Katrina floodwaters not as toxic to humans as previously thought, study says

October 11, 2005

The floodwaters that inundated New Orleans immediately following Hurricane Katrina were similar in content to the city's normal storm water and were not as toxic as previously thought, according to a study by researchers at Louisiana State University. Their study, the first peer-reviewed scientific assessment of the water quality of the Katrina floodwaters, is good news for those who've been exposed directly to the floodwaters, the scientists say.

But the LSU researchers caution that the same floodwaters that were pumped back into Lake Pontchartrain contain high levels of some toxic metals, especially copper and zinc, and could pose a long-term danger to the area's aquatic life, which are more sensitive to the metals than humans. Their findings will appear in the Oct. 11 online issue of the American Chemical Society's journal Environmental Science & Technology.

"What we had in New Orleans was basically a year's worth of storm water flowing through the city in only a few days," says study leader John Pardue, Ph.D., an environmental engineer and director of the Louisiana Water Resources Research Institute at LSU in Baton Rouge. "We still don't think the floodwaters were safe, but it could have been a lot worse. It was not the chemical catastrophe some had expected."

Some experts had predicted that the floodwaters from Katrina could potentially destroy chemical plants and refineries in the area, releasing a deadly brew containing toxic levels of benzene, hydrochloric acid and chlorine. Instead, high levels of bacteria and viruses were the biggest human threat, not exposure to chemicals, Pardue and his associates say.

The researchers obtained 38 floodwater samples from widespread sections of New Orleans, primarily in the area of the city known as the "East Bank," where the main human contact with the floodwaters occurred. The samples, which included both surface waters and bottom samples, were taken within five to nine days after flooding occurred. Additional samples were also obtained from the 17th Street drainage canal, after pumping of the floodwater began, to evaluate the flood's impact on Lake Pontchartrain, the receiving body for the pumped floodwaters.

The researchers found high levels of bacteria, most likely from fecal contamination resulting from sewage. Levels were within the range of typical storm-water runoff in the city, the scientists say. They also detected high levels of lead, arsenic and chromium and noted that levels of these toxic metals were also similar to those typically found in the area's stormwater. In general, these particular findings were similar to those obtained by the Environmental Protection Agency in their initial assessment of the floodwaters, the researchers say.

Gasoline was also a significant component of the floodwaters, as measured by elevated levels of three of its components: benzene, toluene and ethylbenzene. These compounds were somewhat elevated in comparison to typical stormwater runoff, the researchers say. The chemicals most likely came from cars and storage tanks submerged in the floodwaters, they add.

Compounds found in common household chemicals were also detected in the floodwaters, Pardue says. The waters contained chemical compounds from aerosol paints, insecticides, caulking compounds, rubber adhesives and other common substances, they say, but at levels that typically do not create concern for human health.

If the floodwaters had occurred in another location near more industrial sites in the city and if the wind damage or water surge had been more severe, then the resultant floodwaters could have been a more serious toxic threat, Pardue says. "Instead, the city filled slowly, like a bathtub, and the water velocities and forces on the buildings, including chemical storage facilities, were relatively benign," he says. The large volume of floodwater also diluted the potency of many of the chemicals, he adds.

While serious toxicity to human life was largely avoided, the floodwater may pose a chemical risk to aquatic life in the area, Pardue says. He believes that low oxygen levels in the water that is being pumped back into Lake Pontchartrain could result in fish kills. He also says that heavy metals being discharged into the lake, particularly copper and zinc, can be toxic to fish and other marine life and may bioaccumulate and contaminate seafood collected from the region. More studies are needed to assess the long-term impact of the flood on aquatic life, Pardue says.

Funding for this study was provided by the Louisiana Water Resources Research Institute and the LSU Center for the Study of Public Health Impacts of Hurricanes.

The American Chemical Society is a nonprofit organization, chartered by the U.S. Congress, with a multidisciplinary membership of more than 158,000 chemists and chemical engineers. It publishes numerous scientific journals and databases, convenes major research conferences and provides educational, science policy and career programs in chemistry. Its main offices are in Washington, D.C., and Columbus, Ohio.

-- Mark T. Sampson
-end-


American Chemical Society

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