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Chapter 13 Ultratrace Elements 2009 Cengage-Wadsworth 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 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 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 Arsenic • Functions – Formation & utilization of methyl groups generated in methionine metabolism to S-adenosylmethionine • Deficiency – Impairs methionine metabolism 2009 Cengage-Wadsworth Arsenic • Excretion – Mostly via kidneys in urine • Recommended intake – Suggested: 12-25 µg • Toxicity – Fatal at intakes of 70-300 mg 2009 Cengage-Wadsworth Arsenic • Assessment of nutriture – Hair analysis – Atomic absorption spectrometry preferred – Other methods: • Mass spectrometry • Neutron activation analysis • Emission spectroscopy 2009 Cengage-Wadsworth Boron • Sources – Fruits, vegetables, nuts, legumes • Especially avocado, peanuts, peanut butter, pecans, raisins, grapes – Wine, cider, beer • Absorption – Passive diffusion 2009 Cengage-Wadsworth 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 Boron • Excretion – Mostly urine, also feces, sweat • Functions – Embryogenesis – Bone development – Cell membrane function & stability – Metabolic regulation – Immune response 2009 Cengage-Wadsworth Boron • Deficiency – Studied in animals – Symptoms related to suspected functions • Recommended intake – Not established 2009 Cengage-Wadsworth Boron • Toxicity – UL = 20 mg • Assessment of nutriture – Inductively coupled plasma emission spectrometry 2009 Cengage-Wadsworth 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 Nickel • Storage – Throughout body in low concentrations – Highest in thyroid, adrenal glands, hair, bone • Functions – Undefined 2009 Cengage-Wadsworth 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 Nickel • Excretion – Mostly urine, also sweat, bile • Recommended intake – Suggested: <100 µg/day • Toxicity – UL = 1.0 mg soluble Ni salts 2009 Cengage-Wadsworth Nickel • Assessment of nutriture – Flameless atomic absorption spectrophotometry – No valid method for assessing human status available 2009 Cengage-Wadsworth Silicon • Sources – Plants contain more than animals • Absorption – Not well understood • Transport – Bound – Free - orthosilicic acid, Si(OH)4 2009 Cengage-Wadsworth Silicon • Storage – Concentrates in connective tissues • Excretion – Mostly in urine • Functions – Metabolic & structural role – Bone, connective tissue & cartilage formation, growth & development 2009 Cengage-Wadsworth Silicon • Deficiency – Smaller, less flexible long bones & skull deformation • Recommended intake – Suggestions range from ~5-35 mg/day 2009 Cengage-Wadsworth 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 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 Vanadium • Transport – Converted to vanadyl in fluids – Vanadyl binds to albumin & ironcontaining proteins – Enters cells as vanadate using phosphate transport systems 2009 Cengage-Wadsworth Vanadium • Storage – Concentrates in bones, teeth, lungs, thyroid gland • Functions – Many pharmacological effects – No specific biochemical function identified 2009 Cengage-Wadsworth 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 Vanadium • Excretion – Mostly urine, also bile • Recommended intake – Suggested: 10 µg/day • Toxicity – UL = 1.8 mg/day elemental vanadium 2009 Cengage-Wadsworth Vanadium • Assessment of nutriture – Neutron activation analysis – Flameless atomic absorption spectrophotometry (preferred) 2009 Cengage-Wadsworth 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