Distribution and contamination pattern of heavy metals from surface sediments in the southern part of Caspian Sea, Iran

This study concentrates on the speciation and distribution patterns of some heavy metals (Pb, Ni, Cd, Zn, and Cu) in surface sediments in the southern part of the Caspian Sea, the biggest lake in the world, to obtain an overall classification for the origins of metals in the area using a sequential extraction technique. At all sampling stations, Pb, Ni, Zn, and Cu were mostly (>50%) accumulated in the resistant fraction, which indicated that there were no significant anthropogenic inputs of Pb, Ni, Zn, and Cu into the surface sediments of the south Caspian Sea. Guilan province on the west coast of Caspian Sea accumulated higher percentages of non-resistant fractions of Pb and Zn, while Mazandaran and Golestan provinces in the middle and western parts of the Caspian Sea, in the Iranian zone, accumulated higher percentages of non-resistant fractions of Ni and Cu. The present study revealed that the coastal area of the south Caspian Sea is still not seriously contaminated. Cadmium in Guilan and Golestan provinces were dominated by non-resistant fractions (55–69%), which indicated more anthropogenic inputs of Cd on the south coast of the Caspian Sea in comparison with other metals.