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Table 3. Last bioassay results in the involved worker.

show the different chemical forms of uranium in solution, depending on the fluids’ chemical composition:

Carbonate complexes in carbonate-rich fluids – UO 2( CO 3) 4- 3 in plasma at pH 7.4 – UO 2( CO 3) 4- 3 and UO 2( CO 3) 2- 2 in the pancreas at pH 8.3 Hydroxylated forms UO 2( OH) 2 in saliva at pH 6 – 7

Phosphate forms in fluids richer in phosphates, such as urine – UO 2( HPO 4) 2- 2 at pH 4,2 et 8.

In gastric juice, which is less rich in phosphates, the speciation of uranium varies significantly depending on pH: – UO 2- 2 at pH 1 toUO 2( HPO 4) 2- 2 at pH 3,5.

Fig. 3. Graphical representation of urinary measurements compared to predicted values with the ICRP 78 biokinetic model for ingestion with a revised f 1 factor.

7 Discussion � Hypotheses on explanatory mechanism

The metabolism of ingested uranium is not as well understood as that of radium. Wrenn and colleagues( Wrenn et al., 1985) estimated that approximately 1.1 % of ingested uranium is absorbed through the gastrointestinal tract.

The observed increase in digestive absorption of uranium may be linked to the chemical composition of the beverage, particularly the presence of phosphoric acid. Phosphoric acid forms from the reaction of phosphorus with oxygen and water and subsequently recombines into various inorganic or organic phosphates( Wagner et al., 2023). Phosphate metabolism is associated with several key biological functions, including phospholipid metabolism, bone mineralization, adenosine triphosphate( ATP, the cellular energy carrier), and others. In their work, Leggett and Harrison( Leggett et al., 2095) emphasize, based on laboratory data from animal studies, that the absorbed fraction of uranium strongly depends on its ingested chemical form.

Numerous studies demonstrate uranium’ saffinity with phosphates, whether in solid form( e. g., uranium’ s presence in phosphate fertilizers or natural minerals like apatite and monazite) or in solution. In such environments, the formation of uranium-phosphate complexes such as UO 2 H 2 PO 4 þ, UO 2( H 2 PO 4) 2 et UO 2( H 2 PO 4) 2( H 3 PO 4) has been demonstrated in phosphoric acid( Dartiguelongue, 2014).

Calculations of uranium speciation in human biological fluids conducted by Sutton and Burastero( Sutton et al., 2004)

Thus, it can be suggested that the high concentration of phosphoric acid in the carbonated beverage promotes the formation of UO 2( HPO 4) 2

2 + in gastric juice, displacing the

UO 2

2 + form. As shown in various studies( Sandino et al., 2005; Sutton et al., 2004), this chemical form( UO 2( HPO 4) 2

2 +) has a high solubility.

Moreover, data from animal studies provide information on the relative uptake of uranium ingested in different chemical forms, showing that absorption is strongly dependent on the solubility of the compound( ICRP, 2017)

So, we can assume that uranium in this chemical form( UO 2( HPO 4) 2

2 +) has a higher solubility, thereby enhancing

gastrointestinal absorption compared to classic hydroxylated or carbonated chemical forms.

8 Conclusion

This clinical case highlights the critical importance, in dosimetric interpretation, of always cross-referencing hypotheses with data from employee interviews and supplementary information provided by the facility and radioprotection teams.

Any inconsistency between exposure data and the proposed biokinetic model � even if it shows excellent correlation between theoretical curves and measured results � should prompt a re-evaluation of the model and exploration of alternative hypotheses.

This necessitates multidisciplinary collaboration, leveraging expertise across fields such as biology, chemistry, mathematics, and radioprotection.

In this instance, such collaboration advanced understanding of how certain foods( e. g., cola) influence gastrointestinal uranium absorption. Subsequent cases have confirmed cola’ s impact on urinary uranium excretion, making its consumption a routine inquiry when analyses exceed general population background levels.

As the medical adage goes:“ You only find what you look for, and you only look for what you already know.”