Distribution Of Heavy Metals In Reclamation Soils And Their Accumulation In Crops

The study on soil heavy metals pollution and its rehabilitation in mining area is the present focus on mine ecology or the territorial and industrial fields in China. It is provided with great importance to sustainable land use, food security, mining area environment, regional entironment protection and so on. After the systemic, quantized field or laboratorial research of the filling reclamation soil in mining area, theoretical method, mathematical model, experiment techniques, relevant data, software measure and some other achievements were made. They offered the data support and scientific guidance for the state to supervise the land reclamation and ecological construction in mining area, also offered the reference for making related environment policy of mining area.Systematically summarized the development of research at home and abroad on reclamation soil in mining area, this paper focuses on the following five research works:1. Research on filling reclamation soil characteristicsReclamation site observation combined with indoor experiment, the physical, chemical and biological characteristics of filling reclamation soil had been systematically studied, concretely including the permeability, compaction, pore-water conductivity, water content, temperature, pH value, organic matter, nitrogen-phosphorus-kalium, heavy metals, microorganism (bacteria, fungi and actinomyces) species or kinds; Soil compaction had been tested and analyzed using the 2800K1 Guelph---permeability testing machine made in America, W.E.T Sensor Kit---the British three-parameter rapid measure instrument HH2/WET, the American compactness meter. The data conclusions includes: the pH of both the coal-fly-ash and coal-gangue filling reclamation soil (cover soil thickness is 40cm) is between 7.98 and 8.78; the soil water content is 10%-20% higher than natural soil; the permeability coefficient varies from 0.059 to 0.286; the soil compaction is between 200 PSI to 300PSI; organic matter content is lower than natural soil. To sum up, the index values of filling reclamation soil's physical and chemical properties are within the normal area of natural soil, and have no obvious difference. These outcomes have significant reference value to the state for making land reclamation technical standards and to designing and implementing of the reclamation project.2. Research on the distribution of reclamation soil heavy metals The problems about filling reclamation soil heavy metal pollution in mining area were brought forward. Firstly, the research went on the theoretics and methods used for analyzing heavy metal's spatial distribution characteristics in filling reclamation area. Two hundreds and forty five soil samples were collected and processed, and then the heavy metal concentrations of the soil samples, such as As, Cd, Cr, Cu, Hg, Pb, Zn and others were determined. For three kinds of the soil heavy metals, coal-gangue filling reclamation soil, coal-fly-ash filling reclamation soil and natural soil for comparison, the author analyzed and studied theirs distribution by varying multiple, contamination degree and concentrations trend. Based on these, the distributions of seven elements were summarized, and Cd arisen severe pollution, together with Cr arisen slight pollution and Pb in normal were emphatically analyzed. Expounding the spatial distribution of Cd, Cr and Pb by linearity, logarithm, index, power, polynomial, Kriging and other mathematical models, conclusions were made as follows:â‘ Simple model: to a certain degree, the fitted model can figure out the change tendency of microelements, all the grand means of model fitted error of the three sites kept within 30%, thereinto, the site error of coal gangue was the least, and the maximum is 18.4% while the minimum is 8.3%.â‘¡Polynomial model: Making the analog transition diagram by the data inverted has practical meaning. The numerical value of unmensurated points can be deduced from mensurated points using models, and then gained the correspondingly seriate heavy metal contents, the spatial distributions can be analyzed.â‘¢Kriging model: The built models have high fitting precision, taking Cd of coal-fly-ash site as an example. The research results above will provide foundations for rehabilitating the polluted land in mining area and then setting corresponding govern measures.3. Methods and theoretics about the relativity between soil characteristic and heavy metal pollutionThe four important specialties like to effect on soil heavy metals distribution were ascertained first: soil compaction, the pH of soil, soil organic matter as well as soil microorganisms; employing in the Pearson Correlation Coefficient method, how pH affects the distribution of heavy metal, the correlation degree between organic matter and the distribution of heavy metal, the connections between compaction and heavy metal pollution, along with the relevancy between microorganism and heavy metal pollution were analyzed; The data results show that:â‘ The soil pH, soil organic matter and soil compaction of the filling reclamation site all only have slight relativities with heavy metals, and relativity coefficient are amongst -0.6 and 0.6. To a certain extent, this also account for that the spatial distribution of heavy metals has no regularity.â‘¡Soil microorganisms have quite high relativity with soil heavy metals, and this presents much more obvious for a coal-fly-ash site. The quantity of microorganisms has a direct effect on the heavy metal content of soil. Finally, the relationship mechanism between microorganisms and heavy metals was studies by the application of Set Pair Analysis Theory. This has concernful scientific significance for in-depth understanding the complexity of soil heavy metals'migration mechanism, and also can afford definite data support for the further study on the factors related to pollution which difficult to quantify or distinguish.4. Research on heavy metal pollution migration of main cropsInvestigated and compared the Limit Standard of the heavy metal contaminations in wheat, rice and soybeans in primary countries and regions in the world, the selection standards of the heavy metal contaminations quota in wheat and other main crops were advanced. The rhizospheric soil's pollution situations of As, Cd, Cr, Cu, Hg, Pb and Zn were analyzed by single contamination index method, also comprehensive contamination index method. It is concluded that comprehensive contamination index of reclamation soil was less than 1, and all the observation points reached to the secondary standard requirements of soil environment quality. The heavy metals content of wheat's different parts were quantitatively parsed, and confirmed Cd and Cr as contaminations. The followings are the research results:â‘ The distributions and migration tendencies of each different parts of the mature wheat growing on reclamation sites is in consistent.â‘¡There are differences in the distributions and migration tendencies of each different parts of the mature wheat growing on control sites. Root enrichment coefficient ratio was put forward, and curve estimation was done, and Cd regression equation and Cr partial differential equation were established. These research outcomes are provided with important practical value for monitoring the food security in mining area.5. Introduction of the description technique with the software of Surfer and PhotoshopExploringly introducing the software Surfer to produce map, using refutations data from polynomial model, we visualize the reclaimed soil structure of mining area, and intuitively described the vertical and horizontal distribution features of heavy metals in the soil; using the software Photoshop, taking Cd and Cr for example, we produced a quantitative simulation of color mapping maps to describe the migration of heavy metals pollution in the main crops wheat, and obtained a reliable evaluation of the heavy metals pollution levels in different organs of wheat.