Molybdenum

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Molybdenum is a silvery white metal present in the earth's crust and in oceans. Its Periodic Table symbol is Mo and atomic number 42. Its extremely high melting point makes it desirable for industrial uses involving high temperatures. Most (but not all) molybdenum compounds have low solubility in water. The human body contains a low concentration of molybdenum, and molybdenum is present in low concentrations foods such as pork, lamb and beef liver, green beans, eggs, sunflower seeds, wheat flour, lentils, cucumbers and cereal grain. It is an essential dietary nutrient.[1] However, at high concentrations, molybdenum is toxic. Molybdenum is also found in sewage sludge and coal waste.

Uses

Molybdenum is mostly used as an alloying agent in steel, cast iron, and superalloys to "enhance hardenability, strength, toughness, and wear and corrosion resistance."[2] Often molybdenum is used in the form of molybdic oxide or ferromolybdenum, either combined with or in addition to chromium, columbium (niobium), manganese, nickel, tungsten, or other alloy metals.[3] According to the World Health Organization (WHO):[4] "Molybdenum is used in the manufacture of special steels, in electrical contacts, spark plugs, X-ray tubes, filaments, screens, and grids for radio valves, and in the production of tungsten, glass-to-metal seals, nonferrous alloys, and pigments. Molybdenum disulfide has unique properties as a lubricant additive. Molybdenum compounds are used in agriculture either for the direct treatment of seeds or in the formulation of fertilizers to prevent molybdenum deficiency."

Molybdenum and Health

As noted above, the human body contains a low concentration of molybdenum and it is an essential nutrient. In 2001, U.S. Food and Nutrition Board established a Recommended Daily Allowance of 45 micrograms for most adults and 50 micrograms for women who are pregnant or breast-feeding.[5] Most people get the molybdenum they require through their diets, from foods like legumes, grains, leafy vegetables, liver, and nuts.[6] Additionally, some Americans have detectable levels of molybdenum in their tapwater.[7] The exact role of molybdenum in human health is not precisely understood, but it may be important in the development of the nervous system, waste processing in the kidneys, and energy production in cells.[8] Molybdenum deficiencies in humans are not common.

According to the WHO:[9] "In humans, 30–70% of dietary molybdenum is absorbed from the gastrointestinal tract. Following gastrointestinal absorption, molybdenum rapidly appears in the blood and most organs. Highest concentrations are found in the liver, kidneys, and bones. Molybdenum crosses the placental barrier. There is no apparent bioaccumulation of molybdenum in human tissues."

Too much molybdenum can be toxic. Symptoms of molybdenum overdose include tiredness, dizziness, rashes, low white blood cell counts, anemia, and possibly gout.[10][11] In animal studies, molybdenum interacts with sulfate and copper, and the presence or deficiencies of these chemicals can decrease or intensify symptoms of molybdenum poisoning.[12] According to the WHO:[13] "An epidemiological study involving 557 subjects in India indicated that a form of lower-limb osteoporosis may be associated with the high molybdenum content of the cereals consumed by the population."

Presence in Sewage Sludge

Molybdenum is frequently found in sewage sludge. In the Targeted National Sewage Sludge Survey, a 2009 test of 84 samples, the U.S. EPA found molybdenum in all 84 samples, ranging from concentrations of 2.51 to 132 parts per million. In sewage sludge applied to land, the U.S. EPA limits molybdenum to a concentration of 75 parts per million.[14]

Molybdenum in Sludge Poisons Georgia Cows

Georgia dairy farmer Andy McElmurray lost his dairy business due to molybdenum poisoning and the subsequent deaths of many cows after receiving with sewage sludge tainted with molybdenum to spread on his fields from a nearby wastewater treatment plant.[15] Although molybdenum is regulated in sewage sludge applied to land, the wastewater treatment plant providing the sludge did not abide by federal regulations. McElmurray applied the sludge to land where he grew forage for his cattle. McElmurray's cows began falling ill and dying. One symptom of their illness was "an odd reddish tinge to their fading coats, a symptom of molybdenum poisoning." The molybdenum attacked the cows kidneys and livers. Although the particular wastewater treatment plant providing the sludge broke the law by exceeding federal standards for contaminants such as molybdenum, scientists found that had the wastewater treatment plant followed the law, legal levels of molybdenum still would have poisoned the cattle.

Presence in coal waste

Molybdenum is also one of the many heavy metals found in coal and coal waste.[16]

Articles and resources

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References

  1. U.S. EPA, Integrated Risk Information System: Molybdenum, Accessed August 3, 2010
  2. USGS Minerals Information: Molybdenum, U.S. Geological Survey, Accessed August 19, 2010.
  3. USGS Minerals Information: Molybdenum, U.S. Geological Survey, Accessed August 19, 2010.
  4. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  5. Molybdenum, American Cancer Society, Accessed August 19, 2010.
  6. Molybdenum, American Cancer Society, Accessed August 19, 2010.
  7. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  8. Molybdenum, American Cancer Society, Accessed August 19, 2010.
  9. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  10. Molybdenum, American Cancer Society, Accessed August 19, 2010.
  11. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  12. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  13. "Molybdenum in Drinking-water: Background document for development of WHO Guidelines for Drinking-water Quality", World Health Organization, 1996.
  14. Code of Federal Regulations, Title 40, Chapter 1, Subchapter O, PART 503—Standards for the Use or Disposal of Sewage Sludge, Subpart B—Land Application, Pollutant Limits
  15. Andy McElmurray, Testimony Before U.S. Congress, Accessed August 3, 2010
  16. "Heavy Metals Naturally Present in Coal & Coal Sludge" Sludge Safety Project, accessed November 2009

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