Occurrence and Uses
Platinum (Pt) occurs in native form and in a number of mineral forms, including sperrylite (PtAs2), cooperite (Pt,Pd)S and braggite (Pt,Pd,Ni)S. Platinum is sometimes found with palladium as the arsenide and selenide. The concentration of platinum in the Earth’s crust is 0.005 ppm.
Platinum and its alloys are used as catalysts in petroleum reformation, ammonia oxidation, sulphur dioxide oxidation, hydrogenation and dehydrogenation. Platinum is used in the control of automotive emissions, in electrical contacts, electrodes and thermocouples. It is also used in spinnerets for fibrous glass and rayon manufacture, in reflecting or ornamental surfaces and in jewellery. Because of the permanence of platinum, it is utilized for national and international standards for weight, length and temperature measurement. Platinum is manufactured into sheet, wire and foil, and it has wide use in laboratory apparatus.
Nickel, osmium, ruthenium, copper, gold, silver and iridium are alloyed with platinum to increase hardness. Commercially important alloys of platinum are prepared with copper, gold, iridium, rhodium and ruthenium. Alloys with cobalt have become important because of their strong ferromagnetic properties.
Chloroplatinic acid, formed when platinum is dissolved in aqua regia, is useful in the manufacture of catalysts. Potassium hexachloroplatinate is used in the photographic industry, and platinum tetrachloride is used as a catalyst in the chemical industry. Platinum hexafluoride is an extremely powerful oxidizing agent, the first substance to oxidize an inert gas (xenon). Cis-Dichlorodiamineplatinum II, a complex of platinum and related congeners, was found to be active against a broad spectrum of animal tumours. It has been found useful in producing remissions with a number of human cancers.
The toxic and potentially toxic effects of platinum in workers are believed to be related to certain water-soluble platinum salts (e.g., potassium hexachloroplatinate, potassium tetrachloroplatinate, sodium chloroplatinate and ammonium chloroplatinate). Inhalation exposure to these platinum salts is known to give rise to manifestations of respiratory allergy. The first report of such reactions to platinum compounds appeared in 1911 among photographic workers who suffered respiratory and skin disorders. Similar clinical manifestations—rhinitis, conjunctivitis, asthma, urticaria and contact dermatitis—have since been reported mainly in platinum refinery workers and chemists. Allergic respiratory diseases have been reported in a high proportion of refinery workers exposed to soluble hexachloroplatinate salts. Allergic rhinitis and bronchitis in 52 of 91 workers from four platinum refineries in Britain have been described, with most severe symptoms amongst the workers crushing the chloroplatinate salts. The term platinosis has been defined as the effects of soluble platinum salts on people exposed to these occupationally and is characterized by pronounced irritation of the nose and upper respiratory passages, with sneezing, running of the eyes, and coughing. Later asthmatic symptoms of cough, tightness of the chest, wheezing and shortness of breath appear. These symptoms become progressively worse with the length of employment. Some workers may show all three allergic manifestations with involvement of the nasal mucosa, bronchi and skin. Reports of allergy among workers exposed to chloroplatinate salts have appeared from the United States, the United Kingdom, Switzerland, Germany and South Africa.
It is of interest to note that anaphylactic reactions have been noted in some patients who have been treated with platinum anti-tumour agents.
In general, the allergic effects of exposure to platinum have been confined to specific platinum complexes. Sensitized workers when tested by pin prick do not respond to the majority of the platinum compounds used in the refinery. Once sensitized the condition persists, and workers generally have to avoid exposure to platinum. Smoking appears to increase the risk of sensitization by platinum salts.
The emissions from catalytic mufflers containing platinum do not appear to present a health hazard from the point of view of the platinum emission.
Safety and Health Measures
Control of platinum hazards can be achieved only by preventing the release of the soluble complex platinum salts to the atmosphere of the workshop. Since platinum dust is more potentially harmful than is the spray, the soluble complex salts should not be dried unless necessary. Good exhaust ventilation is necessary in platinum refineries. Chemical procedures which may generate these salts should be carried out in ventilated fume hoods. Open centrifuges should not be used. Good personal hygiene, proper protective clothing, and medical surveillance are important preventive measures. Workers with a history of allergic or respiratory disease should be advised not to work with soluble platinum compounds.
Pin prick, nasal and bronchial tests have been devised. Skin prick tests with dilute concentrations of the soluble platinum complexes appear to provide reproducible, reliable and highly sensitive biological monitors of allergic response.