PAHs in sediments: PAHs are deposited to the sedimentary environment by similar processes that govern the deposition to surface soils. In rural areas, the PAHs sorbet to atmospheric particles can settle on the surface of lakes, streams, and oceans by dry or wet deposition. There they are dispersed by currents and eventually become integrated with the sediment. On the other hand, sediments near urban centers are influenced by atmospheric deposition of PAHs. They also receive inputs of PAHs from storm and sanitary sewer effluents as well as roadway runoff. Eventually, some of the PAHs will be sorbet to particles, settle, and become part of the sedimentary record.

Occurrence of PAH in foods: Raw foods should usually not contain high levels of PAH. In areas remote from urban or industrial activities, levels of PAH found in unprocessed foods reflect the background contamination. Processing of food (such as drying and smoking) and
cooking of foods at high temperatures (grilling, roasting, frying) are major sources generating PAH. Levels as high as 200lg/kg of PAH have been found in smoked fish and meat. In barbecued meat, 130lg/kg of PAH has been reported (Standing Committee on Foodstuffs, 2001). Generally, the average background values are in the range of 0.01–1lg/kg in uncooked foods. Contamination of vegetable oils (including olive residue oils) with PAH usually occurs during technological processes like direct fire drying. In this respect, the combustion products may come into contact with the oil seeds or oil. The occurrence of PAH in foods is governed mainly by the same physicochemical factors that determine their absorption and distribution in man. These factors are the relative solubility of PAH in water and organic solvents. Such solubility determines their capacity for transport and distribution between different environmental compartments and their uptake and accumulation by living organisms.

Effect on human health

17 PAHs have been identified as being of greatest concern with regard to potential exposure and adverse health effects on humans and are thus considered as a group. Biological monitoring of exposure to PAHs is of primary interest, due to the widespread diffusion of these compounds and to their toxicological relevance. Some PAHs are well known as carcinogens, mutagens, and teratogens and therefore pose a serious threat to the health and the well-being of humans. The most significanthealth effect to be expected from inhalation exposure to PAHs isan excess risk of lung cancer.

Short-term health effects (acute): The impact of PAHs on human health depend mainly on the length and route of exposure, the amount or concentration of PAHs one is exposed to, as well as the relative toxicity of the PAHs. Occupational exposures to high levels of pollutant mixtures containing PAHs have resulted in symptoms such as eye irritation, nausea, vomiting, diarrhoea and confusion. Nevertheless, it is not
known which components of the mixture were responsible for these effects and other compounds commonly found with PAHs may be the cause of these symptoms. Mixtures of PAHs are also known to cause skin irritation and inflammation. Anthracene, benzopyrene and naphthalene are direct skin irritants. But, anthracene and benzopyrene are reported to be skin sensitizers, i.e. cause an allergic reaction in skin in animals and humans.

Long-term health effects (chronic): Health effects from long-term or chronic exposure to PAHsmay include decreased immune function, cataracts, kidneyand liver damage (e.g. jaundice), and breathing problems,asthma-like symptoms, and lung function abnormalities.Meanwhile, repeated contact with skin may induce rednessand skin inflammation. Naphthalene, a specific PAH, can cause the breakdown of red blood cells if inhaled or ingestedin large amounts. If Man is exposed to PAHs, the harmfuleffects that may occur largely depend on the way of exposure.

Carcinogenicity: Although unmetabolized PAHs can have toxic effects, amajor concern is the ability of the reactive metabolites, suchas epoxides and dihydrodiols, of some PAHs to bind to cellular proteins and DNA. Biochemical disruptions and celldamage occurrence lead to mutations, developmental malformations, tumors, and cancer. Evidence indicates that mixtures of PAHs are carcinogenic to humans. Meanwhile, some PAH-rich mixtures are also classified as carcinogenic to humans. The EPA has classified the following seven PAH compounds: benzoanthracene, benzopyrene, benzofluoranthene, benzofluoranthene, chrysene, dibenzanthracene, and indeno (1,2,3-cd)pyrene as probable human carcinogens.

Effects of PAH on the immune system: It has been reported that the PAHs induce suppress immune reaction in rodents. The precise mechanisms of PAH induced immune-toxicity are still not clear. It was concluded that the immune-suppression may be involved in the mechanisms by which PAH induce cancer. The immune-toxic effects of PAH have been investigated for many years. Whatever the route of exposure, the resulting effects have been considered mostly at the systemic level. Furthermore, it has been reported that some PAH when taken into the diet may induce DNA adducts in the lungs. In addition, translocations from one organ to another may result in ‘‘at distance” effects. It is worth mentioning that most of the immune-toxic effects that are reported for PAH are not Review on polycyclic aromatic hydrocarbons thought to be due to parent compounds but it refers to their reactive epoxide metabolites.

Genotoxicity of PAHs: Geno-toxic 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 geno-toxic by themselves and they need to be metabolised to the diol epoxides which react with DNA, thus inducing geno-toxic damage. Geno-toxicity plays important role in the carcinogenicity process and could be also in some forms of developmental toxicity, PAHs undergo multiple metabolic transformations which may lead to the formation of electrophilic derivatives (e.g. diolepoxides, quinones, conjugated hydroxyalkyl derivatives) capable of covalent interaction with nucleophilic centers of macromolecules. Molecular analysis of p53 mutations in lung cancers of smokers shows a similar prevalence of G > T transversions, possibly
reflecting the contribution of PAH to tobacco smoke carcinogenesis. In addition to base pair substitutions, bulky adducts of PAH to DNA bases can induce frameshift mutations, deletions, S-phase arrest, strand breakage and a variety of chromosomal alterations.

Teratogenicity: Embryotoxic effects of PAHs have been described in experimental animals exposed to PAH such as benzoanthracene, benzopyrene, and naphthalene.Laboratory studies conducted on mice have demonstratedthat ingestion of high levels of benzopyrene during pregnancy resulted in birth defects and decreased body weightin the offspring. It is not known whether these effectscan occur in humans. Nevertheless, it was reported anddemonstratedthat exposure to PAH pollution during pregnancy is related to adverse birth outcomes including lowbirth weight, premature delivery, and heart malformations. High prenatal exposure to PAH is also associated withlower IQ at age three, increased behavior problems at agessix and eight, and childhood asthma. Cord blood ofexposed babies shows DNA damage that has been linkedto cancer.

Conclusion

PAHs enter the environment mainly through the air as a result of industrial and natural thermal processes. Consumers come into contact with PAHs in the form of   contaminated rubber or plastic products and abrasion from rubber products, floorings, or wood preservatives. PAHs are
absorbed via the air, tobacco smoke, and consumption of specific contaminated foodstuffs, such as smoked foods. Many PAHs are carcinogenic, mutagenic, or toxic for reproduction. Due to their chemical and biological stability and their potential for bioaccumulation, they are persistent in the environment and accumulate in organisms. So, its high time to us, to raise awareness about PAHs effects on environment, also we have to less burn fossil fuel until or unless it’s too late.