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(039) Disappearing Doses: Fate and toxicity of TNT in sediment toxicity tests over time.
Conder, Jason*,1, La Point, Thomas, 1 University of North Texas, Denton, TX, USA
ABSTRACT- Little is understood about the toxicity and bioavailability of TNT and its nitroaromatic degradation products in aquatic sediments. Previous toxicity tests conducted with spiked sediments aged 1 d or less may not represent actual contamination scenarios, as TNT can degrade quickly in laboratory experiments. We conducted an experiment to investigate the environmental fate and changes in bioavailability and toxicity in a TNT-spiked sediment. A natural, uncontaminated sediment was spiked with TNT (440, 1409, or 4403 nmol/g, dw) and aged for 1,8, or 29 d before initiating a 28-d toxicity test with sludgeworms (Tubifex tubifex). Sediment and water concentrations and uptake by solid phase microextraction (SPME) fibers were measured at the beginning and end of each toxicity test. TNT degraded rapidly over the 58-d experiment, with 50% of the initial nominal levels disappearing in 0.4-11.2 d in the water/sediment systems. Total quantifiable nitroaromatics (including TNT) in the system also declined rapidly, with 50% of the initial nominal levels disappearing in 3.6-10.1 d. Lethal toxicity of the sediment also declined with time, as mortality in the sediment initially contaminated with 1409 nmol TNT/g decreased from 100% in the tests with 1-d and 8-d aged sediments to 0% in the 28-d aged sediments. The least contaminated sediment was not lethally toxic after all 3 aging periods and there were no effects on reproduction (cocoon and young production). At the termination of the sublethal sediments of all three toxicity tests, neither worms nor SPMEs contained detectable levels of nitroaromatics. These results suggest that TNT toxicity tests with spiked sediments are too unstable for interpretation using traditional toxicity assessment methods. Traditional interpretation of toxicity tests which require long term (> 2-4 d) and/or low (< 1000 nmol/g) TNT concentrations may severely underestimate toxicity of this compound.
Key words: sediment, explosives, Tubifex tubifex, degradation
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