Bioavailability and Toxicity of 2,4,6-Trinitrotoluene in SedimentsEPA Grant Number: U915897
Title: Bioavailability and Toxicity of 2,4,6-Trinitrotoluene in Sediments
Investigators: Conder, Michael J.
Institution: University of North Texas
EPA Project Officer: Cobbs-Green, Gladys M.
Project Period: January 1, 2001 through January 1, 2004
Project Amount: $87,240
RFA: STAR Graduate Fellowships (2001) RFA Text | Recipients Lists
Research Category: Fellowship - Environmental Risk Assessment , Academic Fellowships , Ecological Indicators/Assessment/Restoration
The overall objective of this research project is to study the toxicology and chemistry of the explosive 2,4,6-tritnitrotoluene (TNT) in aquatic sediments. TNT is a prevalent contaminant at many military installations, often accumulating in soils and sediments up to 60-70 percent by weight. Little is known about the bioavailability and ecotoxicity of this compound in aquatic sediments, hampering the ecological risk assessment of sites presumed to be affected by TNT contamination. Simple chemical analyses (such as strong solvent-extractable sediment TNT concentrations) do not relate well to toxicity because they do not attempt to measure the bioavailable fraction of TNT. The specific objective of this research project is to find a biological or chemical measure of TNT availability in sediments that relates well to ecotoxicity.
This research focuses on two methods of TNT exposure analysis: (1) critical body residues (CBRs); and (2) solid phase microextraction fibers (SPMEs). CBRs are organismal toxicant concentrations linked with a toxic endpoint. I plan to investigate the possible link between TNT uptake and reproductive toxicity in sludgeworms (Tubifex tubifex) exposed to TNT-spiked sediments. SPMEs are glass microfibers coated with an organic polymer that absorbs dissolved or weakly bound organic compounds from aqueous matrices.
Data from environmental fate and toxicity studies with TNT revealed that sediment toxicity test procedures required modification to accurately assess sediment TNT toxicity. Key modifications included aging TNT-spiked sediments 8-14 days, basing lethal dose on measured sediment concentrations of the molar sum of TNT and its main nitroaromatic (NA) transformation products (NA), basing sublethal dose on average sediment NA concentrations obtained from integration of sediment NA transformation models, avoiding overlying water exchanges, and minimizing toxicity test durations.
Both CBR and SPME concentrations provided measures of lethal dose independent of exposure scenario (TNT-spiked sediment or TNT-spiked water) for T. tubifex. The median lethal dose (LC50) estimate-based (95% CI) organism concentrations was 172.3 (151.3-196.1) µmol NA/g tissue, wet weight. LC50s estimates (95% CI) based on NA concentrations in sediment and SPMEs were 223 (209-238) µmol NA/g, dry weight and 27.8 (26.0-29.8) µmol NA/mL, respectively. Reproductive effects occurred at slightly lower exposures. Median effective dose (EC50) estimates (95% CI) for Tubifex cocoon production, based on sediment and SPME concentrations, were 118 (114-122) µmol NA/g, dry weight and 21.8 (21.2-22.4) µmol NA/mL, respectively. Bioconcentration experiments with Tubifex revealed that compound hydrophobicity predicted the toxicokinetics and bioconcentration of these compounds from water; however, there was a large discrepancy between the toxicokinetics of absorbed versus metabolically generated aminodinitrotoluenes. A large portion of bioconcentrated, radiolabeled TNT transformation products could not be identified.
In addition to their ability to provide matrix-independent measures of dose, SPME concentrations were more accurate indicators of bioavailable NAs than were sediment concentrations. SPME concentrations were accurate predictors of TNT and NA bioavailability among TNT-spiked water, TNT-spiked sediment, and TNT-spiked, carbon-amended sediment.
Sediment-associated TNT and transformation products are toxic and pose a threat to contaminated aquatic ecosystems. Sites with TNT-contaminated sediments deserve attention, and more research with other species and TNT-contaminated sediments is warranted. The SPME approach should be fully integrated into the ecological risk assessment process, as the results of this research project add to a growing body of research that suggests that SPMEs have a powerful ability to predict bioavailability and toxicity of organic compounds.