The dietary bioavailability of nanoplastics to salmon using an ex vivo gut sac technique

, Clark Nathaniel, Mitrano Denise, Khan Farhan, Boyle David, Thompson Richard.

The dietary bioaccumulation potential of nanoplastics to adult fish remains unclear due to analytical constraints. However, labelling of plastics with inorganic metals allows for quantitative assessments of nanoplastic uptake via inductively coupled plasma mass spectrometry (ICP-MS). By using palladium-doped nano-polystyrene particles (Pd NPs), the aim of this study was to determine if (1) nanoplastics in the fish gastrointestinal tract (GIT) and transported across the gut wall, and (2) identify the region of the GIT where uptake occurs. Salmon (n = 16) were sacrificed and the entire GIT was removed. The GIT was separated into four functional sections (stomach, anterior-intestine, mid-intestine and hind-intestine) and rinsed with physiological gut saline. Each compartment was filled with physiological gut saline containing a known amount of nanoplastics. Control gut sacs with no added Pd were also performed to validate the gut sac method. Gut sacs were closed, placed into physiological gut saline to start the experiment. After 4 h, the tissues were rinsed and the gut tissue was separated into the mucosa and muscularis. Tissues were dried, digested and analysed for total Pd concentrations by ICP-MS. In the control tissue samples, there was negligible background Pd (6 ± 2 ng/g). Nevertheless, gut sacs performed with Pd NPs contained Pd (indicating presence of nanoplastics) in all tissue layers and across the four sections. Most of the Pd, and presumably nanoplastic, was localised to the mucosa (80-98%), regardless of gut region. However, the underlying muscularis is more representative of active uptake. Within the hind-intestine a significant 1.9-3.2 fold higher concentration was found compared to the stomach and mid-intestine (104 ± 19, 32 ± 8 and 55 ± 5 ng/g, respectively). In summary, the presence of Pd in the muscularis suggests nanoplastics are taken up in fish GIT, and that the hind-intestine is the site for greatest transport.

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