| Development of urbanization and industrialization has resulted in a severe heavy metal pollution in the agricultural soils and crops in Pearl River Basin.There are various studies regarding the distribution and speciation of heavy metals in soil from Pearl River Basin. Soil is heterogeneous and complex system composed of different size particles, and the different size-fractions will have different influences on distribution and speciation of heavy metal. Therefore, the objectives of the study are determine the influence factors of heavy metals distribution in different size-fractions, which contribute to reveal the environmental behavior of heavy metal in different scale soil.This study took Pearl River basin soils as experimental objects. It was usually difficult to fractionate and collect fine size fractions, we summarized predecessors’ fraction methods and optimized the ultrasonic-wet sieve-continuous centrifugal methods. We divided soils into 50-250 μm, 5-50 μm, 1-5 μm and 0.1-1 μm four fractions. The physical and chemical properties of different size-fractions were characterized, and the speciations of heavy metal Cd/Pb in different size-fractions were determined. The results are shown as below:1. Via the combination method of ultrasonic-wet sieve-continuous centrifugal,we could get different size-fractions. The particle size was analyzed and confirmed that the method was accurate and effective. Especially for the fine size fractions, the continuous centrifugation method showed better accuracy.2. In soil composition, as the size decreased, all kinds of primary mineral content decreased in the soil fraction, secondary clay mineral(1:1 kaolinite or 2:1montmorillonite) content increased. The specific surface area and the pore volume/area increased obviously while the size decreased. The pore volume of macropore increased most, while the area of mesopore increased most. The Zeta potential of soil fractions(absolute value) decreased slightly while the size decreased,and achieved the minimum in 1-5 μm fraction, however, when in 0.1-1 μm fraction, it slightly increased. With the size decreased, the p H value increased slightly, thecontents of organic matter, free iron/manganese, amorphous iron/manganese increased significantly, however, there were specific samples didn’t follow this rule.3. With the size decreased, the contents of heavy metal Cd, Pb in soil fractions increased generally. Heavy metal Cd in all soil fractions were mainly in environmental activity forms, with the size decreased, exchangeable fraction of Cd increased, but the Fe-Mn Oxides-bound and residual fraction decreased usually.Heavy metal Pb in all soil fractions were mainly in residual forms, with the size decreased, the organic matter-bounded fraction increased, a few samples’ residual fraction decreased.4. The multivariate statistical regression analysis was applied to approach the influence factors of heavy metal distribution in different sizes fraction. In 50-250 μm fraction, the main influence factors of Cd/Pb distribution was the Zeta potential of soil fractions. In 5-50 μm fraction, the main influence factors of Cd distribution were the amorphous manganese and p H value, the main influence factors of Pb distribution was the organic matter. In 1-5 μm fraction, the main influence factor of Cd distribution were also amorphous manganese and p H value, the main influence factors of Pb distribution were organic matter and free iron. In 0.1-1 μm fraction, the main influence factors of Cd distribution were organic matter and free iron/manganese, the main influence factors of Pb distribution was organic matter. Therefore, with the size decreased, the influence factors of heavy metals distribution converted the chemical properties(zeta potential and p H value) to some soil component(oxides and organic matter). |
PDF Full Text Request