15. Heavy Metals II

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Last updated 3:48 AM on 4/8/26
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How does mercury (Hg) exemplify environmental movement of heavy metals?

1) atmospheric Hg comes from natural degassing of crust, volcanic eruptions, & evaporation from oceans & soils

2) human sources (anthropogenic) → 2/3 total atmospheric Hg → coal combustion, smelting, etc.

3) Hg vapour is monatomic gas, retained 1 yr in atmosphere (time to distribute around the world)

4) oxidizes to Hg2+ → returns to earth dissolved in water as rain

5) either reduce & vaporized or incorporated into organic compounds by microorganisms producing methylmercury (MeHg)

6) MeHg enters trophic levels starting w plankton, herbivorous fish, carnivorous fish, sea mammals

7) bioamplification up higher trophic levels (1800-80000x the concentration in surrounding water

<p>1) atmospheric Hg comes from natural degassing of crust, volcanic eruptions, &amp; evaporation from oceans &amp; soils</p><p>2) human sources (anthropogenic) → 2/3 total atmospheric Hg → coal combustion, smelting, etc.</p><p>3) Hg vapour is monatomic gas, retained 1 yr in atmosphere (time to distribute around the world)</p><p>4) oxidizes to Hg2+ → returns to earth dissolved in water as rain</p><p>5) either reduce &amp; vaporized or incorporated into organic compounds by microorganisms producing methylmercury (MeHg)</p><p>6) MeHg enters trophic levels starting w plankton, herbivorous fish, carnivorous fish, sea mammals</p><p>7) bioamplification up higher trophic levels (1800-80000x the concentration in surrounding water</p>
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Toxicokinetics of Hg Absorption

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Toxicokinetics of Hg Distribution

  • into kidneys as cysteine S-conjugate or from the basolateral membrane through OATs & excreted in urine & feces

  • bind to thiol in cysteines & mimics methionine for transport into the brain & placenta via neutral aa carriers (e.g. LAT1)

  • binds to sulfur-rich keratin-containing proteins & accumulates in hair → indicator of exposure

<ul><li><p>into kidneys as <strong>cysteine S-conjugate</strong> or from the basolateral membrane through <strong>OATs</strong> &amp; excreted in urine &amp; feces</p></li><li><p>bind to <strong>thiol</strong> in cysteines &amp; <strong>mimics methionine</strong> for transport into the brain &amp; placenta via neutral aa carriers (e.g. <strong>LAT1</strong>)</p></li><li><p>binds to <strong>sulfur-rich keratin-containing proteins</strong> &amp; accumulates in hair → indicator of exposure</p></li></ul><p></p>
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Toxicokinetics of Hg Elimination

  • conjugation to glutathione → excretion via MRP2 by kidney & liver

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Dose-Dependent Methylmercury Toxicity