SediMite® was one of three activated carbon (AC) amendments used in a field pilot study in the Berry’s Creek Study Area (BCSA) in the Hackensack Meadowlands of northern New Jersey. Sediments in intertidal marshes of the BCSA are dominated by Phragmites reed and contain PCBs, mercury and other contaminants. A resulting fish consumption advisory is in effect due to PCBs.
The field pilot study was completed to assess the effects of AC on the bioavailability of PCBs and mercury, and the viability of an in-situ remediation strategy for marshes at this site. Four 30 x 30-foot test plots were established in the marsh; three plots were treated with AC (granular activated carbon (GAC), GAC plus a thin layer of sand, and SediMite®), and the fourth plot served as the experimental control.
Retention of AC treatment within the surface sediments of the test plots over time was evaluated via periodic depth-discrete sampling and analysis of black carbon. Concentrations of PCBs and methyl mercury were monitored in sediment porewater and biota (e.g., amphipods) prior to and after treatment at intervals over a three-year period. The comparative effects of the three AC treatments on biouptake were assessed using in-situ and ex-situ experiments.
All three AC amendments remained in place over three years following surficial application, including withstanding the effects of Hurricane Sandy in 2012. AC penetrated into the marsh surficial sediment and persisted in treatment plots, with most AC present in the top 3 cm.
PCB concentrations in porewater were substantially lower in AC treated plots compared to the unamended control plot, with reductions up to 97% depending on the type of carbon treatment. Largest reductions were observed in the test plot amended with SediMite®. PCB concentrations in amphipods exposed in the laboratory or in the field were reduced by AC treatment, with reductions up to 98% compared to the unamended control. Again, largest reductions were associated with the SediMite® treatment.
Statistical models indicated that concentrations of total mercury in porewater and field-caged amphipods were significantly lower (up to ~50%) in AC treatment plots compared to the unamended control. Differences in elevation of the plots and duration of tidal inundation among plots influenced redox conditions and confounded the results for methyl mercury. Redox conditions in lower elevation plots (including the unamended control plot) favored the production of methyl mercury compared to plots at higher elevations.
Gilmour, C.C., G.S. Riedel, G. Riedel, S. Kwon, R. Landis, S.S. Brown, C.A Menzie, and U. Ghosh. 2013. Activated carbon mitigates mercury and methylmercury bioavailability in contaminated sediments. Environ. Sci. Technol. 47:13001-13010.
Sanders, JP, NA Andrade, CA Menzie, CB Amos, CC Gilmour, EA Henry, SS Brown, U Ghosh. 2018. Persistent reductions in the bioavailability of PCBs at a tidally inundated Phragmites australis marsh amended with activated carbon. Environmental Toxicology & Chemistry. 37 (9): 2496-2505.