Abstract-The toxicity and toxicokinetics of radiolabeled DDT and its major degradation products, dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE), were determined for the amphipods Hyalella azteca and Diporeia spp. in water-only static renewal exposures. Comparison of the water and tissue concentrations associated with decreased survival revealed large differences in toxicity among the three compounds. In H. azteca, the ratio of the 10-d LR50 values (median lethal tissue residue) for DDT:DDD:DDE was 1:24:195. In Diporeia spp., the 28-d LR50 for DDT was higher than that for DDD by a factor of six, and DDE did not cause significant mortality even at concentrations approaching the solubility limit. Based on the toxicity data, the hazard from exposure to mixtures of DDT and its degradation products should be evaluated on a toxic-units basis and not as a simple summation of the individual concentrations, which ignores the toxicity of specific compounds. Differences in species sensitivity were also detected. The 10-d LR50 values were higher in Diporeia spp. than in H. azteca by a factor of 40 for DDT and eight for DDD. This difference can be only partly attributed to differences in lipid content between H. azteca (7% dry wt) and Diporeia spp. (24% dry wt). The uptake clearance and elimination rate constants were similar among the various compounds in both species. Uptake clearance was typically fourfold greater for H. azteca than for Diporeia spp., however, and the experimentally measured elimination rate was approximately 30-fold greater in H. azteca than in Diporeia spp. The larger rates of uptake and elimination were attributed to the higher exposure temperature, greater surface area-to-volume ratio, and lower lipid content for H. azteca compared with Diporeia spp. In addition, extensive biotransformation of DDT by H. azteca may have contributed to a more rapid compound elimination.

The toxicity and toxicokinetics of radiolabeled DDT and its major degradation products, dichlorodiphenyldichloroethane (DDD) and dichlorodiphenyldichloroethylene (DDE), were determined for the amphipods Hyalella azteca and Diporeia spp. in water‐only static renewal exposures. Comparison of the water and tissue concentrations associated with decreased survival revealed large differences in toxicity among the three compounds. In H. azteca, the ratio of the 10‐d LR50 values (median lethal tissue residue) for DDT:DDD:DDE was 1:24:195. In Diporeia spp., the 28‐d LR50 for DDT was higher than that for DDD by a factor of six, and DDE did not cause significant mortality even at concentrations approaching the solubility limit. Based on the toxicity data, the hazard from exposure to mixtures of DDT and its degradation products should be evaluated on a toxic‐units basis and not as a simple summation of the individual concentrations, which ignores the toxicity of specific compounds. Differences in species sensitivity were also detected. The 10‐d LR50 values were higher in Diporeia spp. than in H. azteca by a factor of 40 for DDT and eight for DDD. This difference can be only partly attributed to differences in lipid content between H. azteca (7% dry wt) and Diporeia spp. (24% dry wt). The uptake clearance and elimination rate constants were similar among the various compounds in both species. Uptake clearance was typically fourfold greater for H. azteca than for Diporeia spp., however, and the experimentally measured elimination rate was approximately 30‐fold greater in H. azteca than in Diporeia spp. The larger rates of uptake and elimination were attributed to the higher exposure temperature, greater surface area‐to‐volume ratio, and lower lipid content for H. azteca compared with Diporeia spp. In addition, extensive biotransformation of DDT by H. azteca may have contributed to a more rapid compound elimination.

No abstract

The amphipods Hyalella azteca and Diporeia spp. were exposed to sediments dosed with dichlorodiphenyltrichloroethane (DDT), and the toxicity and toxicokinetics were determined. The toxicity was evaluated with the equilibrium partitioning (EqP) and critical body residue approaches. The DDT in the sediments degraded during the equilibration period prior to organism exposure. Thus, the toxicity using EqP pore-water toxic units (TUs) was evaluated for DDT and its degradation product, dichlorodiphenyldichloroethane (DDD), as the ratio of the predicted interstitial water concentration divided by the water-only LC50 values. The sum of TUs (sum(TU)) was assumed to best represent the toxicity of the mixture. For H. azteca, the 10-d LC50 was 0.98 and 0.33 sum(TU) for two experiments. For Diporeia spp., no toxicity was found in the first experiment with up to 3 sum(TU) predicted in the interstitial water. However, in the second experiment, the 28-d LC50 was 0.67 sum(TU). These data suggest that the EqP approach approximately predicts the toxicity for the combination of DDT and DDD in sediment, provided a toxic unit approach is employed. The critical body residue approach also used TUs because DDT is biotransformed by H. azteca and because of the dual exposure to DDT and DDD. Because biotransformation was only determined in the second experiment, the critical body residue approach could only be evaluated for that case. The TUs were calculated as the ratio of the concentration in the live amphipods divided by the respective LR50 (residue concentration required to produce 50% mortality) values. The LR50 was 1.1 sum(TU) for H. azteca for the 10-d exposure and 0.53 for Diporeia spp. after a 28-d exposure. Thus, this approach was also quite successful in predicting the toxicity. The accumulation and loss rates for H. azteca were much greater than for Diporeia spp. Thus, 10-d exposures represent steady-state conditions for H. azteca, while even at 28-d, the Diporeia spp. are not at steady state.

No abstract

Abstract. Lumbriculus variegatus was used as a bioassay organism to examine the impact of the sediment-associated polycyclic aromatic hydrocarbon (PAH) fluoranthene on behavior, reproduction, and toxicokinetics. The number of worms increased between the beginning and end of the experiment at 59 g g Ϫ1 fluoranthene, but at the next higher treatment (108 g g Ϫ1 ) the number of worms found was lower and not different from the control. Worms exposed to 95 g g Ϫ1 also exhibited increased reproduction when fed a yeast-cerophyltrout chow mixture. On a total biomass basis, only the 95 g g Ϫ1 exposure with food exhibited a statistically significant increase over the nonfed control. Evaluation of reproduction at the two highest treatments was compromised by a brief aeration failure 2 days before the end of the experiment. The behavioral responses were followed as changes in biological burial rate (sediment reworking rate) of a 137 Cs-labeled marker layer. The biological burial rate increased toward a plateau as the concentration increased from the control (3.9 g g Ϫ1 dry weight total PAH) to 355 g g Ϫ1 dry weight fluoranthene in sediment. The aeration failure had minimal impact on the determination of reworking rate because all the data for the rate determination were collected prior to the aeration failure. Uptake and elimination rates declined with increasing treatment concentration across the range of fluoranthene concentrations, 59 -355 g g Ϫ1 dry weight sediment. The disconnect between the increasing biological burial rates and the decreasing toxicokinetics rates with increasing exposure concentration demonstrates that the toxicokinetic processes are dominated by uptake and elimination to interstitial water. The bioaccumulation factor (concentration in the organisms on a wet weight basis divided by the concentration in sediment on a dry weight basis) ranged from 0.92 to 1.88 on day 10 and declined to a range of 0.52 to 0.99 on day 28 with the lowest value at the highest dose.

No abstract

The amphipods Hyalella azteca and Diporeia spp. were exposed to sediments dosed with dichlorodiphenyltrichloroethane (DDT), and the toxicity and toxicokinetics were determined. The toxicity was evaluated with the equilibrium partitioning (EqP) and critical body residue approaches. The DDT in the sediments degraded during the equilibration period prior to organism exposure. Thus, the toxicity using EqP pore-water toxic units (TUs) was evaluated for DDT and its degradation product, dichlorodiphenyldichloroethane (DDD), as the ratio of the predicted interstitial water concentration divided by the water-only LC50 values. The sum of TUs (sum(TU)) was assumed to best represent the toxicity of the mixture. For H. azteca, the 10-d LC50 was 0.98 and 0.33 sum(TU) for two experiments. For Diporeia spp., no toxicity was found in the first experiment with up to 3 sum(TU) predicted in the interstitial water. However, in the second experiment, the 28-d LC50 was 0.67 sum(TU). These data suggest that the EqP approach approximately predicts the toxicity for the combination of DDT and DDD in sediment, provided a toxic unit approach is employed. The critical body residue approach also used TUs because DDT is biotransformed by H. azteca and because of the dual exposure to DDT and DDD. Because biotransformation was only determined in the second experiment, the critical body residue approach could only be evaluated for that case. The TUs were calculated as the ratio of the concentration in the live amphipods divided by the respective LR50 (residue concentration required to produce 50% mortality) values. The LR50 was 1.1 sum(TU) for H. azteca for the 10-d exposure and 0.53 for Diporeia spp. after a 28-d exposure. Thus, this approach was also quite successful in predicting the toxicity. The accumulation and loss rates for H. azteca were much greater than for Diporeia spp. Thus, 10-d exposures represent steady-state conditions for H. azteca, while even at 28-d, the Diporeia spp. are not at steady state.