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Ultratrace Elements: Arsenic, Boron, Nickel, Silicon, Vanadium

This chapter provides an introduction to ultratrace elements, their sources, absorption, metabolism, functions, excretion, toxicity, and methods of assessment. Specifically, it discusses the elements Arsenic, Boron, Nickel, Silicon, and Vanadium.

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Ultratrace Elements: Arsenic, Boron, Nickel, Silicon, Vanadium

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  1. Chapter 13 Ultratrace Elements 2009 Cengage-Wadsworth

  2. Introduction • Definition • Estimated, established or suspected requirements of <1 mg/day • Some of these were covered in Chapter 12 because an RDA/AI has been set 2009 Cengage-Wadsworth

  3. Arsenic • Sources • Content depends on soil & pollution • Foods of marine origin • Most toxic: inorganic arsenite, trivalent organoarsenicals • Less toxic: pentavalent, methylated arsenic compounds 2009 Cengage-Wadsworth

  4. Arsenic • Absorption • Simple diffusion • Transport • Metabolism • Organic - little or none in liver • Inorganic - reduced, methylated or both in liver • Concentrates in skin, hair, nails 2009 Cengage-Wadsworth

  5. Arsenic • Functions • Formation & utilization of methyl groups generated in methionine metabolism to S-adenosylmethionine • Deficiency • Impairs methionine metabolism 2009 Cengage-Wadsworth

  6. Arsenic • Excretion • Mostly via kidneys in urine • Recommended intake • Suggested: 12-25 µg • Toxicity • Fatal at intakes of 70-300 mg 2009 Cengage-Wadsworth

  7. Arsenic • Assessment of nutriture • Hair analysis • Atomic absorption spectrometry preferred • Other methods: • Mass spectrometry • Neutron activation analysis • Emission spectroscopy 2009 Cengage-Wadsworth

  8. Boron • Sources • Fruits, vegetables, nuts, legumes • Especially avocado, peanuts, peanut butter, pecans, raisins, grapes • Wine, cider, beer • Absorption • Passive diffusion 2009 Cengage-Wadsworth

  9. Boron • Transport • In blood as boric acid, orthoboric acid, borate monovalent anion B(OH)4- • Boron transporter • Storage • Bones, teeth, nails, hair 2009 Cengage-Wadsworth

  10. Boron • Excretion • Mostly urine, also feces, sweat • Functions • Embryogenesis • Bone development • Cell membrane function & stability • Metabolic regulation • Immune response 2009 Cengage-Wadsworth

  11. Boron • Deficiency • Studied in animals • Symptoms related to suspected functions • Recommended intake • Not established 2009 Cengage-Wadsworth

  12. Boron • Toxicity • UL = 20 mg • Assessment of nutriture • Inductively coupled plasma emission spectrometry 2009 Cengage-Wadsworth

  13. Nickel • Sources • Nuts, legumes, grains, chocolate • Absorption • Carrier & passive diffusion • Transport • In blood: binds mainly to albumin, also amino acids, other proteins 2009 Cengage-Wadsworth

  14. Nickel • Storage • Throughout body in low concentrations • Highest in thyroid, adrenal glands, hair, bone • Functions • Undefined 2009 Cengage-Wadsworth

  15. Nickel • Deficiency • Animals: depressed growth, altered mineral distribution, blood glucose changes, impaired hematopoiesis • Interactions with other nutrients • Competes with other metal ions for ligand sites • Iron, copper, zinc 2009 Cengage-Wadsworth

  16. Nickel • Excretion • Mostly urine, also sweat, bile • Recommended intake • Suggested: <100 µg/day • Toxicity • UL = 1.0 mg soluble Ni salts 2009 Cengage-Wadsworth

  17. Nickel • Assessment of nutriture • Flameless atomic absorption spectrophotometry • No valid method for assessing human status available 2009 Cengage-Wadsworth

  18. Silicon • Sources • Plants contain more than animals • Absorption • Not well understood • Transport • Bound • Free - orthosilicic acid, Si(OH)4 2009 Cengage-Wadsworth

  19. Silicon • Storage • Concentrates in connective tissues • Excretion • Mostly in urine • Functions • Metabolic & structural role • Bone, connective tissue & cartilage formation, growth & development 2009 Cengage-Wadsworth

  20. Silicon • Deficiency • Smaller, less flexible long bones & skull deformation • Recommended intake • Suggestions range from ~5-35 mg/day 2009 Cengage-Wadsworth

  21. Silicon • Toxicity • Suggested maximum: 1,750 mg/day • Kidney stones • Assessment of nutriture • Serum/plasma • Mass spectrometry, emission spectroscopy, atomic absorption spectrophotometry (preferred), etc. 2009 Cengage-Wadsworth

  22. Vanadium • Sources • Black pepper, parsley, dill seed, canned apple juice, fish sticks, mushrooms • Absorption • Varies with oxidation states • Vanadate mimics phosphate & uses its transport system 2009 Cengage-Wadsworth

  23. Vanadium • Transport • Converted to vanadyl in fluids • Vanadyl binds to albumin & iron-containing proteins • Enters cells as vanadate using phosphate transport systems 2009 Cengage-Wadsworth

  24. Vanadium • Storage • Concentrates in bones, teeth, lungs, thyroid gland • Functions • Many pharmacological effects • No specific biochemical function identified 2009 Cengage-Wadsworth

  25. Vanadium • Pharmacological effects: • Inhibits Na+/K+-ATPase • Stimulates adenylate cyclase • These together affect transport of amino acids across the intestinal mucosa • Mimics the action of insulin (as vanadate & vanadyl) • Can substitute for zinc, copper, iron in metalloenzyme activity 2009 Cengage-Wadsworth

  26. Vanadium • Excretion • Mostly urine, also bile • Recommended intake • Suggested: 10 µg/day • Toxicity • UL = 1.8 mg/day elemental vanadium 2009 Cengage-Wadsworth

  27. Vanadium • Assessment of nutriture • Neutron activation analysis • Flameless atomic absorption spectrophotometry (preferred) 2009 Cengage-Wadsworth

  28. Cobalt • Part of vitamin B12 • Can substitute for other metals in metalloenzymes in vitro • In vivo? No evidence of this • Little evidence that ionic cobalt is essential in humans 2009 Cengage-Wadsworth

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