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Sargassum collecting at frontal boundary between two water masses just south of Key West, FL. Surface samples were collected just west of the front (KW-F1), at the front (KW-F2) and just east of the front (KW- F3; August 2013).
Source publication
This limited scope, three year SERDP project involves determining the primary biogeochemical factors that control TNT metabolism by natural microbial assemblages in coastal systems. By correlating standard water quality measurements with degradation rates, we can predict turnover times for energetics released into hydrodynamically similar, UXO-impa...
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Citations
... 38 ■ ASSOCIATED CONTENT * sı Supporting Information and final report to the funding agency, SERDP. 68 This report was prepared as an account of work sponsored by an agency of the United States Government. Neither the United States Government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or usefulness of any information, apparatus product, or process disclosed or represents that its use would not infringe privately owned rights. ...
Munitions compounds (i.e., 2,4,6-trinitrotoluene (TNT), octahy-dro-1,3,5,7-tetranitro-1,3,5,7-tetrazocin (HMX), and hexadydro-1,3,5-trinitro-1,3,5-triazin (RDX), also called energetics) were originally believed to be recalcitrant to microbial biodegradation based on historical groundwater chemical attenuation data and laboratory culture work. More recently, it has been established that natural bacterial assemblages in coastal waters and sediment can rapidly metabolize these organic nitrogen sources and even incorporate their carbon and nitrogen into bacterial biomass. Here, we report on the capacity of natural microbial assemblages in three coastal North Carolina (United States) estuaries to metabolize energetics and phenanthrene (PHE), a proxy for terrestrial aromatic compounds. Microbial assemblages generally had the highest ecosystem capacity (mass of the compound mineralized per average estuarine residence time) for HMX (21–5463 kg) > RDX (1.4–5821 kg) ≫ PHE (0.29–660 kg) > TNT (0.25–451 kg). Increasing antecedent precipitation tended to decrease the ecosystem capacity to mineralize TNT in the Newport River Estuary, and PHE and TNT mineralization were often highest with increasing salinity. There was some evidence from the New River Estuary that increased N-demand (due to a phytoplankton bloom) is associated with increased energetic mineralization rates. Using this type of analysis to determine the ecosystem capacity to metabolize energetics can explain why these compounds are rarely detected in seawater and marine sediment, despite the known presence of unexploded ordnance or recent use in military training exercises. Overall, measuring the ecosystem capacity may help predict the effects of climate change (warming and altered precipitation patterns) and other perturbations on exotic compound fate and transport within ecosystems and provide critical information for managers and decision-makers to develop management strategies based on these changes.
... Degradation experiments using seawater from the North Sea also showed slow mineralization rates, with half-life on the order of 5 years (Harrison and Vane, 2010). In contrast, TNT, RDX, and HMX degradation in some coastal waters, especially fresh-saline mixing zones, may occur much more rapidly, on the order of days to weeks (Montgomery et al., 2014). Degradation rates in sediments tend to be faster than those in water (Harrison and Vane, 2010). ...
... RDX and HMX mineralization rates were approximately five-fold lower than those for TNT. In a similar study, RDX and HMX mineralization was observed in water and sediments from sites in Florida (USA), with rates comparable to TNT (Montgomery et al., 2014). ...
Coastal marine environments are contaminated globally with a vast quantity of unexploded ordnance and munitions from intentional disposal. These munitions contain organic explosive compounds as well as a variety of metals, and represent point sources of chemical pollution to marine waters. Most underwater munitions originate from World Wars at the beginning of the twentieth century, and metal munitions housings have been impacted by extensive corrosion over the course of the following decades. As a result, the risk of munitions-related contaminant release to the water column is increasing. The behavior of munitions compounds is well-characterized in terrestrial systems and groundwater, but is only poorly understood in marine systems. Organic explosive compounds, primarily nitroaromatics and nitramines, can be degraded or transformed by a variety of biotic and abiotic mechanisms. These reaction products exhibit a range in biogeochemical characteristics such as sorption by particles and sediments, and variable environmental behavior as a result. The reaction products often exhibit increased toxicity to biological receptors and geochemical controls like sorption can limit this exposure. Environmental samples typically show low concentrations of munitions compounds in water and sediments (on the order of ng/L and μg/kg, respectively), and ecological risk appears generally low. Nonetheless, recent work demonstrates the possibility of sub-lethal genetic and metabolic effects. This review evaluates the state of knowledge on the occurrence, fate, and effect of munition-related chemical contaminants in the marine environment. There remain a number of knowledge gaps that limit our understanding of munitions-related contaminant spread and effect, and the need for additional work is made all the more urgent by increasing risk of release to the environment.
