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IP05 Mercury Bioaccumulation and Remediation of Mercury-Contaminated Systems
(IP037) Metal Profiles in Sediments of a Contaminated NJ Brackish Marsh Indicate Natural Attenuation.
Weis, P.1, Proctor, T.1, Barrett, K.2, Bopp, R. 3, Weis, J. 4, 1 UMDNJ - New Jersey Medical School, Newark, NJ, USA2 Rutgers University CIMIC, Newark, NJ3 Rensselaer Polytechnic Institute, Troy, NY, USA4 Rutgers University, Newark, NJ, USA
ABSTRACT- Eight Day Swamp (8DS), a brackish marsh in the Hackensack Meadowlands, lies downstream from three Superfund sites. 8DS is highly contaminated with metals, including Hg. To determine metal concentration profiles, we cored 17 sites on four transects and analyzed 2 cm slices for As, Cd, Cr, Cu, Hg, Pb, and Zn. High concentrations of all metals were found throughout 8DS and, except for mudflats, throughout the depth profile. Extremely high values of Zn and Cr, >10,000 g/g, were found in individual deep samples. Compared to surface concentrations, levels of all metals were enriched 40X at 14-20 cm, indicating that newer, less contaminated sediments are covering older sediments, a form of natural attenuation. This is supported by a 1978 study that showed mercury peaks in marsh sediments 5-10cm deep. Nevertheless, surficial layers on the marsh remain quite contaminated. Many samples contained concentrations that are potentially significant to benthos. The median concentrations of Cd, Cr, Pb, Zn and Hg in the top 4 cm of marsh sites are still above the Long et al (1995) effects range - median (ERM). The ERM was exceeded in more than 50% of samples for all elements except As and Cu. Hg showed the highest value in ratio to the ERM. Its median concentration (51.4 g/g) was 72 times greater than its ERM. The next highest was Zn with a median concentration of 1286 g/g, 3.1 times its ERM. Three cores analyzed for 137Cs and 210Pb had average sedimentation ranging from 0.33 to 0.50 cm/yr over the past half century. These rates are consistent with the difference between the depth of peak Hg observed in 1978 vs. in this study and indicate that maximum contamination occurred in sediments deposited in the early 1960s. Metal levels in suspended sediments and material from sediment traps were comparable to those of the surficial sediment layers, further supporting the conclusion that less contaminated sediments are burying older, more contaminated layers. The Phragmites australis that dominates 8DS, is known to modify its root zone to an oxic environment, mobilizing some metals and allowing uptake by the roots. We previously showed that this results in recycling of metals from the root zone by direct excretion and via dead leaves that will enter the food web as detritus. The observed natural attenuation of metal levels in the surface sediments indicates that the rate of burial is keeping ahead of this biological process.
Key words: natural attenuation, radionuclide dating, mercury, sediment deposition
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