by Taft Wireback, originally posted on July 3, 2016

It’s no longer a mystery how the pollutant chromium-6 got into Greensboro’s drinking water at detectable levels two years ago.

City officials have traced elevated, 2014 amounts of the chemical, also known as hexavalent chromium, to an additive aimed at controlling the water’s acidity and alkalinity.

The culprit?

“We found high levels of hexavalent chromium in our lime slurry,” said Barry Parsons, the city’s water supply manager.

The slurry was being added to treated drinking water as it left the city’s Mitchell and Townsend treatment plants.

Greensboro water officials have since switched to a new product that does not include chromium-6, Parsons said.

“The good news is we have a contract with another vendor for lime slurry and (the new product) is absent of hexavalent chromium,” he said. “In addition, our latest round of samples revealed no chromium in the drinking water supply.”

Experts consider chromium-6 an emerging contaminant for water systems. It is a known carcinogen when inhaled but not so well-established as a cause for concern when ingested in small amounts in drinking water.

Also known informally as “hex chrome,” the naturally occurring substance made a name for environmental activist Erin Brockovich, who became the subject of a popular movie about a town fighting waterborne contamination caused by a utility that used chromium-6 to control corrosion in some of its equipment.

Nowadays, the U.S. Environmental Protection Agency is studying the chemical to determine how serious a health threat chromium-6 poses in relatively small amounts sometimes found in drinking water.

Greensboro detected elevated levels as part of that EPA initiative, which called on municipal systems and other providers of drinking water to test for it in recent years.

Current EPA regulations do not put specific limits on chromium-6 in drinking water but only cap total chromium that is a blend of both that element and the more common chromium-3.

The more common form, chromium-3, is an essential part of the human diet found in vegetables, fruits, meat, grains, yeast and some multivitamins.

Parsons said the water resources department identified the previous lime additive as the chromium-6 source by testing water at different stages of the treatment process and then by checking the various additives the city uses.

The levels detected during 2014 were slightly above those that triggered “do not drink” warnings to owners of private wells near Duke Energy’s coal ash storage ponds across the state.

But those warnings from state health officials drew criticism from some quarters for being too cautious, and the state Department of Health and Human Services ultimately retracted them.

Parsons said the city’s 2014 levels of chromium-6 were within safety limits, occurred sporadically and never threatened anyone’s health. But he is glad to know the cause and to have eliminated it:

“We do monitor our chemicals on a regular basis and will ensure the continuation of a safe and reliable drinking water supply for the citizens of Greensboro.”