7-22 Not So “Fresh” Water: Microplastics in Shell and Periostracum of Bivalves from New York, USA

Session: Undergraduate Research, Part I (Posters)

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Abstract:

Microplastics are a growing global issue and are hypothesized to pose significant risks to natural ecosystems and human health. Due to their filter-feeding abilities, bivalves have been used to assess microplastic levels in marine environments. Although previous studies have confirmed the presence of microplastics in the soft tissue of freshwater bivalves, no study has investigated microplastics in the shell and periostracum of unionids. We hypothesize that microplastics are present in the shell and periostracum of freshwater clams from northern New York State. 

We examined shell and periostracum of live collected individuals of Elliptio complanata from freshwater lakes and rivers in New York. Calcium carbonate shell material was dissolved in HCl, stained with Calcofluor White with Evans Blue and Nile Red, and passed through 0.4 μm filter paper. Periostracum samples were stained with the same dyes and analyzed under a Nikon Ti Eclipse C2 confocal microscope using 488 nm and 405 nm lasers. The location and shape of microplastics in the periostracum were analyzed using Z-stack scans and a FEI Quanta 450 scanning electron microscope at 1024 × 884 resolution. 

Our preliminary results confirm the presence of microplastics in the shell and periostracum. Microplastics were found on the shell filters, establishing that unionids integrate these contaminants into their shells. Imaging of periostracum samples in 3-D revealed that microplastics were incorporated in or partially embedded in the organic layer.  

This suggests that microplastics in the periostracum may be incorporated via a different pathway than microplastics within the mineral shell. While unionids tightly regulate the intrapallial fluid, where shell biomineralization occurs, microplastics reaching the shell interior would need to traverse mantle epithelial transport pathways, as exchange with extrapallial or inhalant water through mantle tissues is limited. In contrast, periostracum formation occurs at the mantle edge and is followed by direct exposure to external water, which may allow microplastics to adhere to or become partially embedded within the periostracum as it grows. These particles, however, are not incorporated into the underlying mineral shell layers, which remain under biological control. Additional data is needed to better understand the distinct pathways through which microplastics interact with the shell and periostracum. Future work will enable more precise characterization of the location, composition, and size classes of microplastics associated with each shell component.

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