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The speciation of selenium (Se) controls its fate and behavior, determining both its biological and environmental activities. However, in situ monitoring of SeIV presents a significant challenge due to its sensitivity to redox change. A novel diffusive gradients in thin films (DGT) technique containing mercapto-, amino-bifunctionalized SBA15 mesoporous silica nanoparticles was developed and evaluated in a series of laboratory and field deployment tests. The SBA-DGT exhibited a linear accumulation of SeIV (r 2 > 0.997) over a 72 h deployment, with negligible accumulation of SeVI(<5%). Consistent prediction of SeIV occurred within ionic strength and pH ranges of 0.1–200 mmol L–1 and 3.6–8, respectively. Limits of detection of the SBA-DGT were 0.03 μg SeIV L–1, which is suitable for natural waters. Moreover, the properties of the bifunctionalized SBA15 enable it to be fabricated within ultrathin (0.05 mm) gel layers for use in conjunction with O2 planar optode imaging. This new sandwich sensor technology with SBA-DGT was validated by mapping the two-dimensional distribution of SeIV and oxygen simultaneously in rice rhizospheres. This study shows that SBA-DGT provides a selective measurement of SeIV in situ, demonstrating its potential for both environmental monitoring and as a research tool for improving our understanding of Se biogeochemical processes.

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Colloidal organo−mineral associations contribute to soil organic matter (OM) preservation and mainly occur in two forms: (i) as water-dispersible colloids that are potentially mobile (free colloids) and (ii) as building units of soil microaggregates that are occluded inside them (occluded colloids). However, the way in which these two colloidal forms differ in terms of textural characteristics and chemical composition, together with the nature of their associated OM, remains unknown. To fill these knowledge gaps, free and occluded fine colloids <220 nm were isolated from arable soils with comparable organic carbon (C org ) but different clay contents. Free colloids were dispersed in water suspensions during wet-sieving, while occluded colloids were released from water-stable aggregates by sonication. The asymmetric flow fieldflow fractionation analysis on the free and occluded colloids suggested that most of the 0.6−220 nm fine colloidal C org was present in size fractions that showed high abundances of Si, Al, and Fe. The pyrolysis-field ionization mass spectrometry revealed that the free colloids were relatively rich in less decomposed plant-derived OM (i.e., lipids, suberin, and free fatty acids), whereas the occluded colloids generally contained more decomposed and microbial-derived OM (i.e., carbohydrates and amides). In addition, a higher thermal stability of OM in occluded colloids pointed to a higher resistance to further degradation and mineralization of OM in occluded colloids than that in free colloids. This study provides new insights into the characteristics of subsized fractions of fine colloidal organo−mineral associations in soils and explores the impacts of free versus occluded colloidal forms on the composition and stability of colloid-associated OM.

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&lt;p&gt;Organic carbon (OC) in the hyper-arid Atacama Desert soils is known to be extremely low (0.1-0.01%). OC can accumulate on soil colloids (1-1000 nm) and nanoparticles (1-100 nm) due to its high specific surface area. Small-sized colloids may be transferred to deeper depth through the macropores in the soil. However, little is known about the colloidal-OC soil transfer under hyper-arid conditions. In this study, the Water Dispersible Colloids (WDCs, &lt;300 nm) associated OC (WDC-OC) was analyzed using Asymmetric Field-Flow-Field Fractionation (AF&lt;sup&gt;4&lt;/sup&gt;) coupled online to an Organic Carbon Detector (OCD). The experimental site is located at 1450 m altitude near Paposo (Antofagasta region, Chile) and receives &lt;2 mm rain per annum. Samples were taken at 13 points along an alluvial fan transect, and up to a depth of 50-80 cm. Our study examined the vertical distribution of WDC-OC affected by micro-relief. Three colloidal size fractions were identified in all samples: nano-colloids (0.6-24 nm), fine colloids (24-210 nm) and medium colloids (210-300 nm). The vertical contribution of WDC-OC differed distinctively between (i) the active alluvial fan section, (ii) the older inactive alluvial fan section, related to sediment induration and soil crust development, and (iii) the edge between both fan sections. We found that WDC-OC was highest in the active fan with an average of 11.5 mg OC kg&lt;sup&gt;-1 &lt;/sup&gt;compared with the content found in crust-related older fan (0.24 mg OC kg&lt;sup&gt;-1&lt;/sup&gt;) or at the edge between the fan sections (0.19 mg OC kg&lt;sup&gt;-1&lt;/sup&gt;). Notably high WDC-OC in the fan near to the few isolated plant remains were also observed. The increase of biological activities and debris near to the plant contributes to more colloidal-OC (26.8 mg kg&lt;sup&gt;-1&lt;/sup&gt;). The relatively flat hard impermeable surface of the crust-related old fan section may induce colloids loss during high-intensity rainfalls, e.g. occurring during past El Ni&amp;#241;o periods. Furthermore, the relative percentage of WDC-OC as a part of the total was highest in the upper layer (0-1 cm) of the active fan (27-48%) and at the edge (69%), while in the older crust-related sections the highest values were observed in the subsurface (5-10 cm) (19%-29%). Near the plant remains, nano-colloids were dominated in the upper soil accounting for 48% of the WDC-OC, whereas medium colloids were predominant in the older crust-related sections (64%). Dust (colloidal-sized) particles may be deposited at the surface and then are easily trapped near plants. We conclude that WDC-OC depth profiles within the hyper-arid Atacama Desert reflects the differential surface characteristics and the age of the fan surface, i.e., the period of geomorphological inactivity. During the extremely rare rainfall events in the Atacama, both factors will lead to differential infiltration rates, which thus in turn affect the size distribution of colloidal-OC with profile depth.&lt;/p&gt;

The experiment was conducted to study the effect of different dietary supplementation of alanyl‐glutamine dipeptide (AGD) and/or vitamin E (VE) on the growth performance, antioxidant indexes, and the expression of glutathione peroxidase (GPx) and peroxisome proliferator‐activated receptor α (PPARⱭ) genes in juvenile marine medaka (Oryzias melastigma) in seawater acidification. Seven groups of juvenile marine medaka in triplicate were studied in an ecosystem. One of them was in normal seawater (pH 8.1, pH control), and the others were in seawater acidification (pH 7.7) regulated by carbon dioxide (CO2). The juveniles were separately fed for 10 weeks using one of six different diets. The six diets were one control diet (basic feed) without supplements and the other diets with different amounts of additional AGD and/or VE. The juveniles were sampled randomly for analysis of a whole fish in week 0 and week 10. The results showed that different dietary supplementation of AGD and/or VE could considerably promote the growth performance, antioxidant indexes, and the expression of GPx and PPARα genes of juvenile marine medaka in seawater acidification. The optimal diet was D4, with additional AGD 5 g and VE 50 IU per kg of dried feed.