Study On Regulation Of Heavy Metal Pollution In Soil - Vegetable System By Combining Curing Agent

Vegetables and corresponding soils samples were collected from the farmland surrounding a mining area in southern Hunan, China. It may be able to produce the potential health risk to local inhabitants consuming the vegetables grown in the contaminated soils with heavy metals and As. The heavy metals contamination farmland was exerted different combined amendments, for example "Lime+Sepiolite (HS)" and "Zeolite+Hydroxylapatite (FQ)". Three types of vegetables (water spinach, caspinc and white turnip) were planted in the improved dry land with HS or FQ. Analysis was carried out to view the effects of combined amendments on the physical and chemical properties of the reference soil, on contents of different forms heavy metals and As in vegetables tested soils, on vegetable yields and on contents of heavy metals in different parts of vegetables. The main results showed as follows:(1) A significant impact had been observed between combined amendments and physical/chemical properties of the reference soil. The pH level and CEC content were increased with rising of combined amendments, and organic matter (OM) was slightly reduced. The Pearson correlation analysis showed that the physical/chemical properties (pH level and CEC) of the corresponding soils planted three vegetables (water spinach, capsium and white turnip) had a significant positive correlation with the amount of combined amendments.(2) The contents of exchangeable/available/TCLP leaching of heavy metals and As in the corresponding three vegetables soils were significantly reduced as the amount of combined amendments adding increased.When HS was added at8g.kg-1, the contents of exchangeable heavy metals Pb, Cd, Cu, Zn, and As decreased maximally by98.2%,96.3%,50.6%,95.9%, and80.4%, respectively; the maximum decreasing levels were87.6%,87.9%,90.8%,89.5%, and57.3%for available heavy metals, respectively. The TCLP leaching contents reduced the max amount87.3%,73.1%,60.5%,31.4%, respectively, for heavy metals; however, there was no law of the impact on the amount of As.For FQ at8g.kg-1, the exchangeable contents of soil heavy metals Pb, Cd, Cu, Zn, and As decreased by98.5%,98.4%,56.3%,34.4%, and the contents of As was not changed. Available contents of heavy metals were reduced by70.0%,63.0%,75.8%, 61.2%, and there was no law of As. The TCLP leaching contents decreased by97.0%,55.2%,96.5%,45.9%, and no law about the impact on the amount of As.Correlation analysis showed that the pH level had a significant or very significant negative linear correlation with the contents of exchangeable, available and TCLP of soil heavy metals for the referenced treatment soils with HS and FQ.(3) The combined amendments (HS and/or FQ) could be able to promote the yields of vegetables in some extent. There was an increased in the maximum biomass for capsicum, which were25.4%and26.0%, respectively, with the treatment of soils.(4) When the addition of two combined amendments was8g.kg-1, the contents of heavy metals in the edible parts of three vegetables were decreased as increasing of addition amendments (HS). Compared with the control group, the contents of Pb in edibles parts of water spinach, capsicum, and white turnip were decreased by22.8%,97.6%, and58.1%; contents of Cd were reduced by51.8%,82.6%, and26.8%, respectively. While the treatment of FQ, the contents of Pb and Cd in edible parts of water spinach were decreased by72.9%and68.1%; the contents of Pb and Cd in edible parts of capsium reduced by91.2%and61.1%; white turnip content of Pb and Cd were decreased by42.7%and32.2%. There was a significant or very significant negative correlation between the contents of Pb, Cd and As in different parts of vegetables with the amount of addition combined amendments.The contents of Pb and Cd in edible parts of water spinach were still exceeded the limit of national food safety standards (GB2762-2012, Pb≤0.3mg.kg-1, Cd≤0.2mg.kg-1), when the amount of combined amendments was8g.kg-1. However, at the same time, the contents of Pb and Cd in caspium and white turnip were reduced to less than the national food safety standard limits. In summary, capsium was more suitable than water spinach or white turnip for planting in contaminated soils. From curing effect and affordable point of view, the choice of combined amendments HS was better than FQ to fix soil heavy metals and As.Correlation analysis showed that there was a significant or very significant positive linear correlation between contents of exchangeable heavy metals and As in soils with heavy metals in different parts of vegetables.