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Lumbriculus variegatus and Diporeia spp. were exposed to two contaminant pairs 3H-benzo[a]pyrene (BaP) and 14C-2,4,5,2'4',5'-hexachlorobiphenyl (HCBP), and 3H-pyrene (PY) and 14C-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, r2 = 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.

Polycyclic aromatic hydrocarbons (PAHs) are considered to act additively when exposed as congener mixtures. Additive internal concentrations at the site of toxic action is the basis for recent efforts to establish a sum PAH guideline for sediment-associated PAH toxicity. This study determined the toxicity of several PAH congeners on a body residue basis in Diporeia spp. These values were compared to the previously established LR(50) value for a PAH mixture based on the molar sum of PAH congeners and demonstrated similar LR(50) values for individual PAH. These results support the contention that the PAH act at the same molar concentration whether present as individual compounds or in mixture. Aqueous exposures were conducted for 28 d, and the water was exchanged daily to maintain the exposure concentration. The concentration in the exposures declined by an average of 22% between water exchanges across all compounds, and ranged from 11% to 32%. The toxicokinetics were determined using both time-weighted-average (TWA) and time-variable water concentrations and were not statistically different between the two source functions. Toxicity was determined for both mortality and immobility (failure to swim on prodding) and on both a TWA water concentration and a body residue basis. The LC(50) values ranged from 1757 microg l(-1) for naphthalene after 10 d exposure to 79.1 microg l(-1) for pyrene after 28 d exposure, and the EC(50) ranged from 1587 microg l(-1) for naphthalene after 10 d exposure to 38.2 microg l(-1) for pyrene after 28 d exposure. The LR(50) values for all congeners at all lengths of exposure were essentially constant and averaged 7.5+/-2.6 micromol g(-1), while the ER(50) for immobility averaged 2.6+/-0.6 micromol g(-1). The bioconcentration factor declined with increasing exposure concentration and was driven primarily by a lower uptake rate with increasing dose, while the elimination remained essentially constant for each compound.

Temporal effects on body residues of dichlorodiphenyldichloroethylene (DDE) associated with mortality in the freshwater amphipod Hyalella azteca were evaluated. Toxicokinetics and body residues were determined from water-only exposures that varied from 4 to 28 d, and DDE concentrations ranging from 0.0013 to 0.045 µmol L-1. Uptake and elimination parameters were not affected significantly by the various temporal and concentration treatments. Uptake rate coefficients ranged from 134.3 to 586.7 ml g-1 h-1, and elimination rate coefficients ranged from 0.0011 to 0.0249 h-1. Toxicity metric values included body residue for 50% mortality at a fixed sample time (LR50) and mean lethal residue to produce 50% mortality from individual exposure concentrations (MLR50) for live organisms and dead organisms. A twofold increase occurred in the MLR50 values calculated using live organisms compared to MLR50 values using dead organisms. Toxicity and kinetic data were fit to a damage assessment model that allows for the time course for toxicokinetics and damage repair, demonstrating the time-dependence of body residues to toxicity. The DDE appeared to act through a nonpolar narcosis mode of action for both acute and chronic mortality in H. azteca. Furthermore, the temporal trend in the toxic response using body residue as the dose metric is steep and found to be similar to another chlorinated hydrocarbon, pentachlorobenzene, but was more potent than that found for polycyclic aromatic hydrocarbons (PAHs). [ABSTRACT FROM AUTHOR]

Organic carbon is considered the major variable affecting the bioavailability of non-polar, sediment-associated contaminants. Previously,variation in bioavailability for some Great Lakes sediments comparedto a soil material was nearly a factor of 10 after carbon normalization. Because a soil might not truly represent sedimentary materials sediments and soils were gathered from several locations in the UnitedStates, Canada, and Finland. The accumulation kinetics of the amphipod Diporeia spp. were measured for pyrene, benzo[a]pyrene (BaP), 2,4,2',4'-tetrachlorobiphenyl (TCBP), and 2,4,5,2',4',5'-hexachlorobiphenyl (HCBP) sorbed to sediments and soils. The organic carbon content of the sediments ranged from 0.45--21.2% and 32.2--45.0% for soils. The bioavailability, measured as the uptake clearance (amount of sourcecompartment cleared of contaminant per mass of organism per hour), was controlled by the amount of organic carbon, particularly for the chlorinated biphenyls. However, for polycyclic aromatic hydrocarbons (PAH), bioavailability was controlled more by the organic carbon polarity represented by the carbon/nitrogen ratio of the sediment. PAH bioavailability increased as the ratio increased; thus, the more nonpolar the organic matter, the more available the compound. This polarity did not account for any of the chlorinated biphenyl bioavailability. The amount and type of mineral matrix of the sediment did not influence the bioavailability for either compound class. In addition, the amount of oxygen in the sediment was correlated with the bioavailability for BaP after carbon normalization. [ABSTRACT FROM AUTHOR]

Biota-sediment accumulation factors (BSAF) were calculated for Diporeia spp. and oligochaete worms exposed to polychlorinated biphenyls (PCBs) and polycyclic aromatic hydrocarbons (PAHs) from field-collected sediment. These data were compared to the contaminant fraction extracted from sediment with Tenax resin using a 24 h extraction. A previous laboratory study suggested a linear relationship between log BSAF and the contaminant fraction rapidly desorbed from sediment. However, the BSAF data in our study did not fit this relationship. Better predictive regressions for both PCBs and PAHs were found when the log of the lipid-normalized organism contaminant concentrations were plotted against the log of the Tenax-extracted organic carbon-normalized sediment contaminant concentration. Regression lines for the two species had the same slope, but the Diporeia intercept was 2.3 times larger. When adjusted for a 6 h Tenax extraction, based on a regression between 6 and 24 h Tenax extractions, data from this study and two other studies that included multiple oligochaete species fit a single predictive regression. The exception included some PAHs that fell below the regression line. Thus, a single relationship generally predicted bioaccumulation across sediments, compound classes, oligochaete species, and among laboratories. [ABSTRACT FROM AUTHOR]