A Novel In Situ Method for Simultaneously and Selectively Measuring As^III, Sb^III, and Se^IV in Freshwater and Soils

Abstract

Anthropogenic and climatic perturbations redistribute arsenic (As), antimony (Sb), and selenium (Se) within the environment. The speciation characteristics of these elements determine their behavior and biogeochemical cycling, but these redox-sensitive species are challenging to capture, with few methods able to harmonize measurements across the whole plant-soil-ecosystem continuum. In this study, we developed a novel diffusive gradient in thin films (DGT) method based on aminopropyl and mercaptopropyl bi-functionalized mesoporous silica spheres (AMBS) to achieve in-situ, simultaneous, and selective quantification of As III , Sb III , and Se IV , three typical/toxic but difficult to measure inorganic species. When used for environmental monitoring within a river catchment, AMBS-DGT exhibited stable/accurate predictions of these species despite varying water chemistries (ionic strength 0.01−200 mmol L −1 NO 3 − , pH 5−9 for As III and Sb III , and pH 5−7.5 for Se IV ). Furthermore, river deployments also showed that time-averaged species concentrations by AMBS-DGT were reproducible compared with high-frequency sampling and measurement by high performance liquid chromatography coupled with inductively coupled plasma mass spectroscopy. When AMBS-DGT was used for sub-mm scale chemical imaging of soil solute fluxes, the method resolved concomitant redox-constrained spatial patterns of As III , Sb III , and Se IV associated with root O 2 penetration within anaerobic soil. Improved capabilities for measurement of compartment interfaces and microniche features are critical alongside the measurement of larger-scale hydrological processes that dictate the fine-scale effects, with the AMBS-DGT achieving this for As III , Sb III , and Se IV .

Determination of the Isotopic Composition of Aqueous Mercury in a Paddy Ecosystem Using Diffusive Gradients in Thin Films

“…The method detection limits (MDLs = 3 × standard deviations of DGT blanks) and method quantification limits (MQLs = 10 × standard deviations of DGT blanks) were 4.96 ng L –1 (0.03 ng disc –1 ) and 16.53 ng L –1 (0.10 ng disc –1 ), respectively, for a DGT deployment of 24 h at 25 °C. If the Hg­(II) concentration is lower than the MDLs, a longer deployment time and thinner diffusive gels can be used to increase the accumulated mass on the binding gels to lower the MDLs proportionately . Statistical analysis and hypothesis tests were performed using Origin 2020 software using a significance level of 0.05 if not otherwise stated.…”

Atomic spectrometry update – a review of advances in environmental analysis

“…Although the metals were highly labile and so potentially had high toxicity, analysis of tree core samples, surprisingly, revealed little uptake into the xylem of nearby trees. Dissolved As III , Sb III , and Se IV concentrations within a river catchment were successfully mapped 68 using a DGT sampler loaded with aminopropyl and mercaptopropyl bi-functionalised mesoporous silica spheres. The time-weighted average data obtained were comparable to data from high frequency sampling and HPLC-ICP-MS analysis.…”

Atomic spectrometry update: review of advances in elemental speciation

“…For the selective extraction of Sb III (and As III and Se IV , covered in the sections for these elements) from freshwater and soils, Fang et al developed a selective in situ DGT sampling procedure. 25 Selectivity over other forms of the elements in question was achieved through the incorporation of aminopropyl and mercaptopropyl bi-functionalised mesoporous silica spheres into the binding gel. The passive sampling devices were deployed in the river environments for 72 h and the collected analytes eluted with 3 mL of 1 mol L −1 HNO 3 + 1% KIO 3 (m/v) and quantified by ICP-MS. For the measurement of these species in the rhizosphere of growing rice, the binding gel was deployed in the soil for 24 h after 3 weeks of cultivation and the accumulation of the target species in the gels was measured with LA-ICP-MS. Spatially resolved labile fluxes could be visualised because the 3.4 μm microspheres were homogenously distributed throughout the binding gel.…”

“…A passive sampling technique based on DGT has been developed for simultaneous and in situ measurements of As III , Sb III , Se IV species. 115 The gel binding substrate was made of aminopropyl and mercaptopropyl-bifunctionalised mesoporous silica spheres (AMBS). Different techniques were applied: X-ray photoelectron spectra to analyse the chemical states of the elements and confirm thiol and amino groups functionalisation, HPLC-ICP-MS to determine As III , Sb III , Se IV in river water samples resulting from a field deployment trial and LA-ICP-MS for micromapping As III , Sb III , Se IV lability in rice roots.…”

“…Without any further optimisation, almost baseline resolution of the peaks for arsenate, chromate and molybdate was obtained. The spectrometer was operated in collision mode with He as the bath gas and 4 ISs, 72 Ge, 115 In, 103 Rh, 45 Sc, were added to the mobile phase at concentrations of 100 ng mL −1 . Total element concentrations were also measured by ICP-MS, the procedure for which was validated by the analysis of SPS Spectrapure Standards AS (Oslo, Norway) SPS-SW1 (quality control material for surface water analysis).…”