The objective of this project was to demonstrate the efficacy of immunosensors for on-site characterization monitoring of areas contaminated by explosives in soil and groundwater. Two devices were assessed including: (1) the Analyte 2000 Fiber Optic Biosensor (FOB) which uses molecular recognition and evanescent wave sensing to detect a wide variety of analytes; and (2) the FAST 2000 Continuous Flow Immunosensor (CFI) which is based on a displacement assay that uses analyte-specific antibodies as a means of detection. For this study, the analytes TNT and RDX were used.
The performance assessment of the immunosensors focused on precision, cross reactivity, accuracy, false positive/negative results, completeness, comparability to other field and laboratory technologies, sample throughput, ease of use, and cost. These factors were statistically analyzed, the results showing the FOB unit can be predictive for RDX and TNT in soil and groundwater; and, the FAST 2000 CFI unit being predictive for RDX and TNT in soil, predictive for TNT in groundwater at all sites, and predictive for RDX in groundwater at two of the three sites. However, both devices experienced performance problems due to matrix interferences. The U.S. EPA's ETV Report characterizes the CFI unit as imprecise and biased high for TNT and RDX when analyzing water samples. The efficacy of both units on soil and groundwater samples is decribed in the Field Demonstration and Method Validation of NRL Environmental Immunosensors report. The USEPA's Environmental Technology Verification Report on Explosives Detection Technology focuses on the FAST 2000 CFI's performance on groundwater samples.
The use of immunosensors for on-site characterization of explosives in soil and groundwater would substantially reduce costs, provide real-time data, simplify characterization and expedite remediation. The current, most reliable process for site characterization of explosives involves laboratory analysis by EPA SW-846 Method 8330, with analytical costs ranging from $250 to $1,000 per test. The estimated cost per test for on-site immunosensor analysis would range from $3 to $38 (not including initial instrumentation costs).
On-site immunosensors and biosensors can be valuable monitoring tools for confirming remediation process effectiveness. Such analyses could guide excavation procedures, help gauge the effectiveness of pump-and-treat, and monitor the progress of composting and other remediation operations. Matrix interferences and cross-reactivity issues may limit the utility of this technology from being an accurate characterization tool at selected sites. However, recent improvements in sample preparation procedures have been reported that may allow these immunoassay methods to be used as an initial screening technique. (Project Completed - 2000)