| As a typical coal-dependent city,Fuxin is the first pilot city in C hina to carry out economic transformation due to resource exhaustion.As an important place for social and economic activities,the topsoil in the main urban area always records and reflects the dynamic changes of the environment during the transition period.To study the ecological geochemical law and the environmental geochemical baseline of heavy metals in the topsoil of Fuxin can play an important role in understanding the regional environmental status,formulating regional environmental strategies and planning urban development.Based on this,we select main urban area as the research field that is divided into the road traffic area,industrial area,commercial area,residential area and urban green space,and collect seventy-five topsoil samples in the depth of 0 ? 20 cm to test and analyse the granularity composition,p H,organic matter content,total texture and occurrence phase state of Cu,Ni,Zn,Pb,Cr,Cd,Hg,As.Determine the heavy metal geochemical baseline in the topsoil of the main urban area from the methods of iteration removal,box-whisker plot,cumulative frequency curve and normalization,on the basis of using the baseline factor index,Enrichment factor index,Nemerow comprehensive index,pollution load index and Hakanson potential ecological risk index,also combined with RAC risk coding,exposure dose model and risk characterization model respectively analysis topsoil's heavy metal cumulative pollution risks,potential ecological risks and human health risks.At the same time,the spatial structure and the source of heavy metals in the topsoil of the main urban area are discussed in detail by means of the half-variogram model,krigin spatial interpolation,local Moran'I spatial clustering,element correlation analysis,multivariate correspondence analysis,and pedigree clustering heatmap.The main conclusions are as follows:?1?The total texture of topsoil heavy metal elements as Cu,Ni,Zn,Pb,Cr,Cd,Hg and As in the main urban area is 20.00 mg·kg-1?156.58 mg·kg-1 (mean 45.13 mg·kg-1),38.50 mg·kg-1?207.45 mg·kg-1 (mean 91.84 mg·kg-1),40.17 mg·kg-1?510.16 mg·kg-1 (mean 107.96 mg·kg-1)and 27.85mg·kg-1?168.95 mg·kg-1 (mean 63.15 mg·kg-1),75.26 mg·kg-1?1095.42 mg·kg-1 (mean 162.50 mg·kg-1),0.021 mg·kg-1?1.179 mg·kg-1 (mean 0.130 mg·kg-1),0.030 mg·kg-1?0.641 mg·kg-1 (mean 0.113 mg·kg-1)and 0.73 mg·kg-1?8.40mg·kg-1 (mean 4.36 mg·kg-1).The proportion of residue form is the highest?36.21%?93.02%?,followed by organically bound form and oxidation state of iron and manganese?3.16%?30.10%?,and the proportion of exchangeable and carbonate state are the lowest?0.08%?6.81%?.In different functional zones,the content of heavy metal Cd and Hg is higher in road traffic areas and industrial and mining areas,the proportion of acid extraction is also the relative highest.The contents of heavy metals in the topsoil of commercial and residential areas are not different from each other,and the acid extract state of Cd is most prominent.The content and variation degree of heavy metal elements as Ni and Cr are larger in greenbelt areas,and Cd is the heavy metal that has the strongest activity.?2?The average value of four determination methods was used as the final environmental baseline of heavy metals in the topsoil of the main urban area of Fuxin.The environmental baseline value of Cu,Ni,Zn,Pb,Cr,Cd,Hg and As was calculated and they are respectively 42.86 mg·kg-1,89.34 mg·kg-1,92.23 mg·kg-1,60.55 mg·kg-1,145.21 mg·kg-1,0.089 mg·kg-1,0.077 mg·kg-1 and 4.17 mg·kg-1.?3?The spatial structure of eight heavy metal elements in the topsoil of the main urban area has both similarities and differences.The heavy metal elements as Cu,Zn,Cr,Cd,Hg and As all have obvious regional hot spots and freezing points,with obvious spatial clustering characteristics.According to the distribution of high values of ele ment content,the coincident high-value areas of Cu,Zn,Pb,Cd and As are mainly extended to the northwest of Haizhou strip mine in Taiping district,up to the downtown area in the middle of Zhonghua road in Haizhou district.The high-value coincident areas of heavy metals as Ni and Cr are mainly concentrated in the southeast,north and northwest of the main urban areas.The high content of Hg is mainly concentrated in the northeast of the main urban areas.The hot areas with high values of Cu,Zn,Pb,Cd and As correspond to the existing economic areas with relatively large population density and relatively frequent social activities,while the rich areas of Ni,Cr and Hg are mostly underdeveloped or undeveloped urban-rural combined areas with sparse inhabitants and relatively weak social and economic activities.The study of heavy metal sources also shows that Cu,Zn,Pb,Cd and As have strong homology,and the characteristics of human input are obvious.Ni and Cr show strong homology,which represented the accumulative pattern of heavy metals dominated by natural input,but the source pollution phenomenon of individual point is more obvious.The heavy metal Hg has both human and natural input sources and shows the mixed mode.?4?The accumulative pollution risk of heavy metals in the topsoil of main urban areas is mainly light-moderate pollution.The potential ecological risk is basically at the level of slight risk.Among human health risks,the non-carcinogenic risk in adults is weak,the non-carcinogenic risk in children is obvious,and the tolerable carcinogenic risk in the human body is ubiquity.Among the eight heavy metal elements,Cd and Hg are the main pollution elements,Cr is the main non-carcinogenic risk element,As and Cd are the main carcinoge nic risk elements.In different functional zones,the risk of heavy metal accumulative pollution and potential ecological risk are relatively higher in road traffic areas and industrial and mining areas.The non-carcinogenic exposure risk in greenbelt spaces,road traffic areas and industrial and mining areas is relatively higher.Simultaneously,the areas with high pollution risks and potential ecological risks are mainly located on the east and west sides of Haizhou strip mine in Taiping district,the south of Yulong Lake in Xihe district,near People's street to the middle section of Meicheng road,near west Huagong street in Haizhou district,and east section of Yulong road in Gaoxin district.The non-carcinogenic high-risk areas are mainly located near the municipal infectious disease hospital that is in the south of Yulong Lake,the mass grave memorial cemetery in the south of Haizhou strip mine,and the industrial and mining areas in the middle section of the Meicheng road.The high-risk areas almost completely cover the Taiping and Haizhou districts,mainly concentrated in the west of Haizhou strip mine. |
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