Study On The Enrichment Pathway Of Heavy Metals In Typical Crops In Areas With High Geological Background And Exogenous Pollution

Northwest Guizhou is a karst heavy metal geological high background area.Affected by the historical soil zinc smelting,the heavy metal content of atmospheric dust in the area is high,the soil pollution is serious,the heavy metal content of crops exceeds the standard,and there is a risk of food chain.Chinese cabbage（Brassica rapa var.glabra）and potato（Solanum tuberosum L.）were used as test crops.The high geological background soil with relatively consistent soil p H and heavy metal cadmium content and zinc smelting contaminated soil were selected.Pot experiments were carried out in the contaminated area of zinc powder factory and the non-polluted control area to study the contents of heavy metals Cd,Pb,Zn,enrichment coefficient（BCF）and transfer coefficient（TF）in different parts of Chinese cabbage and potato under open air,film mulching and greenhouse cultivation conditions.The study can preliminarily explore the accumulation pathways of heavy metals in leafy vegetables and tuber vegetables,and provide theoretical basis and data support for the health risk management of heavy metals in crops.（1）The soil p H was 5.50～6.00,and the total amount of heavy metal Cd was 5.30～5.50 mg·kg^-1.The proportion of weak acid-soluble Cd,Pb and Zn in zinc smelting contaminated soil was 48%,3.0%and 16%,respectively,which was 3.15,1.01 and 1.57 times higher than that of geological background control soil.The content of heavy metals in atmospheric deposition in the polluted area of zinc powder plant is high.The concentrations of Cd in Chinese cabbage were 0.10～2.08 and 0.10～1.64 mg·kg^-1,the concentrations of Pb were0.12～0.62 and 0.15～0.37 mg·kg^-1,and the concentrations of Zn were 6.72～49.23 and 4.09～34.03 mg·kg^-1 in the polluted area and the control area,respectively.In general,the contents of heavy metals in the polluted area were high,and the concentrations of Cd in potato were 0.01～0.17 and 0.01～0.17 mg·kg^-1,respectively.The concentrations of Pb were 0.11～0.19 and 0.12～0.19 mg·kg^-1,and Zn were 0.38～1.82 and 0.44～2.18 mg·kg^-1.（2）Affected by the activity of heavy metals,the risk of Cd and Zn contents in Chinese cabbage and potato planted in contaminated soil exceeding the national standard was extremely high,which was significantly higher than that in control soil.The control soil in the pollution-free control area did not exceed the standard,and the soil heavy metal activity planting Chinese cabbage and potato had little effect on Pb content,and the effect of atmospheric deposition was greater.The BCF _root-soil of Cd and Zn in Chinese cabbage and potato in contaminated soil was significantly higher than that in control soil,and the BCF _root-soil of Cd and Zn was greater than that of Pb.The TF _shoot-root of Cd and Zn in Chinese cabbage in contaminated soil was significantly higher than that in control soil,and the TF _shoot-root of Pb in contaminated area was significantly higher than that in control area.The enrichment ability of Cd,Pb and Zn in Chinese cabbage and potato was Cd>Zn>Pb.（3）The contribution rates of atmospheric deposition to the accumulation of Cd,Pb and Zn in Chinese cabbage in the polluted area were 2%～52%,21%～63%and 21%～73%,respectively.The content of Pb and TF leaf-vein of Chinese cabbage in the polluted area were higher than those in the control area.The content of Pb showed:open air>film mulching>greenhouse.The accumulation of Cd and Zn in Chinese cabbage was mainly absorbed by roots,while Pb was mainly absorbed by leaves.The content of heavy metals in different parts of potato:stems and leaves>roots>tubers,and the accumulation of Cd,Pb and Zn was mainly absorbed by roots.（4）The average contribution rates of atmospheric deposition to Cd were 37%,21%and 17%in open field,film mulching and greenhouse treatments,respectively.The average contribution rates of atmospheric deposition to Pb were 54%,46%and 26%,respectively.The average contribution rates of atmospheric deposition to Zn were 67%,57%and 21%,respectively.Greenhouse cultivation could significantly reduce the contribution rate of atmospheric deposition and increase the biomass of Chinese cabbage.Three cultivation measures had no effect on the accumulation of heavy metals in potato.There was no difference in the enrichment ability of heavy metals between Chinese cabbage and potato varieties.The zinc smelting pollution in the high geological background area of northwest Guizhou has high activity of heavy metals in soil,and the ability of crops to absorb,transport and enrich Cd and Zn is strong.The accumulation of heavy metals in leafy vegetables is mainly through root absorption,but atmospheric deposition is one of the important ways of Pb accumulation.Potato has a strong ability to absorb heavy metals,but its ability to transport and enrich tubers is relatively weak.The high geological background soil in this experiment can realize the safe production of leafy vegetables and tuber crops.Attention should be paid to controlling the risk of Cd and Zn exposure of crops planted on the soil superimposed with exogenous pollution.Greenhouse planting can effectively reduce the absorption and accumulation of Pb by crop leaves.