Subsequently, nanoplastics (≤ 1 μm 10) have become an area of concern as these are even more prone to passive ingestion 11. Microplastic particles (1 µm to 5 mm in size), in particular, are considered potential hazards to ecosystems, through ingestion by marine biota 3, 4, permeation of trophic levels 5, 6 and as vectors for pollution (e.g., toxic waste, heavy metals, pathogens) 7, 8, 9. Plastic pollution was first reported in the 1970s 1 and has since then been documented in all marine habitats 2. These findings highlight the need for further investigation regarding plastic pollution impacts on calcifying organisms, e.g., the function of LBF as potential plastic sinks and alterations in structural integrity of LBF tests that will likely have larger ecosystem-level impacts on sediment production. While ~ 40% of ingesting LBF expelled all nanoplastics from their cytoplasm, nanoplastics were still attached to the test surface and subsequently encrusted by calcite. Microalgae presence in nanoplastic treatments significantly increased the initial feeding response after 1 day, but regardless of microalgae presence, nanoplastic ingestion was similar after 6 weeks of chronic exposure. Nanoplastic incorporation was associated with formation of new chambers, in conjunction with rapid nanoplastic ingestion and subsequent incomplete egestion.

While previous work on LBF has documented selectivity in feeding behaviour and a high degree of specialization regarding skeletal formation, in this study, abundant cases of nanoplastic encrustation into the calcite tests were observed. Here, we report the first observation of polymer nanoparticles being incorporated into the calcite skeleton of a large benthic foraminifera (LBF), a significant contributor to global carbonate production. Studies on the effects of global marine plastic pollution have largely focused on physiological responses of few organism groups (e.g., corals, fishes).

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