Influence of nitrogen speciation on Cd-induced toxicity in Landoltia punctata.

Nitrogen (N) plays an important role in plant growth and developmental metabolic processes, research on nitrogen speciation regulating Cd accumulation in duckweed is still limited. In this study, the effects of three nitrogen sources (NH4Cl, Ca(NO3)2 and NH4NO3) on the growth, Cd accumulation, and photosynthetic parameters of Landoltia punctata (L. punctata) were analyzed. The results showed that Cd enrichment in L. punctata was significantly reduced (p < 0.05) with different nitrogen treatments compared to the control (CK). Ammonium nitrogen (NH4-N) is more conducive to the accumulation of Cd in L. punctata than nitrate nitrogen (NO3-N). The sum of the cell wall components and soluble components of Cd in the NH4-N treatment group was greater than that in the NO3-N treatment group. The proportion of FNaCl extracts in the NH4-N treatment group was greater than in the NO3-N treatment group. NO3-N led to a greater reduction in photosynthetic pigment content than NH4-N. Overall, applying different forms of nitrogen can alleviate Cd toxicity in L. punctata, and the detoxification effect of the NH4-N treatment is stronger than that of NO3-N treatment. This study will provide theoretical and practical support for the application of duckweed in Cd phytoremediation even in eutrophic aquatic environments.

Cd pollution has become a major global public environmental issue. Duckweed is an ideal species to restore Cd-polluted waters due to its fast growth, easy harvesting and hyperaccumulation Cd. Currently, no definite conclusion has been given on the detoxification effect of nitrogen morphology regulating the accumulation of Cd in plant. In this study, the influence of different nitrogen forms on Cd-induced toxicity in Landoltia punctata were revealed through the changes in biomass, Cd subcellular distribution, Cd chemical morphology and photosynthetic pigment. These findings can provide a new way of analyzing the mechanism of Cd enrichment in plants, and also provide theoretical and technical support for the remediation of Cd pollution by using duckweed resources. The Cd-accumulation duckweed can be pyrolyzed to produce biochar, which can not only control the second pollution by decomposed plant bodies but also realizes the efficient use of waste.

Ferric- and calcium-loaded red soil assist colonization of submerged macrophyte for the in-situ remediation of eutrophic shallow lake: From mesocosm experiment to field enclosure application.

Eutrophication and its resulting harmful algal blooms greatly reduce the ecosystem services of natural waters. The use of modified clay materials to assist the phytoremediation of eutrophic water is a promising technique. In this study, ferric chloride and calcium hydroxide were respectively loaded on red soil for algal flocculation and phosphorus inactivation. A two-by-two factorial mesocosm experiment with and without the application of ferric- and calcium- loaded red soil (FA), and with and without planting the submerged macrophyte Vallisneria natans was conducted for the in-situ repair of eutrophic water and sediment. Furthermore, field enclosure application was carried out to verify the feasibility of the technology. At the end of the mesocosm experiment, the total phosphorus, total nitrogen, and ammonia nitrogen concentrations in water were reduced by 81.8 %, 63.3 %, and 62.0 %, respectively, and orthophosphate phosphorus concentration in the sediment-water interface decreased by 90.2 % in the FA + V. natans group compared with those in the control group. The concentration and proportion of chlorophyll-a in cyanobacteria decreased by 89.8 % and 71.2 %, respectively, in the FA + V. natans group. The content of active phosphorus in V. natans decreased and that of inert phosphorus increased in the FA + V. natans group, compared with those in the V. natans alone group, thus may reducing the risk of phosphorus release after decomposing of V. natans. The sediment bacterial diversity index did not change significantly among treatments. Field enclosure application have also been successful, with chlorophyll-a concentration in the water of treated enclosure decreased from above 200 µg/L to below 10 µg/L, and phosphorus concentration in the water decreased from >0.6 mg/L to <0.02 mg/L. These results demonstrated that the FA in combination with submerged macrophyte planting had great potential for the in-situ remediation of eutrophic water, especially those with severe algal blooms.

Novel Magnetic MnFe2O4-Decorated Graphite-Like Porous Biochar as a Heterogeneous Catalyst for Activation of Peroxydisulfate Toward Degradation of Rhodamine B.

A magnetic MnFe2O4-modified graphite-like porous biochar composite (MnFe2O4/KFS800) was synthesized by the hydrothermal method, and its catalytic activity was evaluated in the activation of peroxydisulfate toward degradation of Rhodamine B. After characterization by SEM, XRD, and the BET method, the specific surface area and total pore volume of the MnFe2O4/KFS800 catalyst reached 121 m2/g and 0.263 m3/g, and exhibited plate-like morphology with good crystallinity. The degradation rate of Rhodamine B by the obtained composite was more than 91.1% when the initial concentration of RhB was 10 mg/L, the dosage of MnFe2O4/KFS800 was 0.2 g/L, and the initial pH was 6.7. Then the anti-interference ability of the obtained composite was studied, and it was found that there was a little effect on the degradation of Rhodamine B with the presence of humic acid. Finally, quenching test, EPR research, and XPS analysis were conducted to reveal the catalytic mechanism, and possible mechanism was a synergistic behavior of free radicals (SO4•-, •OH, O2•-) and nonfree radicals (1O2), and trace amounts of uncarbonized bagasse was also involved in the formation of free radicals.

Large-scale screening and characterization of Cd accumulation and ultrastructural deformation in duckweed.

Cadmium (Cd) pollution in soil, rivers and lakes is a serious problem due to the current industrialization and urbanization in China. Duckweeds are recognized as promising species for Cd phytoremediation. However, intraspecific variations in Cd accumulation in duckweeds remain largely unknown. In this study, 16 accessions selected from 39 geographically isolated duckweed strains were chosen to investigate their Cd remediation abilities. The optimal accession Landoltia punctata named 07SGZP01 (L. punctata 0701) was identified and shown to accumulate maximal Cd in the body while maintaining the highest biomass. The dominant variety treated with different Cd concentrations showed that the biomass of L. punctata 0701 was significantly lower than that of the control group (CK). Cd contents in L. punctata 0701 were substantially increased from 2511.1 to 30,641.01 mg kg-1 with an increase in Cd treatment levels from 0.3 to 20 mg L-1. The transport coefficient (TF) increased as Cd levels increased from 0.3 to 2 mg L-1. In addition, the Cd content in leaves was greater than that in roots (TF > 1) within this Cd concentration range, whereas the Cd content in roots was greater than that in leaves (TF < 1) when the concentration of the Cd treatment was greater than 5 mg L-1. The bioaccumulation factor (BCF) decreased significantly with increasing Cd levels (P < 0.05). The rate of Cd removal in the solution gradually decreased with increasing Cd concentrations, and the removal rate achieved the highest value (75%) when the Cd concentration was 0.5 mg L-1. In addition, Cd treatment (2 mg L-1) not only damaged the ultrastructure of L. punctata 0701, as characterized by chloroplast deformation and cell vacuolation but also caused most of the stomata to close, and the leaf epidermal cells were damaged and ruptured.

Preparation of Gold Nanoplates Using Ortho Carbonyl Compounds as Capping Agents for Electrochemical Sensing of Lead Ions.

In this study, gold nanoplates were synthesized using plant molecules (gallic acid) following a kinetic control mode. The growth of nanoplates is mainly due to the specific adsorption of capping agents on certain crystal facets. Through systematical characterizations, it is found that the distance between two oxygen atoms in ortho carbonyl compounds matches well with the lattice spacing of gold (111) facets exactly, which is beneficial to the formation of twin seeds and further the growth of plate-like gold nanoparticles. The gold nanoplates on glassy carbon electrode show a remarkably improved electrochemical sensing activity of lead ions compared to the bare glassy carbon electrode or spherical gold nanoparticle-modified electrode. The modified electrode is expected to be used in the detection of lead ion concentration in heavy metal wastewater.

Effects of organic selenium on absorption and bioaccessibility of arsenic in radish under arsenic stress.

Arsenic (As) exposure poses a serious threat to human health. The present study investigated the effects of organic Se on As accumulation, migration, and As bioaccessibility in As-stressed radish. The results showed that organic Se can effectively block the accumulation of As in radish, reduce As bioaccessibility, and promote the conversion of As from inorganic to organic form. The total As content decreased with increasing Se application in raw radish roots, the gastric fraction and the gastrointestinal fraction. Compared to the control (CK) group, the As bioaccessibility in the 24Se treatment of the yeast Se and malt Se groups decreased by 26% and 37%, respectively. These findings provide new comprehensive information for the application of organic Se to alleviate the toxicological effects of As and reduce the health risks of As in edible plants. In the future, it is necessary to carry out a deeper study of the interaction between Se and As through advanced analytical methods.

Chemical forms governing Cd tolerance and detoxification in duckweed (Landoltia punctata).

Duckweed (Landoltia punctata) is an ideal species to restore cadmium (Cd)-polluted waters due to its fast growth and easy harvesting. To understand its tolerance and detoxification mechanism, the Cd stress responses, subcellular Cd distribution and chemically bound Cd forms (especially protein-bound Cd) were surveyed in this study. L. punctata, a potential Cd bioremediation plant, was cultured hydroponically with Cd concentrations of 0.0, 0.5, 2.0, and 5.0 mg L-1 for 5 days. The results showed that the Cd content in L. punctata increased significantly as the Cd content increased. The majority of Cd was localized in the soluble fraction (23-55%) and the cell wall fraction (21-54%), and only 14-23% of Cd was located in cell organelles. Analysis of the Cd chemical forms demonstrated that the largest portion of Cd was found in 1 M NaCl extracts, followed by d-H2O and 2% HAc extracts, indicating that Cd was mainly bound to different proteins. Albumin- and globulin-bound Cd forms were predominant, together accounting for over 80% of the total protein-bound Cd in L. punctata. These results indicate that cell wall immobilization and vacuolar dissociation of Cd are possible primary strategies for Cd biosorption and detoxification in L. punctata, which occur mainly through chemical forms changes, especially the binding of Cd to proteins.

Heavy metal accumulation, risk assessment and integrated biomarker responses of local vegetables: A case study along the Le'an river.

In this research, Ganzhou Chinese Cabbage (Brassica rapa pekinensis), Native Purple Garlic (Allium sativum L) and Leping Radish (Raphanus sativus L) widely planted and distributed along the Le'an River were chosen in the present study. Soil physical-chemical properties, nutrients contents as well as heavy metals elements accumulated in both soils and vegetables collected from 24 sites were analyzed by lab analysis combined with statistical method which was also used for calculation of contamination factor, pollution indexes and hazardous index. Heavy metals accumulation in soils were revealed with higher level, and copper and cadmium exceeded the background values by 8.82 and 16.73 times on average, which were also significantly related with the distribution of nonferrous metal processing enterprises. Heavy metal elements accumulated in vegetables were fully consistent with the finding of pollution characteristics in soils. Peroxidase biomarkers in vegetables, including superoxide dismutase (SOD), catalase (CAT), peroxidase (POD), reduced glutathione (GSH) and lipoperoxidation (as TBARS), as well as integrated biomarker responses (IBR) were determined to give a reliable response after exposing of contaminants. Heavy metals accumulation ability and biomarker responses for three vegetables were usually determined in the following decrease trend: Ganzhou Chinese Cabbage > Native Purple Garlic > Leping Radish. Compared with peroxidase biomarkers activities or contents of control site, all the measured biomarkers in polluted sites showed significantly responses, indicating potential relationship between pollutants stresses and biomarker responses. This study also revealed that the IBR values were coordinated well with the pollutants concentrations.

Biomarker responses of rice plants growing in a potentially toxic element polluted region: A case study in the Le'An Region.

Rice plants, planted and grown in the field, were chosen in this study to evaluate the potentially toxic element pollution by combining pollutant analysis and a molecular biomarker response evaluation together in the Le'An Region, a highly polluted area due to anthropogenic activities. Soils and crops at 18 sites classified into four areas based on hydrological, geological and pollutant survey results were collected during the whole growth cycle for chemical and biological analysis. Sediment quality values and pollution indexes were combined with statistical analyses to assess the hazard of potentially toxic elements and evaluate ecological risks. As effective stress-related signals, chlorophyll (Chl), superoxide dismutase (SOD), peroxidase (POD), catalase (CAT), glutathione content (GSH) and lipoperoxidation (as TBARS) were also determined during the rice plant growth period. The results revealed that heavy metal concentrations were significantly higher than corresponding background values and significantly related to those of the soils. The maximum concentration of potentially toxic elements was observed at the tillering stage, followed by the grain filling stage and heading stage. As biomarkers in field monitoring, a significant increase or decrease in Chl, SOD, POD, CAT, GSH and TBARS in crops means a potential relationship between the indexes and pollutants. This study also demonstrates that the integrated biomarker response (IBR) calculated by combining different biomarkers could be used effectively to evaluate the pollutant-induced stress levels in different areas.