The document presents an overview of polycyclic aromatic hydrocarbons (PAHs), detailing their sources, environmental effects, and degradation processes. PAHs, which are harmful compounds resulting from both natural and anthropogenic activities, have significant toxicity and potential carcinogenic properties. The presentation also discusses methods for remediation and the persistence of PAHs in various ecosystems.

1. POLYCYCLIC AROMATIC HYDROCARBONS AND THEIR EFFECT ON
THE ENVIRONMENT
Elegbeleye Oladipo Ayodamope
And
CHARLES BAIDOO ESHUN

2. OUTLINE
• OBJECTIVE
• INTRODUCTION
• SOURCES, USES AND
PROPERTIES OF PAHs
• ENVIRONMENTAL EFFECTS
• ENVIRONMENTAL FATE PROCESSES
• DEGRADATION OF PAHs
• CONCLUSION

3. The aim of this presentation is to review
contemporary information on PAH pollution,
PAH degradation, the fate and risk associated
with the presence of these compounds in the
environment and also to enlighten on some
well-known possible remediations.

4. Polycyclic aromatic hydrocarbons (PAHs) are widely
distributed and relocated in the environment as a
result of the incomplete combustion of organic matter.
Many PAHs and their epoxides are highly toxic,
mutagenic and/or carcinogenic to microorganisms as
well as to higher systems including humans. Although
various physicochemical methods have been used to
remove these compounds from our environment, they
have many limitations.

5. WHAT ARE PAHs?
• Polycyclic aromatic hydrocarbons are
hydrocarbons—organic compounds
containing only carbon and hydrogen—that
are composed of multiple aromatic rings
(organic rings in which the electrons are
delocalized)[1].
• They are a class of carcinogenic organic
molecules that consist of three or more
benzene rings and are commonly produced
by fossil fuel combustion.

6. PAHs are organic molecules that form from a
variety of natural and anthropogenic reactions.
Natural polynuclear aromatic hydrocarbons
form from forest fires and volcanic eruptions.
Man contributes PAHs by burning wood and
incomplete combustion of fossil fuels.
The compounds are numerous in fossil fuels,
such as coal and petroleum.
Anthropogenic sources can be devised into two
categories: the combustion of materials for
energy supply (e.g. coal, oil, gas, wood, etc.) and
combustion for waste minimalization (e.g.
waste incineration) [1,2]

8. Although the emphasis is on avoiding exposure to PAHs, some
of these molecules are useful for making medicines, plastics,
dyes, and pesticides.

10. Polycyclic aromatic hydrocarbons are lipophilic,
nonpolar molecules.
They tend to persist in the environment because
PAHs are not very soluble in water.
They are weakly volatile and dissolve weakly in
water.
All PAHs are solid at room temperature and have
high melting and boiling points.
The movement of PAHs in the environment
depends on properties such as how easily they
dissolve in water and how easily they evaporate in
the air.

11. Table 1. Properties of PAHs [4]

12. Mammals can absorb PAHs by various routes e.g.
inhalation, dermal contact and ingestion.
Plant can absorb PAHs from soils through their
roots and translocate them to other plant parts.
PAHs are moderately persistent in the
environment, and can bio-accumulate.

13. Table 2. Partition of PAHs in Natural Environments [3]

15. PAHs are usually released into the air, or they
evaporate into the air when they are released to
soil or water .
Since PAHs are generally insoluble in water, they
are generally found adsorbed on particulate and
precipitated in the bottom of lakes and rivers, or
solubilized in any oily matter which may
contaminate water.
PAHs have moderate to high acute toxicity to
aquatic life and birds.

16. Degradation of PAHs in the environment occurs
through biological, chemical and photochemical
processes.
These processes may also be utilized for
remedial purposes. However, the degradation
may result in a variety of transformation
products some of which could potentially
accumulate.

17. PAHs are released to the environment through
natural and synthetic sources with emissions largely
to the atmosphere. Synthetic sources provide a
much greater release volume than natural sources.
PAHs are transported from surface waters by
volatilization. In soil and sediments, microbial
metabolism is the major process for degradation of
PAHs. PAHs have a potential effect on the
environment,both directly and indirectly.

18. [1]. [Fetzer, J. C. (2000). "The Chemistry and Analysis of the Large Polycyclic Aromatic
Hydrocarbons". Polycyclic Aromatic Compounds (New York: Wiley) 27 (2): 143.
doi:10.1080/10406630701268255. ISBN 0-471-36354-5.
[2]. WILD S.R., JONES K.C. Polynuclear aromatic hydrocarbons
in the United Kingdom environment: a preliminary source
inventory and budget. Environm. Poll. 88, 91, 1995.
[3]. RAMDAHL T., ALFHEIM I., BJORSETH A. PAH emission from various
sources and their evolution over last decades. In "Mobile source emission
including polycyclic organic species". Eds. D. Rondia et al., D. Reidel
Publishing Company, 277, 1983.
[4]. Polish Journal of Environmental Studies Vol. 8, No. 3 (1999), 131-136