Study on Organic Stabilizers of Heavy Metals in Farmland Soil
|School||Huazhong University of Science and Technology|
|Keywords||Organic stabilizer Stabilization Farmland Soil Heavy metal|
Heavy metal pollution has been a great threat to human health, environment and food security. It has been a serious problem all around the world, especially in China. A great attention has been paid to this problem by the government and the public, and Contaminated Soil Treatment Restoration has been determined to be an important aspect of soil environmental protection. Research and application of organic stabilizers increases rapidly in recent years. However, there is still much controversy about the effect of organic matters on heavy-metal speciations and bioavailability in soil, while different organic compounds can have different effects and different mechanisms.The purpose of the thesis is to disover the efficiency and mechanism of organic stabilizers in farmland soil contaminated by heavy metals, and the effects of organic stabilizers on content and distribution of heavy metals in crops. A bench scale study was carried out firstly. Chicken manure, lignin sulfonate sodium, tartaric acid and humic acid were added into contaminated farmland soil and campus soil, respectively. Water content, pH and clarification of soil, as well as specy, amount and treatment time of organic stabilizers, were adjusted to observe their effects on contents and speciations of Cd, Pb, Cu and Zn in soil. Then a pilot scale study was carried out in a farmland near Daye Nonferrous Metals. Chicken manure and lignin sulfonate sodium were added into the farmland growing wheat and peanuts. Heavy-metal contents in crops, as well as heavy-metal contents, speciations and trends in soil, were analyzed to explore the effect and mechanism of these organic matters.The main conclusions are as follows:(1) Water content shows a negligible influence on heavy-metal contents and speciations in soil, while pH plays an important role. After chicken manure or lignin sulfonate sodium was added, the lowest bioavailable contents of heavy metals were detected in soil samples where pH was not adjusted, and available heavy-metal contents would increase when pH increased or decreased. But after humic acid or tartaric acid was added, the minimon bioavailable contents of heavy metals appeared in (or near) neutral soil samples generally.(2) For heavy-metal contaminated farmland soil, under appropriate conditions and in a certain period, chicken manure (neutral complex organic materials) and lignin sulfonate sodium (alkaline polymer) can stabilize Cd to certain extent, while activate Pb,Cu and Zn. Humic acid (high molecular weight organic acid) exhibits certain stabilizing effect on Cd and Cu, and slight activation effect on Pb and Zn. Tartaric acid (Low molecular weight organic acid) can activate all above heavy metals in farmland soil. Changes of soil properties, heavy-metal contents and treatment time may significantly influence the stabilization effects.(3) In crops (wheat and peanut), specy and organization of crops, as well as heavy-metal specy, can effect the stabilization of heavy metals by chicken manure and lignin sulfonate sodium. Heavy-metal contents and speciations didn’t show obvious changes in soil where the crops grew. Some results are not consistent with the conclusions of the bench scale study. Possible reasons include different physical and chemical properties of soils, the uneven distribution of heavy metals in soil, the selective heavy-metal enrichment of plants, effects of plant root exudates on speciation of heavy metals and interactions between added organic stabilizers and crops. Some other factors, such as irrigation, fertilization, rainfall, airborne particulates , may also influence the contents and speciations of heavy metals in soil.