## 3 Results and Discussion
### Assessment of the PCB Concentration in the Water of Lake Baikal
#### 3.3.2 Statistical Analysis of Biomonitoring Results  
Based on the PERMANOVA data (Table S7), among all studied factors, the year and month of sampling and the age of individuals (year factor--R\({}^{2}\) = 0.193; month factor--R\({}^{2}\) = 0.107; age factor--R\({}^{2}\) = 0.075; \(p\)-value \(<\) 0.05) significantly influenced the concentrations of PCBs in the muscle tissue of _C. migratorius_. The R\({}^{2}\) covariation coefficients indicated that the year of sampling was the main factor of influence followed by the less significant month of sampling and the age of fish (Figure 4b). As the sex of the _C. migratorius_ individuals was not a critical factor (R\({}^{2}\) = 0.002), PCA for _C. migratorius_ was based on the sex-averaged data. PCA of the concentrations of PCB congeners in _C. migratorius_ distinguished three groups of averaged data (Figure 4b). The first group is located in the upper part of the coordinate plane at the border of the first and second quarters and included the data on _C. migratorius_ caught in February 2016 and March 2018 and 2020. The age of the individuals in this group ranged from five to eight years. All fish from this group were characterised by high dl-PCB concentrations ranging from 1.0 to 2.2 ng/g (ww), whose proportion in \(\Sigma_{7}\)PCBs reached 33%, and by relatively low total concentrations of congeners 28 and 52, ranging from 1.1 to 2.6 ng/g (ww). Notably, this group of the _C. migratorius_ fish was caught in the spring during the freezing period on the lake after the winter lifecycle with the corresponding feeding structure [66]. The second group of data located at the border of the first and fourth quarters of the coordinate plane included the results of the determination of PCB concentrations in _C. migratorius_ that were caught at the end of the feeding period in August and September of 2016, 2017, 2018, and 2019. In this group of specimens, the concentration of PCBs was in the \(\Sigma_{7}\)PCB range from 5.2 to 6.8 ng/g (ww) with the concentrations of \(\Sigma_{\rm dl}\)PCBs ranging from 0.7 to 1.2 ng/g (ww). The age of the individuals was from four to seven years and predominated by five-year-olds. The group of points in the fourth coordinate plane includes the data on the _C. migratorius_ specimens that differed in high concentrations of 'light' congeners 28 and 52, with up to 33% of the \(\Sigma_{7}\)PCB concentration. In the third quarter of the coordinate plane, there was the third group of the data on _C. migratorius_ caught in March and August 2014 and September 2018. The presence of PCBs in this group was characterised by the maximum concentrations of \(\Sigma_{7}\)PCBs ranging from 6.8 to 8.7 ng/g (ww) with the dominance of congeners 28 and 52 in the total proportion, with 50% of \(\Sigma_{7}\)PCBs. Individual points in this part of the coordinate plane characterised the _C. migratorius_ individuals caught from March to August 2014 and in September 2017. PCBs detected in these fish specimens had high concentrations of \(\Sigma_{7}\)PCBs, from 10 to 13 ng/g (ww). Noteworthy was the result of the determination of PCBs in an eight-year-old _C. migratorius_ individual. The PCB concentrations in this individual reached extreme values: \(\Sigma_{7}\)PCBs 32 ng/g (ww) and \(\Sigma_{\rm dl}\)PCBs 9.0 ng/g (ww), with minimum total concentrations of 'light' congeners 28 and 52 at less than 7.0% of \(\Sigma_{7}\)PCBs. On the PCA biplot (Figure 4b), the gradient vectors of average data on the PCB concentrations in _C. migratorius_ formed three codirectional groups. The first group included the vectors of indicator congeners 138, 153, and 101, and dl-congeners 126, 118, and 114, together with the vector of the age of individuals. All these characteristics, including the age of individuals, were positively correlated with each other. The second _group_ included the vectors of congeners 28 and 52, whose concentrations were associated with a strong positive correlation with each other and a weaker positive correlation with the vectors of the first group.