additive interaction was predominantly at play in these cases. Furthermore, out of the 66 pairs of correlations analysed among the 12 endpoints in P. viridis, 11 pairs were statistically significant, and seven of them were specifically linked to condition index and energy reserves. These findings suggest the usefulness of the two higher-level physiological changes to integrate the cellular stress responses, particularly the activities of SOD and CAT, which, vice versa, can serve as early-warning biomarkers to reflect the overall health status under the impacts of OA and NPs. |
| Rights: | All rights reserved |
| Access: | open access |
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