Sediment characteristics affecting desorption kinetics of select PAH and PCB congeners for seven laboratory spiked...

Measures of desorption are currently considered important as potential surrogates for bioaccumulation as measures of the bioavailability of sediment-sorbed contaminants. This study determined desorption rates of four laboratory spiked compounds, benzo[a]pyrene (BaP), 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP), 3,4,3',4'-tetrachlorobiphenyl (TCBP), and pyrene (PY), to evaluate the effect of sediment characteristics. The compounds were sorbed onto seven sediments with a broad range of characteristics. Desorption was measured by Tenax-TA extraction from aqueous sediment suspensions. Desorption rates were modeled using an empirical three compartment model describing operationally defined rapid, slow, and very slow compartments. The sediments were characterized for plant pigments, organic carbon (OC), total nitrogen (TN), lipids, NaOH extractable residue, lignin, amino acids, soot carbon, and particle size fractions. Desorption from the rapid compartment for each of the planar compounds BaP, PY, and TCBP was significantly correlated to sediment characteristics that could be considered to represent younger (i.e., less diagenetically altered) organic matter, e.g., plant pigment, lipid, and lignin contents. However, for these compounds there were no significant correlations between desorption and OC, TN, soot carbon, or amino acid contents. HCBP desorption was different from the three planar molecules. For HCBP, the flux from the rapid compartment was negatively correlated (0.1 > p > 0.05) with the OC content of the sediment. Overall, HCBP desorption was dominated by the amount of OC and the particle size distribution of the sediments, while desorption of the planar compounds was dominated more by the compositional aspects of the organic matter.