USGS Develops New Field Method for Detecting Chromium VI in Ground Water
The USGS has developed a new field method for collecting and stabilizing ground-water samples for the analysis of toxic chromium VI (Cr(VI)). The new method enables scientists and resource managers to distinguish—cost effectively—between the toxic and carcinogenic form of chromium (Cr(VI)) and the more benign form, chromium III (Cr(III)). The method overcomes several obstacles for accurately determining the concentration of Cr(VI) in water. Past methods were not very accurate, the instability of Cr(VI) was problematic, and expensive, specialized laboratory equipment was required for the analysis. In contrast, the advantages of the new method are:
- its low detection limit—0.1 microgram per liter (µg/L);
- the small, disposable cation-exchange cartridges that allow Cr(VI) to be separated and stabilized in the field for later analysis; and
- the use of common laboratory equipment that reduces the analytical cost.
The results of the new field method compare well with standard laboratory-based methods.
The new method has been used to characterize chromium-contaminated ground water beneath the Mojave Desert, California, at 29 Palms Marine Corps Air Ground Combat Center, Edwards Air Force Base, and at the Sheep Creek Fan west of Victorville, California. The study found areas with high concentrations of Cr(VI) from natural sources, in addition to Cr(VI) contamination from industrial activities. The natural Cr(VI) is caused by the weathering of dark rocks, such as basalt and amphibolite, in alluvial deposits (sediments deposited by rivers and streams). In addition to distinguishing between the kinds ofchromium , knowing the source of Cr(VI) is important to those tasked with cleaning up contamination and protecting drinking water resources. Resource managers can now consider sources of Cr(VI) when determining the responsibility for cleanup, the levels of cleanup required to reach background concentrations, and the regulatory structure for dealing with the contamination.