TITLE:
Mobilization of Arsenic in Groundwater in the Southern Hanoi City (Vietnam) as Studied by Isotopic and Related Techniques
AUTHORS:
Dang Duc Nhan, Doan Van Canh, Pham Quy Nhan, Nguyen Thi Thanh Thuy, Dinh Thi Bich Lieu, Vo Thi Anh, Dang Anh Minh
KEYWORDS:
Arsenic Mobilization; Isotopic Technique; Groundwater; Nom Bio-Mineralization; As-Bicarbonate Displacement
JOURNAL NAME:
Journal of Environmental Protection,
Vol.4 No.7A,
July
17,
2013
ABSTRACT: Sixteen samples of surface
and groundwater from the most southern part of the Hanoi city (Vietnam) has
been taken and analyzed for the soluble major ions, namely Na+, K+, , Ca2+, Mg2+,
Cl-, , and arsenic as well as
molybdenum content along with isotopic composition of deuterium and oxygen (δ2H and δ18O), tritium activity, and δ13C in DIC. The stable isotopic composition of
groundwater indicates the water in that area is recharged from the local
meteoric and theRed River’s water sources.
The mean residence time of the groundwater should be before 60-ies of the past
century as its 3H activity ranged from LOD of the analytical
technique (0.4 TU) to 2.1 TU only implying that As would not be related to its
recent application. The concentrations of As in the water samples is weakly
correlated with those of Fe2+ (R2 = 0.08) but it strongly did with the
concentrations of bicarbonate (R2 = 0.80). Thus, bicarbonate seems to
liberate As adsorbed on hydrous ferric oxides (Hfo) into water through the
displacement mechanism. The surface adsorption-desorption of As could be proven
by a strong correlation between As and Mo concentrations (R2 = 0.77). The bicarbonate formation in
groundwater was thought to be, partly, due to the bio-mineralization of natural
organic matter (NOM) by bacteria followed by the dissolution of calcite and/or
dolomite present in the sediments. Evidence for the NOM bio-mineralization was
found in the close relationship between δ13C and the concentration of bicarbonate in water.
Therefore, the mobilization of As in groundwater of bicarbonate type in the
southern part of Hanoi city seems to be not only due to the reductive
dissolution of the Hfo but the bicarbonate displacement also should be
considered.