Updated on April 7, 2020 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 published a report in 2019 that concluded, "There is no known link between coal ash and thyroid cancer," some people called for additional research.
New research is welcome. At the same time, any new studies must build on a strong foundation of established science. And here's what decades of existing research tell us about coal ash:
- There is no known connection between thyroid cancer and the constituents in coal ash.
- Nearly all elements in coal ash are below levels established by the U.S. Environmental Protection Agency (EPA) as safe for residential soils.
For those interested in learning more about this robust body of research, I welcome the opportunity to dig deeper.
Hex Chrome and Radium
Given that coal occurs naturally, it's logical that the elements in coal ash would also be found in North Carolina soils. Two such frequently mentioned constituents are hexavalent chromium and radium.
Hexavalent chromium is associated with local geology. Duke University researchers proved the hexavalent chromium in North Carolina wells was naturally occurring and not from coal ash (which can also contain trace amounts of hexavalent chromium); their later study of 1,400 drinking wells found the element was common statewide, including areas far from power plants or coal ash fills.
Radium stems from granite. The U.S. Geological Survey researched coal and coal ash and concluded they "should not be sources of alarm" and "are not significantly enriched in radioactive elements, or in associated radioactivity, compared to common soils or rocks."
Detailed toxicology studies of hexavalent chromium indicate it does not affect the thyroid gland; likewise, Argonne National Laboratory's review of human exposures to radium found no connection to thyroid cancer.
Health and Exposure
Looking beyond thyroid cancer to any form of cancer, only one coal ash constituent is classified as a carcinogen by ingestion: arsenic. Yet arsenic and other trace elements cited by some – without measuring anyone's exposure to such elements – collectively comprise less than 1% of coal ash.
Exposure is critical. The EPA extensively studied over 750 chemicals that people may come into contact with to determine safe exposure thresholds, then developed "health risk based screening levels" that identify the concentrations of each chemical that are safe for air, water and soil.
The upshot: Concentrations of nearly all trace elements in ash are below levels established by the EPA as safe for residential soils – levels protective for daily exposure by adults and children.
Put 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 be exposed to more arsenic from a normal daily diet than from playing in the yard.
And while the EPA looked at these ash elements separately, the European Union conducted over 40 tests on coal ash as a whole, studying inhalation, ingestion, genetic toxicity, reproductive toxicity and aquatic toxicity. All tests showed no adverse effects.
Claims Without Context
I'm a toxicologist who has spent my career studying coal ash. What intrigued me about this issue was how often media characterized this byproduct as "toxic coal ash," as if it were inherently harmful. It's not.
Anything can be toxic. A bottle of aspirin, if you ingest 200 pills rather than two, can be fatal. The fundamental science behind toxicity is that the dose – the amount of exposure – is what differentiates a remedy from a poison.
The coal ash from Marshall Steam Station, including ash located in various structural fills around the community, is neither toxic nor hazardous – not in the way that people are exposed to it.
All available research rules out a link between coal ash and local health concerns. The interest in more study is understandable, and toward that end, the utility has shared decades of data with university scientists examining these issues. As this work moves forward, it's vital to rely on sound science rather than speculative theories to better understand the local, national and global increase in thyroid cancers.