INTERNATIONAL PROGRAMME ON CHEMICAL SAFETY
ENVIRONMENTAL HEALTH CRITERIA 125
Platinum
This report contains the collective views of an international group of
experts and does not necessarily represent the decisions or the stated
policy of the United Nations Environment Programme, the International
Labour Organisation, or the World Health Organization.
Published under the joint sponsorship of
the United Nations Environment Programme,
the International Labour Organisation,
and the World Health Organization
First draft prepared by Dr. G. Rosner, Dr. H.P. König,
and Dr. D. Coenen-Stass, Fraunhofer Institute
of Toxicology and Aerosol Research, Germany
World Health Orgnization
Geneva, 1991
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of the biological action of chemicals.
WHO Library Cataloguing in Publication Data
Platinum.
(Environmental health criteria: 125)
1. Platinum - adverse effects 2. Platinum - toxicity
3. Environmental exposure I.Series
ISBN 92 4 157125 X (LC Classification QD 181.P8)
ISSN 0250-863X
(c) World Health Organization 1991
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CONTENTS
ENVIRONMENTAL HEALTH CRITERIA FOR PLATINUM
1. SUMMARY AND CONCLUSIONS
1.1. Identity, physical and chemical properties,
analytical methods
1.2. Sources of human and environmental exposure
1.3. Environmental transport, distribution, and
transformation
1.4. Environmental levels and human exposure
1.5. Kinetics and metabolism
1.6. Effects on laboratory mammals and in vitro
test systems
1.7. Effects on humans
1.8. Effects on other organisms in the laboratory and field
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1. Identity
2.2. Physical and chemical properties
2.2.1. Platinum metal
2.2.2. Platinum compounds
2.3. Conversion factors
2.4. Analytical methods
2.4.1. Sampling
2.4.2. Sample pretreatment
2.4.3. Detection and measurement
2.4.3.1 Spectrophotometry
2.4.3.2 Radiochemical methods
2.4.3.3 X-ray fluorescence spectroscopy
2.4.3.4 Electron spectroscopy for
chemical analysis
2.4.3.5 Electrochemical analysis
2.4.3.6 Proton-induced X-ray emission
2.4.3.7 Liquid chromatography
2.4.3.8 Atomic absorption spectrometry
2.4.3.9 Inductively coupled plasma
2.4.3.10 Inductively coupled plasma -
mass spectrometry
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1. Natural occurrence
3.2. Anthropogenic sources
3.2.1. Production levels and processes
3.2.1.1 World production figures
3.2.1.2 Manufacturing processes
3.2.1.3 Emissions from stationary sources
3.2.1.4 Emissions from automobile catalysts
3.2.2. Uses
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1. Transport and distribution between media
4.2. Biotransformation
4.3. Ultimate fate following use
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1. Environmental levels
5.1.1. Ambient air
5.1.2. Water and sediments
5.1.3. Soil
5.1.4. Food
5.1.5. Terrestrial and aquatic organisms
5.2. General population exposure
5.3. Occupational exposure during manufacture,
formulation or use
6. KINETICS AND METABOLISM
7. EFFECTS ON LABORATORY MAMMALS AND IN VITRO TEST SYSTEMS
7.1. Single exposure
7.2. Short-term exposure
7.3. Skin and eye irritation; skin and respiratory
sensitization
7.3.1. Skin irritation
7.3.2. Eye irritation
7.3.3. Skin sensitization
7.3.4. Skin and respiratory sensitization
7.3.5. Respiratory sensitization
7.3.6. Sensitization by other routes
7.4. Reproductive toxicity, embryotoxicity, and
teratogenicity
7.5. Mutagenicity and related end-points
7.6. Carcinogenicity and anticarcinogenicity
7.7. Other special studies
7.7.1. Effects on alveolar macrophages
7.7.2. Non-allergic mediator release
7.7.3. Effects on mitochondrial function
7.7.4. Effects on the nervous system
7.7.5. Side effects on cisplatin and its analogues
7.8. Factors modifying toxicity
8. EFFECTS ON HUMANS
8.1. General population exposure
8.1.1. Acute toxicity - poisoning
8.1.2. Effects of exposure to platinum
emitted from automobile catalysts
8.2. Occupational exposure
8.2.1. Case reports and cross-sectional studies
8.2.2. Allergenicity of platinum and
platinum compounds
8.2.3. Clinical manifestations
8.2.4. Immunological mechanism and diagnosis
8.2.5. Predisposing factors
8.3. Side effects of cisplatin
8.4. Carcinogenicity
9. EFFECTS ON OTHER ORGANISMS IN THE LABORATORY AND FIELD
9.1. Microorganisms
9.2. Aquatic organisms
9.2.1. Plants
9.2.2. Animals
9.3. Terrestrial organisms
10. EVALUATION OF HUMAN HEALTH RISKS AND EFFECTS ON THE ENVIRONMENT
10.1. Evaluation of human health risks
10.1.1. General population exposure
10.1.1.1 Exposure
10.1.1.2 Health effects
10.1.2. Occupational groups
10.1.2.1 Exposure
10.1.2.2 Health effects
10.2. Evaluation of effects on the environment
11. RECOMMENDATIONS FOR PROTECTION OF HUMAN HEALTH AND
THE ENVIRONMENT
11.1. Pre-employment screening and medical evaluations
11.2. Substitution with non-allergenic substances
11.3. Employment screening and medical evaluations
11.4. Workplace hygiene
12. FURTHER RESEARCH
13. PREVIOUS EVALUATIONS BY INTERNATIONAL BODIES
REFERENCES
RESUME
RESUMEN
WHO TASK GROUP ON ENVIRONMENTAL HEALTH CRITERIA FOR PLATINUM
Members
Dr V. Bencko, Institute of Hygiene, Charles University, Prague,
Czechoslovakia
Dr R.E. Biagini, Division of Biomedical and Behavioral Sciences,
National Institute for Occupational Safety & Health,
Cincinnati, Ohio, USA (Joint Rapporteur)
Dr I. Farkas, National Institute of Hygiene, Budapest, Hungary
Dr U. Heinrich, Department of Environmental Hygiene, Fraunhofer
Institute of Toxicology and Aerosol Research, Hanover, Germany
Dr R. Hertel, Fraunhofer Institute of Toxicology and Aerosol
Research, Hanover, Germany
Professor G. Kazantzis, Centre for Environmental Technology, Royal
School of Mines, London, United Kingdom
Professor A. Massoud, Department of Community, Environmental and
Occupational Medicine, Faculty of Medicine, Ain Shams
University, Cairo, Egypt (Chairman)
Dr R. Merget, Department of Internal Medicine, Hospital of the
Johann Wolfgang Goethe University, Frankfurt am Main, Germany
Dr G. Rosner, Fraunhofer Institute of Toxicology and Aerosol
Research, Hanover, Germany (Joint Rapporteur)
Dr A.E. Soyombo, Environmental & Occupational Health Division,
Federal Ministry of Health, Lagos, Nigeria (Vice-Chairman)
Observers
Dr C.W. Bradford, Environmental, Health and Safety Services,
Johnson Matthey Technology Centre, Reading, United Kingdom
Dr W.E. Mayr, Industrial Toxicology Department, Degussa AG, Hanau-
Wolfgang, Germany
Secretariat
Dr P.G. Jenkins, International Programme on Chemical Safety,
Division of Environmental Health, World Health Organization,
Geneva, Switzerland
Dr E.M. Smith, International Programme on Chemical Safety, Division
of Environmental Health, World Health Organization, Geneva,
Switzerland
NOTE TO READERS OF THE CRITERIA DOCUMENTS
Every effort has been made to present information in the
criteria documents as accurately as possible without unduly delaying
their publication. In the interest of all users of the environmental
health criteria documents, readers are kindly requested to
communicate any errors that may have occurred to the Manager of the
International Programme on Chemical Safety, World Health
Organization, Geneva, Switzerland, in order that they may be
included in corrigenda, which will appear in subsequent volumes.
* * *
A detailed data profile can be obtained from the International
Register of Potentially Toxic Chemicals, Palais des Nations, 1211
Geneva 10, Switzerland (Telephone No. 7988400 or 7985850).
ENVIRONMENTAL HEALTH CRITERIA FOR PLATINUM
The WHO Task Group on Environmental Health Criteria for
Platinum met in Rome, Italy, from 3 to 7 December 1990. Dr A. Mochi
opened the meeting on behalf of the host country and Dr E. Smith
welcomed the participants on behalf of the heads of the three IPCS
cooperating organizations (UNEP/ILO/WHO). The Task Group reviewed
and revised the draft monograph and made an evaluation of the risks
for human health and the environment from exposure to platinum and
certain platinum salts.
The first draft of this document was prepared by Dr G. Rosner,
Dr H.P. König, and Dr D. Coenen-Stass, Fraunhofer Institute for
Toxicology and Aerosol Research, Hanover, Germany. The second draft
was prepared by Dr G. Rosner following circulation of the first
draft to IPCS contact points. Particularly valuable comments on the
draft were made by the European Chemical Industry Ecology and
Toxicology Centre (ECETOC), the US Environmental Protection Agency,
Food and Drug Administration, National Institute of Occupational
Safety and Health, and Centers for Disease Control, the United
Kingdom Department of Health, and the National Institute of Public
Health, Norway. Dr C.W. Bradford gave valuable assistance in
verifying the nomenclature of platinum compounds. Dr E.M. Smith and
Dr P.G. Jenkins, both members of the IPCS Central Unit, were
responsible for the overall scientific content and technical
editing, respectively, of this monograph. The efforts of all who
helped in the preparation and finalization of the document are
gratefully acknowledged.
* * *
Financial support for the meeting was provided by the Ministry
of the Environment of Italy. The Centro Italiano Studi e Indagini
undertook the organization and provision of meeting facilities.
Partial financial support for the publication of this monograph
was kindly provided by the United States Department of Health and
Human Services, through a contract from the National Institute of
Environmental Health Sciences, Research Triangle Park, North
Carolina, USA - a WHO Collaborating Centre for Environmental Health
Effects.
ABBREVIATIONS
AAS atomic absorption spectrometry
BSA bovine serum albumin
DC direct current
DNA deoxyribonucleic acid
ESCA electron spectroscopy for chemical analysis
ETV electrothermal vaporization
HSA human serum albumin
ICP inductively coupled plasma
Ig immunoglobulin
LC liquid chromatography
LC50 median lethal concentration
MeB12 methylcobalamin
MS mass spectrometry
OVA ovalbumin
PCA passive cutaneous anaphylaxis
PGM platinum-group metals
PIXE proton-induced X-ray emission
PSH platinum salt hypersensitivity
RAST radioallergosorbent test
TLV threshold limit value
TWA time-weighted average
UV ultraviolet
MOLECULAR FORMULAE OF PLATINUM COMPOUNDS
PtO platinum(II) oxide
PtO2 platinum(IV) oxide
PtCl2 platinum(II) chloride
PtCl4 platinum(IV) chloride
Pt(NO3)2 platinum(II) nitrate
Pt(SO4)2 platinum(IV) sulfate
H2[PtCl4] hydrogen tetrachloroplatinate(II)
H2[PtCl6] hydrogen hexachloroplatinate(IV)
(commonly known as hexachloroplatinic
acid)
H2[Pt(NO2)2SO4] hydrogen
dinitrosulfatoplatinate(II)
cis-[PtCl2(NH3)2] cis-
diamminedichloroplatinum(II)
(commonly known as cisplatin)
trans-[PtCl2(NH3)2] trans-
diamminedichloroplatinum(II)
[Pt(NH3)4]Cl2 tetraammineplatinum(II) chloride
[Pt(NO2)2(NH3)2] diamminedinitroplatinum(II)
[Pt(C5H7O2)2] bis(pentane-2,4-
dionato)platinum(II)
(commonly known as
bis(acetylacetonato)platinum(II))
[Pt{NH2)2CS}4]Cl2 tetrakis(thiourea)platinum(II)
dichloride
K2[PtCl4] potassium tetrachloroplatinate(II)
K2[PtCl6] potassium hexachloroplatinate(IV)
K2[Pt(CN)4] potassium tetracyanoplatinate(II)
K[PtCl3(NH3)] potassium amminetrichloroplati
nate(II)
K2[Pt(NO2)4] potassium tetranitroplatinate(II)
Na2[PtCl4] sodium tetrachloroplatinate(II)
Na2[PtCl6] sodium hexachloroplatinate(IV)
Na2[Pt(Oh)6] sodium hexahydroxyplatinate(IV)
Na[Pt(NH3)Cl3] sodium
amminetrichloroplatinate(II)
(NH4)2[PtCl4] ammonium
tetrachloroplatinate(II)
(NH4)2[PtCl6] ammonium hexachloroplatinate(IV)
Cs2[Pt(NO2)Cl3] cesium
trichloronitroplatinate(II)
Cs2[Pt(NO2)2Cl2] cesium
dichlorodinitroplatinate(II)
Cs2[Pt(NO2)3Cl] cesium
chlorotrinitroplatinate(II)
1. SUMMARY
1.1 Identity, physical and chemical properties, analytical methods
Platinum (Pt) is a malleable, ductile, silvery-white noble
metal with the atomic number 78 and an atomic weight of 195.09. It
occurs naturally mainly as the isotopes 194Pt (32.9%), 195Pt
(33.8%), and 196Pt (25.3%). In platinum compounds the maximum
oxidation state is +6, while the states +2 and +4 are the most
stable.
The metal does not corrode in air at any temperature, but can
be affected by halogens, cyanides, sulfur, molten sulfur compounds,
heavy metals, and hydroxides. Digestion with aqua regia or Cl2/HCl
(concentrated hydrochloric acid through which chlorine is bubbled)
produces hexachloroplatinic acid, H2[PtCl6], an important
platinum complex. When heated the ammonium salt of
hexachloroplatinic acid produces a grey platinum sponge. A
dispersive, black powder ("platinum black") results from reduction
in aqueous solution.
The chemistry of platinum compounds in aqueous solution is
dominated by the complex compounds. Many of the salts, particularly
those with halogen- or nitrogen-donor ligands, are water-soluble.
Platinum, like the other platinum-group metals, has a pronounced
tendency to react with carbon compounds, especially alkenes and
alkynes, forming Pt(II) coordination complexes.
There are various analytical methods for the determination of
platinum. Atomic absorption spectrometry (AAS) and plasma emission
spectroscopy provide high selectivity and specificity and are the
method of choice for analysing platinum in biotic and environmental
samples. With these methods detection limits of a few µg/kg or
µg/litre have been obtained for various media.
Inductively coupled argon plasma atomic emission spectroscopy
is superior to electrothermal AAS because of lower matrix effects
and the possibility of simultaneous multi-element analysis.
1.2 Sources of human and environmental exposure
The average concentration of platinum in the lithosphere or
rocky crust of the earth is estimated to be in the region of
0.001-0.005 mg/kg. Platinum is found either in the metallic form or
in a number of mineral forms. Economically important sources exist
in the Republic of South Africa and in the USSR. The platinum
content of these deposits is 1-500 mg/kg. In Canada, platinum-group
metals (platinum, palladium, iridium, osmium, rhodium, ruthenium)
are found in copper-nickel sulfide ores at an average concentration
of 0.3 mg/kg, but are concentrated to above 50 mg/kg during the
refining of copper and nickel. Small amounts are mined in the USA,
Ethiopia, the Philippines, and in Colombia.
World mine production of platinum-group metals, of which 40-50%
is platinum, has steadily increased during the last two decades. In
1971, production was 127 tonnes (51-64 tonnes of platinum).
Following the introduction of the automobile exhaust gas catalyst,
world mine production of platinum-group metals increased to
approximately 270 tonnes (108-135 tonnes of platinum) in 1987. In
1989, total platinum demand in the western world was approximately
97 tonnes.
The principal use of platinum derives from its exceptional
catalytic properties. Further industrial applications relate to
other outstanding properties, particularly resistance to chemical
corrosion over a wide temperature range, high melting point, high
mechanical strength, and good ductility. Platinum is also used in
jewellery and dentistry.
Specific complexes of platinum, particularly cis-
diamminedichloroplatinum(II) (cisplatin), are used
therapeutically.a
Data on emissions of platinum to the environment from
industrial sources are not available. During the use of platinum-
containing catalysts, some platinum may escape into the environment,
depending on the type of catalyst. Of the stationary catalysts used
in industry, only those used for ammonia oxidation emit significant
amounts of platinum.
Automobile catalysts are mobile sources of platinum. According
to limited data, platinum attrition from the old pellet-type
catalyst is between 0.8 and 1.9 µg per km travelled. About 10% of
the platinum is water-soluble.
a This monograph is specifically concerned with platinum and
selected platinum compounds of occupational and/or
environmental importance. A detailed discussion of the toxic
effects of the anticancer drug cisplatin and its analogues in
humans and animals is beyond the selected scope of the
Environmental Health Criteria series as these substances are
used primarily as therapeutic agents. In addition, their toxic
properties are exceptional compared to those of other platinum
compounds.
With the new generation of monolith-type catalyst, results from
engine test stand experiments with a three-way catalyst indicate
that total platinum emission is lower by a factor of 100-1000 than
in the case of pellet-type catalysts. At simulated speeds of 60,
100, and 140 km/h, total platinum emission was found to be between 3
and 39 ng/m3 in the exhaust gas, corresponding to about 2-39 ng
per km travelled. The mean aerodynamic diameter of emitted particles
was between 4 and 9 µm in different test runs. There is limited
evidence that most of the platinum emitted is in the form of the
metal or surface-oxidized particles.
1.3 Environmental transport, distribution, and transformation
Platinum-group metals are rare in the environment, in
comparison with other elements. In highly industrialized areas,
elevated amounts of platinum can be found in river sediments. It is
assumed that organic matter, e.g., humic and fulvic acids, binds
platinum, aided perhaps by appropriate pH and redox potential
conditions in the aquatic environment.
In soil, the mobility of platinum depends on the pH, redox
potential, chloride concentrations of soil water, and the mode of
occurrence of platinum in the primary rock. It is considered that
platinum will be mobile only in extremely acid conditions or in soil
water with a high chloride content.
In in vitro test systems it has been demonstrated that some
platinum(IV) complexes, in the presence of platinum(II), can be
methylated by bacterial methylcobalamin under abiotic conditions.
1.4 Environmental levels and human exposure
The data base concerning environmental concentrations is
extremely limited due to the very low levels of platinum in the
environment and the associated analytical problems.
Concentrations in ambient air samples taken near freeways in
the USA before the introduction of the automobile catalyst were
below the detection limit of 0.05 pg/m3. Some recent data from
Germany indicate that close to roads the platinum air concentrations
(particulate samples) range from < 1 pg/m3 to 13 pg/m3. In
rural areas the concentrations were of a similar order of magnitude
(< 0.6 to 1.8 pg/m3).
Ambient air concentrations of platinum close to roads resulting
from the introduction of pellet-type automobile catalysts have been
estimated on the basis of dispersion models and experimental
emission data. Estimated platinum concentrations near and on roads
ranged from 0.005 to 9 ng per m3 for total platinum. As the total
platinum emission from a monolith-type catalyst is lower, probably
by a factor of 100 to 1000, than that of a pellet-type catalyst, the
platinum concentrations for this type of catalyst would be in the
picogram to femtogram per m3 range.
In roadside dust deposited on broad-leaved plants at various
sites in California, concentrations of 37-680 µg per kg dry weight
were detected. Although the number of samples was limited, the
results indicate that automotive catalysts release platinum to the
roadside environment.
In plant chamber experiments, grass cultures exposed for four
weeks to slightly diluted exhaust gas from an engine equipped with a
three-way catalyst (simulated speed: 100 km/h) contained no platinum
at a detection limit of 2 ng/g dry weight.
Investigations of the platinum concentrations in Lake Michigan
sediments led to the conclusion that platinum has been deposited
there over the past 50 years at a fairly uniform rate.
Concentrations in sediment cores of 1 to 20 cm varied only between
0.3 and 0.43 µg/kg dry weight.
While no platinum levels have been reported for fresh waters,
high concentrations (730 to 31 220 µg/kg dry weight) have been found
in the sediments of a highly polluted cut-off channel of the Rhine
river, Germany.
Samples of limber pines contained platinum levels ranging
between non-detectable and 56 µg/kg (ash weight). However, the
content of the adjacent soils was in the same range, and no
accumulation tendency was indicated by these limited data.
In isolated samples of plants from an ultrabasic soil, platinum
levels of 100-830 µg/kg (dry weight) were found.
Sea-water samples have been found to contain between 37 and 332
pg/litre. In sediment cores from the Eastern Pacific, platinum
concentrations varied between 1.1 and 3 µg/kg (dry weight). The
highest concentration (21.9 µg per kg) was found in offshore ocean
sediments. In marine macroalgae, platinum concentrations of between
0.08 and 0.32 µg/kg dry weight have been found.
Blood platinum levels of 0.1 to 2.8 µg/litre have been found in
the general population. In sera from occupationally exposed workers,
levels of 150 to 440 µg per litre have been reported.
The data base for platinum concentrations at the workplace is
limited. Due to analytical shortcomings, older data (0.9 to 1700
µg/m3) are probably not reliable. However, from these data it can
be assumed that exposure to platinum salts was higher than the
occupational exposure limit of 2 µg/m3 currently adopted by most
countries. In recent workplace studies, concentrations either below
the detection limit of 0.05 µg/m3 or between 0.08 and 0.1 µg/m3
have been measured.
1.5 Kinetics and metabolism
Following a single inhalation exposure (48 min) to different
chemical forms of platinum (5-8 mg/m3), most of the inhaled
191Pt was rapidly cleared from the body. This was followed by a
slower clearance phase during the remaining post-exposure period.
Ten days after exposure to 191PtCl4, 191Pt(SO4)2,
191PtO2, and 191Pt metal, whole body retention of 191Pt was
approximately 1, 5, 8, and 6%, respectively, of the initial body
burden. Most of the 191Pt that was cleared from the lungs by
mucociliary action and swallowed was excreted via the faeces (half-
time, 24 h). A small fraction of the 191Pt was detected in the
urine, indicating that very little was absorbed in the lungs and the
gastrointestinal tract.
In a comparative study on the fate of 191PtCl4 in rats (25
µCi/animal) following different routes of exposure, retention was
highest after intravenous administration, followed by intratracheal
exposure. It was lowest after oral administration. Since only a
minute amount of the 191PtCl4 given orally was absorbed, most of
it passed through the gastrointestinal tract and was excreted via
the faeces. After 3 days, less than 1% of the initial dose was
detected in the whole body. Following intravenous administration,
191Pt was excreted in almost equal quantities in both faeces and
urine. Elimination was slower than after oral dosing. After 3 days
whole body retention was about 65%, and after 28 days it was still
14% of the initial dose. For comparison, after these periods about
22% and 8%, respectively, were retained by the body following
intratracheal administration.
Principal deposition sites are the kidneys, liver, spleen, and
adrenals. The high amount of 191Pt found in the kidney shows that
once platinum is absorbed most of it accumulates in the kidney and
is excreted in the urine. The lower level in the brain suggests that
platinum ions cross the blood-brain barrier only to a limited
extent.
In contrast to the water-soluble salts, the insoluble PtO2
was only taken up in minute amounts even though the salt was
administered in the diet at an extremely high level, which resulted
in a total platinum consumption of 4308 mg per rat over the 4-week
period.
For both the simple platinum salts and cisplatin, it has been
established that there is an initial rapid clearance followed by a
prolonged clearance phase during the remaining post-exposure period,
and that there is no evidence for markedly different retention
profiles. However, cisplatin is, due to high chloride concentrations
suppressing hydration, very stable in extracellular fluids. This
explains why it is excreted mainly in the unchanged form. Its
excretion, in contrast to that of the simple platinum salts, is
primarily via the urine.
1.6 Effects on laboratory mammals and in vitro test systems
The acute toxicity of platinum depends mainly on the platinum
species. Soluble platinum compounds are much more toxic than
insoluble ones. For example, oral toxicity to rats (LD50 values)
decreased in the following order: Na2[PtCl6] (25-50 mg/kg) >
(NH4)2[PtCl6] (195-200 mg/kg) > PtCl4 (240 mg/kg) >
Pt(SO4)2.4H2O (1010 mg/kg) > PtCl2 (> 2000 mg/kg) >
PtO2 (> 8000 mg/kg). For the two latter compounds no LD50 could
be calculated.
In skin testing of albino rabbits, PtO2, PtCl2,
K2[PtCl4], [Pt(NO2)2(NH3)2], Pt(C5H7O2)2 and
trans-[PtCl2(NH3)2] were graded as non-irritant.
(NH4)2[PtCl6], (NH4)2[PtCl4], Na2[PtCl6],
Na2[Pt(OH)6], K2[Pt(CN)4], [Pt(NH3)4]Cl2, and
cis-[PtCl2(NH3)2] appeared to be irritant, but to various
degrees.
In eye irritation tests all tested platinum compounds showed
irritating effects. Trans-[PtCl2(NH3)2] and
(NH4)2[PtCl4] were found to be corrosive.
Intense breathing difficulties were observed after the
intravenous injection of chloro-platinum complexes into guinea-pigs
and rats, presumably due to non-allergic histamine release. This
nonspecific histamine release has complicated the interpretation of
both animal and human studies with respect to the diagnosis of
allergic sensitization.
After subcutaneous and intravenous injection of Pt(SO4)2
three times a week for 4 weeks, there was no induction of an
allergic state, as measured by skin tests (guinea-pigs and rabbits),
passive transfer, and footpad tests (mice). Administration of
platinum-egg-albumin complex also failed to sensitize the
experimental animals.
Attempted sensitization of female hooded Lister rats with the
free salt of ammonium tetrachloroplatinate, (NH4)2[PtCl4],
applied via the intraperitoneal, intramuscular, intradermal,
subcutaneous, intratracheal, and footpad routes, together with
Bordetella pertussis adjuvant, was unsuccessful, as shown by the
direct skin test, passive cutaneous anaphylaxis (PCA) test or a
radio-allergosorbent test (RAST). However, with platinum-protein
conjugates positive PCA results have been reported.
In Cynomolgus monkeys (Macaca fasicularis) exposed to sodium
hexachloroplatinate, Na2[PtCl6], by nose-only inhalation at a
level of 200 µg/m3, 4 h/day, biweekly for 12 weeks, significantly
greater pulmonary deficits were observed by comparison with control
animals. With exposure to ammonium hexachloroplatinate,
(NH4)2[PtCl6], only concomitant exposure to ozone (2000
µg/m3) produced significant skin hypersensitivity and pulmonary
hyper-reactivity.
In oral studies with male Sprague-Dawley rats, the salts
PtCl4 (182 mg/litre drinking-water) and Pt(SO4)2.4H2O (248
mg/litre) did not affect normal weight gain within the observation
period of 4 weeks. With a 3-fold increase in platinum concentration,
weight gain was reduced by about 20% only during the first week,
paralleling a 20% decrease in feed and water consumption.
Only limited experimental data are available for platinum
effects on reproduction, embryotoxicity, and teratogenicity.
Pt(SO4)2 (200 mg Pt/kg) caused reduced offspring weight in Swiss
ICR mice from day 8 to 45 post-partum. The main effect of
Na2[PtCl6] (20 mg Pt/kg) was a reduced activity level of the
offspring of mothers exposed on the 12th day of gestation. Solid
platinum wire or foil is considered to be biologically inert and
adverse effects following implantation into the uterus of rats and
rabbits were probably due to the physical presence of a foreign
object.
After intravenous administration of 191PtCl4 to pregnant
rats (25 µCi/animal) on day 18 of gestation, the placental barrier
was crossed to a limited extent.
Several platinum compounds have been found to be mutagenic in a
number of bacterial systems. In comparative studies cisplatin was
several times more mutagenic than other tested platinum salts. In
in vitro studies with mammalian cells (CHO-HGPT-system), the
relative mutagenic activity of cis-PtCl2(NH3)2],
K[PtCl3(NH3)], and [Pt(NH3)3Cl]Cl was 100:9:0.3. The
mutagenicity of K2[PtCl4] and trans-[PtCl2(NH3)2] was
marginal, whereas [Pt(NH3)4]Cl2 was not mutagenic. No
mutagenic activity was observed for the compounds K2[PtCl4] and
[Pt(NH3)4]Cl2 in the Drosophila melanogaster sex-linked
recessive lethal test, a mouse micronucleus test, and the Chinese
hamster bone marrow test.
Except for cisplatin, no experimental data are available for
the carcinogenicity of platinum and platinum compounds. For
cisplatin there is sufficient evidence for carcinogenic effects on
animals. However, cisplatin and its analogues are rather exceptional
by comparison with other platinum compounds. This is reflected in
the unique mechanism for their anti-tumour activity. Intrastrand DNA
cross-links, formed only by the cis isomer at a certain position of
guanine, are regarded as reasons for this anti-tumour activity. It
appears that replication of DNA in cancer cells is impaired, while
in normal cells the cisplatin lesions on guanine are repaired before
replication.
1.7 Effects on humans
Exposure to platinum salts is mainly confined to occupational
environments, primarily to platinum metal refineries and catalyst
manufacture plants.
The compounds mainly responsible for platinum salt
hypersensitivitya are hexachloroplatinic acid, H2[PtCl6], and
some chlorinated salts such as ammonium hexachloroplatinate,
(NH4)2[PtCl6], potassium tetrachloroplatinate, K2[PtCl4],
potassium hexachloroplatinate, K2[PtCl6], and sodium
tetrachloroplatinate, Na2[PtCl4]. Complexes where there are no
halogen ligands coordinated to platinum ("non-halogenated
complexes"), such as K2[Pt(NO2)4], [Pt(NH3)4]Cl2 and
[Pt{(NH2)2CS}4]Cl2, and neutral complexes such as cis-
[PtCl2(NH3)2], are not allergenic, since they probably do not
react with proteins to form a complete antigen.
The signs and symptoms of hypersensitivity include urticaria,
contact dermatitis of the skin, and respiratory disorders ranging
from sneezing, shortness of breath, and cyanosis to severe asthma.
The latency period from the first contact with platinum to the
occurrence of the first symptoms varies from a few weeks to several
years. Once sensitization is established, symptoms tend to become
worse as long as the workers are exposed in the workplace but
usually disappear on removal from exposure. However, if long-
duration exposure occurs after sensitization, individuals may never
become completely free of symptoms.
Although no unequivocal exposure concentration-effect
relationship can be deduced from the available literature, the risk
of developing platinum salt sensitivity seems to be correlated with
exposure intensity. Metallic platinum seems to be non-allergenic.
With the exception of one single reported case of an alleged contact
dermatitis from a "platinum" ring, no allergic reactions have been
reported.
a The term "platinosis" is no longer used for platinum-salt-
related disease, as it implies a chronic fibrosing lung disease
such as silicosis. Instead, "platinum salt allergy", "allergy
to platinum compounds containing reactive halogen ligands", and
"platinum salt hypersensitivity" (PSH) have been used, the last
being preferred.
The clinical manifestations of platinum salt hypersensitivity
reflect a true allergic response. The mechanism appears to be a type
I (IgE mediated) response. The possibility of IgE antibodies to
platinum chloride complexes developing in sensitive people has been
assumed on the grounds of in vivo and in vitro tests. It is
believed that the platinum salts of low relative molecular mass act
as haptens that combine with serum proteins to form the complete
antigen.
Skin prick tests with dilute concentrations of soluble platinum
complexes appear to provide reproducible, reliable, reasonably
sensitive, and highly specific biological monitors of allergenicity.
The compounds used for routine screening of exposed workers are
(NH4)2[PtCl6], Na2[PtCl6], and Na2[PtCl4]. The
sensitivity and reliability of the skin prick test has not been
achieved by any in vitro test available. In enzyme immunoassays
and in radioallergosorbent tests (RAST), IgE antibodies specific to
platinum chloride complexes have been found. Although a correlation
with the results of prick tests was reported, the applicability of
RAST for screening purposes was questioned because of its
nonspecificity.
Only limited cross-reactivity between platinum and palladium
salts has been found in skin testing and RAST. Reactions to the
platinum-group metals other than platinum have only been seen in
individuals sensitive to platinum salts.
Smoking, atopy, and nonspecific pulmonary hyper-reactivity have
been associated with platinum salt hypersensitivity and could be
predisposing factors.
For the general population, there is a lack of data on the
actual exposure situation in countries where the automobile catalyst
has been introduced. The possible ambient air concentrations,
estimated on the basis of a few emission data and dispersion models,
are at least a factor of 10 000 lower than the occupational exposure
limit value of 1 mg/m3 adopted by some countries for platinum
metal as total inhalable dust. Since the emitted platinum is most
probably in the metallic form, the sensitizing potential of platinum
emissions from automotive catalysts is probably very low. Even if
part of the platinum emitted was soluble and potentially allergenic,
the safety margin to the occupational exposure limit for soluble
platinum salts (2 µg/m3) would be at least 2000.
In a preliminary immunological study, extracts of particulate
automobile exhaust samples were tested on three human volunteer
subjects using a skin prick test. No positive response was elicited.
No data are available to assess the carcinogenic risk of
platinum or its salts to humans. With regard to cisplatin, evidence
for human carcinogenicity is considered inadequate.
1.8 Effects on other organisms in the laboratory and field
Simple complexes of platinum have bactericidal effects. The
discovery that neutral complexes such as cisplatin selectively
inhibit cell division without reducing cell growth of a variety of
gram-positive, and especially, of gram-negative bacteria has led to
their application in medicine as anti-tumour agents.
Growth and yield of the green alga Euglena gracilis were
inhibited by the soluble hexachloroplatinic acid (250, 500, and 750
µg/litre) in a laboratory "microcosm". Cisplatin caused chlorosis
and stunted growth in the water hyacinth Eichhornia crassipes at a
concentration of 2.5 mg/litre.
A 3-week exposure to hexachloroplatinic acid, H2[PtCl6],
resulted in an LC50 value of 520 µg Pt per litre in the
invertebrate Daphnia magna. At concentrations of 14 and 82
µg/litre, reproduction, measured as total number of young, was
impaired by 16 and 50%, respectively.
After short-term exposure to tetrachloroplatinic acid,
H2[PtCl4], in a static bioassay, 24-, 48-, and 96-h LC50
values of 15.5, 5.2, and 2.5 mg Pt/litre, respectively, were found
for the coho salmon (Oncorhynchus kisutch). General swimming
activity and opercular movement were affected at 0.3 mg/litre.
Lesions in the gills and the olfactory organ were noted at 0.3
mg/litre or more. Concentrations of 0.03 and 0.1 mg/litre had no
effect.
There have been studies on the effects of platinum on
terrestrial plants, all conducted with soluble platinum chlorides.
The growth of beans and tomato plants in sand culture was inhibited
by hexachloroplatinic acid at concentrations of 3 x 10-5 to 15 x
10-5 mol/kg (5.9-29.3 mg/kg). Of nine horticultural crops grown in
hydroponic solution with platinum tetrachloride, PtCl4 (0.057,
0.57, and 5.7 mg Pt/litre), dry weights were significantly reduced
in tomato, bell pepper, and turnip tops, and in radish roots at the
highest concentration. At this level, the buds and immature leaves
of most species became chlorotic. In some of the species the low
levels of PtCl4 had a stimulatory effect on growth. In addition,
transpiration was suppressed at the highest platinum concentration,
probably due to increased stomatal resistance. Growth stimulation
was also observed at low levels of platinum (0.5 mg Pt/litre),
administered as potassium tetrachloroplatinate, K2[PtCl4], in
seedlings of the South African grass species Setaria verticillata
grown in nutrient solution. After two weeks, the length of the
longest roots had increased by 65%. At the highest concentration
applied, i.e. 2.5 mg Pt/litre, phytotoxic effects were seen in the
form of stunted root growth and chlorosis of the leaves.
2. IDENTITY, PHYSICAL AND CHEMICAL PROPERTIES, ANALYTICAL METHODS
2.1 Identity
Platinum is a malleable, ductile, silvery-white noble metal
with the atomic number 78 and an atomic weight of 195.09. It occurs
naturally mainly as the isotopes 194Pt (32.9%), 195Pt (33.8%),
and 196Pt (25.3%). In platinum compounds, the maximum oxidation
state is +6, while the states +2 and +4 are the most stable.
The most important platinum compounds are listed in Table 1.
2.2 Physical and chemical properties
2.2.1 Platinum metal
The metal does not corrode in air at any temperature, but can
be affected by halogens, cyanides, sulfur, molten sulfur compounds,
heavy metals, and hydroxides. Digestion with aqua regia or Cl2/HCl
(concentrated hydrochloric acid through which chlorine gas is
bubbled) leads to hexachloroplatinic acid, H2[PtCl6], an
important platinum complex.
Platinum has a coefficient of expansion almost equal to that of
sodium-calcium-silicate glass and the two materials can be used in
combination, e.g., in electrodes.
Some chemical and physical data on platinum and selected
compounds are listed in Table 2.
2.2.2 Platinum compounds
The chemistry of platinum compounds in aqueous solution is
dominated by the complex compounds. Many of the salts, particularly
those with halogen- or nitrogen-donor ligands, are water-soluble. In
biochemical processes, cis-trans effects in the quadratic
coordination of platinum play an important role. Platinum, like the
other platinum-group metals (PGM), has a marked tendency to react
with carbon compounds, especially alkenes and alkynes, forming
Pt(II) coordination complexes.
Table 1. Chemical names, synonyms, and formulae of elemental platinum and platinum compoundsa
Chemical name CAS registry numberb Synonyms Formula
Element
Platinum 7440-06-4 Pt
Binary compounds
Platinum(II) chloride 10025-65-7 platinous chloride PtCl2
Platinum(IV) chloride 13454-96-1 platinum tetrachloride PtCl4
Platinum(II) oxide n.a. platinous oxide PtO
Platinum(IV) oxide 1314-15-4 platinic oxide; platinum dioxide PtO2
Platinum sulfate n.a. - Pt(SO4)2.4H2O
Platinum nitratec n.a. - Pt(NO3)2
Coordination complexes
Hexachloroplatinic acid(IV) 16941-12-1 chloroplatinic acid; dihydrogen H2[PtCl6]
hexachloroplatinate
Sodium hexachloroplatinate(IV) 16923-58-3 disodium hexachloroplatinate; Na2[PtCl6]
sodium chloroplatinate
Potassium hexachloro- 16921-30-5 potassium chloroplatinate; platinic K2[PtCl6]
platinate(IV) potassium chloride
Potassium tetrachloro- 10025-99-7 platinum potassium chloride; K2[PtCl4]
platinate(II) potassium platinochloride
Ammonium tetrachloroplatinate(II) 13820-41-2 ammonium platinous chloride; (NH4)2[PtCl4]
ammonium chloroplatinite
Ammonium hexachloroplatinate(IV) 16919-58-7 ammonium platinic chloride; (NH4)2[PtCl6]
ammonium chloroplatinate; "yellow salt"
cis-Diamminedichloroplatinum(II) 15663-27-1 cisplatin; cis-platinum; DDP; CDDP; cis-[PtCl2(NH3)2]
CPDD; CACP; CPCC; Peyron's chloride
trans-Diamminedichloroplatinum(II) 14913-33-8 trans-dichlorodiammineplatinum(II) trans-[Pt(NH3)2Cl2]
a From: Windholz (1976); Weast & Astle (1981)
b n.a. = not available
c Kral & Peter (1977)
Table 2. Physical and chemical properties of platinum and selected platinum compoundsa
Relative
atomic/ Melting Boiling Relative Crystalline Solubilityd
Chemical name molecular pointb point density formc Cold Hot Other
mass (°C) (°C) (g/cm3) water water solvents
Platinum (Pt) 195.09 1772 3827 21.4520 silver-metallic ins ins sol aq.
(± 100) cubic cr. regia
Platinum(II) chloride 266.00 581b 6.05 olive-green, ins al, eth;
(PtCl2) (in Cl2) hexagonal cr. sl sol sol H5Cl,
NH4OH
Platinum(IV) 336.90 370b 4.303 brown-red cr. v sol v sol sl sol,
chloride (PtCl4) (in Cl2) al, NH3
Platinum(IV) oxide (PtO2) 227.03 450 10.2 black powder ins ins ins acid,
aq. regia
Platinum(II) oxide (PtO) 211.09 550b 14.9 violet-black ins ins sol HCl;
cr. ins aq.
regia
Platinum sulfate 459.27 yellow plates sol dec sol al,
(Pt(SO4)2.4H2O) eth, acid
Hexachloroplatinic 517.92 60 2.431 red-brown v sol v sol sol al, eth
acid(IV) deliquescent
(H2[PtCl6].6H2O) cr.
Sodium hexachloroplatinate(IV) 453.77 yellow, sol sol al
(Na2[PtCl6]) hygroscopic cr.
Table 2 (contd).
Relative
atomic/ Melting Boiling Relative Crystalline Solubilityd
Chemical name molecular pointb point density formc Cold Hot Other
mass (°C) (°C) (g/cm3) water water solvents
Potassium hexachloroplatinate(IV) 486.03 3.50 orange-yellow sl sol sol ins al
(K2[PtCl6]) cr. or yellow
powder
Potassium tetrachloroplatinate(II) 415.26 ruby-red cr. sol
(K2[PtCl4])
Ammonium tetrachloroplatinate(II) 373.00 dark ruby-red sol
((NH4)2[PtCl4]) cr.
Ammonium hexachloroplatinate(IV) 443.91 3.06 orange-red cr. v sol ins al
((NH4)2[PtCl6]) or yellow powder
cis-Diamminedichloroplatinum(II) 300.07 270b orange cr. sl sole
(cis-[PtCl2](NH3)2)
trans-Diamminedichloroplatinum(II) 300.07
(trans-[PtCl2](NH3)2)
a Compiled from: Windholz (1976); Weast & Astle (1981); Neumüller (1987).
b dec = decomposes
c cr. = crystals
d al = alcohol (ethanol); dec = decomposes; eth = ether; ins = insoluble; sl = slightly; sol = soluble; v = very
e Tobe & Khokhar (1977)
Platinum hexafluoride, PtF6, has the highest oxidation state
of the element and is a strong oxidizing agent; the noble gas xenon
can be oxidized to XeF2 and oxygen to O2+ (Hoppe, 1965).
Hexachloroplatinic acid, H2[PtCl6], is formed by the
reaction of platinum metal with aqua regia or Cl2/HCl. When
heated, the ammonium salt of this acid produces a grey platinum
sponge. A black powder ("platinum black") is produced by reduction
in aqueous solution. Depending on the pH value, hydroxides exchange
the halogen ligands with OH- in a stepwise manner, leading to
PtO2.nH2O after dehydration (n = 1, 2, 3, 4). Further heating
gives rise to PtO at 400 °C, which decomposes to platinum and O2
at 560 °C.
By heating hexachloroplatinic acid at 240 °C, PtCl2 can be
obtained. It has a hexameric structure (Pt6Cl12) in the solid
state and is soluble in benzene. This compound forms H2[PtCl4]
in HCl.
Platinum forms a large number of Pt(II) and Pt(IV) complexes
with the formulae:
Pt(IV): [PtX6-n(NH3)n]n-2 where n = 0-6; X = halogen ligand
Pt(II): [PtX4-n(NH3)n]n-2 where n = 0-4; X = halogen ligand
The chemical structures of two of the more important platinum
complexes are shown below.
2.3 Conversion factors
Platinum 1 ppm = 7.98 mg/m3
1 mg/m3 = 0.13 ppm
2.4 Analytical methods
2.4.1 Sampling
Samples of ores, minerals, and preconcentrated technical
products can be obtained in a ground or powdered form. Metals and
alloys can be collected as chips and shavings. Platinum on alumina
pellets or monolithic supports must be comminuted before fusing or
digesting (Potter & Lange, 1981). Electronic scrap may contain
alloyed copper, nickel or lead. Melting with aluminium leads to a
brittle alloy, which can be easily crushed to a powder.
Blood samples may be frozen and lyophilized (Pera & Harder,
1977), homogenized with substances like TRITON-X 100(R) (Priesner
et al., 1981), and separated into plasma ultrafiltrate and proteins
(Bannister et al., 1978) or, if appropriate, analysed directly
without pretreatment.
With biological materials, homogeneous sampling is difficult
and often requires destructive methods resulting in the loss of all
information about the platinum species. Only the total content of
platinum and its isotopes can be determined.
For the analysis of platinum in urine, the untreated original
sample is usually unsuitable. Freeze-drying or a wet ashing
procedure with subsequent reduction of volume is necessary for most
analytical methods.
Other biological and environmental materials being investigated
for very low levels of platinum need to be sampled in large amounts,
with possible difficulty in homogenisation, digestion, storage, and
matrix effects.
2.4.2 Sample pretreatment
Determination of total platinum content in some materials
requires a digestion step, which is the pre-requisite for enrichment
and separation from other elements and organic substances. A modern
wet digestion procedure (Knapp, 1985) avoids contact with materials
other than quartz in order to reduce adsorption losses. In this way,
organic matter is destroyed most effectively and contamination with
platinum from other sources is minimized (Würfels et al., 1987).
In general, separation involves volatilization, distillation,
lyophilization, extraction, coprecipitation, flotation, sorption,
and other instrumental methods, such as electro-deposition,
chromatographic separations, and thermal pre-treatment in atomic
absorption spectroscopy (AAS) procedures (Knapp, 1984).
A selection of extraction and sorption techniques is shown in
Tables 3 and 4, respectively. For coprecipitation procedures,
details can be found in the reports of Fryer & Kerrich (1978),
Stockman (1983), Sighinolfi et al. (1984), Skogerboe et al. (1985),
Amosse et al. (1986), and Bankovsky et al. (1987).
2.4.3 Detection and measurement
2.4.3.1 Spectrophotometry
Unless the native soluble platinum compounds have an inherent
absorption spectrum, they can be treated with inorganic and organic
reagents to form coloured, soluble complexes that can be measured by
absorption spectrophotometry. Careful separation from other elements
is important (see section 2.4.2). The detection limits achieved are
in the low mg/kg (ppm) range (Jones et al., 1977; Brajter & Kozicka,
1979; Mojski & Kalinowski, 1980; Marone et al., 1981; Aneva et al.,
1986; Puri et al., 1986).
2.4.3.2 Radiochemical methods
Neutron-activation analysis is a very sensitive method for
determining submicrogram traces of platinum. It is at least one to
several orders of magnitude more sensitive than the best of the
spectrophotometric methods. For the determination of platinum a
sensitivity of 1 ng absolute was estimated on irradiation of a
sample for 1 month at a neutron flux of 10-2cm-2-second,
followed by a 2-h decay (NAS, 1977).
Radiochemical methods have been applied to the analysis of
platinum in various matrices. The detection limits are 1-2 µg/kg in
rock samples (Stockman, 1983), 30 µg per kg dry weight in plant
material (Valente et al., 1982), 1-3 µg/kg dry weight (0.3 ng
absolute) in plant material and animal tissue (Tjioe et al., 1984),
and 100 µg/kg in airborne particulate matter (Schutyser et al.,
1977).
2.4.3.3 X-ray fluorescence spectroscopy
This method permits the highly selective, sensitive, rapid, and
non-destructive analysis of platinum. Zolotov et al. (1983) obtained
a detection limit of 32 µg Pt per litre in aqueous solutions.
A new variant, total-reflection X-ray fluorescence
spectrometry, has the advantage of small sample size (5 to 40 µg)
with low absolute detection limits (Von Bohlen et al. 1987).
Table 3. Extraction procedures for separating platinum
Species Matrix Chemical modifier Extraction Elements Reference
medium separated
Pt(IV) aqueous 6 M HCl isopentanol Al, Ca, Mg, Aneva et al. (1986)
solutions Mn, Ni, Cr
4-methyl-2- Cu, Pb
pentanone (partially)
Pt(IV) aqueous dithio-oxamide tri-butyl Ir(III), Rh(III) Brajter & Kozicka (1979)
solutions phosphate
Pt(IV) plant- S-(1-decyl)- variety of co-extraction Jones et al. (1977)
processing N,N -diphenyl- organic liquids of noble metals
solutions isothiouronium bromide
Pt(IV) palladium(II) 1,5-diphenylthiocarbazone carbon Pd(II) Marczenko & Kus (1987)
chloride tetrachloride
Pt(IV) palladium triphenylphosphine dichloroethane Pd, Au Mojski & Kalinowski (1980)
metal oxide
Pt(IV) synthetic phenanthraquinonemonoxime molten Fe, Cu, Ni, V, Puri et al. (1986)
aqueous naphthalene Cr, Al, Au, Ag
solutions Ir, Rh, Pd
Pt(IV) aqueous potassium butylxanthate carbon - Singh & Garg (1987)
solutions tetrachloride
Pt(IV) automotive bis-(2-furyl)- trichloromethane V, Mo, W Wiele & Kuchenbecker (1974)
catalysts glyoxaldioxime
Pt(II), synthetic 1,4,7,10,13,16-hexa- 4-methyl-2- Fe(III) Arpadjan et al. (1987)
Pt(IV) aqueous azaoctadecane pentanone
solutions
Table 3 (contd).
Species Matrix Chemical modifier Extraction Elements Reference
medium separated
Pt(II) urine Diethylammonium- trichloromethane Ca, Zn, Fe(II) Borch et al. (1979)
diethyldithiocarbamate, and Mn(II)
NaSH
Pt(II) aqueous sodium co-extraction Mueller & Lovett (1987)
solutions diethyldithiocarbamate of Pd(II),
acetonitrile, NaCl Rh(II)
Pt(II) plasma sodium - Andrews et al. (1984)
ultrafiltrate diethyldithiocarbamate
methanol, H2O
Pt geological sodium tetraborate, molten lead - Millard (1987)
samples KCN
Pt geological KCN, KOH Ag, Au co-extraction Le Houillier & De Blois
samples of noble metals (1986)
Pt blood, hair, HCl, SnCl2 tri-n-octylamine, - Tillery & Johnson (1975)
faeces, urine xylene
Pt geological sodium nickel sulfide - Robert et al., (1971)
samples carbonate
and sodium
tetraborate
Table 4. Sorption techniques for preconcentrating platinum
Species Matrix Sorption medium Eluent Elements Reference
separated
Pt sea water Bio-Rad Ag-1-X2 0.1 M HCl, Ir Goldberg et al. (1986);
0.02 M thiourea Hodge et al. (1986)
Pt geological Srafion NMRR 0.01 M HCl, high selectivity Kritsotakis & Tobschall (1985)
samples 5% thiourea for transition
metals
Pt aqueous polyethenimine- Co(II), Zn, Cd, Geckeler et al. (1986)
solutions methylthiourea In(III), Na
suspended in water
at pH 1
Pt(II), aqueous Dowex 2X-8 75% NH3 in H2O Au Kahn & Van Loon (1978)
Pt(IV) solutions
Pt (IV) geological Bio-Rad Ag-50W-X8 0.1 M HCl - Coombes & Chow (1979)
samples
Pt (IV) geological P-TD 2 M HClO4 Al, Mg, Cu, Grote & Kettrup (1987)
samples Fe, Ni, Cr
Pt (IV) aqueous Hyphan 1 M HClO4 Na, K, Cs, Mg, Kenawy et al. (1987)
solutions Ca, Al
Pt (IV) geological Polyorgs digestion HClO4, coextraction Myasoedova et al. (1985)
samples, H2SO4, HNO3 noble metals
scaps
Pt (IV) aqueous (-CH2-S-)n(n approx. 1000) 6 M HCl Co, Ni, Pb, Fe, Zolotov et al. (1983)
solutions Zn, Cd
2.4.3.4 Electron spectroscopy for chemical analysis (ESCA)
ESCA is a technique typically applied in surface analysis
involving a few surface atomic layers (1-2 nm). This technique is
used for special purposes; for instance, Schlögl et al. (1987)
analysed microparticles from automotive exhaust gas catalysts (see
section 3.2.1.4).
2.4.3.5 Electrochemical analysis
Of the voltametric techniques available for element analysis,
polarography, in particular, has been applied for the determination
of platinum. Alexander et al. (1977a,b) described a pulse
polarography method for the analysis of platinum in ores after fire-
assay separation and preconcentration. By measuring the sensitive
catalytic polarographic wave generated by the Pt(II)-ethylenediamine
complex in alkali solutions a detection limit of 0.025 µg per kg was
obtained. A similar technique was applied to the analysis of urine
by Vrana et al. (1983), and the detection limit was 10 µg/litre.
However, these methods do not allow the direct determination of
platinum in complex solutions due to interferences from some heavy
metals and precipitation of platinum with other metals in the form
of their hydroxides. In this respect, inverse voltametry is
superior. Kritsotakis & Tobschall (1985) used the glassy carbon
electrode for the determination of platinum traces in synthetic
solutions. After preconcentration, 0.04 mg Pt/litre could be
determined. This detection limit is sufficient for determining
platinum in ores.
Using adsorptive cathodic stripping voltametry, Van den Berg &
Jacinto (1988) analysed sea-water samples (see section 5.1.2). The
detection limit was 7.8 pg Pt/litre.
Hoppstock et al. (1989) developed a sensitive volta-metric
method for determining platinum in the ng/kg range in biotic and
environmental materials. The overall recovery of platinum was
reported to be 97% or more.
Nygren et al. (1990) described an adsorptive volta-metric
method for the measurement of platinum in blood. The detection limit
for a 100-µl sample was 0.017 µg per litre.
2.4.3.6 Proton-induced X-ray emission (PIXE)
PIXE requires only small sample sizes (1-10 mg), but is a time-
consuming and labour-intensive method. Owing to the substantially
lower background, the detection limits are lower by a factor of 1000
than for X-ray fluorescence methods. Methods for analysing water
samples, air, and biological tissues have been described by Rickey
et al. (1979), Wolfe (1979), and Thompson et al. (1981).
2.4.3.7 Liquid chromatography (LC)
Marsh et al. (1984) published an adsorption chromatography
method in which the analyte was first separated with an ODS
Hypersil(R) column, reacted with NaHSO3, and then detected by UV
absorption. The detection limit for cisplatin was 40-60 µg/litre.
For the malonate derivates, Van der Vijgh et al. (1984) reported a
detection limit of 300-1200 µg/litre for human body fluids.
Ebina et al. (1983) analysed Pt(II) in aqueous solutions that
were modified with EDTA, ethanoic acid, and maleonitriledithiol. The
spectrophotometric detection limit for this partition ion-pair
method was 0.2 ng per litre.
Using an ion exchange chromatography method, Rocklin (1984)
separated Pt(IV) as the hexachlorocomplex on a polar anion exchange
column and determined the complex by UV. For samples digested in
aqua regia, a detection limit of 30 µg/litre can be obtained without
preconcentration and < 1 µg/litre after preconcentration.
2.4.3.8 Atomic absorption spectrometry (AAS)
AAS is a method of high selectivity and specificity and is
often the method of choice in analysing platinum in biological and
environmental samples. However, there are problems with background
radiation deriving from molecules and radicals, especially from
unseparated matrix. These interferences can be partly overcome by
background compensation through a radiation continuum or by the
application of the "Zeeman" effect. To determine platinum in the
range of the detection limit, an accurate separation from matrix is
essential.
For platinum determinations in biological materials, Farago &
Parsons (1982) recommended wet digestion in nitric acid and the
removal of residual nitrates by hydrochloric acid. Brown & Lee
(1986) proposed totally pyrolytic cuvettes for graphite furnace AAS,
thus achieving a greater sensitivity for refractory metals. These
results were confirmed by Schlemmer & Welz (1986). Although platinum
does not form a stable carbide, there was an effect on the wall
material of the carbon rod. Electro-graphite tubes coated with
pyrolytic graphite were found to be superior to glassy carbon tubes
(Welz & Schlemmer, 1987).
LeRoy et al. (1977) described a method for the detection of
platinum in biological samples that used controlled dehydration and
ashing with rapid sample evaporation to detect low levels of
platinum. This method did not suffer as much from matrix
interference as other AAS graphite furnace methods. The method can
be used to detect platinum down to approximately 30 µg/kg (30 ppb).
Hodge et al. (1986) determined platinum down to pg per litre
levels in marine waters, sediments, and organisms. Sea water was
extracted with an anion exchanger (Table 4), eluted, and purified by
acid digestion. In a second step, platinum was obtained from the
solution with an anion exchanger, stripped again from the bead, and
injected. Using a similar technique, Hodge & Stallard (1986)
determined platinum in roadside dust.
Jones (1976) digested urine and blood samples with nitric and
perchloric acids. The samples were diluted after cooling and
injected onto carbon rods. The minimum detectable platinum
concentration in 5-g samples was 30 µg per litre.
McGahan & Tyczkowska (1987) dried and ashed tissues and fluids
and diluted the residue with different acids before direct
injection. The detection limits were 6 µg per kg or 6 µg/litre.
Bannister et al. (1978) separated protein-bound platinum and
free circulating compounds by centrifugal ultra-filtration. In the
ultrafiltrate, platinum compounds were chelated with
ethylenediamine, extracted on a cation exchange paper disc, eluted,
and injected. The minimum working concentration was 35 µg/litre of
plasma.
Alt et al. (1988) described a simple and reliable method which
included high-pressure ashing (cf. Knapp, 1984), separation by
extraction, and detection by graphite furnace AAS. This method was
recommended for analysing biological and other materials down to the
µg/kg range.
König et al. (1989) determined platinum in the particulate
emissions in engine test-stand experiments (see section 3.2.1.4)
using a high-pressure digestion without a separation. The authors
studied the matrix influences with respect to the concomitant
elements and found interferences from A1, Pb, Ca, Zn, P and, most
severely, from Si, but under the controlled test conditions no
interference effects were observed. In particle-free condensates of
automotive exhaust gas, a detection limit of 0.1 ng/ml was achieved
by the method of signal addition described by Berndt et al. (1987).
2.4.3.9 Inductively coupled plasma (ICP)
The generation of plasmas is a further development of chemical
flame methods. They have a wide temperature range, a transparency
for the UV spectral lines, and are predominantly insensitive against
interfering chemical reactions in the excitation zone that occur
with chemical flames. Plasma excitation allows the determination of
several elements simultaneously and is, because of minor matrix
effects, easy to calibrate over many orders of magnitude. Two
methods of generating a plasma are currently used: firstly with
direct current (DC) and secondly with a high frequency current
(20-80 MHz, inductively coupled plasma, ICP). The ICP method works
with an argon plasma and temperatures of 4000-8000 K. Due to the
increasing ionization effects, the aerosol feeding is controlled by
cooling devices.
Boumans & Vrakking (1987) discussed standard values for a 50-
MHz ICP, considering effects of source characteristics, noise, and
spectral band-width, and obtained a detection limit for the platinum
spectral line at 214.42 nm of 7.2 µg/litre.
Maessen et al. (1986) studied the influence of chloroform on
the platinum signal at 203.65 nm. The detection limits by this
method were affected by chloroform and ranged from 30-400 µg/litre.
Wemyss & Scott (1978) determined platinum-group metals and gold
in ores after three different digestions. The method allowed
determination down to 0.13 mg/litre for the 299.8-nm line.
Fox (1984) reported interferences from aluminium and magnesium
in direct current methods. A buffer of lithium and lanthanum
compounds suppressed this effect.
Lo et al. (1987) described a simple method for determining
platinum in urine with a working range down to 50 µg/litre (50 ppb)
under direct application of acidified samples. Electrothermal
vaporization (ETV) was used for generating plasma-suitable aerosols
by Matusiewicz & Barnes (1983). They determined platinum at the
mg/litre level in human body fluids directly. A similar procedure
was used by Belliveau et al. (1986).
2.4.3.10 Inductively coupled plasma - mass spectrometry (ICP-MS)
Combining ICP with a mass spectrometer has new advantages in
analytical spectroscopy. Elemental ions generated from an aerosol or
an electrothermal vaporization unit are separated by a quadrupole
and detected as isotopes at low level. The ETV device allows
determination down to the pg/ml range.
Thompson & Houk (1986) used an ion-pair reversed-phase liquid
chromatography assay via a continuous flow ultrasonic nebulizer and
an ICP torch with a mass spectrometer. In synthetic solutions
detection limits of 7 µg/litre (7 ppb) were obtained.
Gregoire (1988) compared the results from the ICP-MS-ETV with
neutron activation analysis and the ICP-MS solution nebulization
method in the ng/ml concentration range and found good agreement.
For the analysis of air samples, the NIOSH Manual of Analytical
Methods (Eller, 1984a) describes a method based on inductively
coupled argon plasma atomic emission spectroscopy. The working range
is 0.005-2.0 mg/m3 with a 500-litre air sample. However, long
sampling periods are required for measuring soluble platinum
compounds in the workplace and the method does not distinguish
between soluble and insoluble platinum. Similar methods are
recommended for the analysis of platinum in blood and tissues
(Eller, 1984b) and in urine (Eller, 1984c).
The method recommended by the United Kingdom Health and Safety
Executive (1985) has a precision better than 8%, measured as a
coefficient of variation, for samples of a minimum of 120 litres in
the range 1-15 µg Pt/m3. The sensitivity of this method can be
improved by 100-1000 fold by using ICP-MS instead of carbon furnace
atomic absorption spectrometry.
3. SOURCES OF HUMAN AND ENVIRONMENTAL EXPOSURE
3.1 Natural occurrence
The six platinum-group metals, platinum, palladium, rhodium,
ruthenium, iridium, and osmium, were probably concentrated mainly in
the iron-nickel core during the earth's formation. This explains
their relatively low presence in the lithosphere (rocky crust) of
the earth (Goldschmidt, 1954) where the average concentration of
platinum ranges between 0.001 and 0.005 mg/kg (Mason, 1966, Bowen,
1979).
Platinum is found both in its metallic form and in a number of
minerals. The principal minerals are: sperrylite, PtAs2;
cooperite, (Pt,Pd)S; and braggite, (Pt,Pd,Ni)S. Primary deposits are
associated with ultrabasic, rather than silicic, rock formations.
Economically important sources exist in the Bushveld Igneous Rock
Complex in Transvaal, Republic of South Africa, and in the Noril'sk
region of Siberia, the Kola Peninsula, and in the Nishnij Tagil
region of the Urals, USSR. The platinum content in these deposits is
between 1 and 500 mg/kg. In the Sudbury district of Canada, platinum
metal is contained in copper-nickel sulfide ores at an average
concentration of 0.3 mg/kg but is concentrated to more than 50 mg/kg
during the refining of copper and nickel. In the USA, there is a
platinum-palladium mine in the Stillwater Complex area, Montana
(NAS, 1977; Renner, 1979).
Small amounts of platinum are also mined from secondary or
placer deposits in the USSR (Ural Mountains), Colombia, USA
(Alaska), Ethiopia, and the Philippines. In these deposits platinum
is present in the form of metallic alloys of varied composition
(NAS, 1977).
3.2 Anthropogenic sources
3.2.1 Production levels and processes
3.2.1.1 World production figures
World mine production of platinum-group metals, 40-50% of which
is platinum, has steadily increased during the last two decades. In
1971 production was 127 tonnes (51-64 tonnes platinum) and in 1972
it was 132 tonnes (53-66 tonnes platinum) (Butterman, 1975). In
1975, automobile exhaust gas catalysts were introduced in the USA in
order to meet the stringent emission limits for carbon monoxide,
hydrocarbons, and nitrogen oxides set by the Federal Clean Air Act.
In Japan, the automobile catalyst was introduced at the same time.
As a consequence, world production of PGM increased to 179 tonnes
(72-90 tonnes platinum) in 1975, reaching a plateau of between 200
and 203 tonnes per year (80-102 tonnes platinum) during the period
1977-1983 (Loebenstein, 1982, 1988).
From 1984 onwards world production increased, apparently in
response to the anticipated demand in Western Europe where
automobiles are being increasingly fitted with catalytic converters.
In 1987, world mine production of PGM amounted to about 270 tonnes
(108-135 tonnes platinum) (Loebenstein, 1988).
The future demand for platinum depends on improvements in
engine technology and emission control, but can be expected to
increase further during the coming years. Data on platinum demand
are presented in section 3.2.2.
3.2.1.2 Manufacturing processes
Most native placer platinum is recovered by dredging and, in
less developed areas, by small hand operations. The copper and
nickel sulfide ores are mined by large-scale underground methods and
concentrated by flotation (Stokinger, 1981).
The isolation of pure platinum metal from raw materials
involves two principal stages: (i) extraction of a concentrate of
precious metals from the ore; (ii) refining the concentrate to
separate the platinum-group metals from each other and purify them.
These processes require sophisticated chemical technology and
include precipitating crystallization and liquid-liquid extraction,
often combined with redox reactions to change the oxidation state of
the metals. Further processes involve halogenation and reduction
reactions at annealing temperatures and special distillations
(Renner, 1984).
Potential health hazards of exposure to soluble platinum salts
are encountered during the later stages of the refining process.
After dissolving platinum, palladium, and gold with aqua regia or
Cl2/HCl and the subsequent precipitation of gold by addition of
ferrous salts, ammonium chloride is added to precipitate ammonium
hexachloroplatinate, (NH4)2[PtCl6]. After several purification
processes there is a second precipitation of this complex salt,
which is then filtered off, dried and finally calcined to yield a
spongy mass of platinum metal having purity of 99.95-99.99%. This
can be further purified by a cationic exchange technique (NAS, 1977;
Stokinger, 1981).
Secondary sources in substantial quantities come from the
reclamation of scrap and used equipment, particularly industrial
catalysts. The recycling of platinum-group metals from automobile
catalysts is also increasing (see section 4.3). In principle, the
recycling of platinum involves the same wet-chemical and melting
processes that are applied to its production from ores (Renner,
1984).
3.2.1.3 Emissions from stationary sources
a) Production
Data on emissions of platinum during production are not
available.
b) Stationary catalysts
During the use of platinum-containing catalysts, platinum can
escape into the environment in variable amounts, depending on the
type of catalyst. Of the stationary catalysts used in industry, only
those employed for ammonia oxidation emit major amounts.
The loss of platinum from ammonia oxidation gauzes during
nitric acid production depends on the operating pressure. An average
figure is 0.15 g/tonne of nitric acid (Sperner & Hohmann, 1976). Of
this apparent loss, 70-85% is recovered on gold-palladium catchment
gauzes, reducing the loss to 0.03 g/tonne (Anon., 1990a). The
production of nitric acid in the USA in 1989 was 7 247 837 tonnes
(Anon., 1990b). Thus the amount of platinum "lost" in 1989 in the
USA is calcu-lated to be 217 kg. This is the maximum amount that
could be dissolved or suspended as a colloid in the nitric acid and,
thus, could be introduced into the environment if the nitric acid is
used in fertilizer production.
3.2.1.4 Emissions from automobile catalysts
Automobile catalysts are mobile sources of platinum. Although
these catalysts are designed to function for 80 000 km or more
(Koberstein, 1984), some loss of platinum can occur due to
mechanical and thermal impact. The data on platinum emissions from
automobile catalysts are very limited.
In the mid 1970s unrealistically high assumptions were made for
platinum loss. Brubaker et al. (1975) estimated the loss to be about
12 µg Pt/km, which would mean a total loss of approximately 1 g
after 80 000 km.
Experimental data show much lower emission rates. Malanchuk et
al. (1974) found a platinum concentration of 0.029 µg/m3 in an
inhalation chamber that was fed by catalysed engine exhaust. On the
basis of the chamber volume, flow rate, and the speed simulated on
the engine test stand, an emission rate of 0.39 µg/km was
calculated. In another US EPA study, Sigsby (1976) did not detect
platinum in particulate exhaust emissions (< 5 µm) at a detection
limit of 0.06 µg/g. In exhaust dilution tunnels, platinum was
detected in larger particles in the range of 0.034 to 635 µg/g
sample; whole or fragmented pellets contained the highest
concentrations.
Reliable emission data for the pellet-type catalyst come from a
study conducted by the General Motors Corporation (Hill & Mayer,
1977), in which emission rates as well as the soluble fraction were
determined by a radio-metric method. Platinum emission was found to
be 0.8 to 1.2 µg per km travelled in low-speed runs (starts and
stops, maximum speed 48 km/h) and 1.9 µg per kilometre travelled in
high-speed runs (96 km/h). It should be noted that these results
relate to the first 250 km of catalyst life. Lower loss rates would
be expected with increasing age of the catalyst. Of the particles
collected, 80% had particle diameters greater than 125 µm.
Experiments with an engine test stand using laboratory prepared
catalysts indicated that about 10% of the platinum emitted is water
soluble. However, the statistical significance of these results was
not reported. Even so, these emission data provide the best basis
for the estimation of expected ambient air concentrations resulting
from the introduction of pellet catalysts (see section 5.1.1).
However, this type of automobile catalyst is no longer used on new
cars in the USA, and has never been used in Europe where only
monolithic catalysts are on the market.
Emission data are available concerning the new generation
monolith-type catalyst. In Germany the Fraunhofer Institute of
Toxicology and Aerosol Research (König et al., 1989, König & Hertel,
1990) has conducted engine test stand experiments as part of a
programme of the Ministry of Research and Technology for assessing
the relative risk of this new man-made environmental source (GSF,
1990). First results indicated that platinum emission is lower by a
factor of 100 than in the case of pelleted catalysts: at a simulated
speed of 100 km/h, total loss from a three-way catalyst was
measured, using the AAS method, to be on average about 17 ng/m3 in
the exhaust gas (König et al., 1989). In further experiments this
value was validated (König & Hertel, 1990): the mean platinum
emission from two catalysts was found to be 12 and 8 ng/m3,
respectively. As shown in Table 5, platinum emission seems to be
temperature dependent. At an exhaust gas temperature of 690° C and a
simulated speed of 140 km/h, about 35-39 ng/m3 was found in the
exhaust gas. The mean aerodynamic diameter of the particles
collected after the muffler (silencer) on a Berner impactor varied
between 4 and 9 µm. Preliminary results indicated that approximately
10% of the total platinum penetrated a depth-type filter to be
trapped in the condensate (König et al., 1989), but this single
measurement could not be confirmed by subsequent determinations
where the platinum content in the condensate was below the detection
limit (0.1 ng/ml) (König & Hertel, 1990).
Schlögl et al. (1987) analysed microparticles emitted from
automobile exhaust and collected on several conducting surfaces. In
experiments with diesel and gasoline engines equipped with
catalysts, they found detectable traces of platinum. In diesel
engine exhaust it was presumed that most platinum would be in the
oxidation state 0 (platinum black). A small part was found to be
Pt(IV), probably in the oxide form. The platinum emission from
gasoline engines showed a photoemission spectrum indicating that
platinum is probably emitted mostly in the form of surface oxidized
particles.
Table 5. Mean platinum emissions from two monolith catalysts (1 and 2)
at different engine test stand runsa
Platinum emission
Simulated Number Exhaust gas Exhaust ng per km Mean aerodynamic
speed of samples temperature gas travelledb diameter (µm)
(km/h) (° C) (ng/m3)
(1) (2) (1) (2) (1) (2)
60 18 480 3 4 2 3 6 9
100 39 600 12 8 10 8 4 6
140 18 690 39 35 39 35 6 8
a Adapted from König et al. (in press)
b Calculated assuming that on average 10 m3 exhaust gas is emitted per litre
gasoline and a gasoline kilometrage of 7, 8, and 10 litres per 100 km travelled,
respectively.
3.2.2 Uses
The principal use of platinum derives from its special
catalytic properties. Further applications in industry are related
to other outstanding properties, particularly resistance to chemical
corrosion over a wide temperature range, high melting point, high
mechanical strength, and good ductility. Platinum has long been
known to have excellent catalytic properties. Before the
introduction of catalytic converters in automobiles, most of the
platinum was used as a catalyst in hydrogenation, dehydrogenation,
isomerization, cyclization, dehydration, dehalogenation, and
oxidation reactions. One of its major industrial uses is for
naphtha-reforming to upgrade catalytically the octane rating of
gasoline. Other catalytic uses are in ammonia oxidation to produce
nitric acid, hydrogen cyanide manufacture, the reduction of nitro
groups and, in the automobile catalyst application, the conversion
of carbon monoxide to carbon dioxide and nitrogen oxide to nitrogen
and water (NAS, 1977; Stokinger, 1981).
As shown in Table 6, in the USA in 1973, before the
introduction of the automobile catalyst, most of the platinum was
used for catalytic purposes in the chemical and petroleum industry.
In 1987 the use pattern had completely changed and 71% of the
platinum sold was used by the automobile industry. In 1987, a
typical USA car catalyst contained about 1.77 g of platinum and 10.6
million vehicles with catalysts were produced (Loebenstein, 1988);
this accounts for the 18.8 tonnes shown in Table 6.
Table 6. Platinum sales to various types of industry in the USA
before and after the introduction of automotive catalytic
convertersa
Industry 1973 1987
kg/year % of total kg/year % of total
Automobile - - 18 817 71.3
Chemical 7434 36.3 1920 7.5
Petroleum 3844 18.8 739 2.8
Dental and
medical 868 4.2 479 1.9
Electrical 3642 17.9 1821 7.1
Glass 2255 11.0 285 1.1
Jewellery and
decorative 697 3.4 177 0.7
Miscellaneous 1732 8.5 1430 5.6
Total 20 472 100 25 668 100
a From: Butterman (1975); Loebenstein (1988)
Tables 7 and 8 show the platinum demand by application in the
Western world, also reflecting the increased demand during recent
years. In 1989, total demand was 90 tonnes.
Platinum oxidation catalyst technology, developed to reduce
automobile exhaust emissions, has been extended to other
environmental control applications such as the reduction of carbon
monoxide and hydrocarbon emissions from large gas turbines (Jung &
Becker, 1987) and the transformation of hydrogen molecules into
active hydrogen atoms to reduce chlorohydrocarbons such as
trichloroethylene to ethane in water (Wang & Tan, 1987).
Table 7. Western-world platinum demand (kg/year) by applicationa
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Automobile catalyst
gross 19 278 18 144 18 569 18 285 23 814 27 783 32 318 35 579 37 563 41 107
recovery 0 0 283 850 1276 1984 2551 3260 4536 4961
Chemical 7371 7087 7371 6946 7371 6379 5528 5528 4536 4536
Electrical 5953 5245 4819 4961 5386 5670 5103 5103 5245 5528
Glass 3969 2835 2410 2977 3969 3969 2551 3402 3685 3969
Investment
small 0 0 1276 2551 4819 7371 12 757 6095 9355 3685
large 4536 5528 3260 1843 4252 4819 3544 7796 8505 850
Jewellery 15 876 21 404 21 687 20 270 21 971 22 963 24 097 28 066 33 452 36 996
Petroleum 3685 3969 1843 567 425 425 567 1559 1417 2126
Other 5386 4678 4819 4252 3827 2835 3685 3402 3402 3260
Total 66 054 68 889 65 771 61 802 74 559 80 230 80 511 93 270 102 624 97 096
a From Johnson Matthey (1990)
Table 8. Regional platinum demand (kg/year) by applicationa
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Japan
Automobile catalyst
grossb 5953 5386 4819 4819 4819 5953 7229 8788 9355 10 064
recoveryc 0 0 0 0 0 0 142 425 709 709
Chemical 283 283 283 283 425 425 425 425 425 425
Electrical 425 425 567 567 50 1134 1276 1276 1276 1417
Glass 1134 1417 1276 1701 2126 1701 850 1276 1276 1134
Investment
small 0 0 0 142 425 992 992 1701 3260 992
large 4536 5528 3260 1843 4252 4819 3544 7796 8505 850
Jewellery 12 474 17 718 17 577 15 876 17 718 19 136 20 979 25 515 30 050 32 602
Petroleum 425 425 425 425 567 425 0 0 0 0
Other 1417 1417 1559 1276 1134 850 567 425 425 425
Total 26 647 32 599 29 766 26 932 32 316 35 435 28 632 46 777 53 863 47 200
North America
Automobile catalyst
gross 12 474 12 190 12 899 12 757 18 002 19 845 21 120 19 561 19 561 20 412
recovery 0 0 0 850 1276 1984 2410 2835 3827 4252
Chemical 3260 1417 2268 2835 2835 2126 1843 1559 1559 1559
Electrical 4111 1984 1984 2551 2693 2268 1843 1843 1843 2126
Glass 1417 567 283 425 850 1134 709 709 709 850
Investment 0 0 1134 1134 850 3685 8505 2410 2410 1559
Jewellery 425 425 425 425 425 425 425 425 425 567
Petroleum 3969 1559 567 425 425 283 283 425 425 1134
Other 2126 1701 567 709 992 850 1417 1417 1417 1417
Total 27 782 19 843 20 127 20 411 25 796 28 632 33 735 25 514 24 522 25 372
Table 8 (contd).
1980 1981 1982 1983 1984 1985 1986 1987 1988 1989
Rest of Western world, including Europe
Automobile catalyst
gross 850 567 567 709 992 1984 3969 7229 8647 10 631
recovery 0 0 0 0 0 0 0 0 0 0
Chemical 3827 5386 4819 3827 4111 3827 3260 3544 2551 2551
Electrical 1417 2835 2268 1843 1843 2268 1984 1984 1984 1984
Glass 1417 850 850 850 992 1134 992 1417 1701 1984
Investment 0 0 142 1276 3544 2693 3260 1984 3685 1134
Jewellery 2977 3260 3685 3969 3827 3402 2693 2126 2977 3827
Petroleum 709 1984 850 283 567 283 283 1134 992 992
Other 1843 1559 2693 2268 1701 1134 1701 1559 1559 1417
Total 11 622 16 441 15 874 14 459 16 443 16 159 18 142 20 977 24 096 24 520
a From: Johnson Matthey (1990)
b Gross automobile catalyst demand is purchase of platinum by the auto industry for the manufacture of automobile catalysts.
c Automobile catalyst recovery is platinum recovered from catalytic converters removed from scrapped automobiles.
Platinum and platinum-rhodium alloys have many high-temperature
uses. Thermo-electrical applications arise from the simple and
stable relationship between resistance and temperature that platinum
exhibits over a wide temperature range. This explains its use in
platinum resistance thermometers, thermocouples, and strain gauges.
The high melting point of platinum and its resistance to oxidation
and many chemicals has led to its use in vessels in the glass-making
industry and in the fabrication of spinning jets and bushings for
the production of viscose rayon and fibreglass, respectively. It is
also used for laboratory ware, such as crucibles, combustion boats,
and the tips of tongs. Ships' hulls, propellers, and rudders are
protected against corrosion by "cathodic protection" using platinum-
clad anodes (NAS, 1977).
Platinum and/or its alloys have been used in electric contacts
for relays and switchgears for a variety of reasons, including
hardness and good conductivity. Many printed circuits are made using
preparations that contain platinum. Electrochemical platinum
electrodes have been used in preparative chemistry, since they
support many oxidative reactions although they resist oxidation
themselves (NAS, 1977).
A major use of platinum is in jewellery for making rings and
settings. Platinum is also used to produce a silvery lustre on
ceramic glazes (NAS, 1977).
In dentistry, platinum is used in gold-platinum-palladium
alloys to raise the melting-point range and increase the strength.
However, this use is decreasing, since platinum is being replaced by
other materials including palladium (Anusavice, 1985; NAS, 1977).
Platinum has an important role in neurological prostheses, i.e.
surgically implanted microelectronic devices, such as implants for
treating incontinence, or for recovering some use of paralysed limbs
following spinal accidents (Donaldson, 1987).
Platinum-iridium electrodes are used for long-term electrode
implantation for recording electrical activity and for stimulation
in human tissues and organs, e.g., pacemakers (Theopold et al.,
1981).
All these applications use platinum as a pure metal or in the
form of alloys, but soluble platinum salts are also used in the
manufacture of these products; e.g., hexachloroplatinic acid may be
used in platinizing alumina or charcoal in catalyst production. A
number of salts can be used in the electrodeposition of platinum,
e.g., sodium hexahydroxyplatinate(IV), Na2[Pt(OH)6].2H2O,
diamminedinitroplatinum(II), [Pt(NO2)2(NH3)2], hydrogen
dinitrosulfatoplatinate(II), H2[Pt(NO2)2SO4], and
tetraammineplatinum(II) compounds such as the hydrogenphosphate,
sulfamate, citrate, and tartrate (Baumgärtner & Raub, 1988; Skinner,
1989).
Complexes of platinum, particularly cis-
diamminedichloroplatinum(II) (cisplatin) (see footnote in section
1.2), have been used to treat cancer. In patients with testicular
cancers, remissions rates of more than 90% have been achieved
(Lippert & Beck, 1983).
4. ENVIRONMENTAL TRANSPORT, DISTRIBUTION, AND TRANSFORMATION
4.1 Transport and distribution between media
By comparison with other elements, platinum-group metals are
distributed sparsely in the environment. Since platinum is so
valuable, great care is taken to avoid significant loss during
mining and refining processes, and during use and disposal of used
platinum-containing objects. Up to 1984, about 1050 tonnes of
platinum had been refined. Most of this has been used in the form of
the metal and platinum oxides, which are practically insoluble in
water, resistant to most chemical reactions in the biosphere, and do
not volatilize into air (Renner, 1984).
Part of the platinum released into the air from automobile
emissions (section 5) is deposited close to the roads and could be
washed off by rain into rivers and coastal marine waters (Hodge &
Stallard, 1986). However, only small amounts of platinum have been
detected in environmental samples (see sections 5.1.2. and 5.1.3.).
Large amounts of metals including platinum can be transported
in rivers draining major industrialized regions, leading to elevated
platinum concentrations in sediments (section 5.1.3).
Platinum forms soluble complexes with ammonia, cyanide, amines,
olefins, organic sulfides, and tertiary arsines. However, the level
of these ligands in natural waters is insufficient to make platinum
mobile (Fuchs & Rose, 1974).
Organic matter has a role as a vehicle for the transport of
platinum and for bringing about its precipitation or concentration.
There is a good correlation between high contents of platinum and
organic carbon in polluted stream sediments of the Ginsheimer-
Altrhine river, near Mainz, Germany (see section 5.1.2), and it is
assumed that organic matter such as humic and fulvic acids binds
platinum, aided perhaps by appropriate pH and redox potential
conditions in the aquatic environment (Dissanayake, 1983).
Detailed information about the geochemical behaviour of
platinum-group metals is available from the platinum mining area of
Stillwater, Montana, USA (Fuchs & Rose, 1974). The mobility of
platinum depends on pH, the redox potential, chloride concentrations
in soil water, and the mode of occurrence of platinum in the primary
rock. The relation between redox potentials and pH conditions
indicates that platinum behaviour also depends on the kind of ore it
is associated with. If bound in chromite, it has essentially no
mobility in weathering because of the resistant character of
chromite. On the other hand, platinum in the form of trace mineral
inclusions in sulfides is readily released by oxidation during
weathering. Calculated relations between pH and redox potential
indicate that increased chloride concentrations in soil water will
promote mobility. Thus, platinum will be mobile only in extremely
acid waters or those with a high chloride level (Fuchs & Rose,
1974).
In twigs from four limber pines (Pinus flexilis) in the
platinum mining area of Stillwater, the platinum concentrations were
the same as in the adjacent soil. It was concluded that limber pine
does not concentrate platinum, probably due to the limited mobility
of platinum (Fuchs & Rose, 1974). However, high concentrations of
platinum were found in the roots of nine horticultural crops
(cauliflower, radish, snapbean, sweet corn, pea, tomato, bell
pepper, broccoli, and turnip) grown in Hoagland's hydroponic culture
solution containing platinum tetrachloride concentrations of 0.057,
0.57, or 5.7 mg/litre (Pallas & Jones, 1978; see section 7.3). For
example, at the highest concentration, cauliflower and tomato roots
contained 1425 and 1710 mg Pt/kg, respectively. Only pepper,
cauliflower, and radish accumulated platinum in their tops, but to a
very limited extent. From the data of Pallas & Jones (1978) it is
not clear whether they differentiated between contamination of the
root surface and true uptake of platinum. However, these results
indicate that platinum can enter food crops but the bioavailability
essentially depends on the solubility of the platinum species. It
should be noted that the salt (PtCl4) used by Pallas & Jones
(1978) is soluble in water.
In the context of a German government programme (see section
3.2.1.4), Rosner et al. (1991) conducted engine test stand
experiments with a three-way-catalyst-equipped engine (monolith-type
catalyst) to determine platinum uptake by plants. Grass cultures
(Lolium multiflorum) were placed in continuously stirred tank
reactors and exposed to slightly diluted (1:10/20) exhaust gas for 4
weeks (8 h/day, 5 days/week). Using atomic absorption spectrometry
for the measurement of platinum emissions (see section 2.4.3.8,
König & Hertel, 1990), no platinum could be detected in the shoots
at a detection limit of 2 ng/g dry weight.
4.2 Biotransformation
By analogy, platinum compounds may undergo biotransformation
comparable to processes described for other metals. The
biomethylation of platinum compounds, i.e. [Pt(IV)Cl6]2-,
[Pt(IV)(CN)4Cl2]2-, [Pt(IV)(CN)5Cl]2-, and
[Pt(IV)(SO4)2], has been established only in in vitro test
systems (Taylor, 1976; Wood et al., 1978; Fanchiang et al., 1979;
Taylor et al., 1979; Fanchiang, 1985).
Methylcobalamin (MeB12) reacts with Pt(II) and Pt(IV)
complexes to give a methylated platinum compound. Agnes et al.
(1971) reported that this reaction requires the presence of platinum
in both oxidation states. Spectrophotometric measurements showed the
consumption of one mole of [Pt(IV)Cl6]2- per mole of MeB12,
[Pt(II)Cl4]2- being required only in catalytic quantities.
Aquocobalamin (aquo-B12) and methylplatinum were shown to be the
products of the reaction (Taylor & Hanna, 1977).
From these laboratory data produced under abiotic conditions it
is not, however, possible to conclude that microorganisms in the
environment are able to biomethylate platinum complexes.
4.3 Ultimate fate following use
The value of platinum-group metals has greatly increased and
methods for their recovery from spent catalysts are of economic
importance.
Platinum metal has been successfully recycled from used
chemical and petroleum catalysts for many years, but many companies
are still trying to find a successful formula for retrieving it from
automobile catalysts. The latter accounts for more than 30% of the
total platinum-group metal consumption in the USA. The US Office of
Technology calculated that if 50-60% of catalytic converters were
recovered for their metal value, about 7717 kg platinum per year
could be reclaimed in 1990. However, currently only between 25 to
40% of the used converters are being reclaimed (Agoos, 1986).
According to another estimate, 5443 kg of platinum was recovered in
1989 from automobile catalysts, of which 4666 kg was recovered in
the USA (Johnson Matthey, 1990).
In contrast to automobile catalysts, almost 100% of spent
reforming and gauze catalysts are collected for their metal value.
This is based on their much higher platinum metal content (Agoos,
1986).
5. ENVIRONMENTAL LEVELS AND HUMAN EXPOSURE
5.1 Environmental levels
5.1.1 Ambient air
Few measurements of platinum ambient air concentrations have
been reported. Results obtained before the introduction of cars with
catalytic converters can serve as a baseline. Air samples taken near
freeways in California, USA, and analysed using atomic absorption
spectrometry were below the detection limit of 0.05 pg/m3 (Johnson
et al., 1975; 1976).
No platinum could be detected in two air samples collected by
Ito & Kidani (1982) in an industrial area of Nagoya, Japan, in 1981.
Close to city roads in Frankfurt, Langenbrügge, Germany, the
platinum air concentrations (particulate samples) were measured in
1989 to be between < 1 and 13 pg/m3. In rural areas the
concentrations were < 0.6-1.8 pg/m3