Chemistry Reference
In-Depth Information
CHAPTER
36
Palladium
HIROSHI SATOH
ABSTRACT
of dental restorations. The symptoms that have been
observed include swelling of the lips and cheeks, sto-
matitis, oral lichen planus, itching, dizziness, asthma,
and chronic urticaria. Recently,
103
Pd has been used for
radioactive sources implanted directly into a malig-
nant tumor; no palladium-related complications have
been reported. Although sensitization effects, such as
bronchial asthma, can occur among workers exposed
to palladium and its compounds, its incidence is ex-
tremely low. No data are available on the carcinogenic-
ity, reproductive toxicity, or other effects in humans.
Palladium is one of the six platinum group metals
and possesses strong catalytic activity. Demand for
palladium is high for its uses in electrical equipment,
dental materials, and automobile catalysts. Environ-
mental levels of palladium in water, soil, and ambient
air are not high, and environmental exposure and in-
take from food are not signifi cant, but palladium con-
centrations are increasing in the general environment
because of its increased use in automobile catalysts.
Workers in palladium mines and refi neries are possibly
exposed to palladium, as are dental personnel during
the processing of dental alloys containing palladium.
The general population may be exposed to palladium
through inhalation of ambient respirable particles
from automobile catalytic converters that incorporate
palladium, but relevant data are rare. The oral toxic-
ity of palladium is believed to be low, although it does
depend on the water solubility of the palladium com-
pounds. Therefore, similar intravenous LD
50
values
have been reported for several palladium com-
pounds: from 3-6.4 mg/kg body weight. From a 28-
day toxicity study of tetraammine palladium hydrogen
carbonate in rats performed through gavage, the no-
observed-adverse-effect level (NOAEL) was 1.5 mg/
kg body weight/day. Among the general population,
skin exposure may occur through contact with jewelry
containing palladium. Many case reports exist describ-
ing palladium sensitivity and recovery after removal
1 PHYSICAL AND CHEMICAL PROPERTIES
Palladium, Pd; atomic number, 46; relative atomic
mass, 106.42 (abundance of major natural isotopes are
104
Pd [11.14%],
105
Pd [22.33%],
106
Pd [27.33%],
108
Pd
[26.46%], and
11 0
Pd [11.72%]); density at 20°C (g/cm
3
),
12.02; melting point, 1554°C; boiling point, 2940°C;
steel-white metal; oxidation states: +2, +4.
Palladium is one of the six platinum group metals
(the others being Pt, Rh, Ru, Ir, and Os). These metals
commonly occur together in nature. Palladium, as well
as Pt, and sometimes Ir, is considered to be a precious
and noble metal. Palladium does not tarnish in air at
room temperature. It has a strong catalytic activity
for hydrogenation and oxidation reactions. Under an
oxygen atmosphere, palladium powder may be a fi re
hazard.
