Are Mytilus galloprovincialis populations threatened by the presence of plastic additives and/or microplastics?

• Autor(a) principal: Borges, Luís Filipe Durães
• Data de Publicação: 2023
• Tipo de documento: Dissertação
• Idioma: eng
• Título da fonte: Repositório Científico de Acesso Aberto de Portugal (Repositórios Cientìficos)
• Texto Completo: http://hdl.handle.net/10773/39244
• topic: Mussels; Nylon (PA); Tricresyl phosphate (TCP); Plastic additives; Metabolism; Oxidative stress; Carboxylesterases

The persistence of microplastics (< 5 mm in size) and plastic additives (e.g., flame retardants commonly applied in clothing) in the marine environment is threatening their biota, potentially leading to the loss of ecological functions. To understand the impacts of these emerging contaminants, alone or in combination, in marine environments, the mussel Mytilus galloprovincialis (Lamarck, 1819) (bivalve with ecological, economic, and gastronomic value, and a bioindicator of microplastic pollution) was selected as test species for in vivo and in vitro ecotoxicity assays, under relevant exposure scenarios (i.e., environmentally relevant concentrations, increasing temperatures) and considering the potential sensitivity or resilience of different populations (here, Atlantic vs. Adriatic). Nylon (commonly applied in clothing, fishing gear, and other consumer products) and the plastic additive tricresyl phosphate (TCP, a flame retardant) were privileged as contaminants due to their representativity and prevalence in marine environments. Exposure to nylon microplastics (63-125 μm, ~800 particles/L in the water column) and its ingestion (13 to 17 particles in their whole organisms) seem to affect the antioxidant and detoxification defences (a decrease by ~50 % in catalase, 33 % in glutathione reductase, and up to ~32 % in glutathione peroxidase activities) and neurotransmission (a decrease of ~40 %) in Atlantic mussels. On the other hand, exposure to TCP (1 μg/L) seemed to particularly interfere with the mussel’s biotransformation capacity, mainly in carboxylesterases using p-nitrophenyl butyrate as substrate. The biochemical alterations observed in mussels after exposure to nylon or TCP did not prevail in the co-exposure, meaning that all biochemical responses in mussels exposed to both nylon and TCP remained similar as in control conditions. No lipid damage was observed in mussels exposed to nylon, TCP or both. When considering an increase of 4 ºC (i.e., from 17 ºC to 21 ºC), Atlantic mussels under control conditions revealed an expected increase (by ~57 %) in the aerobic metabolism, conversely to mussels exposed to nylon microplastics whose aerobic metabolism remained similar to the organisms at 17 ºC, indicating that energy is being spent to cope with potential stress caused by the presence of these particles. No other biochemical parameters varied among temperatures and in the presence/absence of nylon in Atlantic mussels. In the presence of different plastic additives and considering carboxylesterases activity that shown higher sensitivity to such contaminants, mussels from Adriatic Sea and Atlantic Ocean revealed similar capacities in in vitro assays, contrary to what was expected as natural (uncontaminated) Adriatic mussels had higher antioxidant, detoxification, and biotransformation basal capacities and greater neurotransmission than Atlantic mussels due to their adaptation to slightly more contaminated waters. Overall, mussels exposed to nylon and TCP (as individual contaminants) revealed impaired antioxidant/detoxificant defences and biotransformation capacity, respectively. Notwithstanding, such alterations did not result in lipid damage, and co-exposure of these two contaminants (which is more likely to happen in natural environments) did not result in significant biochemical alterations, indicating that these contaminants may not have a cumulative effect on mussels. Yet, further research is needed to better understand the long-term effects of exposure to these pollutants.