The Form Distribution And Bioavailability Of Heavy Metals In Greenhouse Soil

Heavy metals in the soil accumulate to a certain amount will lead to soil heavy metal pollution, heavy metals in vegetables to a certain extent would seriously affect their quantity and quality, and affect human health through the food chain. This paper assesses the bioavailability posed by heavy metal content in both soil and tomato in Yangling. The results could be used to guide vegetable safety evaluation.Soil samples of 0~20 cm layer and tomato leaf and fruit were collected from greenhouse in Yangling, carrying on laboratory analysis to study the soil Cd, Cu and Zn form distribution, Cd, Cu and Zn distribution in tomato leaf and fruit, the effect of Cd, Cu and Zn on the rhizospheric microorganism number, preliminary research Cd, Cu and Zn bioavailability. The results were as follows:1. Accumulate coefficient of Cd, Cu and Zn is 2.50, 0.498 and 1.08 respectively, Cd accumulated significant, Zn accumulated small, Cu in soil below background level. There were no obvious interaction between Cd, Cu and Zn.2. To HJ/T 333-2006 for an comprehensive contamination index standard , Cd contamination index raged from 0.7 to 1, were alert levelâ…¡, Soil is still clean. Cu, Zn contamination index below 0.7, were security levelâ… , soil is clean. The study area had not received soil Heavy metals pollution, but Cd had the potential pollution tendency. Need to avoid external Cd into the soil, leading to increased soil pollution. In turn affect food security, cause even greater harm.3. The form alalysis of heavy metals in the greenhouse soil showed that Cd mainly exist in Fe-Mn oxide-bound factions and organically bound form, and Cu mainly exist in residual faction and organic form, with 88.9% in all, Zn mainly exist in Fe-Mn oxide and residual faction, with 75.6% in all. Exchangeable, carbonate, Fe-Mn oxide and residual faction of Cd, Cu and Zn accounted 88.2, 52.4 and 46.1% in the total content separately. Most of heavy metals were in these four forms, which have highly potential risk to the environment, may affect the quality of agricultural products and the agro-ecological environment.4. The content of heavy metals (Cd, Cu and Zn) in the tested tomato fruit were measured all lower to the Chinese Food Hygiene Standard. No sample exceeded the standard, the pass rate of greenhouse tomato fruit content of heavy metals was 100%, meet Chinese Food Hygiene Standards.5. The tomato leaf Cd enrichment capacity is influenced by the available Cd content in soil,and the ability increases along with the available soil Cd content in increase. And the correlations are not obvious between the tomato fruit Cd and each Cd forms in soil. Cu content in soil do not influence the tomato Cu content in leaf and fruit. It has certain relevance between Zn in leaf and fruit of tomato and Zn in soil, and the relevance of different locations not identical. Clearly, the bioavailability was not exactly the same of heavy metals in the soil.6. The proportion of bacteria was more than 90 percent in soil microbial community structure, followed by actinomycetes, at least the number of fungi in the soil. The correlations correlation coefficient between total Cd and the microbes in the soil were negative. And the correlation coefficient between total Zn and microbes were positive. There was no relationship between Cu and the number of soil microorganisms. Heavy metal in soil can affect the soil microbial community structure.