Accumulation of hexahydro-1,3,5-trinitro-1,3,5-triazine in channel catfish (Ictalurus punctatus) and aquatic oligochaetes (Lumbriculus variegatus)

The extensively used military explosive hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) has been widely released to the environment during production, usage, and disposal operations. Toxic effects of RDX have been reported in terrestrial and aquatic receptors, but investigations regarding the bioaccumulation potential of RDX in aquatic systems are scarce. The objective of the present study was to describe the toxicokinetics of RDX during aqueous exposure for the channel catfish (Ictalurus punctatus) and aquatic oligochaetes (Lumbriculus variegatus) and to compare the amount of RDX accumulation in juvenile catfish following aqueous exposure only, dietary exposure only, and a combination of dietary and aqueous exposure. The toxicokinetics measurements included bioconcentration factors (BCFs), uptake rates, elimination rates, and biological half-lives. First-order, single-compartment models described the toxicokinetics for both species. Uptake of RDX into oligochaetes was relatively rapid (uptake clearance constant [k(u)] of 5.17 ml/g/h) compared to that in catfish (k(u) = 1.28 ml/g/h). However, elimination also was more rapid in oligochaetes, with biological half-lives of 0.28 and 1.09 h for oligochaetes and catfish, respectively. Thus, both species had very similar estimated BCFs of 2.1 ml/g for oligochaetes and 2.0 ml/g for catfish. Accumulation of RDX in fish that were fed oligochaetes exposed to an exceedingly high water concentration of RDX was minimal. The present investigation indicates that RDX uptake via the aqueous route is the expected dominant uptake pathway, with dietary uptake contributing minimally to the overall body burden in fish inhabiting RDX-contaminated sites. Because of the exceedingly low bioaccumulative potential and low reported toxicity of RDX, the presence of this explosive in aquatic systems is unlikely to pose unacceptable risks to invertebrates and fish.