Binding and adsorption energy of Cd in soils and its environmental implication for Cd bioavailability

Abstract

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 (△Gbi) and adsorption (△Gad) 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.

Bioavailability of Cd in Plantago weldenii and Sonchus oleraceus Plants: The Effects of a Humic and Fulvic Acids-Based Biostimulant

“…Cd is known to interact with colloidal particles and other soil components. The electrostatic forces between Cd cations and the negatively-charged colloidal surfaces increase at higher pH [39]. Adding the biostimulant could have influenced the pH.…”

Determining soil conservation strategies: Ecological risk thresholds of arsenic and the influence of soil properties

“…The pH and electrical conductivity (EC) were measured in purified water in 1:2.5 (w/v) and 1:5 (w/v) soil–water suspensions, respectively. SOM and cation exchange capacity (CEC) were measured by the dichromate method for the <100-mesh fraction [ 24 ] and ethylenediamine tetraacetic acid–ammonium acetate exchange method for the <100-mesh fraction [ 25 ], respectively. The pipette method was used to determine the clay content in soil samples by using a 10-mesh sieve [ 26 ].…”

Remediation of Cd-Contaminated Soil by Modified Nanoscale Zero-Valent Iron: Role of Plant Root Exudates and Inner Mechanisms

“…At higher Cd concentrations, it can also induce oxidative stress in plants by stimulating the production of more reactive oxygen species (ROS) and lipid peroxidation, and ultimately lead to death. Human activities are the main causes of soil Cd pollution including the application of chemical fertilizer and sludge, wastewater irrigation, mining and smelting, dry and wet atmospheric deposition and solid waste disposal [5]. Therefore, it is urgent to solve or alleviate the problem of Cd pollution in the soil.…”