Coal ash obtained by coal combustion in the "Nikola Tesla A" power plant in Obrenovac, near Belgrade, Yugoslavia, is mixed with water of the Sava river and transported to the dump. In order to assess pollution caused by leaching of some minor and major elements during ash transport through the pipeline, two sets of samples (six samples each) were subjected to a modified sequential extraction. The first set consisted of coal ash samples taken immediately after combustion, while the second set was obtained by extraction with river water, imitating the processes that occur in the pipeline. Samples were extracted consecutively with distilled water and a 1 M solution of KCl, pH 7, and the differences in extractability were compared in order to predict potential pollution. Considering concentrations of seven trace elements as well as five major elements in extracts from a total of 12 samples, it can be concluded that lead and cadmium do not present an environmental threat during and immediately after ash transport to the dump. Portions of zinc, nickel and chromium are released during the ash transport, and arsenic and manganese are released continuously. Copper and iron do not present an environmental threat due to element leaching during and immediately after the coal ash suspension and transport. On the contrary, these elements, as well as chromium, become concentrated during coal ash transport. Adsorbed portions of calcium, magnesium and potassium are also leached during coal ash transport.
The lead concentrations in the water of the ?Barje? lake are presented for
the years 1995 to 1998. Sequential extraction was applied to estimate the
chemical association of lead in the sediments of the ?Barje? lake. Several
lead fractions showed highly significant correlations with the corresponding
substrate (step II: Mn-oxyhydroxides; step III: Fe-oxyhydroxides) suggesting
that lead carbonates were incorporated with amorphous iron and manganese
hydroxides. An explanation for this relation can be in the same
anthropogenic source of these elements.
Investigations presented in this paper were aimed at defining the alterations of n-alkane composition in cases of oil-polluted alluvial sediments. Therefore, oil-polluted groundwater samples, taken in five different time intervals during a period of 28 months, were investigated. Samples of alluvial sediments were taken from two boreholes within an oil refinery at Pancevo, Yugoslavia. In both boreholes significant alterations with characteristic degradation of "oil" n-alkanes with no odd-or even-member predominance were observed, as well as subsequent synthesis of new ones with pronounced even-member predominance, and with maxima at C 16 and C 18 . Since no additional contamination of boreholes was observed by analyses of steranes and triterpanes, the observed changes can only be attributed to microbial activity. It is assumed that for the degradation of oil n-alkanes, as well as for the synthesis of "new" n-alkanes, algae such as dinoflagellates are responsible. This assumption was confirmed by identification of n-alcohols with even-member predominance (C 14 -C 20 ), by identification of cholesterol, as well as of n-fatty acids with even-member predominance (C 14 -C 18 ) in the extract with n-alkane even-member predominance.
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