Abstract

 Trinitrotoluene (TNT) and its degradation products are contaminants of concern typically associated with military activities. The fate of radiolabeled TNT (log Koc = 3.2) in sediments and in benthic invertebrates was examined. TNT spiked to freshwater and marine sediments rapidly transformed to the reduced breakdown products aminodinitrotoluenes (ADNTs) and diaminonitrotoluenes (DANTs) within hours or days. The fraction of the sum radiolabeled molecules or TNT molar-equivalents (S14C-TNT) that corresponds to TNT and quantifiable TNT breakdown products (STNT) in the sediment decreases rapidly with aging and is proportional to the initial spiking concentration. Such a decrease likely occurs because the highly reactive TNT aminated breakdown products covalently bind to organic molecules and become non-detectable by chemical analysis. When TNT-spiked sediment and uncontaminated overlying water are added to beakers, most of the S14C-TNT partitions to the porewater and overlying water rather than remaining associated with the sediment. Therefore, sediment exposures of Chironomus tentans and Leptocheirus plumulosus to TNT and TNT breakdown products were conducted without overlying water renewal. For C. tentans, lethal sediment concentrations were higher for 2,4-DANT than for TNT or 2-ADNT. The fate of TNT in animal tissues is similar to that in sediment, as most of the TNT taken up by invertebrates rapidly transform to ADNTs or DANTs which likely strongly bind to organic molecules becoming non-detectable. Therefore, critical body residues (CBRs) for C. tentans were substantially higher when expressed as S14C-TNT (0.75 µmol/g wet wt.) than when expressed as STNT (0.05 µmol/g). For L. plumulosus, the S14C-TNT CBR was 1.12 µmol/g and STNT were below detection limit (0.005 µmol/g) in the tissues. CBRs determined for C. tentans in water exposures to non-radiolabeled compounds were 0.01 µmol/g for 2-ADNT and 0.04 µmol/g for 2,4-DANT, suggesting that TNT and its major breakdown products act by the same mode of toxic action.