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]

• A large amount of 15N derived from RDX was retained in the biota.
• We modeled 15N derived from RDX in coastal marine biota.
• Bioconcentration factors were examined using four different methods.
• The possible fate of 15N derived RDX was examined.

Hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) is globally one of the most commonly used military explosives and environmental contaminant. 15N labeled RDX was added into a mesocosm containing 9 different coastal marine species in a time series experiment to quantify the uptake of RDX and assess the RDX derived 15N retention into biota tissue. The 15N attributed to munitions compounds reached steady state concentrations ranging from 0.04 to 0.67 μg 15N g dw−1, the bulk 15N tissue concentration for all species was 1–2 orders of magnitude higher suggesting a common mechanism or pathway of RDX biotransformation and retention of 15N. A toxicokinetic model was created that described the 15N uptake, elimination, and transformation rates. While modeled uptake rates were within previous published values, elimination rates were several orders of magnitude smaller than previous studies ranging from 0.05 to 0.7 days−1. These small elimination rates were offset by high rates of retention of 15N previously not measured. Bioconcentration factors and related aqueous:organism ratios of compounds and tracer calculated using different tracer and non-tracer methods yielded a broad range of values (0.35–101.6 mL g−1) that were largely method dependent. Despite the method-derived variability, all values were generally low and consistent with little bioaccumulation potential. The use of 15N labeled RDX in this study indicates four possible explanations for the observed distribution of compounds and tracer; each with unique potential implications for possible toxicological impacts in the coastal marine environment.