Date of Completion

12-16-2016

Embargo Period

12-16-2017

Keywords

TNT, RDX, Biotransfomation, Marine Ecosystems, Sediments

Major Advisor

Prof. Penny Vlahos

Associate Advisor

Prof. Craig Tobias

Associate Advisor

Prof. Robert Mason

Field of Study

Oceanography

Degree

Doctor of Philosophy

Open Access

Open Access

Abstract

The lack of knowledge on fate and transport of explosive compounds, 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in marine ecosystems limits the ability to predict toxicological impacts and natural attenuation of these suspected carcinogens in contaminated coastal sites. This study focuses on improving our understanding of the sorption and transformation of TNT and RDX in coastal ecosystems by using stable nitrogen isotopes.

Abiotic and biotic bench-top experiments using sediment slurries evaluated sorption kinetics and anaerobic biotransformation. Marine silt showed higher compound-uptake rates (> ~100) than freshwater silt for both compounds though equilibrium partition constants (Kp’s) were on the same order of magnitude. Kp’s of TNT and RDX varied linearly with total organic carbon (TOC) in sediment and were inversely correlated to temperature. TNT was transformed from the slurry water at a faster rate than RDX and accumulation in sediment was higher in the TNT microcosms than for RDX. TNT was mineralized to NOX (NO2- and NO3-) and NH4+ via denitration, and deamination, possibly facilitated by iron and sulfate reducing bacteria. RDX was mineralized anaerobically to NOX, NH4+ and N2 gas via denitration, ring breakdown and denitrification.

Studies were extended to mesocosm scales representing subtidal non-vegetated, subtidal vegetated and intertidal marsh to evaluate the fate and transport of RDX in multi-component, coastal settings at steady state conditions. Time series of dissolved RDX, derivatives and mineralization products (NH4+, NOX, N2 and N2O) in surface water, porewater, and solids were analyzed. Transformation of RDX was enhanced by microbial assemblages and lower redox potentials. Nitroso-derivatives were further converted to N2O (primarily) and N2 (secondarily). Subtidal vegetated and intertidal marsh (TOC-rich, fine grained sediments and sulfate reducers) showed higher mineralization of RDX. Subtidal non-vegetated mesocosm (TOC-poor, sandy sediment and iron reducers) yielded the highest persistence of RDX in the system. Sediment sorption decreased from intertidal marsh > subtidal vegetated >subtidal non-vegetated and was correlated to the available TOC (positively) and grain size (negatively) of the sediment though partitioning of RDX and derivatives onto sediment was a negligible sink for RDX. The greatest predictor of RDX fate was prevailing sediment redox conditions in the ecosystem.

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