A modified sequential chemical extraction procedure was developed for partitioning particulate Cd into eight fractions: exchangeable, carbonate-bound, metal-organic complex-bound, easily reducible metal oxide-bound, organic-bound, amorphous mineral colloid-bound, crystalline Fe oxide-bound, and residual. Results of experimental data on 16 surface soils of Saskatchewan, widely varying in physico-chemical properties, indicate the presence of little exchangeable Cd. Cadmium in these soils was predominantly in the form metal-organic complex-bound, accounting for 31-55%, with an average of 40%, of the total Cd present in the soils. The average relative abundance of the different forms of Cd present in these soils is in the order: metal-organic complex-bound (0.107 mg kg-1) > carbonate-bound (0.052 mg kg-1) > residual (0.042 mg kg-1) > organic-bound (0.035 mg kg-1) > crystalline Fe oxide-bound (0.016 mg kg-1) > easily reducible metal oxide-bound (0.010 mg kg-1) > amorphous mineral colloid-bound (0.002 mg kg-1). Statistical treatment of the Cd availability index, measured as ammonium hydrogencarbonatdiethylenetriaminepentaacetic acid (ABDTPA)-extractable Cd, with different particulate-bound Cd species showed high correlation (r = 0 . 9 1 6 , ~ = 6 X 10-7) of the Cd availability index with the metal-organic complex-bound Cd. The beta coefficients obtained from the multiple regression analyses have given an insight into the importance of Al-organic complex-bound Cd species in estimating the bioavailability of Cd in these soils. The relationship of the metal-organic complex-bound Cd and the mobility and bioavailability of soil Cd merits in-depth research in explaining the toxicity and food chain contamination of Cd in the environment.

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Limited information is available on the trace element contents of soils and crops in Saskatchewan. Trace elements, to a large extent, are derived from soil parent materials and partially from anthropogenic activities, such as agricultural application of fertilizers. The objective of this study was to establish levels of trace element concentrations of the surface horizons and parent materials of selected soils, fertilizers, and durum wheat (Triticum durum Desf.). Inductively coupled plasma mass spectrometry (ICP‐MS) having the capacity to determine 60 elements simultaneously at very low detection levels was used. Trace elements for this work are among the most frequently reported in the recent literature. We found a positive relationship between the total contents of trace elements and percent of clays in the soils, except Se. This suggests that the major part of the elements studied are associated with the clay minerals in soils. In two Regina heavy clay soils, total Cu, Zn, Se, and Pb were higher in the surface soil than the subsoil, but this increase was statistically not significant. All the elements, except Zn, Cd, and Pb, were depleted in soils that have lower clay content in the surface horizon than the parent material. Soils having similar clay contents in the surface horizon and subsoil, total V, Cr, Co, Ni, Zn, Cd, Sn, Sb, Tl, and Pb concentrations were higher in the surface horizon, relative to parent material. Only Zn and Cd increases were significant. Enrichment of elements in the surface horizons was, in part, attributed to anthropogenic additions. Experiments with EDTA and DTPA extraction techniques showed that almost half of Co, As and Cd, and other elements in fertilizers were between 4 and 50% in somewhat available form for plants indicating their potential for soil pollution.

A lack of understanding about the selenite adsorption behavior on hydroxyaluminum (HyA)‐ and hydroxyaluminosilicate (HAS)‐interlayered phyllosilicates led us to conduct the present study. The kinetics of selenite adsorption on montmorillonite (Mt), HyA(OH/Al = 2.0)‐Mt, HAS1(OH/Al = 2.0; Si/Al = 0.24)‐Mt, and HAS2(OH/Al = 2.0; Si/Al = 0.48)‐Mt were studied at pH 4.5, with an initial selenite concentration of 0.025 mM, a clay concentration of 0.5 g L−1, temperatures of 288, 298, 308, and 318 K, and background electrolyte concentration of 10−2 M NaNO3 Of the six different kinetic models tested, the second‐order rate equation best described the kinetic data obtained for the initial fast reaction (5–30 min) followed by a slow reaction (30–180 min) in the adsorption systems. Elevated temperatures brought about a substantial increase in the rate constants. Compared with Mt, different HyA/HAS‐Mts had 2 to 21 times higher rate constants for the fast reaction and up to five times higher rate constants for the slow reaction. Silication of HyA‐Mt to form HAS1‐Mt and HAS2‐Mt substantially lowered the rate constants for both the fast and slow reactions. For the fast reaction, Mt had the highest activation energy and HyA‐Mt had the lowest activation energy (around four times lower than Mt); silication increased the activation energy of selenite adsorption on the HAS‐Mts. The pre‐exponential factor, an index of the frequency of selenite collision with the clay surface, was remarkably lower for the HyA/HAS‐Mts in comparison with Mt. The data obtained in the present study are of fundamental significance in understanding the role of Al interlayering and coating and silication of Al polymers on expansible phyllosilicates in influencing the dynamics of Se in soil and related environments.

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