Titanium is the ninth most common element in the Earth’s crust, present mainly as oxides (TiO2), CaTi)3, FeTiO3) with some silicates. These compounds have very limited, if any, bioavailability and there is no indication that titanium is an essential element for any species. However, it has been claimed that titanium ascorbate supplementation of feeds has increased yields of certain fruits and vegetables and improved growth and general condition in pigs. The element is of commercial importance, the dioxide used as a pigment and whitener, the carbide in cutting and drilling tools. Titanium itself is used to provide a resistant coating on other surfaces and to form flexible tubing for a variety of applications such as condensers in power stations. As a relatively lightweight metal it is an important component of ferrotitanium alloys used in aircraft and missiles, and of the alloys (with aluminium and vanadium) used for the manufacture of artificial joint prostheses and dental implants. Currently, an organic titanium compound, titanocene dichloride, is undergoing clinical investigation as a treatment for human solid tumours.
Apart from the tetrachloride, which is a very reactive liquid capable of causing skin damage, titanium as the metal, carbide or dioxide is held to be physiologically inert with exposure causing few effects apart from pulmonary irritation following inhalation of dusts; however, serious alveolar proteinosis arising from pulmonary deposition of titanium dioxide has been reported. With accumulating experience of artificial joint prostheses, concern has grown that titanium ions and debris released or abraded from these implants may have localised toxicological effects and contribute to aggressive granulomatous lesions; the matter is, as yet, unresolved. Initial studies with titanocene dichloride infusions of titanium dose >30 mg/m2 have been associated with renal impairment in terminally ill cancer patients; the contribution of the element alone to this process is unclear.
Laboratory Indices of Exposure
There are few reliable reports of expected concentrations of titanium in tissues and body fluids, but these indicate very low concentrations. Increased urinary excretion has been found in subjects with regular occupational exposure to the metal. Increased titanium concentrations have been reported in synovial fluid, serum and spleen of individuals fitted with titanium-alloy joint prostheses; the toxicological significance of these findings is unclear.
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