Characterization of the dissociation kinetics of Cd and Ni in soils based on diffusive gradients in thin films technique.

A new theoretical method was established for the combinatorial calculation of the dissociation rate constant (K-1) of the metal-organic complexes (MLs), the concentration of free ionic soil metals (CM), the labile concentration of soil metal-organic complexes (CML) based on diffusive gradients in thin-films (DGT) technique with a range of diffusive layer thicknesses (0.053-0.173 mm) in soils. The fitting results agreed well with the determined values. The values of K-1, CML and CM were calculated without other morphological analysis software and the fitting results agreed well with the determined values with some advantages such as the use of fewer hypothetical parameters, ease of calculation, the full embodiment of the contribution of MLs to the labile content. According to the results of model fitting, cation exchange capacity and soil organic matter were found to be the key environmental factors for K-1 values of Cd and Ni, respectively. The labile contents of Cd and Ni in soil were closely related with pH, soil organic matter and the total contents of heavy metals.

[Applications of Geostatistical Analyses and Stochastic Models to Identify Sources of Soil Heavy Metals in Wuqing District, Tianjin,China].

A survey on soil samples was conducted to study the heavy metal pollutions and their potential sources in Wuqing District, Tianjin, China. A total of 578 topsoil samples were collected and the concentrations of eight heavy metals, namely, Cd, Pb, Cu, Zn, Cr, Ni, As (metalloid) and Hg were analyzed. A summary of descriptive statistics, principal component analysis, geostatistical analysis and stochastic forest regression models were applied to study the spatial and temporal variation and identify proportional contribution from either natural or anthropogenic sources for the eight heavy metals in topsoils of the study region. The results indicated that the average concentrations of all the heavy metals except for Cr in the topsoils exceeded their corresponding natural-background values. As, Ni and Cr were mainly contributed by natural sources (i.e., soil parent materials). Cu and Zn originated from both the soil parent materials and sewage irrigation. Pb and Cd originated mainly from non-point source pollution and partially from point source. Hg originated from sewage irrigation. It was proved that combination of multi-technologies provides an effective way to delineate multiple heavy metal pollution sources.