The floodwaters that inundated New Orleans after Hurricane Katrina were not as toxic to humans as previously thought. The findings published by researchers at Louisiana State University are good news for those who were exposed directly to the floodwaters, although say nothing of the physical devastation caused by the flood.

The LSU researchers caution, however, that the same floodwaters pumped into Lake Pontchartrain do contain high levels of some toxic metals, such as copper and zinc, and could pose a long-term problem to the area's aquatic life.

"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 lead researcher John Pardue, 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 would contain hazardous levels of benzene, hydrochloric acid, and chlorine. According to Pardue, high levels of bacteria and viruses posed a greater threat to human health than any chemicals present, although they were no higher than normal storm run-off.

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 of the floods. 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.

Pardue and his colleagues found high levels of lead, arsenic, and chromium, but as with the bacterial and viral load, these were no higher than is seen in the area's normal stormwater. The data paralleled that obtained by the Environmental Protection Agency in its initial assessment. The researchers point out that gasoline was 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, the researchers add.

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

However, aquatic life is much more sensitive to even these low levels of toxic chemicals, Pardue says. 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.

Environ Sci Technol; http://dx.doi.org/10.1021/es0518631