The effect of pH and redox potential on the release of nutrients and heavy metals from a contaminated marine sediment

A laboratory batch experiment was performed to evaluate the release of nutrients and heavy metals from a heavily polluted sediment under various pH and redox conditions and its implications on the various remediation methods. The sediments were equilibrated under various controlled redox (-200, 0, and 300 mV) and pH (5.0, 6.5, and 8.0) conditions. After attaining equilibrium, water samples were collected to determine the concentrations of NH₄⁺, PO₄^3-, Cd, Cu, Fe, Ni, Mn, Pb and Zn released. A decrease in pH and an increase in redox potential caused a substantial release of Cd, Cu, Pb, Ni, Mn and Zn. Soluble Fe, NH₄⁺ and PO₄^3- increased with a decrease in pH and redox potential. The results suggest that dredging and disposal of sediments may enhance the mobilization of enriched heavy metals in sediments due to the more acidic and oxidized conditions after exposure to the atmosphere.