ABSTRACT
The trace metals of Group 5 (vanadium [V], niobium [Nb], and tantalum [Ta]) and Group 6 (chromium [Cr], molybdenum [Mo], and tungsten [W]) of the periodic table are of economic importance especially in metal industries. They have strong lithophilic tendencies, variable oxidation states, and important geochemical characteristics. The two pairs of elements Nb and Ta, and those of Mo and W, have very similar atomic radii and resemble each other in geochemical properties but have different bioavailability and toxicological properties. This entry attempts to summarize the existing literature on the occurrence, industrial and technological applications, environmental geochemistry, and toxicology of vanadium and chromium group elements. It also reviews the existing international, European Union, and U.S. regulatory frameworks and guidelines of these elements in the environment.
