What Is Chromium-6?

The steel used to manufacture tools is often made with Chromium-6.
The steel used to manufacture tools is often made with Chromium-6. Matteo Rinaldi/E+/Getty Images

Chromium-6 is one form of the metallic element chromium, which is listed in the periodic table. It is also called hexavalent chromium.

Characteristics of Chromium

Chromium is odorless and tasteless. It occurs naturally in various types of rock, soil, ore and volcanic dust as well as in plants, animals and humans.

Three Common Forms of Chromium

The most common forms of chromium in the environment are trivalent chromium (chromium-3), hexavalent chromium (chromium-6) and the metal form of chromium (chromium-0).

Chromium-3 occurs naturally in many vegetables, fruits, meats and grains, and in yeast. It is an essential nutritional element for humans and is often added to vitamins as a dietary supplement. Chromium-3 has relatively low toxicity.

Uses of Chromium-6

Chromium-6 and chromium-0 are generally produced by industrial processes. Chromium-0 is used primarily for making steel and other alloys. Chromium-6 is used for chrome plating and the production of stainless steel as well as leather tanning, wood preservation, textile dyes and pigments. Chromium-6 is also used in anti-corrosion and conversion coatings.

Potential Dangers of Chromium-6

Chromium-6 is a known human carcinogen when it is inhaled, and can pose a serious health risk to workers in industries where it is commonly used. Although the potential health risk of chromium-6 in drinking water is a growing concern in many communities and at the national level, there is not yet enough scientific evidence to confirm the actual risk or to determine at what level of contamination it occurs.

Concerns about hexavalent chromium in drinking water supplies periodically crop up. The issue is affecting thousands of residents in Rio Linda, just north of Sacramento, California, a state with comparatively stringent chromium-6 regulatory limits. There, several municipal wells had to be abandoned because of chromium-6 contamination. No clear sources of the pollution have been identified; many residents blame the former McClellan Air Force base, which they say use to engage in aircraft chrome plating operations. In the meantime, the local property tax payers are seeing a rate hike to cover the costs of new municipal water wells.

Hexavalent chromium pollution is also frustrating residents in North Carolina, especially those with wells near coal-fired power plants. The presence there of coal ash pits is elevating chromium-6 levels in the groundwater nearby and in private wells. The concentrations of the pollutant frequently exceed the state's new standards, adopted in 2015 following a large coal ash spill at a Duke Energy power plant. These new standards prompted a do-not-drink advisory letter to be sent to some living in proximity to these coal pits. These events sparked a political storm: high-ranking North Carolina government officials have repudiated the standard and disavowed the state toxicologist. As a response to the officials, and in support of the toxicologist, the state epidemiologist resigned.


Edited by Frederic Beaudry.