Documents\Palladium-contents. Pdf

EHC 226: Palladium
12
1.8
Effects on other organisms in the laboratory and field
Several palladium compounds have been found to have antiviral,
antibacterial and/or fungicidal properties. Standard microbial toxicity
tests   under  environmentally   relevant  conditions  have  rarely   been
conducted. A  3-h EC
50
 of 35 mg/litre  (12.25 mg palladium/litre) has  been
obtained for the inhibitory  effect of tetraammine palladium hydrogen
carbonate on the respiration of activated sewage sludge.
T h o s e palladium compounds that have been tested for effects  on
aquatic organisms have been found to be of significant toxicity. Two
palladium complexes  (potassium tetrachloropalladate(II) and chloro-
palladosamine) present in nutrient solution caused necrosis at 2.5–
10 mg palladium/litre  in the water hyacinth (Eichhornia crassipes). The
acute toxicity (96-h LC
50
) of palladium(II) chloride to the freshwater
tubificid worm Tubifex tubifex was  0.09 mg palladium/litre. A minimum
24-h lethal concentration of 7 mg palladium(II) chloride/litre (4.2 mg
palladium/litre)  has   been  reported for the freshwater fish medaka
(Oryzias latipes). In all cases, palladium compounds had a toxicity
similar to that of platinum compounds.
T oxicity  tests   on  aquatic   organisms   conducted  according  to
Organisation for Economic  Co-operation and Development guidelines
have  been  performe d only for tetraammine palladium hydrogen
carbonate. They resulted in a 72-h EC
50
 value of 0.066 mg/litre (corres-
ponding to 0.02 mg palladium/litre) (cell multiplication inhibition t e s t
with Scenedesmus subspicatus), a 48-h EC
50
 of 0.22 mg/litre  (0.08 mg
palladium/litre) (immobilization of Daphnia magna) and a 96-h LC
50
 of
0.53 mg/litre  (0.19 mg palladium/litre) (acute toxicity to rainbow trout
Oncorhynchus  mykiss).  The  no-observed-effect  concentrati o n s
(NOECs) were given as 0.04 mg/litre (0.014 mg palladium/litre) (algae),
0.10  mg/litre  (0.05 mg palladium/litre) (Daphnia  magna)  and  0.32
mg/litre  (0.11 mg palla dium/litre) (fish). All these values have been
based on nominal concentrations. However, corresponding measured
concentrations have often been found to be much lower and variable,
the reasons for this being unclear. For the immobilization test with
Daphnia magna, values based on the time-weighted mean measured
concentrations have been calculated, resulting in a 48-h EC
50
 of 0.13
mg/litre (0.05 mg palladium/litre) and a NOEC of 0.06 mg/litre (0.02 mg
palladium/litre).  Phytotoxic   effects have also been observed in
terrestrial plants  after addition of palladium(II) chloride to the nutrient

---

Summary
13
solution. They include inhibition of transpiration at 3 mg/litre (1.8 mg
palladium/litre), histological changes at 10 mg/litre (6 mg
palladium/litre)  or  death  at 100 mg/litre (60 mg palladium/litre) in
Kentucky  bluegrass (Poa pratensis). Dose-dependent growth retarda-
tion and stunting of the roots  occurred in several crop plants, the most
sensitive being oats, affected at about 0.22 mg palladium(II) chloride/li-
tre (0.132 mg palladium/litre).
No  information has been located in the literature  on the effects  of
palladium on terrestrial invertebrates or vertebrates.
There are no field observations available.

---

14
2. IDENTITY, PHYSICAL AND CHEMICAL
PROPERTIES AND ANALYTICAL METHODS
2.1 
Identity
Palladium  (Pd)  belongs  to  the  platinum  group  me tals   (PGMs),
which  comprise  six  closely   related  metals:  platinum  (Pt),  palladium,
rhodium  (Rh),  ruthenium  (Ru),  iridium  (Ir)  and  osmium  (Os).  These
metals commonly occur together in nature  and are  among the scarcest
of the metallic elements. Along with gold  (Au) and silver (Ag), they are
known as precious and noble metals. Palladium is a  steel-white metal,
does not tarnish in air and has the lowest density and lowest melting
point of the PGMs. The most important palladium compounds are  listed
in Table 1.
2.2
Physical and chemical properties
2.2.1
Palladium metal
Purified metals between 99.9%  and 99.999% palladium are  avail-
able for chemical or medical u s e as foil, granules, powder, rod or wire
(Aldrich, 1996). Table  2 lists atomic and crystal data as  well as  physical
properties of palladium metal.
Palladium metal resists  oxidation at ordinary temperatures. Palla-
dium has a strong catalytic activity, especially for hydrogenation and
oxidation reactions.
 The reaction of palladium powder with oxygen may cause a fire
hazard. This  is particularly the case in the presence of combustible
substances  (e.g., carbon catalysts). On  contact with palladium powder,
hydrogen peroxide and other peroxides , concentrated formic acid and
hydrazine are expected to decompose rapidly (Degussa, 1995).
2.2.2
Palladium compounds
Several hundred palladium compounds in various oxidation states
(Table  3) are  known  from the scientific  literature, but only  a few of them
are   of   economic   relevance   (see   also   section   3.2.4).  In its

---

Identity, Physical and Chemical Properties, Analytical Methods
15
Table 1. Chemical names, synonyms and formulas of 
selected palladium compounds
a
Chemical
name
Synonyms
Molecular formula
CAS registry
no.
Palladium
Pd
7440-05-3
Ammonium
hexachloro-
palladate(IV)
(NH
4
)
2
PdCl
6
19168-23-1
Ammonium
tetrachloro-
palladate(II)
(NH
4
)
2
PdCl
4
13820-40-1
Bis(1,5-
diphenyl-1,4-
pentadien-3-
one)
palladium(0)
Bis(dibenzylidene-
acetone) palladium
Pd(C
17
H
14
O)
2
32005-36-0
Bis(2,4-
pentane-
dionato)
palladium(II)
Bis(acetylacetonato)
palladium(II)
Pd(C
5
H
7
O
2
)
2
14024-61-4
cis-Diammine-
dichloro-
palladium(II)
Chloropalladosamin
e
(NH
3
)
2
PdCl
2
14323-43-4
trans-
Diammine-
dichloro-
palladium(II)
(NH
3
)
2
PdCl
2
13782-33-7
Diammine-
dinitro-
palladium(II)
Pd(NO
3
)
2
(NH
3
)
2
not available
trans-Dichloro-
bis-(triphenyl-
phosphine)
palladium(II)
[(C
6
H
5
)
3
P]
2
PdCl
2
13965-03-2
Dichloro(1,5-
cyclooctadiene)
palladium(II)
PdCl
2
(C
8
H
12
)
12107-56-1
Hydrogen
tetrachloro-
palladate(II)
Tetrachloropalladou
s acid
H
2
PdCl
4
16970-55-1
Palladium(II)
acetate
Palladium diacetate
Pd(CH
3
COO)
2
3375-31-3
Palladium(II)
chloride
Palladous chloride
Palladium
dichloride
PdCl
2
7647-10-1

---