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(02-06) Toxicity and bioaccumulation of TNT and TNT breakdown products in the midge Chironomus tentans in water and sediment exposures. Lotufo, Guilherme*,1, Farrar, John2, Steevens, Jeffery1, Bridges, Todd1, 1 US Army Engineer Research and Development Center EP-R, Vicksburg, MS2 Analytical Services Inc., Vicksburg, MS ABSTRACT- Nitroaromatic explosive compounds were extensively released to the environment at military sites in the U.S. and throughout the world over the last 100 years, resulting in high levels of contamination in surface water, ground water, soils, and sediments. The toxicity of trinitrotoluene (TNT) and its breakdown products trinitrobenzene (TNB), 2-aminodinitrotolune (ADNT) and 2,4-diaminonitrotoluene (DANT) were determined using the freshwater midge Chironomus tentans. In water exposures, the magnitude of the lethal effects of TNT, TNB and ADNT was similar, whereas DANT was substantially less potent. In sediment, transformation and resistance to solvent-extraction following spiking were observed for all compounds, most extensively for TNT and TNB. TNT and ADNT were more potent than TNB and 2,4-DANT. Toxic effects on growth were observed in water but not in sediment exposures. Mixture experiments were performed to investigate the nature of the toxicological interactions of nitroaromatic compounds. The sum toxic unit LC50 approximated 1 in water and sediment experiments, as expected when compounds interact additively. In water exposures, the lethal body residue (LBR) for all compounds ranged from 0.01 to 0.03 mmol/kg wet wt. for all compounds, except for TNB, which was not detected in tissue extracts. The fate of TNT in tissues and its LBR were examined in 4-day water exposures to radiolabeled TNT. A mass balance of the radioactivity in the tissue revealed that only 60% of the radioactivity was removed by acetonitrile extraction and the total concentration of nitroaromatics measured using HPLC, mostly TNT breakdown products, corresponded to only 7% of the concentration of TNT molar-equivalents. Therefore, most of the TNT taken up from the water was biotransformed to compounds that either were undetected by HPLC or conjugated to organic molecules and resisted solvent extraction. The LBR was 1.25 mmol/kg for TNT molar-equivalents but much lower, 0.04 mmol/kg, for sum measured nitroaromatics. The toxicological significance of the unidentified/unextractable fraction remains unknown. Research aiming to characterize the biochemical fate of nitroaromatic compounds in invertebrate tissues is being conducted to allow a better understanding of the mechanisms of toxic action of these highly reactive compounds. Key words: TNT, Bioaccumulation, Chironomus tentans, Sediment |
