Can simultaneous immobilization of arsenic and cadmium in paddy soils be achieved by liming?

Liming acidic paddy soils to near-neutral pH is the most cost-effective strategy to minimize cadmium (Cd) accumulation by rice. However, the liming-induced effect on arsenic (As) (im)mobilization remains controversial and is called upon for further investigation, particularly for the safe utilization of paddy soils co-contaminated with As and Cd. Here, we explored As and Cd dissolution along pH gradients in flooded paddy soils and extracted key factors accounting for their release discrepancy with liming. The minimum As and Cd dissolution occurred concurrently at pH 6.5-7.0 in an acidic paddy soil (LY). In contrast, As release was minimized at pH < 6 in the other two acidic soils (CZ and XX), while the minimum Cd release still appeared at pH 6.5-7.0. Such a discrepancy was determined largely by the relative availability of Fe under overwhelming competition from dissolved organic carbon (DOC). A mole ratio of porewater Fe/DOC at pH 6.5-7.0 is suggested as a key indicator of whether co-immobilization of As and Cd can occur in flooded paddy soils with liming. In general, a high mole ratio of porewater Fe/DOC (≥ 0.23 in LY) at pH 6.5-7.0 can endow co-immobilization of As and Cd, regardless of Fe supplement, whereas such a case is not in the other two soils with lower Fe/DOC mole ratios (0.01-0.03 in CZ and XX). Taking the example of LY, the introduction of ferrihydrite promoted the transformation of metastable As and Cd fractions to more stable ones in the soil during 35 days of flooded incubation, thus meeting a class I soil for safe rice production. This study demonstrates that the porewater Fe/DOC mole ratio can indicate a liming-induced effect on co-(im)mobilization of As and Cd in typical acidic paddy soils, providing new insights into the applicability of liming practice for the paddy soils.

Arsenic extraction from seriously contaminated paddy soils with ferrihydrite-loaded sand columns.

Reductive dissolution of iron oxides in flooded paddy soils is the most important cause of arsenic (As) release into soil aqueous solution and thus entry into rice. From the perspective of soil cleanup, however, As release under flooded condition could facilitate labile As removal. In this study, a porous column pre-loaded with ferrihydrite (Fh) was constructed, and its efficiency of soil As extraction was investigated using a purpose-designed mesocosm coupled with diffusive gradients in thin films (DGT) for in situ visualization. With Fh-column deployed in aqueous solution, >90% removal of As(III) was achieved within 5 days at initial As (100 mg L-1) of two orders of magnitude higher than in most paddy soil solutions (1-1538 µg L-1). By applying Fh-column in a seriously contaminated paddy soil (102 mg As kg-1), porewater As showed stepwise decreases from 2727 µg L-1 to 129-1455 µg L-1 at a distance-dependent manner over four intermittent extractions during 91 days. Soil DGT-As exhibited similar spatiotemporal changes to porewater As. After four extractions, 17.8% of total soil As was removed by Fh-column in a 10 cm radius range on average and ∼1/3 of As bound to amorphous and crystalline Fe/Al oxides was depleted, which accounted for 88.7% of decline in total soil As. With the post-extracted soil, a 48% lower As accumulation in rice seedlings and a 65% decline in bulk soil DGT-As were attained. This study provides a conceptual foundation for rapid removal of high soluble As by Fh-columns from flooded soils, improving seriously As-contaminated paddies to sustainable resources for safe food production.

Effects of aldo-keto reductase family 1 member A on osteoblast differentiation associated with lactate production in MC3T3-E1 preosteoblastic cells.

Aldo-keto reductase family 1 member A (AKR1A) is an NADPH-dependent aldehyde reductase widely expressed in mammalian tissues. In this study, induced differentiation of MC3T3-E1 preosteoblasts was found to increase AKR1A gene expression concomitantly increased NOx- (nitrite + nitrate), increased glucose uptake, increased [NAD(P)+]/[NAD(P)H] and lactate production but decreased reactive oxygen species (ROS) without changes in endothelial nitric oxide synthase (eNOS) expression in differentiated osteoblasts (OBs). A study using gain- and loss-of-function MC3T3-E1 cells indicated that AKR1A is essential for modulating OB differentiation and gene expression of collagen 1 A1, receptor activator of nuclear factor kappa-B ligand, and osteoprotegerin in OBs. Immunofluorescence microscopy also revealed that changes in AKR1A expression altered extracellular collagen formation in differentiated OBs. Consistently, analyses of alkaline phosphatase activity and calcium deposits of matrix mineralization by Alizarin Red S staining verified that AKR1A is involved in the regulation of OB differentiation and bone matrix formation. In addition, AKR1A gene alterations affected the levels of NOx-, eNOS expression, glucose uptake, [NAD(P)+]/[NAD(P)H] dinucleotide redox couples, lactate production, and ROS in differentiated OBs. Herein, we report that AKR1A-mediated denitrosylation may play a role in the regulation of lactate metabolism as well as redox homeostasis in cells, providing an efficient way to quickly gain energy and to significantly reduce oxidative stress for OB differentiation.

GeSn resonant-cavity-enhanced photodetectors for efficient photodetection at the 2 µm wavelength band.

The 2 µm wavelength band has recently gained increased attention for potential applications in next-generation optical communication. However, it is still challenging to achieve effective photodetection in the 2 µm wavelength band using group-IV-based semiconductors. Here we present an investigation of GeSn resonant-cavity-enhanced photodetectors (RCEPDs) on silicon-on-insulator substrates for efficient photodetection in the 2 µm wavelength band. Narrow-bandgap GeSn alloys are used as the active layer to extend the photodetection range to cover the 2 µm wavelength band, and the optical responsivity is significantly enhanced by the resonant cavity effect as compared to a reference GeSn photodetector. Temperature-dependent experiments demonstrate that the GeSn RCEPDs can have a wider photodetection range and higher responsivity in the 2 µm wavelength band at higher temperatures because of the bandgap shrinkage. These results suggest that our GeSn RCEPDs are promising for complementary metal-oxide-semiconductor-compatible, efficient, uncooled optical receivers in the 2 µm wavelength band for a wide range of applications.

Biochar-assisted phytoextraction of arsenic in soil using Pteris vittata L.

The alkaline nature of biochar provides a potential for soil arsenic (As) mobilization and, hence, enhancing efficiency of As phytoextraction by combining with As hyperaccumulator. To testify the feasibility and potential risk of the above strategy, biochar effect on As transfer in a paddy soil and accumulation in P. vittata was investigated in a pot experiment. By leaching soil (total As concentration 141.17 mg/kg) with simulated acid rain (pH 4.2), As the concentration in leaching eluate increased proportionally with increasing biochar ratio. Coincident with elevated soil As mobility, apparent enhancement in As uptake and translocation in P. vittata was determined with 1-5% biochar amendment after 40 days of plant growth. Furthermore, diffusive gradients in thin film (DGT) technique were employed to characterize any potential risk in vertical downward migration of As at 2-mm resolution. A significantly increasing profile of DGT-As ranging from on average 20 µg/L in CK to 50-100 µg/L in 1-3% biochar treatments was recorded over 0-60 mm depth, with 25-71% lower labile As in the rhizosphere than non-rhizosphere zone with few exceptions. As compared to Chinese quality standard for groundwater (Class IV 50 µg/L), biochar ratio at ≤ 1% was suggested for local water safety while actual application should take the physicochemical characteristic of tested soil into account. Our results demonstrated the biochar-assisted P. vittata phytoremediation can serve as an emerging pathway to enhance efficiency of soil As phytoextraction. The combination of DGT techniques and greenhouse assay provided a powerful tool for evaluating the gradient distribution of heavy metal in rhizosphere and accessing corresponding ecological risk at more precise scale.

GeSn resonant-cavity-enhanced photodetectors on silicon-on-insulator platforms.

We report GeSn p-i-n resonant-cavity-enhanced photodetectors (RCEPDs) grown on silicon-on-insulator substrates. A vertical cavity, composed of a buried oxide as the bottom reflector and a deposited SiO2 layer on the top surface as the top reflector, is created for the GeSn p-i-n structure to enhance the light-matter interaction. The responsivity experiments demonstrate that the photodetection range is extended to 1820 nm, completely covering all the telecommunication bands, because of the introduction of 2.5% Sn in the photon-absorbing layer. In addition, the responsivity is significantly enhanced by the resonant cavity effects, and a responsivity of 0.376 A/W in the telecommunication C-band is achieved that is significantly higher than that of conventional GeSn-based PDs. These results demonstrate the feasibility of CMOS-compatible, high-responsivity GeSn-based PDs for shortwave infrared applications.

AdeR protein regulates adeABC expression by binding to a direct-repeat motif in the intercistronic spacer.

Overexpression of the efflux pump AdeABC is associated with tigecycline resistance of multi-drug resistant Acinetobacter baumannii (MDRAB). A two-component regulatory system, sensor AdeS and regulator AdeR proteins regulate the pump. However, the detailed mechanism of the AdeR protein to enhance the expression of adeABC operon is not well defined. We illustrated the biological characteristics of AdeR proteins by comparing a mutant AdeR protein of a tigecycline resistant MDRAB to the wild AdeR protein. By analyzing a series of deletion constructs, a minimal gene cassette of the intercistronic spacer DNA fragment specifically bound with the adeR protein and resulted in band shifting in electrophoresis mobility shifting assays (EMSA). A conserve direct repeat motif was observed in the intercistronic spacer DNA. We demonstrated the AdeR protein was a direct-repeat-binding protein. Two common residue mutations on the AdeR proteins of tigecycline resistant MDRAB isolates could reduce their binding affinity with the intercistronic spacer. The free intercistronic spacer may then more efficiently support the read-through of the adeABC operon during the co-transcriptional translation in tigecycline resistant MDRAB isolates.