Low Bioavailability of Silver Nanoparticles Presents Trophic Toxicity to Marine Medaka (Oryzias melastigma)

Concerns for the potential risks of silver nanoparticles (AgNPs) to aquatic organisms have increased. The present study investigated the trophic transfer of AgNPs from brine shrimp (Artemia sauna) nauplii to marine medaka. We found that the aggregated AgNPs (20 and 80 nm) and well dispersed 80-nm AgNPs (stabilized by 20 mu M Tween 20) could be readily accumulated by brine shrimp, while far less well-dispersed 20-nm AgNPs were accumulated. The assimilation efficiency (AE) of AgNPs in medaka fed AgNPs-contaminated brine shrimp was low (<6%), resulting in a low trophic transfer efficiency (0.01-0.04) after 28 days of chronic dietary exposure. However, such low bioavailability of dietary AgNPs could inhibit the whole-body Na+/ K+-ATPase and superoxide dismutase (SOD) activity in the fish within the first 2 weeks of exposure. Significant (p < 0.05, two-way ANOVA) inhibition occurred in the high AgNPs-contaminated brine shrimp treatment over 28 days of chronic exposure. Furthermore, reduced growth and water content percentage were also observed in fish fed high dosages of AgNPs-contaminated brine shrimp. Our study highlighted the potential of trophically available AgNPs in bringing toxicity to the marine fish.