Pristine/magnesium-loaded biochar and ZVI affect rice grain arsenic speciation and cadmium accumulation through different pathways in an alkaline paddy soil.

Cadmium (Cd) and arsenic (As) co-contamination has threatened rice production and food safety. It is challenging to mitigate Cd and As contamination in rice simultaneously due to their opposite geochemical behaviors. Mg-loaded biochar with outstanding adsorption capacity for As and Cd was used for the first time to remediate Cd/As contaminated paddy soils. In addition, the effect of zero-valent iron (ZVI) on grain As speciation accumulation in alkaline paddy soils was first investigated. The effect of rice straw biochar (SC), magnesium-loaded rice straw biochar (Mg/SC), and ZVI on concentrations of Cd and As speciation in soil porewater and their accumulation in rice tissues was investigated in a pot experiment. Addition of SC, Mg/SC and ZVI to soil reduced Cd concentrations in rice grain by 46.1%, 90.3% and 100%, and inorganic As (iAs) by 35.4%, 33.1% and 29.1%, respectively, and reduced Cd concentrations in porewater by 74.3%, 96.5% and 96.2%, respectively. Reductions of 51.6% and 87.7% in porewater iAs concentrations were observed with Mg/SC and ZVI amendments, but not with SC. Dimethylarsinic acid (DMA) concentrations in porewater and grain increased by a factor of 4.9 and 3.3, respectively, with ZVI amendment. The three amendments affected grain concentrations of iAs, DMA and Cd mainly by modulating their translocation within plant and the levels of As(III), silicon, dissolved organic carbon, iron or Cd in porewater. All three amendments (SC, Mg/SC and ZVI) have the potential to simultaneously mitigate Cd and iAs accumulation in rice grain, although the pathways are different.

Absorption and Biotransformation of Selenomethionine and Selenomethionine-Oxide by Wheat Seedlings (Triticum aestivum L.).

An in-depth understanding of Se uptake and metabolism in plants is necessary for developing Se biofortification strategies. Thus, hydroponic experiments were conducted to investigate the associated processes and mechanisms of organic Se (selenomethionine (SeMet) and selenomethionine-oxide (SeOMet)) uptake, translocation, transformation and their interaction in wheat, in comparison to inorganic Se. The results showed that Se uptake by the roots and the root-to-shoot translocation factor under the SeMet treatment were higher than those under the selenite, selenate and SeOMet treatments. The uptake and translocation of SeMet were higher than those of SeOMet within 72 h, although the differences gradually narrowed with time. The uptake of SeMet and SeOMet was also sensitive to the aquaporin inhibitor: AgNO3 addition resulted in 99.5% and 99.9% inhibitions of Se in the root in the SeMet and SeOMet treatments, respectively. Once absorbed by the root, they rapidly assimilated to other Se forms, and SeMet and Se-methyl-selenocysteine (MeSeCys) were the dominant species in SeMet- and SeOMet-treated plants, while notably, an unidentified Se form was also found in the root and xylem sap under the SeMet treatment. In addition, within 16 h, SeOMet inhibited the uptake and translocation of SeMet, while the inhibition was weakened with longer treatment time. Taken together, the present study provides new insights for the uptake and transformation processes of organic Se within plants.

Heavy Metals in Agricultural Soils: Sources, Influencing Factors, and Remediation Strategies.

Soil heavy metal pollution is a global environmental challenge, posing significant threats to eco-environment, agricultural development, and human health. In recent years, advanced and effective remediation strategies for heavy metal-contaminated soils have developed rapidly, and a systematical summarization of this progress is important. In this review paper, first, the anthropogenic sources of heavy metals in agricultural soils, including atmospheric deposition, animal manure, mineral fertilizers, and pesticides, are summarized. Second, the accumulation of heavy metals in crops as influenced by the plant characteristics and soil factors is analyzed. Then, the reducing strategies, including low-metal cultivar selection/breeding, physiological blocking, water management, and soil amendment are evaluated. Finally, the phytoremediation in terms of remediation efficiency and applicability is discussed. Therefore, this review provides helpful guidance for better selection and development of the control/remediation technologies for heavy metal-contaminated agricultural soils.

Phytoremediation strategies for heavy metal-contaminated soil by selecting native plants near mining areas in Inner Mongolia.

Phytoremediation technology, as an eco-friendly and cost-effective approach, is widely used to restore soil contaminated by heavy metal(loid)s. However, the adaptability and absorption capacity of plants to multiple elements are the crucial factors affecting the application of phytoremediation in mining areas. In this study, dominant native plant species and their paired soils were collected near a lead-zinc mine in Inner Mongolia, to assess the ecological risk of heavy metal(loid)s and phytoremediation potential. The results showed that Cd and As were the dominant soil pollutants, with levels of 90.91% and 100%, respectively, exceeding the risk intervention values for soil contamination of agricultural land. The rates of Pb, Cu, and Zn exceeding the risk screening values were 69.70%, 60.61%, and 96.97%, respectively. Extremely high ecological risk of heavy metal(loid)s was observed in this area. The ability of native plants accumulating heavy metals varied among species. The bioconcentration factor (BCF) varied from 0.14 to 2.59 for Cd, 0.02 to 0.45 for As, 0.06 to 0.76 for Pb, 0.05 to 2.69 for Cr, 0.15 to 1.00 for Cu, and 0.22 to 4.10 for Zn. Chinese Cinquefoil Herb (Potentilla chinensis Ser.) showed the potential to accumulate multiple toxic elements based on the biomass, shoot content, translocation factor (TF), BCF, and metal extraction rate (MER), while, other species showed the potential to accumulate single toxic element: goosefoot (Chenopodium album L.), Lespedeza daurica (Laxm.) Schindl. and peashrubs (Caragana korshinskii Kom.), Herba Artemisiae Scopariae (Artemisia capillaris Thunb.), alfalfa (Medicago sativa L.), and Moldavian Dragonhead (Dracocephalum moldavica L.) for Cd, As, Cr, Cu, and Zn, respectively. Furthermore, wild leek (Allium ramosum L.), cogongrass (Imperata cylindrica (L.) Beauv.), fringed sagebrush (Artemisia frigida Willd.), and field bindweed (Convolvulus arvensis L.) were selected for phytostabilization of specific elements, considering the heavy metal contents in the roots and low TF values. This study provides a reference for selecting appropriate species for the remediation of heavy metal-contaminated soils in certain mining areas.

[Enrichment Characteristics of Heavy Metals and Health Risk in Different Vegetables].

The health risk caused by heavy metal accumulation in vegetables is of great concern. In this study, a database of heavy metal content in a vegetable-soil system in China was constructed through literature review and field sample collection. A systematic analysis of seven heavy metal contents in edible parts of vegetables and their bioaccumulation capacity among different vegetables was also performed. Additionally, the non-carcinogenic health risks of four types vegetables were assessed by using Monte Carlo simulation (MCS). The mean values of Cd, As, Pb, Cr, Hg, Cu, and Zn in the edible parts of the vegetables were 0.093, 0.024, 0.137, 0.118, 0.007, 0.622, and 3.272 mg·kg-1, and the exceedance rates of the five toxic elements were:Pb (18.5%)>Cd (12.9%)>Hg (11.5%)>Cr (4.03%)>As (0.21%). Leafy vegetables showed high Cd enrichment, and root vegetables showed high Pb enrichment, with mean bioconcentration factors of 0.264 and 0.262, respectively. Generally, legumes vegetables and solanaceous vegetables showed lower bioaccumulation for heavy metals. The health risk results indicated that the non-carcinogenic risk for single elements of vegetable intake was within the acceptable range, with the health risk for children being higher than that for adults. The mean non-carcinogenic risk for single elements were:Pb>Hg>Cd>As>Cr. The multi-element combined non-carcinogenic risks of four types vegetables were:leafy vegetables>root vegetables>legume vegetables>solanaceous vegetables. Planting lower-heavy metal bioaccumulation vegetables in heavy metal-contaminated farmland is an effective method to minimize the health risk.

Transcriptome analysis reveals different mechanisms of selenite and selenate regulation of cadmium translocation in Brassica rapa.

Selenium (Se) inhibits cadmium (Cd) root-to-shoot translocation and accumulation in the shoots of pak choi; however, the mechanism by which Se regulates Cd retention in roots is still poorly understood. A time-dependent hydroponic experiment was conducted to compare the effects of selenite and selenate on Cd translocation and retention in the roots. The underlying mechanisms were investigated regarding Se biotransformation and metal transportation in roots using HPLC and transcriptome analyses. Selenite showed reducing effects on Cd translocation and accumulation in shoots earlier than selenate. Selenite is mainly biotransformed into selenomethionine (80% of total Se in roots) at 72 h, while SeO42- was the dominant species in the selenate treatments (68% in shoots). Selenite up-regulated genes involved in the biosynthesis of lignin, suberin, and phytochelatins and those involved in stress signaling, thereby helping to retain Cd in the roots, whereas essentially, selenate had opposite effects and impaired the symplastic and apoplastic retention of Cd. These results suggest that cell-wall reinforcement and Cd retention in roots may be the key processes by which Se regulates Cd accumulation, and faster biotransformation into organic seleno-compounds could lead to earlier effects.

Source-specific risk assessment for cadmium in wheat and maize: Towards an enrichment model for China.

Cadmium (Cd) pollution of agricultural soil is of public concern due to its high potential toxicity and mobility. This study aimed to reveal the risk of Cd accumulation in soil and wheat/maize systems, with a specific focus on the source-specific ecological risk, human health risk and Cd enrichment model. For this we investigated more than 6100 paired soil and grain samples with 216 datasets including soil Cd contents, soil pH and grain Cd contents of 85 sites from China. The results showed that mining activities, sewage irrigation, industrial activities and agricultural practices were the critical factors causing Cd accumulation in wheat and maize cultivated sites. Thereinto, mining activities contributed to a higher Cd accumulation risk in the southwest China and Middle Yellow River regions; sewage irrigation influenced the Cd accumulation in the North China Plain. In addition, the investigated sites were classified into different categories by comparing their soil and grain Cd contents with the Chinese soil screening values and food safety values, respectively. Cd enrichment models were developed to predict the Cd levels in wheat and maize grains. The results showed that the models exhibited a good performance for predicting the grain Cd contents among safe and warning sites of wheat (R2 = 0.61 and 0.72, respectively); while the well-fitted model for maize was prone to the overestimated sites (R2 = 0.77). This study will provide national viewpoints for the risk assessments and prediction of Cd accumulation in soil and wheat/maize systems.

Dual-mode detection of fluorine-containing pesticides (bifenthrin, flufenoxuron, diflubenzuron) via ratiometric fluorescence and the Tyndall Effect of fluorescent organic nanoparticles.

The Tyndall Effect assay (TEA) has been applied into colorimetric metal ion detection since 2019. However, the TEA-based sensor for pesticide detection has never been reported till now. Herein, a facile fluorescent organic nanoparticle (FON)-based sensor is firstly developed for fluorine-containing pesticide detection through ratiometric fluorescence assay (FLA) and TEA. For FLA, the intensity of the second-order Tyndall scattering peak (STS590nm) and the fluorescence peak of the FON-based sensor would increase and remain unchanged respectively when adding bifenthrin, flufenoxuron, and diflubenzuron. The detection limits were respectively 9.34, 6.91, and 3.60 µg/kg. For TEA, the increased STS590nm intensity displayed a bright and visible light beam. An economical, simple, and portable device was then constructed to visually monitor the analytes. The sensor was successfully used to detect the analytes in teas through FLA and TEA with the recoveries and RSD ranging from 86.27-100.00 %, and 0.00-5.68 %, respectively.

Uptake and translocation mechanisms of different forms of organic selenium in rice (Oryza sativa L.).

Selenium (Se) is an essential trace element for human and animal health, and toward an understanding of the uptake and translocation of Se in plants is important from the perspective of Se biofortification. In this study, we conducted hydroponic experiments to investigate the mechanisms of organic Se [selenomethionine (SeMet) and selenomethionine-oxide (SeOMet)] uptake, translocation, and the interactions between SeMet and SeOMet in rice. We also investigated differences in the dynamics of organic and inorganic Se uptake by rice roots. Concentration-dependent kinetic results revealed that SeMet uptake during a 1 h exposure was 3.19-16.0 times higher than that of three other Se chemical forms, with uptake capacity (Vmax ) values ordered as follows: SeMet>SeOMet>selenite>selenate. Furthermore, time-dependent kinetic analysis revealed that SeMet uptake by roots and content in shoots were initially clearly higher than those of SeOMet, although the differences gradually diminished with prolonged exposure time; while no significant difference was found in the transfer factor of Se from rice roots to shoots between SeMet and SeOMet. Root uptake of SeOMet was significantly inhibited by carbonyl cyanide 3-chlorophenylhydrazone (CCCP) (30.4%), AgNO3 (41.8%), and tetraethylammonium chloride (TEACl) (45.6%), indicating that SeOMet uptake is a metabolically active process, and that it could be mediated via aquaporins and K+ channels. Contrarily, SeMet uptake was insensitive to CCCP, although markedly inhibited by AgNO3 (93.1%), indicating that rice absorbs SeMet primarily via aquaporins. Furthermore, Se uptake and translocation in rice treated simultaneously with both SeMet and SeOMet were considerably lower than those in rice treated with SeMet treatment alone and notably lower than the theoretical quantity, indicating interactions between SeMet and SeOMet. Our findings provide important insights into the mechanisms underlying the uptake and translocation of organic Se within plants.

The combined impacts of selenium and phosphorus on the fate of arsenic in rice seedlings (Oryza sativa L.).

Although the single role of selenium (Se) or phosphorus (P) in regulating the As contamination of rice plants has been reported in some studies, the combined impacts of Se and P on the fate of As and the underlying mechanisms are poorly understood. To address this knowledge gap, the uptake, translocation, and biotransformation of As mediated by Se were investigated in rice (Oryza sativa L.) seedlings hydroponically cultured with P-normal and P-deficient conditions. The results showed Se addition stimulated the uptake of arsenite and arsenate by 15.6% and 30.7%, respectively in P-normal condition, and such effect was more profound in P-deficient condition with the value of 43.8% and 70.8%. However, regardless of Se addition, P-deficiency elevated the As uptake by 47.0%-92.1% for arsenate but had no obvious effects for arsenite. Accompanying with the As transfer factorShoot/Root reduced by 74.5%-80.2% and 71.1%-85.7%, Se addition decreased the shoot As content by 65.8%-69.7% and 59.6%-73.1%, respectively, in the arsenite- and arsenate-treated rice plants. Relative to the corresponding treatments of P-normal condition, P-deficiency reduced the As transfer factorShoot/Root by 38.9%-52.5% and thus decreasing the shoot As content by 35.2%-42.5% in the arsenite-treated plants; while the opposite impacts were observed in the arsenate-treated plants, in which the shoot As content was increased by 22.4%-83.7%. The analysis results of As species showed As(III) was dominant in both shoots (68.9%-75.1%) and roots (94.9%-97.2%), and neither Se addition nor P-deficiency had obvious impacts on the interconversion between As(III) and As(V). Our results demonstrate the regulating roles of Se in As accumulation mainly depend on P regimes and the specific rice tissues, but the effects of P-deficiency on the fate of As were influenced by the form of As added to the culture.

Selenite and selenate showed contrasting impacts on the fate of arsenic in rice (Oryza sativa L.) regardless of the formation of iron plaque.

The different effects of selenite and selenate on the fate of As and the function of iron plaque in the interaction between Se and As are poorly understood. Rice seedlings (Oryza sativa L.) were selected as experimental plants in this study, the hydroponic experiments were conducted to investigate the possible regulatory roles of selenite and selenate on the uptake, translocation, and transformation of arsenite or arsenate accompanied by iron plaque. In arsenite- and arsenate-treated rice, the Fe30 treatments stimulated root uptake by 12.4-39.8% and 18.6-37.0%, respectively, but inhibited the movement of As from iron plaque to the roots, resulting in the absorption of a considerable amount of As on iron plaque. Regardless of the iron plaque formation, selenite (selenate) significantly increased (decreased) the root uptake of arsenite and arsenate by 28.1-53.0% and 40.0%-61.7%, respectively (45.6-56.3% and 42.5-47.7%, respectively). Interestingly, the supply of selenite significantly reduced root-to-shoot As translocation by 71.9-77.3% and 66.2-67.7%, respectively, in arsenite- and arsenate-treated rice seedlings; however, a significant increase (90.5-122.9%) was induced by selenate was found only in the arsenate-treated plants. Furthermore, the translocation of As from iron plaque to the roots was significantly increased (decreased) by selenite (selenate). As and Fe in iron plaque were significantly positively correlated in all As-treated rice plants, and this correlation was more profound than that in the shoots and roots. However, neither Fe treatments nor inorganic Se addition affected the interconversion between As(III) and As(V) obviously; and As(III) was the dominant species in both shoots (68.3-84.9%) and roots (90.7-98.2%). Our results indicate selenite and selenate are effective in reducing the As accumulation in an opposite way, and the presence of iron plaque had no obvious impact on the interaction between Se and As in rice plants.

Accumulation of potentially toxic elements in Chinese tea (Camellia sinensis): Towards source apportionment and health risk assessment.

Tea (Camellia sinensis) is a popular beverage that is consumed globally. However, a better understanding of potentially toxic elements (PTEs) content in tea leaves and infusion is necessary to minimize risk on human health. Therefore, 249 tea samples (grown in different areas) covering six types of tea were collected in China to investigate the PTEs contents, identify their potential source and assess the health risk associated with drinking tea. PTE contents in tea leaves across six tea types were ND-0.900 (Cd), 0.005-2.133 (As), ND-5.679 (Pb), ND-13.86 (Cr), 1.601-22.93 (Ni), ND-2.048 (Se), 0.109-622.4 (F), 13.02-269.9 (Rb), 1.845-50.88 (Sr), and 2.796-53.23 (Ba) mg/kg. The result of tea infusion showed that 14.3 %-44.1 % (green tea), 14.5 %-46.7 % (black tea), 10.5 %-25.3 % (dark tea), 13.6 %-34.2 % (oolong tea), 16.9 %-40.7 % (yellow tea), and 19.9 %-35.1 % (white tea) of F were released. All tea types, except green tea, exhibited comparatively low leachability of Cd, As, Pb and Cr in tea infusion. The source apportionment revealed that PTEs in tea leaves mainly originated from soil parental materials, while industrial activities, fertilizer application, and manufacturing processes may contribute to exogenous Se, Cd, As, and Cr accumulation. Health risk assessment indicated that F in tea infusion dominated the health risk. Humans may be exposed to a higher health risk by drinking green tea compared to that of other tea types. Nevertheless, the long-term tea consumption is less likely to contribute to pronounced non-carcinogenic and carcinogenic risks. This study confirmed that tea consumption is an important and direct pathway of PTEs uptake in humans. The health risk associated with drinking tea should be of concern.

Sulfur reduces arsenic accumulation in rice shoot by enhancing root retention and altering arsenic metabolism.

Rice can potentially pose serious health risks due to its higher arsenic (As) uptake. Sulfur (S) is not only an essential macronutrient, but it also has the ability to decrease As accumulation. In the present study, a hydroponic experiment was conducted to investigate the mechanisms underlying the effects of S on the As uptake and transport at different S (pre-)treatments and additional supply levels. It was found that additional S supply decreased As content by 20%-50% in both S-deficient and S-normal pre-treated shoots compared to the no S supply throughout the treatment; As root-to-shoot translocation factors was reduced by 7%-46% with S supply. On the one hand, additional S supply could elevate levels of thiol compounds (by 15%-280%) and increase the As percentage in soluble cytosol of roots. Additional S supply also enhanced the casparian strip development of rice roots, which could block As transfer in roots apoplast pathway. Moreover, additional S supply lead to the down-regulation of OsLsi2 expression (e.g., reduced by 71% by S at 2 mmol L-1 with the S-normal pre-treatment). Sulfur also promoted the biotransformation of As(III) in shoots into less toxic As species; reducing the As(III) proportion by 25% by 2 mmol L-1 of S under S-normal pre-treatment. These results suggest that S could play an important role in the inhibition of As transfer and the detoxification of As in rice by enhancing root retention (the vacuole sequestration), impeding transportation pathway of root apoplast, and regulating As-related gene expression. Thus, providing a basis for the potential application of S in rice production in As-contaminated paddy soil.

The risks of sulfur addition on cadmium accumulation in paddy rice under different water-management conditions.

Recently, the application of sulfur (S) has been recommended to control the accumulation of cadmium (Cd) in rice in contaminated paddy soil. However, the effects of exogenous S on Cd transfer in paddy rice systems under different water-management practices have not been systematically investigated. Pot experiments were performed to monitor the composition of soil pore water and the Cd accumulation in iron plaque and rice tissue were compared under different S (0 and 200 mg/kg Na2SO4) and water (continuous and discontinuous flooding) treatments. Sulfur application significantly increased Cd concentrations in soil pore water under discontinuous flooding conditions, but slightly reduced them under continuous flooding. Moreover, the oxidation/reduction potential (Eh) was the most critical factor that affected the Cd levels. When the Eh exceeded -42.5 mV, S became the second critical factor, and excessive S application promoted Cd dissolution. In addition, S addition elevated the Cd levels in iron plaque and reduced the Cd transfer from the iron plaque to rice roots. In rice, S addition inhibited Cd transfer from the rice roots to the straw; thus, more Cd was stored in the rice roots. Nevertheless, additional S application increased the Cd content in the rice grains by 72% under discontinuous flooding, although this effect was mitigated by continued flooding. Under simulated practical water management conditions, S addition increased the risk of Cd contamination in rice, suggesting that S application should be reconsidered as a paddy fertilization strategy.

Comparative responses of cadmium accumulation and subcellular distribution in wheat and rice supplied with selenite or selenate.

Cadmium (Cd) contamination of crop plants has aroused a worldwide concern because of the threats posed to human health through accumulation in the food chains. Selenium (Se) can alleviate the Cd-induced phytotoxicity, but the relevant underlying mechanisms are not fully understood. Therefore, with wheat (Triticum aestivum L.) and rice (Oryza sativa L.) chosen as the target plants in this study, the effects of selenite or selenate on Cd accumulation and subcellular distribution were investigated through greenhouse hydroponic experiments; and simultaneously, the effects of pre-Se treatment with selenite or selenate on Cd accumulation and root-to-shoot translocation in the studied plants were also included. Results showed the addition of Se slightly changed the Cd content in plant roots in a time-dependent manner; however, with the obvious decreasing trend on the Cd transfer factor (TF), its content in plant shoots was significantly reduced by selenite or selenate in a plant species-dependent manner. At 48 h of exposure, the supplementation of selenite and selenate significantly decreased the Cd content by 40.4% and 38.0% in wheat shoots, and by 72.2% and 40.9% in rice shoots, respectively. Additionally, the order of Cd proportion distributed to the different subcellular fractions of plant tissues was as follows: cell wall > soluble cytosol > organelle, irrespective of the Se treatments or the plant species. However, selenate increased the Cd percentage in soluble cytosol of wheat shoots, while selenite increased that percentage in the cell wall of rice shoots; and the Cd proportion in soluble cytosol of the studied plant roots was significantly enhanced owing to selenite or selenate addition. Moreover, similar to the co-application, the pre-Se treatment with inorganic Se also reduced the Cd accumulation and translocation both in wheat and rice. Our results proved that the inorganic Se could decline the Cd accumulation and translocation in the crop plants, although selenite was found more effective than selenate regarding such effects.

Cadmium accumulation in wheat and maize grains from China: Interaction of soil properties, novel enrichment models and soil thresholds.

The cadmium (Cd) activity in soil has been widely studied. However, the interactive effects of soil properties (e.g. soil pH, CEC, and SOM) on Cd transfer from soil to grain are generally overlooked. In total 325 datasets including soil pH, CEC, SOM, and soil Cd content were used in this study. The descriptive statistics indicated that Cd content in wheat and maize soils ranged from 0.05 to 10.31 mg/kg and 0.02-13.68 mg/kg, with mean values of 0.87 and 1.14 mg/kg, respectively. Cd contents in wheat and maize grains were 0.01-1.36 mg/kg and 0.001-1.08 mg/kg with average values of 0.15 and 0.10 mg/kg, respectively. The results of SEM demonstrated that the interactive effects of soil properties contributed more to Cd transfer from soil to wheat grain than the soil Cd content. Subsequently, CITs-MLR indicated that the critical factors, including soil pH and total soil Cd content, could mask the contribution of other soil properties on Cd accumulation in grain; soil CEC may prevent Cd from leaching and therefore improve grain Cd level of wheat especially at acidic soil condition. The result of derived Cd thresholds revealed that current Cd thresholds are not completely suitable to wheat and maize grain at different soil conditions. This study provides a new model for further investigation on relationships between soil properties, soil Cd content and grain Cd level.

Arsenic transfer and accumulation in the soil-rice system with sulfur application and different water managements.

Rice (Oryza sativa L.) can readily accumulate arsenic (As), owing to its high capacity to take up As and special flooding cultivation, which poses a potential risk to human health. Although sulfur (S) can influence As accumulation in rice, its behavior in the rice-soil system is not clear under practical water management conditions. In this study, the transfer and soil solution dynamics of As in the whole soil-rice system was investigated under continuous flooding or intermittent drainage, either with S addition or not. The results showed that intermittent drainage effectively reduced As concentration in soil solution regardless of S conditions, and it only reduced As content in rice without S addition. Exogenous S decreased As concentration in soil solution and rice, except in the roots of mature rice, under continuous flooding. Sulfur addition significantly decreased the total As and As(III) contents in rice grains, by 62% and 79% under continuous flooding and by 50% and 76% under intermittent drainage, respectively. Moreover, the addition of S resulted in impaired iron plaque and inhibited binding of As. Sulfur also reduced As translocation from rice roots to shoots. Therefore, S could alleviate the crisis of excessive accumulation of As in rice grains caused by flooded environment through various adjustments to the soil-rice system.

The fate of arsenic in rice plants (Oryza sativa L.): Influence of different forms of selenium.

As contamination of rice plants has aroused worldwide concern because of the threats posed to human health through its accumulation in the food chain. However, no data are currently available on the effect of Se nanoparticles (SeNPs) on the fate of As in higher plants, and previously reported relationships between As and Se are inconsistent. Therefore, in this study, the possible mediating roles of SeNPs or selenite on the uptake, translocation, subcellular distribution, and transformation of arsenite and arsenate in rice seedlings (Oryza sativa L.) were investigated through hydroponic experiments. The results showed that, when supplied as arsenite and arsenate, selenite significantly increased root As uptake by 71.7% and 45.9% but decreased shoot As content by 48.9% and 52.4%, respectively. In comparison, the reducing effect of SeNPs on shoot As content (37.1%) was only significant in arsenite-treated rice plants. Furthermore, selenite significantly reduced and increased the As content of different shoot and root subcellular fractions, respectively; and SeNPs also led to a dramatic decrease in the As content of the different shoot subcellular fractions of arsenite-treated rice plants. Moreover, As(III) and As(V) content was reduced in rice shoots while enhanced in rice roots by selenite. Generally, neither As(III) nor As(V) content in rice tissues was dramatically changed by SeNPs. Our results indicate that both SeNPs and selenite are effective in mitigating As toxicity in rice plants, although selenite showed a stronger inhibiting effect on As translocation.

Dietary supplementation with selenium-enriched earthworm powder improves antioxidative ability and immunity of laying hens.

Selenium (Se) has been recognized as an essential dietary nutrient for decades, and organic Se sources rather than inorganic ones are increasingly advocated as Se supplements. Earthworms have been studied as a feed additive and animal protein source for many yr. The aim of this study was to evaluate the effect of Se-enriched earthworm powder (SEP) on the antioxidative ability and immunity of laying hens. A total of 120 27-wk-old laying hens were randomly divided into 4 groups (30 hens per group). Laying hens were fed diets supplemented with SEP having 0, 0.5, or 1 mg/kg of Se or with earthworm powder alone. After 5 wk of supplementation, serum from the hens was tested for nutritional components (protein, globulin, albumin, triglycerides, total cholesterol, and glucose), antioxidative properties (glutathione peroxidase, superoxide dismutase, catalase, and nitric oxide), and immune responses (lysozymes, immunoglobulin G, IL-2, and interferon gamma). We found that SEP with 1.0 mg/kg of Se upregulated the hens' total protein, albumin, glutathione peroxidase, superoxide dismutase, IgG, and IL-2 and downregulated triglycerides, total cholesterol, glucose, and nitric oxide. These results indicate that SEP improves antioxidative levels and immune function of laying hens, indicating potential benefit from use of SEP as a feed additive in the poultry industry.

Selenite Uptake and Transformation in Rice Seedlings (Oryza sativa L.): Response to Phosphorus Nutrient Status.

Selenite and phosphate share similar uptake mechanisms, as a phosphate transporter is involved in the selenite uptake process. However, the mechanism by which selenium (Se) transformation in plants is mediated by phosphorus (P) remains unclear. In this hydroponic study, the absorption, translocation, and biotransformation of Se in selenite-treated rice (Oryza sativa L.) seedlings were investigated under varying P nutrient status. The results showed that P-deficient cultivation increased the Se concentration in roots with Se-only treatment by 2.1 times relative to that of the P-normal condition. However, co-treating roots with additional P caused the Se concentration to decline by 20 and 73% compared to Se treatment alone under P-normal and P-deficient cultivation, respectively. A similar pattern was also observed in Se uptake by rice roots. With an Se-transfer factor elevated by 4.4 times, the shoot Se concentration was increased by 44% with additional P supply compared to the concentration under Se-only treatment of P deficiency; however, no significant differences were observed regarding P-normal cultivation. P deficiency increased the Se percentage by 28% within the cell wall, but reduced it by 60% in the soluble fraction of Se-only treated roots relative to that of the P-normal condition. Contrarily, compared with the Se-only treatment under P deficiency, additional P supply enhanced Se storage in the root soluble fraction by 1.3 times. The opposite tendency was observed for rice shoots. Moreover, P deficiency reduced the proportion of SeMet by 22%, but increased MeSeCys by 1.3 times in Se-only treated roots compared to those under the P-normal condition. Interestingly, MeSeCys was not detected when additional P was added to the two cultivation conditions. Unlike in the roots, only SeMet was generally detected in the rice shoots. The results demonstrate that the P nutrient status strongly affects the Se biofortification efficiency in rice seedlings by altering the Se subcellular distribution and speciation.