Absorption and metabolism of 5-(4-nitrophenyl)-2,4-pentadienal (Spydust)

5-(4-Nitrophenyl)-2,4-pentadienal (NPPD) was recently alleged to have been used as a tracking agent to monitor the activities of U.S. citizens in the Soviet Union. In order to better assess human risk from possible exposure to this compound the absorption and metabolism of [14C]NPPD has been investigated in male F344 rats. These studies have revealed that NPPD was readily and quantitatively absorbed from the gastrointestinal tract, distributed throughout the tissues, metabolized, and rapidly excreted primarily in urine. NPPD was sparingly absorbed following dermal administration of 0.01, 0.1, and 1.0 mg/cm2. The amount absorbed increased as the dose increased but the percentage of the dose absorbed decreased as the dose increased, e.g., 50% (5 of 10 micrograms applied) of the low dose was absorbed but only 5% (50 of 100 micrograms applied) of the high dose was absorbed. The material absorbed after dermal administration was rapidly excreted and the distribution and metabolism of the dermally administered compound was no different from oral administration. A total of five metabolites, 4-nitrocinnamic acid, 4-acetamidobenzoic acid, 4-nitrohippuric acid, 4-acetamidocinnamic acid, and 4-nitrobenzoic acid, were identified by cochromatography with authentic standards and comparison of UV spectra. These metabolites are formed by oxidative metabolism of the pentadienal side chain, reduction of the nitro group, and/or conjugation of the resulting amino group with acetate or carboxylic acid with glycine.