Influence Of Indigenous Bacterials On Heavy Metals' Speciation Transformation And Bioavailability In Surfical Sediments

Surficial sediments are the important component of the water body and the source and the fate of heavy metals in water. Heavy metals can be riched strongly in sediments. Heavy metals can transfer from liquid phase to solid phase (just from the water to the sediments) by physical, chemical and biological action. Meanwhile, in some cases, the heavy metals in the sediments can be released to the water body by physical, chemical and biological action and engender secondary pollution. However, total metal content of sediments usually provides unconfident information on the availability and mobility of metals. So the study on chemical speciation in sediments is a hot spot. The mechanisms concerning metal accumulation in sediments lead to the existence of five major geochemical forms.1) exchangeable; 2) bound to carbonat; 3) bound to Fe/Mn oxides; 4) boude to organic; 5) resicual. These metal fractions have remarkable differences in mobility, biological availability and chemical behaviors in sediments.Microorganisms, which are the most active colloids in sediments, significantly affect the mobility and fate of heavy metal. Moreover, it is increasingly apparent that microbial processes may be important and even dominating factors in the distribution of specific metals. Microbial transformation of heavy metals may affect their solubility, mobility and bioavailability. Under different environmental condition, the mechanism of interaction between microbial and heavy metals is distinct. Several of the key microbial processes that may affect speciation and bioavailability of heavy metals include: 1) chelation of elements by metabolites; 2) oxidation-reduction of metals; 3) biosorption and bioaccumulation; 4) immobilization due to formation of stable materials; 5) biodegradation of organic complex of metals. The microorganisms as the disintegrator play the vital role in the aquatic system, in the water environment the microorganism participat each chemical element transformation and the movement. The bacterial as the important active components play the key action on the heavy metal migration and transformation. The research on the effect of the microorganisms'activity to the heavy metal speciation and bioavailability transformation in sediments can provide the theory basis for the microorganisms'purification function and the immobilization of the heavy metals, and there is theory guidance significance to the microorganism ecology repairment of the heavy metals.This research embarking from the environmental chemistry view, under the laboratory simulation condition, studied the influence of indigenous bacterials on the heavy metals speciation transformation and bioavailability in the Songhua River sediments. After the bacterials were isolated and riched from the sediments, the bacterials were transferred into the sediments.This research simulated the process of the transformation and migration of the heavy metals in sediments and compared to the sediments without riched bacterials. And using the Tessier's sequential extraction and single extraction analysis the heavy metals speciation and bioavailability in the sediments, and determined the distribution characteristic of the heavy metal in sediments. The enzyme activities were detemined by visible spectrophotometric method, simultaneously, analyzed the correlation between the enzyme activity change and the heavy metal speciation transformation and bioavailability transforms, and determined influence of enzyme activity change on heavy metals speciation and bioavailability. By the laboratory simulation, the procession of heavy metals speciation transformation was compared between the sediments with and without the indigenous bacterials, and determined the chemical speciation that cause the adsorption and desorption, the influence of indigenous bacterials on heavy metals speciation transformation and bioavailability and the contribution of the indigenous bacterials on the transformation and migration of heavy metals.The results indicated that:(1) The Fe/Mn oxides played an important role in Zn, Pb adsorption, but the organic matter occupied the dominant position in Cu adsorption process in the sediments.(2) In the sediments different heavy metals transformation tendency also had different. Cu, Pb speciation mainly transformed to the bound to organic, and Zn transformed to the bound to organic and the residual.(3) The heavy metals bioavailability change correlated with the speciation transformation in sediments, and the release of the heavy metals also correlated with the speciation transformation.(4) In sediments enzyme activities change can affect the process of the heavy metals speciation and bioavailability transformation.(5) In the entire experimental process, the bacterials posed both immobilisation and mobilisation on the mobility and speciation transformation. On the one hand the bacterias may enhance the mobility of heavy metals and make it transform to less stable speciation. On the other hand the bacterials could adsorb, immobilize and complex heavy metals via surface interaction and secretion of chelationg agents, which results in heavy metals transforming to more stable forms. It is correlated with this environmental condition which bacterial located, as well as bacterials action mechanism.(6) The indigenous bacterials could enhance or depress the bioavailability of heavy metals in the entire experimental process. Such as, the indigenous bacterials could increase the HOAc, DTPA extraction capacity of Fe, Mn in sediments and enhance the bioavailability of Fe, Mn. As far as other heavy metals the indigenous bacterial posed both positive and negative impacts on the bioavailability of heavy metals in sediments, depending on the chemical nature of heavy metal and the environmental condition of the sediments.