The ex-vivo intestinal absorption rate of uranium is a two-phase function of supply

The concentration-dependent absorption behaviour of uranium was investigated with surviving intestinal segments of rat jejunums, using an ex-vivo model. The results showed a monotonic slightly nonlinear increase in absorption as uranium concentrations increased. This trend was observed over the entire concentration range tested. In the lower concentration range a slower linear ascent was observed while a steeper linear ascent was found for the higher concentration range. Statistical fit was only slightly poorer for an exponential function in the range of lower values and a logarithmic function in the range of higher values. The proportion of uranium absorbed expressed as percent of uranium concentrations in the perfusion solutions followed a monotonically increasing trend from 20 to around 200 μg/l uranium in the perfusion solutions, which thereafter appears to reach a plateau, as further increase towards concentrations around 400 μg/l is not substantial. The uranium concentration administered had no effect on the vitality and consequently the functionality of the intestinal segments, measured in terms of active glucose transport. The results imply that uranium concentrations of more than 20 μg/l in drinking water, for example, could lead to elevated absorption rates and thus to higher internal exposures to consider when setting of Guideline values in this concentration range.