Zero-valent metals are the main reductants used in ISCR. The most common metal used is iron, in the form of ZVI (zero valent iron), and it is also the metal longest in use. However, some studies show that zero valent zinc (ZVZ) could be up to ten times more effective at eradicating the contaminants than ZVI. Some applications of ZVMs are to clean up Trichloroethylene (TCE) and Hexavalent chromium (Cr(VI)). ZVMs are usually implemented by a permeable reactive barrier. For example, iron that has been embedded in a swellable, organically modified silica creates a permanent soft barrier underground to capture and reduce small, organic compounds as groundwater passes through it.