Considerations for capping metal-contaminated sediments in dynamic estuarine environments

Area of Science:

• Environmental Science
• Marine Chemistry
• Geochemistry

Background:

• Harbor sediments often contain metal contaminants.
• Tidal estuarine environments are dynamic systems influencing contaminant mobility.
• Bioturbation and anoxia play critical roles in metal cycling.

Purpose of the Study:

• To investigate the impact of tides, bioturbation, and anoxia on metal fluxes from contaminated sediments.
• To evaluate the effectiveness of different capping technologies for metal contaminant containment.

Main Methods:

• Experiments using corer-reactors to simulate tidal processes.
• Assessing the influence of sediment-dwelling organisms and their bioturbation activities.
• Testing various capping materials (clean sediment, zeolite/sand, sand) at different thicknesses.

Main Results:

• High zinc fluxes (10-89 mg Zn m(-2) day(-1)) were observed from contaminated sediments.
• Simulated tidal processes increased zinc fluxes fivefold; bioturbation initially decreased but then stabilized fluxes at higher levels.
• 5 mm clean sediment capping was most effective; 10 mm zeolite/sand showed breakthrough; 20 mm sand was ineffective.
• Organism disturbance of caps increased metal fluxes, necessitating greater cap depths.

Conclusions:

• Tidal energy and bioturbation are significant drivers of metal release from contaminated estuarine sediments.
• Effective capping requires sufficient depth (>30 cm) to prevent organism-induced disturbance and ensure long-term containment.
• Clean sediment capping presents a viable strategy for mitigating metal fluxes from contaminated harbor sediments.