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GEOCHEMISTRY OF PAHS IN AQUATIC ENVIRONMENTS: A SYNTHESIS OF DISTRIBUTION, SOURCE, PERSISTENCE, PARTITIONING AND BIOAVAILABILITY
Citation:
Burgess, R M., M. J. Ahrens, AND C. W. Hickey. GEOCHEMISTRY OF PAHS IN AQUATIC ENVIRONMENTS: A SYNTHESIS OF DISTRIBUTION, SOURCE, PERSISTENCE, PARTITIONING AND BIOAVAILABILITY. Chapter 3, P.E.T. Douben (ed.), PAHs: An Ecological Perspective. John Wiley & Sons, Ltd., Chichester, Uk, , 36-45, (2003).
Description:
On the basis of their distributions, sources, persistence, partitioning and bioavailability, polycyclic aromatic hydrocarbons (PAHs) are a unique class of persistent organic pollutants (POPs) contaminating the aquatic environment. They are of particular interest to geochemists and environmental toxicologists for several reasons. First, PAHs are not released into the environment from a single source of origin, as are most industrial, petro- or agricultural chemicals. Rather, PAHs are formed in at least three ways: pyrogenically, petrogenically and diagenetically. Second, when released, PAHs are not in a relatively pure chemical form like most other human-produced organic pollutants entering the environment, e.g. pyrogenic PAHs are frequently associated with soot carbon formed during the combustion process of fossil fuels. Furthermore, petrogenic PAHs in petroleum escape into the environment in complex mixtures of thousands of aromatic and aliphatic compounds. These differences greatly affect their persistence and bioavailability) (see Chapter 6 for persistence and Chapter 7 for partitioning and bioavailability). Third, PAHs, unlike many other POPs, are often metabolized by aquatic organisms, thus reducing their persistence in the environment. Fourth, there are thousands of possible PAH structures present in the environment as compared to the relatively limited numbers of other POPs. Finally, unlike many other harmful organic chemicals that have been banned or limited in discharges, PAHs continue to be released into the environment because of their widespread formation during the burning of fossil fuels and escape during petroleum recovery, transport and use. Ongoing utilization of fossil fuels on a global basis guarantees the continued release of PAHs into the environment. PAHs do share some qualities with other POPs. For example, PAHs are hydrophobic and lipophilic, interact strongly with sedimentary organic carbon, are often sparingly soluble in water, commonly have relatively low volatility, and readily bioaccumulate and are toxic to some aquatic organisms.
Several excellent reviews written over the last 30 years have addressed the geochemistry and bioavailability of PAHs in aquatic environments (e.g. Andelman and Suess 1970; Suess 1976; Neff 1979; McElroy et al. 1989; Meador et al. 1995). Therefore, we provide a current synthesis of the factors affecting PAH bioavailability in aquatic environments rather than a comprehensive review of PAH geochemistry. The most critical aspect of this synthesis is an emphasis on the importance of the freely dissolved form of PAH. This form of PAH appears to be readily bioavailable relative to the forms associated with sediments, colloids, soot carbon and other matrices. To understand and estimate the manifestations of PAH, such as bioavailability, toxicity and bioaccumulation, one must know the quantity of freely dissolved PAH that an organism may encounter. Throughout this overview of the processes affecting PAH sources, persistence, distributions, partitioning and bioavailability, we will re-emphasize this salient point.