Study On The Vertical Transport Rules Of Cd Chelate-induced By EDTA In Soil

Aiming at the potential problem of secondary pollution due to the heavy metals which was chelate-induced by chelates, this paper studied the vertical distribution rule of soil Cd which was chelate-induced by EDTA, the effect of Brassica juncea with different planting density on the vertical distribution of soil Cd induced by EDTA, and the vertical distribution rule of available Cd in the soil, on the basis of adopting soil column simulated and field micro-spot simulated experiments with three different textural soils(sandy, loamy, clay soils) and Brassica juncea as materials. Main results of the experiments were summarized as follows:1. After being activated by EDTA at the surface contaminated soil, Cd could transfer significantly at the direction of vertical in sandy soil column with irrigation water. Within 90 days (equal to two simulated years), Cd even can transfer to the depth of 180cm of the bottom of soil column, and outmigrated from soil column with water. Within a short period, Cd can transfer to deep layer soil with irrigation water, and may contaminate shallow groundwater. The content of total Cd in the soil decreased with the increase of soil layer depth, and the content of available Cd in the soil showed the similar change current. The total Cd in the soil showed extremely significantly linear and positive correlation with the reciprocal of soil depth.2. After being activated by EDTA at the surface contaminated soil, Cd could transfer significantly at the direction of vertical in loamy soil column with irrigation water. Within 270 days (equal to six simulated years), Cd even can transfer to the depth of 180cm of the bottom of soil column, and outmigrated from soil column with water. Within a short period, Cd can transfer to deep layer soil with irrigation water, and may contaminate shallow layer groundwater. The content of total Cd in the soil decreased with the increase of soil layer depth, and the content of available Cd in the soil showed the similar change current. The total Cd in the soil showed extremely significantly linear and positive correlation with the reciprocal of soil depth.3. After being activated by EDTA at the surface contaminated soil, Cd could transfer significantly at the direction of vertical in clay soil column with irrigation water, and it can transfer to the soil depth of 100cm. Within a short period (10 years), Cd could not transfer downward quickly. Hence, the shallow layer groundwater would not be contaminated. At the soil depth of 0~100cm, The content of total Cd in the soil decreased with the increase of the depth of soil layer, and the content of available Cd in the soil showed the similar change current. The total Cd in the soil showed extremely significantly linear and positive correlation with the reciprocal of soil depth.4. After being activated by EDTA at the surface contaminated soil, Cd could transfer significantly at the direction of vertical in sandy soil column adding clay layer with irrigation water. Within 90 days (equal to two simulated years), Cd even can transfer to the depth of 180cm of the bottom of soil column, and outmigrated from soil column with water. At the clay soil depth of 20cm, Cd can transfer to deep layer soil with irrigation water and may contaminate shallow layer groundwater within a short period. The content of total Cd and available Cd in clay soil was significantly higher than that of the sandy soil. The total Cd in the soil showed extremely significantly linear and positive correlation with the reciprocal of soil depth.5. In the field micro-spot experiment, the Brassica juncea with different treatments showed good growth conditions. The accumulation contents of Cd in shoot of Brassica juncea were significantly higher than the root of Brassica juncea. Improving the planting density of Brassica juncea suitably could enhance the accumulation of Cd in soil. Under three different planting densities levels (10, 20, and 30 plants/ barrel), with the increase of planting density, the ability of accumulating Cd of Brassica juncea could be enhanced, and the vertical distribution of available Cd also could be controlled efficiently.6. EDTA not only activated the insoluble Cd in the calcareous soil effectively but also increased Cd accumulation in the shoots and the roots of Brassica juncea significantly. The activated Cd can be concentrated into the surface layer soil by dense roots of Brassica juncea. The activated Cd downwards migration in the soil is more shallow depth with increasing cultivation density of Brassica juncea.