1. Occurrence and Significance
Vanadium (V) is the first element in Group VB in the periodic table. It has an atomic number of 23, an atomic weight of 50.94, and valences of 2, 3, 4, and 5. The average abundance of V in the earth’s crust is 136 ppm; in soils it ranges from 15 to 110 ppm; in streams it averages about 0.9 μg/L, and in groundwaters it is generally <0.1 mg/L. Though relatively rare, vanadium is found in a variety of minerals. Most important among these are vanadinite [Pb5(VO4)3Cl], and patrónite (possibly VS4), occurring chiefly in Peru. Vanadium complexes have been noted in coal and petroleum deposits. Vanadium is used in steel alloys and as a catalyst in the production of sulfuric acid and synthetic rubber.
The dominant form in natural waters is V5+. It is associated with organic complexes and is insoluble in reducing environments. Vanadium is considered essential for microorganisms and mammals in trace amounts.1 Laboratory2 and epidemiological1 evidence suggest that vanadium may play a beneficial role in the prevention of heart disease. Vanadium also has anti-inflammatory properties and is an immune stimulant and an insulin-mimetic.3 However, inhalation of vanadium pentoxide (from fuel-oil ash) damages the lungs, central nervous system, and spermatogenesis.4,5 The United Nations Food and Agriculture Organization recommended maximum level for irrigation waters is 0.1 mg/L.6