The bioavailability of 38 individual polycyclic aromatic hydrocarbon (PAH) compounds was determined through calculation of biota-sediment-accumulation factors (BSAF). BSAF values were calculated from individual PAH concentrations in freshwater mussel, marine clam, and sediment obtained from field and laboratory bioaccumulation studies. Sediment that was amended with different types of soot carbon (SC) was used in some of the bioaccumulation experiments. BSAF values for petrogenic PAH were greater than those for pyrogenic PAH (e.g., 1.57 +/- 0.53 vs 0.25 +/- 0.23, respectively), indicating that petrogenic PAH are more bioavailable than pyrogenic PAH (p < 0.05). This trend was consistent among marine and freshwater sites. Increased SC content of sediment resulted in a linear decrease in the bioavailability of pyrogenic PAHs (r2 = 0.85). The effect of increasing SC content on petrogenic PAH was negligible. SC was considered as an additional sorptive phase when calculating BSAF values, and using PAH-SC partition coefficients from the literature, we obtained unreasonably large BSAF values for all petrogenic PAH and some pyrogenic PAH. This led us to conclude that a quantitative model to assess bioavailability through a combination of organic carbon and soot carbon sorption is not applicable among field sites with a wide range of soot carbon fractions and PAH sources, at least given our current knowledge of PAH-SC partitioning. Our data offer evidence that many factors including analysis of a full suite of PAH analytes, PAH hydrophobicity, sediment organic carbon content, sediment soot carbon content, and PAH source are importantto adequately assess PAH bioavailability in the environment.

Elimination rate constants (k2), biological half-lives (t(1/2)), and the time required to reach 95% of steady-state (t95) are reported for 46 individual polycyclic aromatic hydrocarbons (PAHs) including both parent and alkyl homologues, for the freshwater unionid mussel, Elliptio complanata. Elimination rate constants generally follow first-order kinetics and range from 0.04/day (d) for perylene to 0.26/d for 2,6-dimethylnapthalene, half-lives range from 2.6 to 16.5 d, and t95 values range from 11.3 to 71.3 d. These values compare well with other k2, t(1/2), and t95 values reported in the literature for PAHs and other classes of hydrophobic organic contaminants. A linear regression of k2 versus log Kow demonstrates dependence of PAH elimination on hydrophobicity, as measured by an r2 value of 0.83, and produces the following regression equation: k2 = -0.06 (log Kow) + 0.44. This study provides evidence that mussels experiencing different forms of physiological stress (e.g., handling stress and fungal or bacterial growth) can exhibit large variation in toxicokinetic parameters. These results are particularly relevant to the extrapolation of laboratory results to field situations.

Effective solubility (Es) is the maximum dissolved concentration of a compound at equilibrium between an aqueous and organic phase. Published evaluations of crudeoils suggest that the Es of only the most soluble aromatic compounds exceeds healthbased drinking water goals. But because Es is a function of the concentration of a compound in the oil phase, it changes with weathering. The objective of this study was to evaluate weathering's impacts on the Es of aromatic hydrocarbon compounds. The Es of 20 aromatic hydrocarbons was calculated for Ecuadorian crude oil and 734 oiled soil samples collected in Ecuador. For the crude oil, the Es of mono-aromatic compounds exceeded health-based drinking water goals, while there were no exceedances for any polycyclic aromatic hydrocarbon (PAH). For the soil, the Es of benzene exceeded the health-based drinking water goal in nine (1.2 percent) of the 734 samples. There were no other exceedances. To further evaluate the impact of weathering, two concepts are introduced.The weathering index describes the extent of weathering of the bulk oil phase, while the concentrating factor is the relative change in concentration, and hence Es, of individual compounds. The weathering index and concentrating factor were calculated for 107 soil samples. The weathering index evaluation indicated that the oil associated with the soil was highly weathered. This reduced the Es of the mono-aromatic compounds because they were depleted to a greater extent than the bulk oil. Although the concentrating factor of some PAHs was as high as 256, their Es was still well below health-based drinking water goals. These results indicate that because of rapid weathering of the more soluble aromatics and the low effective solubility of larger PAHs, Ecuadorian crude oil impacted soil is unlikely to result in dissolved concentrations that exceed health-based drinking water goals.

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