Mapping lead in New Orleans soil
April 07, 2013
Howard Mielke has collected thousands of soil samples from urban areas across the United States. Each sample is tested for lead content, allowing him to map the soil lead levels throughout an entire city. He’s mapped several large cities, including Baltimore, Detroit, and Minneapolis. His most recent lead mapping project took shape in the city where he lives and works: New Orleans.
With every point the Tulane Professor plotted on his New Orleans map, it became clearer that the interior of the city was littered with high amounts of lead contamination. Amounts were high enough to pose potential health risks to New Orleans residents, especially children who constantly touch their face and mouth. Mielke’s own daughter, Beverly, suffered from high blood levels when she was younger. It was an experience Mielke says has motivated him to continue his lead mapping research. “It’s possible it created amblyopia for her, which is better known as lazy eye,” he explains.
The Center for Disease control states that exposures of more than six micrograms of lead per day in children can cause a variety of learning and developmental disabilities. “To put that in perspective, think of one of those packets of artificial sweeteners,” says Mielke. “In that packet is one gram of sweetener. That’s one million micrograms. And children only need to be exposed to over six micrograms per day to run into problems.”
To evaluate the lead exposure of children in New Orleans, Mielke and his team combined their soil mapping data with blood lead databases from the Louisiana Childhood Lead Poisoning Prevention Program. This allowed them to see how blood levels in children vary depending on the different types of urban environment’s they’re exposed to in the city and begin creating solutions to reduce the high levels of lead pollution in New Orleans. Their study appeared in Environment International this January.
The researchers divided their soil mapping data into high and low lead areas. Areas of high soil lead contained 100 mg/kg or greater while low lead areas contained less than 100 mg/kg. In both the low and high lead areas, samples were collected near four types of locations that represent potential play areas for children in residential communities: busy streets, residential streets, house sides, and open spaces (parks or large yards located away from houses or streets).
The results of the study were what Mielke expected all along. The median soil lead levels were highest near busy and residential streets. “In the early 1970s, leaded gasoline contained up to 2 grams of lead per gallon,” says Mielke. “Combine that with the fact that cars were less fuel efficient back then and had larger gas tanks, and you start to see how so much lead was introduced into the environment.”
This is all familiar territory for Mielke, a professor at Tulane University. His research helped begin the rapid phasing out lead from gasoline in the 1980s, a process that has drastically reduced lead pollution in the United States and all nations. But now it’s 2013 and Mielke is still battling the leaded gasoline of the past, which now pollutes the soil of historically traffic-heavy areas like New Orleans.
Lead paint is another source of lead contamination that was banned nearly 40 years ago but is still having serious effects on the environment and human health. After busy street locations, soil near the sides of houses contained the highest median soil lead levels due to home renovations dealing with lead paint. Power sanding is thought to be most responsible for lead pollution near houses.
Mielke says New Orleans is an excellent site for this kind of study because of its proximity to the Mississippi River. The city is located on alluvial soils deposited from river sediments, allowing researchers to measure lead levels in the modern sediments and compare those levels against contaminated urban alluvial soils to help evaluate the pollution.
Hurricane Katrina presented another interesting component to the study. Some researchers have claimed lead levels in New Orleans soil have increased dramatically since Katrina struck the city in 2005 due to hasty home renovations that released lead paint into the environment. But Mielke’s results suggest the opposite. “With the storm surge coming into New Orleans, there was a lot of new material that came in from outlying areas,” he says. “There was a layer of that material and the surface of the soil became much cleaner after Katrina.”
Mielke says there’s a lot to learn from the effects Katrina had on New Orleans, and the solution to high levels of lead in urban soil can be found in the cleaner soils outside of the city. Clean soil along the Mississippi River is abundant, containing lead levels of around 5 mg/kg while urban soils contain a median of more than 100 mg/kg. Mielke has already successfully used this cleaner river sediment, paired with a geotextile fabric, to cover lead contaminated soil found in childcare center play areas with success. And the city of New Orleans has already covered 13 parks with this soil.
Along with clean soil cover, Mielke also says that changes need to be made in legislation to help protect the soil quality in urban areas. “The Unites States already has a clean air act and a clean water act. Why not some sort of clean soil program?” A clean soil policy is already underway in Norway, where the government is creating lead-safe playgrounds at childcare centers, schools, and parks to protect children from lead poisoning.
Throughout the years, Mielke’s priority has always been children’s safety. When his daughter Beverly had surgery to correct her eye condition, her father asked doctors to test her blood for high levels of lead and was laughed at. They told him children of good socioeconomic status who lived in nice neighborhoods weren’t at risk for high blood lead levels. But they tested her blood for lead anyway, and Mielke was right.
After that, he began testing any environment including soil his daughter was being exposed to and found that many of her play areas were polluted with extremely high amounts of lead, including her daycare playground. He arranged to have the playground covered with clean soil, and as he expected, his daughter’s blood lead levels soon began to decrease.
Now his daughter is an M.D. working at the University of Washington. “She’s smarter than I am,” laughs Mielke. “She’s a perfect example of the resilience that is possible if you catch and curtail lead exposure at a young age. But you have to keep the kids out of the lead. That’s the key.”