Study On The Effect Of Tea Saponin On Desorption And Plant Uptake Of Cadmium From Soil

Heavy metal in soil is one of the most important pollutants. Heavy metal contamination of soil may pose risks human health through the food chain. Among them, cadmium (Cd) is one of the greatest threat to human health in all toxic trace elements. As a result, the remediation technology of Cd contaminated soil has become a research focus in the field of environmental engineering. At present, heavy-metal contaminated soil could be remediated through chemical, physical and biological processes. Surfactant could complex metal ions in the soil liquid phase and change the existing forms of heavy metals, so it can make the insoluble heavy metals into soluble and desorbed from the surface of soil particles. The presence of surfactant could greatly activate the heavy metals in the soil so it created favorable conditions for both soil washing and plant uptake. We selected tea saponin (TS) as restoration material based on the recent research of the application of surfactant to the remediation of heavy metal-polluted soil. It was expected to provide theoretical basis for choosing appropriate leaching restoration material and chemical enhanced phytoextraction material for heavy metal contaminated soil and also provide theoretical foundation for restoration application. The main original research results were shown as follows:1. Two different types of soils were washed with TS in batch experiments. TS was effective for removal of heavy metals from soils, attaining 74.5% and 64.6% of Cd desorption, respectively. The addition of background electrolyte (NaNO3) resulted in a significant increase in the desorption of Cd by TS. Kinetic studies revealed that Cd adsorption was fast, and 84.3% removal for soil A (Lightly mottled silty paddy soil) and 68.1% for soil B (loamy yellow soil) occurred within the first 10 min of contact time. The kinetic data was fitted to pseudo-second-order kinetic model very well. R2 values were 0.99877 and 0.99975 respectively. The presence of pesticide fenitrothion in the system had a relatively small impact on the desorption of Cd by TS. TS displayed good desorption capacities for Cd.2. We also investigated the potential of tea saponin to enhance uptake of Cd by corn(Zea Mays L.). Cd concentration in roots increased with increasing corn growth, while for shoots, concentration of tested Cd increased rapidly at the beginning and reached the maximum in a short period and then gradually decreased against the uptake time. Over a 5 day growth period, Cd concentration in roots was 116.9 mg/kg while was 104.19 mg/kg in shoots which were both about 1.6 times as that without TS. In addition, the accumulated Cd in corn was greatly influenced by TS concentrations both in shoots and roots.With increasing concentrations of TS, the Cd contents in corn roots and shoots also increased, and the maximum Cd concentration in roots was 183 mg/kg while was 71 mg/kg in shoots which were about 155% and 264% as that without TS. The high Cd accumulation in the roots and shoots indicated that TS had the potential in enhancing the uptake of Cd into corn within a certain range of concentrations. The translocation factor (TF) indicated the ability of plants to translocate heavy metals from the roots to the shoots. TS could increase the TF of Cd in corn. When the concentration of TS increased from 25 mg/kg to 200 mg/kg, TF values also increased, and at 200 mg/kg, it was about 1.74 times to that of control. The differential centrifughtion technique was used to study the subcellular distribution of Cd in the roots, shoots of corn with the presence of TS. Cd was mainly bound to soluble fraction, and then in the cell walls but little was found in the cell organelle fraction in corn cells. Meanwhile, with the presence of TS, Cd in the shoots cells had a trend which were transferred from the soluble fraction to the cell walls.In a word, tea saponin, a representative tea seed-derived biosurfactant, has been effective in the removal of Cd in soil washing experiments and in the phytoremediation to promote the uptake of Cd from soil by corn.