The findings were based on periodic analysis of runoff that drains off Interstate 10 into Baton Rouge's City Park Lake just below the highway. Based on data first gathered in 1999, they revealed high levels of particulates, or microscopic- to millimeter-sized particles of material, as well as high chemical oxygen demand, an indicator of the presence of organic chemicals in oil, gas, grease, cigarette filters and other pollution.
Other research on urban runoff, meanwhile, has detected high levels of toxic metals and nutrients including phosphorus thought to leach from building materials, Sansalone said.
Organic chemicals are particularly dangerous to fish and other aquatic life because they reduce the levels of oxygen in the water, impinging on its ability to support life. Particulates cloud water, reducing sunlight penetration and plant growth. Once they cross a certain threshold, organic chemicals and metals also can be harmful to people.
New Orleans officials remain extremely concerned about bacterial contamination in the flood waters. Typically the result of contamination from untreated sewage, bacteria also can come from urban runoff, Sansalone said. Although it was not measured as part of his published study, other studies have found that such runoff contains heightened levels of bacteria stemming from bird and animal droppings, among other sources.
Sansalone said based on his studies of urban runoff alone, it's critical that environmental officials scour the city of flood residue. "How we clean up this residual matter - which will not be easy - will be
Source:University of Florida