Many cities in the United States and Canada burnt their rubbish and waste in municipal incinerators during much of the last century.
The majority of these facilities were decommissioned by the early 1970s due to worries about the pollution they added to the air, but a new Duke University study reveals that their contamination may still be present in urban soils.
“We found that city parks and playgrounds built on the site of a former waste incinerator can still have greatly elevated levels of lead in their surface soils many decades after the incinerator was closed,” said Daniel D. Richter, professor of soils at Duke’s Nicholas School of the Environment, who co-led the research.
Exposure to lead in soil has been linked to potential long-term health problems, particularly in Lead exposure in soil has been related to long-term health concerns, particularly in children. These include probable brain and nervous system injury, decreased growth and development, and learning and behavioural issues.
Richter and his students collected and analysed surface soil samples from three city parks in Durham, North Carolina, that are located on old incinerator sites that were closed in the early 1940s.
Lead levels in samples collected from a two-acre stretch of East Durham Park exceeded 2000 parts per million, more than five times the current US Environmental Protection Agency (EPA) threshold for safe soils in children's play areas.
Samples collected from Walltown Park mostly contained low lead levels, “but about 10 per cent were concerning and a few were very high,” Richter noted.
Samples collected from East End Park all contained levels of soil lead below the current EPA threshold for children’s safety “and presented no cause for concern,” he said.
The sharp differences in lead levels between the three parks underscore the need for increased monitoring, he stressed.
“Determining where contamination risks persist, and why contamination is decreasing at different rates in different locations, is essential for identifying hotspots and mitigating risks,” Richter said. “Many cities should mobilize resources to do widespread sampling and monitoring, and create soil maps and, more specifically, soil lead maps.”
“That’s where we really need to go,” Richter said.
“Not just in Durham but in hundreds of other cities where parks, as well as churches, schools and homes, may have been built on former waste incinerator and ash disposal sites.”
The Duke team discovered that between the 1930s and 1950s, approximately half of all communities surveyed in the United States and Canada burned solid garbage.
“These incinerators burned all kinds of garbage and trash, including paint, piping, food cans and other products that contained lead back then,” Richter said. The leftover ash, in which lead and other contaminants were concentrated, was sometimes covered with a too-thin layer of topsoil or even spread around parks, new construction sites or other urban spaces as a soil amendment.
“Historical surveys indicate a lack of appreciation for the health and environmental hazards of city-waste incinerator ash. Back then, they didn’t know what we do now,” he said.
New technology might make sampling and monitoring more viable at the thousands of potentially contaminated locations across the country, he suggested. His lab can now perform a preliminary assay on a soil sample for various metals, including lead, in under 20 seconds using a portable X-ray fluorescence device.
Using historical records about garbage incineration and ash disposal could potentially help to locate hotspots faster. Richter and his students provide histories gleaned from archived public works records, old street maps, and newspaper clippings in six sample cities: Los Angeles, New York City, Baltimore, Spokane, Wash., Jacksonville, Fla., and Charleston, S.C.
“This is something you could do for many cities to guide monitoring efforts,” Richter said.
“There’s been a lot of interest in mitigating lead exposure in cities, but most until now has been focused on reducing risks within the home. Our study reminds us that risks exist in the outdoor environment, too,” he said.
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