Introduction
Bivalve aquaculture plays a key role in global seafood production, with many species reared in coastal areas that are highly exposed to anthropogenic contamination, including marine litter (Van Der Schatte Olivier et al., 2020). As sessile and filter-feeding organisms, bivalves are particularly prone to accumulate contaminants and suspended particles, e.g. microplastics, which may pose risks from ecotoxicological and seafood safety standpoints (Tanaviyutpakdee & Karnpanit, 2023). To counteract this pervasive problem, the plastic industry has invested in the development of "eco-friendly" alternative materials made from natural and renewable sources and/or with the capacity to biodegrade (Rosenboom et al., 2022). However, and, in case of bio-degradable polymers this tendency is higher than for conventional plastics, as bio-fragmentation occurs simultaneously to typical fragmentation from natural drivers (UV-radiation, temperature, oxygen and mechanical stress). In addition, literature regarding the ecotoxicological aspects of bio-based plastics is scarce, thus, failing to support the sustainability and "eco-friendliness" claims these materials hold. Hence, this study aimed to investigate the ecotoxicological responses of two bivalve species (Mytilus edulis and Ruditapes philippinarum) extensively farmed in Europe, upon exposure to microplastics derived from commercially relevant petroleum-based (polyethylene terephthalate, PET), partially bio-based (polybutylene succinate, PBS) and bio-based plastics (poly[propylene] 2,5-furandicarboxylate, PPF).
Materials and Methods
M. edulis (~ 20g) and R. philippinarum (~13 g) were kept in glass beakers with ~5 L seawater under optimal rearing conditions (18.0 0.5 ��C, 8.0 0.2 pH, > 7 mg/L O2). During 21 days of trial, bivalves were daily fed with a Tetraselmis spp. solution once a day and exposed via water to 1 mg/mL of three types of microplastics: i) PET; ii) PBS; or iii) PPF. Bivalves were sampled from each treatment after 72 hours (T72) and 14 days (T14) of microplastic exposure and after 7 days (day 21, T21) of depuration period. The digestive glands and gills were collected to evaluate different physiological endpoints: oxidative stress (catalase activity [CAT], superoxide dismutase [SOD], glutathione S-transferases [GST], and lipid peroxidation [LPO]), metabolic enzymes activity (lactate dehydrogenase [LDH] and citrate synthase [CS]), digestive enzymes activity (-amylase, pepsin, and trypsin), and animal condition indexes.
Results and Discussion
In mussels digestive gland, significant differences were found in CAT (T72), SOD (T72, T14, and T21), and GST (T72, T14, and T21). CAT was upregulated by the exposure to PBS (T72). SOD was upregulated by the exposure to both PPF and PBS at T72 and T14, and downregulated after 7 days of the depuration period (T21) in PET treatment. GST was upregulated by PET in both T72 and T21, while a downregulation was observed in PBS at both T72 and T21, and in PPF at T21. These patterns suggest that the antioxidant defense system of the mussels gland was differently activated depending on the polymer type and trial phase. The upregulation observed at T72 indicated an early reponse to oxidative stress in mussels exposed to PBS and PPF exposure. However, the persistence of altered SOD and GST activities at T14, and the downregulation observed after the depuration period (T21), may reflect a prolonged physiological effect or an inability of the antioxidant system to fully recover even after 7 days of ceasing microplastics exposure.
These preliminary results highlight that thee exposure to bio-microplastics may not be as environmentally harmless as it is often claimed. Despite being produced in more sustainable ways, alternative polymers such as PBS and PPF, may induce oxidative stress and disrupt key physiological processes in wild and/or extensively farmed marine species. This raises concerns for the aquaculture sector, because if a shift towards more sustainable and supposably eco-friendlier alternatives occur, it is important to ensure that these materials will not negatively impact animal health, productivity, and ultimately result in microplastic accumulation in the edible fraction of seafood. Therefore, ensuring that novel materials are not only bio-derived but fully biodegradable, as well as non-toxic to marine organisms is important to assure a sustainable aquaculture practices and seafood safety.
Acknowledgment
This research was supported by the NextGenerationEU programme under the Recovery and Resilience Facility Plan for Portugal – Agenda VIAFOOD – Platform for Valorization, Industrialization, and Commercial Innovation for the Agri-Food Sector (no. C644929456-00000040).
References
Rosenboom, J.-G., Langer, R., & Traverso, G. (2022). Bioplastics for a circular economy. Nature Reviews Materials, 7(2), 117–137. https://doi.org/10.1038/s41578-021-00407-8
Tanaviyutpakdee, P., & Karnpanit, W. (2023). Exposure Assessment of Heavy Metals and Microplastic-like Particles from Consumption of Bivalves. Foods, 12(16), 3018. https://doi.org/10.3390/foods12163018
Van Der Schatte Olivier, A., Jones, L., Vay, L. L., Christie, M., Wilson, J., & Malham, S. K. (2020). A global review of the ecosystem services provided by bivalve aquaculture. Reviews in Aquaculture, 12(1), 3–25. https://doi.org/10.1111/raq.12301