Time-dependent toxicity of dichlorodiphenyldichloroethylene to Hyalella azteca

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 micromol 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).