Polyaromatic hydrocarbons (PAHs) are atmospheric pollutants formed through thermal decomposition of organic molecules, commonly found in automobile exhaust, industrial emissions, and smoke. Exposure routes include breathing contaminated air, consuming contaminated food, and handling polluted soil, leading to both short-term and chronic health effects, including carcinogenicity. PAHs pose risks such as developmental malformations and genotoxicity, with notable compounds like benzo(a)pyrene recognized for their carcinogenic properties.

1. Polyaromatic
Hydrocarbons
By: Leonar Jun Gabiana

2. What are polyaromatic
hydrocarbons or PAH?
• Polyaromatic hydrocarbons (PAHs), also
known as polycylic aromatic
hydrocarbons or polynuclear aromatic
hydrocarbons, are potent atmospheric
pollutants that consist of fused
aromatic rings and do not
contain heteroatoms or carry substituents.

3. Polyaromatic Hydrocarbons

4. How are they produced?
• Most of them are formed by a process of thermal
decomposition (pyrolysis) and subsequent recombination
(pyrosynthesis) of organic molecules
• Automobile exhaust, industrial emissions and smoke from
burning wood, charcoal and tobacco contain high levels
of PAHs
• combustion processes produce a mixture of chemicals
with soot being a well known example

5. Chemical characteristics
• high melting and boiling points
• low vapor pressure
• very low aqueous solubility
• highly lipophilic
• very soluble in organicsolvents

6. Sources
Natural Sources
• forest and grass fires
• oil seeps
• volcanoes
• chlorophyllous plants,
fungi, and bacteria
Anthropogenic Sources
• petroleum
• electric power generation
• refuse incineration
• home heating
• production of coke,
carbon black, coal tar,
and asphalt
• internal combustion
engines

7. Uses
• intermediaries in
pharmaceuticals,
• agricultural products
• photographic
products
• thermosetting
plastics
• lubricating materials

8. Some of the PAH used in the
industry
• Acenaphthene: manufacture of
dyes, plastics,
pigments, pharmaceuticals and pesticides
• Anthracene: manufacture of dyes and
pigments;diluent for wood preservatives;
• Fluoranthene: manufacture of dyes,
pharmaceuticals and agrochemicals.
• Fluorene: manufacture of dyes, pigments,
pesticides, thermoset plastic and
pharmaceuticals;
• Phenanthrene: manufacture of pesticides
and resins
• Pyrene: manufacture of pigments

9. How are we exposed?

10. Routes Of Exposure
• breathing ambient and indoor air
• handling contaminated soil or bathing
in contaminated water
• eating food containing PAHs
• smoking cigarettes
• breathing smoke from open fireplaces
• Drinking contaminated water

11. Sources of PAH’s in the diet
• Barbecue
• Smoked foods
• Coffee and tea
• Human milk
• Vegetable oils

12. Metabolism
• Due to the high lipophilicity of this class of
compounds, their bioavailability after
ingestion and inhalation is significant
• Scientific investigations have shown that
detectable levels of PAH occur in almost
all internal organs, particularly in organs
that are rich in adipose tissue
• . The enzyme system primarily responsible
for PAH metabolism is the mixed-function
oxidase system.

13. The mechanism
• The first reaction is an epoxidation
• PAH epoxides can then be conjugated
with glutathione and this is regarded as a
true detoxification reaction.
• The epoxides that are not conjugated with
glutathione are converted into phenols and
diols
• These PAH metabolites, however, are
sometimes not sufficiently polar to be
excreted and are therefore have to be
conjugated with glucuronic or sulfuric
acids to enable excretion

15. Short term health effects
• eye irritation
• nausea
• vomiting
• diarrhea
• Confusion
• Skin irritation

16. Chronic health effects
• decreased immune function,
• cataracts,
• kidney and liver damage (e.g. jaundice),
• breathing problems,
• asthma-like symptoms
• lung function abnormalities
• repeated contact with skin may induce
redness and skin inflammation

17. Carcinogenicity
• ability of the reactive metabolites, such as
epoxides and dihydrodiols, of some PAHs
to bind to cellular proteins and DNA
-which leads to:
*mutation
*formation of tumor
*cancer
*developmental malformations

18. Common cancers caused by
PAH’s
• lung cancer from inhalation,
• stomach cancer from ingesting PAHs in
food,
• skin cancer from skin contact.
**Benzo(a)pyrene is the most common PAH
to cause cancer in animals and this
compound is notable for being the first
chemical carcinogen to be discovered.

19. Teratogenicity
• Embryotoxic effects of PAHs have been
described in experimental animals
exposed to PAH
• Laboratory studies conducted on mice
have demonstrated that ingestion of high
levels of benzo(a)pyrene during pregnancy
resulted in birth defects and decreased
body weight in the offspring

20. Teratogenicity
• exposure to PAH pollution during
pregnancy is related to adverse birth
outcomes, this includes
• low birth weight
• premature delivery
• heart malformations
• lower IQ at age three
• increased behavorial problems at ages six
and eight
• and childhood asthma

21. Genotoxicity
• Genotoxic effects for some PAH have
been demonstrated both in rodents and in
vitro tests using mammalian (including
human) cell lines
• Most of the PAHs are not genotoxic by
themselves and they need to be
metabolised to the diol epoxides which
react with DNA
• Genotoxicity plays important role in the
carcinogenicity process and maybe in
some forms of developmental toxicity as
well.

22. Immunotoxicity
• PAHs have also been reported to
suppress immune reaction in rodents
• immunosuppression may be involved in
the mechanisms by which PAH induce
cancer
• Early immunotoxicology studies of PAHs
such as BaP,DMBA,and 3-
methylcholanthrene demonstrated
suppression of the antibody response to a
variety of T-cell-dependent and T-cell
independent antigens

28. Teratogenicity

35. How are we exposed?

38. Human Health Effects

46. Sources