Effects of nanosilver and silver nitrate exposure on fathead minnows (Pimephales promelas) and zebrafish (Danio rerio)

Silver nanoparticles (AgNPs) due to their unique antimicrobial properties are among the most widely utilized nanoparticle. Because of the nature of the products that utilize AgNPs, environmental release of AgNPs is inevitable. At greatest risk is the aquatic ecosystem due to known toxicity of the Ag + ion to aquatic organisms. Our goal was to use two fish models, fathead minnows (Pimephales promelas; FHMs) and zebrafish ( Danio rerio; ZFs), to study the effects of AgNPs on gill histopathology, Na+/K+-ATPase immunoreactivity, mucus production, bioaccumulation, particle uptake characterization, gill gene expression, and lethality in varying water parameters in comparison to the known toxicities of Ag+ in the form of AgNO3. FHMs were exposed to two nominal concentrations of AgNO3 (2 and 6 μg/L), citrate-AgNPs and polyvinylpyrrolidone–AgNPs (20 and 200 μg/L; 20 nm). All silver groups had significantly higher histopathological abnormalities with citrate-AgNPs having the highest toxicity (index of 10±0.32 versus 2.4±0.6 in controls). Gill Na+/K+-ATPase immunoreactivity was decreased by silver. Control fish produced mucus consistently while silver-treated fish initially produced significantly more mucus but this production was reduced below control concentrations by 96 hr of silver exposure. Silver accumulation was quantitated by inductively coupled plasma mass spectrometry (ICP-MS) after 96 hr AgNO3 and AgNPs exposure. Despite higher exposure concentrations, AgNPs accumulated at lower concentrations than AgNO3 in the gill, skin, and liver with none detected in the brain. AgNPs accumulated in the GI tract more than AgNO3 indicating a possible unique biological target of AgNP exposure. To understand this further, Field-Flow-Fractionation coupled to ICP-MS (FFF-ICP-MS) was utilized to characterize particles in GI tract and gill tissue. Particles were sized between 26-70 nm in GI and 27-30 nm in gill. FHM gill microarrays were performed to compare alterations in gene expression between AgNPs and AgNO3. Analysis revealed 110 commonly differentially expressed genes between all silver treatments compared to control with 185, 423, and 615 unique differentially expressed genes in AgNO3, PVP-AgNPs and citrate-AgNPs, respectively. ZF larvae were exposed 48 hrs to AgNPs and AgNO3 in increasing environmentally relevant concentrations of dissolved organic carbon (DOC) and higher DOCs decreased silver lethality. Overall, while AgNPs displayed some unique particle effects, the majority of the toxicities were consistent with Ag+ release