Low microplastic loads in north sea, mediterranean and atlantic topshells

, Ehlers Sonja, Ellrich Julius, Koop Jochen.

Topshells are common marine snails inhabiting shallow subtidal habitats along shorelines worldwide. These snails feed by browsing particles off the substrate. Ecotoxicologists use topshells as bioindicators for harmful substances such as heavy metals. In this study, we investigate whether topshells can serve as bioindicators for microplastic pollution. For that, we are examining microplastic (particles ¡ 5 mm) loads in topshell (Phorcus turbinatus, Phorcus sauciatus, Steromphala cineraria) and water samples collected at wave-exposed and wave-sheltered locations on the French and Italian Mediterranean coast (in 2007/2008 and 2019), on Helgoland (in 2009/2020) and Madeira island (in 2020). We consistently found relatively low topshell microplastic loads, composed of fragments, fibres, films and spheres of various colours and polymer types such as polyester, polyethylene, polyamide, polystyrene and polypropylene. Interestingly, we found that many microplastics consisted of paint chips. Currently, we are analysing the water samples to evaluate whether the topshell plastic loads reflect environmental microplastic concentrations and compositions. We verified all microplastics using micro-Fourier-transform infrared spectroscopy (µFTIR). This is exceptional, since the few studies that examined microplastics in marine snails verified only small microplastic subsets using µFTIR or relied entirely on visual microplastic identification. However, as microplastic validation studies indicated that up to 70 % of the visually examined particles are actually misclassified as microplastics, our study is the first to report verified microplastic loads in marine snails.

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