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VITEK, T., HEDBAVNÝ, J., MARES, J., SPURNÝ, P.: Trace metal contamination of the Dyje River stretch between Znojmo and Nove Mlýny, Czech Republic. Acta univ. agric. et silvic. Mendel. Brun., 2012, LX, No. 3, pp. 217–224 The analyses of seven trace metals (Hg, Zn, Ni, Cr, Cu, Pb, Cd) in the water, bottom sediments, macroinvertebrates and fi sh tissues were conducted at two localities on the Dyje River, Czech Republic, at diff erent distances downstream from the Znojmo Reservoir (at 12 and 31 km) to evaluate a contamination level. The maximum admissible limits were exceeded in Hg in the water and in the case of Ni in bottom sediments at both localities and also in Hg in zoobenthos sample at locality further from the reservoir. In regard to trace metal contamination of fi sh tissues, it was found that safe limits for mercury, cadmium and lead were not exceeded. Mercury and cadmium contents have declined markedly since the 1990s, but the amount of lead has increased. Human consumption of fi sh caught in the Dyje River is most limited by concentration of Hg in the fi sh muscle. The maximum tolerated intake was set as high as 3.80 kg per week. water quality, sediments, mercury, cadmium, lead, chub (Squalius cephalus), fi sh consumption The substances of high chemical stability tend to accumulation in the ecosystem and help to make it ecologically instable. Trace metals most o en do not have primary lethal eff ect on hydrobionts, but they cause a long-term environmental chronic stress. The bioaccumulation in food webs cause negative impacts especially on top predators of the ecosystem, which are in the case of river ecosystems a predaceous fi sh species and a piscivorous birds and mammals including human (Houserova et al., 2005; Houserova et al., 2007). The sources of trace metals are most o en the waste waters from industry (mining, paper-mills, metallurgy, chemical plants) and agriculture (fungicides). In polluted areas trace metals are stored in the sediments, from which they are released to the water (Zhou et al., 2008). In the case of fragmented rivers, trace metals are settled and fi xed in the reservoir sediment (Kulahci & Dogru, 2006; Ozdemir et al., 2010); thus the water environment in the river below the dam might be less contaminated and the health hazard for top predators connected with the bioaccumulation of such substances might be reduced (Makovský et al., 2010). The store function of the sediment depends upon the physico-chemical stability of the water. Changes in such parameters, namely pH, o en cause the release of trace elements (Simpson et al., 2010) and their transportation to the biota through the biofi lm (Farag et al., 2007). Among fi shes, chub Squalius cephalus (L.) belongs to the most studied species due to its broad occurrence in various ichthyocenoses in a broad range of environmental conditions (Spurný et al., 2002, 2009; Kružikova et al., 2009). In the point of view of human health risk, the mercury and its species, which is detected in higher amounts especially in the fi sh muscle, represents the most danger (Houserova et al., 2006; Havelkova et al., 2008). In the past, the Dyje River was a signifi cantly contaminated stream in the Czech Republic, especially contaminated by mercury and cadmium (Spurný & Mares, 1995; Spurný et al., 1997). 218 T. Vitek, J. Hedbavný, J. Mares, P. Spurný The main aims of this study were 1) to determine the present state of trace metal contamination of the Dyje River stretch between reservoirs Znojmo and Nove Mlýny 2) to evaluate changes in trace metal contamination of fi sh fauna in the above-mentioned stretch by comparing the recent situation from 2008 with the situation from the 1990s and 3) to evaluate the risk of human consumption of fi sh from the Dyje River. MATERIALS AND METHODS

Trace metal contamination of the Dyje River stretch between Znojmo and Nové Mlýny, Czech Republic