Insights into Tissue-Specific Bioaccumulation of Nanoplastics in Marine Medaka as Revealed by a Stable Carbon Isotopic Approach

Despite the high bioavailability and potentially extensive presence of nanoplastics in aquatic environments, the biological fate of nanoplastics is largely unknown because of analytical limitations in detection and quantification. Fluorescently labeled nanoplastics are widely used to detect bioaccumulation, but this method is prone to false-positive results due to the leaching of fluorescent dyes. Here we propose a novel stable carbon isotopic approach to detect and quantify nano- and microplastics in a complex organic matrix. Because carbon is the major component of plastics (>87% in polystyrene), it is possible to investigate tissue-specific bioaccumulation of nano- and microplastics in the medaka Oryzias melastigma by quantifying the contribution of plastic particles as an end-member in the composition of stable carbon isotopes in different tissues. In addition to the digestive organs (e.g., the gut and intestines) that are constantly exposed to the water column via ingestion, nanoplastics were shown to selectively bioaccumulate in the gills and ovary, implying a unique mode of action of bioaccumulation based on the physicochemical properties of the nanoparticles. These findings should improve our understanding of the tissue-specific bioaccumulation of nano- and microplastics in aquatic organisms.