Transcript Slide 1

Arsenic Speciation Analysis of Geothermal
Waters in New Zealand
G.
1
Lord ,
H.
1
Farnfield ,
2
Kim ,
N.
S.
2
Beard ,
K.
2
Luketina
and Prof. N. I.
1
Ward
1.
ICP-MS Facility, Chemistry, School of Biomedical and Molecular Sciences, University of Surrey,
Guildford, Surrey, GU2 7XH
2. Environment Waikato (Waikato Regional Council), PO Box 4010, Hamilton East, Hamilton 3247, New Zealand
INTRODUCTION:
The association of arsenic with geothermal systems is widely known, with elevated concentrations often found in soils or ground waters
due to this natural source. In collaboration with Environment Waikato - a local regional council, geothermal waters from an active
geothermal region – the Taupo Volcanic Zone - in New Zealand were investigated for the trace element arsenic. Geothermal water
samples were analysed by ICP-OES for total elemental arsenic and four arsenic species (As(III), As(V), DMA and MA) via an in-field
separation and preservation technique. Elevated total arsenic levels were found across the entire region, with the highest levels of 8.74 and
8.23 mg L-1 found south of Lake Taupo. Speciation studies revealed inorganic arsenic to be the predominant species, contributing to
>60% of the total arsenic for all samples.
STUDY AREA:
The Taupo Volcanic Zone is a
region of enhanced volcanic and
geothermal activity located in the
North Island of New Zealand. Much
of this activity occurs within the
Waikato district and is closely
monitored by Environment Waikato.
Twenty-seven geothermal water sites
were selected for sampling across
this
region
(Figure
1)
by
Environment
Waikato
in
collaboration with Prof. N. I. Ward
of the University of Surrey.
ARSENIC SPECIATION:
Mokena Geyser
WHO drinking guideline limit of
0.010 mg L-1 As (Smith et al., 2004).
Hells Gate
Waipupumahana
Top Inlet Spring,
Whangapoa
Waikite
Atiamuri School
HT Geyser Wai-O-Tapu
Matapan Rd Spring
South (SE)
Spring
Parekiri Pool
Orakei Korako
Waipapa Spring
Champagne Pool1, Wai-O-Tapu
Champagne Pool2, Wai-O-Tapu
Champagne Pool3, Wai-O-Tapu
Silica Terrace, Wai-O-Tapu
Bridal Veil Falls (bottom), Wai-O-Tapu
Sulphur Mounds Bridge, Wai-O-Tapu
Meeting of two streams, Wai-O-Tapu
Wai-O-Tapu Geyser, Wai-O-Tapu
Oyster Pool, Wai-O-Tapu
Lake Ngakoro Waterfall, Wai-O-Tapu
Matapan Rd Spring
South (SE) Spring, Off Settlers Road
Parekiri Pool, Tirohanga Rd
Waipapa Spring Feature
Manganese Pool, Orakei Korako
Map of Australia, Orakei Korako
Rotokawa Lake, #4A
Taharepa Spring, Taupo
Takarea #5, Tokaanu
Taumatapuhipuhi, Tokaanu
Taharepa Spring
Takarea #5
Taumatapuhipuhi
Figure 1: Sampling locations
Temperature
(°C)
pH
Conductivity
(μS/cm @ 25°C)
Total As
(mg L-1)
94
26
30
45
60.2
60.3
13
56.4
62
71
71
71
71
71
70
71
15
11
18
17
84
71
24
62.8
93
41
54.5
75
81
78.4
66
57
98
7.8
2.1
2.9
8.4
7.7
7.6
6.3
9.2
8.8
5.4
5.4
5.4
5.4
5.4
5.3
5.4
4.8
3.1
2.3
2.4
7.0
5.5
2.4
8.2
7.7
3.2
7.2
7.8
7.8
2.3
7.0
6.3
7.6
10500
4290
2820
908
2060
1850
74
1350
1040
6140
6140
6140
6140
6140
6180
6160
5280
4240
3510
3820
1500
2460
3490
592
2560
1810
1800
1810
1630
4420
1160
9580
9300
0.86
<DL
<DL
0.53
1.02
0.87
<DL
0.46
0.40
2.49
2.33
2.10
2.20
3.22
1.17
1.89
4.15
3.05
0.10
1.29
0.61
0.68
0.29
0.09
0.52
<DL
0.64
0.52
0.57
<DL
0.13
8.74
8.23
Figure 2: Total arsenic analysis results by ICP-OES
LD50 (mg As
8
22
2
916
648
HO
1.10
<DL
<DL
0.17
0.64
0.52
<DL
0.13
0.09
3.48
4.17
4.01
4.03
3.95
4.01
3.97
4.62
3.15
0.29
1.20
0.33
0.60
0.21
<DL
0.56
<DL
0.61
0.39
0.43
0.20
0.11
8.07
8.49
<DL
<DL
<DL
0.20
0.28
0.08
<DL
0.19
0.17
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
<DL
0.06
<DL
<DL
<DL
0.23
0.09
<DL
<DL
0.94
0.34
Mokena Geyser
Small Stream, Hells Gate
Hot water Pool, Hells Gate
Waipupumahana (Horohoro)
Whangapoa - N. Pool, Ohakuri Rd
Whangapoa - S. Pool, Ohakuri Rd
Atiamuri School Spring, Ohakuri Rd
HT Geyser overflow, Waikite Valley Rd
Top Inlet Spring, Waikite Hot Pools
Champagne Pool1, Wai-O-Tapu
Champagne Pool2, Wai-O-Tapu
Champagne Pool3, Wai-O-Tapu
Silica Terrace, Wai-O-Tapu
Bridal Veil Falls (bottom), Wai-O-Tapu
Sulphur Mounds Bridge, Wai-O-Tapu
Meeting of two streams, Wai-O-Tapu
Wai-O-Tapu Geyser, Wai-O-Tapu
Oyster Pool, Wai-O-Tapu
Lake Ngakoro Waterfall, Wai-O-Tapu
Matapan Rd Spring
South (SE) Spring, Off Settlers Road
Parekiri Pool, Tirohanga Rd
Waipapa Spring Feature
Manganese Pool, Orakei Korako
Map of Australia, Orakei Korako
Rotokawa Lake, #4A
Taharepa Spring, Taupo
Takarea #5, Tokaanu
Taumatapuhipuhi, Tokaanu
Figure 9: Arsenic speciation data
As
CH3
OH
HO
As
O
OH
Arsenate
[As(V)]
Arsenite
[As(III)]
HO
O
As
O
CH3
CH3
Monomethylarsonic acid
[MA]
As (mg L-1)
As(V)
HO
OH
kg-1)
As(III)
OH
As
Figure 7: Acute Toxicity of arsenic species (Hughes, 2002)
Rotokawa Lake
TOTAL ARSENIC RESULTS:
Mokena Geyser
Small Stream, Hells Gate
Hot water Pool, Hells Gate
Waipupumahana (Horohoro)
Whangapoa - N. Pool, Ohakuri Rd
Whangapoa - S. Pool, Ohakuri Rd
Atiamuri School Spring, Ohakuri Rd
HT Geyser overflow, Waikite Valley Rd
Top Inlet Spring, Waikite Hot Pools
Chemical Species
Arsenite
Arsenate
MMAIII
MMAV
DMAV
Sample Location
SAMPLES:
Surface water samples were collected for total arsenic analysis and
arsenic speciation analysis via a field-based solid phase extraction
(SPE) technique detailed by Watts et al., 2010.
ANALYSIS:
Standards over the range 0.025 – 10 mg L-1 As measured by ICPOES, Optima 5300 DV, Perkin Elmer, gave R2 values >0.9997 and
calculated detection limit of 0.04 mg L-1 As (193.696 nm).
Sample Location
OH
Dimethylarsinic acid
[DMA]
Figure 8: Arsenic species
% Species in Total As
As(III)
0%
0%
20%
As(V)
MA DMA
50%
40%
60%
L-1 As
[As(III)] ranges from 0.09 – 8.49 mg
[As(V)] ranges from 0.06 – 0.94 mg L-1 As
[DMA] ranges from 0.11 – 0.18 mg L-1 As
[MA] ranges from 0.04 – 0.98 mg L-1 As
80%
100%
100%
Figures 10-12: Hot
water pool, Hells Gate;
Bridal Veil Falls, Wai-OTapu; Rotakawa Lake;
Taumatapuhipuhi,
Tokaanu
CONCLUSIONS:
Figures 3-6: Mokena
Geyser; Champagne
Pool, Wai-O-Tapu;
Manganese Pool,
Orakei Korako; Takarea
#5, Tokaanu
INTER-LABORATORY COMPARISON:
No significant difference was found between the total arsenic
concentrations measured by ICP-OES and ICP-MS (Hill Laboratories
Ltd, Hamilton, New Zealand). Data comparison was via a statistical
paired t-test - |t|cal (0.116) < |t|crit (2.75), (99% confidence level).
o Surface geothermal water samples were collected across the
Waikato region and Taupo Volcanic zone for geochemical
environmental monitoring.
o Variable total arsenic concentrations were established, all of which
exceed the WHO drinking water guideline of 0.010 mg L-1 As.
o SPE speciation studies revealed predominantly inorganic arsenic
fractions; mostly As(III).
o Inorganic As(V) only recovered from water samples with pH>6.3.
o Variable organic arsenic fractions collected across the sample sites.
o Sum of arsenic species differ greatly to measured total arsenic at
various Wai-O-Tapu sites – possible presence of organic matter
interfering in the detection of arsenic by ICP-OES.
REFERENCES:
Hughes, M., Arsenic toxicity and potential mechanisms of action, Toxicol. Lett., 2002, 133, 1-16
Smith, A. and Smith, M., Arsenic drinking water regulations in developing countries with extensive exposure, Toxicol., 2004,
198, 39-44
Watts, M. J., O’Reilly, J., Shaw, R. A., Marcilla, A. and Ward, N. I., Field based speciation of arsenic in UK and
Argentinean water samples, Environ. Geochem. Health, 2010, DOI 10.1007/s10653-010-9321-y.