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Abstract

The influence of soil load with polycyclic aromatic hydrocarbons (PAHs) on their contents in selected plants was investigated. A set of experiments was realized in three years. The influence of extreme soil load with PAHs (soil contaminated by floods and sludge application) on their content in plants was observed in a pot trial. A laboratory column extract trial investigated PAHs transfer from the soil into soil solution in different conditions. The results showed that the transfer of PAHs into plants is influenced mainly by chemical characteristics of the substances (the number and position of aromatic nuclei); by soil characteristics (content and quality of soil organic matter) and by plant characteristics (plant species and plant bodies). The roots of tested plants were loaded with PAHs thanks to the transfer of less-nuclei compounds (2–3 nuclei) in soil solution into the roots and thanks to the binding of more nuclei compounds (4–6 nuclei) on organic substances in epidermis and primary bark of roots. These results were confirmed by a laboratory column trial.

The development of soil limiting values of the protection of the quantity and mainly quality of the crop production tends from empiric values towards critical values, based on ecotoxicity. We present an attempt to derive transfer functions by the means of multiple regression analysis. The substitution of trace elements contents in crops in the prediction equations for fodder or food standards or phytotoxicity limits satisfies the present ecotoxicological demands. We preferred polyfactor relations to simple ones. The exceeding of reference values must be verified by the determination of the hazardous transfer in the field. Therefore the reference values are called testing values. They were derived especially for Cd, Pb, As, Cu, Zn, Ni and Mn. For some trace elements, only protective values can be set up (especially for Cr, Hg, but also for Tl, Be, V). They reflect minimum values that guarantee growing crops without any risks. Experimental data (pot trials) were compared with results obtained in field investigations. The resulting critical values were also compared with the values proposed in Germany.

Sixteen soil samples from agriculturally used soils flooded in August 2002 were taken because new information about the state of soil contamination was required. The area in the Vltava river basin from Pragueto Mělník and in the Laberiver basin from Neratovice to Děčín was investigated. The samples were taken in September 2002 and analysed for the contents of potentially risky elements and persistent organic pollutants, including persistent dibenzodioxins and dibenzofurans. The results were compared with the data from the project Labe 1992. The findings show a low soil load of potentially risky elements and a slight reduction of their contents in soil in comparison with the state in 1992 (except for vanadium). The same situation was observed in the case of persistent organic pollutants. Only the content of DDT was increased in the soils of most localities after floods in August 2002. This finding needs further observations on a larger collection of samples. The dreads resulting from expected soil contamination by dibenzodioxins from Spolana Neratovice factory were not confirmed and their contents in the soils of observed localities meet the requirements for plant production without any reduction.