Release of heavy metals under pre-set redox potentials in Musa estuary sediments, northwestern of Persian Gulf

Highlights: • Release of heavy metals from sediments enhanced in reducing conditions • Redox potential showed a converse relation with DOC and direct relation with pH. • Indexes signified unsuitable water quality for aquatic life. Sediments are capable of adsorbing and desorbing heavy metals (HMs) under various environmental conditions. This study investigated the impact of pre-set redox potential (Eh) on the release dynamics of HMs (Co, Cr, Cu, Ni, Pb, V, and Zn) from sediment in an automated biogeochemical microcosm. The release of Co, Pb, and V under reducing conditions increased that may increase the potential risks in the aquatic environment. This phenomenon could be attributed to the decrease in pH, the reductive dissolution of FeMn oxides, and the complex of HMs with dissolved organic carbon (DOC). However, the soluble Cr, Cu, Ni, and Zn decreased at redox potentials as low as −150 mV. Co, Ni, Pb, and Zn were observed in mobile fractions while Cu primarily existed in the residual fraction (indicating lithogenic source). HPI and HEI indexes showed that water quality concerning HMs would become more unsuitable for aquatic life by reducing Eh.