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A simulated experiment exposing Corbicula fluminea in the Cd contaminated sediment of Lake Taihu was conducted in laboratory to study the bioaccumulation of Cd in Corbicula fluminea and the distribution regularity of Cd in water.The speciation of Cd extracted by DGT and BCR and the releasing regularities were determined in sediments of Lake Taihu to obtain the applicability of predicting sediment quality guidelines.When the contaminated concentration increased,the concentration of Cd extracted by DGT and BCR in overlying water and accumulated in Corbicula fluminea increased.The results showed that the content of Cd in Corbicula fluminea was significantly correlated with the results measured by two methods after 14 days and 28 days exposure.It offered theoretical statistics for the prediction of sediment quality guidelines of Cd.

Fulvic acid (FA) was extracted and purified from natural soil and the effects of such FA on the bioaccumulation of rare earth elements (REEs, La3+, Gd3+ and Y3+) in wheat seedling were investigated. The results indicated that low concentration of FA (0.4 mg C/l to root,0.7 mg C/l to tops (stem and leaves)) could increase the bioaccumulation values of REEs in wheat, but when the concentration of FA was high (0.4 mg C/l to root,1.5 mg C/l to tops) the bioaccumulation values were decreased. Kinetic experimental results suggested that bioaccumulation values of REEs in roots for 30 days were correlated with the kinetic linear growth equation, and correlation coefficients were higher than 0.861. The kinetic bioaccumulation pattern of REEs in tops was different from that in root. The bioaccumulation values of REEs in wheat root were much higher than in wheat tops. Variations of glutamic oxaloacetic transaminase (GOT) enzyme activities in wheat root and tops were determined. A good correlation existed between the bioaccumulation values of REEs and GOT enzyme activities, and the correlation coefficients were higher than 0.922. GOT is an important parameter influencing the bioavailability of REEs.

Humic acid (HA) was extracted from an organic-rich soil in Heilongjian Province of China by 0.5 mol L-1 NaOH. The effects of HA on the distribution of rare earth elements (REEs) in Red Soil, a majo...

Adsorption of metals onto soil clay fractions is one of the most important chemical processes for heavy metal cations occurring in soil or sediment environment. Traditional Langmuir or Freundlich isotherm approaches do not indicate the adsorption mechanism. Surface Complexation Models (SCM's) describe the adsorption process by treating the sorbent surface as composed of various functional groups and have been successfully applied to oxide minerals. However, results from the application of SCM's for constant charged phyllosilicate clay minerals have not obtained universal consensus due to their complicated structures and surface charge features. The major objective of this thesis is to establish a simple surface complexation adsorption model for heavy metal cations onto natural clay minerals. Three representative clay minerals (kaolinite, illite and montmorillonite) and five soil clay minerals from Canada and China were investigated. The adsorption of five heavy metal cations, Cd(II), Cu(II), Ni(II), Pb(II) and Zn(II), onto the clay minerals were studied by batch adsorption experiments as a function of pH and ionic strength. Results suggested there were two dominant processes involved in the adsorption of the metals: (1) at lower pH values, the adsorption occurred on permanently charged surface sites through outer-sphere ion-exchange reactions; (2) at higher pH values, the adsorption occurred on variable charged mineral edges through specific inner-sphere surface complexation reactions. Changes in ionic strength showed a dramatic effect on the first process but had little effect on the second process. The Constant Capacitance Model was used to describe the electrostatic properties on the variable charged edge sites. A surface adsorption model combining both ion-exchange reactions with surface complexation reactions at the variable charged edge sites could successfully predict the adsorption behaviour of the five metals in various ionic strengths for both pure clay minerals and extracted soil clay minerals. The model scheme could be applied to all the studied clay minerals; however the model parameters, such as the adsorption constants and site densities, were different for case to case because of the wide range of structures and surface charge properties of natural clay minerals from various sources.