Contaminative Mechanisms Of Heavy Metals And Soil-Health Dynamics In Phaeozem Of Northeast China

High organic matter contents and large continuous farmland distribution make Phaeozem as an important base for food production in China. The soil health of Phaeozem is being deteriorated with increasing exploitation and utilization, of which heavy metal contamination was one of the reasons for the quality declining of soil health. This work was focused on investigating contaminative mechanisms of heavy metals in Phaeozem in northeast China in order to identify the pollution sources, types, trends and distribution, and making clear about the speciation, mobilization and bioavailability of heavy metals in contaminated Phaeozem. The results showed that cadmium pollution was at the most serious extent in Phaeozem. The contents of cadmium, lead and zinc were increasing in this area, which resulted in the soil contamination mainly distributed in urban area and boundary of the city for their high bioavailability. Industrial emission and wastewater irrigation were the main sources of the contamination in these areas, while the utilization of phosphoric fertilizers for long time was the main reason for cadmium increasing in farmland.According to the previous investigation, cadmium was selected as main element for the further study of contaminative mechanisms. The main behaviors including sorption-desorption and transferring of speciation and bioavailability with or without the interaction of organic chemicals in soils were stated. The results indicated that the Cd2+ was quickly absorbed after having introduced into soil. And these make the possibility of transforming from exchangeable cadmium into bounded forms. Some parts of the sorbed cadmium on soil can be desorbed into equilibrium, which make the speciation transformation into a reversible process. The sorption and transformation forces of Cd2+ in Phaeozem were higher than that in burozem for the physicochemical soil properties. The interaction of acetochlor could enhance cadmium sorption and transformation, while the dichlorvos addition could increase cadmium release in soils. The interaction between cadmium and acetochlor was an antagonism, which could lower the biological toxicity.Chemical immobilization was selected as a remediation method to adjust soil health of Phaeozem contaminated with heavy metals. A synthetic amendment riched in the ligands of H2PO4-,HCO3- and CO32- was confirmed as a potential additive for chemical fixation after the experiments of toxic characteristic leaching process (TCLP), speciation, biological toxicity and microstructure. Although the bioavailability is the key factor for the remediation strategy, the in situ fixation with exterior amendments in low content of metal may offer a promising option, especially for the non-point and light pollution derived from agricultural sources.