Tracking the Uptake, Translocation, Cycling, and Metabolism of Munitions Compounds in Coastal Marine Ecosystems Using Stable Isotopic Tracer
The explosives 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) are common munitions constituents. Both compounds and their derivatives are Environmental Protection Agency (EPA) priority pollutants and are persistent in the environment. In addition to legacy contamination at numerous Department of Defense (DoD) facilities, continued use of RDX and TNT in live fire ranges indicates the likelihood that environmental exposure is ongoing. Within the contiguous 48 United States, there are approximately 41 active DoD installations located within the coastal zone. Exposure of marine/estuarine ecosystems at some sites is well documented, while other installations have a high potential for exposure but limited data on RDX or TNT concentrations in marine end members. Coastal habitats are highly productive, nitrogen-limited, and economically valuable ecosystems. Their response to munitions compounds and their effect on munitions cycling, persistence, bioaccumulation, and mineralization are largely unknown.
The objective of this project is to quantify the pathways and rates of RDX and TNT processing in three typical coastal ecotypes: subtidal vegetated, subtidal unvegetated, and intertidal salt marsh. The following technical questions will be addressed: (1) What are the uptake rates of these compounds at the organismal to ecosystem scales, and which ecosystem components are important regulators of processing? (2) What ecosystem components act as zones of storage for munitions compounds versus those that promote metabolism? (3) Do ecosystem characteristics (e.g., mineralization, autotrophy, redox profile, trophic structure) relate to processing or accumulation of munitions compounds? and (4) What is the ecosystem-scale residence time or clearance rate of these compounds?
Stable isotope (15N)-labeled RDX and TNT will be used in a series of whole-ecosystem tracer experiments designed to track the uptake, translocation, cycling, accumulation, and degradation of RDX and TNT in three characteristic coastal marine ecotypes. This novel approach, used previously for tracking inorganic nitrogen on ecosystem scales, will be applied in a sequence of ecosystem mesocosm (ecocosm) experiments and then applied in situ at sites subject to chronic RDX and TNT exposure. Tracking the flow of 15N from the parent compounds into bulk biotic pools and as RDX or TNT compound-specific pools will distinguish between ecosystem compartments that store these compounds versus those that promote metabolism or mineralization. Isotope tracer modeling will be used to quantify specific uptake rates for each organismal pool, total ecosystem clearance rate, and total capacity of the system to assimilate RDX and TNT. Principal Components Analysis will be used to examine covariance between munitions processing and ecosystem characteristics.
This approach will permit quantitative assessment of marine habitats as bioaccumulators or natural attenuators of these munitions compounds. The kinetic uptake and clearance parameters derived from the isotope tracer studies and modeling are well suited for incorporation into fate and transport models used for range assessments. In addition, establishing covariance between munitions processing rates and ecosystem characteristics will help to identify parameters important for optimization of remediation designs and operating conditions. (Anticipated Project Completion - 2015)
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Ballentine, M., T. Ariyarathna, R.W. Smith, C. Cooper, P. Vlahos, S. Fallis, T.J. Groshens, and C. Tobias. In Revision. Biotic Uptake and Retention of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) Derived Nitrogen Measured in Three Simulated Coastal Habitats. Chemosphere.
Ballentine, M., T. Ariyarathna, R.W. Smith, C. Cooper, P. Vlahos, S. Fallis, T.J. Groshens, and C. Tobias. 2016. Uptake and Fate of hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) in Coastal Marine Biota Determined Using a Stable Isotopic Tracer, 15N–[RDX]. Chemosphere, 153:28–38.
Ballentine, M., C. Tobias, P. Vlahos, R.W. Smith, and C. Cooper. 2015. Bioconcentration of TNT and RDX in Coastal Marine Biota. Archives of Environmental Contamination and Toxicology, 68(4):718–728.
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Smith, R.W., C. Tobias, P. Valhos, C. Cooper, M. Ballentine, and T. Ariyarathna. 2015. Mineralization of RDX-Derived Nitrogen to N2 via Denitrification in Coastal Marine Sediments. Environmental Science and Technology, 49(4):2180–2187.
Smith, R.W., P. Vlahos, C. Tobias, M. Ballentine, T. Ariyarathna., and C. Cooper. 2013. Removal Rates of Dissolved Munitions Compounds in Seawater. Chemosphere, 92(8):898–904.