Persistent toxic substances (PTS) in environment can harm human health through food chain. Most reactions of PTS occur in the environmental interfaces and very complicate due to the characteristics of the pollutants and environmental interfaces and their interaction as well. These reactions will determine the transportation, bioavailability and toxicity of PTS in environment. In recent years, we have carried out investigations on the transportation of PTS in several environmental interfaces. Mechanism and bioavailability assessment method are explored.

Our research showed that all the three surface complexation models, the constant capacitance model, diffuse layer model and triple layer model, could describe the adsorption of metals on sediments. The experimental sorption data were fit well by the models with the errors less than 15% and the adsorption was correlated with pH value. This work, to some extent, elucidated the hypothesis and disputes upon the adsorption of metals on the natural sediments.

We have investigated the reaction mechanism of heavy metals with humic acid based on the established surface complexation model in which the multifunctional groups of humic acid reacted with free metal ions as single reaction site. Based on the dynamics of Pb in the water/sediment interface, we confirmed that most of Pb could not be settled by sediment. By using model soil synthesized with several natural minerals and humic acid, we confirmed that non-selectivity of extractants and readsorption and redistribution of trace metals during the sequential extraction among different geochemical phases. Differences of the heavy metals and the minerals and their interactions determined the process of readsorption and redistribution.

We have established a rhizosphere-based method for the evaluation of bioavailability of metals in soil to plants, which simulates the real-field conditions of plant growth, integrates the soil-root interactions and reflects the effects of soil-plant interactions to the uptake of metals by plants. The key is to emphasize that the important of rhizosphere microenvironments and use low organic molecular weight acids as extractant.

Transportation and uptake of heavy metals in the plant root interface have been investigated. It showed that low organic molecular weight acids increased the net La influx in wheat, barley, corn and perennial fern roots. X-ray absorption spectroscopic techniques provided evidence of La-oxygen environment and established that La was coordinated to 11 oxygen atoms involved in the binding of La to barley roots via carboxylate groups and hydration of La. Relation between the distribution of Se in plant components and the bioavailability of Se was investigated, which indicated that the chemical forms of Se in the Chinese low-Se belt was less bioavailable due to the geochemical environment in this region. This study revealed that the chemical form of Se was hard uptake by plants and the synthesis of GSH-Px was obstructed in human body and therefore Se deficient diseases were caused.