RISK ASSESSMENT AND REMEDIATION OF SOIL AND AMENDMENT TRACE ELEMENTS
Title: Uptake and transformation of soil [14C]-trinitrotoluene by cool-season grasses
Submitted to: Environmental Science and Technology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: July 14, 2010
Publication Date: July 28, 2010
Citation: Duringer, J.M., Craig, A.M., Smith, D.J., Chaney, R.L. 2010. Uptake and transformation of soil [14C]-trinitrotoluene by cool-season grasses. Environmental Science and Technology. 44:6325-6330.
Interpretive Summary: Trinitrotoluene (TNT) in soil causes hazards and must be remediated. The usual remediation, soil removal and burning, is expensive and disruptive. This compound is difficult to degrade because the three nitro groups on the ring make breaking the ring very difficult for living organisms. An alternative method using plants to phytoremediate soil TNT, and grazing ruminant animals to bio-remediate plant TNT is being tested. In this experiment, 14C-labeled TNT was added to a representative Oregon soil and three cool-season grasses (tall fescue, perennial ryegrass and orchardgrass) were grown to learn how well these species could absorb and translocate 14C-TNT, or cause transformation of soil TNT into covalently bound residue which is no longer an environmental hazard. The grasses were cut at three times over a one year growth period. Soils and plants were analyzed for extractable levels of TNT and its metabolites, and 14C in the plants was measured to assess uptake which became bound residue. The plants accumulated 14C-TNT into shoots at about 1% of total soil TNT, throughout the growth period; more 14C-TNT was retained in the roots in bound form, and TNT in the shoots was in the covalently bound form. All three species converted most of the soil 14C-TNT into bound residue during the growth period. The findings are significant because 14C-TNT was accumulated throughout the one year growth period, longer than most previous studies of plant uptake of TNT. And the study confirmed that grasses could effectively reduce the potential for soil TNT risk in the environment by both conversion of TNT into non-toxic bound residue in the soil, and by absorbing some of the soil TNT into shoots where grazing ruminants could further degrade the TNT.
This study investigated the fate and uptake of [14C]-TNT from soil into orchardgrass (Dactylis glomerata), perennial ryegrass (Lolium perenne) and tall fescue (Festuca arundinacea) over a one year period in a greenhouse-controlled environment. Pots (n=4 for each grass, containing 10 mg cold TNT/kg soil + 1.2 mg [14C]-TNT/kg soil and controls with no TNT) were exposed to light and temperature conditions typical of June at 45°N for 369 days. Three plant harvests were made (63, 181 and 369 days) and soil and plant materials were monitored for [14C]-TNT and metabolite concentrations. The 11.2 mg/kg TNT dose was not phytotoxic to the plant species tested. Continual uptake of TNT into grass blades was observed over the one-year period, with a total accumulation of 1.3%, 0.9% and 0.8% of the initial soil [14C]-TNT dose for orchard grass, perennial ryegrass and tall fescue, respectively. All [14C]-TNT residue in plant material was incorporated as bound residue. At final harvest, radioactivity was concentrated most highly in the root>crown>blade for all species. Soil TNT was gradually reduced to aminodinitro-toluenes then further to an unidentified metabolite(s). Overall, orchardgrass appeared to be the most efficient species at taking up TNT.