ENVIRONMENTAL STABILITY OF WINDROW COMPOSTING OF EXPLOSIVES-CONTAMINATED SOILS
|M.L. Hampton and W.E. Sisk, U.S. Army Environmental Center, Aberdeen Proving Ground, Maryland 21010-5401||
Explosives contamination in soils, the result of past manufacturing and packing of conventional munitions, presents a major environmental cleanup challenge at many military installations across the country. The explosives of concern include TNT, RDX, HMX, 2,4-DNT, 2,6-DNT, and tetryl.
Various biotreatment technologies have been evaluated for degradation of the explosive contaminants. One of the most successful field demonstrations has been at the Umatilla Depot Activity, where windrow composting reduced TNT and its transformation products to approximately 1% of original concentrations within the first 20 days, at up to half the cost of incineration.
The success of the windrow composting demonstration generated further studies designed to determine the fate and mobility of the TNT and its byproducts in the composting process. Early tracer studies using 14C-labeled TNT showed that minimal 14CO2 was released in the process, indicating that the degradation products were bound strongly to the treated compost.
Additional studies conducted at Oak Ridge National Laboratory and the U.S. Army Waterways Experimental Station used various aqueous leaching and multiple sequential solvent extraction techniques to confirm the extent of mineralization and to show that the finished compost was highly resistant to further breakdown or release. The Oak Ridge study also examined the effect of long-term exposure on compost stability using EPA Method 1320, a simulated 1,000-year acid rain leaching test.
In three different methods of toxicity testing: direct ingestion of compost material by rats, Ceriodaphnia dubia test of acute and chronic aquatic toxicity, and the Ames Assay as a measure of human health risk, all showed a 90 - 98% reduction in toxicity and mutagenicity as a result of the composting treatment.
The question of the bioavailability of contaminants in treated compost was studied in 1994 at the U.S. Army Center for Health Promotion and Preventive Medicine. Pure 14C-labeled TNT, 14C-labeled TNT-contaminated soil, and subsequent composted materials were installed directly into the lungs of rats, and evaluated for the manner in which the body excreted them. Research on the effects of dermal exposure to composted material, using in vitro testing and the pig skin model, has shown negligible dermal absorption.
This presentation will review the results of these and other studies, and assess how the evidence on windrow composting of explosives-contaminated soils applies to the EPA's requirements for overall reduction in contaminant toxicity and mobility.
Key words: explosives-contaminated soil, windrow composting, toxicity testing, mobility
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