A Novel In Situ Method for Simultaneously and Selectively Measuring AsIII, SbIII, and SeIV in Freshwater and Soils.

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 AsIII, SbIII, and SeIV, 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 NO3-, pH 5-9 for AsIII and SbIII, and pH 5-7.5 for SeIV). 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 AsIII, SbIII, and SeIV associated with root O2 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 AsIII, SbIII, and SeIV.

Validation and Assessment of Diffusive Gradients in Thin-Films (DGT) Technique for Measuring Nutrients in Taihu Lake Water with Algae Bloom.

DGT (diffusive gradients in thin films) technique has been developed for measuring nitrogen in freshwaters and applied to assess the bioavailability of phosphorus in soils/sediments. These two elements are the main nutrients causing algae bloom, but DGT has never been used in the field water conditions with algae bloom. In our study, a pair of DGT devices were used in comparison with grab sampling to characterize the performance of this technique to measure labile NO3-N, NH4-N, and PO4-P concentrations in algae-cultivated Taihu Lake water. The results showed that DGT measurement was highly affected by algae bloom and the environmental conditions using the current assemblies, especially for NH4-N measurement. For in situ measurement of nutrients in the real environment, an improvement to the DGT technique is required. The comprehensive assessment of the level of eutrophication needs to consider a variety of environmental factors rather than just the concentration of nutrients.