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Toxicological responses of red-backed salamanders (Plethodon cinereus) to subchronic soil exposures of 2,4-dinitrotoluene

US Army Center for Health Promotion and Preventive Medicine, Health Effects Research Program, MCHB-TS-THE, Aberdeen Proving Ground, MD 21010-5403, USA.
Environmental Pollution (Impact Factor: 3.9). 06/2007; 147(3):604-8. DOI: 10.1016/j.envpol.2006.10.007
Source: PubMed

ABSTRACT Dinitrotoluenes are used as propellants and in explosives by the military and as such have been found at relatively high concentrations in the soil. To determine whether concentrations of 2,4-dinitrotoluene (2,4-DNT) in soil are toxic to amphibians, 100 red-backed salamanders (Plethodon cinereus) were exposed to either 1500, 800, 200, 75 or 0mg 2,4-DNT/kg soil for 28 days and evaluated for indicators of toxicity. Concentrations of 2,4-DNT were less than targets and varied with time. Most salamanders exposed to concentrations exceeding 1050 mg/kg died or were moribund within the first week. Salamanders exposed to soil concentrations exceeding 345 mg/kg lost >6% of their body mass though no mortality occurred. Overt effects included a reduction in feed consumption and an increase in bucco-pharyngeal oscillations in salamanders. These results suggest that only high soil concentrations of 2,4-DNT have the potential to cause overtly toxic effects in terrestrial salamanders.

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    • "As a result of its extensive use in ordnance and propellant production, 2,4-DNT has been found to contaminate soil at artillery ranges and demilitarization areas and surrounding waste water streams at munitions manufacturing sites leading to its listing on EPA's Contaminate Candidate List (Pontius, 1997). Trinitrotoluene and/or dinitrotoluene (DNT) isomers have been observed to decrease organism weights in birds (Quinn et al., 2007), lizards (McFarland et al., 2012), salamanders (Johnson et al., 2007), rats (Lee et al., 1978; Lent et al., 2012), and mice (Ellis et al., 1979; Hong et al., 1985) along with increasing signs of lethargy in birds (Johnson et al., 2005), lizards (McFarland et al., 2012), and rats (Dilley et al., 1982; Lent et al., 2012; Levine et al., 1984). These observations have been hypothesized to arise via impacts on various components of energy metabolism as observed via transcript expression assays (Deng et al., 2011; Rawat et al., 2010). "
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    ABSTRACT: 2,4-dinitrotoluene (2,4-DNT) is a nitroaromatic used in industrial dyes and explosives manufacturing processes that is found as a contaminant in the environment. Previous studies have implicated antagonism of PPARα signaling as a principal process affected by 2,4-DNT. Here, we test the hypothesis that 2,4-DNT-induced perturbations in PPARα signaling and resultant downstream deficits in energy metabolism, especially from lipids, cause organism-level impacts on exercise endurance. PPAR nuclear activation bioassays demonstrated inhibition of PPARα signaling by 2,4-DNT whereas PPARγ signaling increased. PPARα (-/-) and wild-type (WT) female mice were exposed for 14 days to vehicle or 2,4-DNT (134 mg/kg/day), and performed a forced swim to exhaustion one day after the last dose. 2,4-DNT significantly decreased body weights and swim times in WTs, but effects were significantly mitigated in PPARα (-/-) mice. 2,4-DNT decreased transcript expression for genes downstream in the PPARα signaling pathway, principally genes involved in fatty acid transport. Results indicate that PPARγ signaling increased resulting in enhanced cycling of lipid and carbohydrate substrates into glycolytic/gluconeogenic pathways favoring energy production versus storage in 2,4-DNT-exposed WT and PPARα (-/-) mice. PPARα (-/-) mice appear to have compensated for the loss of PPARα by shifting energy metabolism to PPARα-independent pathways resulting in lower sensitivity to 2,4-DNT when compared to WT mice. Our results validate 2,4-DNT-induced perturbation of PPARα signaling as the molecular initiating event (MIE) for impaired energy metabolism, weight loss and decreased exercise performance.
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    ABSTRACT: Since World War I, trinitrotoluene (TNT) has been the most commonly used explosive. Environmental contamination associated with synthesis, manufacture of weapons, and use during training exercises has been extensive, with soil concentrations reaching 145,000 mg/kg. Some of these areas include habitats for amphibian species. Earlier studies have shown that salamanders dermally absorb TNT from soil. To ascertain what soil concentrations of TNT are toxic to amphibians, red-backed salamanders (Plethodon cinereus) were exposed to one of five concentrations of TNT in soil for 28 d and evaluated for indicators of toxicity. A total of 100 salamanders were randomly sorted by weight and assigned to target TNT concentrations in soil of either 3,000, 1,500, 750, 325, or 0 mg/kg dry weight. Food consisted of uncontaminated flightless Drosophila melanogaster. Survival was reduced in salamanders exposed to 1,500 and 3,000 mg/kg by 10 and 55%, respectively. Most mortality/morbidity occurred within the first week of exposure. Salamanders had a reduction in hemoglobin at 750 mg/kg or greater and a reduction in red blood cell concentration at 1,500 mg/kg or greater. Food consumption was affected in salamanders at 750 mg/kg or greater; a reduction in body mass and liver glycogen content also occurred at and above this concentration. Splenic congestion also was observed in salamanders from these groups. These data suggest that soil TNT concentrations of 373 +/- 41.0 mg/kg or greater result in reduced body mass, reduced feed intake, and hematological effects.
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