polyaromatic hydrocarbons

8/2/2019 Polyaromatic Hydrocarbons

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Polyaromatic

Hydrocarbons

By: Leonar Jun Gabiana



What are polyaromatichydrocarbons or PAH?

• Polyaromatic hydrocarbons (PAHs), alsoknown as polycylic aromatichydrocarbons or polynuclear aromatic

hydrocarbons, are potent atmosphericpollutants that consist of fusedaromatic rings and do notcontain heteroatoms or carry substituents.

http://en.wikipedia.org/wiki/Aromatic

http://en.wikipedia.org/wiki/Simple_aromatic_ring

http://en.wikipedia.org/wiki/Heteroatom

http://en.wikipedia.org/wiki/Substituent

http://en.wikipedia.org/wiki/Substituent

http://en.wikipedia.org/wiki/Heteroatom

http://en.wikipedia.org/wiki/Simple_aromatic_ring

http://en.wikipedia.org/wiki/Aromatic



Polyaromatic Hydrocarbons



How are they produced?

• Most of them are formed by a process of thermaldecomposition (pyrolysis) and subsequent recombination(pyrosynthesis) of organic molecules

• Automobile exhaust, industrial emissions and smoke fromburning wood, charcoal and tobacco contain high levelsof PAHs

• combustion processes produce a mixture of chemicalswith soot being a well known example



Chemical characteristics

• high melting and boiling points

• low vapor pressure

•very low aqueous solubility

• highly lipophilic

• very soluble in organicsolvents

http://toxipedia.org/display/toxipedia/Solvents

http://toxipedia.org/display/toxipedia/Solvents



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 combustionengines



Uses

• intermediaries inpharmaceuticals,

•agricultural products

• photographicproducts

• thermosetting

plastics

• lubricating materials



Some of the PAH used in theindustry

• Acenaphthene: manufacture ofdyes, plastics,pigments, pharmaceuticals and pesticides

• Anthracene: manufacture of dyes andpigments;diluent for wood preservatives;

• Fluoranthene: manufacture of dyes,pharmaceuticals and agrochemicals.

• Fluorene: manufacture of dyes, pigments,pesticides, thermoset plastic andpharmaceuticals;

• Phenanthrene: manufacture of pesticidesand resins

• Pyrene: manufacture of pigments

http://toxipedia.org/display/toxipedia/PVC

http://toxipedia.org/display/toxipedia/Drugs+and+Pharmaceuticals

http://toxipedia.org/display/toxipedia/Pesticides

http://toxipedia.org/display/toxipedia/Pesticides

http://toxipedia.org/display/toxipedia/Drugs+and+Pharmaceuticals

http://toxipedia.org/display/toxipedia/PVC



How are we exposed?



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



Sources of PAH’s in the diet

• Barbecue

• Smoked foods

• Coffee and tea

• Human milk• Vegetable oils



Metabolism

• Due to the high lipophilicity of this class ofcompounds, their bioavailability afteringestion and inhalation is significant

• Scientific investigations have shown thatdetectable levels of PAH occur in almostall internal organs, particularly in organsthat are rich in adipose tissue

• . The enzyme system primarily responsible

for PAH metabolism is the mixed-functionoxidase system.



The mechanism

• The first reaction is an epoxidation

• PAH epoxides can then be conjugatedwith glutathione and this is regarded as atrue detoxification reaction.

• The epoxides that are not conjugated withglutathione are converted into phenols anddiols

• These PAH metabolites, however, aresometimes not sufficiently polar to beexcreted and are therefore have to beconjugated with glucuronic or sulfuricacids to enable excretion



Short term health effects

• eye irritation

• nausea

• vomiting

• diarrhea

• Confusion

• Skin irritation



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

http://toxipedia.org/display/toxipedia/Respiratory+Toxicology+and+Asthma

http://toxipedia.org/display/toxipedia/Respiratory+Toxicology+and+Asthma



Carcinogenicity

• ability of the reactive metabolites, such asepoxides and dihydrodiols, of some PAHsto bind to cellular proteins and DNA

-which leads to:

*mutation

*formation of tumor

*cancer*developmental malformations



Common cancers caused byPAH’s

• lung cancer from inhalation,

• stomach cancer from ingesting PAHs infood,

•skin cancer from skin contact.

**Benzo(a)pyrene is the most common PAH

to cause cancer in animals and thiscompound is notable for being the firstchemical carcinogen to be discovered.

http://toxipedia.org/display/toxipedia/Cancer

http://toxipedia.org/display/toxipedia/Cancer



Teratogenicity

• Embryotoxic effects of PAHs have beendescribed in experimental animalsexposed to PAH

• Laboratory studies conducted on micehave demonstrated that ingestion of highlevels of benzo(a)pyrene during pregnancyresulted in birth defects and decreasedbody weight in the offspring



Teratogenicity

• exposure to PAH pollution duringpregnancy is related to adverse birthoutcomes, this includes

• low birth weight

• premature delivery

• heart malformations

• lower IQ at age three

• increased behavorial problems at ages sixand eight

• and childhood asthma



Genotoxicity

• Genotoxic effects for some PAH havebeen demonstrated both in rodents and invitro tests using mammalian (includinghuman) cell lines

• Most of the PAHs are not genotoxic bythemselves and they need to bemetabolised to the diol epoxides whichreact with DNA

• Genotoxicity plays important role in thecarcinogenicity process and maybe insome forms of developmental toxicity aswell.



Immunotoxicity

• PAHs have also been reported tosuppress immune reaction in rodents

• immunosuppression may be involved inthe mechanisms by which PAH inducecancer

• Early immunotoxicology studies of PAHssuch as BaP,DMBA,and 3-methylcholanthrene demonstrated

suppression of the antibody response to avariety of T-cell-dependent and T-cellindependent antigens



Teratogenicity



How are we exposed?



Human Health Effects



Sources

polyaromatic hydrocarbons

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