Lead Pb

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Lead (Pb)

• (Pb) - Latin for Plumbum.
• Origin for plumbing.
• All known biological effects are bad!
• Pb nonessential, highly toxic heavy metal.
• Both chemical and physical properties are causes
  of distribution in the environment and adsorption
  in living organisms.

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Historical Lead Poisoning

• Egyptians 7000 years ago.
• Evidence for the fall of the Roman empire.
• Franklin Expedition of 1845

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Sources of Lead in the Environment

• Found in nature mostly as Pb(II) sulfides like
  Galena (PbS) and other salts.
• Less frequently as Pb(IV) organic forms.
• Natural weathering and dissolution.
• Anthropogenic emissions.
• Emitted/deposited into air, soil, and water.
• Continuous intercompartmental exchange.

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Refining Lead Ore

• 2 PbS(s) 3O2 (g) ? PbO(s) 2SO2(g)
• 2PbO(s) C(s) ? 2Pb(s) CO2(g)

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Anthropogenic Emissions

• Mining ore.
• Smelting/refining lead.
• Battery production/recyling/disposal.
• Gas additive, TEL.
• Industrial emissions using lead, such as
  plastics.
• Sewage effluent.
• Lead ammo.

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Airborne Distribution

• Dependant on particle size.
• Dry gravitational, gt10 µm, close to source.
• Wet precipitation.
• Global distribution for small particles.

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Lead in Soils

• Highest concentration close to point source.
• Application of sewage sludge, mine waste runoff,
  fly ash, or deposition of atmospheric Pb.
• Depend on particle size, weather, wind, and soil
  surface, and plant surfaces.
• Deposition lowest on smooth leaf surfaces.
• May reach soil when plant dies, or could be
  grazed or cropped.
• Water plays a big role in transport.

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Uptake into Aquatic Plants

• Depends on
• Chemical form, inorganic Pb
• pH
• Hard or soft water

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Uptake by Aquatic Animals

• Uptake via absorption through skin, gills,
  intestine.
• pH dependant
• Hard vs soft water
• Uptake by organic Pb, lipid soluble.

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Uptake by Terrestrial Animals

• Inhalation mainly inorganic Pb salts.
• Max lung retention with Pb species of
• 1.5 2.5 µm diameter.
• 50 Pb inhaled is deposited in lungs
• Almost all is absorbed in the bloodstream

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Ingested Lead by Terrestrial Animals.

• Usually ingested with food or water.
• Higher excretion ratio than inhalation.
• Only 10 absorbed by ingested lead.
• Absorption lower on a full stomach.
• - Inhibits absorption thru intestinal wall.
• - Stimulates excretion.

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Factors of Absorption into Intestine

• Chemical form.
• Physical properties.
• Size matters, lt 180 µm more rapidly absorbed.
• Age
• Calcium levels
• Protein deficiency
• Seasonal

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Physiological Distribution

• -If absorbed, enters bloodstream/circulatory
  system.
• -Deposited within minutes in soft tissue (liver,
  kidney, brain).
• -Acute poisoning more in soft tissue.
• -Chronic is in bone.
• -High liposolubility of organo Pb results in
  accumulation in nonbony tissue.
• -But most Pb toxicity comes from inorganic lead.

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Biomagnification

• Increase in concentration up trophic levels is
  not seen. Just the opposite occurs.

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Effects on mammals

• Inhibits activities of many enzymes.
• Effecting hematology, brain, nervous system
  (central and peripheral), learning, behavior,
  reproduction, and survival.
• Numerous factors influence adsorption
• Age, sex, physiology, environment.
• Other factors can have antagonistic or
  synergistic effects.

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Bloodstream

• Inhibits heme-biosynthetic enzymes such as ALAD
  and heme synthetase.
• Inhibition of ALAD results in accumulation of ALA
  excreted in urine.
• Result is reduced heme production.
• Inhibition of heme synthetase reduces the
  incorporation of Fe2.
• Anemia and reduction of hemoglobin levels.

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• gt400 ppm Pb in soil is considered hazardous.
• 2600 homes near smelter has gt800 ppm Pb in
  soil.
• 14 of children 7 years old and under have PbB
  levels gt 100 µg L-1 (ppb).
• 1 µg L-1 considered Pb poisoning.
• Soil Pb levels directly related to PbB levels in
  children..

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References

• Contaminant Sources and Effects. Chapter 16,
  Lead in the Environment. Pain, Deborah J. CRC
  Press. 1995.
• Environmental Chemistry, 2nd Ed. Bunce, Nigel.
  Wuerz Publishing. Winnepeg. 1994.

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Questions

• What physical characteristic of Pb allows
  competition with Ca.
• Why are children more vulnerable and what are
  some effects of lead poisoning.