Fraction distribution and bioavailability of metals and metalloids in soil of different types

Bioavailability is the amount of a nutrient that is potentially available for absorption from a matrix (e.g., from soil to crops or from food to humans) and when absorbed, utilizable for metabolic processes in the organism. Bioavailability is dependent not only on chemical properties of compounds but also on soil composition and properties, among them pH, granulometric composition or soil texture and organic matter content can be mentioned. The aim of this study was to investigate fraction distribution of elements in soil samples of different types to assess prospective bioavailability of metals and metalloids. Five soil samples were collected in Latvia, considering their representativeness for soils in Latvia. Soil type and texture were identified as follows: fen peat soil (S1); sod-podzolic soil/sandy loam (S2); sod-podzolic soil/sand (S3); sod-podzolic soil/loamy sand (S4); sod-podzolic soil/sandy clay loam (S5). Such parameters as soil pH, soil organic matter expressed as content of humic substances, cation base saturation were determined as well as speciation analysis of soil samples was performed. Consequent extraction was done to obtain element distribution in five fractions: 1) fraction of water soluble compounds; 2) fraction of acid soluble compounds; 3) fraction of reduced forms of compounds; 4) fraction of organic compounds; 5) fraction of sulphide compounds. Ten elements (As, Cd, Co, Cu, Ni, Pb, Rb, Sr, V and Zn) were quantitatively detected in fractions. Fraction distribution of elements revealed differences among soil samples and behaviour of individual elements in soil.