Review of data from several contaminated sediment sites suggested that biota-sediment accumulation factors (BSAFs) declined with increasing contaminant concentrations in the sediment. To evaluate the consistency and possible causes of this behavior, polychlorinated biphenyl (PCB)-contaminated sediment samples from the Hudson, Grasse, and Fox River Superfund sites were used in sediment bioaccumulation tests with the freshwater oligochaete, Lumbriculus variegatus, with PCB concentrations in interstitial water (IW) quantified using polyoxymethylene passive samplers. Measured BSAFs tended to decrease with increasing PCB concentration in sediment, especially for the more highly chlorinated congeners. Measures of partitioning between sediment, IW, and oligochaetes showed that measured sediment-IW partition coefficients (KTOC ) tended to increase slightly with increasing sediment contamination, whereas the ratio of tissue PCB to IW PCB tended to decrease with increasing concentration in IW. Variation in accumulation among sediments was clearly influenced by bioavailability, as reflected by IW measurements, although the specific cause of varying KTOC was not clear. Calculated partitioning between IW and organism lipid (Klipid ) indicated that accumulation was generally 5 to 10-fold higher than would be predicted if Klipid was approximately equal to the n-octanol-water partition coefficient (KOW ). While affirming previous observations of decreasing BSAFs with increasing PCB contamination, the relatively shallow slope of the observed relationship in the current data may suggest that this concentration dependence is not a major uncertainty in sediment risk assessment, particularly if measurements of PCBs in IW are incorporated.

Standard sediment-bioaccumulation test methods specify that Lumbriculus variegatus should not be fed during the 28-day exposure. This lack of feeding can lead to decreases in L. variegatus weight and lipid content during the 28-day exposure period. Differences in intrinsic nutritional content of sediments could lead to additional variability in organism performance and/or contaminant uptake. To evaluate the potential benefits of feeding, sediment-bioaccumulation tests were performed comparing treatments with and without supplemental feeding with tropical fish food and also comparing performance food introduced as blended slurry versus fine flakes. The ration of food provided had to be limited to 6 mg/300-mL beaker with 250 mg of L. variegatus (ww) receiving three feedings per week to maintain acceptable dissolved oxygen (DO) in the test chambers. Relative weight change during exposure varied across sediments in the absence of food from very little change to as much as a 40 % decrease from starting weight. Feeding slurry and flake foods increased the total weight of recovered organisms by 32 and 48 %, respectively, but they did not decrease variability in weight changes across sediments. Lipid contents of the organisms decreased similarly across all feeding treatments during the test. At test termination, lipid contents of L. variegatus across unfed, slurry-fed, and flake-fed treatments were not significantly different per Tukey's honest significant difference test with 95 % family-wise confidence. Feeding resulted in polychlorinated biphenyl residues in L. variegatus being generally slightly less (median 78 %) and slightly greater (median 135 %) than the unfed treatments with slurry and flake formulated foods, respectively.

At contaminated sediment sites, the bioavailability of contaminants in sediments is assessed using sediment-bioaccumulation tests with Lumbriculus variegates (Lv). The testing protocols recommend that ratio of total organic carbon (TOC) in sediment to L. variegatus (dry weight) (TOC/Lv) should be no less than 50:1. Occasionally, this recommendation is not followed, especially with sediments having low TOC, e.g., <1 %. This study evaluated the impacts and resulting biases in the testing results when the recommendation of "no less than 50:1" is not followed. In the study, seven sediments were tested with a series of TOC/Lv ratios that spanned the recommendation. With increasing loading of organisms, growth of the organisms decreased in six of the seven sediments tested. Residues of polychlorinated biphenyls (PCBs) in the L. variegatus were measured in six of the seven sediments tested, and differences in PCB residues among loading ratios across all sediments were small, i.e., ±50 %, from those measured at the minimum recommended ratio of 50:1 TOC/Lv. In all sediment, PCB residues increased with increasing loading of the organisms for the mono-, di-, and tri-chloro-PCBs. For tetra-chloro and heavier PCBs, residues increased with increasing loading of organisms for only two of the six sediments. PCB residues were not significantly different between TOC/Lv loadings of 50:1 and mid-20:1 ratios indicating that equivalent results can be obtained with TOC/Lv ratios into the mid-20:1 ratios. Overall, the testing results suggest that when testing recommendation of 50:1 TOC/Lv is not followed, potential biases in the biota-sediment accumulations factors from the sediment-bioaccumulation test will be small.

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