Distribution pattern of heavy metals in the surficial sediment of Gorgan Bay (South Caspian Sea, Iran)

Abstract

The Gorgan Bay is an important ecosystem receiving discharge from their tributaries. In this study, concentration of Pb, Zn, Ni, Fe, Al, Cu and As was seasonally determined at 22 sampling points during 2012-2013.Sediment samples were collected using a Van Veen grab. The levels of heavy metals were determined by ICP-AES (Inductively Coupled Plasma Atomic Emission Spectrometry) and AAS (Atomic Absorption Spectrophotometer). The percentages of sand, silt, clay and TOM (Total Organic Matter) in the sediment samples were determined (44.4± 15, 53.4 ± 14, and 2.2± 2.2 and 7.2% ± 1.6, respectively). The results showed that range of Al, As, Cu, Fe, Ni, Pb and Zn in the sediment samples were 0.4-2%, 2.6- 8.6 ppm, 8.1-12.4 ppm, 0.9 – 1.2 % , 11.5-16.8 ppm, 5.9-13.6 ppm and 21.8-28.8 ppm, respectively. In spring, both Al and Ni were higher than the guideline level. In the event that arsenic was exceeds the guidelines in summer. In general, according to the results of EF (Enrichment Factor) and PLI (Pollution Load Index) can be concluded, Gorgan Bay is low risk and not contaminated. According to the results of the nmMDS (non-metric Multidimensional Scaling), PCA (Principal Components Analysis) and the map of distribution of heavy metals, it seems Gorgan Bay are divided into two separate zones (the eastern and the western parts).