Variation of ingested microplastic size and quantity in different tissues of juvenile European seabass, Dicentrarchus labrax

Microplastics are a globally recognized emerging contaminant, with growing concern over their translocation from the digestive tract and bioaccumulation in vital organs, especially in commercially farmed fish. In this study, established methods were applied to quantify translocation of ingested microplastic (MP) into blood, intestine, gill, liver and fillet of juvenile European seabass, Dicentrarchus labrax. European seabass consumed fluorescent MP (1-5 μm) particles for 16 weeks in a controlled feeding experiment before organs/tissues were collected and analyzed for quantitative MP contamination. This size range was selected due to its demonstrated potential for tissue translocation and accumulation in aquatic organisms, as well as its relevance to environmental and human health. The average abundance of MPs differed significantly between tissues and was highest in blood samples (54.6 ± 46.3 MP/g) though with high variability, followed by the intestinal tract (26.8 ± 18.7 MP/g) and gills (9.8 ± 9.4 MP/g). In contrast, lower average MP amounts were found in liver with 0.6 ± 1.5 MP/g and in fillet samples with 0.4 ± 0.3 MP/g. A clear trend of MP size distribution was observed within the examined tissues. Smaller MPs (1-2 μm) mainly accumulated in the intestine, blood, and gill samples, while larger MPs (4-5 μm) were more prevalent in the fillet samples. The highest relative abundance of 1 μm of MP was found in intestine, 2 μm in blood and gill, 4 and 5 μm in liver and fillet samples, respectively.