Influences of soil properties on chromium (iii) sorption
The presence of chromium in the environment is widespread due to its usage in many industrial processes. The metallurgic, tanning and plating industries are just a few examples of applications which use chromium on a daily basis (Nriagu and Nieboer, 1988). Chromium is stable in 2 oxidation states: cationic Cr with a valence of 3 and anionic with a valence of 6. Chromium (III) is often considered to be mobile in the environment while the more environmentally stable, Cr(VI), is considered less mobile (Chung, 1998). There are several factors that contribute to the decreased mobility of Cr (III) in soil: strong adsorption onto negative soil surfaces, the ability to form complex molecules with organics found in soil, and formation of oxides and hydroxides and other insoluble materials in soil (Endorf and Zasoski, 1992). Chromium (VI) is considered the most harmful of oxidation states since it is both a mutagen and a carcinogen at low sub-ppm levels (Levis, 1982). Although Cr (III) is generally considered less harmful to human health than its oxidized state, it may be of concern due to its potential to oxidize Cr(VI) and its ability to accumulate to very high solid phase concentrations in some soils (Endorf and Sparks, 1992). Typically calculated health risks are incorporated based on a reference soil dose derived from studies that use soluble aqueous metal species. The metalsequestering of soil may significantly lower bioavailability of Cr, which in turn may influence the decision for remediation at contaminated sites. Thus, action levels set by state regulators concerning the bioavailability of Cr in soil may need to consider specific soil properties instead of using guidelines (Proctor, 1997).