Comparison and Evaluation of Extraction Media and Their Suitability in a Simple Model to Predict the Biological Relevance of Heavy Metal Concentrations in Contaminated Soils

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Abstract
The concentrations of heavy metals in agricultural soils are increasing gradually from various diffuse sources. The metals can transfer from contaminated soils into the growing plants or may affect the respiration rate of soil microorganisms. In the first part of this paper, the following simple model to predict the biorelevant metal concentration in anthropogenically or artificially contaminated soils is reported: log Mp = α + β log [MNaNO3] log MR = α' + β' log [MNaNO3] log MP = log Metal concentration in test plant (mg/kg dry weight) log MR = log percent Redution in the respiration or enzyme activity [MNaNO3] = Metal concentration in NaNO3-soil extract (mg/kg soil) α and β & α' + β' = Intercepts and slopes of the linear regression lines. The model has been tested in laboratory experiments, in growth experiments either in a greenhouse or in the field. Also, an attempt is made to present a theoretical interpretation. Critical concentrations are calculated with the help of the relationship between metal concentration in soil solution [MNaNO3] and metal concentration in plants. The critical concentration, which is able to induce either phyto- or zootoxic concentrations in the plant parts (productive or vegetative) or reduce their growth or to reduce significantly the growth of soil microorganisms, are found to be uniform in a wide range of soils (pH 3 to 8 and CEC 10–50 millimol/100g soil), the critical concentrations of NaNO3 in soil extracts are comparable with the values obtained with plant growth experiments in nutrient solution and also with the concentrations obtained from soil respiration experiments reported in literature.

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