Purpose Cadmium (Cd) is considered a toxic element and its concentrations are relevant to human health and the environment. Therefore, the purpose of the study was to determine the extent to which the bottom sediments of water bodies (artificial lakes and ponds) in the Silesian Upland in southern Poland are contaminated with Cd; an attempt was also made to determine the factors that condition spatial differences in the concentration of this element between individual water bodies in the region. Materials and methods Measurements of the Cd content in bottom sediments were carried out in 35 water bodies in southern Poland in 2011 and 2012. Depending on the surface area and morphometric characteristics, from two to nine samples representative in terms of sediment thickness were collected in each water body. Cadmium concentrations were determined for 92 0.25 g aliquots using the TD-ICP method. Results and discussion Cadmium content in all samples (0.7–580.0 mg kg⁻¹) was higher than the natural range of concentrations for this element in the Earth’s crust (0.1–0.3 mg kg⁻¹) and the geochemical background for Poland (0.5 mg kg⁻¹) and, with a few exceptions, was also higher than the preindustrial concentration (1.0 mg kg⁻¹) and the regional geochemical background (2.5 mg kg⁻¹). Adopting natural Cd concentrations in the Earth’s crust (0.1–0.3 mg kg⁻¹) as the baseline for the geoaccumulation index (I_geo), the sediments examined can be classified as extremely and heavily contaminated (and moderately contaminated in a small number of cases). The assessment of sediment quality based on I_geo, with the regional geochemical background (2.5 mg kg⁻¹) adopted as the baseline, results in non-contaminated and moderately contaminated sediments being dominant with a far smaller number of heavily and extremely contaminated ones. Conclusions In the case of several water bodies, Cd concentrations were at record levels that have not been found anywhere else in the world. On the basis of the I_geo, sediments of varying quality were found—from virtually uncontaminated to extremely contaminated. The I_geo index as an indicator of the quality of bottom sediments is a measure that requires careful interpretation, especially when different concentration levels regarded as natural are used for determining its value.

The paper presents the results of studies of bottom sediments taken from the southern part of the Bratsk Reservoir. The following analyses have been conducted: trace element analysis, particle-size analysis as well as chemical analysis of water, hydrochloric acid and alkaline extracts for 18 samples of the bottom sediments. The granulometric analysis has identified the predominance of fine silt and silty-clayed sediments. The data on the content of trace elements in the bottom sediments of the Bratsk Reservoir is presented in comparison with their content in the natural environment of the Baikal region; the anomaly ratio was used to characterize the excess for trace elements. The chemical analysis of extracts has showed “saline contamination” of mud (silt), high concentration of carbonates in it, as well as the presence of mobile (free) forms of aluminum oxide. In this research, an attempt was made by using a correlation analysis to evaluate the impact of various physical and chemical characteristics of the bottom sediments, such as the content of clay fraction, organic carbon, carbonates, and water-soluble salts on the accumulation of trace elements.

An assessment was carried out of the anthropogenic enrichment of the chemical composition of the bottom sediments of water bodies situated in an area with an urban and industrial character (63.7% of the total area). The endorheic catchments of the water bodies studied are lithologically uniform with sandy formations accounting for more than 90% of the surface area. On the basis of geoaccumulation index values, it was found that the bottom sediments of the water bodies studied were contaminated with the following elements: Cd, Zn, S, As, Pb, Sr, Co, Cr, Cu, Ba, Ni, V, Be, in degrees ranging from moderate to extreme, with lower contamination (or absence of contamination) with the same elements being found in the formations present in the vicinity and in the substrate of the basins of water bodies. It was found that one consequence of the fact that these water bodies are located in urban and industrial areas is that there is anthropogenic enrichment of the chemical composition of bottom sediments with certain basic components (organic matter, Mn, Ca and P compounds) and trace elements: Cd, Zn, Pb, Sb, As, Cu and Co, Br, Ni, S, Be, Cs, Sr, V, Cr, Sc, Ba, U, Ce, Eu and Th, with virtually no enrichment of sediments with the other basic and trace components analysed (La, Rb, K₂O, Nd, Sm, Na₂O, Hf, SiO₂, Zr).

The chemical composition of the bottom sediment, and more particularly the heavy metals content, reflects human developments and impacts on the catchment and reservoir's natural environment. The bottom sediments of the reservoir retained by the Irkutsk Dam have been analysed. The reservoir is mainly supplied by water from Lake Baikal. The following amounts of heavy metals have been found in the sediment samples analysed: cadmium - below detection threshold (<0.5 ppm), cobalt - from 16 ppm to 23 ppm, chromium - from 104 ppm to 243 ppm, copper - from 21 ppm to 35 ppm, mercury - below detection threshold (<1 ppm), molybdenum - below detection threshold (<2 ppm), nickel - from 44 ppm to 80 ppm, lead - from 13 ppm to 17 ppm and zinc - from 73 ppm to 98 ppm. Cobalt, chromium and nickel contents exceeded the natural geochemical background level. This may indicates anthropogenic impacts on the reservoir's geosystem.