Historical changes in distribution and partitioning of natural and anthropogenic shares of heavy metals in sediment core from the southern Caspian Sea

Distribution of seven major and trace elements (aluminum, iron, calcium, cobalt, copper, vanadium and manganese) and total organic matter were assessed for sediment cores, collected from the southwest of Caspian Sea sediment in September 2008. Sedimentation rate of 0.9 cm/year was obtained based on ²¹⁰Pb and ¹³⁷Cs activity study of sediment cores. The major and trace metal distributions over whole lengths of core lengths (14-168 cm) were found to be uniform (except for Al, Fe and Ca). Such uniform distribution of elements over whole lengths of the cores of the study area indicates similarity among the lithogenous material delivered into the Caspian Sea by rivers running into the southern coast. Enrichment factor (EF) and modified Muller's formula of geoaccumulation index I_poll (intensity of pollution) evaluated the degree of sediment contamination. The results of pollution indices are indicative of non-pollution status in the area of study. From the first to third transect, Al, Fe and Mn concentrations increase. Heavy metal concentrations show relatively lower elemental concentrations in the third transect, possibly due to distance from anthropogenic sources. Cluster analysis shows Cu and Co grouped in different clusters, while Mn, V and Fe display closer similarity coefficients and similar sources. The results of partition studies reveal the percentile of loose ions portion of the metals as:

Cu(25.4%) > Co(15.1%) > Mn(7.5%) > V(5.8%) > (0.2%)

It shows that Cu and Co are the most mobile metals that can be easily released into water under changing environmental conditions. There seems to be a slight increasing trend in the pollution level of the sediments of the study area for copper and cobalt over the last 60 years.