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Halogenated Aromatic Hydrocarbons

Halogenated Aromatic Hydrocarbons. PCBs (polychlorinated biphenyls) , PCDDs (dioxin). Introduction. Important because provides a classic example of chemicals developed and used with no thought to environmental consequences

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Halogenated Aromatic Hydrocarbons

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  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

  5. Chemistry (con’t) • Halogenation - location/type of halogen changes properties a. Increases MW –> increases specific gravity, melting/boiling point –> 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

  6. Amounts and Uses • Amounts - 1.3 billion lbs produced between 1930 and 1976 –> 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 –> 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)

  8. 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, 63:1–18.

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

  10. Dioxin poisoning Ukranian presidential candidate Victor Yushchenko before and after being poisoned with dioxin.

  11. 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 –> 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 “

  12. Conclusion • huge problem that is slowly going away –> still lots of cause for concern NJ DEP sign on lower Passaic River, NJ

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