1. G. Lord 1, H. Farnfield 1, N. Kim 2, S. Beard 2, K. Luketina 2 and Prof. N. I. Ward 1 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 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. 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-Tapu Atiamuri 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 R 2 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 947.8105000.86 Small Stream, Hells Gate 262.14290<DL Hot water Pool, Hells Gate 302.92820<DL Waipupumahana (Horohoro) 458.49080.53 Whangapoa - N. Pool, Ohakuri Rd 60.27.720601.02 Whangapoa - S. Pool, Ohakuri Rd 60.37.618500.87 Atiamuri School Spring, Ohakuri Rd 136.374<DL HT Geyser overflow, Waikite Valley Rd 56.49.213500.46 Top Inlet Spring, Waikite Hot Pools 628.810400.40 Champagne Pool 1, Wai-O-Tapu 715.461402.49 715.461402.33 715.461402.10 715.461402.20 715.461403.22 Champagne Pool 2, Wai-O-Tapu 705.361801.17 Champagne Pool 3, Wai-O-Tapu 715.461601.89 Silica Terrace, Wai-O-Tapu 154.852804.15 Bridal Veil Falls (bottom), Wai-O-Tapu 113.142403.05 Sulphur Mounds Bridge, Wai-O-Tapu 182.335100.10 Meeting of two streams, Wai-O-Tapu 172.438201.29 Wai-O-Tapu Geyser, Wai-O-Tapu 847.015000.61 Oyster Pool, Wai-O-Tapu 715.524600.68 Lake Ngakoro Waterfall, Wai-O-Tapu 242.434900.29 Matapan Rd Spring 62.88.25920.09 South (SE) Spring, Off Settlers Road 937.725600.52 Parekiri Pool, Tirohanga Rd 413.21810<DL Waipapa Spring Feature 54.57.218000.64 Manganese Pool, Orakei Korako 757.818100.52 Map of Australia, Orakei Korako 817.816300.57 Rotokawa Lake, #4A 78.42.34420<DL Taharepa Spring, Taupo 667.011600.13 Takarea #5, Tokaanu 576.395808.74 Taumatapuhipuhi, Tokaanu 987.693008.23 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] Arsenite Arsenate Figures 3-6: Mokena Geyser; Champagne Pool, Wai-O-Tapu; Manganese Pool, Orakei Korako; Takarea #5, Tokaanu Chemical SpeciesLD 50 (mg As kg -1 ) Arsenite8 Arsenate22 MMA III 2 MMA V 916 DMA V 648 Figure 7: Acute Toxicity of arsenic species (Hughes, 2002) Figure 1: Sampling locations Figure 8: Arsenic species Sample Location As (mg L -1 ) % Species in Total As As(III) As(V) MA DMA As(III)As(V) Mokena Geyser 1.10<DL Small Stream, Hells Gate <DL Hot water Pool, Hells Gate <DL Waipupumahana (Horohoro) 0.170.20 Whangapoa - N. Pool, Ohakuri Rd 0.640.28 Whangapoa - S. Pool, Ohakuri Rd 0.520.08 Atiamuri School Spring, Ohakuri Rd <DL HT Geyser overflow, Waikite Valley Rd 0.130.19 Top Inlet Spring, Waikite Hot Pools 0.090.17 Champagne Pool 1, Wai-O-Tapu 3.48<DL 4.17<DL 4.01<DL 4.03<DL 3.95<DL Champagne Pool 2, Wai-O-Tapu 4.01<DL Champagne Pool 3, Wai-O-Tapu 3.97<DL Silica Terrace, Wai-O-Tapu 4.62<DL Bridal Veil Falls (bottom), Wai-O-Tapu 3.15<DL Sulphur Mounds Bridge, Wai-O-Tapu 0.29<DL Meeting of two streams, Wai-O-Tapu 1.20<DL Wai-O-Tapu Geyser, Wai-O-Tapu 0.33<DL Oyster Pool, Wai-O-Tapu 0.60<DL Lake Ngakoro Waterfall, Wai-O-Tapu 0.21<DL Matapan Rd Spring <DL0.06 South (SE) Spring, Off Settlers Road 0.56<DL Parekiri Pool, Tirohanga Rd <DL Waipapa Spring Feature 0.61<DL Manganese Pool, Orakei Korako 0.390.23 Map of Australia, Orakei Korako 0.430.09 Rotokawa Lake, #4A 0.20<DL Taharepa Spring, Taupo 0.11<DL Takarea #5, Tokaanu 8.070.94 Taumatapuhipuhi, Tokaanu 8.490.34 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, 1-16 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.