G. Lord1, H. Farnfield1, N. Kim2, S. Beard2, K. Luketina2 and Prof. N. I. Ward1

Arsenic Speciation Analysis of Geothermal Waters in New Zealand

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 ZealandINTRODUCTION: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.

Waipupumahana

HT Geyser

Whangapoa

Parekiri Pool

Rotokawa Lake

Waipapa Spring

Taharepa Spring

South (SE) Spring

Orakei Korako

Top Inlet Spring, Waikite

Hells Gate

Wai-O-TapuAtiamuri School

Taumatapuhipuhi

Takarea #5

Mokena Geyser

Matapan Rd Spring

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.

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 ICP-OES, Optima 5300 DV, Perkin Elmer, gave R2 values >0.9997 and calculated detection limit of 0.04 mg L-1 As (193.696 nm).

TOTAL ARSENIC RESULTS:Sample Location Temperature

(°C) pH Conductivity (μS/cm @ 25°C)

Total As (mg L-1)

Mokena Geyser 94 7.8 10500 0.86Small Stream, Hells Gate 26 2.1 4290 <DL

Hot water Pool, Hells Gate 30 2.9 2820 <DLWaipupumahana (Horohoro) 45 8.4 908 0.53

Whangapoa - N. Pool, Ohakuri Rd 60.2 7.7 2060 1.02Whangapoa - S. Pool, Ohakuri Rd 60.3 7.6 1850 0.87

Atiamuri School Spring, Ohakuri Rd 13 6.3 74 <DLHT Geyser overflow, Waikite Valley Rd 56.4 9.2 1350 0.46

Top Inlet Spring, Waikite Hot Pools 62 8.8 1040 0.40

Champagne Pool1, Wai-O-Tapu

71 5.4 6140 2.4971 5.4 6140 2.3371 5.4 6140 2.1071 5.4 6140 2.2071 5.4 6140 3.22

Champagne Pool2, Wai-O-Tapu 70 5.3 6180 1.17Champagne Pool3, Wai-O-Tapu 71 5.4 6160 1.89

Silica Terrace, Wai-O-Tapu 15 4.8 5280 4.15Bridal Veil Falls (bottom), Wai-O-Tapu 11 3.1 4240 3.05Sulphur Mounds Bridge, Wai-O-Tapu 18 2.3 3510 0.10Meeting of two streams, Wai-O-Tapu 17 2.4 3820 1.29

Wai-O-Tapu Geyser, Wai-O-Tapu 84 7.0 1500 0.61Oyster Pool, Wai-O-Tapu 71 5.5 2460 0.68

Lake Ngakoro Waterfall, Wai-O-Tapu 24 2.4 3490 0.29Matapan Rd Spring 62.8 8.2 592 0.09

South (SE) Spring, Off Settlers Road 93 7.7 2560 0.52Parekiri Pool, Tirohanga Rd 41 3.2 1810 <DL

Waipapa Spring Feature 54.5 7.2 1800 0.64Manganese Pool, Orakei Korako 75 7.8 1810 0.52Map of Australia, Orakei Korako 81 7.8 1630 0.57

Rotokawa Lake, #4A 78.4 2.3 4420 <DLTaharepa Spring, Taupo 66 7.0 1160 0.13

Takarea #5, Tokaanu 57 6.3 9580 8.74Taumatapuhipuhi, Tokaanu 98 7.6 9300 8.23

Figure 2: Total arsenic analysis results by ICP-OES

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).

ARSENIC SPECIATION:WHO drinking guideline limit of 0.010 mg L-1 As (Smith et al., 2004).

[As(III)] [As(V)]

Monomethylarsonic acid[MA]

Dimethylarsinic acid[DMA]

OH

OH

OH

As OOH

OH

OH

As

OOH

CH3

OH

As

CH3

CH3

OOH As

Arsenite Arsenate

Figures 3-6: Mokena Geyser; Champagne Pool, Wai-O-Tapu; Manganese Pool, Orakei Korako;

Takarea #5, Tokaanu

Chemical Species LD50 (mg As kg-1)

Arsenite 8Arsenate 22MMAIII 2MMAV 916DMAV 648

Figure 7: Acute Toxicity of arsenic species (Hughes, 2002)

Figure 1: Sampling locations

Figure 8: Arsenic species

Sample LocationAs (mg L-1) % Species in Total As

As(III) As(V) MA DMAAs(III) As(V)

Mokena Geyser 1.10 <DLSmall Stream, Hells Gate <DL <DL

Hot water Pool, Hells Gate <DL <DLWaipupumahana (Horohoro) 0.17 0.20

Whangapoa - N. Pool, Ohakuri Rd 0.64 0.28Whangapoa - S. Pool, Ohakuri Rd 0.52 0.08

Atiamuri School Spring, Ohakuri Rd <DL <DLHT Geyser overflow, Waikite Valley Rd 0.13 0.19

Top Inlet Spring, Waikite Hot Pools 0.09 0.17

Champagne Pool1, Wai-O-Tapu

3.48 <DL4.17 <DL4.01 <DL4.03 <DL3.95 <DL

Champagne Pool2, Wai-O-Tapu 4.01 <DLChampagne Pool3, Wai-O-Tapu 3.97 <DL

Silica Terrace, Wai-O-Tapu 4.62 <DLBridal Veil Falls (bottom), Wai-O-Tapu 3.15 <DLSulphur Mounds Bridge, Wai-O-Tapu 0.29 <DLMeeting of two streams, Wai-O-Tapu 1.20 <DL

Wai-O-Tapu Geyser, Wai-O-Tapu 0.33 <DLOyster Pool, Wai-O-Tapu 0.60 <DL

Lake Ngakoro Waterfall, Wai-O-Tapu 0.21 <DLMatapan Rd Spring <DL 0.06

South (SE) Spring, Off Settlers Road 0.56 <DLParekiri Pool, Tirohanga Rd <DL <DL

Waipapa Spring Feature 0.61 <DLManganese Pool, Orakei Korako 0.39 0.23Map of Australia, Orakei Korako 0.43 0.09

Rotokawa Lake, #4A 0.20 <DLTaharepa Spring, Taupo 0.11 <DL

Takarea #5, Tokaanu 8.07 0.94Taumatapuhipuhi, Tokaanu 8.49 0.34

0% 50% 100%Figure 9: Arsenic speciation data Figures 10-12: Hot water pool, Hells Gate; Bridal Veil Falls, Wai-

O-Tapu; Rotakawa Lake; Taumatapuhipuhi,

Tokaanu

[As(III)] ranges from 0.09 – 8.49 mg L-1 As[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

CONCLUSIONS: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, 1-16Smith, A. and Smith, M., Arsenic drinking water regulations in developing countries with extensive exposure, Toxicol., 2004, 198, 39-44Watts, 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.