Assessment of lead uptake in reptilian prey species.

As part of an investigation determining the trophically available fraction of metals in a model terrestrial food web, i.e., invertebrate prey to Western fence lizards (Sceloporus occidentalis), we evaluated the ability of several invertebrate prey to bioaccumulate lead and to form metals-rich granules, which are hypothesized to be non-available to predators. Crickets (Acheta domestica), tenebroid beetle larvae (Tenebrio molitor), and isopods (Porcellio scaber) were selected as model prey organisms. Lack of standard exposure methodologies for these species has presented a barrier to trophic transfer evaluations, as each species has particular requirements that create challenges for designing exposure conditions. We were able to devise exposure conditions for all three species that allow long-term exposure studies. All prey organisms accumulated lead from contaminated food, and for all species the majority of the accumulated Pb was associated with the exoskeleton (>50%), with metals-rich granules accounting for most of the remaining accumulated lead.

Gene expression profiles in fathead minnow exposed to 2,4-DNT: correlation with toxicity in mammals.

Toxicogenomics, the genome-wide analysis of gene expression to study the effect of toxicants, has great potential for use in environmental toxicology. Applied to standard test organisms, it has possible applications in aquatic toxicology as a sensitive monitoring tool to detect the presence of contaminants while providing information on the mechanisms of action of these pollutants. We describe the use of a complementary DNA (cDNA) microarray of the fathead minnow (Pimephales promelas) a standard sentinel organism in aquatic toxicology, to better understand the mechanisms of toxicity of 2,4-dinitrotoluene (2,4-DNT) which is released in the environment through military and industrial use. We have constructed a fathead minnow microarray containing 5000 randomly picked anonymous cDNAs from a whole fish cDNA library. Expression profiles were analyzed in fish exposed to 2,4-DNT for 10 days at three concentrations (11, 22, and 44 microM, respectively) below the measured median lethal concentration (58 microM). Sequence analysis of cDNAs corresponding to differentially expressed genes affected by exposure revealed that lipid metabolism and oxygen transport genes were prominently affected in a dose-specific manner. We measured liver lipids and demonstrate that lipid metabolism is indeed perturbed following exposure. These observations correlate well with available toxicological data on 2,4-DNT. We present possible modes of action of 2,4-DNT toxicity and suggest that fathead minnow cDNA microarrays can be useful to identify mechanisms of toxicity in fish and as a predictive tool for toxicity in mammals.

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.