## 3 Results and Discussion
### Assessment of the PCB Concentration in the Water of Lake Baikal
#### 3.3.3 Analysis of Correlations  
The heatmap in Figure 5a shows an analysis of correlations between the concentrations of various PCB congeners and the \(\Sigma_{7}\)PCB concentrations in Baikal water. Between all concentrations of PCBs and \(\Sigma_{7}\)PCBs, there were significant positive (\(p<0.05\)) pairwise correlations with correlation coefficients ranging from 0.6 to 0.9. Among all correlation clusters, a group of indicators stood out, including the concentrations of congeners 52, 101, and 153, dl-congener 118 and \(\Sigma_{7}\)PCBs in the water with a high pairwise correlation (correlation coefficient from 0.85 to 0.98). Additionally, there was the correlation group of congeners 138 and 180. The correlation coefficients of the concentrations of these congeners with each other, with the concentrations of other congeners, and with \(\Sigma_{7}\)PCBs had lower values (from 0.75 to 0.85). The concentration of congener 28 was distinguished by the minimum correlation coefficient with the concentration of congener 180 (0.6). The results of the correlation analysis of the indicator PCBs in Baikal water indicated a strong agreement in the change in the concentrations of chlorobiphenyls (28, 52, 101, and 118) with each other and with the concentration of \(\Sigma_{7}\)PCBs. An increase or a decrease in the concentrations of one of these congeners was accompanied by an increase or a decrease in the concentrations of all congeners from the abovementioned group. The concentrations of congeners 138 and 180 were less correlated with the concentrations of other PCBs. Obviously, various factors determined the qualitative composition of PCB congeners in Baikal water: PCB sources (local and long-range atmospheric transport), water solubility and hydrophobicity, sorption on the particles of the solid phase of the water column, and transition to the bottom sediments. PCBs identified in the tissues of _C. migratorius_ were characterised by more complicated pairwise correlations between the concentrations of different congeners compared to the results of the corresponding analysis of PCBs in Baikal water (Figure 5b). Positive values of the correlation coefficients above 0.5 (\(p<0.05\)) were classified as significant. Based on the range of pairwise correlation coefficients and the clusterisation results, all PCB congeners were divided into three groups. The first group included the concentrations of congeners 153, 180, 101, and 118 together with the concentration of \(\Sigma_{7}\)PCBs. In this group, the concentrations of the components were positively correlated with each other and with the rest of the PCB congeners. The second group included congener 138 and dl-congeners 105, 123, and 156. The concentrations of congeners from this group were associated by high correlations with each other (r > 0.7) and a small correlation with congeners from the first group (0.3 < r < 0.6). There was no significant correlation between the concentrations of congeners from the second group and congeners 28 and 52, and dl-congeners 114 and 126. The third group included congeners 114 and 126 and dl-congeners 114 and 126 that had high correlations with each other (r > 0.7) and weak correlations with congeners from the first group (0.3 < r < 0.6). There was no significant correlation between the concentrations of congeners from the third and the second groups. The ages of the _C. migratorius_ individuals were significantly correlated with the concentrations of congeners 138, 101, and 153 and dl-congeners 123, 105, and 118. At the same time, the correlation coefficients were relatively small, from 0.3 to 0.5. Figure 5: Heatmaps reflecting the calculations of pairwise correlation coefficients (a) between the concentrations of indicator congeners and \(\Sigma_{p}\) PCBs in Balkal water samples and (b) between the concentrations of indicator congeners and \(\Sigma_{p}\) PCBs in the tissues of \(C\). _migraturals_ and the age of the investigated Omul individuals from Lake Balkal.