bly as a result of gradual dissolution of DU fragments. Results from a battery of computer-based neurocognitive tests suggest a statistical relationship between elevated urinary uranium levels and “problematic performance on automated tests assessing performance efficiency and accuracy” (McDiarmid et al., 2000). Traditional tests of neurocognitive function (pen-and-pencil tests) did not show any statistical differences in performance between the veteran cohort and a control group.
The committee found several methodological issues that make it difficult to draw firm conclusions from this study. The authors did not adequately define their neurocognitive testing methods or the method for deciding the expected level of performance. The procedures involved calculating two “impairment indexes” for each test subject—one for the automated and one for the traditional neurocognitive measures. They calculated the impairment indexes for the neurocognitive tests by dividing the total number of scores that were below the expected score by the total number of scores obtained from each test battery. However, the investigators did not indicate how they chose the cutoff value that defined “expected” performance, nor did they explain how they chose the decision cut points.
As acknowledged by the authors, the number of individuals with high uranium levels in urine was small, “and it appeared that a few veterans with complex histories may have contributed appreciably to the observed variance.” Further studies may help explain the lack of correlation between the computer-based tests, which showed abnormalities, and the standard written tests, on which the subjects performed normally. Continued follow-up of this cohort will provide insight into any potential neurocognitive effects of depleted uranium.
In summary, the evidence regarding exposure to uranium and diseases of the nervous system is not strong enough to form a firm conclusion. In studies on Gulf War veterans, the search for evidence of neurological effects will require careful neurocognitive measurements, correlation of these with clinical dysfunction, and comparison of exposed veterans to control groups chosen to illuminate various facets of the complex exposure history of Gulf War veterans.
The committee concludes that there is inadequate/insufficient evidence to determine whether an association does or does not exist between exposure to uranium and diseases of the nervous system.
Nonmalignant respiratory effects from inhaled uranium aerosols will depend in part on where in the lung the inhaled particles come to rest. Deposition depends primarily on particle size and solubility. Particle clearance mechanisms will remove a portion of deposited particles primarily by mucociliary action, which operates in the upper respiratory tract to sweep particles up to the pharynx