## 3 Results and Discussion
### Ecological Conditions of the Caspian Sea
#### 3.3.3.1 Pesticide Contamination
In contrast to these species, the _Rutilus rutilus_ accumulates HCH in a higher concentration up to 371-424 ug/kg, with 100% occurrence in all samples taken. In _Acipenseridae_ and _Clupeidae_ fish species, the maximum accumulation of hexachloro-cyclohexane was found in the desalinated pre-estuary zone of the Volga River, and the maximum for _Rutilus rutilus_ was recorded in the northern coast and in the pre-estuary space of the Ural River (Figure 17). In 20% of the analyzed _Rutilus rutilus_ HCH was found above the normative level. DDT metabolites accumulate in fish at a higher level than HCH, with the exception of _Rutilus rutilus_. The maximum permissible level (MPL) is not a biological, but a sanitary norm established for limiting and evaluating the nutritional qualities of fish products. According to [53], the presence of these toxic compounds in reservoirs that are genetically uncharacteristic of the composition of natural waters can have a harmful effect both on hydrobionts and on human health. The above mentioned data demonstrates that the sections of the strongest water pollution by various toxicants and their maximum accumulation in the muscles of ichthyofauna are almost identical. Against the background of the above mentioned results on the accumulation of petroleum products, metals and pesticides in the organs and tissues of fish, a general pattern was observed: a higher concentration of metals, pesticides and other toxicants occurs in the liver in internal fat and sexual products of fish than in muscle tissue [63,64]. This is also confirmed by studies [65,66], according to which the most common forms of polychlorinated biphenyls (Arochlor 1254) in the ecosystem of the gulf of Escambia (Florida) are distributed as follows: in water-up to 1 mg/L, in fish muscles--4.5 mg/kg, in fish liver--76-184 mg/kg. In the literature, there is a huge number of research work related to the description of the accumulating ability and stability of hydrobionts in relation to heavy metals [11,12,67]. Figure 17: Organochlorine pesticides (DDT and HCCH) in muscular of _Acipenseridae_ and _Rutilus rutilus_ fish breeds. At the same time, the authors note that the level of bioaccumulation of heavy metals by hydrobionts is due to a variety of environmental factors affecting it [67]. Particular attention is paid to the issues of biological availability of certain heavy metals, taking into account the environmental conditions, as well as the characteristics of a particular reservoir [13; 14; 68]. According to the research of [PERSON] et al. [69], done in 2000-2005, the metal content in the liver of _Sander lucioperca_ from the Azov Sea was higher than in the muscles for zinc by 2.5 times for males and 2.0 times for females, for copper by 3.1 and 4.6 times, respectively, for cadmium 2.0 and 12 times. In contrast to these elements, the concentration of lead was often higher in the muscle tissue of the studied fish than in their liver. According to a number of other authors, copper, zinc and cadmium ions enter the body of fish mainly with food [70], but in conditions of a lack of trace elements in food and a high concentration of heavy metal in water, the arrival of water also plays a significant role [71; 72]. In general, a similar result was founded by [PERSON] and co-authors [73], noting that metals and other toxicants enter the fish body directly from water in the process of biosorption through the gills and skin-parenteral nutrition, and as part of food through the food tract-oral alimentation. The high concentrations of cadmium and zinc in the fish are in values higher than their MPL, according to a number of scientists [70; 74] is explained by their presence in the cells of other aquatic organisms that form the basis of the food chain for these species. In the scientific literature, there is also information that inorganic complexes or free ions have a high penetrating power in the fish body [75; 76].