10th Asian Regional Conference of IAEG (2015)

Change in Chemical Species of Arsenic in Groundwater and Surface Water
Asumi SAKAGUCHI(1), Mingming XIE(2), and Toshifumi IGARASHI(3)(1) Graduate School of Engineering, Hokkaido University, Japan
E-mail: sakaguchi@trans-er.eng.hokudai.ac.jp(2) Pacific Consultants Co., Ltd., Japan(3) Faculty of Engineering, Hokkaido University, Japan
Abstract
Groundwater is used for melting snow in several cities in Hokkaido. The mixture ofgroundwater and melted snow is released to the surrounding rivers. This is an energy-saving
system by using higher temperature groundwater. However, if the groundwater contains
arsenic (As), the impact of using the groundwater should be evaluated. In this study, theconcentrations and chemical species of As in groundwater and surface water in a city wereanalyzed to evaluate the fate of As-bearing groundwater. The As concentration ingroundwater ranged from 23 to 95 µg/L, and the major chemical species of As wasdissolved arsenite (As(III)). However, once the groundwater was discharged to the nearbyriver, the major chemical species of As were changed to suspended one due to the oxidationof ferrous ion coexistent in the groundwater and the subsequent formation of ironprecipitate. Thus, the change in chemical species of As is important to evaluate the impactof As on the environment.
Keywords: arsenic, groundwater, chemical species, oxidation
1.

Introduction

2.

Arsenic (As) is one of toxic elements, andrecently it is well known that naturally occurring As
contributes to serious health problems in the world(Acharyya et al., 2000; Akai et al., 2004; Berg et al.,
2001; Das et al., 1996; Del Razo et al., 1990;
Dowling et al., 2002; Nickson et al., 2002; Smedley
and Kinniburgh, 2002; Williams et al., 1996).
Groundwater with higher As concentration is used forsnow melt in a city. The Quaternary layers of the city
lie thick, and the groundwater is rich. In theenvironmental assessments of the use of thegroundwater, the chemical species of As should beevaluated because the toxicity of As depends on its
chemical species. Also, evaluating chemical speciesof As is important to understand the behavior of As inthe environment.
In this study, chemical properties, in particularchemical species of As, of groundwater and surface
water in the city where groundwater is used for snow
melt were investigated by periodic sampling
campaigns.

Samples and Methods

2.1 Samples
Seven water samples, two groundwater samples(S-1 and S-2) and five surface water samples (TJ, MO,TR, TD, and HA) were taken in the city for analysis.
Figure 1 shows the location of sampling points. S-1
and S-2 are groundwater samples. Sample TJ is notaffected by groundwater from snow melt pits. The
drainage from sampling point of S-1 and the drainage
from the other snow melting pits join at the sampling
point of HA. The drainage from the sampling point of
S-2 and the drainage from the other snow melting pits
join at the sampling point of MO. The sampling pointof TR is located downstream of the sampling points
of TJ and MO.
Groundwater samples were taken once a monthfrom October 2013 to September 2014. Surface water
samples were also taken once a month from October
2013 to December 2014.

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10th Asian Regional Conference of IAEG (2015)

3.

Results

3.1 Groundwater
Figure 2 shows changes in the total As
concentration of groundwater. The total As
concentration changed from 23 to 95 µg/L. Figure 3
presents the chemical species of As and Fe of S-2
collected in June 2014. The major species of As wasdissolved As(III). The major species of Fe wasdissolved Fe. This means that the chemical species ofFe is ferrous ion (Fe2+) by considering the pH range.
The pH of groundwater samples was almost
neutral, and the EC was around 20 mS/m. The
temperature ranged from 10 to 15 ℃, and the Eh wasaround 150 mV. The major cation was Na of around20 mg/L. The dissolved Fe concentrations of S-1 andS-2 were around 50 and 20 mg/L, respectively, andthe Si concentration was around 20 mg/L.

Fig. 1 Location of sampling points

2.2 Analysis of samples
The temperature, pH, electrical conductivity (EC)and oxidation-reduction potential (ORP) ofgroundwater samples were measured in situ. Only thetemperature and EC were measured in situ, and thepH and ORP were measured in the laboratory forsurface water samples. Groundwater samples werefiltrated with 0.45 µm Millex® membrane filters insitu whereas surface water samples were filtrated
with the same filters in the laboratory. This is due tothe difference in the redox condition between
groundwater and surface water.
Chemical analyses were conducted in thelaboratory. Bicarbonate ion (HCO3-) concentration
was measured by titration with 0.01 mol/L sulfuric
acid until pH 4.8. The concentrations of anions(chloride ion (Cl-), sulfate ion (SO4-), and nitrate ion(NO3-)) were analyzed by an anion chromatograph(ICS-1000, Dionex Corporation, USA). The
concentrations of other elements (sodium (Na),potassium (K), calcium (Ca), magnesium (Mg), iron(Fe), and silica (Si)) were determined by inductively
coupled plasma atomic emission spectrometer(ICP-AES) (ICPE-9000, Shimadzu Corporation,Japan). Filtrated samples with 0.45 µm membranefilters were provided for anion analysis. For ICP-AES
analysis, 1 or 1.5% hydrochloric acid (HCl) or nitricacid (HNO3) was added to both original and filtrated
samples to dissolve precipitates. For Fe and Si, total
and dissolved concentrations were measured. To
determine As concentration, hydride generation(HVG-1, Shimadzu Corporation, Japan) attached toICP-AES was used. Sep-Pak® cartridges (WatersCorporation, USA), were also used to remove As(V)from filtered samples. Thus, As can be divided into
three species, dissolved As(III), dissolved total As,
and total As including suspended solid. Dissolved
As(V) can be calculated by subtracting dissolved
As(III) from dissolved total As.

Fig. 2 Changes in total As concentration ofgroundwater

Fig. 3 Chemical species of (a) As and (b) Fe of
S-2 collected in June 2014
3.2 Surface water
Figure 4 shows changes in the total As
concentration of surface water samples. The total As
concentration varied from 2 to 71 µg/L. Higher As2

10th Asian Regional Conference of IAEG (2015)

concentration was observed in January 2014. Figure 5
presents the major chemical species of As and Fe of
HA collected in June 2014. The major species of As
and Fe were suspended ones. These results indicatethat the higher As concentration is due to the higher
suspended solids in surface water.
The pH was almost neutral, and the EC wasaround 30 mS/m. The Eh varied 200 to 400 mV. Themajor cations were Na and Ca ranging from 20 to 60
mg/L. The Si concentration was around 10 mg/L.

formed in the river. It is likely that the resultant Fehydroxides adsorb As or Fe and As coprecipitate
because iron hydroxides have a high affinity to As(Tokoro et al., 2001).
Figure 6 shows the relationship between total As
concentration and total Fe concentration. There is apositive correlation between total As and total Fe.
This relationship implies that Fe plays an importantrole in As mobility in the aquatic environment.
Environmental assessments of the use ofgroundwater should be conducted by considering thechanges in chemical species of As.

Fig. 4 Changes in total As concentration ofsurface water

Fig. 6 Total As concentration vs. total Fe
concentration

5.

Conclusions

The results obtained in this study are as follows:(1) The As concentrations in groundwater and surface
water ranged 23 to 95 µg/L and 2 to 71 µg/L,respectively.
(2) The major chemical species of As in groundwater
was dissolved As(III) whereas that in surface water
was suspended As.
(3) The major chemical species of Fe in groundwater
was dissolved Fe(II) whereas that in surface water
was suspended Fe.
(4) The above results indicate that dissolved As(III)in groundwater is oxidized to dissolved As(V), andthen precipitated with Fe hydroxides in surfacewater.

Fig. 5 Chemical species of (a) As and (b) Fe of
HA collected in June 2014

4.

Discussion
Major chemical species of As in groundwater wasdissolved As(III) whereas that in surface water wassuspended As. On the other hand, major chemical
species of Fe in groundwater was dissolved Fe, that isFe(II), whereas that in surface water was suspended
Fe. These indicate that the dissolved As(III) anddissolved Fe(II) in groundwater were oxidized todissolved As(V) and Fe(III) once the groundwater
flowed into rivers, and that Fe(III) hydroxides wereReferences
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