Accumulation Dynamics And Metabolic Toxicity Of Silver Nanoparticles In Gills Of Cyprinus Carpio

Silver nanoparticles'effects on aquatic environment pollution and health have attracted much attention.Gills are the main respiratory organism in fish,which have a huge surface area and a direct contact with pollutants in water.Gills are the primary target organism of silver nanoparticles in water ecological environment.However,the enrichment kinetics and toxic mechanism in gills of silver nanoparticles are still unknown.Therefore,in this research,through acute exposure in artificial water distribution,we used silver nitrate(AgNO₃)as a control,different size of silver nanoparticles(15nm/50nm)as the research materials,aiming to reveal the silver nanoparticles'enrichment kinetics and toxicity mechanism of in the gills of Cyprinus carpio.The main results are as follows:(1)The acute toxic effect of silver nanoparticles on gills was revealed by the method of acute exposure,histological section and silver staining.In artificial water distribution,the 96h half lethal concentration(LC₅₀)of AgNPs-15nm was 3.929 mg/L,the LC₅₀ of AgNPs-50nm was bigger than 2 mg/L.After 24h acute exposure at the concentration of 1/2 LC₅₀,the gill tissues were all damaged to varying degrees,mainly manifested as:twisted and disordered of the gill slices,proliferated and fused of the gill epithelial cells,swollen at the ends of gill lamellae and so on.The damage degree of silver nanoparticles with small particle size to gill tissue was greater than that with large particle size.The silver staining results showed that different size of silver nanoparticles both can accumulate in gill and the accumulation of silver nanoparticles with small particle size was more than that with large particle size.The order of acute toxicity of different size of silver from large to small was:AgNPs-15nm>AgNPs-50nm.(2)Using the enrichment kinetic model,the enrichment kinetic process of silver nanoparticles in gills was revealed.The results indicated that the enrichment behavior of silver nanoparticles with different particle size was completely different.The enrichment of AgNPs-15nm in gills was basically conformed to the biological ligand model and its affinity constant(Log K)was 6.5,site density(B_max)was 49;The enrichment of AgNPs-50nm has a low fitting degree to the biological ligand model with Log K of 7.4 and B_max of 92.The enrichments of different forms of silver in gills were quite rapid,and the maximum enrichment was reached after exposure of 2 hours.AgNPs-15nm has a low degree of fit to the first-order kinetic model.The uptake rate(K_u)and the elimination rate(K_e)are 0.08±0.47 L/g/h and 0.08±0.03 L/g/d,respectively;AgNPs-50nm has a higher degree of fit to the first-order kinetic model than AgNPs-15nm,the uptake rate K_u=0.19±0.15 L/g/h and the elimination rate K_e=1.19±0.14 L/g/d.The uptake rate of AgNPs-50nm was 2.4 times higher than that of AgNPs-15nm,while the elimination rate was more than 14 times higher than that of small size.The bioconcentration coefficients(BCF)of AgNPs-15nm,AgNPs-50nm were 0.94 and 0.16 respectively,in ascending order:AgNPs-15nm>AgNPs-50nm,which was consistent with the order of toxicity.The bioconcentration coefficient of AgNPs-15nm was 5.8 times higher than that of AgNPs-50nm.(3)Using non-targeted metabolomics technology,the effect of silver nanoparticles on the metabolism was described.Exposed to the 1/2 LC₅₀ concentration for 24 hours,compared with the control group,AgNPs-15nm,AgNPs-50nm respectively produced307 and 258 kinds of differential metabolites,and 199 kinds of differential metabolites were shared by the two groups.Compared with the control group,different particle size of silver nanoparticles both changed the expression level of lysophosphatidylcholine,glycerophosphorylcholine,ceramide,dihydrosphingosine.These differential metabolites involved 20 biological metabolic pathways,mainly related to protein digestion and absorption,nucleotide metabolism,cell signal transduction,and lipid metabolism.It is worth noting that silver nanoparticles and silver nitrate also showed their unique metabolic effects.After silver nanoparticles exposure,the expression level of metabolism tetrahydrocortisone in gills was increased significantly(FC=8.28),while in dissolved silver ion,the metabolite of pelargonidin 3-sophoroside(FC=8.27)was significantly expressed,indicating that different forms of silver may have the different regulation ways to face oxidative stress.