Estimating Cr(VI) in Coal-Derived Fly-Ash

The two common chromium oxidation states, Cr(III) and Cr(VI), differ greatly in their impacts on the environment and human health. Cr(III) in most common forms in the environment is normally not a major concern to public health because it is not very soluble and therefore poorly adsorbed by the body. In contrast, Cr(VI) in the form of chromates is usually readily soluble and, because of its oxidizing capability, can have severe adverse effects on the human body, including cancerous tumor formation and gene damage. Although chromium is normally only present at the 10 ppm level in coal, the approximately one billion tons of coal used annually for electricity generation in the U.S. implies that about 10,000 tons of chromium are processed through electricity generating plants each year, most of which ends up as a component in fly-ash, the major waste product from coal combustion. Disposal practices for coal-derived fly-ash vary greatly, but much of it is stored in isolated surface piles or in impoundments. Even so, there is still a finite risk that elements such as chromium may be leached from coal ash and eventually contaminate local groundwater and drinking water supplies.