Effect of redox potential on the heavy metals binding phases in estuarine sediment: Case study of the Musa Estuary

Heavy metals (HMs) exist in various chemical forms in marine sediments, and environmental factors like the redox potential (Eh) can affect labile-bound HMs, harming aquatic life and human health. This study utilized the Tessier sequential extraction to investigate how Eh affects the binding forms of elements, including Cd, Co, Cu, Ni, Pb, Zn, Fe, and Mn. The results revealed that decreasing Eh from 120 to 50 mV resulted in the release of weakly bound forms of Cd, Co, Ni, Pb, and Zn into the water, some of which were re-adsorbed by the residual fraction as Eh decreased further to -150 mV. Manganese was consistently bound to Fe-Mn oxides, while Cu and Fe were predominantly associated with the more stable binding phase. Based on EF, Igeo, and CF, sediment was only polluted by As nearby an industrial zone, while water pollution indices indicated significant HMs contamination in all water samples.