Polycyclic aromatic hydrocarbons case studies

The next eight chapters will be devoted to the ecotoxicology of groups of compounds that have caused concern on account of their real or perceived environmental effects and have been studied both in the laboratory and in the field. These are predominantly compounds produced by humans. However, a few of them, for example, methyl mercury, methyl arsenic, and polycyclic aromatic hydrocarbons (PAHs), are also naturally occurring. In this latter case, there can be difficulty in distinguishing between human and natural sources of harmful chemicals. 

When epidemiological studies form the basis for the risk assessment of a single chemical or even complex mixtures, such as various combustion emissions, it may be stated that in those cases the effects of combined action of chemicals have been incorporated. Examples can, for instance, be found in the updated WHO Air Quality guidelines (WHO 2000). Thus, the guideline value for, e.g., ozone was derived from epidemiological studies of persons exposed to ozone as part of the total mixture of chemicals in polluted ambient air. In addition, the risk estimate for exposure to polycyclic aromatic hydrocarbons was derived from studies on coke-oven workers heavily exposed to benzo[fl]pyrene as a component of a mixture of PAH and possibly many other chemicals at the workplace. Therefore, in some instances the derivation of a tolerable intake for a single compound can be based on studies where the compound was part of a complex chemical mixture. 

Hubert et al. [101] state that accelerated solvent extraction compared to alternatives such as Soxhlet extraction, steam distillation, microwave extraction, ultrasonic extraction and, in some cases, supercritical fluid extraction is an exceptionally effective extraction technique. Hubert et al. [ 101 ] studied the effect of operating variables such as choice of solvent and temperature on the solvent extraction of a range of accelerated persistent organic pollutants in soil, including chlorobenzenes, HCH isomers, DDX, polychlorobiphenyl cogeners and polycyclic aromatic hydrocarbons. Temperatures ofbetween 20 and 180 °C were studied. The optimum extraction conditions use two extraction steps at 80 and 140 °C with static cycles (extraction time 35 minutes) using toluene as a solvent and at a pressure of 15 MPa. 

Soclo, H.H., Garrigues, P.H., Ewald, M., 2000. Origin of polycyclic aromatic hydrocarbons (PAH) in coastal marine sediments Case studies in Cotonou (Benin) and Aquitaine (France) areas. Mar. Pollut. Bull. 40, 387-396. 

International co-operation in the development and application of matrix reference materials case study polycyclic aromatic hydrocarbons (PAH) and total petrol hydrocarbons (TPH) in soil. BERM8, Berlin... 

The last entry of table 1, tetrahexylammonium benzoate, is an example of the use of molten salts as electrolytes. In this particular case, the salt is liquid at room temperature, but it has been reported that tetrabutylammonium nitrate at 150° can be used for polarographic and preparative work 7Sa-> (oxidation of polycyclic aromatic hydrocarbons). The use of molten salts as SSE s is of great interest because of the high conductivities of such media as compared to conventional SSE s and deserves further studies. 

Recently, several nucleophilic reagents have been used to establish the mode of action of the metabolites of polycyclic aromatic hydrocarbons (PAH). Among them, several phosphodiesters have been examined to clarify the possibility of reaction of PAH epoxides with the phosphate groups(P-alkylation) of nucleic acids (22). In this context we have studied the reaction of 3,4-epoxyprecocene II with dibenzyl phosphate under a variety of conditions. In all cases, instead of the formation of phenol or phosphotriesters observed with PAH epoxides, we obtained predominantly dimer XI. This compound was also the main component of the mixtures obtained by reaction of the above precocene epoxide with other acid catalysts, along with dimers XII and XII. Dimer XII was formed almost exclusively by thermal treatment. The structure and configuration for compound XII has been established by spectral and X-ray diffraction analyses (23). 

Phosphorescence was employed to study the dynamics of polycyclic aromatic hydrocarbons with SDS micelles [62]. Equation (25) was applied with the assumption that k i, is negligible. In the case of 1-bromonaphthalene, the val-... 

The final statement from the Swedish study concludes, In the case of key emission species (polycyclic aromatic hydrocarbons, and dibenzodioxins and furans), there is a markedly higher... 

Saber et al. [128] provide a case study that demonstrates the success of CSIA for the analysis of polycyclic aromatic hydrocarbons (PAHs) to determine whether the PAHs in a lakebed sediment could have originated from a former manufactured gas plant site. 

Case study 2 Estimate the residence time of polycyclic aromatic hydrocarbons (PAHs) in the water column of the Mediterranean. In this hypothetical scenario, PAHs sorbed to settling particles are the only removal process. Average water column... 

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