Toxicity and bioconcentration evaluation of RDX and HMX using sheepshead minnows in water exposures

Lethal effects of the explosives RDX and HMX were assessed using ten-day water exposures to juvenile sheepshead minnows ( Cyprinodon variegatus). For RDX, maximum mortality occurred during the first two days of exposure with a 10-d median lethal concentration (LC50) of 9.9 mg L −1. The RDX 10-d median lethal residue (LR50) was 9.6 mg kg −1 (34.9 μmol kg −1) wet weight (ww), the first RDX critical body residue reported for fish. Previous investigations reported that RDX body residues in marine amphipods up to 96 μmol kg −1 ww and in marine mussels up to 86 μmol kg −1 ww failed to result in significant mortality. The highest HMX concentration tested, corresponding to its apparent solubility limit in seawater (2.0 mg L −1), and the associated mean body residue (3 mg kg −1 or 14 μmol kg −1 ww) resulted in no significant mortality for exposed minnows. The mean 10-d bioconcentration factors for RDX (0.6–0.9 L kg −1) and HMX (0.3–1.6 L kg −1) were typically lower than 1, reflecting the low bioaccumulative potential for these compounds.