DDT toxicity and critical body residue in the amphipod Leptocheirus plumulosus in exposures to spiked sediment

The lethal and sublethal toxicity of dichlorodiphenyltrichloroethane (DDT) to the estuarine amphipod Leptocheirus plumulosus was determined using sedi ment spiked with C-14-labeled compound. Juvenile amphipods were exposed to concentrations up to 9.9 nmol/g dry weight (3.5 mug/g). Acute effects on su rvival were determined in a 10-day experiment. Chronic effects on survival, growth, and reproduction were assessed in a 28-day experiment The DDT in t he sediments transformed to dichlorodiphenyldichloroethane (DDD), dichlorod iphenyldichloroethylene (DDE), and polar metabolites during the 14-day sedi ment storage prior to exposing the amphipods. The mixture of DDT and its br eakdown products (tDDT) was comprised mostly of DDT at the beginning of the exposures. DDD was the prevalent compound at termination of the 28-day exp osure. Complete mortality occurred at sediment concentrations of tDDT as lo w as 7 nmol/g (2.3 mug/g) in both acute and chronic experiments. Most of th e mortality appeared to have occurred within the first 4 days of exposure. No sublethal reductions in growth or reproduction were observed in the 28-d ay experiment. In the, 10-day experiment, where amphipods did not receive s upplemental food, growth was significantly increased in DDT treatments wher e survival was not affected. The concentration of tDDT in amphipod tissues was determined at exposure termination. In the 10-day experiment, a mean bo dy residue of 14 nmol/g wet weight was associated with significant mortalit y (30%). Lower critical body residues were observed in the 28-day experimen t, where the median lethal tissue residue (LR50) was 7.6 (6.8-8.4, 95% conf idence interval) nmol/g wet weight. Based on previous studies, the lethal c ritical body residue for L. plumulosus is similar to those determined for f reshwater amphipods and substantially lower than those determined for clado cerans and polychaetes.