Demonstrating the translocation of nanoplastics across the fish intestine using palladium-doped polystyrene in a salmon gut-sac

[Display omitted] •Nanoplastic uptake by the gut of fish is difficult to quantify.•Use of a palladium label in the nanoplastic allows quantitative uptake assessment.•Evidence of uptake from the gut lumen into the tissue layers.•After 4 h, ∼700,000 particles (0.6% taken up) translocated into the serosal saline.•Concerns over transfer to tissues and higher trophic levels (e.g., humans). Fish are widely reported to ingest microplastics with low levels accumulating in the tissues, but owing to analytical constraints, much less is known about the potential accumulation of nanoplastics via the gut. Recently, the labelling of plastics with inorganic metals (e.g., palladium) has allowed measurements of nanoplastic uptake. The aim of the current study was to quantitatively assess the uptake of nanoplastics by the fish gut using palladium-doped nanoplastics (with a mean hydrodynamic radius of 202 ± 7 nm). By using an ex vivo gut sac exposure system, we show that in 4 h between 200 and 700 million nanoplastics (representing 2.5–9.4% of the administered nanoplastics dose) can enter the mucosa and muscularis layers of the intestine of salmon. Of the particles taken up, up to 700,000 (representing 0.6% of that taken into the tissue) of the nanoplastics passed across the gut epithelium of the anterior intestine and exit into the serosal saline. These data, generated in highly controlled conditions provide a proof-of-concept study, suggesting the potential for nanoplastics to distribute throughout the body, indicating the potential for systemic exposure in fish.