Duke Study Finds that Problem with Cancer-Causing Chemical Not Limited to Coal Ash
The carcinogen can leak into groundwater from certain kinds of natural rock formations
Researchers at Duke University have discovered that North Carolina's problem with a carcinogen often blamed on power plants is not limited to coal ash.
The scientists have published a study finding that hexavalent chromium—a carcinogen known to many from the Julia Roberts movie Erin Brockovich and one of the toxins at the center of a controversy regarding contaminated water supplies near coal ash pits—can leak into groundwater from certain kinds of naturally-occurring rock formations found throughout the Piedmont, which makes up a large part of central North Carolina. More than 90 percent of the wells sampled by the researchers contained detectable levels of the toxin.
Together with selenium, lead, and arsenic, hexavalent chromium—also known as chromium-6—is one of the toxins that scientists have been most worried about regarding the contamination of local water supplies close to 14 current and former coal-fired power plants. Strife over letting well owners located near coal ash pits regarding whether or not their water was safe to drink, and in particular about the type of health risk posed by hexavalent chromium, lies at the center of an ongoing controversy involving Governor McCrory's administration as well as some of the state's top public health scientists.
The study suggests that coal ash is probably not responsible for depositing the toxin in wells located near those power plants.
"I don't think they should be relieved by this information. This is an indication they have a much bigger problem," stated Avner Vengosh, professor of geochemistry and water quality at Duke's Nicholas School of the Environment and lead author of the study. "The fact we are evaluating a naturally occurring source doesn't mean we're giving a green light to coal ash."
According to Vengosh, these findings bring up a bigger public health problem in addition to any threats posed by coal ash contamination. He noted that his previous work as well as other research indicates that coal ash was leaking from the sites where it is stored into water supplies, thereby spreading selenium and arsenic into well water.
"The bottom line is that we need to protect the health of North Carolinians from the naturally occurring threat of hexavalent chromium while also protecting them from harmful contaminants, such as arsenic and selenium, which our previous research has shown do derive from leaking coal ash ponds," he said. "The impact of leaking coal ash ponds on water resources is still a major environmental issue."
The findings contradict two major assumptions about hexavalent chromium made prior to the study. For a long time, scientists have assumed that significant levels of the toxin are indications of human activities.
The study, however, shows that the high levels of the chemical found in well water should not necessarily be blamed on coal ash.
"There are still a lot of questions that will need to be scrutinized in the study," said Sam Perkins, the Catawba Riverkeeper. Perkins is one of many environmental advocates who have been pressuring Duke Energy to clean up coal ash sites.
"However, decades of research has concluded that hexavalent chromium 'rarely occurs naturally,'" he added, referring to the EPA's topological profile for chromium-6.
Perkins believes that the discovery of naturally-occurring hexavalent chromium should not lessen the pressure to clean up coal ash from unlined pits located throughout the state.
"The most important thing to remember is that Dr. Vengosh's research has for years identified problems and contamination from unlined coal ash," Perkins said. "A paper from Dr. Vengosh earlier this year concluded unlined coal ash was indeed contaminating groundwater. Duke Energy's own data and engineering reports have confirmed this."
This is not the first time the chemical has been found in nature. As Vengosh noted, studies in both California and Mexico found naturally-occurring chromium-6 leaking into water from rock formations. However, he said, this is the first time that it seems to have happened from the kinds of rock found in North Carolina.
Debates over exposure to the chemical have also brought up the environmental balance between chromium-6 and chromium-3, a less toxic chemical relative. Although high levels of the letter can be poisonous, the EPA says that it is an "essential human dietary element" in fruits, vegetables, and meat. It is harder and more expensive to test for a particular kind of chromium than for total chromium, and it has most often been assumed that most of the chemical measured would be of the nontoxic kind.
David Buchwalter is an associate professor in North Carolina State University's Department of Biological Sciences. "In normal groundwater environments, you'd expect most of the chromium to be chromium-3," he said.
But according to Vengosh's study, the Piedmont of North Carolina is not a typical environment.
"The concentration of hexavalent chromium in groundwater is almost identical to the concentration of total dissolved chromium, measured by a totally different technique" Vengosh said. "That means, when you will find chromium in groundwater, it is actually composed of its toxic form of hexavalent chromium, not the less toxic trivalent form."
This fact, said Buchwalter, raises "a big red flag" about how safe the drinking water is in the wells located in the studied area. According to him, the paper brings up more pressing matters besides the policy issues on coal ash that it may address and the future research it could inspire.
"My first inclination would not be a research question, but a practical question of how we're going to provide safe water for these people," he said.
The questions regarding the meaning of the presence of chromium have been at the center of an unusual and very public dispute between Governor McCrory's administration and a number of the state's top public health scientists. State toxicologist Ken Rudo alleged in depositions that the state was misleading homeowners regarding how safe their drinking water was by citing safe drinking water guidelines set by the federal government.
The consequence of that deposition was severe blowback from top administration officials. McCrory's chief of staff, Thomas Stith, accused Rudo of lying under oath. However, Rudo has maintained the veracity of his testimony both in a public statement and in a subsequent deposition. As a result of the controversy, North Carolina's chief epidemiologist, Dr. Megan Davies, resigned in protest against the "false narrative" that the administration was circulating about coal ash.
Currently there is no federal drinking water standard for chromium-6, though there is one for total chromium of 100 parts per billion. It assumes that most of the chemical will be of the nontoxic chromium-3 variety.
Out of all 50 states, California is the only one with a statewide chromium-6 standard, which is set at 10 parts per billion.
It is this dearth of guidance and jumble of regulations, said Vengosh, that makes it difficult for those who rely on wells for their drinking water to know how to react.
"If you are a homeowner and you have these values for chromium, you really don't know how it relates to any health standard," he said.
Vengosh cautioned that he was not a health expert, but said that California's hexavalent chromium standard appears to be a reasonable point at which concern should begin. The study discovered wells—both close to and far from coal ash pits—that exceeded the standard.
This fact, according to Vengosh, will probably pressure additional states to set their own chromium-6 standards, and it also indicates the necessity for the federal government to set guidelines rather than leaving the problem to the states.
"We need urgently a standard for hexavalent chromium," Vengosh said. "We need to know what thousands of well owners should be doing. ... This is an emergency even worse than coal ash."