PAH
Polycyclic aromatic hydrocarbons (PAHs), are emitted from incomplete combustion of organic (carbonaceous) material, are ubiquitous contaminants in ambient air (Straif et.al, 2013). Atmospheric PAHs are chief contaminants in the urban air because of their carcinogenic and mutagenic properties (Lv et.al, 2016). Polycyclic aromatic hydrocarbons (PAHs) are pervasive contaminants of the human environment, while some PAHs are comparatively potent carcinogens. In the environment, PAHs are subjected to various chemical and photochemical processes, out of which, some result in degradation to less toxic products, while others result in the formation of nitro-substituted compounds which show greater carcinogenicity. As a result, polycyclic hydrocarbons are extensively distributed in the human environment. They commonly occur in the air we breathe, the food we eat, and the water we drink (Neilson, 2013). PAHs consist of two or more fused aromatic rings and are made up of carbon and hydrogen atoms. About 500 different PAHs have been detected in air, but a lot of the measurements focus on benzoapyrene (BaP) as a characteristic of the whole PAH family. Many of the atmospheric PAHs are carcinogenic, and their carcinogenic potential headed to BaP being promoted to a Group 1 known human carcinogen. The United States Environmental Protection Agency (EPA) observe 16 priority PAHs in air due to health concerns: naphthalene, acenaphthylene, acenaphthene, fluorene, anthracene, phenanthrene, fluoranthene, pyrene, chrysene, benza anthracene, benzobfluoranthene, benzok fluoranthene, BaP, indeno1,2,3-cdpyrene, benzog,h,i-perylene, and dibenza,hanthracene (Figure). A number of PAHs (naphthalene, chrysene, benzob fluoranthene, benzokfluoranthene, BaP, dibenza,hanthracene, dibenzoa,epyrene and dibenzoa,lpyrene, and anthanthrene) have been found to be carcinogenic in investigational animals after inhalation or intratracheal ingestion (Straif et.al, 2013). The actual importance of PAH is the role played by high molecular mass PAHs as most of them are carcinogenic and associated with fine aerosol particles. Subsequently, inhalation deposition mainly depends on particle sizes, as these fine particulates which are loaded with PAHs can travel deep into the human respiratory system and lead to direct health impact (Lv et.al, 2016).
Fig: PAH in ambient air
(An asterisk (*) denotes a US EPA priority pollutant. (C) indicates that the compound is carcinogenic by inhalation or intratracheal administration in experimental animals)
Human exposure to PAHs
Humans are also exposed to PAHs via air, water and the contaminated food they consume. Routes of PAHs exposure include ingestion, inhalation, and dermal contact in both occupational as well as non-occupational locations. The foremost route of exposure to PAHs population is from breathing ambient indoor air, eating food containing PAHs, smoking cigarettes, or household activities like incense, dhoop, and mosquito coil burning, etc. PAHs in the atmosphere are often measured for air quality assessment. PAHs are well-known environmental pollutants, therefore it is impossible to avoid exposure to them. (Lawal, 2017)
PAHs may be found in the gas and particulate phases. BaP is the traditional indicator of PAH exposure. Some studies showed that the total PAH exposure is given as BaP toxic equivalency concentrations. (Straif et.al, 2013)
Effect of PAHs exposure
Exposure from various activities and emission of high levels of pollutant mixtures containing PAHs results in eye irritation, nausea, vomiting, and diaorrhea. Mixtures of PAHs in the atmosphere are also well-known to cause skin irritation and inflammation. Some PAHs mixtures like anthracene, benzo(a)pyrene, and naphthalene are direct skin irritants whereas anthracene and benzo(a)pyrene are testified as skin sensitizers in animals and humans. Studies identified BaP and Pyrene as the cause of cancer in laboratory animals. With recurring skin contact to the PAH, naphthalene can result in redness and inflammation of the skin. The long-term exposure to PAHs may raise the risks of cell damage through gene mutation and cardiopulmonary mortality. (Lawal, 2017)
PAH in Air
PAHs are complex hazardous organic compounds that are generated in the atmosphere as byproducts of partial combustion processes. PAHs in the ambient air present in vapor phase which gets adsorb into airborne particulate matter depending on the atmospheric conditions (temperature, relative humidity, etc.), the origin and properties of the aerosol, and the properties of the specific PAH. (Lawal, 2017)
Toxicity, carcinogenicity, and mutagenicity of PAHS
The increasing rate of industrialization is steadily leading to contamination and deterioration of the environment which increases the pollution levels. As PAHs are the major pollutants, the public concern over their deleterious effects has grown rapidly due to the identification of their toxicity, carcinogenicity, and teratogenicity. Benzo(a)pyrene (BaP) possesses the highest carcinogenic potential among the different PAHs. PAHs are widespread in various ecosystems and are pollutants of great concern due to their potential toxicity, mutagenicity, and carcinogenicity. There are , probably 12 carcinogenic PAHs (i.e., phenanthrene (Phe), anthracene (An), fluoranthene (Fluo), pyrene (Pyr), benzaanthracene (BaA), chrysene (Chry), benzobfluoranthene (BbF), benzokfluoranthene (BkF), benzoapyrene (BaP), indeno1,2,3-cdpyrene (Ind), dibenza,hanthracene (Da,hA), and benzog,h,iperylene (Bg,hP); and 7 probable human carcinogens (i.e., benz(a)anthracene, benzo(a)pyrene, benzo(b)fluoranthene, benzo(k) fluoranthene, chrysene, dibenz(ah)anthracene, and indeno(1,2,3-cd) pyrene). (Lawal, 2017)
PAHs are considered to be important, extremely hazardous and priority pollutants which can adversely affect human health as well as the environment. PAHs are ubiquitous environmental pollutants that are potent human mutagens and carcinogens that are toxic to all living organisms. Therefore, human exposure to them is unavoidable. These health effects include confined skin effects, pulmonary and respiratory problems, genetic reproductive and developmental effects, behavioral, neurotoxic, liver toxicity and other organ system effects. PAHs, mainly benzoapyrene, lead to more cancers in humans, predominantly lung cancers, than any other carcinogen. Atmospheric PAHs may cause respiratory problems, impair pulmonary function, asthma in children and cause bronchitis. (Lawal, 2017)
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