| With MSWIP(municipal solid waste incineration plant)being applied widely,tail gas of MSWIP will influent on environment.MSW(municipal solid waste)is collected with mixed method in China,containing a great quantity of heavy metals.Then tail gas will discharge into the atmosphere,and eventually reach into the soil though wet and dry depositionis collected with mixed method in China,containing a great quantity of heavy metals.In spite of being equipped with modern tail gas treatment system to comply with the very strict emission limits imposed by legislation,tail gas of MSWI is still a problem.Because of the continuous emission of tail gas and difficult migration of heavy metals,heavy metals will easy to enrich in soil around MSWI(municipal solid waste incineration)and become a potential pollution accident.The research object was soil heavy metals surrounding MSWI,the correlations between the basic physicochemical characteristics of soil and the heavy metals content was studied,space and vertical distribution of heavy metals concentration was analyzed,their main sources were explored,the pollution of heavy metals was assessed.It is significant to option of MSWIP location,environmental risk assessment,pollution prediction and tail gas treatment on heavy metal in soil surrounding MSWI.1.The basic characteristics of soil surround in MSWIP were studied by FT-IR(Fourier infrared ray),XRD(X-ray diffraction).The results show that the moisture content of soil is 1.05%.Dry soil mainly contains silicate minerals.2.Physicochemical characteristics analysis results show that the soil is paddy soil under weak acidic,Ti,Cr,Mn,Fe,Cu,Zn and Pb had no correlation with pH value.The average of conductivity was 51.14 μs/cm.And Soil conductivity had significant negative correlation with content of Pb.The average of soil cation exchange capacity(CEC)was 21.47cmol/kg.CEC had significant negative correlation with content of Pb.Total organic carbon(TOC)had high positive correlation with contents of Cu,Zn and Pb with average value of 1.98%.The average contents of clay,silt and sand were 0.86%,62.64%and 36.5%.Clay content had high positive correlation with concentration of Fe,the contents of Ti,Cu,Zn and Pb had significant negative correlation with silt content,sand content had high positive correlation with Ti,Cu,Zn and Pb.3.The average contents of Ti,Cr,Mn,Fe,Cu,Zn and Pb were 8.97g/kg,285.32mg/kg,1132.06mg/kg,63.11g/kg,34.28mg/kg,80.98 mg/kg,and 39.47mg/kg respectively.The spatial variability of Ti,Cr,Mn,and Fe were irregular.The spatial variability of Cu,Zn and Pb were like island and block.High content of Cu were in locations which are respectively 400 and 2400 metre away from MSWIP in east direction,and which is 2000 metre away form MSWIP in southeast direction.High concentration of Zn located in which are 400 and 800 away from MSWIP in south direction,the rest locations were the same with Cu.Pb content was much higher in that was 2400 metre away from MSWIP in west direction and near it,the content in west area was much higher than east area with the average content of 42.14 mg/kg.The heavy metals contents ratio between surface and deep soil showed that,ratio values of Ti,Cr,Mn,and Fe were close to one,it didn’t be polluted.Cu and Zn may be contaminated by anthropogenic activities in some areas.No mattere in surface soil or in deep soil,Pb contents is high.Because of Pb infiltration,partial the deep soil had been contaminated.4.The classified results using correlation analysis,or cluster analysis,or PCA(principal component analysis)show that Ti,Cr,Mn and Fe were the first category,Cu and Zn were the second category,Pb was the third category.PCA and spatial variability maps show the results as follows.The first PC was Ti,Cr,Fe and Mn,they belonged to one category.Ti,Cr,Fe and Mn are always recognized as natural factor making elements of soil,so the source of this category might be nature.The spatial variability maps of Ti,Cr,Fe and Mn concentrations were random and irregular.External environment had little influence on this category of heavy metals.While,forming soil-forming progress and soil erosion impacted on them evidently.So,first PC was mainly attributed to the geochemical action of soil itself.The second PC was Cu and Zn,the spatial variability maps of them shows that as the increase distance from the high concentration location,the Cu and Zn concentration gradually decreased.The concentration of Cu and Zn had no correlation with the diastance from MSWIP.The growing progress of fruits and vegetables was sprayed pesticides,which caused that Cu and Zn enriched to a high content in soil.Thus,the second PC could be thought as pesticide effect.The third PC was Pb.Combining wind direction diagram,the Pb concentration promoted as the increase of distance from stack in dominant downwind direction(W,NW).Furthermore,Pb concentration had significant correlation with distance(p<0.05),and similar horizontal diffusion of the concentration distribution trend appeared in y direction.Consequently,the third PC might stand for influence that caused by MSWI tail gas diffusion and deposition.The wind led to the change of Pb concentration in different locations,it was closely related to wind direction and frequency.Accumulation effect of heavy metals from tail gas in soil surrounding MSWI plant was unneglectable.5.The Single Factor Index show that more than sixty percent of Ti,Cr,Mn and Fe contents were lower than background content and the average of their P values were less than one,so the soil was not contaminated by Ti,Cr,Mn and Fe in general.Cu pollution state of 61.43%of sampling points was light,2.85%was moderate,and 1.43%was heavy.Zn pollution state of 77.14%of sampling points was light,1.43%was moderate.95.72%of sampling points was contaminated slightly by Pb and Pb pollution state of 2.85%of sampling points was moderate.From the Nemerow Comprehensive Index,PN value of all heavy metals was 1.36,and its pollution state was light.And Cu,Zn and Pb were has contributed enormously to soil pollution. |
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