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Konietzka, Rainer

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Konietzka
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Rainer
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2014 - 20152
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Thema: Resorption ×

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  • Vorschaubild nicht verfügbar
    Veröffentlichung
    Gastrointestinal absorption of uranium compounds A review
    (2015) Konietzka, Rainer
    Uranium occurs naturally in soil and rocks, and therefore where it is present in water-soluble form it also occurs naturally in groundwater as well as in drinking water obtained from groundwater. Animal studies suggest that the toxicity of uranium is mainly due to its damage to kidney tubular cells following exposure to soluble uranium compounds. The assessments of the absorption of uranium via the gastrointestinal tract vary, and this has consequences for regulation, in particular the derivation of e.g. drinking water limit values. Absorption rates vary according to the nature and solubility of the compound in which uranium is presented to the test animals and depending on the animal species used in the test. No differences for sex have been observed for absorption in either animals or humans. However, human biomonitoring data do show that boys excrete significantly more uranium than girls. In animal studies neonates took up more uranium than adults or older children. Nutritional status, and in particular the iron content of the diet, have a marked influence on absorption, and higher uranium levels in food intake also appear to increase the absorption rate. If the pointers to an absorption mechanism competing with iron are correct, these mechanisms could also explain the relatively high concentration and chemical toxicity of uranium in the kidneys. It is here (and in the duodenum) that divalent metal transporter 1 (DMT1), which is primarily responsible for the passage of iron (or uranium?) through the cell membranes, is most strongly expressed.Quelle: http://www.sciencedirect.com
  • Vorschaubild nicht verfügbar
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    The ex-vivo intestinal absorption rate of uranium is a two-phase function of supply
    (2014) Konietzka, Rainer
    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 ìg/l uranium in the perfusion solutions, which thereafter appears to reach a plateau, as further increase towards concentrations around 400 ìg/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 ìg/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.Quelle: http://www.sciencedirect.com