New Orleans soils get clean bill of health—almost
Recent hurricane activity didn’t significantly contribute to pollution in sediments in Lake Pontchartrain or soils in and around New Orleans.
Reports of a “toxic soup” flooding the streets of New Orleans and the surrounding region surfaced in the aftermath of Hurricane Katrina. But a year after the disaster, scientists from the U.S. Geological Survey (USGS) and elsewhere conclude that the water that coursed through the city and the soils that remain hold few surprises. They say that most contamination that could pose concerns lingered in urban areas since before the hurricane.
Samples collected before and after Hurricane Katrina showed some hot spots, but overall, the region seems to be below toxic regulatory levels for many of the metals and compounds tested. Even water-column and sediment samples from Lake Pontchartrain have turned out to be relatively benign, according to research published today on ES&T’s Research ASAP website (DOI: 10.1021/es060933g).
“Compared to lake sediments all over the country, Lake Pontchartrain sediments are similar,” says Peter Van Metre of USGS, who is the lead author of the ES&T research. “There’s a lot of urban contamination, and Lake Pontchartrain is typical of that.” Still, Van Metre and his colleagues found that pollutants were concentrated at the mouth of the 17th Street Canal, through which much of the flood water was pumped out of the city.
The team analyzed mud from the city and sediments from canals and Lake Pontchartrain for a long list of possible urban contaminants. In some cases, particularly for fragrances, newer pesticides, and cholesterols, they used novel methods. Zinc, PCBs, and DDT, among other compounds, appeared in mud and lake-sediment samples at the mouths of several canals. High concentrations at many sites dissipated weeks after the hurricane passed. Lake Pontchartrain “is big enough and the circulation is strong enough in and out of the Gulf of Mexico” to dissipate those inputs, Van Metre says.
In some places on land, Hurricane Katrina dumped many centimeters of sludge, which was the consistency of chocolate frosting, says Geoff Plumlee of USGS. At the September meeting of the American Chemical Society (ACS), he presented results from the urban center of New Orleans as well as from outside parishes that showed a wide range of contaminant levels. In Chalmette, for example, the samples had distinct marsh-soil signatures, showing that Katrina pulled up those soils from marshes and dumped them inland, Plumlee said.
The clues to the soil’s identity included tiny framboidal (raspberry-shaped) grains of pyrite. The iron–sulfide mineral generally appears in mine tailings, and it has the potential to oxidize, leading to acidic runoff. Plumlee suggested that a small chance exists that this could occur in soils in the region, but he added that it would take years, depending on how the soil is exposed.
High levels of arsenic and lead, as well as cadmium and other metals, showed up in soil samples from downtown New Orleans, but many were similar to historic levels measured pre-Katrina, Plumlee said. Bill Foreman of USGS, also a coauthor on the ES&T paper, reported at the ACS meeting that dieldrin (banned in the 1970s) and other pesticides used for treating termites had high residues in urban areas. In some downtown “hot spots,” Foreman said, dieldrin hit 46–92 micrograms per kilogram. Benzo[a]pyrene, a PAH from combustion, exceeded U.S. EPA levels downtown and in some residential areas, he said.
In general, Plumlee emphasized, the levels found outside the downtown area for metals and other potentially hazardous compounds tended to be below federal standards for soil exposures (as shown by an initial USGS open-file report published last February). In the urban center, lead levels were the most elevated—the residue of decades of industrial activity, left behind in historic deposits from paint, industrial applications, and leaded gasoline.
In the past decade, Howard Mielke of Xavier University and co-workers showed that the lead in New Orleans’ soil caused high blood-lead levels in children who played on contaminated schoolyards and other “leaded” dirt in the city. By chance, Mielke’s group took soil samples the week before Hurricane Katrina, partly to check the success of a remediation program that included dumping lead-free soil onto those sites. Some tests already had showed a decrease in the blood-lead levels of children playing on the treated sites.
With more sampling post-Katrina, Mielke and co-workers showed that Katrina did not change those historic lead levels. The hurricane neither dumped sediments to cover up the lead-bearing soils, nor did it carry them away.
Still, Mielke sees the hurricane as an opportunity to advocate remediation that dovetails with the post-hurricane cleanup. He suggests a central distribution center with clean soil to dump atop the lead-contaminated areas in the center of the city.
“If you go out and sample in a place as historic as New Orleans, you will find contaminants from historical use,” says Sven Rodenbeck, an environmental engineer and commissioned officer in the U.S. Public Health Service. He also points out that the historic parts of New Orleans were farthest from the levees breached. “As far as moving existing contamination, the strength of floodwaters [had] pretty much dissipated” by the time they reached those sites.
Environmental groups have disagreed with EPA and other organizations on this point ever since the disaster. Still, “with the exclusion of the Murphy Oil spill,” southwest of the city, Rodenbeck says, “the floodwaters did not result in any widespread contamination of the New Orleans area.”
