Raijeli Taga

Relationship of arsenic speciation and bioavailability in mine wastes for human health risk assessment

Environmental context X-ray absorption near-edge spectroscopy (XANES) was applied to give arsenic chemical forms directly in the solid phase of mine wastes from two mine sites, including fluvial dispersion. The arsenic speciation data explained the variation of in vitro bioaccessibility and in vivo bioavailability (rat uptake) data of the mine wastes. The As speciation from XANES fitting supported the hypothesis that when soil intake is adjusted for bioaccessibility, the potential health risk estimate to local residents is significantly lower. Abstract X-ray absorption near-edge spectroscopy (XANES) was used for arsenic speciation in mine processing and waste samples from two mines in northern Australia. XANES fitting of model compound spectra to samples was used, in combination with in vitro bioaccessibility data for the pure compounds, to predict bioaccessibility of each mine waste sample (Pearson’s correlation R2=0.756, n=51). The XANES fitting data for a smaller set of the samples (n=12) were compared with in vivo bioavailability and in vitro bioaccessibility data. The bioavailability of arsenic (As) in the mine wastes, which is dependent, at least in part, on its oxidation state, was found to be <14% (0.9–13.5%) for arsenite (AsIII) and <17% (3.5–16.4) for arsenate (AsV). Arsenic bioaccessibility in the mine wastes ranged from 8–36% in the stomach to 1–16% in the intestinal phase, indicating that a small portion of the total As concentration in the mine waste was available for absorption. A significant correlation showed that bioaccessibility can be used as a predictor of bioavailability. The XANES results support that bioavailability and bioaccessibility results were very similar and show a strong association with the presence of ferric arsenate and As sulfides. It can be concluded that, when soil intake is adjusted for bioaccessibility, the potential health risk estimate to local residents exposed to the mine waste was significantly lower than that estimated based on a 100% bioavailability often employed for the risk assessment.

X-ray absorption spectroscopy for lead speciation of dispersed mine waste

The Lead Pathway Air Study (2007-2012) was a large study [1] on the human exposure to lead undertaken at Mount Isa, Queensland, Australia. Mount Isa Mines is located west of the city and has mined and processed lead-zinc and copper ores since the 1930s. The Australian health risk assessment framework [2] was followed by using bioavailability and bioaccessibility tests of lead availability together with supporting measurements using sophisticated analytical techniques. Human exposure to lead is from ingestion of <250 μm sized particles via the digestive system and inhalation of <10 μm sized particles into lungs; absorption via skin is insignificant. Extensive sampling and analysis of the mine site and city houses provided physico-chemical characteristics using synchrotron-based X-ray absorption spectroscopy (XAS) using x-ray absorption near-edge spectroscopy (XANES) for estimating lead speciation/composition, high resolution lead isotope measurements and other techniques (XRD, SEM and particle size analysis) to describe multiple sources. Extensive application of lead LIII edge XANES was undertaken by recording spectra of over 300 samples at the Australian National Beamline Facility, located at the Photon Factory (KEK), Tsukuba, Japan. XANES spectra were analysed using a series of steps, as part of a well-defined statistical procedure, to determine the composition of the lead minerals or lead compounds from mineral processing present, including principal component analysis (‘PCA’) followed by target transformation to select the set of model compounds for linear combination fitting. Bioavailability testing on 10 composites using rats was correlated with bioaccessibility on <250 μm fractions using PBET (physiologically-based extraction test) simulating the human digestive tract. Lead solubilised in the stomach is transferred with food nutrients to the intestine where absorption occurs. Average pH with fast, semi-fed and full-fed states of the stomach and near neutral intestine pH provided an intermediate pH for PBET testing. Inhalation is <5 % of total exposure for people living in Mount Isa, while ingestion is >95 %. PM10 air particulates were not the major source of human lead exposure via inhalation in Mount Isa city for this sampling. Ingestion of <250 μm diameter dust is from ground deposition; lead isotope ratios showed lead originated from mining Urquhart Shale and city area outcrops. The XANES analysis of PM10 air particulates exiting from the Mount Isa lead smelter stack contained negligible lead sulfide whereas near surface samples of dust and fallout from the lead smelter/ sinter plant area collected at the surface or at 2-3m above ground usually contained lead sulfide. Lead sulfide in fallout, PM10, carpet dust samples in the city indicated that some of the material collected originated from mining and/or processing activities. However, large proportions of lead–goethite in these samples made it impossible to rule out dusts from other sources, such as garden and exposed soils in the city, haul roads and tailings dams. While lead isotope ratios can show origin of lead regardless of chemical or mineral form, XANES analysis gives the chemical form. XANES analysis may show differences even when lead isotope ratios are shown to be the same.

Identification of lead chemical form in mine waste materials by X‐ray absorption spectroscopy

X‐ray absorption spectroscopy (XAS) provides a direct means for measuring lead chemical forms in complex samples. In this study, XAS was used to identify the presence of plumbojarosite (PbFe6(SO4)4(OH)12) by lead L3‐edge XANES spectra in mine waste from a small gold mining operation in Fiji. The presence of plumbojarosite in tailings was confirmed by XRD but XANES gave better resolution. The potential for human uptake of Pb from tailings was measured using a physiologically based extract test (PBET), an in‐vitro bioaccessibility (BAc) method. The BAc of Pb was 55%. Particle size distribution of tailings indicated that 40% of PM10 particulates exist which could be a potential risk for respiratory effects via the inhalation route. Food items collected in the proximity of the mine site had lead concentrations which exceed food standard guidelines. Lead within the mining lease exceeded sediment guidelines. The results from this study are used to investigate exposure pathways via ingestion and inhalation for p...