Grazing the plastisphere: Trophic transfer of the bioaccumulated metals to Artemia salina

In any aquatic environment, microplastics (MPs) are rapidly colonized by microbial communities, forming a biofilm known as plastisphere, which modifies their surface properties. The biofilm has been shown to dramatically increase metal accumulation. Yet, the impact of biofilm community structure on the level of the metallic load remains poorly understood, especially the role of seawater nutrients. In addition, contaminants bioaccumulation raises the question of the grazing (or ingestion) of biofouled MPs by higher trophic level. To address this issue, the development and growth of the plastisphere was constrained through controlled conditions in mesocosms. Biofilms prokaryotic and eukaryotic diversity were determined in different dissolved nutrients conditions while using naturel seawater from Toulon Bay (French North-Western Mediterranean Sea). Dissimilar obtained biofilm communities show significant difference in copper loading after nutrients addition. MPs colonized by biofilms were then used as grazing food for Artemia salina populations. After one week of exclusive grazing, Artemia salina showed a significative increased in metal loading, correlated with the conditions presenting significative higher accumulation in the biofilm. Higher metallic bioaccumulation in the plastisphere caused an increase in the amount of bioaccumulated Cu, thus demonstrating trophic transfer. Even if the relationship between Cu concentration in biofilm and Artemia remains to specify in further study, as well as the range of grazers actually concerned in marine ecosystems, this raises a crucial new question about the impact of plastic pollution in the oceans.