Risk element assessment in sediments of the Olše River and its significant tributaries

The main objective of research was to assess the current level of bottom sediment and water pollution of the Olše River and its tributaries. The Olše River is an important stream in the Upper Silesian Basin which was significantly affected by coal mining and industrial activities in the past (Martinec et al. 2006). Monitoring of the area by the Povodí Odry State Enterprise (the Odra River management) has shown that the water quality in the river has significantly improved due to the development of municipal wastewater treatment plants. Currently, saline waters from coal mines in the Karviná sub-basin are considered to be the biggest threat to the river environment. A total of 19 river sediment and 9 surface water samples were collected (Fig. 1). The elemental content was determined using X-ray florescence spectroscopy (XRF); for selected river sediments, the organic carbon content was determined using the Elementar Vario TOC CUBE device. The loading of river sediments by elements was evaluated using Igeo Class. The content of major ions (HCO3–, K+, Ca2+, Na+, Mg2+, SO42– and Cl–) in the surface water samples was determined in the laboratory. The water in the Olše River belongs to the hydrochemical type of Ca-HCO3. The water in the Karvina Creek near the mining works is highly mineralised and represents a single case of the Na-Cl hydrochemical type. Despite the significant mineralisation level, the water from this creek does not significantly affect the quality of the water in the Olše River. The highest enrichment of river sediments compared to the natural background was found for Zn (Table 1) at all sites. Zinc is one of the elements with rather high mobility and tends to be bound to hydrated Fe and Mn oxides that occur in rather large quantities on adjacent spoil heaps in the area and can thus enter the system very quickly. The Mn (340 to 2,553 mg/kg) as well as Sr (71 to 1,836 mg/kg) concentrations are elevated compared to those in global shales (850 mg/kg and 300 mg/kg, respectively; Turekian – Wedepohl 1961). Their contents in the Upper Silesian Coal Basin river sediments should be systematically monitored. The Olše River sediments were slightly to moderately contaminated with Cr and Pb (Table 1). This is not considered to be related to mining but rather to road runoffs and the fact that the river flows through industrial areas.