Polynuclear aromatic compounds carcinogens

Higher-molecular-weight polynuclear aromatics can cause problems during processing of crude. They are known to contribute to deposit formation and fouling of refining equipment and fuel combustion furnaces. Also, some polynuclear aromatic compounds found in crude oil have been determined to be human carcinogens. 

IARC (International Agency for research on cancer). 1985. Polynuclear Aromatic compounds Bituminous, coal tar and derived products, shale oils and soots. Monographs on the Evaluation of the Carcinogenic Risks of Chemicals to Humans, 35 4. 

In classical structure-activity studies, most of the attempts concentrated on correlating the activity with one of the molecular properties— e.g., the carcinogenic activity of polynuclear aromatic compounds with their electronic structure (18, 19), the narcotic activity with lipophilicity 20, 21), the insecticidal activity of cyclodienes with their three-dimensional molecular silhouette 22), etc. Sometimes the activity correlated well with only one of the molecuar parameters. In our approach these are special cases where other physicochemical properties do not play critical roles in determining the variation in the activity within a set of congeners so that the coefficients defining these other properties are zero. 

IARC. 1985. Polynuclear aromatic compounds. Part 4, Bitumens, coal-tars and derived products, shale-oils and soots. IARC monographs on the evaluation of the carcinogenic risk of chemicals to humans. International Agency for Research on Cancer. 35 39-81. 

Most of these polynuclear aromatic compounds are acutely toxic, as well as potentially carcinogenic. To circumvent these obstacles, polymerizable photosensitizers, or their polymers have been used, e.g., 9-(2,3-ep-oxypropyl)carbazole (= A -glycidylcarbazole) or 9-(2-vinyloxyethyl)carb-... 

EP(D)M is not classified as a hazardous material. It is not considered carcinogenic according to OSHA Hazard Communications Standard and lARC Monographs. Commonly used paraffinic extender oils contain less than 0.1 wt% polynuclear aromatic compounds PNAs. 

Coal tar, or pitch, is the black organic resin left over from the distillation of coal. It is nearly waterproof and has been added to epoxy amine and polymide paints to obtain coatings with very low water permeability. It should be noted that coal tar products contain polynuclear aromatic compounds, which are suspected to be carcinogenic. The use of coal tar coatings is therefore restricted or banned in some countries. 

Outside of carbon monoxide for which the toxicity is already well-known, five types of organic chemical compounds capable of being emitted by vehicles will be the focus of our particular attention these are benzene, 1-3 butadiene, formaldehyde, acetaldehyde and polynuclear aromatic hydrocarbons, PNA, taken as a whole. Among the latter, two, like benzo [a] pyrene, are viewed as carcinogens. Benzene is considered here not as a motor fuel component emitted by evaporation, but because of its presence in exhaust gas (see Figure 5.25). 

The fused 3+ ring aromatics in petroleum include both cata- and peri-condensed stmctures (see Table 4, Fig. 8). The cata-condensed species are those stmctures where only one face is shared between rings, the peri-condensed molecules are those that share more than one face. The fused ring aromatics form the class of compounds known as polynuclear aromatic hydrocarbons (PAH) which includes a number of recognized carcinogens in the 4+ ring family (33). Because of the potential health and environmental impact of PAH, these compounds have been studied extensively in petroleum. 

PNA (polynuclear aromatic) any of numerous complex hydrocarbon compounds consisting of three or more benzene rings in a compact molecular arrangement. Some types of PNA s are known to be carcinogenic (cancer causing). 

Many chemicals are metabolized to carcinogens by processes that do not seem to involve free radicals a well-understood example is the oxidation of benzo(a)pyrene [B(a)P] to the diol epoxide by the cytochrome P450 system. However, the oxidation of B(a)P and other polynuclear aromatic hydrocarbons (PAH) to carcinogenic compounds can involve radicals. This statement, while once controversial, now has ample evidence (12.,22,25.). Although it is clear that some products arise from radical-mediated metabolism of PAH, the involvement of these products in tumorigenesis is less clear nevertheless, I believe that such evidence does now exist (12,12). 

The Suzuki cross-coupling reaction is recognized as a novel, abbreviated method for the synthesis of 2-hydroxychrysene, 2-hydroxy-5-methylchrysene, and 8-hydroxy-5-methyl-chrysene from easily accessible reactants (Eq. (8)) [23]. These phenolic compounds constitute precursors for the synthesis of dihydrodiol and bay-region diol epoxide derivatives of chrysene and 5-methylchrysene, which are implicated as the active forms of carcinogenic polynuclear aromatic hydrocarbons. 

In our industrialized society, pollutants are being released into our atmosphere in the form of gases and chemical compounds adsorbed onto tiny particles. For example, one such class of compounds which is of concern is polynuclear aromatic hydrocarbons (PAH) since some of these compounds are reported to be carcinogenic. Three PAHs which can be formed during incomplete combustion have been identified in steel coking operations, automobile exhaust, and cigarette smoke. 

Other studies on coal were performed using pyrolysis, such as the measurement of the level of sulfur containing compounds in coal [27,28], or evaluation of polynuclear aromatic hydrocarbons (PAH) in coal [29]. The generation of PAH in coal pyrolysis is an important issue, as some of these compounds are known to have carcinogenic properties. A list of PAHs identified in coal pyrolysates is given in Table 14.2.2. The yield of PAH in coal pyrolysate depends to some extent on the coal type but mainly on the pyrolysis temperature. The variation of PAH levels as a function of temperature for several bituminous coals is shown in Figure 14.2.3. The yields of other pyrolysis products of coal were also shown to be temperature dependent [30]. 

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