Absorption And Accumulation Characteristics And Physiological Response Of Different Vegetables To Cadmium And Lead

Cadmium and lead pollution in vegetables is a serious problem reducingquality of vegetable products and harming human health. Pakchoi (Brassicacampestris ssp. Chinensis L. var. communis Tsen et lee) and radish (Raphanussativus L.), two kinds of vegetables widely eaten by people, were selected asstudying objects, soil culture and solution culture experiments as well aschemical analysis were managed. We studied the absorbing and accumulatingcharacters of cadmium and lead in pakchoi and radish, as well as theirphysiological responses to the toxicity of cadmium and lead. We also studiedthe kinetics and mechanism of cadmium uptake of vegetables roots, as well aschemical forms of cadmium and lead in the tissues of vegetables, and wediscussed the relationship between chemical forms of cadmium and lead andtheir absorbing and accumulating characters and toxicity. The main results areas follows:1. All growing stages soil culture experiment of pakchoi and radishshowed that, under the condition of cadmium and lead single pollution ,cadmium and lead concentrations in pakchoi and radish were significantlylinearly correlated to the added cadmium and lead levels in the soil. Under thecondition of cadmium and lead compound pollution, cadmium and leadconcentrations in pakchoi and radish were not only mainly affected by theadded cadmium and lead levels respectively, but also by co-existent heavymetal element. The interactions of cadmium and lead showed that, cadmiumnot only inhibited lead absorption of roots, but also inhibited lead transferencefrom roots to aerial part, while lead not only enhanced cadmium absorption ofroots, but also enhanced cadmium transference from roots to aerial part.Cadmium and lead concentrations in the aerial part of pakchoi were lower thanthose in the roots, while cadmium and lead concentrations in the aerial part ofradish were higher than those in the roots.2. Under single pollution, the thresholds of cadmium and lead in soil forpakchoi were 0.890mg/kg,164mg/kg. The thresholds of cadmium and lead forradish were 1.04mg/kg,188mg/kg. The thresholds of cadmium and lead forradish were higher than those for pakchoi. Under compound pollution, thethresholds of cadmium and lead in soil for pakchoi were 0.785mg/kg,212mg/kg. The thresholds of cadmium and lead for radish were 0.877mg/kg,231mg/kg.The thresholds of cadmium under compound pollution were lowerthan those under single pollution, while the thresholds of lead under compoundpollution were significantly higher than those under single pollution. 3. Under low concentration of cadmium (0-0.8 μg/ml), the uptake of rootsof pakchoi and radish for cadmium was mainly active absorption, the relationof cadmium uptake rate and cadmium concentration fitted intoMichaelis-Meten model well, and cadmium uptake rate firstly increased, thendecreased as the increase of temperature, and the uptake rate was sensitive tometabolic inhibitor. The value of Imax,Km and αof pakchoi were higher thanthose of radish. Under high concentration of cadmium (0.8-10μg /ml ) , theuptake of roots of pakchoi and radish for cadmium was mainly passiveabsorption, cadmium uptake rate under high concentration was significantlylinearly correlated to the cadmium concentration ,and cadmium uptake rate wasa linear function of temperature, and the uptake rate was less sensitive tometabolic inhibitor than that under low concentration. Under the samecadmium concentration, the uptake rate of pakchoi was higher than that ofradish. 4. NaCl extractable cadmium was the main form of cadmium in pakchoiand radish. Under compound pollution, because of the interaction of cadmiumand lead, compared with single pollution, percent of NaCl extractable cadmiumand deioned water extractable cadmium increased, while percent of acetic acidextractable cadmium decreased obviously, which resulted in the enhancementof transportation and toxicity of cadmium in vegetables. The ratio of cadmiumin ethanol extractable form and deioned water extractable form wassignificantly relevant to the chlorophyll contents of leaves and the ratio ofcadmium accumulation in leaves and roots, which indicated that the chemicalforms of cadmium might be relative with its toxicity and transportation in...