Total and exchangeable concentrations of heavy metals in soils near Bytom,an area of Pb/Zn mining and smelting in Upper Silesia, Poland

High concentrations of several heavy metals were suspected in soils in an a rea of some contemporary and extensive historical mining and smelting of Pb and Zn near the town of Bytom. In order to investigate the spatial distrib ution of heavy metals, 152 soil samples were taken at hi,oh sampling densit y in an area of 14 km(2) on a regular grid as well as along an 11 km transe ct. The samples were analysed for total Pb, Zn and Cd content by ICP-AES; a selection of samples were also analysed for total As content. Significant levers of contamination were found. Median topsoil concentratio ns (0-10 cm) for Pb, Cd, Zn;and As were 430 mu g g(-1), 13 mu g g(-1), 1245 mu g g(-1) and 35 mu g g(-1), respectively. The detected levels of Pb, Zn and Cd were mostly in reasonable agreement with findings from a previous lo w-density study, but As concentrations were up to 6 times higher than had p reviously been reported for the area. Additional zones of particularly high concentrations could be identified for all 4 elements by this higher-densi ty survey. Contaminant concentrations were generally found to decrease subs tantially with increasing depth, on average by a factor of 3.5 for Cd, 3.0 for Zn and 2.6 for Pb. However, significant subsoil contamination (40-50 cm ) was also detected, in particular for Zn, Pb and As, which appeared to be enriched at depth in certain locations. To assess the potential availability of the metals to plants, the exchangea ble fraction (0.5 M MgCl2) was estimated for Pb, Zn and Cd for 84 samples. Levels were strongly influenced by soil pH and were generally low for Pb (l ess than 1% of total, max 15.6%), moderate for Zn (less than 10% of total, max 32.4%), and high for Cd (mean 35% of total, max 59.8%). For Zn and Pb, there seemed to be a threshold pH value of about 6, below which a significa nt increase in the exchangeable fraction was observed. No such threshold va lue appeared to exist for Cd, which was found to be relatively labile even in slightly alkaline soils (mean of 27.6% exchangeable Cd in pH range 7-8). The detected levers of total metal contamination exceed various national an d international thresholds, indicating the need for further investigation a nd an assessment of the suitability of the land for agricultural use, parti cularly in view of the high levels of exchangeable Cd. The pattern of spati al variation of the metals in the topsoil indicates that a variety of sourc es might be responsible for the contamination, historical mining and smelti ng probably being the most important. (C) 1999 Elsevier Science Ltd. All ri ghts reserved.