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and the sudden infant death syndrome. Biolnot~an. Chern. 1:289-294. Robertson, D. S. F. 1970. Selenium-a possible teratogen. Lancet 1:518-519. Rosenfeld, I., and 0. A. Beath. 1964. Selenium: Geobotany bio- chemistry, toxicity and nutrition. Academic Press, New York. 411 pp. Schroeder, H. A., and M. Mitchener. 1971a. Selenium and tellurium In rats: Effect on growth, survival and tumors. J. Nutr. 101:1531- 1549. Schroeder, H. A., and M. Mitchener. 197lb. Toxic effects of trace elements on the reproduction of mice and rats. Arch. Environ. Health 23:102-106. Schwarz, K. 1967. Discussion in Symposium: Selenium In biomedi· cine, 0. H. Muth, J. E. Oldfield, and P. H. Weswig (eds). AVI Publishing Co., Westport, Conn. 225 pp. Scott, R. C., and P. T. Voe,eli, Sr. 1961. Radiochemical analysis of ground and surface water In Colorado, 1954-1961. Colo. Water Conserv. Boatd Basic Data Rept. No.7. 27 pp. Slwnbet~er, R. J. 197l.ls selenium a teratogen? Lancet 11:1316. Shambe!Jer, R. J., and D. V. Frost. 1969. Possible protective effect of selenium against human cancer. Can. Med. Assoc. J. 100:682. Selenium 63 Slwnbe~Jer, R. J., and G. Rudolph. 1966. Protection against car- cinogenesis by antioxidants. Experientia 22:116-118. Slwnbe!Jer, R. J., and C. C. Willis. 1971. Selenium distribution and human cancer mortallty./n CRC Critical Reviews In Clinical Laboratory Sciences. CRC Publishing Co., Oeveland, Ohio. pp. 211-221. Sprinker, L. H., J. R. Harr, P.M. Newberne, P. D. Whanger, and P. H. Weswig. 1971. Selenium deficiency lesions in rats fed vitamin E-supplemented rations. Nutr. Rept Int. 4(6):335- 340. Thompson, J. N., and M. L. Scott. 1968. Selenium In practical chicken feeds. In Proceedings of the Cornell Nutrition Confer· ence for Feed Manufacturers, Ithaca, N.Y. pp. 121-125. Thompson, J. N., and M. L. Scott. 1970.1mpaired lipid and vitamin- E absorption related to atrophy of the pancreas In selenium· deficient chicks. J. Nutr. 100:797-809. Tureltian, K. K., and K. H. Wedepohl. 1961. Distn"bution of the elements In some major units of the earth's crust. Geol. Soc. Am. Bull. 72:175-192. Wells, N. 1967. Selenium content of soil-form in& rocks. New Zea· land J. Geo1. Geophys. 10:198-208.
VIII Tellurium JAMES E. OLDFIELD, Chairman William H. Allaway, Herbert A. Laitinen, Hubert W. Lakin, 0. H. Muth CHARACTERISTIC GEOCHEMISTRY AND SOURCES Tellurium was discovered in a complex group of gold tellu- ride minerals in the ores of Transylvania by F. J. Muller von Reichenstein in 1782. It is characteristic of tellurium to form its own minerals in metallic sulfide deposits, although it is very rare-having about the same crustal abundance as gold. Tellurium is a semimetallic element; its atomic number is 52 and its atomic weight, 127.6; it exists in eight stable isotopes. Tellurium metal occurs in either an amorphous or a crystalline form. Brown to black amorphous tellurium is produced by reduction of tellurium solutions; whereas grayish-white, lustrous, brittle, crystalline tellurium has a trigonal structure. The crustal abundance of tellurium is not known pre· cisely. The element is so rare that sufficiently sensitive ana- lytical methods have not been devised to determine tellu- rium in igneous rocks with adequate reliability . Efforts have been made to estimate the abundance of tellurium based on selenium/tellurium ratios in materials containing enough of both elements to be measured; however, this gives rise to a second-generation error because the abun· dance of selenium is arrived at similarly by use of sulfur/ selenium ratios. Recent estimates of the abundance of tellurium are 0.001, 0.002, and O.OOX ppm. The selenium/ 64 tellurium ratio in copper produced from porphyry copper deposits in the United States is 2.5; the same ratio for Sudbury ores of Canada is 15. Using 0.05 ppm as the crustal abundance of selenium, one may calculate 0.02 ppm tellurium for the United States porphyry copper ores, and 0.003 ppm tellurium for the pyrrhotite-chalcopyrite- pentlandite ores of Sudbury. This divergence in the se- lenium/tellurium ratios is indicative of fundamental differ- ences in the geochemistry of these elements. Sulfur, selenium, and tellurium belong to a family of elements whose physical and chemical properties change progressively from sulfur through selenium to tellurium. An example of how these changes can effect dispersion of the elements during volcanism is seen in their respective boiling points. Sulfur, selenium, and tellurium boil at 444, 688, and 1890 C, respectively. Hydrogen sulfide is a stable gas at ambient temperature; hydrogen selenide decomposes in moist air to give metallic selenium and water; hydrogen telluride is even less stable than H2 Se. Where sulfur dioxide is a relatively stable gas at ambient temperatures, both selenium and tellurium dioxides are solids that sublime at 317 and 450 C, respectively. These data suggest that sulfur is very mobile and may be carried great distances in the atmosphere. In contrast, selenium and tellurium will be found close to the volcanic source. Differences in ionic radii materially affect the distribu· tion of the three elements. The ionic radius of S2 - is 1.84 A;
ofSe2 -, 1.98 A; and ofTe2 -, 2.21 A. Selenium can readily substitute for sulfur in sulfide minerals, but the tellurium ion is too large to replace sulfur. Consequently selenium iso- morphously replaces sulfur in sulfide minerals, whereas tel- lurium does not, but occurs instead as independent telluride minerals. The rarity of tellurium makes mineral formation difficult, unless it is enriched in mineralizing solutions or encounters some metal with which it forms exceedingly stable complexes. Such stable complexes are produced with gold, silver, bismuth, and mercury tellurides; in fact, 18 of the 26 known tellurides contain one or more of these ele- ments. In the oxidative zone of weathering at or near the earth's surface, tellurium is readily oxidized to tellurites (Te03 2 -) from tellurides (Te2 -) through the normal pH range of 3-8. At relatively high, but feasible, oxidation potentials, tellu- rites are oxidized to tellurates (Te04 2 -) in alkaline environ- ments (pH 6-8.5). This oxidation is verified by presence of minerals consisting of ferric tellurite, Fe2 (Te03 ) 3 , and lead, bismuth, ferrous, and mercurous tellurates. The ready oxidation of tellurides can give rise to the dispersal of tel- lurium in groundwater. In the acid environments produced by the oxidation of pyrite, tellurium is captured in the iron oxide gossans, pre- sumably as basic ferric tellurites. Gossans have been found that contain as much as I percent tellurium. Tellurium is not recognized as essential for either animal or plant life. It occurs in minute quantities in plants and animals, but the concentrations are so small that they are not easily measured. To illustrate, a limber pine, Pinus flexilus (Hubert, 1971), was found to contain O.OS ppm tellurium in twigs, 0.012 ppm in bark and >O.OOS ppm in the wood. This tree was collected in the Cripple Creek mining district of Colorado, where soils are unusually rich in tellurium; the soil in which it grew contained 0.5 ppm tellurium to a depth of 24 in. and I ppm tellurium in the 24-30-in. layer. The selenium/tellurium ratio in coal used in certain southwestern United States power plants varies from SO to 100. Up to 0.2 ppm tellurium is found in the fly ash of power plants burning this coal. INDUSTRIAL USES About 80 percent of the 221 ,000 lb of tellurium used in the United States in 1968 went into the primary-metal industries. It is used in iron or steel to reduce the absorp- tion of nitrogen, to act as a weak deoxidizer, and to mini· mize pinhole porosity. Low-carbon steels, containing 0.02- 0.2 percent tellurium, have improved machinability. Less than I percent tellurium in copper improves its cutting properties without affecting its electrical conductivity or hot-working properties. Lead containing O.OS percent of tellurium has increased resistance to corrosion. Tellurium 65 The rubber industry accounted for about I 0 percent of the tellurium used in the United States in 1968. Tellurium is used both in its elemental form and as tellurium diethyl- dithiocarbamate in synthetic and natural rubbers to in- crease their resistance to heat and abrasion, to increase the rate of vulcanization, and to improve the aging prop- erties of the elastomer. The remaining I 0 percent of the tellurium consumed in 1968 was for many diverse but important uses. Tellurium is used as a catalyst in oxidation, hydrogenation, dehydroge- nation, chlorination, dechlorination, hydroxylation, and phenol condensation. Selectivity, good yield, and resistance to poisoning are noteworthy properties of tellurium cata- lysts. Tellurium has been used as a colorant in ultramarine, black, blue, red, and brown glasses and ceramics. Organic tellurides have been used as antioxidants for lubricants, greases, hydraulic fluids, and hydrocarbon fuels. Tellurium is also used in blasting caps, batteries, thermoelectric de- vices, solar cells, infrared windows, and semiconductor devices. Tellurium compounds are used as antimicrobial and therapeutic agents. Cyclotelluropentane-3,5-diones and various derivatives are very powerful germicides. Tellurium has been used in the treatment of leprosy with good results, and tellurium dioxide suspensions are effective in the treat· ment of seborrheic dermatitis of the scalp. Selenium may be used as a substitute for tellurium in metallurgy, ceramics, rubber, and thermoelectric devices. Lead may be used to replace tellurium to achieve machin· ability in steel. In 1968, the United States provided about 121 ,000 lb, or about 4S percent, of the free-world total production of tellurium and about 30 percent of the world total produc- tion. About 71,000 lb of tellurium were imported from Canada and Peru in 1968, and the remaining 29,000 lb of the 221,000 lb consumed in the United States in that year came from industrial stocks already available. Tellurium is recovered as a by-product in electrolytic refining of copper and lead. Over 80 percent of the tel- lurium produced in commerce is a by-product of the cop- per industry. A ton of copper contains about 0.4 lb of tellurium, but only 0.17 lb is produced per ton of copper in the United States under methods practiced by the industry in 1968. EFFECTS OF TELLURIUM ON HEALTH Mead and Gies ( 190 I) observed that oral doses of O.S-1 g of tellurium oxide or sodium tellurate administered to dogs retarded gastric digestion and induced violent vomiting, anorexia, and somnolence. If tellurium tartrate was injected in large doses ( 1.45 g subcutaneously), it caused restlessness, tremor, somnolence, diarrhea, and paralysis in the animals. Muehlberger and Schrenk ( 1928) found that sodium tel-
66 THE RELATION OF SELECTED TRACE ELEMENTS TO HEALTH AND DISEASE lurite was more toxic than sodium tellurate to rats. They reported that the minimum lethal dose ( M L D) in milligrams per kilogram of body weight was 1.4 for sodium tellurite and 30.5 for the corresponding tellurate given intravenously to the rat. Franke and Moxon ( 1936) reported the range of dosage lethal to 75 percent of the experimental rats within 48 h after intraperitoneal injection was 2.25-2.50 mg/kg of body weight for sodium tellurite, and 20.0-30.0 mg/kg for sodium tellurate. The M L o 's for oral administration to the rabbit were 31 mg for sodium tellurite and 56 mg for so- dium tellurate. Dietary tellurium, as sodium tellurite and sodium tel- lurate, is toxic to animals at levels of 25 and 50 ppm (Franke and Moxon, 1937); growth was reduced, but the element had no adverse effect on hematopoiesis. Elemental tellurium is much less toxic than its compounds; a level of 1,500 ppm tellurium in the diet had only a slight effect on growth in rats in studies by DeMeio (1946). DeMeio and Jetter ( 1948) studied the symptoms of tellurium dioxide toxicity for rats and reported that they included failure to grow, loss of hair, redness and edema of digits, and temporary paralysis of the hind legs. Internal lesions ob- served in poisoned animals included necrosis ofhepato· cytes and of the epithelial cells of the renal tubules. Limited studies suggest that tellurium is not apparently carcinogenic to rats (Schroeder and Mitchener, 1971 ), but metallic tellurium fed to pregnant rats in doses having no obvious toxic effects in the dams throughout gestation was associated with development of communicating hydro- cephalus in the offspring (Garro and Pentschew, 1964; Agnew et al., 1968). Tellurium also causes hydrocephaly when fed to weanling mice at modest dose levels for short periods of time. Carlton and Kelly ( 196 7) have reported myocardial hemorrhage and necrosis and central-nervous- system damage in ducklings poisoned with tellurium. Widespread discrepancies exist in published reports on concentrations of the element in human tissues, but it is known that excess exposure causes nausea, vomiting, and depression of the central nervous system in man. POLLUTION Pollution from tellurium is not defmitely established as a problem, but industrial use of the element presents a po- tential problem. Exposure of workers to the fumes of tel- lurium oxide has been discussed by Steinberg et al (1942), who recognized five symptoms of tellurium absorption: garlic odor of the breath, dryness of the mouth, metallic taste, somnolence, and garlic odor of sweat. These com- plaints, associated with exposure to tellurium oxide fumes, have been confirmed by Amdur ( 194 7) and have been suc- cessfully reduced in intensity with British anti-lewisite (BAL). Amdur (1958), however, reported that 75 mg of tellurium oxide in peanut oil, injected intramuscularly, did not have a particularly high degree of toxicity for guinea pigs, and that BAL enhanced the toxicity of intramuscularly administered oxide of tellurium for this species. The toxi- cology of tellurium compounds has been reviewed by Cerwenka and Cooper ( 1961 ). RECOMMENDATIONS FOR RESEARCH 1. Analytical methods should be further refmed, and information on concentrations in plants and forages should be extended. 2. Studies on tissue concentrations of tellurium in ani· mats and in man should be greatly expanded under a variety of environmental conditions. 3. Research should be initiated to determine whether tellurium in environmentally available concentrations af. fects health in animals or man. 4. Interactions among tellurium and other trace metals and availability of tellurium under differing environmental conditions should be investigated. 5. The metabolic role of tellurium in biological systems should be elucidated. 6. Industrial emanations should be examined for the presence of tellurium to determine whether contamination is a problem. REFERENCES Agnew, W. F., F. M. Fauvre, and R. H. Pudenz. 1968. Tellurium hydrocephalus: Distribution of tellurium between maternal, fetal, and neonatal tissues of the rat. Exp. Neurol. 21: 120... 132. Amdur, M. L. 194 7. Tellurium, accidental exposure and treatment with BALin oil. Occup. Med. 30:386-391. Amdur, M. L. 1958. Tellurium oxide, an animal study in acute toxicity. Arch. Ind. Health 17:665-667. Carlton, W. W., and W. A. Kelly. 1967. Tellurium toxicosis in Peldn ducks. Toxicol. Appl. Pbarm. 11:203-214. Cerwenka, E. A., Jr., and W. C. Cooper. 1961. Toxicology of sele- nium and tellurium and their compounds. Arch. Environ. Health 3:189-200. DeMeio, R. H. 1946. Tellurium: I. The toxicity of ingested ele- mentary tellurium for rats and rat tissues. J. Ind. Hyg. Toxicol. 28:229-232. DeMeio, R. H., and W. W. Jetter. 1948. Tellurium: Ill. The toxicity of ingested tellurium dioxide for rats. J. Ind. Hyg. Toxicol. 30: 53-58. Franke, K. W., and A. L. Moxon. 1936. A comparison of the mini- mum fatal doses of selenium, tellurium, arsenic, and vanadium. J. Pbarm. Exp. Ther. 58:454-459. Franke, K. W., and A. L. Moxon. 1937. The toxicity of orally in- gested arsenic, selenium, tellurium, vanadium, and molybdenum. J. Pbarm. Exp. Ther. 61:89-102.
