| Phosphate rock is a kind of common slow released fertilizer, used in agricultural production. It is also an economic environmental soil amendment for soil heavy metal pollution. With industrial development, heavy metal pollution has become a world environmental problem. More and more attention had been paid on it. Crops and vegetables growing in heavy metal contaminated soil will enrich heavy metals in varying degrees. The enriched heavy metals may enter human body through the food chain, causing various diseases and great threat to human health. Therefore, the domestic and foreign scientists are looking for scientific and effective methods to reduce the toxicity of heavy metals in polluted soil, improve the quality of crops and vegetables.A pot experiment with lettuce was conducted in greenhouse. Tessiers sequential extraction procedures for heavy metal fractionation was adopted to analysis form changes of Cu and Cd in the soil which was treated with Nanzhang and Baokang phosphate rock. The content of Cd and Cu in different parts of lettuce, the growth and quality indicators of lettuce were determined at the same time. The aim of the research is to evaluate the effect of phosphate rocks and activated phosphate rocks on heavy metal contaminated soil remediation through the study on the content changes of different forms of heavy metals in soil and physical and chemical properties changes of soil. We hope to provide scientific basis for the production of safe vegetables in heavy metal contaminated soil.The main results are outlined as follows:(1) The content of the soil exchangeable Cu and Cd was reduced after applying phosphate rock and activated phosphate rock. Compared with the control (added no phosphate rocks), the content of the exchangeable Cd and Cu in soil was decreased by 12.50%～20.30%,24.6%～47.03% with application of Nangzhang phosphate rock; 20.30%～37.10%,45.38%～49.10% with application of Nangzhang activated phosphate rock; 0.37%～0.95% 18.76%～48.82% with application of Baokang phosphate rock; 10.70%～21.50%,53.61%～56.22% with application of Baokang activated phosphate rock. (2) The content of the soil residual Cu and Cd was increased after applying phosphate rock and activated phosphate rock. Compared with the control (added no phosphate rocks), the content of the residual Cd and Cu in soil was increased by 63%～103%,31.70%～39.85% with application of Nangzhang phosphate rock; 82%-161%, 12.56%～37.47% with application of Nangzhang activated phosphate rock; the content of the residual Cd in soil was increased by 164%～187%,131%-181% with application of Baokang phosphate rock and activated phosphate rock, while the content of residual Cu was not significantly increased.(3) Phosphate rocks and activated phosphate rocks can reduce Cu, Cd content in different parts of the lettuce. Compared with the control, the Cd and Cu content was decreased up to 18.10%,40.05% in shoot,29.10%,31.34% in root with application of Nangzhang phosphate rock; 41.10%,52.97% in shoot,55.10%,42.71% in root with application of Nangzhang activated phosphate rock; 21.10%,29.11% in shoot,39.10%, 49.22% in root with application of Baokang phosphate rock; 59.30%,53.40% in shoot, 44.70%,55.24% in root with application of Baokang activated phosphate rock.(4) Application of phosphate rocks and activated phosphate rock could increase the plant height of lettuce, the SPAD-502 value of leaf, the Vc content in each part of lettuce, and activated phosphate rocks have a more significantly effect. The effect of Phosphate rocks and activated phosphate rocks on nitrate accumulation is largely determined by the available phosphorus content and nitrogen levels of the soil.(5) The phosphate rocks and activated phosphate rocks can change the basic physical and chemical properties of the soil. The soil pH, available phosphorus content, exchangeable Ca+ and Mg2+ content increased with the amount of phosphate rocks and activated phosphate rocks applied increasing.In short, the phosphate rocks and activated phosphate rocks can reduce the exchangeable Cu and Cd content, improve the residual Cu and Cd content, reducing its mobility in soil, and the effect of activated phosphate rocks is more pronounced. Phosphate rocks and activated phosphate rocks in the appropriate application can promote the growth of lettuce and improved its quality, reduced heavy metals Cu, Cd uptake, and affected the physical and chemical properties of the soil. Phosphate rocks activated by oxalic acid have a better effect on immobilization of heavy metals than phosphate rocks. Therefore, phosphate rock activated by oxalic acid is a new type passivation agent for the immobilization of heavy metal in contaminated soil. |
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