But the water – and the muck it isleaving behind — also owes its contamination to a source as mundane asit is unexpected: Toxins common in most urban environments that madetheir way en masse into the water as it stagnated atop the city.
Sosays a University of Florida professor who has spent years studying theharmful contaminants that turn up in urban runoff, or rainwater thatwashes across streets and other hard surfaces in cities. Environmentalengineering professor John Sansalone’s perspective is especiallyrelevant because it is based on field research in New Orleans and BatonRouge, where he was a professor at Louisiana State University beforetaking a job at UF this summer.
“What we see in New Orleans isthat when you put a lot of water in contact with the urban environment,all the potential contaminants that stayed around in that environmentare now back in the water – definitely, to our horror,” Sansalone said.
Federaland Louisiana officials continue to sound alarms about the contaminatedwaters and scum left behind by the retreating flood. Early Septembertest results released late last week showed high levels of bacteria,lead and harmful levels of chemicals including arsenic, according tothe Environmental Protection Agency.
While the sources of theseand other contaminants remain under investigation, public scrutiny hasfocused on broken sewer pipes and other major failures in the city’sinfrastructure attributed to Hurricane Katrina. Though these arecertainly real problems, it’s also highly likely that the stagnantwaters are contaminated because they’ve soaked up “legacy” pollutantsthat accumulated during normal conditions on the city’s streets,sidewalks, roofs and other impermeable surfaces, Sansalone said.
Thesepollutants, which normally appear in urban runoff, are more toxic thancommonly understood, he said. In a study published last month in WaterEnvironment Research, Sansalone and three co-authors report that runofffrom an elevated section of Interstate 10 in Baton Rouge contained somecontaminants at levels “greater than those found in untreated municipalwastewater from the same service area,” according to the study.
Thefindings were based on periodic analysis of runoff that drains offInterstate 10 into Baton Rouge’s City Park Lake just below the highway.Based on data first gathered in 1999, they revealed high levels ofparticulates, or microscopic- to millimeter-sized particles ofmaterial, as well as high chemical oxygen demand, an indicator of thepresence of organic chemicals in oil, gas, grease, cigarette filtersand other pollution.
Other research on urban runoff, meanwhile,has detected high levels of toxic metals and nutrients includingphosphorus thought to leach from building materials, Sansalone said.
Organicchemicals are particularly dangerous to fish and other aquatic lifebecause they reduce the levels of oxygen in the water, impinging on itsability to support life. Particulates cloud water, reducing sunlightpenetration and plant growth. Once they cross a certain threshold,organic chemicals and metals also can be harmful to people.
NewOrleans officials remain extremely concerned about bacterialcontamination in the flood waters. Typically the result ofcontamination from untreated sewage, bacteria also can come from urbanrunoff, Sansalone said. Although it was not measured as part of hispublished study, other studies have found that such runoff containsheightened levels of bacteria stemming from bird and animal droppings,among other sources.
Sansalone said based on his studies of urbanrunoff alone, it’s critical that environmental officials scour the cityof flood residue. “How we clean up this residual matter – which willnot be easy – will be a chronic issue to the health of the city,” hesaid.
He said the contamination in New Orleans also highlightsthe need for other cities nationwide to do more to remove the toxins inurban runoff before, rather than after, it gets washed into waterways.There are several good strategies, he said. Increasingly affordable“permeable pavements” allow runoff to be stored, evaporate or percolatethrough pavement and into the ground, where soil and microorganisms canhelp filter the contaminants. Planting vegetation and especially treesalso creates aesthetically pleasing buffer zones, providing storm waterflooding control and other benefits. Finally, cities can use high-techstreet sweeping equipment that is very effective at capturing pavementcontaminants.
“If you pick up this potentially toxic materialbefore it gets into the hydrological cycle, it is far more economicalthan if you try to take it out of the water after the fact,” he said.
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