Little evidence for bioaccumulation or biomagnification of microplastics in a deep-sea food web

Microplastic contamination is documented in marine organisms, but little is known about bioaccumulation or biomagnification of microplastics, especially in tissues external to the gastro-intestinal (GI) tract. The objective of this work was to explore microplastic contamination in GI tracts and other tissues (abdomen and tail in crustaceans; mantle in cephalopods; fillets in fishes) of species at different trophic levels sampled in a deep-sea food web in Monterey Bay, CA, USA. The species included are tuna crab Pleuroncodes planipes, market squid Doryteuthis opalescens, northern lampfish Stenobrachius leucopsarus, chub mackerel Scomber japonicus, California halibut Paralichthys californicus, and Chinook salmon Oncorhynchus tshawytscha. After chemical digestion, microplastics in GI tracts were quantified and identified to material type using mu-Raman spectroscopy and in other tissues using pyrolysis-GC/MS. The concentrations of microplastics in GI tracts were significantly different among species, and microplastic contamination was dominated by microfibers. The concentrations of microplastics (mainly polyethylene and polyvinyl chloride) in other tissues also varied among species. A significant positive correlation between body size and plastic concentration in other tissues was observed for halibut only, suggesting bioaccumulation may not be ubiquitous. The trophic magnification factor for microplastics beyond the GI tract was <1, suggesting that biomagnification is not occurring in tissues. However, we did observe evidence for biomagnification of microplastics in the GI tracts. Future studies are needed to better understand these patterns and the mechanisms for translocation, bioaccumulation, and biomagnification of microplastics in aquatic organisms.