Mark Ballentine Penny Vlahos Richard W. Smith Christopher Cooper J.K. Bohlke Stephen Fallis Thomas J. Groshens Craig R. Tobias Thivanka Ariyarathna 2019 <p><span>Coastal&nbsp;marine habitats&nbsp;become contaminated with the munitions constituent, Hexahydro-1,3,5-trinitro-1,3,5-trazine (RDX), via military training, weapon testing and leakage of unexploded ordnance. This study used&nbsp;</span>¹⁵<span>N labeled RDX in simulated aquarium-scale coastal marine habitat containing seawater, sediment, and biota to track removal pathways from surface water including&nbsp;sorption&nbsp;onto particulates, degradation to nitroso-triazines and mineralization to&nbsp;dissolved inorganic nitrogen&nbsp;(DIN). The two aquaria received continuous RDX inputs to maintain a steady state concentration (0.4 mg L</span>⁻¹<span>) over 21 days. Time series RDX and nitroso-triazine concentrations in dissolved (surface and porewater) and sorbed phases (sediment and suspended particulates) were analyzed. Distributions of DIN species (ammonium, nitrate + nitrite&nbsp;and dissolved N</span>₂<span>) in sediments and overlying water were also measured along with geochemical variables in the aquaria. Partitioning of RDX and RDX-derived breakdown products onto surface sediment represented 13% of the total added&nbsp;</span>¹⁵<span>N as RDX (</span>¹⁵<span>N-[RDX]) equivalents after 21 days. Measured nitroso-triazines in the aquaria accounted for 6–13% of total added&nbsp;</span>¹⁵<span>N-[RDX].&nbsp;</span>¹⁵<span>N-labeled DIN was found both in the oxic surface water and hypoxic porewaters, showing that RDX mineralization accounted for 34% of the&nbsp;</span>¹⁵<span>N-[RDX] added to the aquaria over 21 days. Labeled&nbsp;ammonium&nbsp;(</span>¹⁵<span>NH</span>₄⁺<span>, found in sediment and overlying water) and nitrate + nitrite (</span>¹⁵<span>NO</span>_X<span>, found in overlying water only) together represented 10% of the total added&nbsp;</span>¹⁵<span>N-[RDX]. The production of&nbsp;</span>¹⁵<span>N labeled N</span>₂<span>(</span>¹⁵<span>N</span>₂<span>), accounted for the largest individual sink during the transformation of the total added&nbsp;</span>¹⁵<span>N-[RDX] (25%). Hypoxic sediment was the most favorable zone for production of N</span>₂<span>, most of which diffused through porous sediments into the water column and escaped to the atmosphere.</span></p> application/pdf 10.1016/j.scitotenv.2018.07.404 en Elsevier Tracing the cycling and fate of the munition, Hexahydro-1,3,5-trinitro-1,3,5-triazine in a simulated sandy coastal marine habitat with a stable isotopic tracer, 15N-[RDX] article