Consumption of crops grown in cadmium-contaminated soils is an important Cd exposure route to humans. The present study utilizes statistical analysis and in vitro digestion experiments to uncover the transfer processes of Cd from soils to the human body through rice consumption. Here, a model was created to predict the levels of bioaccessible Cd in rice grains using phytoavailable Cd quantities in the soil. During the in vitro digestion, a relatively constant ratio between the total and bioaccessible Cd in rice was observed. About 14.89% of Cd in soils was found to be transferred into rice grains and up to 3.19% could be transferred from rice grains to the human body. This model was able to sufficiently predict rice grain cadmium concentrations based on CaCl₂ extracted zinc and cadmium concentrations in soils (R² = 0.862). The bioaccessible Cd concentration in rice grains was also able to be predicted using CaCl₂ extracted cadmium from soil (R² = 0.892). The models established in this study demonstrated that CaCl₂ is a suitable indicator of total rice Cd concentrations and bioaccessible rice grain Cd concentrations. The chain model approach proposed in this study can be used for the fast and accurate evaluation of human Cd exposure through rice consumption based on the soil conditions in contaminated regions.

Cadmium (Cd) contamination of soil can strongly impact human health through the food chain due to uptake by crop plants. Inorganic immobilizing agents such as silicates and phosphates have been shown to effectively reduce Cd transfer from the soil to cereal crops. However, the effects of such agents on total Cd and its bioaccessibility in leafy vegetables are not yet known. Pak choi (Brassica rapa L. ssp. chinensis) was here selected as a representative leafy vegetable to be tested in pots to reveal the effects of silicate–phosphate amendments on soil Cd chemical fractions, total plant Cd levels, and plant bioaccessibility. The collected Cd contaminated soil was mixed with control soil at 1:0, 1:1, 1:4, 0:1 with a view to Cd high/moderate/mild/control soil samples. Three heavy metal-immobilizing agents: wollastonite (W), potassium tripolyphosphate (KTPP), and sodium hexametaphosphate (SHMP) were added to the soil in order to get four different treatment groups, i.e., control (CK), application of wollastonite alone (W), wollastonite co-applied with KTPP (WKTPP), application of wollastonite co-applied with SHMP (WSHMP) for remediation of soils with different levels of Cd contamination. All three treatments increased the effective bio-Cd concentration in the soils with varying levels of contamination, except for W under moderate and heavy Cd contamination. The total Cd concentration in pak choi plants grown in mildly Cd-contaminated soil was elevated by 86.2% after WKTPP treatment compared to the control treatment could function as a phytoremediation aid for mildly Cd-contaminated soil. Using an in vitro digestion method (physiologically based extraction test) combined with transmission electron microscopy, silicate and phosphorus agents were found to reduce the bioaccessibility of Cd in pak choi by up to 66.13% with WSHMP treatment. Application of silicate alone reduced soil bio-Cd concentration through the formation of insoluble complexes and silanol groups with Cd, but the addition of phosphate may have facilitated Cd translocation into pak choi by first co-precipitating with Ca in wollastonite while simultaneously altering soil pH. Meanwhile, wollastonite and phosphate treatments may cause Cd to be firmly enclosed in the cell wall in an insoluble form, reducing its translocation to edible parts and decreasing the bioaccessibility of Cd in pak choi. This study contributes to the mitigation of Cd bioaccessibility in pak choi by reducing soil Cd concentration through in situ remediation and will help us to extend the effects of wollastonite and phosphate on Cd bioaccessibility to other common vegetables. Therefore, this study thus reveals effective strategies for the remediation of soil Cd and the reduction of Cd bioaccessibility in crops based on two indicators: total Cd and Cd bioaccessibility. Our findings contribute to the development of methods for safer cultivation of commonly consumed leafy vegetables and for soil remediation.

Li, J.; Song, Y.; Mao, C., and Li, T., 2018. Assessing the distribution characteristics of surface water geochemistry and pollution of heavy metals within soil in the Changjiang River Delta, China. In: Wang, D. and Guido-Aldana, P.A. (eds.), Select Proceedings from the 3rd International Conference on Water Resource and Environment (WRE2017). Journal of Coastal Research, Special Issue No. 84, pp. 109–113. Coconut Creek (Florida), ISSN 0749-0208. This study aimed to understand the spatial distribution and geochemical characteristics of heavy metals in soil in Changjiang River Delta, and also the impact of surface water geochemistry on the mobility of heavy metals in soil. The levels of Ca²⁺ and Na⁺ in surface water reached 80% of total cation level, ranging 33.00–97.50 mg/L and 9.00–334.90 mg/L, respectively. HCO₃⁻ was more than 50% of total anion concentration, making the type of surface water as Ca-HCO₃ or Ca-Na-HCO₃. The concentration of cations and anions followed the order: coastal > middle > inland. The soils were strongly polluted with Cd in this study. More than 50% of Cd concentration exceeded the standard. Spatial changes in As, Cd, and Pb levels followed the order: middle > coastal > inland, same as that for soil pH. Speciation results of heavy metals showed that more than 50% of Cd was exchangeable. Principal component analysis results showed that the change in exchangeable fraction of As, Hg, and Pb followed the same order: middle > coastal > inland. Exchangeable Cd followed a trend different from that of Cr. Three areas were characterized by the mobility of As, Hg, and Pb. Scores of samples from different areas implied the influence of surface water on the mobility of heavy metals in soil. Geochemical variation in surface water indicated the mobility of heavy metals through correlation and spatial analysis of geochemistry of surface water and speciation of heavy metals in soil.