Superfund Research Program
Use of Sediment Core Analyses in Site Characterization
Across the United States, large quantities of diverse toxic contaminants are dispersed in the environment and significant quantities of organic and inorganic contaminants continue to be released to the air, soil and water. The development of sound management plans for the protection and remediation of environmental systems requires in-depth understandings of contaminant sources, how contaminants move through the air, water and soil, and how contaminants are impacted by physical, chemical and biological systems. SBRP-funded scientists are working to develop sampling and analytical methods to provide information critical to characterization of sites contaminated with hazardous wastes.
As part of the Mount Sinai School of Medicine's SBRP, Dr. Richard Bopp of Rensselaer Polytechnic Institute leads a team using sediment cores to study the distribution and fate of persistent contaminants in the Hudson River watershed. As a first step in the evaluation of sediment cores, Dr. Bopp's team establishes depth profiles of radionuclide activities and other temporal indicators. The compounds used to build the profiles include:
- Cesium-137 -- entered the environment as fallout from atmospheric nuclear weapons tests in the 1950s and 1960s. Cesium-137 first appeared in sediments around 1954, a small peak occurred in 1958-1959, and the largest signal is associated with fallout in 1963-1964.
- Beryllium-7 -- produced in the atmosphere and has a radioactive half-life of 53 days. Consequently, the presence of beryllium-7 at measurable levels in a core section indicates that portion of the sediment accumulated within six months to a year prior to collection.
- Lead (Pb) isotopes Pb-204, Pb-206, Pb-207 and Pb-208 -- the presence and ratios of these isotopes at various depth sections can be used as fingerprints to provide additional temporal data.
Detection of these compounds and determination of their distribution in a sediment core enables the researchers to estimate the age of depth sections of sediment cores and to establish rates of sedimentation.
Dr. Bopp's team pioneered the use of a powerful method of studying the biogeochemical behavior of contaminants in sediments - comparison of "matched cores". The researchers use information from radionuclide and stable isotope analyses to identify and compare sections of different cores that were deposited at approximately the same time. Comparison of core sections from different locations or different times allows the researchers to identify sources of contamination, pathways and rates of contaminant transport through an ecosystem and rates of contaminant degradation.
Temporal Matching Comparison of cores collected at the same location but at different times allows researchers to identify changes in the contaminant within the sediment during the time between core collections. The SBRP researchers used this approach to study the depositional chronology of pollutant metals and selected chlorinated organic contaminants in the Hudson River. Dr. Bopp's study of PCB dechlorination rates in sediments provided critical information to regulatory agencies responsible for identifying an appropriate remediation strategy for the Hudson River Superfund site. His student, Anne McNulty, found that while significant dechlorination of PCBs occurred soon after deposition in the sediments, the rate significantly decreased after about a year, and in the following decades PCBs were not dechlorinated nearly as rapidly as predicted by laboratory studies.
In on-going studies, Dr. Bopp's team, in collaboration with researchers from SUNY Stony Brook, is using the matched core approach to study the post-depositional behavior of nonylphenol ethoxylates (NPEOs) in sediments from Jamaica Bay. NPEOs are high production volume surfactants used as detergents, wetting agents, and emulsifiers in various commercial and industrial products worldwide. The biodegradation of NPEO mixtures (in wastewater treatment facilities or in the environment) results in a decrease in the relative abundance of NPEOs with long ethoxy chains and an associated increase in the relative abundances of the shorter ethoxy chain NPEOs. Accumulation of short ethoxy chain NPEOs in the aquatic environment raises concern because of their potential acute and chronic toxicity in sediments and because several of these compounds have been reported to act as environmental endocrine disruptors. Dr. Bopp's team collected core samples eight years apart at a single location. Analyses of matched samples provides insight on the function of the biological sewage processes at nearby wastewater treatment plants with respect to NPEO and revealed that shorter ethoxy chain NPEOs accumulate and can persist for decades in sediments. Characterization of NPEO levels in dated sediments from throughout the Hudson basin is underway.
Spatial Matching Comparison of dated cores collected at different locations can provide information on contaminant sources as well as rates of contaminant transport and deposition. For example, trace metal and stable lead isotope measurements on a pair of sediment cores collected 24 miles apart on the upper Hudson River indicated that inputs from a pigment manufacturing plant were responsible for the high levels of lead, chromium and cadmium found in the sediments. Dr. Bopp's team was also able to determine the magnitude of sediment sources to this reach of the river, information that is critical to determination of contaminant dilution factors. The analyses suggested that on average, three to four times more sediment entered the river between the two coring sites than was transported from upstream.
The information gained from these studies can be applied to evaluate human, ecological and environmental risks and to guide remediation decision making. In fact, Dr. Bopp has established a collaborative relationship with the New York State Department of Environmental Conservation (NYSDEC) that has resulted in NYSDEC adopting radionuclide dating as an indispensable tool in the investigation of contaminated sediments. The use of matched core comparisons is applicable to hazardous waste sites across the country and has great potential to provide valuable input into efforts to address multi-source, multi-contaminant issues facing environmental and public health decision-makers.
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To learn more about this research, please refer to the following sources:
- Chillrud SN, Hemming S, Shuster EL, Simpson HJ, Bopp RF, Ross JM, Pederson DC, Chaky DA, Tolley L, Estabrooks FD. 2003. Stable lead isotopes, contaminant metals and radionuclides in upper Hudson River sediment cores: implications for improved time stratigraphy and transport processes. Chemical Geology 199(1-2):53-70.
- Ferguson PL, Bopp RF, Chillrud SN, Aller RC, Brownawell B. 2003. Biogeochemistry of nonylphenol ethoxylates in urban estuarine sediments. Environ Sci Technol 37(16):3499-3506. PMID:12953858
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