G. Lord 1 , H. Farnfield 1 , N. Kim 2 , S. Beard 2 , K. Luketina 2 and Prof. N. I. Ward 1

1. Mokena Geyser Hells Gate Waipupumahana Top Inlet Spring, Waikite Whangapoa Atiamuri School Wai-O-Tapu HT Geyser Matapan Rd Spring South (SE) Spring Parekiri Pool Orakei Korako Waipapa Spring Rotokawa Lake Taharepa Spring Takarea #5 Taumatapuhipuhi Arsenic Speciation Analysis of Geothermal Waters in New Zealand G. Lord1, H. Farnfield1, N. Kim2, S. Beard2, K. Luketina2 and Prof. N. I. Ward1 • 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: WHO drinking guideline limit of 0.010 mg L-1 As (Smith et al., 2004). Arsenate Arsenite [As(V)] [As(III)] Monomethylarsonic acid Dimethylarsinic acid [MA] [DMA] Figure 7: Acute Toxicity of arsenic species (Hughes, 2002) Figure 8: Arsenic species Figure 1: Sampling locations 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: 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: • Surface geothermal water samples were collected across the Waikato region and Taupo Volcanic zone for geochemical environmental monitoring. • Variable total arsenic concentrations were established, all of which exceed the WHO drinking water guideline of 0.010 mg L-1 As. • SPE speciation studies revealed predominantly inorganic arsenic fractions; mostly As(III). • Inorganic As(V) only recovered from water samples with pH>6.3. • Variable organic arsenic fractions collected across the sample sites. • 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. Figures 3-6: Mokena Geyser; Champagne Pool, Wai-O-Tapu; Manganese Pool, Orakei Korako; Takarea #5, Tokaanu Figure 2: Total arsenic analysis results 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. 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).