Effects Of Ionic Strength On Physicochemical And Toxicological Properties Of Silver Nanoparticles In The Environment

The widespread use of silver nanoparticles(AgNPs)will lead to their release into the environment,and the interaction between AgNPs and environmental factors will be transformed,so that its physicochemical properties and toxicological effects significantly different from those of the pristine forms.However,the related transformation characteristics,toxicological effects and the correlation between them are still unknown.In this study,the influence of ionic strength on the physicochemical properties,biological effects of AgNPs and the correlation between them were discussed with Caenorhabditis elegans(C.elegans)as the research object and different ionic strength solutions as environmental factors.In addition,the accumulation,transmission,ecotoxicological effects and related mechanisms of AgNPs in the food chain under the action of ion strength were investigated by using Escherichia coli(E.coli)-C.elegans as a simple binary food chain model.The main findings of this study are as follow:1.Effects of ionic strength on physicochemical properties of AgNPs:1)With HRTEM,UV-vis and DLS we found that smaller nanoparticles appeared around the pristine AgNPs after incubation in EPA or KM for 5 days.2)The concentration of dissolved silver and silver species as free Ag+were decreased with the ionic strength of medium increased.3)The different ionic constituents of EPA and KM attached to the surface of AgNPs could cause etching to the pristine AgNPs that resulting in the formation of smaller nanoparticles.2.Effects of ionic strength on biotoxicity of AgNPs:We compared the toxicity of AgNPs after incubation in different ionic strength medium with the germ cell apoptosis,brood size,and lifespan assay as the endpoints.We found that the toxicity of AgNPs to C.elegans was enhanced with an increase in ionic strength.3.The correlation between the changes of AgNPs properties and biological effects:1)The concentration of small particles formed in EPA and KM was dramatically increased compared with in H2O both for 25 nm and 75 nm AgNPs.2)The gem cell corpses assay showed that the small AgNPs(PVP5)was more toxicity for C.elegans than PVP25 and PVP75.3)There was a clear inverse linear relationship between EC50 values of brood size and percentage of small particles that was formation after exposure in different ionic strength media.These data indicated that the enhanced toxicity of AgNPs to C.elegans could be attributed to the formation of small particles.4.Effects of ionic strength on ecotoxicity of AgNPs:With E.coli-C.elegans as a food chain model,the effect of ionic strength on the ecotoxicity of AgNPs was studied by using the end point of germ cell corpses,brood size,lifespan,head trash and body bend.The results indicated that ionic strength significantly enhanced the reproductive toxicity and neurotoxicity of AgNPs to C.elegans.5.The mechanism of the change of ecotoxicity:The higher ionic strength increased bioaccumulation of AgNPs in E.coli and the resulting Ag body burden of E.coli affected the transfer of AgNPs to C.elegans,which might be responsible for the increased toxicity to nematodes.2)With the strain of sod-3::GFP,hsp-6::GFP and sod-3 deletion,we found that the reactive oxygen species(ROS)level in C.elegans was significantly increased after exposed to E.coli contaminated with ionic strength-treated AgNPs,which might play another important role for the enhanced toxicity of AgNPs.Our data provided a new idea for the study of the transformation and biotoxicity effects of AgNPs in the environment.The results provide new evidence for the study of the transport and ecotoxicity effects of AgNPs in biological systems.