Pyrene PAHs

Benzo(a)pyrene (PAHs) zero 0.0002 Reproductive difficulties increased risk of cancer Leaching from linings of water storage tanks and distribution lines... 

Benzo(a)- pyrene (PAH) Carcinogenic Mutagenic Teratogenic H Bioaccumulation H L H H... 

Aerobic, Anaerobic, and Combined Systems. The vast majority of in situ bioremediations ate conducted under aerobic conditions because most organics can be degraded aerobically and more rapidly than under anaerobic conditions. Some synthetic chemicals are highly resistant to aerobic biodegradation, such as highly oxidized, chlorinated hydrocarbons and polynuclear aromatic hydrocarbons (PAHs). Examples of such compounds are tetrachloroethylene, TCE, benzo(a)pyrene [50-32-8] PCBs, and pesticides. 

One of the most studied of the polyaromatic hydro-carbone (PAH) is benzo(a)pyrene (BaP), which is present in coal tar at coke oven plants. The BaP content of coal tar is between 0.1% and 1 % and it contributes to the serious potential health effects on employees exposed to coke oven emissions. The largest sources of BaP are open burning and home heating with wood and coal. The latter alone contributes 40 percent of all the BaP released each year in the USA. 

Figure 3 depicts profiles of Total PAH fluxes vs. time (36). The following polycyclic hydrocarbons have been determined by high performance liquid chromatography, variable wavelength absorption detection Naphthalene, acenaphthylene, 7,12-dimethylbenzanthracene, 2-methylnaphtalene, fluorene, acenaphtene, phenanthrene, 2,3-dimethylnaphtalene, anthracene, fluoranthene, 1-methylphenanthrene, pyrene, 2,3-benzofluorene, triphenylene, benz(a)anthracene, chrysene, benzo(b)fluoranthene, benzo(k)fluoranthene, perylene, benzo(e)pyrene, 1,2,3,4-dibenzanthracene, benzo(a)pyrene, and 1,2,5,6-dibenzanthracene. 

Benzo[a]pyrene, a molecule with five, fused, hexagonal rings, is among the most carcinogenic of the polycyclic aromatic hydrocarbons (PAHs). Such biological activity may be related to the electronic structure of benzo[a]pyrene and its metabolites. Ionization energies of these molecules therefore have been investigated with photoelectron spectroscopy [28]. 

The pollutant (xenobiotic) forms a stable covalent bond with its target. Examples include the phosphorylation of cholinesterases by the oxon forms of OPs, the formation of DNA adducts by the reactive epoxides of benzo[a] pyrene and other PAHs, and the binding of organomercury compounds to... 

Benzo[ z]pyrene and other Mutagens and PAHs carcinogens... 

The structures of some PAHs of environmental interest are given in Figure 9.1. Naphthalene is a widely distributed compound consisting of only two fused benzene rings. It is produced commercially for incorporation into mothballs. Many of the compounds with marked genotoxicity contain 3-7 fused aromatic rings. Benzo[a] pyrene is the most closely studied of them, and will be used as an example in the following account. 

PAHs, such as benzo[a]pyrene and 3-methyl cholanthrene, induce P450 lAl/2 (Chapter 2). 

There is evidence for immunosuppressive effects of PAHs in rodents (Davila et al. 1997). For example, strong immunosuppressive effects were reported in mice that had been dosed with benzo[fl]pyrene and 3-methyl cholanthrene, effects that persisted for up to 18 months (Environmental Health Criteria 202). Multiple immu-notoxic effects have been reported in rodents, and there is evidence that these result from disturbance of calcium homeostasis (Davila et al. 1997). PAHs can activate protein tyrosine kinases in T cells that initiate the activation of a form of phospholipase C. Consequently, release of inositol triphosphate—a molecule that immobilizes Ca + from storage pools in the endoplasmic reticulum—is enhanced. 

Turning to the acute toxicity of PAH, terrestrial organisms will be dealt with before considering aquatic organisms, to which somewhat different considerations apply. The acute toxicity of PAHs to mammals is relatively low. Naphthalene, for example, has a mean oral LD50 of 2700 mg/kg to the rat. Similar values have been found with other PAHs. LC50 values of 150 mg/kg and 170-210 mg/kg have been reported, for phenanthrene and fluorene, respectively, in the earthworm. The NOEL level for survival and reproduction in the earthworm was estimated to be 180 mg/ kg dry soil for benzo[a]pyrene, chrysene, and benzoMfluoranthene (Enviromnental Health Criteria 202). 

Two types of reactions are important in the photochemical transformation of PAHs, those with molecnlar oxygen and those involving cyclization. lllnstrative examples are provided by the photooxidation of 7,12-dimethylbenz[a]anthracene (Lee and Harvey 1986) (Fignre 1.14a) and benzo[a]pyrene (Lee-Ruff et al. 1986) (Figure 1.14b), and the cyclization of CM-stilbene (Figure 1.14c). 

Pyrene is a common PAH contaminant and may occur in drinking water. Chlorination of water with or without bromide that may be present in coastal environments has been examined. Both chlorinated and brominated pyrenes with halogen substituents at the 1,3-, 1,6-, and 1,8-positions were found, and could putatively be produced by reaction of pyrene with hypochlorous acid and hypochlorite (Hu et al. 2006). 

The use of subcritical water at 275°C was successful in removing PAHs with two to six rings (including the carcinogenic benzo[a]pyrene) from soil at a contaminated site, and the wastewater that was produced appeared to be suitable for further exploitation (Lagadec et al. 2000). 

Polychaete worms belonging to the genera Nereis and Scolecolepides have extensive metabolic potential. Nereis virens is able to metabolize PCBs (McElroy and Means 1988) and a nnmber of PAHs (McElroy 1990), while N. diversicolor and Scolecolepides viridis are able to metabolize benzo[a]pyrene (Driscoll and McElroy 1996). It is worth noting that apart from excretion of the toxicant, polar, and mnch more water-soluble metabolites such as the glycosides formed from pyrene by Porcellio sp. (Larsen et al. 1998) may be mobile in the interstitial water of the sediment phase. 

---