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Polychlorinated Biphenyls (PCBs)

Biphenyl:

PCBs have Cl substituents at any site on the biphenyl structure→ 209 possible unique structures – “congeners”

Mixtures produced commercially under different trade names, with different compositions

E.g., Monsanto: “Aroclor”;

General Electric: “Pyranol”

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PCB propertiesPhysical & chemical properties vary significantly for different

congeners but in general PCBs have:– low vapour pressures– low solubility in water, high solubility in organic solvents– low flammability

As expected, smaller PCBs have higher VPs and water solubilities:

E.g., VP Solubility

[mm Hg] [mg L-1]“PCB 1” (1 Cl) 1.4×10-3 4.8“PCB 163” (several Cls) 5.8×10-7 0.0012

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Uses of PCBs

High chemical stability and low flammability made PCBs ideal for many applications:

– dielectric fluids for capacitors & transformers

– heat transfer fluids, lubricating & cutting oils

– additives in pesticides, paints, adhesives, sealants, plastics, flame retardants, surgical implants

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History

Commercial production of PCBs began in 1929 (Monsanto)

General Electric released about 95,000 kg and 590,000 kg of PCBs into the Hudson River from two industrial plants –PCBs spread throughout river and foodchain

Concerns about impact on health in 1960s led to bans in Sweden (1972), USA (1977), & elsewhere

To date, many countries have restricted or banned PCB production & use (Stockholm Convention, 2001)

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Health effects of PCBs

Main exposure route through inhalation, drinking

water, or consumption of contaminated food

Health effects vary with congener:

- “non-ortho-PCBs” and “coplanar PCBs”

In exposed workers:- chloracne (see Fig.)- changes in blood & urine, possibly arising

from liver damage- Babies born to women with high PCB intake had symptoms of

weight reduction, possible effects on immune system, lower IQ scores, problems with motor skills & short-term memory

PCBs are probably carcinogens (WHO, EPA)

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Health effects of PCBs

In animals, PCBs affect most health end-points:

immunological, reproductive, developmental, body weight

Cancer was observed in rats exposed to PCBs

PCBs may affect estrogen levels and cause reproductive problems:

- feminisation of males and influence on sexual differentiation

- so-called Endocrine Disruptor Chemicals, which affect the endocrine system and reproduction of top-level predators

E.g., polar bears and whales

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PCBs in the Environment

1.2 million tons of PCBs were estimated to have been produced worldwide, until restrictions in the 1970s

Current sources of PCBs entering the environment are through use of existing PCB-containing components and disposal of old electrical equipment

Since the 1980s, decreasing concentrations of PCBs have been found in air and rainwater

Concentrations of PCBs indoors up to 10 times higher than outside ambient air

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PCBs in the Environment

PCB concentrations in airCanada, NW Territories 0.002 – 0.07 ng m-3

Germany, industrial area 3.3 ng m-3

Germany, noncontaminated area 0.003 mg m-3

Sweden 0.8 – 3.9 ng m-3

PCB concentrations in waterGerman rivers 5 – 103 ng L-1

Netherlands, the Rhine 100 – 500 ng L-1

Sweden, water supply 0.5 ng L-1

Globally, 60% of PCBs are in the oceans, 39% in terrestrial & coastal environments

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PCBs in the Environment

Adsorb strongly to soil & sediment, especially more chlorinated PCBs → 2:1 PCBs in suspended particulates compared to dissolved in water

Half-life in soil or sediment is months to years

Volatilisation & biodegradation are main methods of removing PCBs from soil, but are very slow processes

Vapourisation is the dominant route for PCB removal from water

In atmosphere, reaction with OH is major removal mechanism, with half-life from 3 to 80 days

Owing to PCBs high solubility in fats and high chemical stability, get bioaccumulation

→ bioaccumulation increases with higher Cl substitution

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PCBs in the Great LakesIn the Great Lakes, harm to

wildlife was linked to PCBs:- reproductive failures in mink, cormorants, terns, gulls

Great Lakes are focal point for PCB studies because high levels of PCBs and importance of the Lakes for sport-fishing

Long residence time for water and large surface area make them vulnerable to PCB contamination

PCB concentrations in air (ng m-3)

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PCBs in the Great Lakes

Of the GL, those farthest from urban centres have lowest PCB levels

PCB half-lives depend on amount in bottom sediment

20-50% of PCBs attached to particulates, while the rest is dissolved

PCB accumulation in sediments

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PCBs in the Great Lakes

Fluxes into the Lakes include:

- wet & dry deposition

- inflow from tributaries

- outflow

- gas exchange

- sedimentation

Estimates of loadings and losses of PCBs

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PCBs in the Great Lakes

Lake Trout – evidence for PCB

affecting ability to reproduce- bans exist to keep children and pregnant women from consuming fish from the Lakes

Sharp decrease in PCBs in Lake Trout from 1970’s to 80’s- PCB concentration relatively constant since 80’s

Most top predators get PCBs from the foodweb, not though gill transfer from H2O – clear evidence for biomagnification

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Destruction of PCBs

Besides slow natural degradation processes:

- incineration at high temperature (> 1200ºC, > 2 sec, excess O2)

- ultrasound in water

- irradiation using γ-rays

- microbial degradation

- chemical destruction:

- nucleophilic substitution: remove Cl using ethylene glycol

- reaction with H2 at 700 - 930ºC to form benzene and HCl

- reduction with strong reducing agents in aprotic solvents

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Analysis of PCBs

Typically analysed using gas chromatography (GC) with either and electron capture detector (ECD) or a mass spectrometer (MS)

For biological samples, there are usually 3 steps:

1) extraction from sample matrix with one or more solvents

2) removal of impurities on single or multiple columns

3) quantification using GC with ECD or GC-MS

For air samples:

- pump sample air through glass fibre filter and adsorbent trap

- extraction and GC analysis

Water samples: extraction with solvent and GC analysis

Soil,sediment, or solid waste: soxhlet extraction