| As one of directly edible crops, pollutionless vegetable's development became increasingly popular since the people care more for their own health. At present, people pay close attention to pesticide and nitrate, instead of heavy metals little with the development of vegetable. Heavy metals are some kind of pollutants that aren't easy to control, some studies show that if the heavy metals in soil were accumulated to some extent they could harm the soil-plant system, the people's health will be influced both directly and indirectly by through food chain. There are two ways to control heavy metals pollution: one is to move away the polluted soil totally, the other is to reduce the activity of heavy metal and prevent the entry of the content into plant. In the first way, the cost of physical-chemistry method is expensive and phytoremediation will be time-consuming, it can't be suit for vegetable plot that the contradiction of man-land is very prominent. The second way is a kind of convenient and practical steps today, although it couldn't resolve the problem fundamentally.Based on the current situation of vegetable's heavy metal pollution in Chongqing, pot experiments and simulation test were employed to elucidate the possible mechanism and effect that plants absorbed heavy metals involving Hg, Cd, Pb in soil after added limestone, humus, sodium selenite and sodium sulfide to screen out economically effective chemical additives and application levels whichcould prevent Hg, Cd, Pb in soil from transferring into vegetables, providing reliable technical measure to control the pollution of heavy metals in vegetable base. The results showed as follows:Different kinds of chemical additives and application levels had different effects on phyto-availability of heavy metals in soil. In this experiment, limestone could reduce or obviously reduce phyto-availability of three kinds of heavy metals. With increased addition of limestone, the content of Hg, Cd, -Pb in -plants gradually decreased and maximum reduction was 9.2%, 36.0%, 35.7% respectively. Althouth humus could reduce the activity of Hg, Pb in soil, it enhanced the phyto-availability of Cd. The content of Hg in plants reduced by 6 7-jQ% rafter ^j9t.hm~^ of limestone was added. The content of Pb implants reduced by -23.0%.-after 3.0t.hm"2 of limestone was used. The addition of .1.5t.hm"2 caused a 173% increase in plant Cd. Sodium sulfide only reduced the activity of Pb. The effect of sodium selenite treatment on Hg uptake by plants-was different-with its application levels. At medium levels of sodium selenite addition restrained the Hg .uptake by plants was enhanced.Different kinds of chemical additives and application levels had obvious effect upon the distribution of heavy metals in plants. Limestone could affect the distribution of Cd in plants with the different addition levels. -When the additive level of limestone was 7.5t.hm"2, the distributionvof Cd coefficient in the part of stem reduced; when the addition levels was 22.5t.hm"2 the coefficient in the part of leaf decreased. Humus could restrain Hg accumulation in the part of leaf effectively and reduce the coefficient of distribution of Pb in stem and leaf obviously. The coefficient of distribution of Hg in the part of stem reduced obviously when sadium selenite was added and so did the content of root Pb, but the proportion of Pb in the part of stem and leaf increased.No matter what kind of heavy, metal-contaminated -soil, the biomass of asparagus lettuce reduced after limestone was .added. The biomass reducedsubstantially among the soils polluted with Cd, Pb with decreases by 47.0% and 63.9% respectively. Humus facilitated the growth of lettuce in soils contaminated with Hg, but restrained the growth asparagus lettuce in soils polluted with Cd, Pb. Sodium sulfide could restrain the growth asparagus lettuce in soils polluted with Cd, Pb, sodium selenite enhanced lettuce growth in soils polluted with Hg.Different kinds of chemical additives could change the characteristics of adso...
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