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Updated on November 26, 2019 to include links to research and additional resources

By Lisa J.N. Bradley, Ph.D., DABT

Dr. Bradley has a Ph.D. in toxicology from the Massachusetts Institute of Technology, has 25 years of experience in risk assessment and toxicology, and is certified by the American Board of Toxicology. For the past decade, she has focused much of her time on helping the public better understand coal ash.

When the North Carolina Department of Health and Human Services (DHHS) published a report earlier this year that stated, “There is no known link between coal ash and thyroid cancer,” some people downplayed its conclusions because the report was based on current information and didn’t call for new research.

New research is welcome – there is important work taking place in the Lake Norman, N.C., area as university scientists, health departments, and local and state leaders try to better understand increasing rates of thyroid cancer. At the same time, any new research always builds on a strong foundation of existing science. And here’s what decades of existing research tell us about coal ash:

  • Coal ash does not cause thyroid cancer.
  • Coal ash is not hazardous.

Some critics have already made up their minds – even sound science won’t change that. But for those interested in learning more, I welcome the opportunity to dig deeper.

Radioactive Iodine vs. Radium

Radiation is the only known environmental exposure that has been clearly linked to thyroid cancer. And coal ash contains radium at low levels. So how can we know coal ash doesn’t cause thyroid cancer? In short: Studies have shown radioactive iodine causes thyroid cancer, while radium does not.

Two very specific types of radiation are associated with thyroid cancer: external ionizing radiation and exposure to iodine-131. Yet as DHHS noted, extensive tests show no community exposures to this type of radiation around the McGuire Nuclear Station site during the past 40 years.

Radium is different. It stems from granite and naturally occurs in North Carolina rocks and soils. The U.S. Geological Survey researched coal ash and concluded, “Radioactive elements in coal and fly ash should not be sources of alarm. The vast majority of coal and the majority of fly ash are not significantly enriched in radioactive elements, or in associated radioactivity, compared to common soils or rocks.”

Additionally, Argonne National Laboratory conducted a comprehensive review of human exposures to radium – none resulted in thyroid cancer. And while some claim coal ash may contain three to five times as much radium as normal soil, consider this: The radium levels examined in the Argonne study were many, many times higher than the levels of radium in coal ash.

Toxicity, Health and Exposure

Looking beyond thyroid cancer to any form of cancer, there’s only one coal ash constituent classified as a carcinogen by ingestion: arsenic. Yet arsenic and other ash elements repeatedly cited by critics – without measuring anyone’s exposure to such elements – comprise less than 1% of coal ash.

Exposure is critical. The U.S. Environmental Protection Agency (EPA) extensively studied over 750 chemicals to determine the amount of exposure that’s safe versus harmful, and then developed “health risk based screening levels” that identify the concentrations of each chemical that are safe for air, water and soil.

Given the inaccurate claims by some that coal ash fills are “everywhere” across Iredell County, consider this: The concentrations of nearly all trace elements in ash are below the levels established by the EPA as safe for residential soils – levels that are protective for daily exposure by adults and children.

To put it another way, if the soil in one’s entire yard – under the lawn, in and around flower beds and shrubs – were replaced with coal ash, a child in that home would still be exposed to more arsenic from foods in a normal daily diet than from playing in the yard.

And while the EPA looked at ash elements separately as detailed in this article, in the European Union (EU), toxicity tests were conducted on coal ash as a whole – over 40 tests for specific types of toxicity, such as short- and long-term inhalation, short- and long-term ingestion, genetic toxicity, reproductive toxicity and aquatic toxicity. All tests showed no adverse effects, and coal ash is classified in the EU as posing no hazard.

Claims Without Context

I’m a toxicologist who has spent my career studying coal ash, how it moves in the environment and how it may impact human health. What intrigued me about this field was how ash was consistently portrayed in the media as “toxic coal ash,” as if the ash were inherently harmful. It’s not.

Here’s what you need to know about toxicity: Anything can be toxic. A bottle of aspirin, if you ingest 200 pills rather than the recommended two, can kill you. The fundamental science behind toxicity is that it’s the dose – the amount of exposure – that differentiates a poison from a remedy. This article helps explain the issue further

The distortion of coal ash as “toxic” was originally triggered by environmental extremists trying to foster fear to drive public policy decisions. Locally, some of these same paid protestors have misled the public about “clean water,” consistently omitting the fact that Marshall Steam Station’s ash basin impacts are limited to the groundwater on Duke Energy property. Extensive science shows drinking and recreational water supplies remain safe from coal ash impacts and will continue to be safe in the future.

If we really want to get to the root of local health issues, we must move past reductionist labels about “toxic ash,” “radioactive soil” or “carcinogenic elements” that lack context on who is being exposed and how. The coal ash from Marshall Steam Station, including ash located in various structural fills around the community, is neither toxic nor inherently harmful – not in the way that people are exposed to it.

So far, all available research rules out a connection between coal ash and thyroid cancer. Given citizens’ concerns, more study is appropriate – and toward that end, Duke Energy is collaborating with the Duke University scientists examining these issues on a local level. As this work moves forward, it is critical to rely on sound science and measurable data rather than speculative theories if we are to better understand the local, national and global increase in thyroid cancers.