Researchers: Carcinogen Can Occur Naturally in Water
Representatives of the U.S. Fish & Wildlife Service and Duke Energy take samples on the Dan River, which was polluted by a coal ash spill. Scientists have found that hexavalent chromium in well water, long attributed to coal ash contamination, may occur naturally.
Hexavalent chromium is a carcinogen found in drinking water supplies. Many have thought its presence is due to human activity, but a new study finds the contaminant can be traced to natural sources.
The inquiry was made after North Carolina water quality officials announced that potentially harmful levels of hexavalent chromium had been found in wells near coal plants across the state. The immediate assumption was that the high levels of chromium correlated with the high levels found in coal ash and, therefore, contamination was due to leaking coal ash ponds. Scientists discovered drinking water wells far away from these ponds also had high levels of hexavalent chromium.
Contaminant Found in Volcanic Rock
Duke University scientists discovered that hexavalent chromium originates in volcanic rock. The presence of manganese-oxide minerals and other soil conditions also can contribute to its natural formation. The substance, over time, leaches into groundwater under the Piedmont region. Similar geological formations are found across the Southeastern United States, which, according to Avner Vengosh, lead author of the study, may mean millions of people could be at risk of exposure to hexavalent chromium and not know it.
The announcement by water quality officials sparked controversy and confusion across the state, particularly surrounding the connection with coal ash. Roughly half of North Carolina uses wells as the source of residential drinking water and the discovery originally prompted the state to issue health advisories, which were later rescinded.
Water was collected from 376 wells of varying distances from coal ash ponds. The carcinogen was found in roughly 90 percent of all the wells tested. In some cases, the level detected is considered unsafe in drinking water.
The researchers looked at trace elements using forensic isotope analysis. The contaminants in coal ash also include boron, strontium, and arsenic. They found the water containing hexavalent chromium had “a totally different chemistry.”
Because high levels of the contaminant were found across a large area, despite proximity to a coal ash pond, he says, this supports their conclusion that ash isn’t the source.
However, Duke University’s Vengosh says their study does not mean coal ash ponds are harmless. Other studies show they leak other contaminants including arsenic and selenium.
Kenneth Rudo, a state toxicologist, told The Charlotte Observer:
- From a public health standpoint, it doesn’t matter whether it’s naturally occurring or from a man-made source. The toxicity risk is the same and the cancer risk is the same
Duke Energy, which operates the plants suspected in the contamination, promptly issued a statement supporting the peer-reviewed study. Harry Sideris, Duke Energy’s senior vice president of environmental, health and safety, stated:
- When combined with previous research, there is overwhelming evidence that coal ash basins are not impacting water quality in neighbor wells. This study is an extraordinary development, particularly for hundreds of plant neighbors who have been needlessly concerned that ash basins contributed hexavalent chromium or other substances to their wells.
Duke Energy will continue providing alternative water sources to owners of contaminated wells near its plants. It also supports the completion of a U.S. Environmental Protection Agency scientific review to identify an appropriate standard for hexavalent chromium in drinking water.
Hexavalent Chromium Standards Under Review
Both the state of North Carolina and the EPA may change their standards or institute new regulations regarding hexavalent chromium. At present, only the state of California has a state standard for the presence of hexavalent chromium, which occurs there naturally, too.
The research was funded by Foundation for the Carolinas via the Duke University Nicholas School of the Environment and the North Carolina Water Resources Research Institute.