Mobility and risk assessment of heavy metals by sequential extraction in coastal sediment south Mediterranean Sea, Egypt

Abstract

The chemical speciation of metals (Cd, Zn, Cu, and Fe) for coastal marine sediment samples collected from ten locations in the Western Harbour (main harbour) in Egypt and has been studied in two surveys which were determined using the four-step sequential extraction procedure. A sequential extraction technique was used to quantify exchangeable, oxides (reducible), organic/sulphidic, and acid-soluble (residual) fraction. It was noticed that Cd and Zn have the highest capability to be released from the sediment, more mobile and bioavailable, by the simple ion exchange mechanism in the W.H than Cu and Fe which were present at higher percentages in the acid-soluble fraction, meaning that these two metals were strongly bound to the sediments. Considering the percentage of metals extracted in the most labile fractions (F1 + F2 + F3), the order of mobility (from most to least bioavailable) was: Cd (94%) > Zn (64%) > Cu (22%) > Fe (3.5%). Risk assessment code (RAC) analysis indicated that the sediments show no risk for Fe and a low risk for Cu and low-to-medium risks for Zn and medium-to-high risks for Cd with RAC values greater than 11% and 30%, respectively, indicating a substantial risk of metal mobilization from sediments across the entire study region.