Fate and effects of Composition B in multispecies marine exposures

The vast majority of investigations into the bioavailability and toxicity of explosives to receptors in aquatic environments has focused on deriving toxicity metrics for discrete chemical exposures to single species using pure compounds at relatively high concentrations. This study assessed the environmental fate and potential for biological effects of a common military formulation, Composition B, under more realistic exposure scenarios (e.g., those that more closely simulate a breached artillery round or residual exposure following a low-order detonation). We used a novel approach incorporating multiple species and toxicity endpoints in sediment exposures over a 34-d exposure period. Composition B fragments exposed at the sediment surface rapidly released 2,4,6-trinitrotolune (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) to the overlying water column. In comparison, burial of fragments resulted in dramatically reduced exposure, bioconcentration, and toxicity. The addition of a conservative flow rate to the aquaria also reduced water and tissue concentrations by factors of two to three. Although the exposure system likely represented a worst-case scenario relative to most conditions found in coastal and estuarine environments, overlying water concentrations generally did not approach known toxicity thresholds, while porewater concentrations were sufficiently elevated above toxicity thresholds immediately adjacent to the fragments, limiting hazardous exposure only to very localized scales. Bioconcentration correlated closely with observed toxicity and was either not detectable (buried), or low (exposed), as is expected based on the low hydrophobicities of TNT and RDX.