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| Titel |
Radioactivity in rocks and soil and interaction with groundwater in an arid region |
| VerfasserIn |
Dalal Alshamsi, Ahmed Murad, Ala Aldahan, Xiaolin Hou, Ayman El Saiy |
| Konferenz |
EGU General Assembly 2014
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| Medientyp |
Artikel
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| Sprache |
Englisch
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| Digitales Dokument |
PDF |
| Erschienen |
In: GRA - Volume 16 (2014) |
| Datensatznummer |
250098026
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| Publikation (Nr.) |
 EGU/EGU2014-13661.pdf |
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| Zusammenfassung |
| Interaction of groundwater with soil and rocks changes the chemical composition
of the water both spatially and temporally. In arid regions, surficial recharge of
groundwater is generally limited to sporadic rainfall events which may cause rapid
interaction between the recharge water and the aquifers materials. Among the elements
that commonly increase in concentration as groundwater interact with the aquifer
materials are the radioactive elements such as uranium and thorium and their decay
chain products. Here, we present data on 235U, 238U, 232Th as well as 137Cs in
some sediments and rock aquifers located in the United Arab Emirates (UAE) in
southeastern Arabian Peninsula. The Quaternary sediments are composed of silt, sand
and gravel with varying proportions of quartz, carbonates, feldspars, evaporites,
while the carbonates are mainly limestones, dolomitic limestones, dolomite and
calcareous mudstones. These carbonate rocks cover ages extending from 10-230 Myr.
After complete digestion using fluoric and nitric acids and chemical separation, the
isotopes were measured using ICP-MS. The 235U, 238U and 232Th concentrations
ranges are 2.66-32.5 ng/g, 354.7-4453 ng/g and 13.2-1367 ng/g respectively in the
carbonate rocks. In the sediments the concentrations are 4.6-17.5 ng/g for 235U,
631.7-2406 ng/g for 238U and 25.6-799.6 ng/g for 232Th. Although it is difficult to
quantify the amounts of uranium isotopes that enter the hydrological system from
the aquifers, it seems that in the presence of carboxyl ions, uranium forms highly
soluble complexes which can be transported to large distances in groundwater. The
variations in 232Th concentrations are probably controlled by the availability of sulfate
salt rocks (like gypsum) interacting with thorium and forming soluble thorium
compounds which can also explain the highly variable concentrations in groundwater. |
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