Agent Name
RARE EARTH METALS
Synonyms
CLASSES; Scandium (Sc), Yttrium (Y), Lanthanum (La), Cerium (Ce), Praseodymium (Pr), Neodymium (Nd), Promethium (Pm), Samarium, (Sm), Europium (Eu), Gadolinium (Gd), Terbium (Tb), Dysprosium (Dy), Holmium (Ho), Erbium (Er), Thulium ™, Ytterbium (Yb), Lutetium (Lu); [Ullmann] Rare earth compounds;
Category
Rare Earth Metals
Description
17 metals with atomic number ranging from 21-71; [Ullmann]
Sources/Uses
Rare earth minerals are the source of these metals and include: bastnaesite, monazite, xenotime, and gadolinite. Since the rare earth metals occur together in the same minerals and their chemical and physical properties are similar, isolation of the individual elements is technically difficult and costly. [Ullmann] Used in alloys for control rods in nuclear reactors, permanent magnets, and cigarette lighter flints; Also used in laser crystals, glass coatings, superconducting ceramics and metals, and magnetic memory for computers; Cerium oxide is used as a polish for glass lenses. [Hendrick, p. 179] Used in metallurgy, catalysts, colorants of glass and ceramics, magnets, and phosphors; Used in zeolite cracker catalysts to improve gasoline yield; in the paint industry as dryers; and in the textile industry; [Ullmann]
Comments
The characteristic oxidation state of rare earth elements is 3+. Europium oxidizes readily, but the other rare earth elements react with oxygen in air at room temperature slowly. All of the rare earth metals ignite in air at elevated temperatures. [Ullmann] Since the rare earth metals have high radiodensity, some of pneumoconioses reported are thought to be benign pneumoconioses. Cases were reported among workers exposed to cerium oxide and other lanthanoid metals in the glass manufacturing, lens polishing, and photoengraving industries. Findings have included small nodular lung opacities by chest x-ray, restrictive and obstructive defects by spirometry, and respiratory tract symptoms. Unfortunately, there is very little histopathology data on these cases. [Harber, p. 501-2] The 14 lanthanide elements are associated with "rare earth pneumoconiosis," a condition most commonly reported among workers who were exposed to the fume from carbon arc lamps, and also reported in lens polishers and workers manufacturing cerium oxide polishing powder. The carbon arc lamp uses blends of lanthanide minerals as a metal core to stabilize the arc. With use of the carbon arc lamp, the carbon rod and metal core are eventually vaporized to form respirable fume and dust. Carbon arc lamps are used in movie projection, lithography, photoengraving, and floodlights. Respiratory symptoms in exposed workers were first reported in the 1930s. It is debated whether or not the stable lanthanides can cause pneumoconiosis. Some scientists believe that the lung disease is caused by radioactive contaminants such as thorium-238 and cerium-44. Recent animal studies support the view that the stable lanthanide elements can cause granulomatous and fibrotic lesions in the lungs. [Hendrick, p. 178-9] Promethium is classified as a rare earth metal, but "promethium probably does not occur in nature or in a stable form. . . . However, no toxicity data specific to promethium were identified." [Reference # 1] Therefore, promethium is not linked to pneumoconioses.
Diseases
Occupational diseases associated with exposure to this agent:
Processes
Industrial Processes with risk of exposure:
Activities
Activities with risk of exposure: