| Heavy metal pollution in the soil will have an adverse impact on the ecological environment,and it can also endanger human health in various ways.Identifying the influencing factors of heavy metals in the soil and evaluating environmental risks are of great significance in the management of soil environment.However,the current research on the influencing factors of heavy metals ignores the relationship between the spatial distribution pattern of heavy metals and environmental factors,as well as the influence of the nonlinear relationship between the factors.In the risk assessment,the contribution from the source is also ignored.And under the background of unique landform types and special geological environment in the Karst area,the distribution of heavy metals in the soil and its influencing factors may have certain particularities.Based on this,in this study,the Houzhai River Basin in Puding County was used as the study area to analyze the spatial distribution characteristics of soil heavy metals chromium,nickel,copper,zinc,cadmium,and lead,and to assess their pollution.Geographical Detector(GDM)is used to identify the key influencing factors and types of spatial distribution of heavy metals in the soil,and to define heavy metal enrichment risk areas.Combine the positive matrix factor method(PMF)of the receptor model and the ecological health risk model to identify and quantify the ecological health risk of heavy metal pollution sources under different land use methods,and analyze the impact of source distribution on the risk.Research indicates:(1)The risk of heavy metals in the study area to crop growth and soil ecological environment is low and can be ignored.Under the three types of land use(agricultural land,construction land,and forest land),the maximum values of the six heavy metals all appear in agricultural land,indicating that agricultural activities may be the main source of heavy metals.Enrichment analysis shows that the accumulation of heavymetals is mainly concentrated in agricultural land.Among them,the accumulation degree of Cd in forest land is relatively large.Cu and Pb are mainly accumulated in construction land and agricultural land.The enrichment of Zn is largely affected by human activities,such as agricultural activities.In terms of spatial distribution,the areas with high heavy metal concentrations mainly extend from the middle to the northwest of the study area.The distribution of elements Cr,Cu,Zn,and Ni are mainly in the middle and lower reaches of the watershed,and the high value areas of element Pb are mainly distributed in the north of the study area to The spread of the Northwest has a certain relationship with the distribution of land use.The soil heavy metal pollution risk in the study area is mild to moderate,and the pollution index and ecological risk in the north are high.The element Cd is the main contribution of ecological risk to heavy metals,and its contribution accounts for 57%.It shows that the potential ecological risk is related to the control source of element Cd.The risks in the eastern part of the study area are largely affected by this source.(2)The operation results of the Geographic Probe(GDM)show that land use and distance from the river are the main influencing factors of Cd.At the same time,soil type,slope,NDVI and altitude also have certain influences;in addition to altitude and soil type,land use and residents Land also has a certain influence on the elements Cu and Zn.Roads,land use and residential areas are also the main influencing factors of the elements Cr and Pb.The residential areas also have a certain explanatory power for Ni.Therefore,when carrying out environmental prevention and protection of the area,more attention can be paid to the area with these environmental factors.Factor interaction results show that the interaction between the river and the altitude improves its ability to explain the distribution of Cd content by 90%.For the remaining five heavy metals,although the river has the least influence on it,the river is helpful to improve the explanatory power of the heavy metal content distribution.Based on the key influencing factors and environmental types,the enrichment risk zone of each element is defined.The Cd risk area is mainly concentrated in the eastern part of the study area,and its characteristics are mainly as follows: the lime soil is higher than the yellow soil in the soil,the vegetation coverage type is mainlygrassland and shrub,and the slope is large.The remaining five heavy metal risk zones mainly extend from the middle to the west.The Pb element risk area is mainly near the construction land,and the soil type is mainly yellow soil.The risk areas of Cr,Ni,Cu and Zn are close to roads and residential areas.The areas with small DEM and small slopes are yellow soil and the land use method is paddy field.The distribution of these risk areas shows that the areas determined based on the key influencing factors and their types of influence have the role of providing an indication for the risk of heavy metals and can provide an important basis for the implementation of prevention and control measures.In the prevention and control of heavy metal pollution,priority should be given to these areas.(3)Identify four types of pollution sources of heavy metals in the soil,of which agricultural activities are the main source(33.72%),followed by traffic emissions,natural resources and industrial activities.The ecological risk assessment results of the sources show that the source with the largest overall contribution is natural(40%).In forest land and agricultural land,the source of agricultural activities is second only to natural sources,accounting for 25% and 29%,respectively.The distribution of ecological risk and source contribution shows that in the middle of the study area(the area with high potential ecological risk),transportation contributes the most to ecological risk.Therefore,although the overall dominant factor of ecological risk is natural sources,in areas of higher risk,the contribution of traffic emission sources is the main source.Explain that traffic emission sources are the priority sources of influence in the development of environmental and ecological risk prevention policies in the region.(4)Although the non-cancer risks and cancer risks of children are higher than those of adults,the contribution of health risk sources of the two groups of people shows the same trend under different land use types.Children are more susceptible to non-cancer risks and cancer risks.On the whole,agricultural activities are the leading factor in cancer risks,contributing 38%.Industrial activity is the largest source of non-cancer risks(36%)and the second largest source of cancer risk(27%)after agricultural activity.This shows that sources containing dangerous heavy metals(Cr,etc.)are more likely to cause health risks.In terms of spatial distribution,children’s high-cancer risks areas and non-cancer risk areas are mainly concentrated in the northern part of the study area.And the contribution of traffic activity sources to cancer risk is also concentrated in the central and northern regions.Therefore,although in general,agricultural activities are the main source of cancer risks,industrial activities are the main source of non-cancer risks.However,areas with non-cancer risks are mainly affected by traffic activities.It shows that traffic emissions and agricultural activities are the main sources of health risks.When preventing and controlling heavy metals in the soil to human health risks,we should focus on the impact of these two sources.Therefore,source-based ecological health risk analysis can provide an important basis for formulating measures to control soil heavy metal pollution from the source and manage key pollution sources. |
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