Chlorinated polycyclic aromatic hydrocarbon

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Chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs) are a group of compounds comprising polycyclic aromatic hydrocarbons with two or more aromatic rings and one or more chlorine atoms attached to the ring system. Cl-PAHs can be divided into two groups: chloro-substituted PAHs, which have one or more hydrogen atoms substituted by a chlorine atom, and chloro-added Cl-PAHs, which have two or more chlorine atoms added to the molecule. [1] They are products of incomplete combustion of organic materials. They have many congeners, and the occurrences and toxicities of the congeners differ. [2] Cl-PAHs are hydrophobic compounds and their persistence within ecosystems is due to their low water solubility. [3] They are structurally similar to other halogenated hydrocarbons such as polychlorinated dibenzo-p-dioxins (PCDDs), dibenzofurans (PCDFs), and polychlorinated biphenyls (PCBs). Cl-PAHs in the environment are strongly susceptible to the effects of gas/particle partitioning, seasonal sources, and climatic conditions. [4]

Contents

Sources

Chlorinated polycyclic aromatic hydrocarbons are generated by combustion of organic compounds. Cl-PAHs 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 Cl-PAHs reveal that the dominant process of generation is by reaction of PAHs with chlorine in pyrosynthesis. [5] Cl-PAHs 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. [1] 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. [6] In addition, the combustion of polyvinylchloride and plastic wrap made from polyvinylidene chloride result in the production of Cl-PAHs, suggesting that combustion of organic materials including chlorine is a possible source of environmental pollution. [7]

A specific class of Cl-PAHs, polychlorinated naphthalenes (PCNs), are persistent, bioaccumulative, and toxic contaminants that have been reported to occur in a wide variety of environmental and biological matrixes. Cl-PAHs with three to five rings have been reported to occur in air from road tunnels, sediment, snow, and kraft pulp mills. [8]

Recently, the occurrence of particulate Cl-PAHs has been investigated. Results have shown that most particulate Cl-PAH 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 Cl-PAHs dominated in warmer seasons and high molecular weight Cl-PAHs dominated in colder seasons. [4]

Toxicity

Some Cl-PAHs have structural similarities to dioxins, they are suspected of having similar toxicities. [5] These types of compounds are known to be carcinogenic, mutagenic, and teratogenic. Toxicological studies have shown that some Cl-PAHs possess greater mutagenicity, aryl-hydorcarbon receptor activity, and dioxin-like toxicity than the corresponding parent PAHs. [2]

The relative potency of three ring Cl-PAHs was found to increase with increasing degree of chlorination as well as with increasing degree of chlorination. However, the relative potencies of the most toxic Cl-PAHs assessed up to now have been found to be 100,000-fold lower than the relative potency of 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD). [9] Even though Cl-PAHs aren’t as toxic as TCDD, it has been determined using recombinant bacterial cells that the toxicities of exposure to Cl-PAHs based on AhR activity were approximately 30-50 times higher than that of dioxins. [4] Cl-PAHs 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). [10] The AhR-mediated activities of Cl-PAHs have been determined by using yeast assay systems. Aryl Hydrocarbon Receptor (AhR) is a cytosolic, ligand-activated transcription receptor. Cl-PAHs 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. [11]

Several Cl-PAHs have been determined to be AhR-active. One such Cl-PAH, 6-chlorochrysene, has been shown to have a high affinity for the Ah receptor and to be a potent AHH inducer. [12] Therefore, Cl-PAHs may be toxic to humans, and it is important to better understand their behavior in the environment.

Several Cl-PAHs have also been found to exhibit mutagenic activity toward Salmonella typhimurium in the Ames assay. [1]

Related Research Articles

Hydrocarbon Organic compound consisting entirely of hydrogen and carbon

In organic chemistry, a hydrocarbon is an organic compound consisting entirely of hydrogen and carbon. Hydrocarbons are examples of group 14 hydrides. Hydrocarbons from which one hydrogen atom has been removed are functional groups called hydrocarbyls. Hydrocarbons are generally colourless and hydrophobic with only weak odours. Because of their diverse molecular structures, it is difficult to generalize further. Most anthropogenic emissions of hydrocarbons are from the burning of fossil fuels including fuel production and combustion. Natural sources of hydrocarbons such as ethylene, isoprene, and monoterpenes come from the emissions of vegetation.

Polychlorinated biphenyl

A polychlorinated biphenyl (PCB) is an organic chlorine compound with the formula C12H10−xClx. Polychlorinated biphenyls were once widely deployed as dielectric and coolant fluids in electrical apparatus, carbonless copy paper and in heat transfer fluids.

Polychlorinated dibenzodioxins (PCDDs), or simply dioxins, are a group of polyhalogenated organic compounds that are significant environmental pollutants.

Polycyclic aromatic hydrocarbon Hydrocarbon composed of multiple aromatic rings

A polycyclic aromatic hydrocarbon (PAH) is a hydrocarbon—a chemical compound containing only carbon and hydrogen—that is composed of multiple aromatic rings. The group is a major subset of the aromatic hydrocarbons. The simplest of such chemicals are naphthalene, having two aromatic rings, and the three-ring compounds anthracene and phenanthrene. The terms polyaromatic hydrocarbon or polynuclear aromatic hydrocarbon are also used for this concept.

Reductive dechlorination is Chemical reaction of chlorinated organic compounds with reductants. The reaction breaks C-Cl bonds, and releases chloride ions. Many modalities have been implemented, depending on the application. Reductive dechlorination is often applied to remediation of chlorinated pesticides or dry cleaning solvents. It is also used occasionally in the synthesis of organic compounds, e.g. as pharmaceuticals.

Benzo(<i>a</i>)pyrene Chemical compound

Benzo[a]pyrene is a polycyclic aromatic hydrocarbon and the result of incomplete combustion of organic matter at temperatures between 300 °C (572 °F) and 600 °C (1,112 °F). The ubiquitous compound can be found in coal tar, tobacco smoke and many foods, especially grilled meats. The substance with the formula C20H12 is one of the benzopyrenes, formed by a benzene ring fused to pyrene. Its diol epoxide metabolites (more commonly known as BPDE) react and bind to DNA, resulting in mutations and eventually cancer. It is listed as a Group 1 carcinogen by the IARC. In the 18th century a scrotal cancer of chimney sweepers, the chimney sweeps' carcinoma, was already known to be connected to soot.

An organochloride, organochlorine compound, chlorocarbon, or chlorinated hydrocarbon is an organic compound containing at least one covalently bonded atom of chlorine that has an effect on the chemical behavior of the molecule. The chloroalkane class provides common examples. The wide structural variety and divergent chemical properties of organochlorides lead to a broad range of names and applications. Organochlorides are very useful compounds in many applications, but some are of profound environmental concern.

Persistent organic pollutants (POPs), sometimes known as "forever chemicals" are organic compounds that are resistant to environmental degradation through chemical, biological, and photolytic processes. Because of their persistence, POPs bioaccumulate with potential adverse impacts on human health and the environment. The effect of POPs on human and environmental health was discussed, with intention to eliminate or severely restrict their production, by the international community at the Stockholm Convention on Persistent Organic Pollutants in 2001.

Aryl hydrocarbon receptor

The aryl hydrocarbon receptor is a protein that in humans is encoded by the AHR gene. The aryl hydrocarbon receptor is a transcription factor that regulates gene expression. It was originally thought to function primarily as a sensor of xenobiotic chemicals and also as the regulator of enzymes such as cytochrome P450s that metabolize these chemicals. The most notable of these xenobiotic chemicals are aromatic (aryl) hydrocarbons from which the receptor derives its name.

Aryl hydrocarbon receptor nuclear translocator

The ARNT gene encodes the aryl hydrocarbon receptor nuclear translocator protein that forms a complex with ligand-bound aryl hydrocarbon receptor (AhR), and is required for receptor function. The encoded protein has also been identified as the beta subunit of a heterodimeric transcription factor, hypoxia-inducible factor 1 (HIF1). A t(1;12)(q21;p13) translocation, which results in a TEL-ARNT fusion protein, is associated with acute myeloblastic leukemia. Three alternatively spliced variants encoding different isoforms have been described for this gene.

Polychlorinated dibenzofurans

More thorough treatise of all groups with similar actions and binding to aryl hydrocarbon reeceptor is given in Dioxins and dioxin-like compounds.

Dioxins and dioxin-like compounds

Dioxins and dioxin-like compounds (DLCs) are a group of chemical compounds that are persistent environmental pollutants (POPs). Some of them are highly toxic, but the toxicity among them varies 30,000-fold. They are grouped together, because their mechanism of action is the same. They activate aryl hydrocarbon receptor, albeit with very different binding affinities, leading to high differences in toxicity and other effects. They are mostly by-products of burning or various industrial processes - or, in case of dioxin-like PCBs and PBBs, unwanted minor components of intentionally produced mixtures. They include:

Polychloro phenoxy phenol

Polychloro phenoxy phenols are a group of organic polyhalogenated compounds. Among them include triclosan and predioxin which can degrade to produce certains types of dioxins and furans. Notably, however, the particular dioxin formed by degradation of triclosan, 2,8-DCDD, was found to be non-toxic in fish embryos.

Environmental impact of paper

The environmental impact of paper is significant, which has led to changes in industry and behaviour at both business and personal levels. With the use of modern technology such as the printing press and the highly mechanized harvesting of wood, disposable paper became a relatively cheap commodity, which led to a high level of consumption and waste. The rise in global environmental issues such as air and water pollution, climate change, overflowing landfills and clearcutting have all lead to increased government regulations. There is now a trend towards sustainability in the pulp and paper industry as it moves to reduce clear cutting, water use, greenhouse gas emissions, fossil fuel consumption and clean up its impacts on local water supplies and air pollution.

2,3,7,8-Tetrachlorodibenzodioxin

2,3,7,8-Tetrachlorodibenzo-p-dioxin (TCDD) is a polychlorinated dibenzo-p-dioxin with the chemical formula C
12H
4Cl
4O
2. Pure TCDD is a colorless solid with no distinguishable odor at room temperature. It is usually formed as an unwanted product in burning processes of organic materials or as a side product in organic synthesis.

Pentachlorobenzene

Pentachlorobenzene (PeCB) is a chemical compound with the molecular formula C6HCl5 which is a chlorinated aromatic hydrocarbon. It consists of a benzene ring substituted with five chlorine atoms. PeCB was once used industrially for a variety of uses, but because of environmental concerns there are currently no large scale uses of PeCB. Pentachlorobenzene is a known persistent organic pollutant (POP) and banned globally by the Stockholm Convention on Persistent Organic Pollutants in 2009.

Toxic equivalency factor (TEF) expresses the toxicity of dioxins, furans and PCBs in terms of the most toxic form of dioxin, 2,3,7,8-TCDD. The toxicity of the individual congeners may vary by orders of magnitude.

Dibenzopyrenes

Dibenzopyrenes are a group of high molecular weight polycyclic aromatic hydrocarbons with the molecular formula C24H14. There are five isomers of dibenzopyrene which differ by the arrangement of aromatic rings: dibenzo[a,e]pyrene, dibenzo[a,h]pyrene, dibenzo[a,i]pyrene, dibenzo[a,l]pyrene, and dibenzo[e,l]pyrene.

Benzo(<i>c</i>)fluorene Chemical compound

Benzo[c]fluorene is a polycyclic aromatic hydrocarbon (PAH) with mutagenic activity. It is a component of coal tar, cigarette smoke and smog and thought to be a major contributor to its carcinogenic properties. The mutagenicity of benzo[c]fluorene is mainly attributed to formation of metabolites that are reactive and capable of forming DNA adducts. According to the KEGG it is a group 3 carcinogen. Other names for benzo[c]fluorene are 7H-benzo[c]fluorene, 3,4-benzofluorene, and NSC 89264.

Heptachlorodibenzo-<i>p</i>-dioxin

1,2,3,4,6,7,8-Heptachlorodibenzo-para-dioxin (often referred to as 1,2,3,4,6,7,8-HpCDD) is a polychlorinated derivative of dibenzo-p-dioxin and can therefore be categorized as polychlorinated dibenzo-p-dioxin (PCDD), a subclass of dioxins which includes 75 congeners. HpCDD is the dibenzo-p-dioxin which is chlorinated at positions 1, 2, 3, 4, 6, 7, and 8. It is a polycyclic heterocyclic organic compound, since HpCDD contains multiple cyclic structures (two benzene rings connected by a 1,4-dioxin ring) in which two different elements (carbon and oxygen) are members of its rings. HpCDD has molecular formula C12HCl7O2 and is an off-white powder, which is insoluble in water.

References

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  6. ↑ Ma, J.; Horii, Y.; Cheng, J.; Wang, W.; Wu, Q.; Ohura, T.; Kannan, K. (2009). "Chlorinated and Parent Polycyclic Aromatic Hydrocarbons in Environmental Samples from an Electronic Waste Recycling Facility and a Chemical Industrial Complex in China". Environmental Science & Technology. 43 (3): 643–9. Bibcode:2009EnST...43..643M. doi:10.1021/es802878w. PMID   19244996.
  7. ↑ Wang, D.; Xu, X.; Chu, S.; Zhang, D. (2003). "Analysis and structure prediction of chlorinated polycyclic aromatic hydrocarbons released from combustion of polyvinylchloride". Chemosphere. 53 (5): 495–503. Bibcode:2003Chmsp..53..495W. doi:10.1016/S0045-6535(03)00507-1. PMID   12948533.
  8. ↑ Horii, Y.; Ok, G.; Ohura, T.; Kannan, K. (2008). "Occurrence and Profiles of Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons in Waste Incinerators". Environmental Science & Technology. 42 (6): 1904–9. Bibcode:2008EnST...42.1904H. doi:10.1021/es703001f. PMID   18409611.
  9. ↑ Horii, Y.; Khim, J. S.; Higley, E. B.; Giesy, J. P.; Ohura, T.; Kannan, K. (2009). "Relative Potencies of Individual Chlorinated and Brominated Polycyclic Aromatic Hydrocarbons for Induction of Aryl Hydrocarbon Receptor-Mediated Responses". Environmental Science & Technology. 43 (6): 2159. Bibcode:2009EnST...43.2159H. doi:10.1021/es8030402. PMID   19368229.
  10. ↑ Huang, Chao; Xu, Xiong; Wang, Donghong; Ma, Mei; Rao, Kaifeng; Wang, Zijian (2018). "The aryl hydrocarbon receptor (AhR) activity and DNA-damaging effects of chlorinated polycyclic aromatic hydrocarbons (Cl-PAHs)". Chemosphere. 211: 640–647. Bibcode:2018Chmsp.211..640H. doi:10.1016/j.chemosphere.2018.07.087. PMID   30098559.
  11. ↑ Blankenship, A. L.; Kannan, K.; Villalobos, S. A.; Villeneuve, D. L.; Falandysz, J.; Imagawa, T.; Jakobsson, E.; Giesy, J. P. (2000). "Relative Potencies of Individual Polychlorinated Naphthalenes and Halowax Mixtures to Induce Ah Receptor-Mediated Responses". Environmental Science & Technology. 34 (15): 3153. Bibcode:2000EnST...34.3153B. doi:10.1021/es9914339.
  12. ↑ Ohura, T.; Kitazawa, A.; Amagai, T.; Makino, M. (2005). "Occurrence, Profiles, and Photostabilities of Chlorinated Polycyclic Aromatic Hydrocarbons Associated with Particulates in Urban Air". Environmental Science & Technology. 39 (1): 85–91. Bibcode:2005EnST...39...85O. doi:10.1021/es040433s. PMID   15667079.
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