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Polynuclear Aromatic Hydrocarbons

The poly nuclear aromatic hydrocarbons or simply PAH have long been recognised as chemical carcinogen compounds considered to be the root cause of human malignancy. Benzo pyrene found almost everywhere and an environmental pollutant resulting from the incomplete pyrolysis of organic compounds or materials appears to be among the most active carcinogenic agents which human kind is exposed to.

Almost every nation has tonnes of these hydrocarbon carcinogen getting released in the environment every year causing much damages to both the immediate surroundings as well as the living organisms exposed to chemo hazards. Extensive studies have revealed the method by which these carcinogens are transferred from substances like tar and coal into our biological systems.

 

Polynuclear Aromatic Hydrocarbons Definition

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The poly nuclear aromatic hydrocarbon or better known as poly cyclic aromatic hydrocarbon comprise of fused rings of benzene and the count may vary from two to as many specified for the molecule.

These benzene rings which are fused together can join directly or through other carbon chain, these rings may or may not have any substituents attached to their structure. The substituents role in these fused rings of benzene is to provide distinct characteristics or feature and flavour of the poly aromatic hydrocarbons.

There are several forms of poly aromatic hydrocarbons around us. They are either used for fringe utility or for chemical treatment against pests. Examples are biphenyl, diphenyl methane, tri phenyl methane, naphthalene, anthracene and phenanthrene. 

Polynuclear Aromatic Hydrocarbons Aromatic Polynuclear Hydrocarbons

The potential relevance of arene oxides as primary metabolites in the conversion of aromatic compounds to phenols, trans di hydro-diols and glutathione conjugate is many mammals was found to have mechanism for the detoxification and excretion of a variety of xenobiotic aromatic substrates and that includes environmental pollutants, drugs, and natural products which are either inhaled, ingested, injected or used topically. 
The metabolic oxidative process of polycyclic aromatic hydrocarbon compounds in mammals are activated by a category of mono oxygenase, cytochrome P 450. The activity of cytochrome P 450 is localised in cellular endoplasmic reticulum of skin, kidney liver or even intestine, with the highest localisation found in liver.

The metabolic activation of large polycyclic hydrocarbons proceeds in a manner very similar to that of shown by naphthalene with an exception of additional class of metabolites, the Quinone. This shows a higher carcinogenicity. A knowledge of the mechanism for the poly cyclic aromatic hydrocarbons by which an arene oxide rearrange to produce phenols is also very important as far as biological disposition is concerned. 

The arene oxide isomerisation reaction has been studied extensively and no evidence that enzymatic processes are shown in the isomerisation of 1, 2 naphthalene oxide into 1 naphthol. 

Polynuclear Aromatic Hydrocarbons in Water

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The limited number of freshwater data base for Polynuclear aromatic hydrocarbon availability makes the statement for chronic toxicity in water.  The available Polynuclear aromatic hydrocarbon shows that acute toxicity to salt water aquatic life occurs at a very low concentration. There is no such data available for chronic toxicity of Polynuclear aromatic hydrocarbon to sensitive saltwater aquatic life.

Wherever and whenever a sanitary survey is carried out or sampling is allowed an inspection of the whole water supply is more appropriate. The presence of Polynuclear aromatic hydrocarbon in water resources like water tanks and open pipeline need closer examination to trace Polynuclear aromatic hydrocarbon.

The pipeline which carries potable water need to have several characteristics and do not allow potential potable water out or contaminate water from outside. These pipelines needs to be protected from the repeated problem from rodents and allow specific protection against such mammals as the acidity in water or presence of scouring particulate matter in pipeline could disintegrate these rodents and finally contaminate the pipeline water.

The corrosion of pipelines also creates another huge problem and chances of the Polynuclear aromatic hydrocarbon getting into the potable water supply becomes higher. Some pipelines with pitch fibre lining and these are found to have spread Polynuclear aromatic hydrocarbon into the water flowing through.

The garden hose pipes are again another big concern for the Polynuclear aromatic hydrocarbon as these are not exactly suitable for water transport as these materials have chances of leaching Polynuclear aromatic hydrocarbon into the garden plants.

The organic leaching from many coal fields shows soluble level of around 10 – 50 ng / L of some individual Polynuclear aromatic hydrocarbon. These are available at around 25 C. The predominant compound types observed in these leach materials are not that highly carcinogenic but are still harmful for any living kind on the long run.

There are also polar materials leached from coal but neither these or Polynuclear aromatic hydrocarbon causes severe adverse effects on aquatic life. The Polynuclear aromatic hydrocarbon typically considered carcinogens and inducers in mammals were found to initiate mixed function oxidase or simply MFO induction in fishes.

For specific carcinogen benzo pyrene a minimum concentration of about 300 ng / Kg in fish tissues are found and it’s necessary to induce mixed function oxidase. The lipophilic organic compounds are associated with particular coal fraction of the leach and can be efficiently released through steam distillation process that leads to natural setting.

The development of rapid and selective techniques for general synthesis of alkylated Polynuclear aromatic hydrocarbon can help in the characterization process. The sensitive and versatile high performance liquid chromatography (HPLC) and gas chromatography are designed for better analysis of these Polynuclear aromatic hydrocarbon in water and tissues of the aquatic life animals.

The field studies of these aquatic life animals shows a content for Polynuclear aromatic hydrocarbon as well as mixed function oxidase quite high in areas close to the coal fields where leaching is natural. 

Determination of the relative importance of uptake Polynuclear aromatic hydrocarbon from food as compared to water and particulate gives the estimation of maximum bio concentration potential of Polynuclear aromatic hydrocarbon in all kinds of aquatic life animals.

Polynuclear Aromatic Hydrocarbons List

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There are several forms of Polynuclear aromatic hydrocarbon around us but some common types are mentioned below. The following are the Polynuclear aromatic hydrocarbon / Polynuclear aromatic hydrocarbon group.

Naphthalene 
$C_{1}$ – naphthalene 
$C_{2}$ – naphthalene 
$C_{3}$ – naphthalene 
$C_{4}$ – naphthalene 
Acetaphthene
Acetaphthylene bi phenyl
Acetaphthylene di benzo furan
Anthracene 
Phenanthrene 
$C_{1}$ phenanthrene / Anthracene
$C_{2}$ phenanthrene / Anthracene
$C_{3}$ phenanthrene / Anthracene
$C_{4}$ phenanthrene / Anthracene
Fluorene
$C_{1}$ Fluorene
$C_{2}$ Fluorene
$C_{3}$ Fluorene
Di benzo thiophenes 
$C_{1}$ Di benzo thiophenes 
$C_{2}$ Di benzo thiophenes 
$C_{3}$ Di benzo thiophenes 
$C_{4}$ Di benzo thiophenes 

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