Tungsten [W, 74]

Tungsten (W), known also as wolfram, is a rare metal of group 6 in the periodic table of elements. In the Earth’s crust it occurs only as chemical compounds, at an average content of about 1.5 mg/kg. Tungsten’s average content in the worldwide soils is estimated to be 1.7 mg/kg. Tungsten sources in soils are from fly ash and some sludge used for soil amendments. Although most of W minerals are slightly soluble, its global mobility is relatively high. The median W concentration in seawaters is estimated to be 0.1 µg/L. Tungsten is relatively easily available to plants. A lower uptake from acidic soils suggests that W is absorbed in anionic species. Tungsten content of human body is estimated to be 20 µg, and its concentrations in blood is 1 µg/L and in bones 0.2 µg/kg. Tungsten is irritating to the skin and eyes, on contact. Its inhalation will cause irritation to the lungs and mucus membrane.