Determining Steady-state Tissue Residues for Invertebrates in Contaminated Sediment

Abstract

Risk assessment of contaminated sediments often involves quantification of compounds in tissues via laboratory bioaccumulation exposures of benthic invertebrates. However, the standard 28-day exposure duration may not be adequately long for some compounds to reach steady state, defined as a stable concentration in exposed organisms. Steady-state tissue residues can be estimated using uptake and elimination rate constants. Experiments were conducted using two marine sediments from New York Harbor to assess bioaccumulation of PAHs, PCBs, chlorinated pesticides, dioxins, and Hg by sampling tissue during seven successive time points over an exposure of 56 days for the polychaete worm Nereis virens and 119 days for the clam Macoma nasuta. Exposure time required to attain steady state was organism and compound specific. Generally, N. virens tissues reached steady state more rapidly and accumulated higher contaminant residues. Nereis virens attained apparent steady state within roughly 28 days for PAHs, Hg, and most PCBs, but longer exposure was needed for some dioxins and pesticides. Steady state in M. nasuta was generally attained after 28 days of exposure for most compounds (some times after 100 days). Thus, some 28-day tissue residues may underestimate bioaccumulation and subsequently risk to benthos and higher trophic level organisms. The results of this study allow development of site-specific correction factors for estimating steady-state residues from 28-day exposures.

Novel control and steady‐state correction method for standard 28‐day bioaccumulation tests using Nereis virens

“…For the 28-d HR sediment bioassay completed in the present study, steady-state concentrations predicted by the bioaccumulation model were within 11% of concentrations measured in the worms by the conclusion of the bioassay. Model-predicted results for the long-term 60-d HR sediment bioassay of Kennedy et al [28] were within 2.5% of the concentrations measured in worms at the conclusion of the bioassay. For the Arthur Kill sediment bioassays of Kennedy et al [28], the bioaccumulation model overpredicted PCB 49 concentrations relative to those measured in worms after 60 d of Biota-sediment accumulation factors were calculated for bioassay worms exposed to the contaminated HR sediments and are summarized in Figure 4.…”

“…Model-predicted results for the long-term 60-d HR sediment bioassay of Kennedy et al [28] were within 2.5% of the concentrations measured in worms at the conclusion of the bioassay. For the Arthur Kill sediment bioassays of Kennedy et al [28], the bioaccumulation model overpredicted PCB 49 concentrations relative to those measured in worms after 60 d of Biota-sediment accumulation factors were calculated for bioassay worms exposed to the contaminated HR sediments and are summarized in Figure 4. The BSAF values were calculated using steady-state adjusted polychaete PCB concentrations.…”

“…3. Uptake of PCB congeners 49 and 180 by Nereis virens from Hudson River sediments from the present study (A,B), Hudson River sediments from a longterm bioaccumulation study [28] (C,D), and Arthur Kill sediments from a long-term bioaccumulation study [28] (E,F). Solid, dashed, and dotted lines in each panel represent the bioaccumulation model fit derived using the general whole-body elimination constant (k tot ) versus log K OW relationships for 13 C-PCBs derived from the Hudson River, New York Bight, and Sequim Bay exposures, respectively.…”

“…Monte Carlo simulations were performed to estimate errors associated with congener-specific C Org(SS) estimates. Standard deviations of C Org (28) and C Org(c) were obtained from replicate measurements and assumed to follow log-normal distributions. A relative standard deviation for k tot was derived from the mean residuals established from the predictive relationship between log k tot and log K OW and applied to all congeners.…”

“…The latter assumption was considered valid because the bioassay duration approached or exceeded the estimated t 90 times predicted for the congeners of study ( Table 1). As a validation exercise, the model was also applied to a longer-term sediment bioassay study completed with N. virens and two types of sediments collected from New York Harbor, including the Hudson River materials sampled for the present study [28]. Model simulations were successful in predicting PCB congener bioaccumulation trends observed for worms across the range of experimental data, including the independent data set.…”