View source for Chlorinated polycyclic aromatic hydrocarbon

'''Chlorinated polycyclic aromatic hydrocarbons''' ('''ClPAH'''s) are a group of compounds comprising [[polycyclic aromatic hydrocarbon]]s with two or more [[aromatic ring]]s and one or more [[chlorine]] atoms attached to the ring system. ClPAHs can be divided into two groups: chloro-substituted PAHs, which have one or more hydrogen atoms substituted by a chlorine atom, and chloro-added ClPAHs, which have two or more chlorine atoms added to the molecule.<ref name="Nilsson1993">Nilsson, U. L., Oestman, C. E. Chlorinated polycyclic aromatic hydrocarbons: method of analysis and their occurrence in urban air. Environ. Sci. Technol. 1993; 27 (9);1826&ndash;1831. {{doi|10.1021/es00046a010}}</ref> They are products of incomplete combustion of organic materials. They have many [[congener]]s, and the occurrences and toxicities of the congeners differ.<ref name="Kitazawa2006">Kitazawa A., Amagai, T., Ohura, T. Temporal Trends and Relationships of Particulate Chlorinated Polycyclic Aromatic Hydrocarbons and Their Parent Compounds in Urban Air. Environ. Sci. Technol. 2006; 40 (15); 4592&ndash;4598. {{doi|10.1021/es0602703}}</ref> ClPAHs are hydrophobic compounds and their persistence within ecosystems is due to their low water solubility.<ref>Cerniglia, C. E. Biodegradation of polycyclic aromatic hydrocarbons. Biodegradation. 1992; 3; 351&ndash;368.</ref> They are structurally similar to other halogenated hydrocarbons such as [[polychlorinated dibenzo-p-dioxin]]s (PCDDs), [[dibenzofuran]]s (PCDFs), and [[polychlorinated biphenyl]]s (PCBs). ClPAHs in the environment are strongly susceptible to the effects of gas/particle partitioning, seasonal sources, and climatic conditions.<ref name="Ohura2008">Ohura, T., Fujima, S., Amagai, T., Shinomiya, M. Chlorinated Polycyclic Aromatic Hydrocarbons in the Atmosphere: Seasonal Levels, Gas-Particle Partitioning, and Origin. Enviro. Sci. Technol. 2008; 42 (9); 3296&ndash;3302. {{doi|10.1021/es703068n}}</ref>

== Sources of ClPAHs ==

Chlorinated polycyclic aromatic hydrocarbons are generated by [[combustion]] of organic compounds. ClPAHs enter the environment from a multiplicity of sources and tend to persist in soil and in particulate matter in air. Environmental data and emission sources analysis for ClPAHs reveal that the dominant process of generation is by reaction of PAHs with chlorine in pyrosynthesis.<ref name="Ohura2007">Ohura, T. Environmental Behavior, Sources, and Effects of Chlorinated Polycyclic Aromatic Hydrocarbons. The Scientific World. 2007; 7; 372&ndash;380. {{PMID|17334629}}</ref> ClPAHs have commonly been detected in [[tap water]], fly ash from an incineration plant for [[radioactive waste]], emissions from coal combustion and municipal waste incineration, automobile exhaust, snow, and urban air.<ref name="Nilsson1993"/> They have also been detected in electronic wastes, workshop-floor dust, vegetation, and surface soil collected from the vicinity of an electronic waste (e-waste) recycling facility and in surface soil from a chemical industrial complex (comprising a coke-oven plant, a coal-fired power plant, and a [[chlor-alkali plant]]), and agricultural areas in central and eastern China.<ref>Ma, J., Horii, Y., Cheng, J., Wang, W., Wu, Q., Ohura, T., Kannan, K. Chlorinated and Parent Polycyclic Aromatic Hydrocarbons in Environmental Samples from an Electronic Waste Recycling Facility and a Chemical Industrial Complex in China. Enviro. Sci. Technol. 2009; 43 (3); 643&ndash;649. {{doi|10.1021/es802878w}}</ref> In addition, the combustion of [[polyvinylchloride]] and plastic wrap made from [[polyvinylidene chloride]] result in the production of ClPAHs, suggesting that combustion of organic materials including chlorine is a possible source of environmental pollution.<ref>Wang, D., Xu, X., Chu, S., Zhang, D. Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride. Chemosphere. 2003; 53; 495&ndash;503. {{doi|10.1016/S0045-6535(03)00507-1}}</ref>

A specific class of ClPAHs, Polychlorinated naphthalene’s (PCNs), are persistent, bioaccumulative, and toxic contaminants that have been reported to occur in a wide variety of environmental and biological matrixes. ClPAHs with three to five rings have been reported to occur in air from road tunnels, sediment, snow, and kraft pulp mills.<ref>Horii, Y., Ok, G., Ohura, T., Kannan K. Occurrence and Profiles of Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons in Waste Incinerators. Environ. Sci. Technol. 2008; 42 (6); 1904&ndash;1909. {{doi|10.1021/es703001f}}</ref>

Recently, the occurrence of particulate ClPAHs has been investigated. Results have shown that most particulate ClPAH concentration detected in urban air tended to be high in colder seasons and low in warmer seasons. This study also determined through compositional analysis that relatively low molecular weight ClPAHs dominated in warmer seasons and high molecular weight ClPAHs dominated in colder seasons.<ref name="Ohura2008"/>

== Toxicity ==

ClPAHs are hybrids of dioxins and PAHs, they are suspected of having similar [[toxicity|toxicities]].<ref name="Ohura2007"/> These types of compounds are known to be carcinogenic, [[mutagenic]], and teratogenic. Toxicological studies have shown that some ClPAHs possess greater mutagenicity, aryl-hydorcarbon receptor activity, and dioxin-like toxicity than the corresponding parent PAHs.<ref name="Kitazawa2006"/>

The relative potency of three ring ClPAHs was found to increase with increasing degree of chlorination as well as with increasing degree of chlorination. However, the relative potenices of even the most toxic ClPAHs have been found to be 100,000-fold lower than the relative potency of [[2,3,7,8-tetrachlorodibenzo-p-dioxin]] (TCDD).<ref>Horii, Y., Khim, J. S., Higley, E. B., Giesy, J. P., Ohura, T., Kannan K. Relative Potencies of Individual Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons for Induction of Aryl Hydrocarbon Receptor-Mediated Responses. Environ. Sci. Technol. 2009; 43 (6); 2159&ndash;2165. {{doi|10.1021/es8030402}}</ref> Even though ClPAHs aren’t as toxic as TCDD, it has been determined using recombinant bacterial cells that the toxicities of exposure to ClPAHs based on AhR activity were approximately 30-50 times higher than that of dioxins.<ref name="Ohura2008"/> ClPAHs demonstrate a high enough toxicity to be a potential health risk to human populations that come into contact with them.

== DNA interaction ==

One of the well-established mechanisms by which chlorinated polycyclic aromatic hydrocarbons can exert their toxic effects is via the function of the [[aryl hydrocarbon receptor]] (AhR). The AhR-mediated activities of ClPAHs have been determined by using yeast assay systems. Aryl Hydrocarbon Receptor (AhR) is a cytosolic, ligand-activated transcription receptor. ClPAHs have the ability to bind to and activate the AhR. The biological pathway involves translocation of the activated AhR to the nucleus. In the nucleus, the AhR binds with the AhR nuclear translator protein to form a heterodimer. This process leads to transcriptional modulation of genes, causing adverse changes in cellular processes and function.<ref>Blackenship, A. L., Kannan, K., Villalobos, S. A., Villeneuve, Daniel L., Falandysz, J., Imagawa T., Jakobsson, E., Giesy, J. P. Relative Potencies of Individual Polychlorinated Naphthalenes and Halowax Mixtures to Induce Ah Receptor-Mediated Responses. Enviro. Sci. Technol. 2000; 34 (15); 3153&ndash;3158. {{doi|10.1021/es9914339}}</ref>

Several ClPAHs have been determined to be AhR-active. One such ClPAH, 6-chlorochrysene, has been shown to have a high affinity for the Ah receptor and to be a potent AHH inducer.<ref>Ohura, T., Kitazawa A., Amagai T., Makino M. Occurrence, Profiles, and Photostabilities of Chlorinated Polycyclic Aromatic Hydrocarbons Associated with Particulates in Urban Air. Environ. Sci. Technol. 2005; 39 (1); 85&ndash;91. {{doi|10.1021/es040433s}}</ref> Therefore, ClPAHs may be toxic to humans, and it is important to better understand their behavior in the environment.

Several ClPAHs have also been found to exhibit mutagenic activity toward ''Salmonella typhimurium'' in the Ames assay.<ref name="Nilsson1993"/>

== References ==
{{Reflist|2}}

{{DEFAULTSORT:Chlorinated Polycyclic Aromatic Hydrocarbon}}
[[Category:Organochlorides]]
[[Category:Incineration]]
[[Category:Persistent organic pollutants]]
[[Category:2Fix]]