Lead levels decline in soil, blood in post-hurricane New Orleans.

Zahran, S, HW Mielke, CR Gonzales, ET Powell and S Weiler. 2010. New Orleans before and after hurricanes Katrina/Rita: A quasi-experiment of the association between soil lead and children’s blood lead. Environmental Science and Technology http://dx.doi.org/10.1021/es100572s.

Lead levels in both soil and children declined dramatically after hurricanes twice flooded New Orleans in 2005. The researchers who report the results propose that the flooding altered the soil lead conditions, thereby lowering children's exposure to the neurotoxin.

Few studies have examined the impact of these specific natural distasters on environmental health outcomes. The results suggest a need for tougher policies that address soil contamination within children’s play areas on both private and public property.

In almost all of the neighborhoods tested, soil lead levels fell by almost 50 percent to well below federal safety standards. At the same time, children's blood lead levels decreased more than 30 percent.

Surprisingly, the change in soil lead levels predicted the change in blood lead levels. The changes in blood lead levels were observed even when soil lead levels decreased by as little as 1 percent. Declines in blood levels were largest in neighborhoods with more than 50 percent change in soil lead levels.

In 2005, Hurricanes Katrina and Rita – and the subsequent failure of the levees – resulted in 80 percent of New Orleans being flooded. Flooding water can carry and deposit soil or wash away the top soil layers.

Lead is a well characterized pollutant that can disrupt brain development, memory and learning in young children. The Centers for Disease Control blood lead guideline for children is 10 micrograms per deciliter (µg/dL), but negative effects to the human brain have been observed at lead levels as low as 2 µg/dL. Many experts believe there is no safe level of exposure.

Lead-based paint – which was phased out in the early 1970s – continues to be a primary and familiar source of children's lead exposure. Another lesser known, yet important source, is soil. Lead from peeling house paint and fallout from now banned leaded gasoline and some industrial sources pollute soil. Children who play in the contaminated soil may have higher blood lead levels, particularly in urban areas like New Orleans where soil lead levels have been historically elevated.

Researchers collected 874 soil samples from 46 different neighborhoods both pre- and post-hurricanes. They measured blood lead levels from 13,306 children younger than six years old: 11,191 were measured before the hurricanes and 2,115 were measured after the hurricanes. Researchers were not able to measure each child more than once. Instead they grouped the children by neighborhood. All analyses examined changes in soil and blood lead at the neighborhood level.

The researchers at Colorado State University and Tulane University found that, on average, soil lead levels declined 46 percent after the hurricane-related events. In the pre-hurricane period, 15 of 46 census tracts, or neighborhoods, exceeded the U.S. Environmental Protection Agency's regulatory standard of 400 miligrams per kilogram (mg/kg) of lead; whereas, in the post-hurricane period, only six of the 46 neighborhoods exceeded the standard.

This decline in soil lead levels was correlated with a parallel decrease in children’s blood lead levels. When researchers compared average blood lead levels by neighborhood, they found that blood levels decreased 33 percent in the post-hurricane period to 3.45 µg/dL from 5.14 µg/dL.