PAHs, bioaccumulation factors

Another entry point for accumulation of organic in animal tissue and animal food products is direct ingestion of contaminated soil by grazing animals [44]. The compounds of main concern are the halogenated aromatics, including PCBs, organochlorine pesticides, PCDDs and PCDFs, which are resistant to metabolization and tend to accumulate in animal fat. The bioaccumulation factor (the ratio of the concentration of animal tissue or produce to the concentration in the diet) can be as high as 5-6 [43]. Compounds such as PAHs and phthalate esters are readily metabolised and excreted by the animals and thus do not accumulate in animal tissue or products. 

Fig. 6 Log-log plot of estimated bioaccumulation factor vs. octanol-water partition coefficient of PAHs in Lake Erie (data from [137])...

Human exposure to PAHs in the environment today appears to be practically unavoidable. Charcoal grilling of meat (Rivera et al., 1996) and bioaccumulation of PAHs in fish (van der Dost et al., 2003) are two ways by which food may become contaminated with PAHs. Workers involved in the clean-up of hazardous wastes may be at risk from PAH exposure, although smoking is also a factor (Lee et al., 2002). 

Elimination Kinetics. Determination of the rate of elimination is a useful exercise that can be used to calculate the half-life ty and determine the persistence of PAHs in tissue, in addition to modeling steady-state tissue burdens. The balance between uptake and elimination will determine the bioconcentration or bioaccumulation factor, which can be compared to an expected value (for example, see BCFpred in Appendix). Computation of half-life is also a good benchmark for interspecific comparison of the per-... 

Fig. 16. Bioaccumulation factor (normalized to organism lipid and sediment organic carbon) as a function number of aromatic rings in PAHs. Mean and standard error of the mean BAFi c for PAHs consists of 2-6 aromatic rings. Each mean represents several PAHs and sediments (sites = 7 for amphipod = 5 for polychaete). [See Table 1 for PAHs and ring categories.] Polychaete (Armandia brevis) and amphipod (Rhepoxynius abronius) individuals were exposed to Raritan-Hudson estuary (New York) sediments for 10 d. See Appendix for BAFioc definition. (Data from Meador et al. 1995.)...

In summary, a variety of biomarkers in different bivalves have been assessed after acute or subchronic exposure to PAHs. Results are variable and dependable to numerous factors. Toxicity of PAHs to bivalves however is probable, since bioaccumulation in invertebrates soft tissues is significant. 

The presence of organisms in the sediment has been shown to increase PAH concentrations in overlying water, which may be an important factor in assessing bioaccumulation for some species. For example, it has been shown that the presence of a tubiculous polychaete (Nereis virens) can enhance the flux of sediment-sorbed benz[a]anthracene to the water column (McElroy et al. 1990). This increased flux to the water column could elevate tissue concentrations in those animals that take in PAHs through gill membranes by ventilating overlying water. 

Some of the observed patterns of accumulation of PAHs from laboratory and field studies may be explained by the rates of uptake and elimination. These rates can be affected by several environmental and physiological factors hence, care must be taken to define the conditions under which bioaccumulation is observed. A laboratory investigation that compared accumulation of PAHs in oysters Crassostrea virginica) and clams Mercen-aria mercenaria) from field-contaminated sediments found that the oyster accumulated about three times as much PAH as the clam (Bender et al. 1988). For most individual PAHs, the ratios between oyster and clam tissue concentrations were between 1 and 5. The authors found no species differences in uptake clearance k and concluded that the differences in equilibrium BCF values resulted from the higher elimination rate k in the clam for most PAHs, which would lead to lower body burdens for a given... 

Ideally, the best species to use for monitoring bioavailable PAH contamination in the environment would be a polychaete or bivalve species with minimal metabolic capacity for PAHs. It should be noted, however, that even though species with low biotransformation activity may be the best candidates for monitoring PAH bioaccumulation, many factors affecting uptake and elimination, including factors that impair animal health, will influence PAH body burden. This is an important consideration for any study of PAH bioaccumulation in field-collected organisms. 

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