Graduate Thesis Or Dissertation
 

The uptake, transformation, and physiological response of the marine red macroalga Portieria hornemannii to the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT)

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https://ir.library.oregonstate.edu/concern/graduate_thesis_or_dissertations/h989r5664

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  • The capability of the marine red macroalga Portieria hornemannii to remove and detoxify the nitroaromatic explosive 2,4,6-trinitrotoluene (TNT) in a seawater environment was evaluated using an axenic microplantlet suspension culture system. Microplantlets were challenged with TNT dissolved in seawater at concentrations of 1 to 50 mg L-1 in well-mixed photobioreactors under both batch and continuous additions. Photosynthetic activity was monitored by chlorophyll a fluorescence and oxygen evolution rate (OER) to determine the effects of TNT on the microplantlet photosynthetic viability. Microplantlets in 1.1 gFW L-1 suspension effectively removed 100% of TNT from seawater medium at concentrations under 10 mg L-1 within approximately 72 h of exposure. First-order rate constants for TNT uptake were 0.025 to 0.037 L g FW-1 h-1 under both illuminated and dark conditions. Biotransformation products of TNT, 2-ADNT and 4-ADNT, were identified as the immediate transformation products. However, these products only accounted for 29% of initial TNT. A mass balance of 14C-labeled TNT in radioisotope tracer studies however, indicated that over 60% of 14C-label taken up by microplantlets was released back into the liquid medium, primarily in the form of polar and ionic metabolites. Polar metabolites were responsible for a change in liquid medium to a yellow color. These metabolites were tentatively identified by mass spectrometry to be Meisenheimer TNT complex (H-TNT) and tetranitro-hydrazotoluene (TN-HydrazoT) dimerization products. In contrast, only 26% of the 14C-label, primarily as solvent-extactable compounds, accumulated within the biomass tissue. Futhermore, bound residues of TNT metabolites accounted for less than 5% of initial TNT added. Exposure to TNT inhibited photosynthetic activity in microplantlets by a rapid reversible mechanism. The extent of inihibition was dependent on TNT concentration, with higher concentrations causing permanent damage to the photosynthetic apparatus. A flow-recirulation bioreactor was developed to monitor real-time oxygen OER of microplantlets exposed to pulse and continuous additions of TNT. Pulse additions of TNT caused a rapid decrease in oxygen evolution by microplantlets, with the recovery of OER following TNT uptake dependent on the intial concentration. Microplantlets were able to continuously take up and transform TNT during 20 d perfusion additions of 0.35 and 2.5 mg TNT d-1, even though at the higher concentration photosynthesis was significantly suppressed.
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