## 3 Results and Discussion
### Ecological Conditions of the Caspian Sea
#### 3.3.2 Heavy Metal Contamination  
Studies conducted in 2003-2005 and 2008-2010 showed the presence of a range of heavy metals such as copper, zinc, nickel, etc. in the Caspian Sea water, their concentrations exceeding the regulatory limits [56; 57]. The concentration and distribution of metals in the area of the Ural River inflow are characterized by a high variability from year to year. During spring 2005, the content of Cu, Ni, Co, Cd, and Cr decreased in comparison with 2003. The other elements increased slightly (Figure 10). The inter-annual and seasonal differences of metal concentrations in the Caspian Sea water are a result of different ratios of fresh river water and both brakish and salty lake water at sampling points, which in turn depends on both wind direction and river flow, and the sedimentation of river sediments in this transition zone. The concentration of heavy metals in the water of this zone, except cadmium, exceeds the MPC level. The Casian Sea water east from Ural River mouth in 2003-2005 was characterized by higher metal concentrations in comparison with the transition zone between the Volga River and the Ural River. The deep water zone in the South-East of the pre-estuary coast of the Ural River, was characterized by increased metal concentrations during the same time. Our own studies in 2007, covering the southern coast of the eastern part of the Northern Caspian Sea and the eastern coast of the Middle Caspian Sea, showed significant increase of copper concentrations in the water in the direction to Cape Sarzha up to 14.2 ug/L, i.e., 2.8 MPC for Caspian Sea water (c.f. Table 1). Figure 9: Petroleum hydrocarbon concentrations in the muscular of _Acipenseridae_ and _Clupeidae_ fish species in the north-eastern section of Caspian Sea. More detailed information on the distribution of heavy metals across the entire water area of the Kazakh sector of the Caspian Sea was obtained in 2008-2010. The analytical material is presented in Table 2. The data indicate a large concentration variability of the analyzed metals in the space-time relation. Figure 11 shows the average concentrations of the most priority metals in the water of certain regions of the Kazakh sector of the northern Caspian Sea in 2008-2010. The spatial distribution of heavy metals in the water over the entire area of the northeastern Caspian Sea for the remaining seasons is more clearly shown in Figure 12[51, 57]. The illustrations above show first of all a significant difference in the concentration and distribution of metals by seasons. For zinc, copper and lead, the maximum concentrations and their wider distribution over the considered Caspian Sea area were registered in spring time. Zinc concentrations above the fishery MPC (50 \(\upmu\)g/L) have been measured at almost all sampling points during the same season in 2010, while they exceed the MPC in autumn, detected only at three points located in the influence zone of the Volga River flow. \begin{table}
\begin{tabular}{c c c c c} \hline
**Sampling Time** & **Cu** & **Zn** & **Pb** & **Cd** \\ \hline
2008, August & 22 & 34 & 3.5 & 4.7 \\ \hline
2009, May & 20 & 25 & 31 & 6.1 \\ \hline
2009, August & 29 & 28 & 28 & 5,6 \\ \hline
2010, May & 33 & 66 & 5.3 & 2.9 \\ \hline
2010, August & 23 & 37 & 3.2 & 4.5 \\ \hline MPC & 5 & 50 & 10 & 10 \\ \hline \end{tabular}
\end{table} 
Table 2: Average heavy metal concentrations in water of the Kazakh sector of the Caspian Sea, in \(\upmu\)g/L. Figure 10: Average heavy metal concentrations in water of the pre-estuary coast of the Ural River. Figure 11: Average heavy metal concentrations in water of certain areas of the north-eastern Caspian Sea. Figure 12: Cont. Although the content of lead in the Caspian Sea water did not exceed the MPC (10 \(\upmu\)g/L), its elevated concentrations from 7.5 to 9.2 \(\upmu\)g/L were more widespread in the studied part of the Caspian Sea during spring.