Interview with Steve Presley
Following an on-site assessment of the environmental impact of massive flooding in New Orleans after Hurricane Katrina, lead investigator Steve Presley answered questions about the pollution and contamination findings made by his team. Presley is an associate professor in the Department of Environmental Toxicology and a researcher at The Institute of Environmental and Human Health at Texas Tech University.
Q: When did you and your team go to New Orleans?
Steve Presley: Our first trip was Sept. 14 through Sept. 20, about 16 to 20 days after Katrina. The research findings we are publishing in this issue of Environmental Science and Technology are from this trip. We made a subsequent trip and those samples are being analyzed now, and we expect the results will be published in the new year.
Q: What prompted you to do this study?
SP: More than anything else, we recognized the real potential for dispersion of huge amounts of hazardous materials in the floodwaters and wanted to get baseline information on what kinds of contaminants or toxicants were present in the soil, the water and the whole area as a result of the flood. We had two principal goals:
First, to find out what was there and what immediate human health threats were posed to recovery workers or returning residents. And second, to establish baseline data to develop predictions on the extent of environmental damage that might result, including to wildlife in the Lake Pontchartrain wetlands ecosystem due to the floodwaters being pumped into the lake.
Q: Where did you conduct the study? Were you primarily in the city or did you collect samples from a large area?
SP: Because we were limited in time and resources we tried to get a good cross section of the area both inside and outside the city. We established a transect [line that cuts across the area] that ran from the French Quarter northward to Lake Pontchartrain. We took samples every half mile along that transect, which ran along Esplanade Avenue all the way to Bayou St. John and along Wisner Boulevard. This was not an extremely poor, nor an extremely affluent area. Socio-economically it was kind of a middle of the road area.
Q: Were you taking samples down flooded streets?
SP: When we were there, most of the French Quarter and city had been drained. The Ninth Ward was still mostly under water and off limits. New Orleans was still under lockdown and a curfew was enforced. They weren’t letting people into the city on Interstate 10, unless they had authorization. There were certain areas our team could not get into.
Q: How did your team collect its samples?
SP: We basically collected the top two to five centimeters of sediment and soil at each of the sampling sites. We made no attempt to differentiate between soil and sediment because you could not at that point. We took water samples at each sampling site where there was remaining floodwater. We also took samples in the canals in the city and from an industrial canal that drains the city. In the wetland areas, we collected mosquitoes, various snake species and an alligator that had been freshly hit on the road. Organs such as the liver and kidney and fat tissues were excised and tested for toxicants.
Q: What were the biological hazards your group encountered?
SP: There was concern about Saint Louis encephalitis and West Nile virus throughout the entire Hurricane Katrina path of destruction. Our intent was to collect as many mosquitoes as possible, screen them for St. Louis encephalitis and West Nile virus to help detect and prevent an outbreak. However, the U.S. Air Force and U.S. Centers for Disease Control and Prevention were very aggressively conducting mosquito control operations, and the insect problem was essentially eliminated.
Q: What about bacteria and molds?
SP: We found very high levels of Aeromonas species bacteria, which thrive in water that is polluted, brackish and even in freshwater. Aeromonas species are typically pathogenic to humans through ingestion, such as in drinking water, and can cause diarrhea and vomiting. The potential for these bacteria to infect wounds is just now getting looked at. We found E. Coli and Vibrio, and those are pathogenic as well. We focused on Aeromonas because it is an emerging health threat and not much is known about it. We did not collect samples for or screen for molds on our first trip.
Q: What makes Aeromonas so dangerous?
SP: It’s been reported from a study out of Texas Tech that Aeromonas can become resistant to antibiotics if it is in water polluted with heavy metals. Actually Dr. John Zak of our team, who specializes in Aeromonas and other water-borne microorganisms, can discuss Aeromonas much more intelligently with you.
Q: Why is Aeromonas dangerous?
SP: It is an opportunistic pathogen and can cause wound infection. In a situation like Katrina or a tsunami, if there are people who are injured or scratched, that is an opportunity for it to get past the protective skin barrier and infect the wound. We found very high levels around the Superdome and Charity Hospital.
Q: The data your team found expanded upon and complemented a study by Purdue and others at Louisiana State University, which essentially said the Katrina floodwaters were the same as any other urban floodwaters. Could you explain how and why your studies differed?
SP: In the LSU study, researchers collected columnar water samples at different depths in the floodwaters immediately after Hurricane Katrina. Because there were such vast amounts of water, the toxicant levels that they found were not alarming. Our findings looked at soil and sediment and remaining pools of floodwater left in low-lying areas -- such as in yards and along streets after the floodwaters were gone. Other than superficially, we really can’t compare our findings with those of the previous study. The two-week time period between the studies made a big difference because most of the floodwater had been pumped out.
Q: What kinds of contaminants were found?
SP: We found elevated levels -- elevated but not “the-sky-is-falling” levels -- of lead and arsenic and the usual suspects you would expect in an urban flooding situation.
Q: By what do you gauge high or low levels of contaminants?
SP: The Region 6 Office of the U.S. Environmental Protection Agency has established what is called Human Health Soil Screening Levels for acute exposure. That means if you have a toxicant or contaminant that exceeds those levels in the soil, then it’s a threat to human health.
The EPA also has High Priority Bright Line Screening Levels. Those are used in prioritizing and making plans for cleaning up a site where hazardous materials exist. If you exceed those thresholds, then that area or site gets prioritization for hazardous materials cleanup. Concentrations for the Bright Line Screening Levels are typically higher than for the Human Health Soil Screening Levels.
Q: So, what exactly did you find?
SP: We found several metals like lead and arsenic that exceeded both the Human Health Soil Screening Levels and the High Priority Bright Line Screening Levels. We also found pesticides that exceeded the Human Health levels. There are others, but those were the ones that were of the most concern.
Q: How do your findings affect the cleanup approach?
SP: These toxicants are not a risk factor unless people are exposed to them continuously. If the soil particles become airborne along with the toxicants, people could breathe in those contaminants. If the soil undergoes hazardous materials cleanup, work crews will dig it out and dump it, creating a lot of dust that people could breathe. The potential exposure of small children playing outside in soils that contain high lead concentrations, whether at their home, school playgrounds, or at city parks is a concern we consider valid and must be addressed.
Q: The sun may have killed off a lot of the bacteria, but if it rains again, what happens to the bacteria in the soil and sediment, such as Aeromonas?
SP: We are investigating that further. If it floods again, and floodwaters puddle, will Aeromonas populations explode again? We don’t have the answer to that.
Q: On Sept. 6, officials began pumping water out of the city into Lake Pontchartrain. Can you comment on the effects of that?
SP: Most of New Orleans is below sea level and the city must pump water into Lake Pontchartrain to prevent flooding normally. Lake Pontchartrain is shallow with a lot of swampy marshlands. Those wetlands are very sensitive ecosystems where toxicants can very rapidly devastate wildlife, plant life, and the natural balance in the lake.
Q: So, what could be the outcome of the contaminated water running into the lake and wetland areas?
SP: Some animals like snakes and alligators will bio-accumulate toxicants or contaminants over time from contaminated fish and other prey that they ingest. Eventually they will accumulate toxicant levels that are dangerous to the animal and it could affect their reproduction.
Q: As for humans, is the city safe for habitation?
SP: That’s a really tough question to answer. There are definitely some areas, as one would expect, where the exposure hazard to certain chemicals and other toxicants is high. There were other areas that were fairly clean or fairly typical. Our purpose was and is not to advise on whether New Orleans is safe for habitation. That is for the elected decision-makers to do. Our job is to analyze and present the scientific results of our study to them and explain the implications of those findings.
Q: Describe the scope of the contamination in the city.
SP: The sediment didn’t just all drain into the street, get pumped out and dry. It’s in houses. It’s on top of houses and in cars. It’s everywhere you can imagine. So cleaning up the contamination is a lot bigger issue than just taking a grader and front-end loader and cleaning up the streets. Residents are having to tear out the drywall and insulation in homes and buildings. In a lot of those older homes there could be contaminants like asbestos that may have been there for 50 or 100 years that are now being exposed.
Q: What should people do to protect themselves?
SP: During the rebuilding process, it’s a good idea to wear a dust mask. What we’re hoping to do by publishing our findings is to help planners -- whether it’s the Army Corps of Engineers, the CDC or the EPA -- come up with ways to better protect people. That’s ultimately the goal of this project.
Q: At the end of November, city planners reopened a school in New Orleans. What should the parents of children in New Orleans be doing to make sure their children remain safe?
SP: As I said before, our job is to provide accurate, validated and sound scientific findings of our study to the agencies and individuals that are charged with making the decisions and advising the citizenry regarding threats/risks to public health and safety. We are prepared and ready to assist those agencies and authorities in further assessing risk factors and long term environmental effects.