Organic Chemicals in the Environment

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Organic Chemicals in the Environment

• COURSE CONTENT
• Polycyclic aromatic hydrocarbons (PAHs)
• Chemical and physical properties and their
  influence on environmental fate of pollutants
• Persistent Organic Pollutants (POPs)
• The Dirty Dozen and DDT
• Polychlorinated biphenyls (PCBs)
• Dioxins
• Degradation mechanisms
• Regulation and monitoring

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Focus of the course
Molecule type and structure How physical and
chemical characteristics influence distribution
and fate in the environment Sources and
uses Toxicity
References Van Loon Duffy, Environmental
Chemistry Baird, Environmental Chemistry Finlayson
-Pitts Pitts, Atmospheric Chemistry
Fundamentals Experimental Techniques Alloway
Ayres, Chemical Principles of Environmental
Pollution Hester Harrison, Chlorinated Organic
Micropollutants Schwartzenbach, Gschwend,
Imboden, Environmental Organic Chemistry
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Polycyclic Aromatic Hydrocarbons (PAHs)

• Group of more than 100 different chemicals
  containing 3 or more fused aromatic rings
• E.g.,
• anthracene naphthacene
• coronene
• Health hazard many PAHs are known carcinogens
• Formed mainly as a result of incomplete
  combustion widespread and strongly associated
  with human activity
• Associate with particulate matter, soils, and
  sediments

Also known as polyaromatic hydrocarbons or
polynuclear aromatic hydrocarbons
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PAH structure

• PAHs have multiple, fused 3 7 member rings
• Benzene and naphthalene are not formally PAHs
• PAHs do not include heteroatoms such as N or S
• Not all PAHs are fully conjugated aromatic
  molecules
• (cf., Hückel Rule of (4n 2) p electrons)
• Fries Rule
• Most stable form of a polynuclear hydrocarbon is
  the
• one with the maximum number of rings with a
• benzenoid arrangement of 3 double bonds
• E.g., Naphthelene (but NOT a PAH!)

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History of PAHs

• 1775 Sir Percival Pott reported high rates of
  scrotum cancer in London chimney sweeps.
  Attributed to a carcinogenic component in
  fireplace soot
• 1880s High rates of skin cancer reported for
  workers in paraffin refinery, shale oil, and coal
  tar industries
• 1915-8 Japanese scientists showed that repeated
  painting ears of rabbits with coal tar induced
  tumors
• 1922 Organic extracts of soot are carcinogenic
• 1933 Kennaway et al. isolation of the coal
  tar carcinogen, Benzo(a)pyrene first example of
  a pure chemical compound demonstrating
  carcinogenic activity
• 1942 Extracts of ambient particulate matter are
  carcinogenic

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History of PAHs

• 1949 Benzo(a)pyrene identified in domestic soot
• 1952 B(a)P found in ambient particles in the UK
• 1954 Extracts of respirable ambient particulates
  from L.A. photochemical smog are carcinogenic
• 1970s Carcinogenic activity of organic extracts
  of ambient and primary combustion particles was
  higher than sum of known carcinogenic PAHs
  excess carcinogenicity
• - carcinogenic activity could be 100 1000
  times higher than that of B(a)P content ? many
  unknown chemicals of high biological activity
  must exist in organic extracts of ambient
  particles and particulate organic matter (POM)

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History of PAHs

• 1970s (cont.)
• - testing of compound carcinogenicity greatly
  speeded up with introduction of the Ames
  Salmonella mutagenicity assay, a sensitive
  bioassay for bacterial mutagens
• - organic extracts of fine particles contained
  not only promutagens, such as B(a)P, but also
  direct-acting mutagens
• - some PAHs react with environmental NO2, HNO3,
  or O3 to form directly mutagenic nitro-PAH and
  oxy-PAH
• Ames test
• direct mutagen (-S9) requires no metabolic
  activation
• promutagen (S9) requires mammalian enzymes

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Sources of PAHs

• PAHs are predominantly anthropogenic and are
  formed by
• - incomplete combustion of organic matter such
  as coal, wood, oil, petrol and diesel
• - coke and Al production, bitumen production,
  vehicle and aircraft exhaust
• - smoking cigarettes
• - charbroiled meats
• PAHs are also found in natural fuel deposits
• A few PAHs are used to produce medicine, dyes,
  plastics, pesticides
• Natural sources of PAHs include volcanoes and
  natural fires

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Sources of PAHs

• PAHs can be found in water also as a direct
  pollution from industries or from road runoff
• They can settle in the sediment, remain in the
  water or be taken up by organisms like plankton,
  mollusks and fish, thereby entering the food
  chain
• E.g., In the USA, residential wood and coal
  combustion produces about 700 tons/yr of PAHs
  compared to 1 ton/yr by coal power stations

B(a)P in foodstuffs µg/kg Charcoal broiled steak
8 Margarine 1-36 Sausages 4-50 Roasted
coffee 1-13 Toast 0.5
Source Heating, power production 51 Industria
l producers 20 Incineration open
burning 28 Vehicles 1
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Sources of PAHs

• Mechanism of formation during combustion
• - radicals formed by pyrolysis of hydrocarbons
  between 500 and 800ºC in zone of flame with
  insufficient O2
• - C1 and C2 fragments combine in reducing
  atmosphere to form condensed aromatics
• - on cooling, PAHs condense onto existing
  particles their distribution reflects their
  differing thermodynamic stability in O2 deficient
  flame

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Physical and chemical properties

• Vapour pressure
• - VPs vary enormously between PAHs, up to 107
  difference
• - Larger PAHs have much lower VPs
• E.g., naphthalene mainly found in gas phase
  larger PAHs tend to adsorb onto particles
• Solubility
• - PAH solubility low in water (ng/L to mg/L)
• - Smaller PAHs are more soluble
• - Oxidation to more polar species greatly
  increases solubility

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Physical and chemical properties

• Spectra
• - All PAHs have highly structured absorption in
  the ultraviolet actinic UV radiation
• - Strong absorption arises from aromatic
  structure

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Environmental Fate

• Usually enter air when released to the
  environment, often attaching to particles in air.
  Can be transported far from their sources.
• Do not dissolve in water but stick to soil or
  sediment to be found at the bottom of lakes.
  Some can be transported into groundwater.
• Higher concentrations in urban areas than rural
  areas
• PAHs are quite persistent in the environment and
  can bioaccumulate
• PAHs break down by photolysis and chemical
  reaction over days and weeks
• Microorganisms also break down PAHs over time

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Environmental Fate

• PAHs can breakdown by reacting with sunlight and
  other chemicals (OH radicals) in the air over
  days to weeks
• Besides B(a)P, other PAHs are emitted or formed
  in the atmosphere which account for additional
  mutagenicity. Gas-phase reactions can convert
  volatile PAHs to nitro-PAHs and nitro-PAH
  lactones, which are strong "direct-acting"
  mutagens
• The presence of nitro-PAH lactones formed in the
  atmosphere contributes significantly to the
  mutagenicity of ambient air
• Several reaction products of B(a)P and ozone are
  strong mutagens
• a major contributor has been identified as
  benzoapyrene-4,5-oxide, an animal metabolite,
  which is a strong direct mutagen

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Toxicity of PAHs

• The toxicity of PAHs varies across this large
  group of compounds
• - Some PAHs are carcinogenic and some are even
  mutagenic
• - Some seem to have no toxic effects at all
• A large percentage are not even studied
• Toxicity depends on whether the compound is
  inhaled as a gas, inhaled as a particle or
  adsorbed onto or absorbed into preexisting
  particles

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Health Effects of PAHs

• Once released into the atmosphere, airborne PAHs
  can be inhaled into the body on carrier
  particles
• These particles have a diameter lt 2.5 ?m and can
  be inhaled into the lungs
• The particles are too small to be removed by the
  upper respiratory tract

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Health Effects of PAHs

• Not clear if PAHs cause short term effects but
  may be responsible for eye irritation, nausea,
  vomiting, diarrhea and confusion
• Long term cataracts, kidney and liver damage,
  jaundice, breakdown of red blood cells
• Because certain PAHs are carcinogenic, exposure
  to high levels of these PAHs can lead to an
  increased risk of developing tumours of the
  lungs, skin and bladder

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16 EPA priority PAH pollutants
Naphthalene Acenaphthylene Acenaphthene Fluo
rene Phenanthrene Anthracene Fluoranth
ene Pyrene Benzo(a)anthracene Crysene Benzo(b
)fluoranthene Benzo(k)fluoranthene
Benzo(a)pyrene Dibenzo(a,h)anthracene Indeno(1
,2,3-cd)pyrene Benzo(ghi)perylene
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Benzo(a)pyrene (B(a)P)

• Benzo(a)pyrene (B(a)P) is one of the more common
  PAHs and is also one that is known to have toxic
  effects
• Widely distributed and strongly carcinogenic
• - regarded as the most dangerous PAH
• Is not produced or used commercially but is a
  result of incomplete combustion
• Short-term red blood cell damage, leading to
  anemia suppressed immune system
• Long-term developmental and reproductive
  effects, cancer

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Benzo(a)pyrene (B(a)P)

• 1915-1918 Japanese scientists discovered that
  painting the ears of rabbits and mice with coal
  extracts produced tumours, some of which were
  malignant
• 1933 B(a)P and B(e)P were synthesised
• Confirmation of carcinogenicity of B(a)P came
  when all 5 survivors of a group of 10 mice whose
  backs had been painted with synthetic B(a)P
  developed tumours
• The isomer B(e)P is not carcinogenic

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Benzo(a)pyrene (B(a)P)

• B(a)P concentrations in Fleet Street London have
  been falling 1962-1963 39 ng m-3, 1972-1973 10
  ng m-3, 1987 2 ng m-3
• However a reduction in B(a)P levels does not
  necessarily mean a reduction in potential health
  hazards
• There are two dominant removal processes for
  B(a)P
• physical loss processes for the particles on
  which B(a)P resides
• adsorbed phase reactions of B(a)P on the
  particles

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Benzo(a)pyrene (B(a)P)

• Considering only physical removal processes, the
  lifetime of B(a)P due to particle dry deposition
  is about ten days.
• However, in the adsorbed phase the chemical
  reactions include photolysis and reaction with
  O3, SO2, NO2, HNO3 and N2O5
• It is difficult to estimate an atmospheric
  lifetime for B(a)P due to chemical reactions
  and/or photolysis. Based on available
  information, the atmospheric lifetime of B(a)P is
  a few hours in polluted urban atmospheres during
  the summer months. This may explain the low
  concentrations of B(a)P measured in the ambient
  air during summer