Elevated levels of explosives [cyclotrimethylenetrinitramine (RDX), octahydro-1,3,5,7-tetranitro-1,3,5,7-tetrazocine (HMX), 2,4-dinitrotoluene (2,4-DNT), 2,6-dinitrotoluene (2,6-DNT), and 1,3,5-trinitrobenzene (TNB)] can be found at Department of Defense (DoD) and Department of Energy (DOE) sites. Currently, screening-level values protective of ecologically relevant soil receptors are not available for explosives in soil to determine if further evaluation is required in a baseline Ecological Risk Assessment. Scientifically based ecological soil screening levels (Eco- SSL) are needed to identify contaminant levels in soil that present an unacceptable ecological risk to such receptors.
The objective of this project was to determine the toxicity and potential for bioaccumulation of explosives-related contaminants in soil invertebrates and plants with the ultimate goal of developing ecotoxicological benchmarks.
Sassafras sandy loam, a natural soil supporting relatively high bioavailablity of energetic materials (EM), was amended with a range of concentrations to determine the toxicity for soil invertebrates and plants. A portion of the amended soils was subjected to a simulated weathering and aging process prior to bioassays to approximate EM bioavailability in the field. Soil invertebrate assays were conducted with an earthworm, potworm, and collembola. Plants species included alfalfa, perennial ryegrass, and Japanese millet. Bioaccumulaton potential of nitramine EMs in terrestrial plants and in the earthworm was assessed with [14C]-RDX or [14C]-HMX amended soil using a microcosm system designed for mass-balance studies. Bioaccumulation of nitramine and nitroaromatic EMs also was determined using unlabeled materials and U.S. Environmental Protection Agency Method 8330. Ecotoxicological parameters were determined using measured chemical concentrations.
This project generated experimental data on the toxicity of RDX, HMX, 2,4-DNT, 2,6-DNT, and TNB for terrestrial plants and soil invertebrates. Ecotoxicological testing was specifically designed to meet the criteria for Eco-SSL derivation. Draft Eco-SSL values were derived for freshly amended and for weathered/aged amended soil using the effective concentration that caused a 20% reduction (EC20) level of the EM effects on plant growth or soil invertebrate reproduction measurement endpoints. Studies showed that nitramine EM bioaccumulation potential is relatively high for plants and moderate for earthworms. Little or no accumulation of TNB or of the DNTs was observed in plants, indicating that bioaccumulation potential for nitroaromatic EMs is low.
Eco-SSL values for EMs derived from toxicological benchmarks developed in this project and the bioconcentration factors for these EMs will be used to screen contaminated DoD and DOE sites. Scientifically based Eco-SSLs will identify contaminant concentrations in soil that present an acceptable ecological risk and can thereby reduce the number of sites requiring cleanup early in the ecological risk assessment process, generating a significant cost saving. (Project Completed - 2003)