Investigating the Fate of Residual Organophosphonate Nerve Agent in Soil.
Ronald T. Checkai1, Mark V. Haley1, Michael Simini1, Carlton T. Phillips1, Charles L. Crouse2, and Kathy L. Matson2. (1) U.S. Army Edgewood Chemical Biological Center, AMSRD-ECB-RT-TE E3150 / Environmental Toxicology, 5183 Blackhawk Road, Aberdeen Proving Ground, MD 21010-5424, (2) Geo-Centers, Inc., P.O. Box 68, Aberdeen Proving Ground, MD 21010-0068
Why “all clear” may mean future danger: Surface-controlled reactions affecting hydrolysis of organic compounds in the environment can predominate over bulk solution hydrolysis, especially in soil environments. Unpredicted residual levels of chemical warfare agents (CWA) at threat levels in the field necessitated the development of new methods for investigating the fate of CWA delivered onto soil. Design and fabrication of Soil System Units now allows determination of the fate of CWA in soil, as well as investigation of the soil chemical and physical characteristics affecting the persistence of threat from continuing presence of CWA in soil, under conditions that represent those in the field. Initial results show that the Soil System Unit approach is highly effective for investigating the fate of CWA in the soil environment. Using the Soil System Unit approach we were able to replicate and investigate under controlled conditions the residual levels of CWA that were unpredicted but found at hazardous levels in the field. Results of our initial experiment showed that persistence of Soman (methylphosphonofluoridic acid 1,2,2-trimethylpropyl ester; GD) in soil can be expected for days-to-weeks following contamination. Furthermore, we established that life threatening atmospheric levels of GD may be expected to successively reoccur in response to increasing moisture in soil contaminated with GD. This result had not been previously observed or documented. In order to further investigate the fate of GD in soil, the extractability of GD from soil constituents was explored. Experimental results showed that longer contact times of GD with air-dry soil constituents resulted in less GD being extracted. Twenty-four-hour extractions of GD using isopropanol yielded recoveries from sand of 90-100% when GD was in contact <24hrs, 45% when GD was in contact 48hrs, and 16% when GD was in contact 72hrs. Twenty-four-hour extractions of GD using isopropanol yielded recoveries from montmorrillonite clay of approximately 40% when GD was in contact <48hrs, deceasing to approximately 30% when GD was in contact 72hrs. Additional investigation into the fate of GD in soil constituents using the Soil System Unit approach is ongoing, and will give insight into the factors affecting persistence.