Effects Of Leaching On Soil Microbial Communities In Cadmium-contaminated Remediation Soil

Due to metal mining activities,agricultural soils surrounding mining areas were severely contaminated with heavy metals(HMs)occurs widely in China.HMs contamination has become a serious challenge for food security.Among lots of remediation technologies for HMscontaminated soil and ways for their safe use for agriculture production,soil washing can remove some HMs pollutants in the soil,so as to meet the needs of safe utilization of agricultural soils.However,soil washing may not only remove some HMs pollutants in the soil,but also lead to the loss of nutrients and major elements,the activation of HMs,and the residue of washing agents,which may lead to significant changes in soil ecological functions.Previous studies have reported that soil enzymes and microbial communities have a good response to the remediation effect of soils contaminated with HMs.Therefore,in the process of washing remediation of agricultural soils surrounding mining areas,it is very necessary to evaluate the ecological effect of washing remediation by studying the impact of washing on soil enzyme activities and microbial community.In order to evaluate the effect of washing on the microbial community of soil contaminated by cadmium,a simulation soil washing was performed with two severely Cd-contaminated agricultural soils collected around mining area in Baiyin city(NW)and Huidong county(SW).The effects of three commonly used washing agents,ethylene-diaminetetra-methylene phosphoric acid(EDTMP),ethylene diamine tetraacetic acid(EDTA)and ferric chloride(FC),on the activity of soil sucrase,urease,acid phosphatase and catalase,the structure of microbial communities,chemical forms of Cd and some physicochemical properties of the test soils were compared.The main results were as follows:(1)All three washing solutions had certain removal effects on Cd in both soils.The removal efficiencies reached 13.27%-38.94%.In NW and SW soil,their removal efficiency followed the order of EDTMP > EDTA > FC and EDTA > EDTMP > FC,respectively.The removal efficiency of EDTMP in SW soil is lower than that in EDTA,this may be related to the photodegradation of EDTMP.(2)The active fractions of Cd in the two soils decreased significantly after washing.After the washing of EDTMP,compared with CK,the stable fractions significantly increased,which may be related to the breakdown product of EDTMP had a certain stabilizing effect on soil Cd.(3)Washing agents affects the remediation effect of Cd and the chemical form of Cd in the soil by changing soil p H,SOM,TN,AP and CEC.(4)After washing,the activity of acid phosphatase,urease and catalase significantly changed.The GMean index and the TEI showed that FC and EDTA was more conducive to the recovery of biochemical function than EDTMP.(5)After soil washing,the microbial community structure changed,and the diversity of soil bacterial community decreased after the washing of EDTMP.(6)The results of correlation analysis and redundancy analysis(RDA)indicated that these three washing agents influenced the activities of enzymes and the structure of microbial community by reducing the concentration of Cd,altering the chemical forms of Cd,soil p H and main soil nutrient contents.