TECHNOLOGY UPDATE Native aquatic plants remove explosives A recent phytoremediation demonstration project has shown that native aquatic plant species and poplar hybrids need no chemical assistance to serve as a polishing treatment for explosive-contaminated soil and groundwater. The demonstration, which ended in March, inspired a full-scale project, begun in May, at the Iowa Army Ammunition Plant. The project involves using native aquatic plant species in the creation of wetlands at an excavation site where an estimated 1-5% of the original explosives remain after a major removal action. "It's the first use of these native aquatic species without addition of other chemicals to degrade TNT" said Jerald Schnoor of the University of Iowa's Department of Civil and Environmental Engineering Laboratory studies confirmed the ability of the native aquatic plants— pondweed, arrowroot, and coontail—to actively degrade TNT and RDX, thanks to their production of the enzymes laccase, mono- and dioxygenase, and nitro reductase. When the scientists conducted a pilot test in the field this spring, however, they found that the removal rate was much better than expected. "We're getting a rate that's almost an order of magnitude better, simply because we have photolytic activity occurring," said Jerry L. Miller, a research civil engineer with the Army Corps of Engineers' Waterways Experiment Station. Based on the field test, Miller calculated that the created wetlands at the Iowa site could be expected to remove at least 0.016-0.019 mg of TNT/L per day and at least 0.133-0.291 mg RDX/L per day (at 25 °C in steady state). Poplars, planted at the rim of the wetland area, also do a good job of degrading the explosive compounds, said Schnoor. "The ability of the poplars to take RDX all the way up to their leaves was a surprise," he added. The scientists plan to moni-
tor the leaves to make sure they don't accumulate too much RDX. Schnoor estimates that the total cost will be about $60,000/acre, which he characterizes as "cheap." —KELLYN S. BETTS
Lysimeters promoted for pesticide research EPA is reviewing the pros and cons of lysimeters, a technology popular in Europe for evaluating pesticide contamination of groundwater. During a day-long symposium on April 14 at the American Chemical Society's meeting in San Francisco, European scientists said lysimeter technology can provide accurate and inexpensive evaluations of how agrochemicals behave in soil. Lysimeters take large core samples of undisturbed soil and relocate them to an outdoor experimental station where they are lowered into vertical pipes in the ground. Pesticides marked with radioactive tracers are applied to the soil surface, and researchers collect the leachate at the bottom of the lysimeter. Weather and environmental conditions are monitored carefully. According to Fritz Fuhr of the Institute of Chemistry and Dynamics
of the Geosphere: Radioagronomy in Germany, lysimeter data "can provide a more profound evaluation of the risks and benefits of a compound." Roland Kubiak, of Staatl. Lehrund Forschungsanstalt in Germany, presented results from a comparison of lysimeters and field tests. The experiment involved building tunnels under a field to collect leachate on bromide and benazolin-ethyl, an herbicide. After two years, Kubiak observed "no significant difference" between the two types of tests. "Leaching processes in lysimeters with undisturbed soil cores are transferable to the field situation " Kubiak concluded. Nonetheless, Lars Bergstrom of the Swedish University of Agricultural Sciences warned scientists using lysimetry to be careful when extrapolating lysimeter data and carrying out pesticide risk assessments. "There still are considerable uncertainties about the mechanisms controlling the transport of pesticides through soil," said Bergstrom. EPA's Office of Pesticide Programs presented several lysimeter papers at the meeting. Elizabeth Behl of the Environmental Fate and Effects Division said EPA has allowed European-
An undisturbed soil core being excavated into a lysimeter casing. The lysimeter will be used to evaluate pesticide behavior at the Institute of Chemistry and Dynamics of the Geosphere: Radioagronomy. (Courtesy Thomas Puetz, ICG-5, Forschungszentrum, Juelich, Germany)
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style lysimeter tests of pesticide field dissipation, but has no policy. She believes that lysimeters could be useful for testing a new generation of pesticides that are applied at very low rates, ounces per acre rather than pounds. "In these cases, more controlled lysimeter studies might be a good approach," said Behl. —JANET BYRON
Toluene boosts bioremediation of TCE Native bacteria successfully biodegraded trichloroethene (TCE) in the groundwater at an Edwards Air Force Base, Calif., demonstration project completed in March. Researchers believe the in situ bioremediation technique can be applied to anaerobic and aerobic processes involving a wide variety of chlorinated solvents. "The test has shown that this method can successfully reduce the levels of TCE in groundwater by 96% to 98%," said project head Perry McCarty of Stanford University. "While we were specifically applying this to the cometabolism of TCE, there are many other applications where one needs to bring chemicals and contaminants and bacteria together." McCarty reported results of the full-scale demonstration at the American Chemical Society's meeting in April. McCarty's team built two dual-screen groundwater circulation wells into the contaminated aquifers and added oxygen and toluene to break down the TCE into carbon dioxide, water, and chloride. The toluene was degraded by 99.98% over the course of the project to a final concentration of 1.21.3 pg/L, a level well below EPA's threshold of 1000 pg/L and the California state maximum of 100 pg/L. To modulate bacterial growth and prevent clogging the pores of the aquifer with excess bacterial growth, the researchers injected hydrogen peroxide into the wells. In fact, the hydrogen peroxide represents the "major cost of concern" to McCarty. "Clogging wasn't as big a problem as we feared." McCarty's team used a hydrological model to evaluate the effects of factors such as adsorption and transport. "The results and the modeling came out very close together," he said, stressing that the technique requires advance modeling with sitespecific data. —KELLYN S. BETTS
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