Chemistry Reference
In-Depth Information
CHAPTER
43
Titanium
TAIYI JIN AND MATHS BERLIN
ABSTRACT
Bronchoalveolar lavage cells from rats instilled
intratracheally with TiO
2
particles induce hrpt-gen
mutations in rat alveolar cells
in vitro
. Intramuscular
injections of powdered titanium metal have induced
fi brosarcomas and lymphosarcomas in rats; similarly,
the organotitanium compound titanocene has induced
fi brosarcomas in rats. Several epidemiological studies
have suggested that TiO
2
dust has no carcinogenic ef-
fect on human lungs. IARC has listed titanium diox-
ide within Group 2B. There is suffi cient evidence from
experimental animal studies for the carcinogenicity of
TiO2, but no adequate evidence exists for the carcino-
genicity of titanium oxide in humans. A soluble titan-
ate given to rats in their drinking water was found to
disturb their reproduction in a three-generation study
on rats.
There is no evidence indicating that titanium is an
essential element for humans or other animals. Tita-
nium belongs to the fi rst transition group; its chemi-
cal behavior is similar to that of silica and zirconium.
Although titanium compounds are, in general, absorbed
poorly through ingestion and inhalation, titanium still
can be detected in the blood, brain, and parenchyma-
tous organs of individuals in the general population,
with the highest concentrations being found in the
hilar lymph nodes and the lungs. Titanium is excreted
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 phar-
maceuticals have not indicated any signifi cant local
effects on tissues, but, under certain circumstances,
cases of infl ammatory reactions and systemic effects
have been observed. Thus, titanium cannot always be
considered as being inert and biocompatible, as was
once believed. Titanium tetrachloride, a strong irri-
tant to mucous membranes and the eyes, can cause
skin burns through accidental exposure. Experimental
animal studies, clinical studies, and some epidemio-
logical surveys have indicated that titanium dioxide is
generally biologically inert, but cases of adverse reac-
tions have been reported. In experimental studies on
animals, titanium carbide, hydride, nitride, and bo-
ride have exhibited slight fi brogenic activity. Artifi cial
fi bers—such as potassium octatitanate and titanium
phosphate fi bers—possess fi brogenic properties.
1 PHYSICAL AND CHEMICAL PROPERTIES
Titanium (Ti): atomic weight, 47.9; atomic number, 22;
density, 4.5 g/cm
3
at 20°C; melting point, 1660 ± 10°C;
boiling point, 3287°C; silver-grey; water-insoluble.
Titanium is one of the most common components of the
earth's crust (ninth in abundance). It occurs naturally
as ilmenite (iron titanate) and rutile (titanium diox-
ide). Titanium exhibits both metallic and nonmetallic
characteristics; metallic compounds include titanium
chloride, phosphate, sulfate, and nitrate; nonmetallic
properties are exemplifi ed by the calcium, iron, and
sodium titanates. Titanium forms four distinct oxides:
titanium monoxide (TiO), dititanium trioxide (Ti
2
O
3
),
titanium dioxide (TiO
2
), and titanium trioxide (TiO
3
).
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861
Handbook on the Toxicology of Metals 3E
