Bioconcentration, PAH

PAHs can be bioconcentrated or bioaccumulated by certain aquatic invertebrates low in the food chain that lack the capacity for effective biotransformation (Walker and Livingstone 1992). Mollusks and Daphnia spp. are examples of organisms that readily bioconcentrate PAH. On the other hand, fish and other aquatic vertebrates readily biotransform PAH so, biomagnification does not extend up the food chain as it does in the case of persistent polychlorinated compounds. As noted earlier, P450-based monooxygenases are not well represented in mollusks and many other aquatic invertebrates (see Chapter 4, Section 4.2) so, this observation is not surprising. Oxidation catalyzed by P450 is the principal (perhaps the only) effective mechanism of primary metabolism of PAH. 

PAH bioconcentration factor (BCF) for selected species of aquatic organisms... 

Table 25.6 PAH Bioconcentration Factors (BCF) for Selected Species of Aquatic Organisms...

PAHs are widely distributed in the environment as evidenced by their detection in sediments, soils, air, surface waters, and plant and animal tissues. However, the ecological impact of PAHs is uncertain. PAHs show little tendency for bioconcentration despite their high lipid solubility (Pucknat 1981), probably because most PAHs are rapidly metabolized. Sims and Overcash (1983) list a variety of research needs regarding PAHs in soil-plant systems. Specifically, research is needed to establish the rates of PAH decomposition in soils the soil PAH levels above which PAH constituents adversely affect the food chain and enhancement factors that increase degradation rates of PAHs, especially PAHs with more than three rings. Once these factors have been determined, PAH disposal into soils may become feasible at environmentally nonhazardous levels. 

Eadie, B.J., W.R. Faust, P.F. Landrum, and N.R. Morehead. 1984. Factors affecting bioconcentration of PAH by the dominant benthic organisms of the Great Lakes. Pages 363-377 in M. Cooke and A.J. Dennis (eds.). Polynuclear Aromatic Hydrocarbons Mechanisms, Methods and Metabolism. Battelle Press, Columbus, OH. 

Because PAHs are hydrophobic, they tend to accumulate in lipids of organisms that are unable to metabolize them. There are several partition coefficients that can describe the accumulation of PAHs in organisms. Direct partitioning of aqueous phase PAHs to an organism is described by the bioconcentration factor ... 

High lipid levels in zebra mussels also contribute to their susceptibility to bioaccumulation of hydrophobic organic contaminants including PAHs [132], However, lipid content varies seasonally in zebra mussels and Bruner et al. [136] found that bioconcentration of hydrophobic PAHs such as benz[a]pyrene were higher in high lipid, pre-spawn mussels than in low lipid, post-spawn mussels. On the other hand, the BCF of a less hydrophobic PAH, pyrene, was not affected by lipid content. Lipid content varied from 4 to 20% of the mussel dry mass and BCFs ranged from 1.3 x 104 to 3.5 x 104 for pyrene and from 4.1 x 104 to 8.4 x 104 for benz[a]pyrene. Lipid normalized BCFs ranged from 8.4 x 105 to 1.9 x 106 and from 3.1 x 106 to 4.7 x 106 for pyrene and benz[a]pyrene, respectively. 

The problem of chemical intake via the aquatic food chain is gradually being eliminated by regulatory action to limit or withdraw chemicals that bioconcentrate or are biomagnified in the environment. One alert for this is a log Kow of 3.0 or greater, and this is followed by specific studies on bioconcentration that take into account metabolism and depuration. For example, PAHs could theoretically bioconcentrate in vertebrate tissues but are rapidly metabolized and depurated, so bioconcentration does not occur in practice. 

Eadie BJ, Faust WR, Landrum PF, et al. 1983. Bioconcentrations of PAH by some benthic organisms ofthe Great Lakes. In Cook M, Dennis AJ, eds. Polynuclear aromatic hydrocarbons Formation, metabolism and measurement. Columbus, OH Battelle Press, 437-449. 

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