Estimate of the time-zero lung burden of depleted uranium in Gulf War veterans by the 24 hour urinary excretion and exponential decay analysis

Aim: Significant presence of depleted uranium (DU) in the urine of British, Canadian, and United States veterans nine years after inhalational exposure in the Desert Storm conflict has been reported in the studies of DU urine analysis by mass spectrometry. The aim of this study is to report an estimate of the amount of DU in the respiratory system at the time of exposure from the quantitative current rate of daily excretion. Materials and Methods: Mass spectrometry (TIMS) analysis of 24-hour urinary excretion of the isotopes of DU in five positive (238U/235U > 191.00) and six negative (238U/235U < 138.25) veterans were utilized in the mathematical estimation of the pulmonary body burden at the time of exposure. The mathematical analysis of the estimated DU concentration in the lungs corresponds to the pulmonary fraction of DU that is excreted in urine, representing a minimum lung burden. Integrating the fundamental half-life equation (dN/dt = -b*N) gives the traditional decay equation (N No*e-bt). Substituting the half-life equation into the decay equation relates the initial DU concentration to the rate of excretion, total time, and an unknown decay constant (No = (dN/dt)*ebt/b). A minimum value for the biological half-life of ceramic DU oxide in the lungs was derived from the Batelle report of minimum dissolution time in simulated interstitial lung fluid corresponding to 3.85 years. The concentration of DU at time zero can also be determined by finding the minimum value of the function (No (dN/dt)*ebt/b) with respect to the biological half-life constant, thus estimating DU concentration at the time of exposure. Results: The average depleted uranium concentration was 3.27 x 10-5 mg / 24 hours in DU positive veterans and 1.80 x 10-8 in DU negative veterans. By the use of the Batelle report of the dissolution rate of ceramic uranium oxide in simulated interstitial lung fluid, the estimated lung burden was 0.336 mg in the DU positive and 0.0002 mg in the DU negative veterans. The absolute minimum concentration was 0.294 mg in the positive and 0.0002 in the DU negative veterans. Conclusion: Our work provides a model of estimating the minimum pulmonary concentration of DU at time zero by utilizing gravimetric and mass spectrometric data of the DU isotopes in 24-hour urinary samples and theoretical model of DU dissolution time in simulated interstitial lung fluid. The results provide the conclusive evidence that the pulmonary concentration of DU at time zero can be quantitated as late as nine years after inhalational exposure