Effect of mercury and Gpi-2 genotype on standard metabolic rate of eastern mosquitofish (Gambusia holbrooki).

Previous studies demonstrated differential mortality among mosquitofish of different Gpi-2 genotypes during acute mercury and arsenate exposures. Mercury-exposed mosquitofish also had Gpi-2 genotype-specific differences in glycolytic and Krebs cycle metabolite pools. The mortality and metabolite data suggested that mosquitofish bearing specific Gpi-2 genotypes might differ in metabolic efficiency, with less efficient Gpi-2 genotypes having higher standard metabolic rates (SMRs) and shorter times to death during acute mercury exposure. Effect of Gpi-2 genotype on SMR was assessed with a factorial arrangement of six Gpi-2 genotypes and two exposure sequences (Control - Control; Control - 100 microg/L Hg). The SMRs were estimated by measuring oxygen consumption using an indirect, closed-circuit, computer-controlled respirometer. A 48-h exposure to 100 microg/L of mercury resulted in a 16.7% elevation of SMR above control levels (p = 0.001). The Gpi-2 genotype and the number of heterozygous loci per individual had no significant effect on SMR in mercury-exposed mosquitofish. The experimental results do not support the hypothesis that Gpi-2 genotype-specific differences in glycolytic and Krebs cycle metabolite pools and mortality in mosquitofish exposed to mercury are associated with differences in SMR.

Using metal-ligand binding characteristics to predict metal toxicity: quantitative ion character-activity relationships (QICARs).

Ecological risk assessment can be enhanced with predictive models for metal toxicity. Modelings of published data were done under the simplifying assumption that intermetal trends in toxicity reflect relative metal-ligand complex stabilities. This idea has been invoked successfully since 1904 but has yet to be applied widely in quantitative ecotoxicology. Intermetal trends in toxicity were successfully modeled with ion characteristics reflecting metal binding to ligands for a wide range of effects. Most models were useful for predictive purposes based on an F-ratio criterion and cross-validation, but anomalous predictions did occur if speciation was ignored. In general, models for metals with the same valence (i.e., divalent metals) were better than those combining mono-, di-, and trivalent metals. The softness parameter (sigma p) and the absolute value of the log of the first hydrolysis constant ([symbol: see text] log KOH [symbol: see text]) were especially useful in model construction. Also, delta E0 contributed substantially to several of the two-variable models. In contrast, quantitative attempts to predict metal interactions in binary mixtures based on metal-ligand complex stabilities were not successful.

Tolerance of the nematode Caenorhabditis elegans to pH, salinity, and hardness in aquatic media.

The toxicity of many chemicals depends on the physical conditions of the test environment, and any change or adjustment made to the tests can alter the results. Therefore it is important to establish the sensitivity of the test organism over a range of test conditions to determine when it is necessary to make adjustment and to what extent. In this study, we established the tolerance range of the nematode Caenorhabditis elegans for pH, salinity and hardness using 24- (without food source) and 96-h (with food source) aquatic toxicity tests. The tests were performed in two media: K-medium and moderately hard reconstituted water (MHRW). C.elegans has high tolerance under these test conditions. In K-medium worms survived a pH range of 3.1 to 11.9 for 24 h and 3.2 to 11.8 for 96 h without significant (p > 0.05) lethality. In MHRW the pH range was 3. 4 to 11.9 for 24 h and 3.4 to 11.7 for 96 h. Salinity tolerance tests were approximated with NaCl and KCl individually. Up to 15.46 g/L NaCl and 11.51 g/L KCl were tolerated by C. elegans in K-medium without significant lethality (p> 0.05). In MHRW higher salt concentrations were tolerated; about 20.5 g/L NaCl and 18.85 g/L KCl did not show any adverse effect compared to control. Hardness tolerance was tested by adding NaHCO3. The nematode could tolerate 0. 236 to 0.246 g/L of NaHCO3. The high tolerance of C. elegans to these test conditions (pH, salinity, and hardness) allows more versatility than other organisms commonly used in aquatic toxicity tests. It also allows the monitoring of effluents and receiving waters from freshwater or estuarine sources without dilution or adjustment.