TRACE METALS BIOAVAILABILITY IN TERRESTRIAL ENVIRONMENT: METHODOLOGICAL ISSUES
Beside anthropogenic sources, trace metals can be found in the parent material from which the soils develop. Whether these inputs will become toxic and to what degree mobile depends on a number of factors: specific chemical and physical trace metal characteristics, soil type, land use, geomorphological characteristics within the soil type and exposure to emission sources. Processes that control the mobility, transformation and toxicity of metals in soil are of special importance in the soil root developing zone – the rhizosphere. For this reason, there is a considerable interest in understanding trace metals behaviour in soil, with special emphasis on the way they enter the soil and on processes by which plants take them up. Full understanding and prediction of chemical behaviour of an element in the environment is possible only by identification of all forms in which that element can be found under different environmental conditions. Various chemical methods, geochemical models and biotests are used for assessment of the bioavailable metal fraction in soil. However, these methods are not universally applicable for all elements and different soil characteristics. Chemical methods for assessment of metal bioavailability are commonly grouped within methods for identification of total metal content in soil, methods for assessment of currently available and potentially available fractions, as well as methods for prediction of metal speciation in soil solution. This article offers a critical review of methodologies available for assessing metal speciation in solid and liquid phases in soils taking into consideration the array of parameters that might influence uptake and effects upon the plant.
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