When the floodwaters of Hurricane Katrina rampaged through New Orleans five years ago, they left behind a toxic legacy — soil contaminated with dangerous levels of arsenic and lead in and around playgrounds, schools, backyards, and elsewhere. Five years out from the tragedy, researchers are starting to piece together the story of how floodwaters stirred up and moved around these toxic heavy metals. They found that the floodwaters carried arsenic-laden soils into residential areas where children play, but in many areas lead levels actually decreased as a result of the flooding.
The Katrina floodwaters covered nearly 80 percent of the city and, when they receded, left behind a one-inch thick layer of sediment that coated streets, sidewalks, backyards and playgrounds. In the months following Hurricane Katrina, researchers from the Environmental Protection Agency (EPA), state agencies, and universities collected soil samples from around the city. They found that, in many areas, arsenic and lead levels far exceeded state and federal standards meant to protect health.
More than 90 percent of the soil samples tested by EPA contained arsenic levels that exceeded the EPA’s human health soil screening level of 0.39 parts per million (ppm), which is meant to protect people from cancer. Soil in the New Orleans region contains natural stores of arsenic at levels of about 5 ppm. Still, more than a third of the samples exceeded the Louisiana Department of Environmental Quality’s soil screening level of 12 ppm.
Prolonged exposure to arsenic is linked to increased risk of bladder, lung, and skin cancer as well as to brain and neuron damage, skin lesions, heart and lung problems, and possible reproductive problems. Children are especially vulnerable to toxic metals because they come in direct contact with soil. Young children frequently put their fingers to their mouths, and children of all ages track soil into homes where metals can stick to dust and migrate onto cooking and eating surfaces.
Katrina’s floodwaters appear to have brought arsenic into closer contact with children, according to work done by a collaboration of scientists from Tulane, Dillard, and Xavier Universities in New Orleans and the Natural Resources Defense Council (NRDC). Prior to the hurricane, little was known about arsenic contamination in city soils, so it was impossible to tell whether the post-hurricane arsenic levels were preexisting or were due to the floodwaters. The scientists located soil samples that had been collected and archived at Xavier University in Louisiana. All of the archived soil samples had lower levels of arsenic than did the post-hurricane samples, suggesting that the floodwaters were the source of the arsenic contamination. “Arsenic was not a widespread contaminant prior to the hurricane. Its distribution throughout the city was very likely due to the flooding,” says Miriam Rotkin-Ellman, a scientist at NRDC and co-author of the study.
The source of the arsenic is unclear — it may have come from arsenic-contaminated industrial areas, sediments stored in nearby Lake Pontchartrain, wooden playground equipment treated with arsenic-based preservatives, or a combination of these sources.
Lead … and leaded gasoline
Lead was also found throughout the city at levels that exceeded the EPA’s human health soil screening level of 400 ppm for children’s play areas. However, in a study published in June, researchers noted that many parts of the city had lower levels of lead than they did before hurricanes Katrina and Rita hit in the summer of 2005. For the study, the researchers looked at lead levels in 46 census tracks around the city. Prior to the hurricanes, 15 of 46 census tracts had soil lead concentrations of more than 400 ppm, versus only six after the hurricanes. Soil lead levels dropped in a total of 29 of the 46 tracts. Soil lead levels dropped on average 39 percent from a median level of 329 ppm to 203 ppm.
What is more, these declines in soil lead levels correlated with drops in blood lead levels in children. The median blood level dropped 33 percent, from about 5 μg/dL to 3.5 μg/dL. Blood lead levels dipped by 53 percent on average in census tracts where soil lead levels fell by 50 percent or more. The lowest blood levels were found in children born after the hurricanes. Scientists set safe soil levels based on estimates about the amount of soil people come in contact with over time through activities such as playing.
The lowered blood lead levels are reassuring, but it is not time to get complacent, according to Howard Mielke, a research scientist at the Tulane/Xavier Center for Bioenvironmental Research and a co-author on the study. According to Mielke, these children are still being exposed to potentially damaging levels of lead. A soil lead level of 400 ppm will produce a blood lead level of 5 micrograms per deciliter (µg/dL) in a child age 6 or younger. Although this is below the action level of 10 µg/dL set by the U.S. Centers for Disease Control and Prevention (CDC), a number of studies have found that lead levels of 5 µg/dL can damage the developing brain and potentially cause problems with learning and behavior.
Mielke has been monitoring lead levels in New Orleans soil since the 1990s and has found that although post-hurricane lead levels declined in some areas, they remain high in many others. “The parts of the city that got really heavy flooding were the outlying areas which already had lower levels of lead to begin with,” says Mielke. “The higher ground tended to have the higher levels of lead.”
This lead has been laid down over decades, says Mielke. Although most lead cleanup initiatives have focused on lead-based paint, a significant and underappreciated source is leaded gasoline. As vehicles burned gasoline, the exhaust carried lead particles out into the air where they settled on the ground. “From the 1950s to 1982, over 17 million pounds of lead were exhausted into the city of New Orleans,” says Mielke.
Leaded gasoline was used widely across the U.S. until its final ban in 1994. Cities across the nation are grappling with this legacy, said Mielke, yet because the lead is widely distributed, the extent of the damage is hard to measure. “You can’t see it but that doesn’t mean it isn’t there.”
Lead contamination is an environmental justice issue, especially in large cities where the more affluent families moved to less densely populated, and less contaminated, suburbs. Katrina’s floodwaters brought toxic metals from an already polluted environment into contact with a population who has suffered many other hardships due to Hurricane Katrina, including loss of life and livelihood. Because toxic metals can work over periods of decades to cause cancer and derail human brain development, it is very important to address these contamination issues, says Rotkin-Ellman. “At the five-year anniversary mark, it is really important to not forget about the long tentacles of these disasters that last many years after the event,” says Rotkin-Ellman.