Toxicity of molybdenum

McConnell, R.P. 1977. Toxicity of molybdenum to rainbow trout under laboratory conditions. Pages 725-730 in W.R. Chappell and K.K. Peterson (eds.). Molybdenum in the Environment. Vol. 2. The Geochemistry, Cycling, and Industrial Uses of Molybdenum. Marcel Dekker, New York. 

To summarize, molybdenum toxicity in animals includes anemia, anorexia, profound diarrhea, joint abnormalities, osteoporosis, hair discoloration, reduced sexual activity, and death (Table 18.10). Diets which are low in sulfate and copper enhance the toxicity of molybdenum. A high molybdenum intake also decreased feed intake by cattle and pigs, while molybdenum levels in the serum, hair, ribs, kidneys, and cerebrum reflect significant intake of the... 

Molybdenum occurs naturally in various ores the principal source being molybdenite (MoS ). Molybdenum compounds are used primarily in the production of metal allo). Molybdenum is also considered an essential trace element with the provisional recommended dietary intake of 75-250 pg/day for adults and older children. There is no information available on the acute or subchronic oral toxicity of molybdenum in humans. Subchronic and chronic Reference Concentrations (RfC) for Mo are not available. Information on the inhalation toxicity of Mo in humans following acute and subchronic exposures is also not available. The chronic oral Reference Dose (RfD) for Mo and Mo compounds is 0.005 mg/kg/day, based on biochemical indices in humans. The subchronic RfD is also 0.005 mg/kg/day. Mo is placed in EPA Group D, not classifiable as to carcinogenicity in humans. ... 

Under unusual circumstances, toxicity may arise from ingestion of excess amounts of minerals. This is uncommon except in the cases of fluorine, molybdenum, selenium, copper, iron, vanadium, and arsenic. Toxicosis may also result from exposure to industrial compounds containing various chemical forms of some of the minerals. Aspects of toxicity of essential elements have been pubhshed (161). 

Information on the toxic effects of molybdenum in humans is scarce. A high incidence of gout was reported in a locale in Armenia where the soil contained exceptionally high levels of both molybdenum and copper (15). However, the significance of the suggested correlation is questionable because of the lack of information on the study population and the absence of a control group. 

Although molybdenum is an essential element, excess levels can have deleterious effects. The LD q and TLV values of the most common Mo compounds are Hsted in Table 3 (63,64). In general the toxicity of Mo compounds is considered to be low. For example, M0S2 has been found to be virtually nontoxic even at high levels. Certain Mo compounds such as MoCl and Mo(CO), have higher toxicity because of the chemical nature and reactivity of these compounds rather than the Mo content. Supplementary dietary Cu ", thiosulfate, methionine, and cysteine have been shown to be effective in alleviating Mo toxicity in animals. 

Coatings, Paints, and Pigments. Various slightly soluble molybdates, such as those of zinc, calcium, and strontium, provide long-term corrosion control as undercoatings on ferrous metals (90—92). The mechanism of action presumably involves the slow release of molybdate ion, which forms an insoluble ferric molybdate protective layer. This layer is insoluble in neutral or basic solution. A primary impetus for the use of molybdenum, generally in place of chromium, is the lower toxicity of the molybdenum compound. 

Biomedical Uses. The molybdate ion is added to total parenteral nutrition protocols and appears to alleviate toxicity of some of the amino acid components in these preparations (see Mineral NUTRIENTS) (97). Molybdenum supplements have been shown to reduce iiitrosarnine-induced mammary carcinomas in rats (50). A number of studies have shown that certain heteropolymolybdates (98) and organometaUic molybdenum compounds (99) have antiviral, including anti-AIDS, and antitumor activity (see Antiviral agents Chemotherapeutics, anticancer). 

When heated to about 60°C, nickel carbonyl explodes. Eor both iron and nickel carbonyl, suitable fire extinguishers are water, foam, carbon dioxide, or dry chemical. Large amounts of iron pentacarbonyl also have been reported to ignite spontaneously (189). Solutions of molybdenum carbonyl have been reported to be capable of spontaneous detonation (190). The toxicity of industrial chemicals including metal carbonyls may be found in references 191-194. 

Reclamation, Disposal, and Toxicity. Removal of poisons and inorganic deposits from used catalysts is typically difficult and usually uneconomical. Thus some catalysts are used without regeneration, although they may be processed to reclaim expensive metal components. Used precious metal catalysts, including automobile exhaust conversion catalysts, are treated (often by the suppHers) to extract the metals, and recovery efficiencies are high. Some spent hydroprocessing catalysts may be used as sources of molybdenum and other valuable metals. 

Ahsanullah, M. 1982. Acute toxicity of chromium, mercury, molybdenum and nickel to the amphipod Allorchestes compressa. Austral. Jour. Mar. Freshwater Res. 33 465-474. 

Buck, W.B. 1978. Copper/molybdenum toxicity in animals. Pages 491-515 in F.W. Oehme (ed.). Toxicity of Heavy Metals in the Environment. Part I. Marcel Dekker, New York. 

Hamilton, S.J. and K.J. Buhl. 1990. Acute toxicity of boron, molybdenum, and selenium to fry of chinook salmon and coho salmon. Arch. Environ. Contam. Toxicol. 19 366-373. 

Koizumi, T. and Y. Yamane. 1984. Protective effect of molybdenum on the acute toxicity of mercuric chloride. III. Chem. Pharm. Bull. 32 2316-2324. 

Kubota, J. 1975. Areas of molybdenum toxicity to grazing animals in the western United States. Jour. Range Manage. 28 252-256. 

Morgan, J.D., D.G. Mitchell, and P.M. Chapman. 1986. Individual and combined toxicity of manganese and molybdenum to mussel, Mytilus edulis, larvae. Bull. Environ. Contam. Toxicol. 37 303-307. 

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