In the span of a week, Illinois-Indiana Sea Grant will have two speakers at NOAA Brown Bag seminars. Today, December 8, Priscilla Viana, IISG Knauss Fellow, will give a talk titled Transport of contaminants from sediments to the water column and environmental remediation strategies. On December 15, Susan Boehme, coastal sediment specialist, will present Unwanted Medicines and Educating our Communities: What Have we Learned, How are we Doing and What are the Next Steps? Experiences from the Great Lakes States.
Here is Priscilla’s abstract for today’s talk:
Transport of contaminants from sediments to the water column and environmental remediation strategies
Contaminants, such as polycyclic aromatic hydrocarbons (PAHs), polychlorinated biphenyls (PCBs) and heavy metal contaminants have accumulated on the bottom of rivers and lakes due to chemical interactions and transformations and due to their relatively long environmental persistence. Gas ebullition, in addition to normally occurring diffusive and advective transport of contaminants, increases contaminant availability to the bioactive zone and water column. Increased incidences of fish disease and decreased species biodiversity in pollution-impacted benthic/aquatic environments are some of the costs to ecological and human health posed by these contaminants.
My study focuses on quantifying and modeling the transport of contaminants from sediments to the water column and on investigating the effectiveness of active capping as a mitigation strategy to minimize the release of these contaminants. Active capping both isolates contaminated sediments from the water phase while offering degradation and/or sequestration of contaminants by the active materials. I modeled the transport of Cd, Cr, Pb, Ag, As, Ba, Hg, CH3Hg and CN through sand (25 cm), granular activated carbon (GAC, 2 cm), organoclay (2 cm), shredded tires (10 cm) and apatite (2 cm) caps by deterministic and Monte Carlo methods. Sand caps performed best under diffusion due to the greater diffusive path length. Apatite had the best advective performance for Cd, Cr and Pb. Organoclay performed best for Ag, As, Ba, CH3Hg and CN. Organoclay and apatite were equally effective for Hg. Monte Carlo analysis was used to determine output sensitivity. Sand was effective under diffusion for Cr within the 50% confidence interval (CI), for Cd and Pb (75% CI) and for As, Hg and CH3Hg (95% CI). Under diffusion and advection, apatite was effective for Cd, Pb and Hg (75% CI) and organoclay for Hg and CH3Hg (50% CI). GAC and shredded tires performed relatively poorly. Although no single cap is a panacea, apatite and organoclay have the broadest range of effectiveness.
I am also quantifying and modeling metal contaminant and PAH transport from the sediment to the water column due to gas ebullition as recent research suggests that another important factor affecting cap performance is gas ebullition due to organic matter biodegradation primarily under methanogenic conditions. Gas bubbles may damage the cap layer, opening preferential holes in the cap or even rupture the cap. Additionally, my results demonstrate that gas ebullition may be an important pathway for release of PAH and heavy metal pollutants to the water column. Comparison of diffusive and advective release rates (measured through a benthic chamber study) to field ebullition facilitated rates suggest that PAHs are released at >10 times greater rates by biogenic gas production. Although the increase in release rate is not as great for metals, ebullition facilitated release rates are frequently much greater.
Using our field study and modeling results, we worked with the Wetlands Initiative and the Metropolitan Water Reclamation District of Greater Chicago (MWRD-GC) to improve the stewardship of the highly contaminated local aquatic resources. We proposed placement of an organoclay mat with an underlying sloped sand layer and a high permeability gas venting system to allow biogenically-produced gas migration to shoreline collectors through an innovative support grid. The project design included an overlaying wetland to remove nutrients from the adjoining Chicago River and to provide a public recreational space.