Societies have always faced risks of one type or another, however, recent terrorist activities have put many of these risks into sharp focus. Our nation has taken strong steps to guard against terrorist activities. But, it will take time for effective implementations to take hold owing to uncertainty in how to deploy a defensive strategy and lack of adequate technology ready to meet the challenge.
This article examines a new commercial technology designed for automated screening of water supplies infiltrated with chemical weapons and other hazardous compounds. Safeguarding the nation’s water supply is a daunting task given the delocalization and accessibility of water supplies and the inadequacy of most existing technology to meet the needs for an effective early warning system.
Threat scenarios
Before a new technology can be deemed useful, the application must be validated and the case for technology well defined. The threat scenario for chemical and biological weapons contamination of water supplies is credible. A dose of several milligrams of nerve agent in water may be lethal. One milliliter of these agents strategically placed could lead to hundreds of fatalities. Based on Department of Defense Tri-Services guidelines for safe chemical weapons levels in water, the determined acute concentration (impairment, not death) for civilian short-term doses has a value of about 0.5 mg/L for nerve agents. This level of contamination could be achieved by dumping a 55-gal drum of nerve agent into a 100 million-gal reservoir servicing a population of about one million people. Smaller quantities could induce similar impairment to a smaller population segment by contaminating the supply in the distribution system.
A screening technology must be able to detect--with high accuracy--illicit compounds at short-term, sub-acute levels. One solution may be, the Radiance Pro CW, a high-speed, high-throughput analyzer that enables automated screening at 45 seconds per sample. Water samples are collected in vials and directly loaded into an autosampler vial tray for analysis. The analyzer is preloaded with a vast and upgradeable chemical weapons database. The instrument returns a red light indicator if any of the targeted compounds are present at preset threshold levels and the measured intensities for all compounds for the samples are logged in a spreadsheet compatible data file.
System performance
The Radiance Pro CW analyzer is based on patented photoionization mass spectrometry technology that enables the analysis of trace compounds in complex matrices without the use of a chromatographic separation front-end such as gas chromatography of liquid chromatography. This enables fast analysis and simple operation. The detection limits for the above chemical weapons compounds, measured at U.S. Army surety laboratories are at or below the acute levels for the entire major chemical weapons agents.
Another key performance metric is the false negative and false positive rates. A chemical weapon simulate mixture comprised of DMMP, DEMP, DEEP and DIMP2, was prepared in concentrations of zero (blank sample), 0.01 and 0.03 mg/L in water.
Figure 2 above shows the signal levels for 20 repeated measurements for all three concentrations for the signature ion for DMMP. The 3s mean detection limits ranged from 0.006 mg/L for DMMP to 0.033 for DIMP. For all alarm thresholds chosen, the false positive rate was 0%. The false negative rate depends on the threshold and concentration. For the 3s or 0.03 mg/L thresholds, the false negative was 0% for all chemical weapon stimulant compounds at 0.10 mg/L concentration, well below the acute levels for chemical weapon agents.
Water utilities such as those in the city of Phoenix and the city of Houston are employing the Radiance Pro CW analyzer as a fast screening device for chemical weapon agents and other compounds.
For example, Houston has added atrazine and dursban to the targeted compound list. As an early warning system, they collect samples from key locations and bring them back to a central lab for screening and, if necessary, further analysis. The total resource time for screening is generally well under an hour including the automated baseline calibration—which takes 5–10 minutes—preceding analysis.
The chemical weapon mass spectral library that is loaded with the system is important because chemical weapon standards are generally unobtainable.
