Research And Development Of New Devices Based On Diffusive Gradients In Thin-films (DGT) To Assess Cadmium Bioavailability In Soils

Heavy metals in soil biological toxicity depended not only on the full amount, it was determined by its speciation. Speciation of heavy Metals changed with the environmental conditions changing, and showed different behavior and toxicity. The technique of diffusive gradients in thin-films (DGT) was a novel technique to extract heavy metals bioavailability. Many studies showed that, DGT than the traditional extraction method better reflected the situation plants to absorb heavy metals. By screening adsorption material in binding phase, physical and chemical properties of the membrane diffusion contrast, the impact of soil properties on grain Cd content in rice and comparative study of different extraction methods of cadmium bioavailability in soil, the following conclusions:There were chelex-100, thiol-modified phyllosilicate, sepiolite powder, attapulgite, zirconia, titania (5nm), montmorillonite as adsorbent. Adsorption capacity of seven kinds of the adsorbent material varied. Thiol-modified phyllosilicate had a strongest adsorption of Cd, reaching 158.84mg/g. Attapulgite, zirconia, titania (5nm) Cd almost had no adsorption capacity for Cd. Adsorption ability of the four kinds of material:thiol-modified phyllosilicates>chelex-100> montmorillonite> sepiolite powder, and desorption rates were 99.9%,96.8%,98.1% and 97.5% respectively, thiol-modified phyllosilicate had strongest adsorption and desorption capacity. But because of its use as an adsorbent material in the binding phase, larger particles easily aggregated. Therefore, chelex-100 was preferably used as the adsorbent in the binding phase of DGT.Dialysis membrane had advantage in application, storage and price, while hydrogel was more customization. At low ionic strength (less than 0.001mol L-1), the effect of ionic strength on both of the dialysis membrane and hydrogel was large. With increasing ionic strength, effect of diffusion coefficients of two types of membranes by the ionic strength was small. Diffusion coefficients of two types of membranes at pH 5-9 had little difference. Cd complexes passed through D10000, D15000 and hydrogel took 97.65s,109.65s and 652.25s, respectively. Cd complexes were more prone to dissociation through hydrogel than through dialysis membranes. The thickness of diffusion boundary layer of D10000, D15000 and hydrogel respectively were 0.039cm,0.052 cm and 0.052cm in the neutral static water at 0.1mol L-1 ionic strength. Effect of diffusion boundary layer on dialysis membranes was larger than on hydrogel, and was not neglectable in the neutral static water.Cd accumulation in rice grain and six soil properties indicators correlation were pH> full amount of Cd in soil>silt>sand>clay>DOC. pH, soil Cd content and Cd in the rice grain had a significant linear correlation, and correlation coefficients were -0.371 and 0.272. The remaining four indicators were almost no correlation between Cd in the rice grain. The correlation coefficient of Cd in rice grain and CaCl2 extraction Cd, Cd content in the soil solution, the chelex-100 DGT extraction Cd were 0.586,0.347,0.608, respectively. Chelex-100 DGT prediction model was the best in the rice grain Cd predictive models built in pH ang 3 kinds of extraction Cd. Therefore chelex-100 DGT could better predict Cd in rice grain than CaCl2 and soil solution extraction.