Biogeochemical monitoring of composition of chemical elements in Caspian Sea

The aim of the research was to conduct biogeochemical monitoring of heavy metals composition in the ecosystem of the northwestern part of the Caspian Sea. The objects of the research were the water of the northwestern part of the Caspian Sea, bottom sediments, different types of crustaceans, mollusks, fish, as well as the Caspian seal. As a result of the research, metal concentrating aquatic organisms in the Caspian Sea were identified. Thus, gammarus accumulates Zn, shrimp – Cu, crab – Pb and Ni, balanus – Hg, Pb, Cd; mollusk Didacna accumulates mainly Zn, Cd, and Hg; mytilaster – Cu, Co; cerastoderma – Pb; vobla – Zn and Hg; benthophilus - Pb and Mn; needlefish – Cu, Pb, Cd, and sprat – Zn and Hg. Specific features of metal accumulation by hydrobionts have been found out: Zn, Pb and Cd are accumulated mainly by invertebrates; Cu, Co, Mn are accumulated to the greatest extent by representatives of Crustacea; Ni – by Mollusca species; Hg is accumulated to the greatest extent by vertebrates. There have been revealed the regularities in distribution of chemical elements concentrations in the organs and tissues of aquatic organisms occupying the tops of the trophic pyramids: Zn, Cu, Hg are predominantly accumulated in the liver, Co, Ni, Zn, Pb and Cd are accumulated in the kidneys, Pb, Co, Mn are accumulated in the gills, Hg – in muscle tissues. In Phoca caspica Pb accumulates in the adipose tissue and lungs, Hg, Cu, Zn, Mn, Cr, and Co – in the liver, and Pb, Cd and Ni – in the kidneys. Taking into account the calculated coefficients of chemical elements accumulation, it was inferred that Hg and Zn can accumulate in almost all links of the trophic chain; Cu, Co, Ni, Cd, Pb are accumulated mainly by invertebrates; Cr and Mn accumulate to a greater extent in bottom sediments.