Accumulation of chemical elements and occurrence of microplastics in small pelagic fish from a neritic environment

Acknowledgements : We would like to thank the Portuguese Institute for the Sea and Atmosphere (IPMA) for fisheries assessment surveys to conduct this work under the EU Data Collection Framework (EU-DCF) through the program for biological data collection in the fisheries sector in Portugal - “Programa Nacional de Amostragem Biologica ´ (PNAB)”. This study benefited from the strategic program of MARE, financed by the Foundation for Science and Technology (FCT; Portugal) (MARE - UID/MAR/04292/2020). Financial support provided by FCT and MARE through the project ECOLIND – Seabirds and fish as ecological indicators of contaminants and health in the North Atlantic relevant to ocean resources assessment (MFM/2017/0003), and the transitory norm contracts DL57/2016 to FRC (DL57/2016/CP1370/CT90), ACN (DL57/2016/CP1370/CT89). LMFA acknowledge his grant (SFRH/BD/122082/2016) attributed by FCT and the European Social Fund (POPH,EU). The project was also partly funded by the project BLUESHARKER (PTDC/CTA-MB/29136/2017), financed by FCT and co-financed by COMPETE2020 (POCI-01-0145-FEDER-029136). The funding sources had no involvement in this study.

The assessment of contaminant exposure in marine organisms often focuses on the most toxic chemical elements from upper trophic level species. Information on mid-trophic level species and particularly on potentially less harmful elements is lacking. Additionally, microplastics have been considered emergent contaminants in aquatic environments which have not been extensively studied in species from mid-trophic levels in food chains. This study aims to contribute to an overall assessment of environmental impacts of such chemicals in a community of small pelagic fish in the North Atlantic. The concentrations of 16 chemical elements, rarely simultaneously quantified (including minerals, trace elements and heavy metals), and the presence of microplastics were analysed in sardines (Sardina pilchardus) and mackerels (Scomber spp. and Trachurus trachurus) sampled along the Portuguese coast. Biochemical stress assessments and stable isotope analyses were also performed. The chemical element concentrations in S. pilchardus, T. trachurus, and Scomber spp. were relatively low and lower than the levels reported for the same species in the North Atlantic and adjacent areas. No clear relationships were found between chemical elements and oxidative damage in fish. However, the concentration of several chemical elements showed differences among species, being related with the species’ habitat use, trophic niches, and specific feeding strategies. The presence of plastic pieces in the stomachs of 29% of the sampled fishes is particularly concerning, as these small pelagic fish from mid-trophic levels compose a significant part of the diet of humans and other top predators. This study highlights the importance of multidisciplinary approaches focusing on the individual, including position data, stable isotopes, and oxidative stress biomarkers as complementary tools in contamination assessment of the marine mid-trophic levels in food chains.

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