Chromium is used for metal plating, the production of CCA-treated wood, tanning processes, pigment manufacturing, and other industrial applications.  Chromium is the second most common heavy metal found at sites contaminated by this class of pollutants. 

In the environment chromium does not exist in its elemental state but rather occurs in the Cr⁺³ [Cr(III)] and Cr⁺⁶ [Cr (VI)] ionic states.  Cr (III) forms a relatively insoluble chromium hydroxide [Cr(OH)₃] in reducing environments.  Cr(VI) combines with oxygen to form the soluble chromate (CrO₄^-2) ion above pH 6 or dichromate (Cr₂O₇^-2) ion below pH 6 in oxidizing environments. Both the chromate and dichromate ions are mobile in shallow aquifers, but chromium hydroxide is not mobile. Click here to learn more about redox chemical reactions, oxidizing and reducing environments, and pH.

Cr(III) has a relatively low toxicity but Cr(VI) is acutely toxic, mutagenic and carcinogenic. 

View a Material Safety Data Sheet (MSDS) for CCA preservative. As you read through the information on the sheet what indicators tell you that this material is toxic to humans? Aside from saving River City's water supply from contamination, why else would we want to avoid having the CCA liquid enter the Buffalo River?

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