Acute Toxic Effect And Influence Mechanism Of Ag Nps On Daphnia Magna In Different Water Quality Conditions

AgNPs is widely used because of its superior properties,and eventually inevitably flows into waste treatment sites such as landfills and sewage treatment plants.Landfill leachate and domestic sewage are discharged directly into the surrounding water environment due to accidental leakage,illegal discharge,substandard treatment,etc.,which poses serious environmental risks.The complex environmental factors in wastewater can change the physicochemical properties of AgNPs and subsequently affect its biological toxic effect,such as ion strength（IS）,humic acid（HA）concentration and p H value.However,in the past,the toxicity research of AgNPs was mostly concentrated in culture media or relatively simple water systems,and the complex water bodies represented by landfill leachate and domestic sewage were relatively lacking.Therefore,in this study,landfill leachate and domestic sewage were selected as background solutions,IS,HA concentration and p H value were used as the investigation variables,and the inhibition rate and mortality rate of Daphnia magna were used as experimental indicators to systematically evaluate the effects of different water quality conditions on the biological toxic effect of AgNPs,and the toxicity mechanism was explored by combining the physical and chemical properties of AgNPs.The main findings of this thesis are as follows:（1）AgNPs had a significant acute toxic effect on Daphnia magna,with a 48 h-EC₅₀ value of 29.94μg/L.And both landfill leachate and domestic wastewater reduced the toxic effect of AgNPs to different degrees,with landfill leachate significantly stronger than domestic wastewater,which was related to the high concentration of Na⁺,Ca²⁺and Cl^-ions in the landfill leachate.The IS,HA concentration and p H value of the two wastewater were changed respectively,and there were similarities and differences in the change trend of the acute toxic effect of AgNPs on Daphnia magna:1)the same degree of IS increased,and the acute toxic effect of AgNPs on Daphnia magna in landfill leachate was first rapidly weakened and then enhanced,while domestic sewage showed continuous weakening;2)The acute toxic effect of AgNPs on Daphnia magna in both wastewaters continued to increase with the same degree of elevated HA concentration and p H value,but the effect of landfill leachate was slightly stronger than that of domestic wastewater.（2）For water environment containing higher chloride（>10 m M）,such as landfill leachate and domestic sewage with higher IS（Na Cl concentration）,the aggregation behavior of AgNPs dominated the acute toxic effect of AgNPs on Daphnia magna,and basically showed the law that the agglomerated particle size of AgNPs increased to reduce its toxic effect.For water environment with low chloride concentration（≈2m M）,such as domestic sewage with different HA concentration and p H value,the aggregation behavior（negative correlation）and dissolution behavior（positive correlation）of AgNPs jointly affected the acute toxic effect of AgNPs on Daphnia magna,and the contribution of AgNPs aggregation behavior was stronger than that of dissolution behavior.In summary,IS,HA concentration and p H value will affect the biological toxic effect of AgNPs in landfill leachate and domestic sewage with varying degrees,and the degree of change of the toxic effect of AgNPs depends on its aggregation behavior.The results of the study can be used to reduce the toxic effect of AgNPs in wastewater treatment processes and to reduce the AgNPs content in the effluent.