A method is described for conducting 14-d in situ sediment bioaccumulation tests with the freshwater oligochaete Lumbriculus variegatus, at the bottom of a slow-flowing river. The in situ test exposure chambers were constructed from cylindrical plastic tubes with flow-through mesh screens and were attached to a wire basket that was weighted to the river bottom at seven sites in the lower Grasse River in New York State, USA. This design was successful in exposing L. variegatus to native sediment and overlying water under field conditions, with adequate organism mass recovery (87 ± 19%). Results compared well with ex situ laboratory bioaccumulation conducted in parallel, expressed in terms of tissue concentration, biota-sediment accumulation factors (BSAFs), and bioaccumulation factors (BAFs). Bioaccumulation of polychlorinated biphenyls (PCBs) in L. variegatus (µg PCB/g wet wt) in laboratory and field tests was found to be within a factor of 2. The small variation between in situ and ex situ may have been caused by differences in water exchange rate under the two exposure scenarios, or other factors affecting organism behavior. Values of BSAF showed a hyperbolic trend with KOW, peaking at BSAF of 7 for congeners with log KOW of 6. Bioaccumulation factors also peaked at a value of 106.5 for congeners with log KOW value of 6 but remained steady around that value for the higher KOW congeners. These observations may reflect under-equilibration or reduced bioavailability of more hydrophobic PCBs in worm tissues or other analytical artifacts. Environ. Toxicol. Chem. 2010;29:2851–2858. © 2010 SETAC
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