WP1 Sediment Quality Assessment
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() Sorption of polycyclic aromatic hydrocarbons to diesel soot.

White, K1, Shea, D1, 1 Department of Environmental and Molecular Toxicology, North Carolina State University, Raleigh, NC, USA

ABSTRACT- Black carbon has been shown to be present in sediment and soils and may significantly decrease availability of polycyclic aromatic hydrocarbons (PAHs). However, sorption of PAHs to black carbon in complex systems is not well understood. In this research, we measured sorption isotherms, using the polyoxymethylene solid phase extraction method, of pyrene-d10 to diesel soot over a wide range of equilibrium concentrations (0.068-15 g/L). Adsorption at low concentrations was linear and decreased at high concentrations (>5 g/L), indicating saturation of sorption sites at higher aqueous concentrations. The measured Freundlich exponent (1/n) was 0.89 (r2 =0.97) and is higher than previously published values of 0.67-0.71. The Freundlich black carbon-water distribution ratio (log KF ) was 5.98 (L/kg) and is consistent with literature values of 6.12-6.24. Measured total native PAH concentrations in our diesel soot (136 mg/kg) were higher than in diesel soot used by others (37 mg/kg) and may have contributed to the differences in Freundlich parameters. The Langmuir model also fit the data well. The maximum site sorption capacity (qmax ) was 0.26 (mg/g) and the Langmuir site sorption affinity was 0.21 (L/g) (r2 =0.99). Soot-water partition coefficients (Ksoot ) were measured for 40 native PAHs including alkylated PAHs and some heterocyclic compounds. Log Ksoot ranged from 3.37-7.55 (L/kg). This research indicates that the contribution of diesel soot to decreases in PAH availability is dependent on the aqueous PAH concentration. At low aqueous concentrations sorption sites on diesel soot are available and high Ksoot values are expected. At high aqueous concentrations lower Ksoot values are expected, increasing the role of other sorbents (i.e. natural organic matter) in PAH availability. This research has important implications on modeling PAH bioavailability and our ability to predict degradation, exposure, and toxicity of PAHs in sediment.

Key words: PAH, black carbon, bioavailability, sorption

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