Halogenated Aromatic Halogenated Aromatic HydrocarbonsHydrocarbons

PCBs (polychlorinated PCBs (polychlorinated biphenyls) , PCDDs (dioxin)biphenyls) , PCDDs (dioxin)

IntroductionIntroduction Important because provides a classic example of Important because provides a classic example of

chemicals developed and used with no thought to chemicals developed and used with no thought to environmental consequencesenvironmental consequences– For first 40 years of manufacture many were thought to For first 40 years of manufacture many were thought to

be biologically inactive!be biologically inactive!

A large problem because of wide-spread use and A large problem because of wide-spread use and persistencepersistence– DioxinDioxin – discharged from paper mills, coal fired utilities, – discharged from paper mills, coal fired utilities,

metal smelting, diesel trucks, land application of sewage metal smelting, diesel trucks, land application of sewage sludge, burning treated wood, trash burn barrels sludge, burning treated wood, trash burn barrels

– PCBsPCBs - used in transformers, capacitors, hydraulic fluids - used in transformers, capacitors, hydraulic fluids

Natural follow-up topic to pesticides because Natural follow-up topic to pesticides because PCBs have toxicological properties that are PCBs have toxicological properties that are similar to pesticides (although never designed to similar to pesticides (although never designed to be released into the environment)be released into the environment)

ChemistryChemistry1.1. Very complex because have multiple congeners Very complex because have multiple congeners

(different attachment points to base molecules) (different attachment points to base molecules) 209 different PCBs 209 different PCBs

2.2. Most environmentally important are PCBs Most environmentally important are PCBs (p(polychlorinated biphenyls) and PCDDs and PCDDs ((polychlorinated dibenzo-p-dioxin)

3.3. Formed by covalent bonding of halogens (Cl, Br, Formed by covalent bonding of halogens (Cl, Br, F, etc) to 6 carbon ring structures (benzene, F, etc) to 6 carbon ring structures (benzene, biphenyls (two fused benzenes)biphenyls (two fused benzenes)

a.a. Easy (cheap) to form bonds, hard to break bondsEasy (cheap) to form bonds, hard to break bondsb.b. Halogenation changes properties of parent structureHalogenation changes properties of parent structure

both above useful for cheaply making lots of both above useful for cheaply making lots of compounds that do not break down.compounds that do not break down.

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

Chemistry (con’t)Chemistry (con’t)

4.4. Halogenation - location/type of halogen changes Halogenation - location/type of halogen changes propertiesproperties

a. Increases MW –> increases specific a. Increases MW –> increases specific gravity, melting/boiling point –> many industrial gravity, melting/boiling point –> many industrial applications.applications.

b. Increases stability (C - halogen stronger b. Increases stability (C - halogen stronger than C - H) = persistentthan C - H) = persistent

5.5. Lipophilicity - tend to accumulate in fatty tissueLipophilicity - tend to accumulate in fatty tissue

Note: high persistence + high lipophilicity = Note: high persistence + high lipophilicity = high bioconcentration potential high bioconcentration potential

Amounts and UsesAmounts and Uses Amounts - 1.3 Amounts - 1.3 billion billion lbs produced between 1930 lbs produced between 1930

and 1976 –> 1.25 billion in U.S. by Monsantoand 1976 –> 1.25 billion in U.S. by Monsanto

Uses - heat exchange and hydraulic fluids, Uses - heat exchange and hydraulic fluids, lubricants, dielectric fluids in lubricants, dielectric fluids in transformers/capacitors, plasticizerstransformers/capacitors, plasticizers

Widely used, especially industrial countriesWidely used, especially industrial countries

Partially banned in US in ‘76, fully banned by ‘79 Partially banned in US in ‘76, fully banned by ‘79 except special applications (no release) - illegal to except special applications (no release) - illegal to manufacture, process or distributemanufacture, process or distribute

Distribution and FateDistribution and Fate Not realized a problem for 45 yrs –> distributed world-wideNot realized a problem for 45 yrs –> distributed world-wide

Enter environment viaEnter environment viaa.a. direct discharge from manufacturing facilities (most common)direct discharge from manufacturing facilities (most common)b.b. improper disposal (especially landfills)improper disposal (especially landfills)c.c. incinerationincinerationd.d. volatilizing, leaching, ocean currents, particle transfervolatilizing, leaching, ocean currents, particle transfer

Not all released chemical is environmentally availableNot all released chemical is environmentally available

For all PCBs produced in USFor all PCBs produced in US– 30% is degraded30% is degraded– 58% is inaccessible58% is inaccessible– 2% is in 2% is in Mobile Environmental ReservoirMobile Environmental Reservoir (MER) = biologically (MER) = biologically

availableavailable

Tending to decline in biological systems (Great Lakes fish Tending to decline in biological systems (Great Lakes fish tissue) but some “hot spots” (Upper Hudson River, St. tissue) but some “hot spots” (Upper Hudson River, St. Lawrence River, New Bedford Harbor)Lawrence River, New Bedford Harbor)

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.

U.S. Dietary Intake of DioxinU.S. Dietary Intake of Dioxin

EffectsEffects

most work done on aquatic orgs./fishmost work done on aquatic orgs./fish

A.A. Laboratory animals (most data available) Laboratory animals (most data available) 1.1. Reproductive effectsReproductive effects

2.2. Developmental “Developmental “

3.3. Immunological “ Immunological “

4.4. Neurological “Neurological “

5.5. Integumentary “Integumentary “

Dioxin poisoningDioxin poisoning

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

B.B. WildlifeWildlife- - basically agree with lab studies but lots less databasically agree with lab studies but lots less data

1.1. Fish Fish a.a. LCLC5050 for PCBs in 10 to 300 ppm range (chronic = lower) for PCBs in 10 to 300 ppm range (chronic = lower)b.b. decreased growth (thyroid effects) and reproductiondecreased growth (thyroid effects) and reproductionc.c. MFO (mixed function oxidase) system effects (bioindicator)MFO (mixed function oxidase) system effects (bioindicator)

2. Birds2. Birds- generally more resistant than mammals (except chickens!)- generally more resistant than mammals (except chickens!)– most susceptible –> fish eating birdsmost susceptible –> fish eating birds– generally little field mortality showngenerally little field mortality shown– chronic exposure followed by starvation a problemchronic exposure followed by starvation a problem– some repro, growthsome repro, growth

3.3. InvertebratesInvertebrates

- acute doses vary with organism- acute doses vary with organisma.a. hydra LC50 = 10,000 ppmhydra LC50 = 10,000 ppm

b.b. D. magnaD. magna LC LC5050 = 1.3 = 1.3 ppbppbc.c. diatom “ = 0.1 “diatom “ = 0.1 “

ConclusionConclusion huge problem that is slowly going huge problem that is slowly going

away –> still lots of cause for away –> still lots of cause for concernconcern

NJ DEP sign on lower Passaic River, NJ