45 μm enclosed syringe filter unit and aliquots transferred to colourimetric reagents or subject to appropriate acid preservation. For on-site separation of As(III) species about ∼50 mL of 0.45 μm-filtered water was passed through solid arsenic-speciation cartridges
(Metalsoft) and preserved with concentrated HCl. The cartridge contains highly selective aluminosilicate that adsorbs As(V) and allows only As(III) to pass through the column (Le et al., 2000). For cations and trace metals, 50 mL of filtrate was preserved with 0.3 mL of concentrated HNO3−. For anions, the filtrate was pre-treated with 2 g per 50 mL of cation exchange resin [BioRad AG50W-XB (142–1421)] to prevent metal precipitation and subsequent scavenging of anions. All the water samples were protected
from sunlight and stored at 4 °C until further selleck chemicals analysis. Spectrophotometric analysis was performed on the same day of sample collection for dissolved Fe2+ and total Fe (FeTot) by the 1,10 Phenanthroline method (APHA, 2005); sulfide by the methylene blue method (Cline, 1969); alkalinity by the bromophenol blue method (Sarazin et al., 1999); phosphate by the ammonium molybdate method (Murphy and Riley, 1958); and ammonia by the salicylate method (Chemetrics® vacuvials kits). Additional UV–visible spectra were collected Ku-0059436 chemical structure on a filtered aliquot of each sample using an ocean optics portable spectrophotometer equipped with a 10 mm path length quartz cell (Dahlen et al., 2000). Arsenic was analyzed by Hydride Generation Atomic Absorption Spectrophotometry (HG-AAS; AA280FS, VARIAN Australia Pyt Ltd, Australia) (McCleskey et al., 2004) with a detection limit of 3.4 nM and a precision within 5%. Individual samples were analyzed in quadruplicate and data presented are means. Major cations, anions and trace elements were analyzed at the Environmental Analysis Laboratory (EAL), Southern Cross University (SCU). Cations (Na, K, Ca, Mg), trace elements (arsenic, Methocarbamol manganese, boron, molybdenum, vanadium, silver, mercury, silicon, iron, lead, chromium, cobalt, zinc, nickel, copper, barium, cadmium, aluminum and selenium) and anions (chloride, sulfur, phosphorus
and bromide) were analyzed by inductively coupled plasma mass spectrometry (ICP-MS) (Perkin-Elmer ELAN-DRCe). For the purposes of this study, sulfur was assumed to be primarily SO42−, as S(-II) was below detection limits. Nitrate, nitrite and fluoride were analyzed by flow injection analysis (FIA) (LACHAT QuikChem 8000). Saturation indices (SI) were calculated using PHREEQC-2 for Windows V 2.15.06 (Parkhurst and Appelo, 1999) with stability constants derived from the Minteq database. Tubewell geochemical data are summarized in Table 1 and presented in relation to the depth of tubewell in Fig. 2. The groundwater is circum-neutral with pH (6.7–7.5) and the redox potential (pE) between 0.9 and 4.1 indicating the groundwaters are predominately moderately reducing and suboxic.