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					     Pb


Nicole Beckman
    Biol 464
    Physical and Chemical Properties
• Atomic number: 82
• Metallic lead, Lead acetate, Lead chloride,
    Lead chromate, Tetraethyl lead,
    Tetramethyl lead
•   Atomic weight: 207.2
•   Metal, blue grey in color, malleable
•   Resistant to corrosion
•   Oxidation state: +2, sometimes +4
•   Insoluble in water (some form slightly
    soluble or soluble in water)
•   Boiling Point: 2013 K, 1740°C
•   Melting Point: 600.75 K, 327.6°C
•   Physical State (at 20°C and 1atm): solid   http://library.thinkquest.org/10676/Period/b0082.gif
                          Uses
•   storage batteries
•   construction material
•   shot and ammunition
•   for X-ray and atomic radiation protection
•   pigments for paints and other organic and inorganic lead
    compounds
•   gasoline additives
•   bearing metal and alloys
•   in ceramics, plastics and other lead alloys
•   in the metallurgy of steel and other metals
•   fishing weights
                Production History
• Usually found in the form of galena ores (PbS)
• Global production began with the discovery of cupellation
    (separating silver from lead ores) around 3000 BC
•   Industrial Revolution increased production significantly
•   Beginning of 20th century, annual lead mine production ~1 million
    metric tons
•   Early 1990s 5.5 million metric tons produced
•   Secondary smelting (recycling) of lead accounts for almost half of
    world refined lead production
•   About 50 nations mine lead in quantities ranging from a few
    hundred metric tons to more than half a million metric tons
•   2002: Australia leading producer of lead, followed by China, US,
    Peru and Mexico
         Mode of Entry into Aquatic
               Environment
• Abundance in sw: 0.003 ppm
• Lead enters the aquatic environment through surface
    runoff and deposition of airborne lead
•   Lead mining and the refining and smelting of lead and
    other metals
•   Lead concentrations are highest in soils and organisms
    close to roads where traffic density is high
•   The availability of lead to organisms in the environment
    is limited by its strong adsorption to environmental
    components, such as soil sediment, organic matter, and
    biota
•   Lead weights from fishing
               Isotopes, half-life

• Four naturally occurring isotopes:
  204Pb(1.4%), 206Pb(25.2%), 207Pb(21.7%),
  208Pb(51.7%)

• Half life:
  – 27 min to 15,000,000 years
  – in bone: more than 20 years
  – in soft tissue: 19-21 days
           Toxicity to Aquatic Life

• The toxicity of inorganic lead salts is strongly dependent on
    environmental conditions such as water hardness, pH, and salinity
•   the 96-h LC50s for fish vary between 1 and 27 mg/L in soft water,
    and between 440 and 540 mg/L in hard water
•   Invert LC50s vary by species and form of lead: Mussel (Mytilus
    edulis) 96 hour 0.27 mg/L (tetramethyl lead); Crab (Scylla serrata)
    96 hour >370 mg/L (lead nitrate)
•   Fish LC50s vary by species, pH, and form: Bluegill sunfish (Lepomis
    macrochirus) 48 hour 24.5 mg/L (lead chloride), 6.3 mg/L (lead
    nitrate), 1.4 mg/L (tetraethyl lead); Rainbow trout (Oncorhynchus
    mykiss) 96 hour 1.0 mg/L
•   Lead salts: acutely toxic to aquatic invertebrates between 0.1 and
    >40 mg/L (fw) and between 2.5 and >500 mg/L (marine)
                       Toxic Effects
• Typical symptoms of lead toxicity include spinal deformity and
    blackening of the caudal region (rainbow trout)
•   Muscular atrophy, paralysis, deformation of caudal fin, hyperactivity,
    loss of equilibrium, erratic behavior, decreased growth, and death
•   Selenastrum and Chlorella: lead increased the average cell volume
    significantly and reduced the growth rate (Selenastrum was exposed
    to lead concentrations varying between 0.09 and 1.44 mg/L)
•   Most studies show no effect on eggs (lead is adsorbed onto the
    surface of the egg and excluded from the developing embryo)
•   The earlier life stages are more vulnerable
•   Fathead minnow: no Pb-induced mortality observed
               Toxic Effects cont…
• Frog and toad eggs: <1 mg/L in standing water and 0.04 mg/L in
    flow-through systems may cause arrested development and delayed
    hatching
•   No significant effects in adult frogs at levels <5 mg/L in aqueous
    solutions, but lead in the diet at a concentration of 10 mg/kg may
    cause some biochemical abnormalities
•   Larvae of the oyster Crassostrea gigas had inhibited growth when
    incubated in water with a lead nitrate concentration of 0.01 or 0.02
    mg/L
•   Long-term exposure of adult fish to inorganic lead induces sub-
    lethal effects on morphology as well as enzyme activities and
    avoidance behavior at lead concentrations of 10-100 mg/L
•   Generally lead does not appear to bioconcentrate significantly in fish
•   However, accumulation over time in kidney of rainbow trout occurs
    Mode of Entry into Organisms
• The gill is the primary site for Pb uptake; the intestine
    may also be a site of uptake
•   Through milk into infants
•   Lead shot
•   Lead uptake by aquatic organisms is slow and reaches
    equilibrium only after prolonged exposure
•   Aquatic organisms at low trophic levels show a much
    higher accumulation of lead than those at higher trophic
    levels
•   Biomagnification of lead does not take place
•   Uptake is lower in hard water as Ca2+ is believed to
    compete with lead for uptake
Molecular Mode of Toxic Interaction

• Main mode: Ionoregulatory disruption
• Pb indirectly disrupts plasma Na+ levels
• Pb competes with Ca2+ at the intestine
  and decreases plasma Ca2+ levels, which
  may trigger regulatory mechanisms (such
  as the up regulation of Na+ K+ ATPase) to
  increase Na+ levels
• Pb has been shown to inhibit Na+ K+
  activity in the intestine
    Toxic Mechanisms of Lead
• Modifies the folding, binding
  characteristics or enzymatic activity of
  proteins by binding to sulfhydryl, amine,
  phosphate, and carboxyl groups
• Can replace calcium in some reactions
• Can replace zinc in the catalytically active
  site of enzymes
• Induces oxidative stress
   Metabolism and Detoxification

• Inorganic lead is not metabolized
• High levels of calcium and phosphorus
  decrease intestinal absorption of lead and
  decreases its toxicity
• Low iron and high zinc levels increase the
  absorption and toxicity of lead
            Defense Strategies
• Fathead minnow (Pimephales promelas): increased
  dissolved organic carbon concentration decreased Pb
  accumulation
• Lead is accumulated in the kidneys and then excreted at
  a rate of 0.08-0.12 μgPb/kg/h in rainbow trout
• Organolead compounds metabolized in liver by oxidative
  dealkylation catalyzed by cytochrome P450
• Lead is excreted in the urine following glomerular
  filtration in the kidneys and by the intestines (by
  transmucosal losses or through biliary clearance in the
  form of organolead conjugates)
                               Bibliography
•   Alves, L.C. & Wood, C.M. 2006. The chronic effects of dietary lead in freshwater juvenile rainbow
    trout (Oncorhynchus mykiss) fed elevated calcium diets. Aquatic Toxicology. Volume 78: 217-232.
•   environmentalchemistry.com/yogi/periodic/Pb.htm
•   Mager, E., et. al. (2008). Toxicogenomics of water chemistry influence on chronic lead exposure
    to the fathead minnow (Pimephales promelas). Aquatic Toxicology. Volume 87: 200-209.
•   National Research Council (U.S.). Committee on Minerals and Toxic Substances in
    Diets and Water for Animals, National Council (U. S.), National Research Council
    (U.S). Subcommittee on Mineral Toxicity in Animals Published. 2005. Mineral
    Tolerance of Animals. National Academies
    http://books.google.com/books?id=k0wYvnlydGIC&pg=RA2-PA215&lpg=RA2-
    PA215&dq=tolerance+to+lead+in+aquatic+animals&source=web&ots=E152xEb4h7
    &sig=yZ1vmFfo5HtcFHq3TlBpmelh5Ig&hl=en
•   Patel, M., et. al. 2006. Renal responses to acute lead waterborne exposure in the freshwater
    rainbow trout (Oncorhnchus mykiss). Aquatic Toxicology. Volume 80: 362-371.
•   Rogers, J.T., Richards, J.G., & Wood, C.M. 2003. Ionoregulatory disruption as the acute toxic
    mechanism for lead in the rainbow trout (Oncorhynchus mykiss). Aquatic Toxicology. Volume 64:
    215-234.
•   www.chemicalelements.com/elements/pb.html
•   www.qivx.com/ispt/elements/ptw_082.php
•   www.globalleadnet.org/pdf/5.pdf
•   www.inchem.org/documents/ehc/ehc/ehc85.htm
•   www.intox.org/databank/documents/chemical/lead/ukpid25.htm

				
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