Measurement Of The Cadmium Bioavailability In The Soil Of Sugarcane Field Based On The Diffusive Gradients In Thin Films Technique

The diffusive gradients in thin films （DGT） is one of the most promising in situ samplingtechniques for trace metal in-situ accumulation, since its invention in the mid-1990s, DGT with solidform binding phases has been widely used for collection and measure of available heavy metals inwaters, soils or sediments in situ, but that with liquid binding phase was primarily used in the analysisof heavy metals in waters in-situ. In this paper, based on field investigation and the ICP-MS technique,sugarcane samples and rhizosphere soils around them at18sites in Guangxi Province of China werecollected, and the concentrations of cadmium （Cd） were determined on acetic acid（H Ac）,ethylenediaminetetraacetic acid disodium salt （EDTA-2Na）, magnesium chloride hexahydrate （MgCl2）extractions, and by DGT with a solid form binding phase of chelex100（chelex100-DGT, CD） andmodified DGT with a liquid form binding phase of sodium polyacrylate （CDM-PAAS-DGT, CPD）. Thecapability, accuracy and development of the DGT technique in studying the Cd bioavailability in soilsof sugarcane field were discussed. The modified DGT device had been used innovatively for measuringand assessing the Cd bioavailability in soils, which was with the sodium polyacrylate solution as thebinding phase and a dialysis membrane as the diffusive layer.The results showed that,（1） the condition stability constant of PAAS and Cd²⁺was11.47, whichgave us the information that they could bond strongly. The maximum and effective Cd adsorptioncapacities of PAAS used in this study were limited to4.98μmol·L-1.（2）Although simple linearregression analyses between concentrations of Cd in plants and those in soils measured using DGT andchemical extractions showed good fits in all of roots, unpolished stalks and leaves, the correlationcoefficients of those obtained by DGT were higher than those based on chemical extractions; Therelationships between Cd contents in soils measured by DGT with both of the two binding phases andCd in the roots, leaves and unpolished stalks of sugarcane were positively and significantly correlated,meanwhile, the extraction ability of the CPD was much higher than that of the CD.（3） In addition,principal component analyses were used to assess the impact of pH, cation exchanged capacity （CEC）,soil organic matter （OM） and texture. Two principal components were extracted. The first was wellcorrelated with pH and CEC, while the second primarily correlated well with organic matter and claypropotion.（4）Then the linear regression models cluding both of the two principle components wereestablished. The results indicated that the multiple linear regression of the DGT measurementquantitatively incorporates the main factors affecting the bioavailability of Cd in soils; predictions of theDGT model were hardly affected by the physical and chemical properties of soils chosen in this paper.The bioavailability of Cd in soils could be predicted more accurately by DGT than chemical extractions;moreover, the Cd bioavailability in soils could be accurately predicted by the CPD technique, whichexpanded its applicable field.