Characteristics of cadmium remobilization in tributary sediments in Three Gorges Reservoir using chemical sequential extraction and DGT technology.
The Three Gorges Reservoir (TGR) is the largest reservoir in China. Cadmium (Cd) is a primary pollutant in the TGR, and its speciation and bioavailability have attracted extensive attention since TGR submergence. In this study, Chelex-100 DGT (diffusive gradient in thin films) and the sequential extraction method were used to investigate the bioavailable Cd in sediments obtained from a typical tributary (Meixi) and mainstream (Yangtze) in the TGR. The total Cd concentrations in sediments of the four stations were also determined. In comparison to the concentrations of labile Cd measured by DGT (CDGT-Cd) in four profiles, CJ and MX-upstream/downstream were at potential risk for Cd release from surface sediments using the apparent diffusion flux across the interface numerical model. The order of CDGT-Cd in surface sediments was as follows: CJ > MX-downstream > MX-upstream > MX-midstream. Additionally, a positive correlation was demonstrated between CDGT-Cd and Cd in the exchangeable fraction (F1) in the surface sediments, indicating that Cd in the exchangeable fraction was readily captured by DGT. A negative correlation was observed between CDGT-Cd and CDGT-Fe, CDGT-Mn in the sediment-water-interface (SWI), suggesting that Fe/Mn oxides did not control the release of labile-Cd from sediments. Furthermore, a positive correlation existed between the CDGT-Cd in the surface sediments and Cd in the oxidizable fraction (F3), illustrating that Cd sorbed or bound with organic matter or sulfide was labile and released into the water phase from the surface sediments. A dark area was found in the AgI gel, which further demonstrated that Cd simultaneously was released with sulfide in this area.
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China; Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China.
Dongyu
D
Xu
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China; Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China. Electronic address: gaosky34@hotmail.com.
Bo
B
Gao
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China.
Li
L
Gao
State Key Laboratory of Simulation and Regulation of Water Cycle in River Basin, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China; Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China.
Huaidong
H
Zhou
State Key Laboratory of Water Environment Simulation, School of Environment, Beijing Normal University, Beijing, 100875, China.
Xingjuan
X
Zhao
Department of Water Environment, China Institute of Water Resources and Hydropower Research, Beijing, 100038, China.
Shuhua
S
Yin
D002104:Cadmium / Q000032:analysis*; D002681:China; D004784:Environmental Monitoring / Q000295:instrumentation / Q000379:methods*; D019015:Geologic Sediments / Q000032:analysis*; D045483:Rivers / Q000737:chemistry*; D013440:Sulfides / Q000032:analysis; D014874:Water Pollutants, Chemical / Q000032:analysis*
D013440:Sulfides; D014874:Water Pollutants, Chemical; D002104:Cadmium
BCR sequential extraction; Cadmium; Diffusive gradients in thin films (DGT); Sediment-water interface; Three Gorges Reservoir (TGR)