| With the rapid development of industry,agriculture and urbanization,human activities have caused a large number of pollutants containing heavy metals to enter the soil through different channels,resulting in the increasing degree of heavy metal pollution in the soil.Heavy metals pollution in cultivated land not only leads to ecological environmental damage,but also poses a serious threat to human and animal health,among them.It not only causes the destruction of ecological environment,but also poses a serious threat to human and animal health.Chaoyang city is mainly agricultural,and the agricultural land area covers 66.8%of the total land area of the city.Since the 12th five-year plan period,with the rapid development of industrial agriculture and transportation,it has a complicated influence on soil environment.However,there is no systematic study on the status and risk assessment of heavy metal pollution in cultivated land in this area.It is great significance for ecological civilization construction,to evaluate the status of soil heavy metal pollution in this area.To this end,this paper collected the samples of 402 grain samples from the surface soil samples of cultivated land in five agricultural areas under the jurisdiction of the city.According to the requirements of soil environmental quality detection technology,the samples of As,Cu,Zn,Cd,Hg,Pb,Ni and Cr were analyzed.On this basis,based on the environment-ecological-health effect of multi-target risk assessment of heavy metals in soil have carried on the comprehensive evaluation in the study area from the content of heavy metals in soil and grain distribution in space-space,mutation-pollution,levels–environ mental risks-health risks-source resolution-risk during the identification and control.Main conclusions are:1.Spatial distribution characteristics of soil heavy metal As Cu Zn Cd Hg Pb content have certain similarity.The data of these heavy metals are in the right skewed distribution,with strong spatial variability.As?Cu?Zn?Cd and Pb were high in the west,low in east.Hg is high southwest and low northeast.The mean contents of Cu,Zn,Cd,Hg and Pb are 1.51,1.36,3.49,1.48 and 1.67 times of the local soil background values,respectively.It indicates that these elements have varying degrees accumulated in the local soil.2.The content of heavy metals in soil are at general safe level,and some individual elements have exceed the standard.The average CPI in the whole area was 0.42,indicating that the soil in this area was at general clean level.The results show that the soil Cd was"mildly polluted"and the remaining elements were"pollution-free".The soil quality of the92.83%area belongs to class II of soil environmental quality classification,namely safety level.3.The overall level of soil ecological environment is acceptable.The result of Hakanson ecological index evaluation shown that various heavy metal elements have little impact on environmental risks.The results of ecological risk quotient evaluation show that Ni Zn Cu had significant effects on biological species?Ni medium?and ecological processes?Zn medium,Cu slight?,respectively.Other elements have no obvious effect.4.The exposure risk of soil heavy metals is acceptable.The non-carcinogenic comprehensive health risk index HI was 0.02?adult?and 0.39?children?were less than 1.The carcinogenic risk index DMN is 8.33×10-5,between 10-610-4.It shows that the risk level of carcinogenic and non-carcinogenic risk caused by soil heavy metals exposed by the residents in this area is negligible.5.The content of heavy metals in grain is generally at a safe level,only individual element in individual point have exceeded the standard?GB 2762-2017?.The ratios of Cr,Cd,and Pb in grain samples exceeding the standard value are 4.11%,1.37%,12.33%,respectively.None of the remaining elements were superscalar.The results of the grain target risk assessment showed that the health risk index of both adults and children was less than 1,indicating that the risk of heavy metal in grains was mild.6.There are differences in the sources of heavy metals in different soils.Comprehensive multivariate statistical analysis,PMF model and UNMIX model analysis results showed that the soil Cr and Ni in the study area were homologous,mainly from the soil parent material.Zn and Pb have strong homology,mainly from traffic,Cu and As are mainly from agriculture,Cd and Hg are mainly from industrial and atmospheric deposition sources.The contribution rate of each pollution source of soil heavy metals is ranked as:transportation and the comprehensive source of soil and soil,>industrial source>agricultural source>large gas source.7.The cultivated soil environment of chaoyang city is generally good,suitable for the development of ecological agriculture and organic agriculture.Only 6.71 per cent of heavy metal contamination was found.There are Cd and Zn elements in the middle and southwest of chaoyang county.There are Zn and Cu elements in north,east and south of jianping county.There are Cd,Cu and Zn elements in the north and central part of the county.There are some Cu,Zn and Cd elements in the north ticket market.The city also has Cr,Cu,Zn,Cd and Pb.We will establish a system of identification and control over superscalar areas to curb the spread of pollution. |
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