Organic and inorganic colloids impacting total iodine behavior in groundwater from the Datong Basin, China

Kun Qian; Junxia Li; Xianjun Xie; Yanxin Wang

doi:10.1016/j.scitotenv.2017.05.127

Organic and inorganic colloids impacting total iodine behavior in groundwater from the Datong Basin, China

Sci Total Environ. 2017 Dec 1:601-602:380-390. doi: 10.1016/j.scitotenv.2017.05.127. Epub 2017 May 30.

Authors

Kun Qian¹, Junxia Li¹, Xianjun Xie², Yanxin Wang³

Affiliations

¹ State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China.
² State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China. Electronic address: xjxie@cug.edu.cn.
³ State Key Laboratory of Biogeology and Environmental Geology, School of Environmental Studies, China University of Geosciences, 430074 Wuhan, China. Electronic address: yx.wang@cug.edu.cn.

PMID: 28575821
DOI: 10.1016/j.scitotenv.2017.05.127

Abstract

The geochemical behaviors of colloids in aquifers played an important role in determining the fate of iodine in groundwater system. To decipher the impact of colloids on iodine mobilization in aquifers, three successive pore-sized colloids filtration (0.45μm, 30kDa and 5kDa) were conducted on in-situ during groundwater sampling. The results showed that the distribution ratios (f) of total iodine (I_T) and iron in the dissolved solution (i.e., 5kDa ultrafiltered) were from 0.78 to 0.99 and from 0.56 to 0.94, respectively. Natural organic matter (NOM) in the colloidal fractions obtained the f values ranging from 0.14 to 1.00. The decreased Eh values from recharge area to discharge area indicated redox potential of groundwater system changed from oxidizing to reducing along groundwater flowpath, and interestingly, the corresponding iodine fractions in groundwater were decreasing in dissolved solution and increasing in colloidal fractions. Inverse correlation between Fe and DOC and positive correlation between iodine and DOC suggested the occurrence of reductive dissolution of iron oxyhydroxides and degradation of organic iodine in groundwater system. Iodine distribution increased in dissolved solution and decreased in colloids with pH increase. Moreover, as pH increased, f (Fe) and f (DOC) decreased in dissolved solution and increased in colloids. Relatively weak correlation of f (I_T) with f (Fe) and strong relationship between f (I_T) and f (DOC) in the large grain size fractions suggested the Fe-OM complexes controlled iodine distribution in groundwater, which depends on the presence of Fe bridges. Negligible association of iodine with Fe and NOM in the small grain size fractions might be attributed to the effects of abundant OH^- content in groundwater.

Keywords: Colloids; Desorption; Grain size fractionation; Iodine; Redox potential.