The Fate And Transportation Of Silver Nanoparticles,and Its Toxicity To Microorganism

Silver nanoparticles(AgNPs;1-100 nm in size)with specific mechanical,optical,electronic,and catalytic properties,are widely used in consumer and medical products.AgNPs released to the natural environment undergo profound chemical transformations that can affect their stability,bioavailability,and toxicity.Indeed,the release of AgNPs into the environment has a severe effect on numerous organisms,including microbial communities,fungi,algae,plants,vertebrates,invertebrates,and human cells.The bactericidal activity of AgNPs is attributable to the controlled release of silver ions(Ag+)and nano-specific effects of AgNPs that can be internalized by the bacterial capsule and bind to proteins,enzymes,and DNA,disrupting normal cell function and even causing cell death.DOM is ubiquitous in natural water,but the interaction between AgNPs and DOM is not well-understood.During the release of AgNPs into aquatic environments,DOM plays an important role in altering the surface charge of AgNPs,and thus their stability.Phanerochaete chrysosporium(white-rot fungi)was selectted as the model organism,as it has been widely used to treat waste water streams containing heavy metals and toxic organic pollutant.CYS is a strong,silver ligand,known for its affinity to complex with free Ag+.Several studies have demonstrated that CYS decreases AgNP dissolution,and attenuates the toxicity of AgNPs.The presence of CYS proteins within the solution can stabilize the AgNPs against aggregation.BSA reduced the toxicity of AgNPs to Nitrosomonas europaea by chelating the released Ag+,and further reduced toxicity by binding to the surface of the AgNPs.CYS and BSA are two different types of dissolved organic matter(DOM),they are ubiquitous in natural water and both CYS and BSA are thiol-containing biomolecules.The transport and environmental persistence of silver nanoparticles(AgNPs)after exposure to dissolved organic matter(DOM)are influenced by their stability and dissolution.In addition,their toxicity to microorganisms is influenced by the release of silver ions(Ag+).Here,we characterize the stability and dissolution of citrate-stabilized AgNPs,and their toxicity to a white-rot fungus,Phanerochaete chrysosporium(P.chrysosporium),following exposure to either cysteine(CYS)or bovine serum albumin(BSA).The results indicated that both CYS and BSA changed the diameter,zeta potential,and Ag+ dissolution of AgNPs.Bacterial viability and intracellular reactive oxygen species(ROS)levels were investigated to determine the toxicity of AgNPs to P.chrysosporium.In this study,CYS decreased the inhibitory effects of 100 ?g/L Ag+ and 10 mg/L AgNPs in a concentration-dependent manner.At higher concentrations of CYS,the toxicity of Ag+ and AgNPs was reduced dramatically.However,cell viability decreased at higher BSA concentrations(? 50 mg/L),suggesting a more complex reaction than simply binding to the released Ag+.Addition of 10 mg/L AgNPs significantly stimulated ROS production,but the addition of CYS and BSA decreased the ROS level in a concentration-dependent manner.In summary,our results provide useful information to understand the fate,transformation,and toxicity of citrate-stabilized AgNPs in the natural environment.