Toxicities of TNT and RDX to Terrestrial Plants in Five Soils with Contrasting Characteristics

This study was designed to produce scientifically defensible benchmark data for the development of ecological-based soil screening levels for 2,4,6-trinitrotoluene (TNT) and hexahydro-1,3,5-trinitro-1,3,5-triazine (RDX) for terrestrial plants. The physical and chemical properties of different soils may alter the bioavailability and toxicity of TNT and RDX to plant species. We investigated individual ecotoxicities of TNT and RDX to alfalfa (Medicago sativa L.), Japanese millet (J. millet; Echinochloa crus-galli L. [Beauv.]), and perennial ryegrass (Lolium perenne L.) in five natural soils that varied in pH, organic matter, and clay contents. On the basis of EC50 values (the TNT or RDX concentrations that produce 50% reductions in selected measurement endpoints) and 95% confidence intervals for shoot fresh and dry masses (SDM), TNT weathered-and-aged (W-A) in soils significantly reduced (p 0.05) growth of alfalfa, J. millet, and perennial ryegrass. RDX W-A in soil was moderately inhibitory to growth of J. millet and perennial ryegrass in all five soils but did not affect growth of alfalfa. No statistically significant correlations between TNT toxicity and these soil properties were identified; however, statistically significant (p 0.05) inverse relationships were identified between the RDX EC50 values for perennial ryegrass SDM and soil clay content and pH.