## 3 Results and Discussion
### Assessment of the PCB Concentration in the Water of Lake Baikal
#### 3.3.3 Analysis of Correlations
Rows and columns in the heatmaps cluster by the proximity of the spectra of the correlation coefficients. Insignificant values of the correlation coefficients are replaced with zero values; dI-PCBs are marked in green. The division of the investigated congeners in C. _migratorius_ into three groups was likely related to the mechanisms of their accumulation and metabolism in fish bodies. Some indicator congeners of PCBs had a wide range of hydrophobicity properties (log K\({}_{\rm{ow}}\) = 5.67-7.36 [67]), and the level of their accumulation in the tissues of fish corresponded to their hydrophobicity. For this reason, congeners 28 and 52 predominated in the water, having the minimum log K\({}_{\rm{ow}}\) values among indicator congeners. The concentrations of congeners with the maximum numbers of chlorine atoms in the structure increased with the age of individuals. Consequently, the ratio of congeners in fish tissues did not reflect their ratio in water samples. The change in the ratio of congeners in fish tissues was likely owing to not only hydrophobicity of chlorobiphenyls but also to the faster metabolism of congeners with a low degree of chlorination [68]. It was also due to the barriers that occurred during their passage through lipid membranes of cells and (or) to the adsorption caused by the low water solubility [69; 70]. Analysis of the relationship between the levels of PCB concentrations in Baikal water and the tissues of C. _migratorius_ averaged over years using the Mantel test (Figure 6a) revealed the low and insignificant (\(p>0.05\)) Spearman correlation coefficient. This indicated that the change in the concentrations of PCBs in Baikal water did not lead to similar changes in the level of the PCB concentrations in the tissues of C. _migratorius_. The relationship between average annual concentrations of PCBs in the water and their accumulation in the tissues of C. _migratorius_ was not statistically confirmed. Pairwise correlation analysis between average annual concentrations of PCBs in Baikal water and C. _migratorius_ (Figure 6b) also did not revealed significant correlations. All pairwise correlation coefficients between the concentration of the investigated PCB congeners in the water and their accumulation in C. _migratorius_ did not significantly differ from zero (\(p>0.05\)), confirming the conclusions of the Mantel test. For the Mantel test and correlation analysis between the pairs of dependent and insignificant variables, we took the same-year data on both the water and C. _migratorius_. Perhaps, due to this fact, there was no relationship between the concentrations of PCBs in the water and their accumulation in the tissues of C. _migratorius_. Omuul accumulates PCBs gradually during several years, and not only the current concentration of PCBs but also the impact of PCBs in previous years determines the concentrations of the investigated congeners in the tissues of C. _migratorius_. Identification of this relationship requires long series of observations (ten years or more), taking into account other factors that are difficult to consider. These factors affect the processes of PCB accumulation in omul during the observation period, particularly, the change in the qualitative composition of dominant phytoplankton and zooplankton species that are part of C. _migratorius_ food web. They also lead to interannual changes in temperature and ice regimes of the lake, which change the speed and direction of migrations and feeding behaviour in fish. Moreover, various factors also affect the qualitative composition of PCB congeners in the water of the lake: PCB sources (local and long-range atmospheric transport), hydrophobicity and water solubility of PCBs, their sorption on particles of the solid phase of the water column, and transition to the bottom sediments.