Titanium

There is no evidence indicating that titanium is an essential element for humans or other animals. Titanium belongs to the first transition group; its chemical behavior is like that of silica and zirconium. Although titanium compounds are, in general, absorbed poorly by ingestion and inhalation, titanium still can be detected in the blood, brain, and parenchymatous organs of individuals in the general population, with the highest concentrations being found in the hilar lymph nodes and the lungs. Titanium is eliminated by excretion in urine; information on other routes of excretion is lacking. Studies on titanium alloys used in implants and titanium compounds—such as its salicylate, oxide, and tannate derivatives—used in cosmetics and pharmaceuticals have not indicated any significant local effects on tissues, but, under certain circumstances, inflammatory reactions and systemic effects have been observed. Thus, titanium cannot always be considered as inert and biocompatible, as was once believed. Titanium tetrachloride, a strong irritant to mucous membranes and the eyes, can cause skin burns through accidental exposure. Experimental animal, clinical, and some epidemiologic studies have indicated that titanium dioxide is generally biologically inert, but cases of adverse reactions have been reported. In animal studies, titanium carbide, hydride, nitride, and boride have exhibited slight fibrogenic activity. Artificial fibers—such as potassium octatitanate and titanium phosphate fibers—possess fibrogenic properties. Cells from bronchoalveolar lavage of rats instilled intratracheally with TiO2 particles induce Hrpt-gene mutations. Intramuscular injections of powdered titanium metal have induced fibrosarcomas and lymphosarcomas in rats; similarly, the organotitanium compound titanocene has induced fibrosarcomas in rats. Several epidemiological studies have suggested that TiO2 dust is not carcinogenic in human lungs. The International Agency for Research on Cancer has listed titanium dioxide in Group 2B. There is sufficient evidence from experimental animal studies to suggest the carcinogenic potential of TiO2, but no adequate evidence exists for the carcinogenicity of titanium oxide in humans. A soluble titanate given to rats in their drinking water was found to disturb their reproduction in a three-generation study. With the rapid development of nanotechnology, more and more titanium nanoparticles (TNPs) are used in daily life. Therefore, human exposure to TNPs is becoming more frequent. Nanoparticles are considered a threat to the environment and human health. In vivo and in vitro studies have shown that TNPs are toxic to lungs, cardiovascular system, and nervous system. Although there are a few epidemiological studies showing no increased risk for respiratory cancer, further evaluation of TNPs toxicity is needed.