The interaction of Cd and other heavy metals with soil colloidal particles controls the sequestration, mobility and bioavailability of Cd in soils. In this study, the binding (△G_bi) and adsorption (△G_ad) energies of Cd on colloidal particles of 18 soils were determined by the Wien effect method. The binding energy of Cd on soil colloidal particles varied from 5.3 to 9.9 kJ mol⁻¹, depending on the soil characteristics including pH, Mn‐oxide content and dissolved organic carbon in the soil. The Cd adsorption energy correlated positively with Mn‐oxide content and pH. In parallel, the extended X‐ray absorption fine structure (EXAFS) spectroscopy was used to determine the speciation of Cd in Cd‐saturated soil samples, which revealed that the outer‐sphere Cd was the predominant species, accounting for 32.2–73.7% of the total adsorbed Cd, and positively correlated to the binding and adsorption energies. Humic acid‐Cd (10.4–42.2%) and montmorillonite‐Cd (2.5–51.2%) were also major species that were identified by EXAFS spectroscopy. The toxicity (log EC₅₀) of Cd in soils to three organisms (earthworm, Collembola and Chinese cabbage) was found to correlate positively with the binding energies, indicating the predictive capability of using binding energies of Cd in different soils as an indicator for evaluating Cd bioavailability and toxicity in soils.

中文翻译：

---

Cd在土壤中的结合和吸附能及其对Cd生物利用度的环境意义

Cd和其他重金属与土壤胶体颗粒的相互作用控制了Cd在土壤中的固存，迁移和生物利用度。本研究采用维恩效应法测定了18种土壤胶体颗粒上Cd的结合能（△G _bi）和吸附能（△G _ad）。Cd在土壤胶体颗粒上的结合能在5.3至9.9 kJ mol ^{-1之间变化}，取决于土壤的特性，包括pH，二氧化锰含量和土壤中溶解的有机碳。镉的吸附能与锰氧化物含量和pH呈正相关。同时，利用扩展的X射线吸收精细结构（EXAFS）光谱确定了Cd饱和土壤样品中Cd的形态，这表明外层Cd是主要物种，占Cd的32.2–73.7％。吸附的镉总量与结合能和吸附能呈正相关。腐植酸-镉（10.4–42.2％）和蒙脱石–镉（2.5–51.2％）也是EXAFS光谱法鉴定的主要物种。毒性（log EC ₅₀）土壤中的Cd被发现与三种生物（ear，Collembola和大白菜）的结合能呈正相关，表明利用不同土壤中Cd的结合能作为评估Cd在土壤中的生物利用度和毒性的指标的预测能力。