| In recent years, the problems of food safety due to heavy metals pollution were more and more frequently concerned by people. Vegetable is indispensable in people’s daily life, there exists a close relationship between the quality of vegetables and human health. Heavy metals in soil and atmospheric deposition can be enriched in vegetables, which would harm to human health through the food chain. Related researches shown that one of the main sources of heavy metals in crops and vegetables is atmospheric deposition.Therefore, according to the project of National Natural Science Foundation (41271472):Pollution effects of heavy metals in urban dry and wet deposition on soil-vegetable system, this study selected the suburbs of Shanghai as a representative, and elements of Pb, Hg, Cd, Cr, As, Zn and Cu in soil-vegetable system as the main study objects. Meanwhile, discussed the temporal and spatial distribution characteristics of heavy metals in the medium soil-vegetables system by systimatic field investigation, and clarify the human health risk of heavy metals through ingestion of vegetables. To comparative analysis the concentrations and dynamic accumulation process of heavy metals in edible parts of vegetables on the inside and outside of greenhouse based on the field exposure test. And through the simulation experiment of dry deposition chamber, to reveal the pollution effects of heavy metals in dry deposition falling in different ways on soil-vegetable system, building the contribution model of atmospheric deposition to heavy metals accumulated in vegetables based on bioavailable heavy metals. With these efforts, this study aimed to improve the development of biogeochemical theory of heavy metals in the gas-soil-organism interface. The experimental analyses could be summed up with following conclusions.1)The average concentrations of Pb, Cd, Zn, Cr, Cu, Hg and As in vegetable soils in the suburbs of Shanghai were 25.982,0.116,127.035,127.322,32.122,4.030 and 15.027 mg/kg, respectively. All the heavy metals (except for Hg) were lower than the limit of soil, but the average level of Zn, Cr, Hg and As were higher than that of the primary standard of soil environment. The evaluation of the index of geoaccumulation showed that the vegetable soils of Shanghai suburbs had happened Hg, Cr, As, Pb, Zn pollution. The concentrations of Hg in vegetable soils had reached more than moderate level of pollution. In all sample areas, the pollution level of heavy metals in the soil of PD was highest, and of MHZF was lowest. The average concentrations of Pb, Cd, Zn, Cr, Cu, Hg and As in road dust near the vegetable field were 117.56,3.63,896.10,373.92,147.90,2.03 and 12.21mg/kg, respectively. The concentrations of heavy metals in road dust were significantly higher than that of vegetable soils in the suburbs of Shanghai, and the road dust should be regularly cleaned.2)The average concentrations of Pb, Cd, Zn, Cr, Cu, Hg and As in the edible parts of vegetables in the suburbs of Shanghai were 0.542,0.243,48.583,9.620,8.675, 0.029 and 1.191mg/kg, respectively. Compared with the national food safety standards,38.12%,54.07%,92.37%,100%,31.75%,53.71% and 53.49% vegetable samples were respectively beyond the limits of safety standard. The concentrations of heavy metals in edible parts of vegetables was higher than radish, unwashed vegetables was higher than of washing vegetables. The health risk index of heavy metals in vegetables for adult were consistent with for children, but the risk value of children was higher than that of adult. By eating vegetables, daily intake of As had been far more than the maximum allowed value (RfD). For As, the contribution of green vegetables, cabbage, cabbage and Yau Ma Tei is larger. The concentrations of heavy metals(except for As) were lower than the maximum allowed value (RfD), belonging to the security level.3)Field experimental results showed that the average concentrations of Pb, Cd, Zn, Cr, Cu, Hg and As in the edible parts of vegetables, in the open air, were 0.485, 0.263,70.213,9.307,8.124,0.080 and 0.439mg/kg, respectively. And the average concentrations of heavy metals in vegetables, in plastic house, were 0.222,0.143, 49.453,8.169,5.302,0.189 and 0.263mg/kg, respectively. The concentrations of heavy metals(except for Hg) in edible parts of vegetables, in the open air, were significantly higher than vegetables, in plastic house. The concentrations of Pb, Cd and As in edible parts of vegetables, in the open air, was two times as much as that of corresponding vegetables,which growed in plastic house. This phenomenon indicated that atmospheric deposition could increase the concentrations of heavy metals in vegetables.4)In the whole growth period, the concentrations of Cu, Cr in edible parts of green vegetables in the open air, increased at a similar pace. The process of dynamic accumulation of other heavy metals showed in consistency. The accumulation process of Pb of green vegetables, which grown in plastic house, was consistent with that of green vegetables in the open air. The accumulation process of Zn, Hg and As of green vegetables, in plastic house, was consistent with that of green vegetables in the open air, but the concentrations of Zn and Hg increased significantly in the final stage. The concentrations of Pb, Zn and Cu in edible parts of lettuce,in the open air, increased rapidly at the beginning of germination, then kept in balance or decreased significantly, which may be related to some leaves rotting.The concentrations of Pb, Zn in edible parts of lettuce in plastic house, increased continuously. Cr was rapidly accumulated in 10 days and 24 days after germination, and increased to the value of lettuce in the open air, then started to decline. The concentrations of Pb, Cu, Cr and Hg in edible parts of amaranth in the open air, increased to be continuous. The accumulation rate of Pb, Cu, was decreasing gradually. The concentrations of Pb, Cd and Hg in edible parts of amaranth in plastic house, increased with time. The accumulation rate of Pb, Cd in each stage also showed a good consistency. The accumulation process of Cu, As and Cr showed consistency. All increased at first stage and then decreased lately. The concentrations of heavy metals(except for As) in edible parts of spinach in the open air, increased with time. The accumulation process of Zn, Pb and Hg in edible parts of cabbage in plastic house, showed consistency. The concentrations of Cd, As in 10 days after germination was relatively stable, and that of Cr, Cu in 17 days after germination tended to balance.5)The simulation experiment results of dry deposition showed that the total amount of heavy metals in the edible parts of vegetables, without accepting dust, from high to low was the spinach, lettuce, green vegetables. This result was consistent with that of corresponding vegetables in the suburbs of Shanghai. Comparison showed that atmospheric deposition could increase the concentrations of heavy metals in green vegetables more than lettuce.Three methods of dustfall could increase the concentrations of heavy metals in the edible parts of vegetables. And it could increase the concentrations of heavy metals in green vegetables more than lettuce and spinach. Foliar dust had biggest contribution for spinach and green vegetables to accumulate heavy metals. Soil surface dust had biggest contribution for lettuce to accumulate heavy metals.6)Multiple linear regression analysis showed that the concentrations of Pb in spinach root was fully compliant with the Voutsa contribution model fitting, if accepted foliar dust.The concentrations of other heavy metals in vegetables was not compliant with the Voutsa contribution model fitting, if accepted foliar dust or leaf-soil dust. The reason may be that in this study, only dry deposition could be simulated. Wet deposition, atmospheric deposition and isotope tracer experiment should be simulated and to made a further Voutsa contribution model. |
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