Duke University scientists found a new way to trace coal ash in soil. (Spoiler alert: It’s found near Lake Norman)
This story has been updated with comments from Duke Energy.
Coal ash particles have been found in soil near two coal-fired power plants: Duke Energy’s Marshall Steam Station on Lake Norman near the Iredell-Catawba county line in North Carolina, and Bull Run Steam Plant, operated by the Tennessee Valley Authority, in Clayton, Tenn., scientists announced this week.
The presence of particles, specifically of fly ash, in soil suggests they originated from the plants, the study says.
Avner Vengosh and Heather Stapleton were among six scientists from Duke University and Appalachian State to conduct the study. The results were published July 20 in the peer-reviewed journal Environmental Science & Technology.
Concentrations of toxic elements found in the ash — mercury, arsenic, lead, chromium, cadmium, radium — did not exceed human health guidelines for soil.
But “low concentrations of toxic metals in soil does not equal to no risk,” Vengosh, distinguished professor of Environmental Quality at Duke’s Nicholas School of the Environment, said in a press release announcing the study results.
Coal ash was also historically used as structural fill beneath parking lots, roads and on farm land. Last September, a sinkhole developed in a parking lot in Mooresville; the area had been backfilled with 46,000 tons of coal ash, according to state records.
“We need to understand how the presence of fly ash in soils near coal plants could affect the health of people who live there. Even if coal plants in the United States are shutting down or replaced by natural gas, the environmental legacy of coal ash in these areas will remain for decades to come.”
Until this study, testing methods using could not definitively trace certain elements in the soil back to coal ash. The new methods, though, used advanced geochemistry — lead and radium isotopes — to determine coal ash, even at very low levels, was the source.
“Because of the size of these particles, it’s been challenging to detect them and measure how much fly ash has accumulated,” Vengosh said. “Our new methods give us the ability to do that – with high level of certainty.”
In response to the study, a Duke Energy spokesman said, “Our testing extends well beyond air emissions, and decades of scientific monitoring of Lake Norman and the air around Marshall Steam Station demonstrates that residents are well-protected.”
The scientists compared soil known not to contain coal ash with 20 surface soil samples in parks and residential areas in Mooresville, near Lake Norman; most of the samples were collected downwind of the Marshall Steam Station. Low levels of fly ash were found in all of them.
By tracing the chemical fingerprint of these particles, scientists can better understand where the ash came from and where it is.
“It confirms that our new tools perform consistently and, when used together, provide a reliable method for detecting contamination that other tests might miss,” Vengosh said.
This is important not only from an environmental perspective, but also for public health reasons. Ash contains and other toxic elements. People and pets can track fly-ash contaminated soil into private homes from yards and parks; the ash can even show up in house dust.
“It underscores the need to regularly monitor sites in close downwind proximity to a coal-fired power plant, even if levels of contamination are below current safety thresholds. Fly ash accumulates over time, and risks can grow with repeat exposures to playground dust or home dust,” Vengosh said.
Many residents who live near the Marshall Steam Plant are concerned about the number of thyroid cancer cases in two zip codes that include Lake Norman. Here, the rate of that type of cancer is significantly above the state average, according to state Cancer Registry data. State health officials, though, have not identified a cancer cluster there.
Former Mooresville resident Susan Wind, whose teenage daughter had thyroid cancer — she has recovered but the cancer has returned — held several fundraisers for the study. (The National Science Foundation co-funded it.) “This is just the beginning,” Wind said. ” More will continue to come out about the dangers of living among this coal ash. Until the EPA starts putting the health of the people first and not the profits for these companies, we will continue to watch people fall ill in these areas. Denial and deflection can only work for so long.”
Researchers have yet to identify a potential source or sources, but thyroid cancer is linked to radiation exposure. However, radium is also naturally occurring in some soils, so it is important to determine its origin through advanced testing.
Coal-fired power plants are required to install pollution control systems to reduce carbon emissions. If tracer studies find high levels of carbon in the ash, then it could indicate the material was released decades ago, before the formation of the EPA and the passage of the Clean Air Act. Lower levels of carbon could signal that the ash is more recent.
The Duke Energy spokesman said electrostatic precipitators have been in place at Marshall Steam Station since the early 1970s; they remove more than 99% of the ash generated from coal combustion. “The addition of flue gas scrubbers in 2006-07 increased this ash capture efficiency to better than 99.7% under continuous testing, in full compliance with the very strict emissions standards designed to protect public health,” he said.
Scientists plan to use the new tracer method to detect fly ash in house dust. “We continue to evaluate the occurrence of coal ash across North Carolina,” Vengosh said. “Hopefully, we will be able to complete the new study in a few months.”
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