Uranium Distribution and Fluorescence Properties along the Salinity Gradient

초록

Uranium distribution and fluorescence properties of estuarine waters have been examined in the Han River and Keum River estuaries. Water samples were collected across a salinity gradient, ranging from 0.2 to 31.3‰, and dissolved uranium and organic matter have extracted by C-18 (Sep-Pak) cartridge after pre-treatment. Extraction of uranium by C-18 cartridge after complexation with APDC/DDDC shows about 90% recovery. Result shows that uranium extraction recovery efficiency depends on acidification of the sample. Better recovery efficiency at low pH (2.5-2.8) during the pre-treatment of sample presumably relates with destabilization of uranium-carbonate complex. In both the estuaries, uranium shows typical conservative behavior along the salinity gradient above 5‰ (y=0.3312x+1.5175, r2=0.926). The current result substantiates earlier reports that uranium is conservatively transported from the river to the ocean. However, uranium distribution in the upper stream of Keum River showed U-shaped distribution, which implies strong tendency of uranium removal at the low salinity range below 5‰. Fluorescence of extracted organic matter shows distinctive two fluorophores having maximum fluorescence at 280EX/330EM nm (biomacromolecule: BM) and at 330EX/430EM nm (geomacromolecule: GM). After concentration of sample onto C-18 cartridge, GM and BM have been sequentially extracted by 50% and 100% acetonitrile, respectively. Interestingly, degree of uranium extraction is higher in the moderately hydrophobic/hydrophilic organic fraction (humic substance, GM) than in the highly hydrophobic organic fraction (BM). The present results suggest that dissolved humic fraction (GM) is more important in organo-uranium complex and substantial uranium removal in the estuarine system.