Halogenated Aromatic Hydrocarbons

1
Halogenated Aromatic Hydrocarbons

• PCBs (polychlorinated biphenyls) , PCDDs (dioxin)

2
Introduction

• Important because provides a classic example of
  chemicals developed and used with no thought to
  environmental consequences
• For first 40 years of manufacture many were
  thought to be biologically inactive!
• A large problem because of wide-spread use and
  persistence
• Dioxin discharged from paper mills, coal fired
  utilities, metal smelting, diesel trucks, land
  application of sewage sludge, burning treated
  wood, trash burn barrels
• PCBs - used in transformers, capacitors,
  hydraulic fluids
• Natural follow-up topic to pesticides because
  PCBs have toxicological properties that are
  similar to pesticides (although never designed to
  be released into the environment)

3
Chemistry

• Very complex because have multiple congeners
  (different attachment points to base molecules) ?
  209 different PCBs
• Most environmentally important are PCBs
  (polychlorinated biphenyls) and PCDDs
  (polychlorinated dibenzo-p-dioxin)
• Formed by covalent bonding of halogens (Cl, Br,
  F, etc) to 6 carbon ring structures (benzene,
  biphenyls (two fused benzenes)
• Easy (cheap) to form bonds, hard to break bonds
• Halogenation changes properties of parent
  structure
• both above useful for cheaply making lots of
  compounds that do not break down.

4
Polychlorinated biphenyl (PCB)
Polychlorinated dibenzo-p-dioxin (PCDDs or dioxin)
TCDD
2,3,7,8-tetrachlorinated dibenzo-p-dioxin
3,4,5,4,5 pentachloro-biphenyl
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Chemistry (cont)

• Halogenation - location/type of halogen changes
  properties
• a. Increases MW gt increases specific gravity,
  melting/boiling point gt many industrial
  applications.
• b. Increases stability (C - halogen stronger
  than C - H) persistent
• Lipophilicity - tend to accumulate in fatty
  tissue
• Note high persistence high lipophilicity
  high bioconcentration potential

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Amounts and Uses

• Amounts - 1.3 billion lbs produced between 1930
  and 1976 gt 1.25 billion in U.S. by Monsanto
• Uses - heat exchange and hydraulic fluids,
  lubricants, dielectric fluids in
  transformers/capacitors, plasticizers
• Widely used, especially industrial countries
• Partially banned in US in 76, fully banned by
  79 except special applications (no release) -
  illegal to manufacture, process or distribute

7
Distribution and Fate

• Not realized a problem for 45 yrs gt distributed
  world-wide
• Enter environment via
• direct discharge from manufacturing facilities
  (most common)
• improper disposal (especially landfills)
• incineration
• volatilizing, leaching, ocean currents, particle
  transfer
• Not all released chemical is environmentally
  available
• For all PCBs produced in US
• 30 is degraded
• 58 is inaccessible
• 2 is in Mobile Environmental Reservoir (MER)
  biologically available
• Tending to decline in biological systems (Great
  Lakes fish tissue) but some hot spots (Upper
  Hudson River, St. Lawrence River, New Bedford
  Harbor)

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U.S. Dietary Intake of Dioxin
Levels of Dioxin in U.S. Food Supply (1995)" from
May 2001 study by Arnold Schecter et. al.,
Journal of Toxicology and Environmental Health,
Part A, 63118.
9
Effects

• most work done on aquatic orgs./fish
• Laboratory animals (most data available)
• Reproductive effects
• Developmental
• Immunological
• Neurological
• Integumentary

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Dioxin poisoning
Ukranian presidential candidate Victor Yushchenko
before and after being poisoned with dioxin.
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• Wildlife
• - basically agree with lab studies but lots less
  data
• Fish
• LC50 for PCBs in 10 to 300 ppm range (chronic
  lower)
• decreased growth (thyroid effects) and
  reproduction
• MFO (mixed function oxidase) system effects
  (bioindicator)
• 2. Birds
• - generally more resistant than mammals (except
  chickens!)
• most susceptible gt fish eating birds
• generally little field mortality shown
• chronic exposure followed by starvation a problem
• some repro, growth
• Invertebrates
• - acute doses vary with organism
• hydra LC50 10,000 ppm
• D. magna LC50 1.3 ppb
• diatom 0.1

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Conclusion

• huge problem that is slowly going away gt still
  lots of cause for concern

NJ DEP sign on lower Passaic River, NJ