Deposition, Retention, and Clearance of Depleted Uranium and Tungsten Following Inhalation Exposure: Biokinetic Analysis and Implications for Long-term Health Effects.

OBJECTIVE: This study evaluates respiratory deposition and subsequent biokinetic behavior of DU and W aerosols using computational modeling informed by reported military exposure conditions.

METHODS: Particle deposition fractions in the respiratory tract were calculated using REDCALdep, which implements the ICRP Publication 66 respiratory tract deposition model with relevant updates from ICRP Publication 130. Deposition fractions were used as initial conditions within the Radiological Exposure Dose Calculator (REDCAL) framework, a Python-based computational toolkit, to estimate time-dependent biokinetic distributions following inhalation. A representative activity median aerodynamic diameter (AMAD) of 5 μm was assumed for respirable aerosols, and DU (19 g cm-3) and W (19.3 g cm-3) were modeled as moderately soluble (Type M). Additional sensitivity analyses were conducted for AMADs of 1, 5, and 10 μm and absorption types F, M, and S.

RESULTS: Increasing density from the ICRP Publication 130 default value to DU and W values shifted deposition toward deeper lung regions. Modeled retention profiles indicate systemic distribution beyond the respiratory tract, including systemic organs, with substantial early urinary and fecal excretion. Despite model uncertainties, patterns were consistent with published experimental and epidemiological observations reported for DU and W inhalation exposures.

CONCLUSION: The findings contribute to understanding mechanistically plausible pathways associated with long-term internal retention relevant to symptom profiles described in Gulf War Illness literature, while supporting improved exposure assessment and risk characterization for military and occupational settings.