| Metal smelting is the main source of the soil heavy metal pollution.Heavy metal moved to agricultural soil by the way of atmospheric deposition and in the “soil-plant-microbial” system transformation,through food chain harm for human health seriously.In recent years,there are many incidents involving soil environmental pollution,soil govern and repair is particularly urgent.This study was dynamic monitoring,analysis and evaluation the agricultural soil pollution by heavy metal of shaanxi Feng County county for three years,in order to understand the migration characteristics of heavy metals in the contaminated soil.On this basis,we can choose different kind and amount of modifier and different plant types.To the selected land adopt Phyto-Chemistry Combined Remediation technology develop two-year field experiment,in-depth exploration the repair mechanism,optimization the repair technological parameter,and for the repair of heavy metal contaminated soil provided theoretical foundation and technological guidance.The main research results were summaried as follows:(1)The topsoil in the proximity of smelter,especially the smelter area and county seat,were highly polluted by HMs in contrast to the river basins.Fractionation of Cd and Zn in soil samples revealed higher proportion of mobile fractions than other HMs.The soil Cd and Zn contents decreased vertically,but still exceeded the second level limits of Environmental Quality Standard for Soils of China(EQSS)within 80 cm.The dominated soil pollutant(Cd)had higher ecological risk than Cu,Ni,Zn and Pb.The potential ecological risk(PER)factor of Cd were 65.7% and 100% in surrounding county and smelter area,respectively.The long-term smelter dust emission mainly contributed to the HMs pollution and posed serious environment risk to living beings.(2)We surveyed the native plant in an area of 200 mu surrounding the zinc smelter in Feng County,and got 28 classes and 56 genera in total.Most of them were herbaceous plants,and followed by shrubs and small trees.The dominate plant was belong in class Asteraceae,with account for 19.29% of the total number of species.Such as Chenopodium album Linn.,Cirsium segetum,Tagetes erecta,Senecio scandens and Setaira viridis(L.)Beauv.Heavy metal pollution had enormous adverse influences on the biomass of plant,which was generally small in polluted areas.Lighter polluted areas can cause larger plant biomass.The top 5 biomass plants were Radix Phytolaccae(455.5 g),Silpniumper foliatum L.(334.0 g),Symphytum officinale Linn.(195.5 g),Cirsium segetum(194.8 g),Robinia pseudoacacia Linn.(121.6 g).Different plants had many differences on the absorption and accumulation characteristics of heavy metals,and the same plant absorbed differently in different polluted degree of soils.The plants whose upground part can uptake greatest of Cd,Zn and Pb were Brassica juncea(L.)Czern.,Cirsium segetum and Brassica juncea(L.)Czern.In the meanwhile,the plants whose underground part can uptake greatest of Cd,Zn and Pb were Iris lactea var.chinensis,Cynanchum wilfordii(Maxim.)Hemsl.and Lithospermum arvense L.The plants with highest transfer factor(TF)of Cd,Zn and Pb were Iris lactea var.chinensis,Leonurus japonicus Houtt.and Silpniumper foliatum L,respectively.The heavy metal content of upground part which beyond the recognized screening threshold for Cd(100 mg·kg-1)were Kummerowia striata,Symphytum officinale Linn.,Sonchus arvensis Linn.,Brassica juncea(L.)Czern.and Iris lactea var.chinensis;and for Pb(1000 mg·kg-1)were Iris lactea var.chinensis,Symphytum officinale Linn.Overall,considering the plant biomass and the ability of heavy metals accumulatation and transferring,Symphytum officinale Linn.and Iris lactea var.chinensis can be defined as ecological restoration of pioneer species in zinc smelter area of Feng County.(3)We investigated the influence of heavy metals(HM)in total soil bacterial population and its diversity pattern from 10 km distance of a Zinc smelter in Feng County,Qinling Mountain,China.We characterized and identified the bacterial community in a HMs polluted soil using 16 S rDNA technology.Out result,indicate that the maximum soil HM concentration and the minimum bacterial population were observed in S2 soil,whereas bacterial diversity increased with the sampling distance increase.The bacterial communities were dominated by the phyla Proteobacteria,Acidobacteria and Actinobacteria in cornfield soils,except Fimicutes phylum was dominated in hilly area soil.The soil CEC,humic acid(HA)/ fulvic acid(FA)and microbial OTUs increased with the sampling distance increased.Shewanella,Halomonas and Escherichia genera were highly tolerant to HM stress in both cultivated and non-cultivated soil.Finally,we found a consistent correlation of bacterial diversity with total HM and SOM along the sampling distance surrounding the zinc smelter,which would be further provide a new insight into the bacterial community-assisted and phytoremediation of HM contaminated soils.(4)Adding biochar could significantly improve the rhizosphere soil pH and CEC after harvesting the plant of two seasons.While it had a slight inhibition effect on the soil EC,and had a concentrated effect on soil N,P,K.Higher biochar addition amount can significantly increase the soil humus and HA/FA,as a result increasing the soil organic matter content,finally promote the growth of plants.Biochar could decrease the bioavilibility of Cd and Pb,and increase the content of stable fractions(oxidation and residue fraction),so keep less harm to the environment.Biochar addition amount of 5-10 g·kg-1 decrease the bioavilibility of Zn.10 g·kg-1 addition level treatment had inhibitory effect on Cu and Zn adsorption maybe due to the adsorption of other pollutants.5-10 g·kg-1 biochar treatment significantly reduced the soybean and maize root,grain and stem leaf accumulation of Cu,Zn,Pb and Cd.In this process,the cumulants of Cu and Zn in different parts of rapeseed and wheat significantly reduced,because the biochar adsorption immoblization effect will be affected by the characteristics of heavy metals.Considering plant biomass accumulation characteristics,enrichment of heavy metalsand the parameters changes of rhizosphere soil,the 5 g·kg-1 was the best addition amount for biochar application in the farmland blocks.(5)Different zero-valent iron(ZVI)treatment could affect biomass accumulation characteristics of the four plants.2 g·kg-1 ZVI treatment lead to soybean biomass accumulation and growth enhancing.And 6 g·kg-1 ZVI treatment handled most conducive to the corn biomass accumulation.Compared to the control,the biomass(dry weight)of upground part of wheat decreased significantly,so the ZVI treatment has adverse effect to the biomass accumulation of wheat grain.The root biomass of rapeseed was the highest in the four plants,can absorb more heavy metals.Soybeans,corn and rapeseed shared the same order in heavy metals accumulation in different parts of plant,the order as: stem > root > grain,while the order of wheat was,root > stem > grain.Heavy metals in seeds and root of soybean decreased with the ZVI applying amount increasing.In general,ZVI treatment can reduce the uptake of heavy metals.The iron rich material extracted from the ZVI treatment soil was determined high heavy metals content.Cd content was 155.8 mg·kg-1(three times to the original Cd content in soil),and zinc content was six times to the original soil as high as 29525 mg·kg-1.Modern physical characterization reveals that the corrosion of ZVI in soil produced many kinds of iron oxide with possible adsorption of heavy metal reaction,so as to achieve the immobilization effect of soil remediation.(6)When added lime and sodium sulphide treatment,the soil pH value increased significantly,after a period of time it weakened.With the increase of adding amount of lime and sodium sulphide,the crop biomass of every quarter has the consistent increase trend.For the crops of the first quarter,the biomass of soybean and maize growing on the treatment soil that added lime and sodium sulphide increased significantly.Add lime can promote more increasing of the biomass of soybeans and maize,and the effect of add sodium sulphide treatment was more obvious on wheat production.The treatment of add lime and sodium sulphide can basically inhibit metal accumulation at different position of the two quarter crops.The content of heavy metal accumulation in the crop root that growing in the sodium sulphide treatment was lower than in the lime treatment.This indicated that sodium sulphide treatment can significantly inhibit the accumulation of heavy metals in plants,but high application amount easily leads to soil harden.In conclusion,lime can be used as an ideal improver in situ passivating repair cadmium pollution agricultural soil.(7)Adding citric acid and EDTA treatment were significantly reduced the soil pH value,the greater of the amount add citric acid and EDTA,the greater of the soil pH value reduction.Especially for the crops of the first quarter,the soil pH value had a greater influence.Adding citric acid and EDTA decreased soil EC content,the influence of citric acid on soil EC content was greater than EDTA.EDTA increased the biomass of wheat and rape,reduce the biomass of the maize;citric acid increased the biomass of soybean.Citric acid and EDTA treatment can promote the accumulation of heavy metals at different positions of crops at two quarters.Especially citric acid could significantly improve the absorption of zinc on maize.EDTA can significantly promote the absorption of various heavy metals accumulation on the aerial part of wheat.In general,citric acid increased the enrichment coefficient of different heavy metals in all plant at different level.EDTA can improve plant transfer coefficient,but add too much may lead to a drop-in enrichment coefficient of the aerial parts of plants.Overall consideration the characteristic of plant biomass and the accumulation of heavy metals in the different part of plant,the best application amount of citric acid and EDTA was 15 mmol·kg-1 and 10 mmol·kg-1,respectively. |
PDF Full Text Request