| Cadmium is a dispersed element that usually has a very low background content in the soil matrix. However, specific natural processes and/or anthropogenic activitiessuch as industrial and agricultural production can lead to the localized and significant accumulation of Cd that pose a serious risk to the natural environment and human health. Guizhou province that is located in Karst area is covered by large area of carbonate rocks where the average soil Cd content is much higher than in other parts of the country due the high geochemical background Cd concentrations. This Cd pollution of the soils is a matter of great concern. On the other hand, sewage irrigation leads cadmium acculation in the soil which is a threat to cultivated land and shallow groundwater. So the research subject in this study is Cd spatial distribution, migration and transformation mechanism in soils. Adsorption and desorption behavior of cadmium in yellow soil and limestone soil in Guizhou Province; Special distribution, fractions and mobility of cadmium in soil profile in contaminated carbonate rock areas, Guizhou Province, China; Effect on the constraction and distribution of Cd in soil and shallow groundwater. Some of the main conclusions were as follows.(1)Within the test range, Cd adsorption was increased with its increasing initial concentration, and limestone soil had a much higher Cd adsorption capacity than yellow soil. While the adsorption rate declined. When the Cd concentration in adsorption equilibrium was 310 mg·L-1, the amount of adsorbed Cd was 2626 mg·kg-1 in limestone soil, but 1507 mg·kg-1 in yellow soil. While the limestone soil and yellow soil of the adsorption rate of Cd were 84.74% and 48.64%. The adsorption isotherm of Cd in the two soils could significantly conform to Freundlich and Henry equations, while Langmuir and Temkin equation was not applicable to describe the isothermal adsorption process of Cd in yellow soil and limestone soil. Within the test range, Cd desorption was increased with its increasing initial concentration. The desorption rate was increased gradually tend to be stable: yellow soil desorption rate of Cd eventually stabilized at between 25%-30%, limestone soil desorption rate of Cd in 6%-7%. Adsorption capacity of Cd in limestone soil was significantly higher than that of yellow soil.(2) Special distribution, fractions and mobility of cadmium was investigated in 5 carbonate rock area,where were Pb/Zn mining and smelting areas, waste sewage irrigation areas. The concentration of Cd was much higher in top horizon in every area, it gradually reduced within the depth of 0.8 m, then increased sharply between 0.8 m to 1.2 m depth, sequentially precipitated at this horizon. The mobility of Cd along the vertical horizon was mainly affected by organic carbon in Pb/Zn mining and smelting areas, Cd mostly accumulated with soil clay in non contaminated areas, it affected by soil texture as control. Cd mainly existed in reducible Fe-Mn oxides and acid exchangeable fraction, its accounted for 60-80% of total Cd in contaminated areas with low soil pH, which could easily transfer from soil to food chain and water. This issue could lead to human health and environmental risks.(3)A conclusion is made by the short term sewage irrigation simulation experiment: Sewage irrigation can make heavy metal cadmium acculated in surface layer and the bottom layer of soil; For the acidic soil, sewage irrigation makes cadmium traslated to a steady fraction( the residuel fraction)in the soil; And the leaching liquid gets little harm to the shallow groundwater by a short termsewage irrigation. |
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