Ecological Soil Screening Levels for Plants Exposed to Tnt: Supporting Range Sustainability for Training and Testing

Abstract : Ecological Soil Screening Levels (Eco-SSL) are those screening concentrations of chemicals in soil that present an acceptable risk to ecological receptors. We investigated the ecotoxicity of TNT to the plant species alfalfa (Medicago sativa L.), Japanese millet (Echinochloa crusgalli L. (Beauv.)), and perennial ryegrass (Lolium perenne L.) in five natural soils: Sassafras sandy loam (SSL), Teller sandy loam (TSL), Richfield clay loam (RCL), Kirkland clay loam (KCL), and Webster clay loam (WCL). According to USEPA Eco-SSL criteria, relative bioavailability scores for organic chemicals in these soils were rated high for SSL and TSL, medium for RCL and KCL, and low for WCL soil. We amended TNT into these soils and subjected them to wetting/drying cycles (8 weeks) in order to represent field conditions. Phytotoxicity studies were conducted with each soil separately in environmentally controlled growth chambers. Nonlinear regression models were used to determine 20% (EC20) or 50% (EC50) effect concentration values for seedling emergence, fresh mass, and dry mass. The geometric mean of EC20 values was used to determine draft Eco-SSL for each soil type. Results of these studies will undergo quality assurance before inclusion in the U.S. EPA national Eco-SSL database.