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Influence of Sediment Mixing Induced by the Gallery-Diffusor Hediste diversicolor on the Burial of Different Microplastic Particles: A Comparative Tracer Study
Summary
Common marine worms that burrow through seafloor sediment can drag microplastic particles as deep as 5.5 inches underground, burying them at similar rates regardless of the plastic's size or density. This matters because it shows how microplastics may become long-term "locked away" in ocean sediments rather than staying near the surface where they're more likely to be eaten by fish and other seafood we consume, though more research is needed to know whether burial ultimately reduces or simply delays human exposure through the food chain.
Although marine sediments are recognized as a sink for marine microplastic particles, investigations into the fate of once deposited particles have received relatively little interest so far. Through interactions with sediment-dwelling organisms, these particles are subject to potential burial in the wake of bioturbation. In this study, we analyzed the effect of sediment reworking by the polychaete Hediste diversicolor O.F. Müller, 1776, using different particle tracers—luminophores, polyethylene (PE), and polyamide (PA). Transport induced by H. diversicolor was observed to extend to sediment depths up to 14 cm with similar biodiffusive and advective transport rates for all tracer types. Local transport (Db) was 1.09 cm2 yr−1 for luminophores; microplastics showed slightly lower local transport with Db of 0.81 cm2 yr−1 (PA) and 0.57 cm2 yr−1 (PE). Non-local transport (r) was comparably low for all particle types, ranging from 0.69 yr−1 for luminophores and 0.95 yr−1 (PA) and 1.27 yr−1 (PE) for microplastics. Food addition did not significantly increase bioturbation activity of H. diversicolor. Despite differences in size and density, the particle tracer types in this study showed no significant differences in modeled bioturbation coefficients or burial depth, emphasizing that bioturbation of microplastics is not governed by particle properties alone but also by the functional ecology of the bioturbator.