Aging And Adsorption Behavior Of Microplastics And Its Effect On Copper Migration In Soil

Microplastics,as a new pollutant of great concern,have been known to cause great harm to Marine ecology,and have a high content in soil,which will affect soil properties and ecological environment.At the same time,soil heavy metal pollution is widespread,and the accumulation of microplastics may greatly change the ecological impact of the original heavy metals in the soil.Therefore,to explore the interaction between microplastics and heavy metals and the influence of microplastics pollution in soil on copper migration is of practical significance to understand the harm of microplastics in terrestrial ecosystems and the treatment of soil heavy metals.This study selected fertilizer bags of the main material of polyethylene(PE),polypropylene(PP),as far as possible to simulate the micro plastic ageing process in the natural environment,using modern analysis and detection means to explore the process of PP and PE ageing dynamic change rule of physical and chemical properties and their effect on the adsorption of copper ion,at the same time discusses the typical organic compounds on the absorption of copper microplastics.Based on the classical adsorption theory,the adsorption model of copper ions on microplastics was established to reveal the adsorption mechanism of copper ions on microplastics.Furthermore,the change of soil properties and the law of copper migration after microplastic input were further discussed to find out the influence of microplastic input on the change of heavy metal migration in the soil.Through the experiment,the following conclusions can be drawn:(1)The adsorption of Cu(Ⅱ)on original microplastics(PP/PE)reached equilibrium after 72h,Langumir model is more suitable for the fitting of isothermal adsorption experimental data.The adsorption mechanism tends to the single molecular layer on the surface of microplastics.And the maximum adsorption capacity of PP is greater than PE.In addition,Cu(Ⅱ)adsorbed on PP is desorbed faster than that on PE,with a higher desorption rate.In the first 120 days of aging,The adsorption capacity of PP to Cu(Ⅱ)decreases with the decrease of additive.After 120 days,the additive content became stable,the carbonyl index became larger,the oxygen-containing functional groups increased,and the adsorption of PP to Cu(Ⅱ)was enhanced.During PE aging,the additives were continuously lost,and the carbonyl index was small and the oxidation was not obvious,which led to PE’s adsorption capacity of Cu(Ⅱ)decreased with the increase of aging time.(2)Soil DOM,Citric acid,Humic acid and protein inhibited the adsorption of Cu(Ⅱ)by microplastics;The adsorption of Cu(Ⅱ)on microplastics had obvious promoting effect by fulvic acid and glucose.The complexation constant(K)of Cu(Ⅱ)with each organic matter:Humic acid>Soil DOM>Citric acid>Glucose>Fulvic acid>protein;Complexation capacity(C)of Cu(Ⅱ)with each organic matter:Humic acid>Soil DOM>protein>Glucose>Citric acid>Fulvic acid.(3)The influence of PP and PE on the leaching of Cu in soil is related to time.PP significantly improves the mobility of Cu after adding 10 d.The mobility of Cu was improved at the initial stage when PE was added.Over time,the promotion effect decreased,and even reduced the mobility of Cu at 40d.Then in 165-225d,it improves the mobility of Cu,and the more PE is added,the stronger the effect of Cu migration is.Soil CEC was negatively correlated with leached Cu.Both PP and PE can promote the increase of DOC and DON,and the higher the amount added in the soil,the greater the increase of DOC and DON.After the addition of PP and PE,there was a significant correlation(P<0.01)between Cu leaching amount and DOC content in the soil.