Experimental Studies of Molybdenum Physiology and Toxicity
Accumulation, storage and distribution of molybdenum in animals
In experimental animals given lethal or near lethal doses, however administered, of molybdenum trioxide, calcium molybdate or ammonium heptamolybdate the rate of excretion of molybdenum was less than the rate of absorption [Underwood, 1962; Kolomiitseva et al., 1968; Schroeder et al., 1970]. The amount accumulating in the tissues increased with increasing size and number of doses. After administration of molybdenum had ceased the molybdenum content of the tissues dropped quite rapidly. For example, in guinea pigs exposed to molybdenum trioxide for eight days total molybdenum had dropped to the control value four days after the dose had ceased. [Fairhall et al., 1945] The percentage drop for bone was least so it appears that there is some preferential storage of molybdenum in bone. In general absorption and excretion of molybdenum are rapid and a high proportion (ca 95%) of molybdenum added to the diet is excreted and rather little molybdenum is stored in the tissues. Additional studies involving rats gave the following breakdown of absorbing organs; 3.6% stomach, 9.5% duodenum and 8.2 % in the ileum [van Campen and Mitchell, 1965]. However, as stated, many other groups have found that the process of absorption and retention is dependent on dose, mode of administration and the age of the experimental animal.
Underwood, E. J.,Trace Elements in Human and Animal Nutrition, Academic Press, London, 2nd Ed., 1962, 100.
Kolomiitseva, M. G., Polonskaya, M. N. and Osipov, G. K.,Mikroelem. Sel. Khoz. Med., 1968, 4, 183
Schroeder, H. A., Balassa, J. J.and Tipton,I. H., J. Chronic Diseases, 1970, 23, 481.
Fairhall, L. T., Dunn, R. C., Sharpless, N. E. and Pritchard, E. A., U. S. Public Health Bull., 1945, 293, 1.
Van Campen, D. R., Mitchell, E. A. (1965), J. Nutr., 86, 120-124.
In lactating goats, 99MoO3 , administered orally was found in skeleton, liver, skin, muscles, blood, kidney, ovary and hair 4 days later. Molybdenum was also detected in the milk of goats fed molybdenum trioxide [Anke et al., 1971].
The concentration of molybdenum in cows' milk increased after daily feeding of 500 mg ammonium molybdate [Mills and Davis, 1987].
Fairhall, L. T., Dunn, R. C., Sharpless, N. E. and Pritchard, E. A., U. S. Public Health Bull., 1945, 293, 1.
Venugopal, B. and Luckey, T. D., Metal Toxicity in Mammals, 1978, Vol. 2, Chemical Toxicity of Metals and Metalloids, Plenum Press, New York.
Anke, M., Hennig, A., Dieltrich, M., Hoffmann, G., Wicke, G. and Pflug, D.,Arch. Tierernaehr., 1971, 21, 205.
Mills, C. F. and Davis, G. K., in :Trace elements in Human and Animal Nutritution, Metrz, W., ed., 1987, 429, Academic Press, New York.
Fischer rats given subcutaneous injections of N-methyl-N-benzylnitrosamine and fed dietary sodium molybdate (2 ppm) had increased molybdenum concentrations in the esophagus, forestomach, blood serum, and liver. Xanthine oxidase activities were also increased in the esophagus and forestomach, but not in the liver [Komada et al., 1990]. Radioactivity was detected in the liver, bone, heart, lungs, blood, and kidneys 2.5 hours after rats were fed a single dose (13.34 mg) of 99Mo. The concentrations of radioactivity were higher in the intestine, kidney, and bone than in other tissues 51 hours after dosing. It was estimated that 35% of the administered dose was absorbed [Neilands et al., 1948].
Komada, H., Kise, Y., Nakagawa, M., Yamamura, M., Hioki, K. and Yamamoto, M., Cancer Res., 1990, 50, 2418.
Neilands, J. B., Strong, F. M. and Elvehjem, C. A., J. Biol. Chem., 1948, 172, 431.
In dogs receiving 99Mo by injection, molybdenum was selectively concentrated in the liver, kidneys and endocrine glands (pancreas, pituitary, adrenal and thyroid). The brain, bone marrow and fat contained neglible amounts of the injected molybdenum [Clayton and Clayton, 1981].
Clayton, G. D. and Clayton, F. E., eds, Patty's Industrial Hygiene and Toxicology, 3rd Ed., 1981, 2A, 1493. John Wiley and Sons, New York.
The absorption, tissue distribution and excretion patterns of molybdenum in rabbits are similar to those found for other species as described above. Increased molybdenum intake by experimental animals has been shown to increase tissue levels of xanthine oxidase; liver, intestine and kidney; [Luo et al., 1983].
Luo, X. -M., Wei, H. -J. and Yang, S. P., J. Nat. Cancer Inst.,1983, 71, 75.
Exposure to molybdenum trioxide dust (30 mg/m3 ) for 5.5 months increased serum and urinary ascorbic acid levels in rabbits but no similar effects occurred in rats [Lukashev and Shishkova, 1971].
Lukashev, A. A. and Shishkova, Tr. Nauch.-Issled. Inst. Kraev. Patol. Alma Ata, 1971, 22, 152, 175, 191.
Absorption of molybdenum experimental animals
In animals (guinea pigs, rabbits, rats, sheep) water-soluble molybdenum compounds and also molybdenum trioxide and calcium molybdate, but not molybdenum disulfide, are readily absorbed from the intestinal tract and lungs. Concentrations of molybdenum in the tissues, bones, and blood rise rapidly after administration of molybdenum compounds [Rosoff and Spencer, 1964].
Rosoff, B. and Spencer, H., Nature, 1964, 202, 410.
Molybdenum Retention in Animals
| Animal |
Administration |
Amount given /mg |
Form |
Time /h |
Percent remaining |
| Rat |
Oral |
13.3 |
Mo |
51 |
3 |
| Calf |
Oral |
16.8 |
MoO3 |
288 |
21 |
| Calf |
Intra-venous |
11.0 |
MoO3 |
96 |
52 |
| Goat |
Oral |
- |
Mo |
- |
35 |
Neilands, J. B., Strong, F. M., and Elvehjem, C. A., J . Biol. Chem., 1948, 172, 431.
Comar. C. L., Singer, L., and Davis, G. K., J. Biol. Chem., 1980, 1949, 913.
Excretion of molybdenum in animals
With animals the concentration of molybdenum in the urine and faeces rises rapidly after administration of molybdenum trioxide and molybdates. Molybdenum is excreted mainly in the urine probably as the molybdate anion. With human subjects injected intravenously with a single tracer dose of 99Mo, after five days 16.6-27.2% of the 99Mo had been excreted in the urine and only 1-6.8% in the faeces [Rosoff and Spencer, 1964]. It has been estimated that the average excretion of molybdenum by humans is about 50-70 microg per day [Friberg and Lener, 1986]. The amount of molybdenum excreted and the route are affected by sulfate (added to, or as part of, the diet). For cattle, sheep and rats the total amount of molybdenum excreted and the proportion in the urine increases with increasing sulfate in the diet [Dick, 1969]. A study using radiomolybdenum to trace the excretion process in cattle found that the biological half-life of molybdenum was 19.9 ± 1.4 h [Robinson et al., 1968].