Masses of Very Fine Particles Emitted from Ground Zero
NEW YORK, New York, February 11, 2002 (ENS) - Air quality experts say New York City air now is little influenced by the World Trade Center collapse, especially since the fires are out and the debris pile has cooled.
But at Ground Zero rescue and cleanup workers and nearby residents have been coughing and complaining. They say pollutants released into the air when terrorist strikes turned the World Trade Center into more than a million tons of rubble are making them sick. Ground Zero air - contaminated with metals, asbestos, benzene, dioxins and PCBs - is the subject of investigation by a Senate sub-committee.
"We are very encouraged that the results from our monitoring of air quality and drinking water conditions in both New York and near the Pentagon show that the public in these areas is not being exposed to excessive levels of asbestos or other harmful substances," Whitman said on September 18. "Given the scope of the tragedy from last week, I am glad to reassure the people of New York and Washington, D.C. that their air is safe to breath and their water is safe to drink," she said.
But today, following the most thorough analysis yet of the dust and smoke blown through lower Manhattan after the collapse of the World Trade Center, researchers from the University of California-Davis described unprecedented clouds of very fine particles that they say should be considered in evaluating the health problems of rescue workers and New York residents.
"No one has ever reported a situation like the one we see in the World Trade Center samples," said UC Davis researcher Thomas Cahill, Ph.D., an international authority on the constituents and transport of airborne particles.
Many different metals were found in the samples of very fine particles, and some were found at the highest levels ever recorded in air in the United States.
Although some asbestos was used in the buildings for fireproofing and in floor tiles, and the scientists checked for it carefully using an electron microscope, they found very few asbestos fibers, even in the very fine particles.
Cahill, a UC Davis professor emeritus of physics and atmospheric sciences and a research professor in applied science, heads the UC Davis DELTA Group (for Detection and Evaluation of Long-range Transport of Aerosols), a collaborative association of aerosol scientists at several universities and national laboratories.
The DELTA Group has made detailed studies of aerosols from the 1991 Gulf War oil fires, volcanic eruptions, global dust storms, and most recently Asia.
The Manhattan air samples were collected at the request of a U.S. Department of Energy scientist from October 2 through mid-December, by a DELTA Group air monitor placed on a rooftop at 201 Varick Street, one mile north-northeast of the World Trade Center complex. The results presented today are from samples collected October 2 through 31.
The DELTA team analyzed the samples for the unique chemical and physical signatures of dozens of substances, including elements from concrete and glass, such as silicon; from burning fuel oil, such as sulfur, vanadium and nickel; and from burning computers and electrical systems, such as lead. They also looked for carbon based compounds from burning wood, plastic and carpets. And they tested for glass shards and asbestos.
Cahill said the very fine particles contained high levels of sulfur and sulfur based compounds, which in early analyses appear to have been dominated by sulfuric acid. The very fine particles also contain high levels of very fine silicon, potentially from the thousands of tons of glass in the debris.
Cahill said even those large amounts were likely to be smaller than those present at Ground Zero and some other parts of Lower Manhattan, since weather data show that typically only part of the dust clouds traveled directly over the sampling site.
"Even on the worst air days in Beijing, downwind from coal fired power plants, or in the Kuwaiti oil fires, we did not see these levels of very fine particulates," Cahill said. The amounts of very fine particles, particularly very fine silicon, decreased sharply during the month of October.
"From 50 air samples taken, Whitman said then, "the vast majority of results are either non-detectable or below established levels of concern for asbestos, lead and volatile organic compounds."
Very fine particles can travel deep into human lungs. Such small particles may have no immediate apparent health effects in moderate concentrations, but they typically are removed from the lungs through the bloodstream and heart, increasing the possibility of health impacts.
Coarse particles are typically filtered by the nose or coughed out of the throat and upper lungs. They can irritate the mucous membranes, causing coughs and nosebleeds. In some individuals, they can cause allergic reactions such as dry eyes; nose, throat and skin irritation; coughing, sneezing and respiratory distress. They can also cause breathing problems or aggravate pre-existing breathing problems, such as asthma.
There are no established safe limits for inhaled very fine particles. The closest reference is the U.S. EPA "PM2.5" standard, which limits the allowable mass of airborne particles in the size range 2.5 micrometers to 0 micrometers. That standard is based on health studies of typical air samples, in which very fine particles are a small fraction of the total mass.
Based on their findings, the UC Davis researchers recommend specific cleaning methods for contaminated apartments, offices and schools.
The presence of large amounts of very fine particles as late as October means that indoor clean up should be done carefully, Cahill said. Very fine particles will have penetrated crevices and fabrics in a way normal dust does not, and they are easily re-suspended, which re-exposes the room's occupants to them.
Cahill supports the recommendations made by the New York Department of Health regarding washing with water. He says do not use vacuum cleaners or brooms because they re-suspend particles. Do use wet rags, mops and wet-vacuum type cleaners.
Wipe all surfaces, including window blinds, picture tops and door frames, with wet rags.
Drapes and curtains should be washed or dry cleaned. Furniture fabrics should be steam cleaned. Carpets should be wet cleaned.
Use high efficiency electrostatic or HEPA air filters in furnaces and air conditioners, and keep humidity reasonably high indoors, to keep very fine particles from floating around.