( Broken sewers flooded industrial plant...)Toxic flood lifts lid on common urban pollution problem

But the water - and the muck it is leaving behind -- also owes its contamination to a source as mundane as it is unexpected: Toxins common in most urban environments that made their way en masse into the water as it stagnated atop the city.

So says a University of Florida professor who has spent years studying the harmful contaminants that turn up in urban runoff, or rainwater that washes across streets and other hard surfaces in cities. Environmental engineering professor John Sansalone's perspective is especially relevant because it is based on field research in New Orleans and Baton Rouge, where he was a professor at Louisiana State University before taking a job at UF this summer.

"What we see in New Orleans is that when you put a lot of water in contact with the urban environment, all the potential contaminants that stayed around in that environment are now back in the water - definitely, to our horror," Sansalone said.

Federal and Louisiana officials continue to sound alarms about the contaminated waters and scum left behind by the retreating flood. Early September test results released late last week showed high levels of bacteria, lead and harmful levels of chemicals including arsenic, according to the Environmental Protection Agency.

While the sources of these and other contaminants remain under investigation, public scrutiny has focused on broken sewer pipes and other major failures in the city's infrastructure attributed to Hurricane Katrina. Though these are certainly real problems, it's also highly likely that the stagnant waters are contaminated because they've soaked up "legacy" pollutants that accumulated during normal conditions on the city's streets, sidewalks, roofs and other impermeable surfaces, Sansalone said.

These pollutants, which normally appear in urban runo
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Source:University of Florida