Geochemical fractionation of heavy metals in sediments of the Red Sea, Saudi Arabia

Abstract

Summary The geochemical fractionation of heavy metals, including Mn, Fe, Cu, Pb, Zn, Cd and Ni, collected from the surface sediments of the Jeddah coastal zone of the Red Sea in Saudi Arabia was determined using a sequential extraction technique. The data obtained from the five fractions indicated that the concentration of metals varies among different locations in the study area. The total metal concentrations (%) in the exchangeable (F1), carbonate (F2), reducible (F3) and organic-bound (F4) fractions were measured to determine the mobility of each studied metal. The sum of the two fractions F3 and F4 represented 70% of the Cu, 72% of the Zn and 36% of the Pb. However, the sum of the three fractions F2, F3 and F4 represented 76%, 74%, 68% and 58% of the Cd, Ni, Fe and Mn, respectively. Approximately 46% of the total copper was related to organics, which could reflect a high mobility of copper in these sediments. The maximum mobility of metals in the sediments was confirmed by the bioavailability factor (BF), which was within the ranges of 0.47–0.93, 0.34–0.92, 0.62–0.95, 0.69–0.95, 0.24–0.82, 0.54–0.98, and 0.60–0.95 for Fe, Mn, Cu, Zn, Pb, Cd, and Ni, respectively. Based on the BF, the metals exhibited the following order: Cu ≈ Zn > Cd ≈ Ni ≈ Fe > Mn > Pb. The high levels of BF for the studied metals could reflect the potential for toxic metals to be easily released into the marine environment. The risk assessment code for Cd showed a medium risk in five sediment samples of the northern and southern regions and a high risk to the aquatic environment in the other sediment samples. However, the speciation of Fe, Mn, Cu, Zn, Pb and Ni in the studied sediments exhibited low to medium risks to the aquatic environment.