Trang Huynh

Evaluation and Application of the Diffusive Gradients in Thin Films Technique Using a Mixed-Binding Gel Layer for Measuring Inorganic Arsenic and Metals in Mining Impacted Water and Soil

The diffusive gradients in thin films (DGT) equipped with a Chelex or ferrihydrite binding gel has been designed to enable the measurement of either labile metal species or inorganic arsenic, respectively. In the mine impacted environment, metals and metalloids commonly coexist in a variety of species. This study, for the first time reports the performance of the DGT with a mixed-binding layer (MBL), consisting of Chelex and ferrihydrite for measurements of both metals and arsenic in a single assay. The MBL that consists of a combination of Chelex and ferrihydrite at a ratio of 1:2 has the greatest binding capacity for arsenic (As), cadmium (Cd), copper (Cu), lead (Pb), and zinc (Zn). The elemental concentrations measured by using MBL-DGT (C(DGT)) were comparable (92-104%) with the original test solution concentrations (C(SOL)). The measurement of As by using MBL-DGT was consistent across a wide pH range (3-8) and ionic strength (0.001-0.1 M). At high pH (9), As measurement was slightly affected (∼80%). The measurements of Cd, Pb, and Zn were affected at low pH (<3) and high pH (9). Measurements of Cd, Cu, and Pb were affected at low ionic strength (0.001 M). At high ionic strength (0.1 M), measurements of Cd; Cu and Pb were slightly affected. The capacity of MBL-DGT for quantitative measurement in a multielements solution is effectively limited to 15 μg for As and 70 μg for metals per MBL-DGT device. Good correlations (p < 0.01) between MBL-DGT measurements and ferrihydrite or Chelex DGT were obtained for As, Cd, Cu, Pb, and Zn in water and soil with exception for Cd and Cu (p < 0.05) when deployed in soil.

Phytoextraction of heavy metals by willows growing in biosolids under field conditions

Biosolids produced by sewage treatment facilities can exceed guideline thresholds for contaminant elements. Phytoextraction is one technique with the potential to reduce these elements allowing reuse of the biosolids as a soil amendment. In this field trial, cuttings of seven species/cultivars of Salix(willows) were planted directly into soil and into biosolids to identify their suitability for decontaminating biosolids. Trees were irrigated and harvested each year for three consecutive years. Harvested biomass was weighed and analyzed for the contaminant elements: As, Cd, Cu, Cr, Hg, Pb, Ni, and Zn. All Salix cultivars, except S. chilensis, growing in soils produced 10 to 20 t ha(-1) of biomass, whereas most Salix cultivars growing in biosolids produced significantly less biomass (<6 t ha(-1)). Salix matsudana (30 t ha(-1)) and S. × reichardtii A. Kerner (18 t ha(-1)) had similar aboveground biomass production in both soil and biosolids. These were also the most successful cultivars in extracting metals from biosolids, driven by superior biomass increases and not high tissue concentrations. The willows were effectual in extracting the most soluble/exchangeable metals (Cd, 0.18; Ni, 0.40; and Zn, 11.66 kg ha(-1)), whereas Cr and Cu were extracted to a lesser degree (0.02 and 0.11 kg ha(-1)). Low bioavailable elements, As, Hg, and Pb, were not detectable in any of the aboveground biomass of the willows.

Effects of phytoextraction on heavy metal concentrations and pH of pore-water of biosolids determined using an in situ sampling technique

Heavy metal concentrations and pH of pore-water in contaminated substrates are important factors in controlling metal uptake by plants. We investigated the effects of phytoextraction on these properties in the solution phase of biosolids and diluted biosolids in a 12-month phytoextraction column experiment. Phytoextraction using Salix and Populus spp. temporarily decreased pore-water pH of the substrates over the experimental period followed by a return to initial pH conditions. Salixxreichardtii and Populus balsamifera effectively extracted Ni, Zn and Cd and actively mobilized these metals from the solid to the solution phase. S.xreichardtii had the stronger effect on mobilization of metals due to its larger root system. Phytoextraction did not affect Cu in the solution phase of the biosolids. Heavy metals were leached down to lower depths of the columns during the phytoextraction process.

Measurement of labile arsenic speciation in water and soil using diffusive gradients in thin films (DGT) and X-ray absorption near edge spectroscopy (XANES)

The Diffusive Gradients in Thin Films technique is an in-situ sampling technique that can concentrate labile arsenic species from solution. This technique has provided a way to measure the total concentration of labile arsenic, which may be toxic in the environment. A previous study measured arsenic speciation in the solution extracted from the FB-DGT gel deployed in water using coupled high-performance liquid chromatography and hydride generation atomic fluorescence spectrometry (HPLC-HG-AFS). However, the extent of change in arsenic speciation during the extraction process is unknown. By identifying the arsenic species in the FB-DGT gel directly, using X-ray absorption near edge spectroscopy (XANES) fitting with model arsenic compounds, we obtain a better understanding of the ability of FB-DGT to measure labile arsenic species in solution. The results presented herein confirm that FB-DGT accumulated labile inorganic and methylated arsenic species. Arsenic species bound to the FB-DGT gel were stable for up to two weeks following deployment. However, caution should be applied when interpreting the proportion of As species measured by HPLC-HG-AFS in solution extracted from FB-DGT because the distribution of arsenic species in extracted solutions was found to be modified by the extraction process. Some (~ 20 %) of arsenate was converted to arsenite, and a significant amount (~ 25 %) of dimethylarsinic acid (DMAsV) was converted to monomethylarsonic acid (MMAsV) or arsenate (AsV). Only inorganic arsenite (iAsIII) was stable during the extraction process. These findings suggested that, based on the XANES measurement, although As species were quantitatively accumulated in the FB-DGT gel, the FB-DGT technique was still unsuitable for studying As speciation. This is because the XANES technique is not suitable for routine measurement and changes in arsenic speciation were observed to occur during gel extraction, prior HPLC-HG-AFS measurement.

EFFECT OF PLANTS ON THE BIOAVAILABILITY OF METALS AND OTHER CHEMICAL PROPERTIES OF BIOSOLIDS IN A COLUMN STUDY

The effects of metal-accumulating plants (Salix x reichardtii and Populus balsamifera) on the chemical properties and dynamics of metals in biosolids were investigated using different techniques including diffusive gradients in thin films (DGT), sequential extraction procedures and partitioning coefficient (Kd). Plants could effectively extract Cd, Ni, and Zn and decreased dissolved organic carbon (DOC). The presence of plants increased the potential bioavailability of these metals, as assessed by an increase in the ratio of metal measured by DGT and metals in the solution. The plants affected the Cd, Ni, and Zn pools (soluble/exchangeable; Fe/Mn oxide and organic matter bound) characterised by sequential extraction and Kd but did not reduce the total metals in either substrate. However, plants had no effect on Cu, presumably because of the effective buffering of available Cu by organic matter in both solution and solid phases. A high density of plant roots was associated with increased leaching of metals.

Metal uptake and organic acid exudation of native Acacia species in mine tailings

Phytostabilisation with native plant species has been advocated as a cost-effective approach to rehabilitate mine tailings containing phytotoxic metal-bearing minerals. For this purpose, five Acacia species (natural colonisers) native to north-west Queensland region of Australia were investigated for metal uptake and root exudation characteristics in response to growth for 3 weeks in three different mine tailings (Cu and Cu-Pb-Zn) differing in their degree of weathering. Root tissues of the plant species grown in the three types of tailings accumulated up to 0.9 mg Cd kg–1, 10 mg Co kg–1, 177 mg Cu kg–1, 38 mg Pb kg–1 and 4800 mg Zn kg–1 (DW basis) – being suitable for phytostabilisation purposes. However, elevated levels of root exudates in rhizosphere tailings enhanced the bioavailability of metals, leading to the accumulation of high levels of some metals in Acacia shoots (e.g. shoot concentrations of 140 mg Zn kg–1 in Acacia acradenia F.Muell. and 230 mg Zn kg–1 in Acacia hilliana Maiden). Positive correlations (P < 0.05) between citric acid levels and metal root uptakes suggested that citric acid production in these plant species may be the main driver for metal mobilisation. The results suggest that the native acacia species have the potential to mobilise metals (albeit in mineral forms) in the tailings, when used for phytostabilisation.

Indicators of metal pollution in prospective mining regions: a case study from Philippines

Understanding the baseline geochemistry of stream waters in a prospective mining area is the key to responsible life-of-mine planning and the protection of local rivers. This can be sometimes challenging due to the presence of abandoned mines, small scale mining, and geogenic sources of metals in the same area, particularly under a tropical humid climates with rivers carrying intermittently high solid loads. This study is focused on the Pula Bato, Danlag, Altayan, and Taplan Rivers in such a climatic setting in Philippines. The rivers are located in the vicinity of the Tampakan ore deposit. It was observed that elemental concentrations in water samples from Pula Bato were generally higher when compared to concentrations from Danlag, Taplan, and Altayan samples. In particular, SO42−, TDS, Al, Cu, Fe, Mn, Ni, and Zn present considerably higher concentrations in the water samples from Pula Bato. It was shown that water quality of Pula Bato is influenced by the natural weathering of sulphide minerals which is further enhanced by the small scale mining activities and old underground workings. The mining effects on the water of Pula Bato River were not apparent in the water of the Altayan due to the possible dilution of the uncontaminated water from Danlag River and sorption processes occurring during the course of contaminants transport. The geochemical indicators and water distinctions can be used in future for catchment-scale geochemical balance modelling.

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...

Decision process for comparison of partial and complete XANES spectra

If the range of XANES spectra varies between sets of scans, it may be impossible to compare sets of spectra unless a restricted part of the spectra is used. The paper derives a decision process for comparison of partial and complete XANES spectra, taking lead as an example. Lead L3‐edge XANES spectra were collected at the Australian National Beamline Facility (BL‐20B) Photon Factory, Tsukuba, Japan over the energy range 13,000–13,150 eV (ring conditions: 2.5 GeV, 300–400 mA). The monochromator step size was reduced to 0.25 eV per step in the XANES region (13,000–13,100 eV and 13,040–13,100 eV) to collect high‐resolution spectra. XANES data for samples and model compounds were collected at ambient temperature and pressure in fluorescence, using simultaneous collection of a Pb metal reference foil for energy calibration (first derivative peak of elemental Pb was 13,050 eV). XANES spectra were fitted using spectral deconvolution and least‐squares linear combination fitting (LCF). Detailed XANES results with ...