Historical Changes Of Heavy Metals Content And Sequential Extraction In A Sediment Core From The Gorgan Bay, Southeastern Caspian Sea

摘要

In the present investigation sedimentation rate, contents of heavy metals (Zn, Co and Ni), enrichment factors and speciation of Zn, Co and Ni of a sediment core from Gorgan Bay have been studied. Sedimentation rate in the study area has given an ample opportunity to track contents of Zn, Co and Ni with different sedimentary phases for the past 500 years (1500 to 2002). Sedimentation rate of 1.4 mm/yr was obtained based on ~(210)Pb activity study of sediment core. A very low content of Al and Fe in the core compared to those of the mean crust was observed. Heavy metal contents increase towards the top of the sediment core. Chemical partitioning studies revealed that percentiles and amounts of Zn, Ni and Co in non-lithogenous phases increase slightly towards the top of the core sediment sample. There seems to be a slight increasing trend in pollution level of the sediments of the study area over the last 70 years. Further, despite many research reports, application of Enrichment Factors (EFs) for determination of origin of heavy metals in sediments and pollution detection may lead to incorrect results due to naturally lower concentration of Al than the mean crust and/or higher contents of heavy metals in sediments than those in the crust, as the EFs in the present investigation were high even in 17th century when there were no significant sources of pollution. The results of Igeo values, on the other hand, show that minor elements fall within non-polluted classification which can obviously show the error of the enrichment factor calculations with the use of Al as earth reference element.