Alfreda B. Gibson

Chronic toxicity of Great Lakes sediments to Daphnia magna: elutriate effects on survival, reproduction and population growth.

Seventeen Great Lakes sediments ranging in degree of expected toxicity were evaluated using a 21 day sediment elutriate bioassay with Daphnia magna. Sediments differed in their effects on survival, age at first reproduction, the number of broods produced and the total number of young produced per adult. Sediments producing low survivorship (50–60%) also had negative effects on reproduction. However, both positive and negative effects on reproduction were found among sediments producing high survivorship. To integrate all test end-points, a stochastic matrix population model was constructed and parameterized with survival and reproduction data from each sediment. By including estimates of variability in vital rates, the model output provided quantitative estimates of uncertainty in projected population size. Sediment effects on survival and reproduction translated into large differences in projected population growth; mean estimates of projected population size at day 28 of the simulations ranged over two orders of magnitude among the 17 sediments. Reproductive timing (e.g. age at first reproduction), followed by fecundity and survivorship, had the largest effect on population growth. Results of this study also indicate that the presence of suspended sediment in elutriates may confound toxicity evaluations using cladocerans. The concentration of total suspended solids was negatively correlated with age at first reproduction and positively correlated with measures of fecundity and population growth. In order to realize the potential benefits of chronic testing we must develop ecologically relevant ways of interpreting sediment bioassay results and expressing the uncertainty associated with our estimates of ecological risk.

Toxicity and bioaccumulation of 2, 4, 6‐trinitrotoluene in fathead minnow (Pimephales promelas)

Few studies have determined the toxicity and bioaccumulation potential of explosive compounds in freshwater fish. In the present study, fathead minnow (Pimephales promelas) were exposed to a range of 2,4,6-trinitrotoluene (TNT) concentrations (0.44-44 micromol/L [0.1-10 mg/L] and 4.4-22.0 micromol/L [1.0-5.0 mg/L] in 4- and 10-d experiments, respectively). Median lethal concentrations of 11.93 micromol/L (2.7 mg/L; 95% confidence limit [CL], 10.29-13.83 micromol/L) and 9.68 micromol/L (2.20 mg/L; 95% CL, 9.17-10.22 micromol/L) were calculated in the 4- and 10-d experiments, respectively, and median lethal body residue of 101.0 micromol/kg (95% CL, 86.0-118.7 micromol/kg) was calculated in 4-d experiments. To study bioaccumulation, fish were exposed to 4.4 micromol/L (1 mg/L) of TNT for 12 h. Rapid bioaccumulation of TNT occurred within the first 10 min of exposure (ku = 30.4 L/kg/ h). Elimination of sigmaTNT (molar sum of TNT and degradation products 2- and 4-aminodinitrotoluenes) was fast, with an elimination rate (ke) of 2.24/h and a short half-life (0.31 h). The bioconcentration factors determined using 6-h mean tissue and water concentrations of sigmaTNT were 8.40 and 4.68 L/kg for the uptake experiment and the uptake portion of the elimination experiments, respectively. To determine the target organ for TNT in fish, juvenile fathead minnow were exposed to 2.2 micromol/L (0.5 mg/L) of [14C]TNT for 10 d. Radiolabeled compounds primarily bioaccumulated in the visceral tissues and spleen in comparison to gill, brain, muscle, and remainder tissue groups. The present study demonstrates the low bioaccumulation potential and rapid uptake of TNT in the fathead minnow.