U.S. EPA Response to the “Peer Review of the U.S. Environmental Protection Agency’s Final Report on the World Trade Center (WTC) Dust Screening Study” December 2006

EPA has completed a substantial study to re-evaluate use of the presence of slag wool fibers as a potential marker for World Trade Center (WTC)-derived dust contamination. Slag wool is an insulating material (made from blast furnace slag) that was used in the construction of the WTC. Large quantities of slag wool were released into lower Manhattan by the collapse of the WTC. Samples of dust collected in the immediate vicinity of the WTC site within a few days after the collapse were found to contain very high levels of slag wool fibers. Logically the presence of slag wool fibers in dust samples at high levels would provide an indication of the presence of WTC dust and possible contamination at the sample location. The WTC Expert Technical Review Panel recommended using the presence of slag wool fibers in dust in substantial amounts as an indicator of possible contamination as a result of the WTC collapse.