| The quality and safety of vegetable is directly related to human health, and the problem of heavy metal pollution has become a focus to people. Because of heavy metals’migration and transformation in the soil-crop-human body system affected comprehensivly by heavy metal species, physical and chemical properties of soil, and other environmental factors, the total amount of heavy metals in the environment can’t truly reflect heavy metals in crops, and even can’t represent the content eventually absorbed by the body. Currently, our country’research on heavy metals’migration and transformation between vegetables and human body (namely the bioaccessibility of heavy metal) reported less, while the world use more in vitro simulation method to research on this. To scientific evaluation the heavy metals’migration and transformation process and potential risk to human health in soil-vegetable-human pathway, firstly, this study carried on the ananlysis of heavy metals in 4 class 8 kinds vegetables in last spring from the main vegetable wholesale market of different administrative regions in Guangzhou City, so as to understand the pollution characteristics and carry on the health risk assessment; secondly, taking the soil-vegetables-human body as the baseline, and through the pot experiment to study the influence factors of the migration and transformation of Cd in soil-Lactuca sativa L and soil-Ipomoea aquatica Forsk system; finally, using the in vitro gastrointestinal simulation to study the health risks of the bioavailability of Cd in the aboveground part of potted vegetables. The main results of this study are as follows:(1) The Cu and Zn content in the 8 kinds of vegetables were far below the limits of food hygiene standard limit; the exceeded rate of Cr is relatively high, up to 91.67%; the Pb exceeding vegetables including lettuce, towel gourd, tomatoes and carrots, which is as high as 35.71% and carrot is the most serious of exceeding; tomato is the only Cd exceeded vegetables, the exceeded rate is up to 31.25%; Ni exceeding vegetables including leaf lettuce, water spinach and flowering cabbage, the highest exceeded rate is 8.33%. The comprehensive integrated pollution degree of heavy metals in vegetables showed leafy>fleshy root class>stem class vegetables>eggplants; the pollution levels of 8 kinds of vegetables are as follow:water spinach, leaf lettuce, cabbage, radish and carrot are in alert level, while lettuce, towel gourd and tomato are belong to the security level, this proves that vegetable samples were tested are in security and still clean pollution levels.(2) The health risk assessment shows that the daily consumption of more Ipomoea aquatica Forsk, Brassica campestris L and Lactuca sativa L crowd among Guangzhou residents, the heavy metal cumulative health risks is much higher, and Cr by dietary intake may cause harm on human health, and Cd has a potential health risks to the human body. Oral intake of heavy metals in vegetables may cause exposure risk to children and higher than the adults.(3) Group with applied 0.6% biological humic fertilizer and 0.3% sodium silicate is the best way to passivate Cd in two soils among all the treatments, and the decline of Cd in Lactuca sativa L soil and Ipomoea aquatica Forsk soil were as high as 7.44%, 56.86% respectively; single application of biological humic fertilizer or sodium silicate had a certain passivation effect on Cd in soil, but the effect was not obvious,and differ from the crop species.(4) After adding different treatments of sodium silicate and biological humic fertilizer, the fractions of Cd in soil have changed, and the pH, organic matter, CEC, AP, NH4+N, AK and silicon in soil are all the factors that affect the Cd fractions. Single application of biological humic fertilizer can reduce the content of weak acid extractable state and reducible state of Cd, a decline of 14.49%,8.80% respectively, and increase the content of oxidizable state and residual state of Cd, an increase of 26.50%,27.90% respectively. Single application of sodium silicate, it can reduce the content of weak acid extractable state of Cd in Lactuca sativa L Soil, a drop of 8.41%; and the content of reducible state of Cd in two soils decreased with the increase of applied amount of sodium silicate, a drop of 26.85%, while the content of residual state of Cd was increased significantly, the increase was as high as 141.62%. Equipping applied biological humic fertilizer and sodium silicate, can reduce the activity of Cd in soil, and the effect is better than that of single application.(5) The treatment of single application of biological humic fertilizer can promote the growth of vegetables, and significantly increased the plant height and aerial part dry biomass of Lactuca sativa L and Ipomoea aquatica Forsk:compared with the control group (CK), the plant height of the 2 kinds of vegetables increased significantly with the increase of the amount of the biological humic fertilizer, and the increase was up to 6.34%; the growth rate of dry biomass was up to 39.08%. The treatment of single application of sodium silicate has a certain inhibitory effect on the growth of two kinds of vegetables:the plant height and aboveground dry biomass of Lactuca sativa L and Ipomoea aquatica Forsk were lower than the control group (CK), and the decline of height was up to 15.66%, and the aboveground dry biomass of Lactuca sativa L incressed slightly with the increase of applied amount of sodium silicate, while the aboveground dry biomass of Ipomoea aquatica Forsk decreased significantly with the increase of applied amount of sodium silicate, and the biggest decline was 68.32%. The treatment of applying 0.6% biological humic fertilizer and 0.3% sodium silicate had the best effect on the increase of the height of two kinds of vegetables, which was better than the treatment of applying 0.6% biological humic fertilizer; and the effect of aboveground dry biomass of two kinds of vegetable was better than the other two groups with treatment, but no match for the treatment of applying 0.6% biological humic fertilizer.(6) The aboveground content of Cd in Lactuca sativa L and Ipomoea aquatica Forsk were less than the underground content of Cd, expressed as root>stem and leaf, indicating that the accumulation ability of Cd in this two kinds of vegetables are not strong. All treatments could play a role on restraining the absorption effect of Cd by Lactuca sativa L and Ipomoea aquatica Forsk, and the treatment of applying 0.6% biological humic fertilizer and 0.3% sodium silicate could significantly reduce the underground content of Cd in Lactuca sativa L to a minimum, a decline of 44.04%; while the treatment of applying 0.6% biological humic fertilizer and 0.6% sodium silicate could significantly reduce the aboveground content of Cd in Ipomoea aquatica Forsk to a minimum, a decline of 68.32%. The correlation analysis showed that the main factors affecting the content of Cd in Lactuca sativa L and Ipomoea aquatica Forsk were the content of reducible state-Cd and oxidizable state-Cd in soil.(7) Under different treatments, the bioaccessibility of Cd in stomach stage of two kinds of vegetables were higher than the bioavailability of Cd in the small intestine stage, showed that t the bioaccessibility of Cd in stomach stage of Lactuca sativa L was between 4.44%-6.52%, and the bioaccessibility of Cd in stomach stage of Lactuca sativa L was between 0.69%-2.92%; and the bioaccessibility of Cd in stomach stage of Ipomoea aquatica Forsk is between 4.44%-6.52%, the bioaccessibility of Cd in stomach stage of of Ipomoea aquatica Forsk is between 0.69%-2.92%. Correlation analysis showed that weak acid extractable-Cd and reducible-Cd were the main contributor to the bioavailability of Cd in vegetables. The potential health risk assessment of Cd in two kinds of vegetables showed that after the treatment of applying 0.6% biological humic fertilizer and 0.3% sodium silicate, the risk of cancer and non-cancer risk of Ipomoea aquatica Forsk was the minimum than other treatments; and the carcinogenic risk and non carcinogenic risk in small intestinal phase were lower than the results of the gastric phase; and the HQ values of intestinal stage were far less than 1, the CR values were out of acceptable range, indicating that uptaking of Lactuca sativa L andIpomoea aquatica Forsk would not bring no-carcinogenic harm to humans, but might bring the potential cancer risk to adults and children, and the harm for adults was higher than children。In summary, the group of applying 0.6% biological humic fertilizer and 0.3% sodium silicate has an good effect in improving soil physical and chemical properties, promoting the growth of vegetables, inhibitting the absorption of Cd by vegetables and reducing the health risk of the Cd in vegetables absorbed by the body, and can be regarded as the best combination of repair methods in experimental study. |
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