Methods for the Retrospective Detection of Exposure to Toxic Scheduled Chemicals: Analysis of Free Metabolites

In cases of investigations into alleged use of chemical warfare agents, biomedical samples such as urine or blood may be collected from casualties for forensic analysis. Analysis of biomedical samples may also be undertaken for diagnostic purposes, to ensure appropriate medical treatment, and for occupational exposure monitoring, e.g. in workers engaged in demilitarization activities. Metabolites excreted in urine, or circulating in the blood, provide unequivocal biological markers of exposure. Metabolic pathways have been identified for the blister agent sulfur mustard and organophosphorus nerve agents. Sensitive analytical methods have been developed for the major metabolites, based on gas or liquid chromatography combined with single stage or tandem mass spectrometry. Methods developed primarily for application in investigations of alleged use of chemical warfare agents have focused on achieving low levels of detection combined with high selectivity. A significant trend over the last decade has been the development of higher throughput methods, aimed primarily at homeland security applications, e.g. in the case of terrorist use. Selected metabolites have been validated in cases of accidental or deliberate human exposure to sulfur mustard, and the nerve agents sarin and VX. Putative metabolites have been identified in animal studies for other nerve agents, nitrogen mustards, Lewisite and the incapacitant BZ. Phosgene and hydrogen cyanide have received much less attention with respect to retrospective identification of exposure in a chemical warfare context. Many analytical methods are available for metabolites of cyanide but significant background levels are present in the general population. A disadvantage of free metabolites is that they are relatively rapidly excreted. The window for identification following an exposure is estimated to be in the region of 14 days, depending on the severity of the exposure and the limit of detection of the analytical method. Covalent adducts with proteins and DNA may offer longer lived biomarkers of exposure.