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Hexavalent ChromiumU.S. Department of Energy

In 2009, ion exchange tanks for treating chromium-contaminated groundwater are trucked to the Hanford Site in Richland, Washington, a mostly decommissioned nuclear production complex operated by the U.S. government.

The dangerous compound made famous by the movie Erin Brockovich can occur naturally or through industrial pollution

Hexavalent chromium, a toxic compound sometimes found in water, is a carcinogenic form of the metal chromium in an oxidation state. It’s also known as chromium-6 or Cr (VI). It’s both odorless and tasteless, and it can be found naturally in rocks, soil, and plants.

It also can comes from industrial sources, finding its way into our drinking water through erosion and leakage. For instance, high levels of hexavalent chromium recently were observed in groundwater near a power plant in Georgia, and some suspect coal ash from the plant is responsible. In Detroit, high groundwater concentrations of hexavalent chromium were recently found near an electroplating facility and pouring onto a thoroughfare.

Health Concerns and Regulation

Hexavalent chromium can cause liver damage, reproductive problems, and developmental problems. In 2008 research by the National Toxicology Program and other bodies prompted the California Office of Environmental Health Hazard Assessment to conclude it causes cancer in humans.

The U.S. Environmental Protection Agency limit for chromium is 100 parts per billion (ppb) for total chromium in water, but it encompasses all forms of chromium, also including chromium-3, another common form of the metal found in the environment. While hexavalent chromium is toxic, chromium-3 is an essential element of human diet, but the two forms can transform into one another and back again in the body or in water. The EPA regulation, therefore, assumes all chromium in water is hexavalent chromium. In recent years, many states have set limits at 50 ppb of total chromium in drinking water. California’s limit is a mere 10 ppb.

The Erin Brockovich Chemical

Hexavalent chromium was made famous by environmental health advocate Erin Brockovich. As a legal researcher, she helped bring a lawsuit against Pacific Gas and Electric Co. for groundwater contamination near Hinkley, California, that was linked to one of the utility’s plants. The company ultimately entered into a $333 million settlement. The events were used as the basis of the 2000 Steven Soderbergh film, Erin Brockovich.

According to a 2016 study of EPA data by the independent advocacy group Environmental Working Group (EWG), roughly 200 million people across every U.S. state have high levels of hexavalent chromium in their tap water. The assessment used a threshold of .02 ppb, which is the California public health goal (PHG) for protecting humans from disease, even though the state’s legally enforceable limit is 10 parts per billion. The study concludes that hexavalent chromium could cause 12,000 or more new cases of cancer in the U.S.

Incidence of High Hexavalent Chromium Levels

The EWG study found the highest average levels in drinking water supplies in Phoenix, St. Louis, Houston, Los Angeles, and Suffolk County, New York. Combined, these drinking water systems serve almost 10 million people. The highest average statewide levels were found in Oklahoma, Arizona, and California.

Since then, a 2020 study found 470 out of 865 North Carolina water wells tested exceeded the N.C. Health Advisory Level of 0.07 µg/L. While the study focused on N.C., the widespread groundwater chromium contamination in the Piedmont region could mean a public health risk in large swaths of the eastern U.S.

Despite regular focus on water-related contamination, the Occupational Safety and Health Administration estimates that approximately 558,000 people are exposed to hexavalent chromium at work. This includes people who weld stainless steel and other chromium-containing alloys. The compound also can be found in other industrial materials such as dyes, paints, inks, plastics, and coatings.

Problems With Regulation

Regulating hexavalent chromium levels in water supplies across the U.S. remains a contentious issue. The fact that there are no separate limits for hexavalent chromium — only total chromium — concerns public health advocates, including Brockovich.

Opinions remain deeply divided as the scientific inquiry continues.

The Environmental Working Group concluded:

Cleaning up water supplies contaminated with chromium-6 will not be cheap. […] And the fact that some unknown level of chromium-6 contamination comes from natural sources does not negate Americans’ need to be protected from a known carcinogen.

Treating Water for Hexavalent Chromium

The Water Research Foundation identifies the water treatment technologies that are commonly used for hexavalent chromium removal as:

  • Reduction, coagulation, and filtration (RCF)
  • Adsorption onto regenerable strong base anion (SBA) resin
  • Adsorption onto disposable weak base anion (WBA) resin.

Each method creates unique waste with divergent handling and disposal methods that can make the cost of treatment prohibitive for very small water treatment systems.

Contact the experts at Fluence if you need help designing a system to remove hexavalent chromium from your water supply.