| 摘 要： | It has recently been proposed that recalcitrant dissolved organic carbon(DOC) in groundwater plays a potent etiological role in the peculiar distribution of chronic kidney disease of unknown etiology(CKDu).This study aims to elucidate the interactions of Ca~(2+)and SO_4~(2-)with a model organic fraction of humic acid(SHA) to determine the possible relationship of CKDu incidence with the DOC in drinking water.XPS and FT-IR methods respectively determined the surface functional groups and chemical composition of protonated dissolved organic carbon(HDOC) in a CKDu high-risk zone(HR) of Sri Lanka and in SHA.Higher surface C composition(87.9%) and lower O(11.4%) were observed for HDOC from the HR region than for SHA(C: 73.8%, O: 24.7%).Aromatic C with less Ocontaining functional groups was observed in HDOC.The IR band at 1170 cm~(-1) confirms the formation of organic sulfonate(C–SO_3~-) on SHA.A band at 1213 cm~(-1) due to organic sulfonate in HDOC from the CKDu HR region was also identified.The IR band at 866 cm~(-1) evidenced the formation of CaCO_3 on SHA above pH 7.4.XPS data confirmed the presence of sulfur oxidation states corresponding to SO_3~(2-)and SO_4~(2-)at 168.9 eV and 170.1 eV binding energies,respectively.The binding energies at 347 eV and 351 eV for Ca 2p_(3/2) and Ca 2p_(1/2) eV,respectively, confirmed the bidentate complexation of Ca~(2+)with COO-and sulfonate groups on SHA.The organic sulfonate formed is postulated as a uremic toxicant.
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