engleski

Sediment-borne metal content of the overbank fines from the Sava river

Samples of overbank sediments were collected along the main channel of the Sava river. Five sampling sites are situated downstream of the Croatian-Slovenian national border, namely Samoborski Otok and Kušnjačić (gravel- pits, upstream of Zagreb), near SRCE (University Com- puting Center, Zagreb), "Abesinija" (gravel-pit, down-stream of Zagreb) and Hrastelnica (upstream of Sisak), and are located at distances of ca. 100-200 m from the river channel. Vertical sediment sequences were cut to a depth of 2.5 m, 1.8 m, 0.85 m, 1.9 m and 3.2 m respectively. All profiles, except for SRCE, were sampled over 10- to 20-cm intervals ; at the SRCE site three bulk samples were taken down to a depth of 23 cm, 55 cm and 85 cm. The samples were air dried and a minus 0.125 mm fraction was used for geochemical and mineralogical analysis. Mineralogical analysis revealed that the alluvial overbank fines are mainly composed of quartz, calcite, dolomite, muscovite, chlorite and plagioclase. Total element concentrations were analysed by ICP-MS after the four acid digestion while Hg was determined by cold vapour AAS after the aqua regia digestion (ACME laboratories in Vancouver, Canada). 8 major elements (Al, Ca, Fe, K, Mg, Na, Ti, P) and 34 trace elements (Hg, Ag, As, Au, Ba, Be, Bi, Ce, Cd, Co, Cr, Cu, Hf, La, Li, Mn, Mo, Nb, Ni, Pb, Rb, S, Sb, Sc, Sn, Sr, Ta, Th, U, V, W, Y, Zn, Zr) were determined. 40 selected samples were subsequently analysed by LECO IR-212 on organic carbon. Comparison of arithmetic means with means for Slovenian soils showed increased concentrations of several trace elements, most notably for Hg, Pb and Sb. Mercury contents (Arit. mean = 1351.92 ppb, Min = 140 ppb, Max = 6510 ppb) are highest at Samoborski Otok showing slightly to highly increased values throughout the profile (except for 90-100 cm interval). The concentrations are significantly higher in the lower part of the profile, thus being indicative of intensive mining activity in the past, the source of which is somewhere in the Slovenian catchment area (possibly the area around Celje). Further downstream sediments contain less Hg (Max values: 615, 300, 75, 720 ppb). The lower half of the profile Samoborski Otok is enriched in Pb (Max = 225.1 ppm) relative to the upper part as well as to the downstream sediments. Sb-anomaly (12.5 ppm) is present within 30-40 cm interval of the profile Samoborski Otok. Results, with few exceptions though (Hg, Pb), don't show vertically any clear variation in trace element levels in the first two profiles, while distribution of elements in the profile SRCE seems to be influenced by soil forming processes and municipal activities. Overall upper-lower change of heavy metal concentrations within the last two profiles probably relate to the pollution (urban activities and road traffic). Generally speaking, it could be concluded that the results obtained from this study (which is in its early phase) point at the highly contaminated profile Samoborski Otok regarding Hg and slight increases of heavy metals towards the surface of the last two profiles (i.e. "Abesinija" and Hrastelnica).

Sava river alluvium; overbank fines; chemical composition; mineral composition

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