Anthropogenic PAH

As PAHs are widespread contaminants produced as a result of natural cycles (e.g., forest fires, plant decomposition and petrogenesis), as well as industrial activities, identification of anthropogenic PAHs contaminant sources is a challenge, particularly as atmospheric emissions are subject to long-range atmospheric transportation processes (Lockhart et al., 1992 ... 

It can be seen that there are natural inputs of pyrolytic PAHs to the environment as there are for atmospheric carbon dioxide. However, unlike C02, anthropogenic PAH contributions in contemporary sediments exceed natural inputs. This increase in environmental burden may, therefore, be significant in its effects on organisms. 

In many cases, reported emission factors have been obtained from a relatively small number of measurements, sometimes only one, and are thus not representative. Emission factors from a particular source will depend on the state of maintenance (e.g., for incinerators, how often the chimneys are scrubbed) and any special measures that have been taken to limit the extent of PAH emission. More PAH data than is presently available is therefore needed for > 90% of all anthropogenic PAH sources in order to... 

B[a]P is the representative of PAHs, generally emitted as a result of incomplete combustion of fossil fuels. Anthropogenic PAH emissions are predominant in Europe so that emissions from natural sources (volcanic eruptions, forest and grassland fires) were neglected [31]. Industrial and non-industrial combustion, public... 

Sediments are important compartments for many organic contaminants in the aquatic environment, in particular for hydrophobic POPs such as PAHs and PCBs. Sediments have been recognised as important sinks for these compounds but with the reduction in levels of them in water, the question arises of whether the older highly contaminated sediments will function in the future as secondary sources of the compounds or whether burial by recent, cleaner sediment will prevent exchange with the water phase. This will depend on the strength of turbulence/bioturbation and on anthropogenic influences such as dredging. 

Polycyclic aromatic hydrocarbons (PAHs, sometimes also called polynuclear aromatics, PNA) are a hazardous class of widespread pollutants. The parent structures of the common PAHs are shown in Fig. 4 and the alkylated homologs are generally minor in combustion emissions. PAHs are produced by all natural combustion processes (e.g., wild fires) and from anthropogenic activity such as fossil fuels combustion, biomass burning, chemical manufacturing, petroleum refining, metallurgical processes, coal utilization, tar production, etc. [6,9,15,18, 20,24,131-139]. 

Polycyclic aromatic hydrocarbons (PAHs) polycyclic aromatic hydrocarbons are a suite of compounds comprised of two or more condensed aromatic rings. They are found in many petroleum mixtures, and they are introduced to the enviromnent predominantly through natural and anthropogenic combustion processes. 

Technically PAHs are a contaminant but are generally considered as a serious organic pollutant due to their large anthropogenic source, high toxicity, and lipophilic nature. 

The Pettaquamscutt data are from a sufficiently deep core to allow us to assess the PAH burden prior to 1900. The PAH concentrations are at a low and constant level ( <200 ppb) for the 50 yr previous to the turn of the century. This level may be indicative of PAH from natural combustion processes such as forest fires. Contributions from natural processes appear to be insignificant in areas or periods of high anthropogenic activity. 

There are many more PAHs than the EPA s 16 priority compounds shown in Fig. 1. These include other parent compounds as well as alkylated species. The large number of possible PAHs provides power to elucidate sources of PAHs to the Great Lakes. Because different sources produce different relative amounts of each PAH, the relative concentrations of PAHs in environmental media can be used to identify significant sources back out their contributions to environmental levels. Some compounds that are particularly helpful in the elucidation of sources, or may have both natural and anthropogenic sources are shown in Fig. 2. 

The many natural and anthropogenic sources of PAHs in combination with global transport phenomena result in the worldwide distribution of these compounds. The concentration of PAHs in any given area can vary widely, depending on the level of industrial development and transport processes. In a study of different soils collected from rural and urban areas (not from grossly contaminated locations such as near gas works or refineries) at 49 locations in Wales, UK, Jones et al.21 found a range of PAH contamination from between 0.1 to 55 fig/g soil. 

PAHs enter the environment from both natural and man-made sources, and the anthropogenic point and nonpoint sources are the major sources. The nonpoint sources are diffuse sources disseminated through the air and waterways. In aquatic systems, PAH-enriched particles or floes may settle to the lake s bottom under calm conditions and accumulate in the sediments. Once the PAH-enriched particles have accumulated in the lake s floor, they may undergo a number of changes that are mediated by chemical or microbial activities. As a result, the bound PAHs can be released from the sediment into the water phase. Once they enter the water column, they may also enter phytoplankton. The PAHs in phytoplankton may then bioaccumulate in the food web. This can cause both acute and chronic effects in fish, birds and other mammals that feed on aquatic organisms (Zhang, 1998). 

PAHs in soil can be attributed to natural processes and human activities. Individual PAH concentrations in soils produced by natural processes like vegetation fires and volcanic exhalations have been estimated to be in the range of 1-10pgkg-1. Anthropogenic contribution has greatly affected the soil PAH concentrations. At present, even the lowest... 

Because anthropogenic activities are the main sources of PAHs, the levels of PAHs in soils in urban areas are approximately 2-10 times higher than those in rural areas. An extensive and systematic survey has been undertaken by Tang et al. (2005) to evaluate the PAH contamination of urban soils in Beijing, China. Soil samples were collected from campuses of universities, schools and kindergartens, public squares, fallow land, and roadsides, and were analyzed for 16 PAHs by GC-MS. There was a high variability in the total PAHs (EPAHs) concentrations, ranging from less... 

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