## 3 Results and Discussion  
### Heavy Metal Contamination in River Water and Sediments  
One of the priority contaminants of the Ural River are heavy metals. According to registered data [22; 23], the river water within the territory of Kazakhstan contains on average: copper-up to 18 \(\upmu\)g/L (18 MPC), zinc--35 \(\upmu\)g/L (3.5 MPC), lead and cobalt--40 \(\upmu\)g/L (4 MPC), nickel--80 \(\upmu\)g/L (8 MPC) and chromium--60 \(\upmu\)g/L (3 MPC) in comparison with the standards for fishery reservoirs [c.f. Table 1].  
Numerous objects of mining and metallurgical industry are the determining factors of the technogenic transformation of the chemical composition of river water in the upper reaches of the Ural River within the territory of the Russian Federation for 50-60 years or more [19; 24]. Long-term industrial development, emissions and accordingly mineral deposits in the Southern Trans-Ural are reasons for the formation of an increased background content of heavy metal ions and many other contaminants. All this, according to authors opinions, led to a significant weakening of such stability parameters (surge capacity) of river systems like deterioration of the drinking water quality, of the biodiversity conditions and of the sturgeon fish species reproduction.  
The largest contamination is caused by the Magnitogorsk Metallurgical Plant, Burbiaevsk, Gaisk, Uchalinsk Mining-and-Processing Integrated Works, Sibaysk and Bashkirsk copper and sulfur plants, Orsk oil refinery, South Ural nickel plant, Orsk-Khalilovsk metal-lurgical plant, Orenburg oil refinery, etc. [19; 24]. From Magnitogorsk to Orsk, the authors determined the presence of 20 major contamination sources of surface waters. These sources are responsible for the high contamination level of the Ural River and its tributaries. Among them heavy metals, especially very high iron, zinc and copper concentrations are wide spread, and constantly exceed the level of fisheries MPC. Also the waters of some Ural River tributaries can be characterized by high and extremely high levels of these metals.  
Studies [25] have shown that the level of heavy metal accumulation in the bottom sediments of the Ural River is characterized by the following data: the concentration of gross forms of iron exceeds the MPC (25000 mg/kg) at all sampling points by 1.6 to 2.4 times, the content of manganese showed an excess of the MPC (1500 mg/kg) in the Spasskiy village to 1.4 MPC, in the village Primorskiy and in the Magnitogorsk water reservoir--1.2 MPC.  
The cadmium concentration of in the river sediments varied from 0.7 to 1.75 mg/kg, which is 1.2 times higher than the permissible norms (1.5 mg/kg). The level of lead varied from 8.8 to 152.5 mg/kg, i.e., the maximum permissible concentration (32 mg/kg) was 4.8 times higher.  
Consequently, bottom sediments are powerful sources of secondary contamination of river water with these toxic compounds. It was found [32] that as a result of sewage emissions from the Orsk oil refinery almost all benthic groups and macrophytes sensitive to environmental conditions were killed in the Ural River at a site 15 km below the sewage discharge. The concentration of petroleum products in the floodplain soils reached 21.3 mg/kg, in some places--152 mg/kg.