Geochemical speciation, bioavailability and source identification of selected metals in surface sediments of the Southern Caspian Sea

Geochemical speciation of As, Cd, Co, Cr, Cu, Ni, Pb, V and Zn were determined in the surface sediments of the southern Caspian Sea. A five-step sequential extraction technique was used to determine the chemical forms of metals. Mean concentrations (ppm) of heavy metals were (mean ± S.D.) As: 9.94 ± 1.71, Cd: 0.87 ± 0.23, Co: 14.85 ± 2.80, Cr: 72.29 ± 19.48, Cu: 18.91 ± 4.48, Ni: 32.87 ± 5.25, Pb: 12.48 ± 3.22, V: 86.07 ± 20.71 and Zn: 66.85 ± 10.11. Among the metals, Cu, As, Pb and Zn exhibited relatively higher mobility, while Cd, Co, Cr, Ni and V were found mainly in the residual fractions. Cu and As showed the highest percentages in the exchangeable phase while Co and Cr had the lowest percentages in the phase. The Risk Assessment Code (RAC) values indicated that As, Cu and V had medium risk at some sampling sites. According to pollution load index (PLI), sediments from some sampling sites were polluted.