When the unexpected happens: Strict quality control measures and its impacts on microplastic concentrations in the Southern Ocean key species Antarctic krill, Euphausia superba

Microplastics are of major concern to the environment, the economy, and human health. To fully understand the impacts on food webs and food safety, monitoring microplastics is highly important. In addition, it provides feedback on the efficiency of regulatory measures for reducing microplastics. One of the key areas for monitoring is the Southern Ocean and Antarctica, as this area is considered less affected by direct human plastic input and may serve as a baseline area. Further, Antarctic krill, Euphausia superba, is a keystone species in the Southern Ocean food web, acting as a direct energy source between primary producers (phytoplankton) and higher tropic levels, up to penguins, seals and whales. Therefore, krill can serve as an optimal bioindicator for microplastics pollution. In this study, we investigated the stomach content of 60 krill specimens at three locations for microplastic presence. Different sample volumes and extraction approaches were tested, and all samples were analyzed by hyperspectral imaging Fourier-transform infrared spectroscopy (µFTIR). As the initial results indicated high concentrations of microplastics, strict quality control was applied to the generated results. Here, it was found that a high load of unexpected residual materials in the samples hampered the analysis. For pooled samples, it avoided a reliable determination of putative microplastic particles. Individual krill stomachs displayed lipid-rich residues of krill. Untreated, these resulted in false assignments of polymer categories and, hence, false high MP particle numbers. However, reliable results were achieved after re-treating the samples with hydrogen peroxide. Microplastics were identified in four stomachs out of 60, with only one microplastic particle per stomach. These results highlight the importance of strict quality control in all steps of the analytical process, especially for the chemical analysis, before coming to a final decision on environmental microplastic contamination. Also see: https://micro2024.sciencesconf.org/557960/document