# Organochlorines Accumulation in Caged Mussels
## 4 Discussion
### OC Accumulation in Relation to Biological Parameters  
The accumulation of OCs in mussels depends on the complex interaction between the environment and the organism. Physiological parameters such as size, age, and lipid content and its composition may influence contaminant accumulation in mussels [10; 13; 14; 15; 16; 17; 18], while the contaminant content in soft mussel tissue depends, to a large extent, on their concentration in the water [15; 18]. Pearson analysis (Table 2) confirmed that accumulation of OCs in mussels decreases with age by revealing a relationship between the age of the mussels and OCPs, \(p\),\(p^{\prime}\)-DDTs, and PCBs, as well as ANOVA analysis (Table 1) showing significant differences in tissue levels of \(p\),\(p^{\prime}\)-DDTs (p = 0.039 *) and PCBs (p = 0.037 *) between 1- and 2-year-old mussels, except for OCPs levels (p = 0.085). Somatic growth (CI) increased 1.85- and 1.56-fold, respectively, in 1- and 2-year-old mussels transplanted to Kastela Bay, and 1.07- and 1.11-fold in Mali Ston Bay, respectively (Figure 2). Pearson analysis also showed a relationship between CI and OC content in 1-year-old (1-ym) and 2-year-old (2-ym) mussels, with values of OCPs: r1-ym = 0.159 and r2-ym= 0.119; \(p\),\(p^{\prime}\)-DDTs: r1-ym = 0.127 and r2-ym = 0.048; PCBs: r1-ym= 0.198 and r2-ym = 0.214 (Table 2). It is quite certain that the main reason for contaminants decreasing with mussel age is related to the metabolism and physiology of the mussels [13; 14; 15]. Since large and aged mussels tended to pump less water through their body per body unit, the intake of contaminants is lower than in smaller species, due to their faster growth rate. Respiration rate and other physiological parameters (ingesion rate, filtration rate, excretion rate, and others) depend strongly on body size [22; 26]. Results in this study are in accordance with the results from other studies investigating the effect of age (body size) on the accumulation of organic lipophilic compounds in mussels [13; 14; 15]. Contrarily, the increase of PCB content in mussels with increased body size was reported by [PERSON] et al. [29] in bivalve _Scrobiscularis plana_ and [PERSON] et al. [30] in _Dreissena polymorpha_ and _D. bugensis_. Variations of PCB content in mussels are often explained by differences in lipid content [12; 30; 31]. Lipids in mussels are the primary sites where chlorinated hydrocarbons are stored. Seasonal changes in OC content in mussel tissues are considered to be attributed to specific metabolic processes of storingand mobilizing lipid reserves during the reproductive cycle (gametogenesis, spawning, and dormancy) and changes in the mass of total tissue and organs during the reproductive cycle [32]. In our experiment, the statistical analysis did not generally confirm the significant influence of lipid content on the accumulation of OCs in mussel tissue because mussels of the same size and age were selected. The significant influence of lipids on OCs accumulation was observed for 2-year-old mussels (p < 0.05; OCs: r = 0.449 *; _p,p'_-DDTs: r = 0.492 *) but not for PCBs (r = 0.331). For 1-year-old mussels, the relation was rather small (r = \(-\)0.065). Lipid content in tissues of 1-year-old mussels during bimonthly exposures increased 1.33-fold, while in 2-year-old mussels, it increased 1.23-fold (Kastela Bay). In Mali Ston Bay, lipid content increased 1.01-fold and 1.14-fold in 1- and 2-year-old mussels, respectively (Figure 2). Many environmental parameters may affect the feeding activity of the mussels and their physiology, such as climate change factors (salinity, pH, temperature) [24; 33], fluctuations in phytoplankton, algal, and chlorophyll concentration, and phytoplankton species [11; 34]. Mussels from the S1 are the best fed because S1 is located at the shallowwest part of Kastela Bay, where the availability of suspended matter rich in organic content is the highest.