Cadmium Adsorption And Desorption Characteristics In Soils And Impacts Of Cadmium Contamination On Rice

By pot experiment and laboratory mechanism exploration, it discussed cadmium bioavailability in the soil, relationship of cadmium adsorption and desorption characteristics to soil properties, parameter significance of adsorption equations and applying range of adsorption equations.The results of rice pot experiment showed that Cadmium content being able to induce rice bearing obstacle in flood culture was probably great, for the growth of rice in this experiment didn't exhibit being restrained. When cadmium concentration was high in the soil, cadmium would enhance content of amylose in unpolished rice to a certain extent. Cadmium content in unpolished rice was significantly related to bioavailable cadmium content in the air-dry soil and total cadmium content in the soil respectively. Rice was very sensitive to cadmium menace before booting stage, after heading stage rice was gradually accustomed to cadmium menace. Cadmium in rice plant was mostly from cadmium accumulation in nutritional growth stage. Most of cadmium in grain was accumulated after heading stage by rice adsorption directly from the soil, and cadmium content in photosynthesis outcome transported from leaf to spike was little. Desorption rate of cadmium in the soil decreased with the increase of both soil pH and soil moisture. Soil pH was a little lower at tillering period than that of other treatments, accordingly bioavailable cadmium content in the soil was bigger at tillering period than that of other treatments. Contemporarily, cadmium content in rice xylem exudates was higher at tillering period than that of other treatments.There were several conceptions used to express cadmium sorption capability of soils, such as sorption potential, sorption rate and average distribution coefficient. Average distribute coefficient may be used to express sorption potential and sorption rate. The characteristics of cadmium adsorption were investigated in different paddy soils under the condition of constant temperature. Results indicated that sorption potential, sorption rate and average distribution coefficient were only able to conditionally reflect cadmiumsorption characteristics by soils. If cadmium sorption may be simulated by Langmuir equation, the parameter of Langmuir equation, viz. Ke X b, can be used to show sorption characteristics of soils, and Ke b was defined as sorption energy. Sorption potential, sorption rate, average distribution coefficient and sorption energy all intuitively reflect increasing rate of sorption amount with cadmium concentration in equilibrium solution and embody sorption intensity of soils. Sorption energy was significantly (p<0.01) related to sorption potential, sorption rate, average distribution coefficient, which proved that they were correlative in physical meaning. Relativity analysis also showed that sorption energy was significantly (p<0.01) related to constants of Freundlich equation and Langmuir equation except constant of b in Langmuir equation. It indicated that those parameters were all connected with sorption intensity. As sorption intensity was affected by soil properties, those parameters were used to simulate the relationship between sorption intensity and soil properties. Simulation results revealed that sorption energy best expressed the relationship.All cadmium adsorption curves could be well described by Langmuir, Freundlich and Henry equations, with better fitness by Langmuir and Freundlich equations. With pH, content of organic carbon and CEC increasing, soil adsorbed more cadmium. pH affected the sorption amount more than other soil properties. The relationship between cadmium concentration in desorption equilibrium and sorption amount can be expressed as c=k x, where c was cadmium concentration in desorption equilibrium, k was distribute coefficient, and x was sorption amount. The desorption of cadmium was positively related to content of CEC and soil clays. When pH increased, amount of cadmium desorption declined.Alkaline soils would adsorb a great deal of cadmium when cadmium was added at lo...