DISTRIBUTION OF Cr, Pb, Cu, Cd AND Zn IN SEDIMENTS OF THE DOBCZYCE DAM RESERVOIR (SOUTHERN POLAND)

Sediments play a fundamental role in the behaviour of contaminants in aquatic systems. Various processes in sediments, eg adsorption-desorption, oxidation-reduction, ion exchange or biological activities, can cause accumulation or release of metals and anions from the bottom of reservoirs, and have been recently studied in Polish waters [1-3]. Sediment samples from layer A: (1 divided by 6 cm depth in direct contact with bottom water); layer B: (7 divided by 12 cm depth moderate contact); and layer C: (12+ cm depth, in theory an inactive layer) were collected in September 2007 from six sites representing different types of hydrological conditions along the Dobczyce Reservoir (Fig. l). Water depths at the sampling points varied from 3.5 to 21 m. We have focused on studying the distribution and accumulation of several heavy metals (Cr, Pb, Cd, Cu and Zn) in the sediments. The surface, bottom and pore water (extracted from sediments by centrifugation) samples were also collected. Possible relationships between the heavy-metal distribution in sediments and the sediment characteristics (mineralogy, organic matter) as well as the Fe, Mn and Ca content of sediments, have been studied. The 02 concentrations in water samples were also measured. The heavy metals in sediments ranged from 19.0 to 226.3 mg/kg of dry mass (ppm). The results show considerable variations in heavy-metal concentrations between the 6 stations, but not in the individual layers (A, B, C). These variations are related to the mineralogy and chemical composition of the sediments and their pore waters

Distribution of heavy metals in sediments of Dobczyce reservoir

Osady denne stanowią istotny składnik środowiska wodnego, akumulując składniki mineralne, w tym metale ciężkie. Zbiornik Dobczycki, będąc rezerwuarem wody pitnej dla aglomeracji krakowskiej, spełnia bardzo ważną funkcję gospodarczą. W badaniach osadów dennych Zbiornika Dobczyckiego wykonano analizę wierzchniej ich warstwy w 17 punktach pomiarowych. Pozwoliło to na opisanie dystrybucji metali w czaszy zbiornika oraz ocenę czynników warunkujących tę dystrybucję. Analizę wykonano dwoma metodami: metodą atomowej spektrometrii absorpcyjnej oraz metodą PIXE. Stwierdzono, z wykorzystaniem narzędzi statystycznych, że ze względu na stężenie metali, punkty poboru próbek można podzielić na dwie grupy: leżące poza dawnym nurtem rzeki Raby (niższe stężenia metali ciężkich) oraz usytuowane w dawnym nurcie rzeki (wyższe stężenia). Odpowiada to zmieniającym się właściwościom sorpcyjnym osadów, zależnym m.in. od uziarnienia, składu chemicznego i mineralnego oraz zawartości materii organicznej. Zastosowanie metody PIXE umożliwiło wykonanie wielopierwiastkowej analizy składu bez wstępnej procedury przygotowania próbek, z wystarczającą czułością oznaczeń, lecz mniejszą precyzją niż metoda ASA. Metody te mogą być komplementarne z punktu widzenia potrzeb analiz środowiskowych.Sediments constitute important part of water systems, accumulating mineral compounds, such as heavy metals. Dobczyce Reservoir, being the main drinking water source for the city of Krakow, is important from the economical point of view. In the present research, analysis of elemental composition of sediment samples (upper 10 cm layer) in 17 sampling points was performed. It enabled us to analyse distribution of analysis of elements in Dobczyce Reservoir and to assess what factors influenced that distribution. The analysis was carried out by means of two instrumental methods, namely PIXE and ASA. Based on the statistical analysis of the results, it was found that all the sampling points could be divided into two groups – one situated out of the Raba river current (characterized by lower concentration of elements) and the other along the river current (higher concentration of elements). Such a division results from the differences in chemical and mineralogical composition of sediments as well as from their organic matter content and physical properties. The use of PIXE method makes it possible to analyze sediments in a multielemental mode without sample pretreatment, obtaining satisfactory sensitivity but less precision than with the use of AAS method. Both methods could be considered as complementary in environmental analysis