| Silver nanoparticles(Ag NPs)is widely used in medicine,chemical industry and daily necessities,which can be inevitably released into aquatic environment,and induced toxic effect to Cyprinus carpio.Gill,as a respiratory organ of Cyprinus carpio,is the primary target organ for Ag NPs exposure in water environment.However,it is still largely unknown that the specific mechanism for the toxicity of Ag NPs to fish gill.This study combined the Biotic Ligand Model(BLM)with silver nitrate as the silver ion control,the enrichment of silver in gills tissue,determination of the activity of four antioxidant enzymes,counting of respiratory frequency,standard metabolic rate,determination of critical oxygen tension,microscopic and ultrastructural observation of Cyprinus carpio gills were studied under different exposure conditions of Ag NPs.The kinetics of bioaccumulation of Ag NPs in gills,damage to microscopic structure and ultrastructure of gills,induced oxidative stress effects,and effects on the respiratory metabolism of carp were analyzed.It reveals the toxic effects and toxic mechanisms of Ag NPs on Cyprinus carpio.The main results are as follows:(1)Ag NPs can produce an enrichment toxic effect in the gill of carp tissue.The affinity constant of gills tissue to Ag NPs is log K=5.1,and the maximum absorption flux Bmax is 1.5±0.2 ?g/g/d.The affinity constant of gills tissue to silver ion(silver nitrate)is log K=7.8,Bmax.= 0.95 ± 0.07 ?g/g/d.These results indicate that the maximum absorption flux of gills on Ag NPs is larger than that on silver nitrate,but the affinity with Ag NPs is smaller than that with silver nitrate.(2)0.4 mg/L and 0.8 mg/L AgNPs caused histopathological damage of the gills under acute exposure conditions at 24 h and 168 h.Microscopic observations revealed that Ag NPs exposure resulted the separation of flat epithelial cells,vacuolization,epithelial cell proliferation,edema,and inflammation in gill small lamellae.The statistical results of the cells showed that the number of chlorinated cells,mucous cells,squamous epithelial cells,and columnar cells increased significantly with the increase of Ag NPs exposure time in the 168 h acute exposure experiment.The average diameterof chlorinated cells and squamous epithelial cells increased significantly.In the 24-hour(3)AgNPs induced oxidative damage of gills tissue under acute exposure conditions.In the Ag NPs,acute exposure test of 24 h,the enzyme activity of superoxide dismutase was inhibited,the Na+/K+ATPase activity and malondialdehyde content increased significantly,and the lactate dehydrogenase had no significant change with the increase of exposure concentration.In the acute exposure test of a lower concentration(0.4mg/L)and a higher concentration(1.2mg/L)Ag NPs for 168 h,there was no significant change in superoxide dismutase enzyme activity and malondialdehyde content with the increase of exposure time.However,Na+/K+ATPase and lactate dehydrogenase activity increased significantly.(4)Ag NPs had no significant effect on the basal metabolic rate(SMR)of carp(SMR = 202.64±23.64 mg O2/ kg/h,n=24;ANOVA,P=0.572).Under the 24 h acute exposure conditions,the critical oxygen tension in the 0.6 mg/L group and the 0.8 mg/L group increased significantly compared with the control group as the exposure concentration of Ag NPs increased.Among them,compared with the control group,the critical oxygen tension values in the 0.6 mg/L and 0.8 mg/L groups increased by 73%and 93%,respectively;the critical oxygen tension values in the 0.4 mg/L Ag NPs exposure group exposed to the acute exposure conditions at 168 hours.The increase of time shows an upward trend,which is a 25% increase from 0h.The increase in the critical oxygen tension indicates the decrease of anoxic tolerance.It is due to the Ag NPs caused tissue oxidative damage to gills.As a result,the baboon tissues absorb oxygen and the gills energy metabolism decreases.In summary,the results of the above studies indicate that silver nanoparticles can be rapidly enriched in Cyprinus carpio gills,and their maximum flux is greater than that of silver ions,but their affinity is lower than that of silver ions.Ag NPs exposure can lead to the damage of tissue structure and ultrastructure of carp,and inhibit the enzyme activity of superoxide dismutase and the oxidative damage to the mitochondrial cells of carp tissue,resulting in a decrease in the energy metabolism ability of carp.At the sametime,Ag NPs exposure can induce increased mucus cells in the gills tissue,resulting in weakened oxygen binding capacity of the gills blood and water,eventually resulting in hypoxic damage and hypoxia tolerance.The results of this study revealed the rapid accumulation of Ag NPs in Cyprinus carpio gills,induced lesions in Cyprinus carpio gills,and thus affected the respiratory mechanism of the toxic mechanism,which can provide a reference for the prediction and assessment of the risk of ecotoxicity of Ag NPs water. |
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