A Duke University scientist says new data shows dangerous levels of a cancer-causing heavy metal occur naturally across North Carolina, and can be a concern in drinking water wells.
Duke earth sciences professor Avner Vengosh said data from 1,400 drinking water wells shows hexavalent chromium is widespread in North Carolina, especially in rock formations in the Piedmont region – including Wake and Mecklenburg counties.
About half the wells had concentrations above state safety standards, Vengosh said.
Vengosh has been studying hexavalent chromium in drinking water for years, including a 2016 study of wells near coal ash sites. He said the new data supports his previous conclusion that hexavalent chromium occurs naturally, and is not related to coal ash -- a toxic byproduct of burning coal.
"This new study reinforces that, because we are finding hexavalent chromium all over the state and the concentration is really related to the geology … not to any proximity or relationship to coal ash," Vengosh said.
"Coal ash has its own issues," he added. It does contain hexavalent chromium that can leach into groundwater. But he says in most cases -- including near coal ash sites -- the presence of the toxic substance has nothing to do with coal ash.
But Vengosh and his co-author, grad student Rachel Coyte, did raise a red flag. They noted that state standard for hexavalent chromium is significantly stricter than federal standards for all chromium. That means wells meeting only the federal standard pose an increased risk of cancer. Only one well tested didn't meet the federal standard, but 470 of the 865 wells tested failed to meet the state standard.
“If you follow the EPA guidance, we have no problem," Coyte said in a press release from Duke University. "But if you look at the N.C. health recommendations, there is a significant population exposed to hexavalent chromium concentrations at or exceeding a one-in-one-million lifetime risk of cancer. Why is this gap not being addressed?”
She said nearly 4 million people statewide rely on groundwater for drinking water.
“The areas where we see the largest number of groundwater users, like Wake and Mecklenburg Counties, coincide with some of the highest probabilities for the occurrence of hexavalent chromium above the health advisory level,” Coyte said.
The study was published this week in the journal Science of the Total Environment.
CORRECTION: This article has been updated to correct that the state standard for hexavalent chromium is stricter than the federal standard.