The role of desorption for describing the bioavailability of select polycyclic aromatic hydrocarbon and polychlorinated biphenyl congeners for seven laboratory-spiked sediments

Lumbriculus variegatus and Diporeia spp. were exposed to two contaminant pairs H-3-benzo[a]pyrene (BaP) and C-14-2,4,5,2'4',5'-hexachlorobiphenyl (HCBP), and H-3-pyrene (PY) and C-14-3,4,3',4'-tetrachlorobiphenyl (TCBP) sorbed to each of seven field-collected sediments of varying composition. Toxicokinetic coefficients, bioaccumulation factors (BAF), and biota-sediment accumulation factors ([BSAF], BAF normalized to the organism lipid content and sediment organic carbon content) were determined. The contaminant desorption rates from sediments were measured with a Tenax resin extraction technique. The desorption rate constants for rapid, slow, and very slow contaminant compartments and the fractions of contaminant in each compartment were compared with the toxicokinetic coefficients, BAF and BSAF to describe contaminant behavior across sediments, among compounds, and between species. The best description of the bioavailability was the log BSAF regressed against the fraction rapidly desorbed (F-rapid) across all sediments and compounds for both species, r(2) = 0.67 and 0.66 for L. variegatus and Diporeia, respectively. Use of a calculated fraction desorbed in 6 h or 24 h, which has been suggested as a surrogate for F-rapid, did not produce as predictive a regression because of uneven desorption in a fixed duration for each compound among the sediments. Thus, F-rapid, provided a good surrogate for the bioavailability of the sediment-sorbed contaminant as represented by BSAF across seven sediments and four compounds with predictions within a factor of approximately two of the measured value.