The results, says scientist Curtis Olsen of the University of Massachusetts at Boston (UMB), an author of the EOS paper along with university colleagues and scientists from the U.S. Department of Energy and the U.S. Geological Survey, provide new information for assessing the potential environmental and human health impact of the World Trade Center catastrophe, and for validating sediment and contaminant transport models already developed for the lower Hudson River estuary (an estuary is the meeting ground of freshwater flowing downstream from rivers, and currents carrying saltwater inland from the ocean).
Explains Larry Clark of the National Science Foundation
(NSF)'s division of ocean sciences, which funded the research, "The destruction of the World Trade Center and the resulting deposition of dust and ash into the Hudson River have provided scientists with a definitive geochemical signal. This research provides valuable information on geochemical processes in New York Harbor and the Hudson River estuary, and has applications to other estuaries and coastal oceans, as well."
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The combination of the collapse of the towers, the fires that burned at the excavation site for three months after the World Trade Center attack, and subsequent site-remediation activities, released dust, debris, and associated contaminants into the surrounding urban environment. Explains Olsen, "Determining the variations in particle and contaminant dynamics can be difficult, since fine-particle transport involves numerous shortterm episodes of deposition and resuspension, and because intense, short-term events [storms and catastrophes] are often more important than those that occur during normal flow conditions. One of the tools available for finding out the fate of fine particles and contaminants released into estuarine systems is the measurement of geochemical 'tracers' that have known sources and histories of input into the system, such as those from the World Trade Center."
The legacy of the World Trade Center attack, Olsen and colleagues found, is recorded in New York Harbor sediments as a layer containing high concentrations of several elements, copper, zinc, calcium, strontium, and others. Results indicate that the deposition of World Trade Center ash, via fall-out from the atmosphere, urban runoff in streams or site remediation activities, could account for all of these elevated concentrations.
The samples of ash and debris were collected near Ground Zero a week after the collapse, and sediment cores were collected on October 12, 2001, in two inactive New York Harbor slips, Pier 32 and Pier 40, along the lower West Side of Manhattan. The high levels of calcium, strontium, and sulfur concentrations found in the near-surface sediments of the cores, are consistent with presence of gypsum as a parent material. Gypsum is extensively used as drywall in building construction. Copper and zinc are also common components of building materials. The scientists observed that this near-surface sediment layer also contained silica-rich fibers and rods, which may reflect the input of fiberglass from ceiling tiles and other materials in the World Trade Center towers.
"We also found, unexpectedly, short-lived radioactive iodine, produced for medical treatments and diagnostic procedures, in New York Harbor sediments," says Sarah Oktay of UMB, lead author of the EOS paper. "This is most likely related to urban waste-water discharges and appears to be unrelated to the collapse of the trade center buildings."
The scientists believe that the fingerprint of the World Trade Center attack will provide a better understanding of the processes that affect the dispersal and fate of particles and contaminants in New York harbor. In the future, they plan to extend the framework of their study to determine whether the legacy of the terrorist attack on the World Trade Center has been preserved in the sedimentary record of New York harbor, or resuspended and dispersed by coastal currents.
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