Accumulation Characteristics And Influencing Factors Of Heavy Metal Cadmium In Dryland Soils In Different Pollution Areas In Northwest Guizho

As high background values and impact of indigenous zinc smelting produce serious accumulation of Cd(Cadmium),Pb(lead)and Zn(Zinc)in soils of Northwest Guizhou Province,China,leading to complex cause of pollution.Because of high over-standard rates of heavy metals,such as Cd,Pb and Zn,they possess high human health risk in food chain,posing great challenges to the safe utilization of regional land resources,the precise control of heavy metal pollution sources,and the scientific prevention and control of ecological risks.In this tudy,three typical dryland soils in Weining County,Heishitou(HST)agricultural farming area,Shuanglong(SL)geological high background area and Jinzhong(JZ)zinc smelting plant pollution area were selected,and the soils covered with natural vegetation was used as the control.On this basis,the study contents involving following three aspects: 1)Concentration and chemical form of Cd in the surface and profile soil;2)Influence of topography,soil physical,and chemical properties on spatial distribution characteristics of soil Cd in different pollution areas through geographical detector exploration.The results are as follows :(1)The surface soil Cd(0.17～24.10 mg/kg)in the study area showed the characteristics of high content and uneven spatial distribution.The available Cd content accounted for 33 %～78 %,indicating high pollution risk.In soil profiles,concentration of Cd in the surface soil was significantly higher than in the lower layer,and tillage promoted enrichment of Cd in surface soil.(2)The average concentration of Cd in the surface soil of HST farmland was 1.14 mg/kg,1.68 times of the corresponding background value,and there is no accumulation of Cd.The average content of Cd in SL surface soil was 2.24 mg/kg,3.39 times of the background value,and75 % of the sampling points had moderate accumulation.The Cd content in the surface soil of JZ farmland was 8.32 mg/kg,12.6 times of the background value,indicating a strong accumulation phenomenon.(3)pH,organic matter and elevation were the main influencing factors of soil Cd accumulation and spatial distribution in the study areas.The q values of single factor explanatory power were 0.358,0.482 and 0.402,and the q values of interaction with each influencing factor were between 0.494 and 0.765.The main factors affecting the distribution of available Cd content were pH,organic matter,clay and silt content,and the explanatory power q value was greater than0.400,indicating degree of influence was significant.The q value of interaction among these factors was greater than 0.932,showing that the effect of interaction among factors on soil heavy metals in the study area was higher than that of single factor,indicating that the accumulation of soil heavy metals was controlled by many factors,and the combination of multiple factors led to the increase of soil Cd accumulation.(4)The main influencing factors of Cd in HST contaminated area were pH,slope and soil particle size,and the interaction q value among factors was 0.350～0.632.There was a great relationship between Cd distribution and topography and soil properties in SL contaminated area,and the influence q value was greater than 0.359.The interaction among organic matter,particle size and CEC,slope and aspect had great explanation for the difference of Cd spatial distribution in JZ contaminated area,and all interaction q values were higher than 0.640.In summary,the accumulation of soil Cd in the study areas are obvious and the spatial distribution is uneven.The accumulation of soil Cd is mainly affected by the interaction of soil physical,chemical properties,and topographic factors.The accumulation degree was the strongest in the metal smelting area,while the soil in the agricultural farming area characterizes with strong acidity,high bioavailability of Cd and high ecological risk.The source control of heavy metals in metal smelting should be paid more attention;to prevent the accumulation of Cd in slope soil producing by soil erosion in agricultural farming areas;at the same time,regulation for acidified soil is necessary to reduce the bioavailability of Cd and environmental ecological risks.