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Carnegie Mellon University Scientists reveal new ways of studying, resolving PCB contamination in U.S. rivers

Carnegie Mellon Universtity : 11 August, 2006  (Technical Article)
The distribution and movement of polychlorinated biphenyls in the environment has threatened scarce water supplies, ecosystems, tourism and the world's fragile fishing industry. In the three decades since PCB production and use were banned, sediments of many lakes and waterways continue to provide a source of these deadly toxins to the water and ultimately to fish and people.
Now, in a series of integrated studies, a multidisciplinary team of biologists and engineers from Carnegie Mellon University has discovered key aspects of processes that govern PCB fate in sediment and developed methods to monitor, measure, track and contain these synthetic compounds. These scientific sleuths are deploying everything from DNA fingerprinting to a fine mesh of carbon particles to augment the traditional sand caps that trap dangerous PCBs in sediments.

Organized by Carnegie Mellon faculty, the American Chemical Society symposium, 'PCBs in Freshwater and Marine Sediments: Transport, Transformation and Treatment,' will feature five presentations on Carnegie Mellon findings from work in PCB-contaminated rivers, including the Hudson and Grasse Rivers in upstate New York and the Anacostia River in Washington, D.C.

Much of the research is supported by the David and Lucile Packard Foundation Interdisciplinary Science Program (ENVR 12, 203, 37, 38). The capping research (ENVR 68) is supported by a U.S. E.P.A.-Funded Hazardous Substance Research Center at Louisiana State University and supplemented by Alcoa.

The following findings will be presented:

ENVR 12. Microbial communities in two river sediments demonstrate distinct anaerobic PCB dechlorination patterns. (Christine Wang, Department of Biological Sciences, presenting) Bacteria are one of Mother Nature's most promising weapons to break down persistent, toxic PCBs. Now, Carnegie Mellon scientists have used DNA fingerprinting to discover distinct bacteria populations that decompose PCBs differently in the first ever side-by-side comparison of sediments taken from separate, contaminated rivers. Future studies that modify sediment nutrients from contaminated sites with little or no bacterial activity also could reveal ways to coax poor PCB-eaters into developing healthy appetites for these toxins. Ultimately, PCB-digesting microbes will need to be examined in each contaminated lake or river to understand the fate of PCBs at different sites, said the investigators. (See 'PCB Breakdown in Rivers Depends on Sediment-Specific Bacteria, Find Carnegie Mellon University Scientists.')

ENVR 203. Critical oxygen concentrations for biodegradation of PCBs (Jeanne VanBriesen, Department of Civil and Environmental Engineering, poster) Carnegie Mellon investigators have shown for the first time that PCBs undergo no biological breakdown whatsoever in river sediments with low but detectable dissolved oxygen levels. The findings up-end assumptions that some microbes, either those that use oxygen or those that don't, are always at work to break down these toxins. At dissolved oxygen concentrations between 0.5 and 4 ppm, the team found no oxygen-using bacteria at work digesting PCBs in sediments taken from the Grasse River in upstate New York. These findings will complicate in situ bioremediation efforts.

ENVR 37. Statistical method to evaluate the occurrence of PCB transformations in river sediments (Sandra Karcher, Department of Civil and Environmental Engineering, presenting) Finding out how PCBs are broken down over time is difficult if you don't know which of the 209 PCBs (called congeners) were released initially. During manufacturing, companies made different lots of PCB mixtures called Aroclors, but poor record-keeping has confused efforts to track PCB breakdown at different sites. Now, in a statistical tour-de-force, Carnegie Mellon scientists have developed a way to identify true shifts in specific PCB congener distributions over time in river sediments by tracking pairs of PCB congeners whose ratios do not vary from Aroclor lot to Aroclor lot. This computationally intensive procedure, which was tested using extensive data available from the Hudson River, provides a method for evaluating the extent of biological degradation of PCBs from any field sediment data where Aroclors were dumped. By simply tracking changes in these congener pairs in future studies, scientists now will no longer need to know exactly which PCB congeners were released initially at a site.

ENVR 38. Temperature effects on PCB fate and transport in anaerobic near-surface sediment. (Kathleen McDonough, Department of Civil and Environmental Engineering, presenting) The lazy flow of the Hudson and Grasse Rivers in summer belies their elevated release of dangerous PCBs during this time, according to findings made by Carnegie Mellon engineers, who demonstrate that changes in river water (and hence sediment) temperature is a major driver of PCB release from sediments. Microbes appear to be one of the major culprits, releasing PCB-containing gas bubbles that percolate through river sediments. Microbes, as well as larger creatures living in the sediment, abound during warm summer months and churn their surroundings. Higher temperatures also increase natural diffusion and solubility of these toxins, say the investigators. Their results will aid in the interpretation of field data and in the design of management strategies, including sediment caps.

ENVR 68. In place management of PCB-contaminated sediments: Performance evaluation and field placement of sorbent-amended sediment caps (Paul Murphy, Department of Civil and Environmental Engineering, presenting) A sediment capping mat developed by Carnegie Mellon engineers soaks up PCBs and could prevent their long-term release into waterways, according to the researchers, who are evaluating it in field trials in Washington, D.C.'s contaminated Anacostia River. The mat contains a thin layer of carbon-adsorbent particles embedded in a plastic mesh, which is itself enclosed in geofabric. This thin 'active' mat, which can be rolled out and placed within a conventional sand cap, could provide an important alternative to dredging, which is estimated to cost at least $500 million along the Hudson River alone. (See 'Carnegie Mellon University Researcher Tests New Tools for Protecting Anacostia River Ecosystem from PCBs').
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