Effect of soil characteristics on toxicity of TNT to plants

TNT (2,4,6-trinitrotoluene) is toxic to terrestrial plants as a soil contaminant. Physical and chemical properties of different soil types may alter TNT toxicity to plants. We investigated the ecotoxicity of TNT to alfalfa (Medicago sativa L.), Japanese millet (Echinochloa crusgalli L. (Beauv.)), and perennial ryegrass (Lolium perenne L.) in five soil types having different levels of organic matter, clay content, and pH. Nominal TNT concentrations of 1, 10, 20, 40, 80, 160, 320 and 640 mg/kg were weathered and aged in soils in a greenhouse for 8 weeks. TNT concentrations in soil were measured by HPLC before toxicity testing. Phytotoxicity studies were conducted independently with each soil series in environmentally-controlled growth chambers. Negative, solvent, and positive controls were included in each test. Measurement endpoints were seedling emergence, fresh shoot mass, and dry shoot mass. Preliminary results showed significant (P < 0.05) TNT toxicity to all species tested. Phytotoxicity benchmark values for each soil type were derived from concentration-response curves generated by regression analyses of the data. Toxicity data are discussed in relation to soil properties.