This study focused on the associations of U and Pu with humic substances and the implications for migration in deciduous broadleaf and coniferous forest soils. Humic substances were isolated from soil samples by (i) solvent extraction (0.045 M Tris-borate and 0.1 N NaOH) and (ii) novel gel electrophoretic extraction (pH 8.5; 0.045 M Tris-borate as running buffer). Gel electrophoresis was also used to extract humic substances from soil that had been 'pre-equilibrated' with a solution containing <sup>236</sup>U or <sup>242</sup>Pu (pH 4.2). The relative concentrations of humic substances in the solvent and electrophoretic extracts were obtained by UV-visible spectrophotometry (A<sub>254</sub> <sub>nm</sub>) whilst the <sup>238</sup>U concentrations in the extracts were determined by inductively coupled plasma-mass spectrometry (ICP-MS). In addition, the molecular size and functional group content of the humic molecules in selected fractions of the gel electrophoretic extracts were investigated using gel filtration chromatography and FTIR spectroscopy, respectively. The methodology developed in this study enabled identification of several operationally defined soil actinide pools: (i) labile (< 0.2 mm, at pH 4.2), (ii) hydrophilic-mobile (< 0.15 mm, negatively-charged at pH 8.5) and (iii) immobile (> 0.15 mm and/or uncharged at pH 8.5). The adopted procedures avoid the extremes of pH used in the traditional methods of extraction (pH 13) and fractionation (pH < 2) which may alter humic substances. It was found that the <sup>238</sup>U content of the hydrophilic-mobile pool (i.e. the gel electrophoretic extract) accounted for 14-41 % and 15-34 % of the total <sup>238</sup>U in the deciduous broadleaf and coniferous forest soils, respectively. In general, these values were grater than those obtained by 0.045 M Tris-borate solvent extraction but less than those obtained using 0.1 N NaOH as the solvent. A further advantage of the new methodology was that the distribution of <sup>238</sup>U within the humic extract could be investigated.
| Identifer | oai:union.ndltd.org:bl.uk/oai:ethos.bl.uk:663288 |
| Date | January 2000 |
| Creators | Vinogradoff, Susan I. |
| Publisher | University of Edinburgh |
| Source Sets | Ethos UK |
| Detected Language | English |
| Type | Electronic Thesis or Dissertation |
| Source | http://hdl.handle.net/1842/14611 |
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