Effects Of Dissolved Organic Matter On The Form And Toxicity Of Silver In Water,Which Is Under The Light-Dark Condition

With the development of technology,nanomaterials(NM)are increasingly used in medical,commercial and industrial industries.Due to this increasingly widespread use,NM will be released to the environment during use,especially the water environment in.Nano silver is one of the most used nano materials,once nano silver enters the water environment,there will be a series of morphological changes of silver in water,which include the mutual transformation between silver ions and nano silver.Dissolved Organic Matter is an important part of the ecosystem,A series of direct or indirect photochemical reactions can be induced by solar radiation.In this paper,the effects of DOM on the transformation of silver ion nano silver under light and dark conditions,as well as the process of toxicity change,are studied.It is of great significance to evaluate its bioavailability and toxicity and evaluate its environmental risk.The main research results obtained in this paper are as follows.(1)DOM(HA/FA)-Reduction experiment of Ag~+by light,the reduction of Ag~+in water by dissolved organic matter under light was studied.We have studied the effect of dissolved organic matter on the morphology and toxicity of silver in water,which is for closer understanding of the entire process,such as(time,DOM,silver ion concentration,p H).With the increase of time,the increase of DOM concentration and silver ion concentration are beneficial to the reduction of silver ions and the increase of cell activity,moreover,the concentration of DOM at 15 and 20mg/L is more than that of reduced AgNPs at 5 and 10 mg/L;The reduction of Ag~+accelerated with the increase in p H,especially in the weak alkaline range.In addition,compare with FA,there are more AgNPs reduced by HA.This is because HA has stronger reducing ability than FA.(2)In the oxidative dissolution experiment of AgNPs by DOM(HA/FA)under dark conditions,We have studied the effect of dissolved organic matter on the morphology and toxicity of silver in water,we found that the dissolved Ag~+concentration increases with time;The higher the HA/FA concentration,The higher of p H value,the faster of AgNPs oxidative rate,the higher content of the oxidized nano silver.The oxidation of AgNPs by HA under dark conditions is also p H-dependent,with the decreasing of solution p H,the concentration of dissolved Ag~+enhanced accordingly.HA compared with the FA,the change trend of HA and FA is consistent.But the higher the FA concentration there is the faster of AgNPs oxidation dissolution rate,the more silver ions generated,and the stronger the toxicity.(3)In the end,in order to understand the changes of silver in the natural environment more accurately,further simulation experiments are needed.In the simulation experiment,with the increase of time,the solution changed from a transparent light yellow to a cloudy yellow,and there was a grey-black precipitate at the bottom of the container after standing for a period of time.AgNPs(prepared as light experiment)or Ag~+(20 mg/L)reacted with HA for 10 days.When HA was increased from 5mg/L to 20mg/L,the SPR of AgNPs increased significantly and the content of Ag~+decreased significantly.During the experiment,SPR absorption and Ag~+concentration of AgNPs in AgNPs-HA and Ag~+-HA systems showed similar waveform curves.We further measured the toxicity of AgNPs/Ag~+in the day-night cycle.The Ag~+-HA system can be seen that with the increase of time,the overall silver ion concentration increases.The oxidation reaction at 12 hours of simulated night is stronger than the reduction reaction at 12 hours of simulated daylight,which is making the overall toxicity greater.In the AgNPs-HA system,on the contrary,the oxidation reaction was dominant,and AgNPs was oxidized to Ag~+,so the overall toxicity increased.The toxicity of AgNPs/Ag~+in the AgNPs-HA system increased with time,which was in line with the Ag+release trend.However,the toxicity of Ag~+-HA system decreased slightly with the increase of days.The results show that the concentration of DOM and sunlight are very important for the change of silver morphology.It will not only indirectly cause toxic damage to aquatic organisms,but also damage the ecological environment.This means that we need to understand and do more research to understand the effect of dissolved organic matter on the morphology and toxicity of silver in water.