Floodwater Not as Toxic As Feared, Experts Say

Industrial chemicals, such as polychlorinated biphenyls (PCBs) and brominated flame retardants (PBDEs), either were not found in the fish or were in the same concentrations as before the storm. Previous studies had shown no contamination from oil-derived chemicals.

The floodwater samples in the new study were collected on Sept. 3 from the residential Lakeview area and on Sept. 7 from Tulane-Gravier, a downtown neighborhood that includes the Louisiana Superdome and Charity Hospital. The hurricane struck the city on Aug. 29.

Pardue, the LSU researcher, and his colleagues -- traveling in a three-boat flotilla that included armed guards -- sampled surface and bottom water, which was 10 feet deep in some places.

The floodwater averaged about 100,000 coliform bacteria per 100 milliliters of water, far above the government standard of 200 for swimming and other "primary contact." For drinking, the standard is zero. After the storm, Lake Pontchartrain's coliform level was about 1,000 bacteria per 100 milliliters, suggesting that the water the city pumped in was substantially dirtier.

However, that level of contamination "was generally within the range . . . for storm water discharges . . . during normal wet weather flow," the researchers wrote.

Fecal bacteria do not necessarily cause diseases.

The tests showed that the water contained zinc and copper levels 10 times as high as is tolerated by freshwater fish, but well below the safe limits for drinking water.

The water pumped into the lake apparently did not kill fish, probably because it was so depleted of oxygen that fish had moved away, Pardue said.

The dissolved metal will settle to the bottom of the lake, he said. "Will that provide a source of metal that will be released over time? That is an unanswered question," he added.

The concentration of lead averaged 38 micrograms per liter. The limit for drinking water is 15 micrograms per liter. For arsenic, it was 50, with a drinking-water limit of 10. There was little evidence, however, that people were drinking the floodwater, which was a quarter as salty as seawater.

Given the huge volume of water from Katrina, the concentration of metals and arsenic would have been much lower if they had come only from roads, lawns and other surfaces. Pardue believes the other sources were submerged vehicles and houses.

There is copper in electrical wiring and brake pads; arsenic in brake linings; lead in batteries; and zinc in many plated metals.

Despite the visible sheen on the water in many places, the concentration of various gasoline compounds was very low. Dangerous substances such as benzene and toluene evaporate quickly, with "half-lives" of two to 20 hours, and are unlikely to remain in the sludge.

Staff writer Peter Whoriskey in New Orleans contributed to this report.