Metal release from contaminated coastal sediments under changing pH conditions: Implications for metal mobilization in acidified oceans

- Metal mobility from sediment to overlying water is increased due to acidification.
- Release rate of metals in contaminated sediments is correlated to the pH decreases.
- pH decreases change the forms and bioavailability of some of the metals.
- Metal release from acidified sediments potentially causes impacts to water quality.
- Metal mobilization strengthened the existed contamination gradients.

To investigate the impacts and processes of CO2-induced acidification on metal mobilization, laboratory-scale experiments were performed, simulating the scenarios where carbon dioxide was injected into sediment-seawater layers inside non-pressurized chambers. Coastal sediments were sampled from two sites with different contamination levels and subjected to pre-determined pH conditions. Sediment samples and overlying water were collected for metal analysis after 10-days. The results indicated that CO2-induced ocean acidification would provoke increased metal mobilization causing adverse side-effects on water quality. The mobility of metals from sediment to the overlying seawater was correlated with the reduction in pH. Results of sequential extractions of sediments illustrated that exchangeable metal forms were the dominant source of mobile metals. Collectively, our data revealed that high metal concentrations in overlying seawater released from contaminated sediments under acidic conditions may strengthen the existing contamination gradients in Maluan Bay and represent a potential risk to ecosystem health in coastal environments.