An assessment of the dietary bioavailability of silver nanomaterials in rainbow trout using an ex vivo gut sac technique

Abstract

The uptake of engineered nanomaterials (ENMs) by the gut of fishes is poorly understood. This study assessed the utility of the ex vivo gut sac method for measuring bioavailability following exposures to silver nanoparticles (Ag NPs) or silver sulphide nanoparticles (Ag₂S NPs). Whole gut sacs were prepared from rainbow trout and filled with saline containing control (no added Ag) or 1 mg L⁻¹ Ag as AgNO₃, Ag NPs or Ag₂S NPs and then incubated for 4 h. The mucosa and muscularis were analysed for total silver concentrations. The amount of Ag associated with the gut ranged from 2% to 20% of the exposure dose, with the majority being associated with the mucosa. For the muscularis in the AgNO₃ treatment, the anterior, mid and hind intestine had significantly more Ag (4, 6 and 6 fold higher) compared to the oesophagus and stomach (∼75 ng g⁻¹ dry weight tissue). For Ag NPs, there was a similar pattern of total Ag concentrations in the mucosa, with proportionally more total Ag in the mid (1506 ± 907 ng g⁻¹ dw) and hind (732 ± 258 ng g⁻¹ dw) intestine, but not statistically different from the equivalent AgNO₃ treatment. For Ag₂S NPs, there were no differences in total Ag by anatomical region, or compared to AgNO₃, for the mucosa. Crucially, sometimes the muscularis from the AgNO₃ treatment showed much higher Ag concentrations than either NP treatment. Overall, the gut sac method can determine the bioavailability of ENMs. Both NPs were less bioavailable than the metal salt and with no material-type effects.