Search

Humidity diffusion can stimulate soil deformation. However, evidence for triggering water-induced excessive floor deformation in underground structures remains elusive. This study investigated the issue by solving a case of a loess tunnel affected by floor heave. First, the study tracked the development of field damage during tunnel operation and examined the potential influence of base moistening on inverted arch uplift. Subsequently, a large-scale field tunnel model test was conducted to analyze the moisture distribution, stress, and deformation development at the tunnel base during the humidification process. Finally, the mechanical properties of the base loess at the humidification stages were tested to assess the degradation caused by moistening. Results showed that the moisture distribution at the tunnel base changes from W- to U-shaped during long-term humidification. Moreover, after base humidification, the soil pressure at the arch foot initially decreases sharply and then increases, while the soil pressure at the inverted arch continues to increase. Furthermore, the lining at the arch foot shows an increase in compressive stress, while the inverted arch shows an increase in tensile stress. The differential settlement between the arch foot and inverted arch widens, transitioning to uplift deformation of the inverted arch and ultimately causing floor heave. Laboratory tests showed that the floor heave is primarily caused by the deterioration of the mechanical properties of the loess resulting from humidity diffusion in the tunnel foundation. A time-dependent floor heave model was established by combining the water content, shear strength, compressive strength, and compressibility of the tunnel-base loess, and its feasibility was verified. The model exhibited a sequential decrease in the influence of the internal friction angle, compressive strength, cohesion, and compression coefficient on the floor heave. The findings of this study are considerably important with respect to uncovering the mechanism of floor heave during the operation of loess tunnels and advancing the prediction of damage. [ABSTRACT FROM AUTHOR]

• Established quantitative evaluation method for the inverted arch health status inverts. • Combining variable weight theory and extension cloud model to determine the indicator's weight. • Propose countermeasures for dangerous sections of inverted arches. Accurate assessment of the inverted arch's health status in tunnels is pivotal for preventing floor heave and ensuring traffic safety. This study investigated the condition of inverted arches in 237 highway tunnels in Gansu Province, China. An evaluation system was developed to assess the health of inverted arches, focusing on the disease characteristics and occurrence frequencies of tunnel pavements. Additionally, a new variable weight calculation method was established, incorporating the extension cloud and variable weight theory based on cloud correlation degrees. Established grading standards were used to assign scores for determining the health status of the inverted arches. The completed health status evaluation model was applied to a case study of the Taiyangshan tunnel, demonstrating its effectiveness and applicability. The results show that the evaluation method, applying variable weights based on health levels of indicators, effectively uncovers potential risks to deteriorating inverted arches. In the Taiyangshan tunnel, three inverted arches were classified as sub-healthy, relatively dangerous, and dangerous. Intensified inspection is required for sub-healthy sections. For areas categorized as relatively dangerous, employing 'miniature steel pipe piles + H-shaped steel support' has proven effective. This methodology yields essential insights for developing effective treatment strategies for inverted arches in similar tunnel engineering projects. [ABSTRACT FROM AUTHOR]

The activity of catalyst could be enhanced by the temperature rising, so it is a suitable way to reduce the noble metal loading for the catalyst. However, the corrosion of carbon supports will be remarkable in the high temperature proton exchange membrane fuel cells (HT-PEMFC, >100 °C). This report demonstrated a novel Ti 3 C 2 T x and CNT hybrid material as the catalytic support, and Pt nanowires (Pt NWs) is loaded on the hybrid support to construct the catalyst for HT-PEMFC. The Pt NWs/Ti 3 C 2 T x -CNT performs higher electrochemical activity, better stability than that of commercial Pt/C. The mass activity and specific activity of Pt NWs/Ti 3 C 2 T x -CNT catalysts are 3.89 and 3.02 times as that of Pt/C, respectively. The power densities of HT-PEMFC showed 155.4 mW cm−2 and 182 mW cm−2 at 150 and 180 °C, respectively. • The mass activity of Pt NWs/Ti3C2Tx-CNT is 3.89 times as that of Pt/C. • The catalyst superior performance is mainly ascribed to the synergistic effect. • The peak power density based on Pt NWs/Ti3C2Tx-CNT achieves 182 mW cm-2 at 180 °C. [ABSTRACT FROM AUTHOR]

Corncob was torrefied under nitrogen and carbon dioxide atmospheres at 220–300 °C, obtaining solid products with mass yields of 69.38–95.03% and 67.20–94.99% and higher heating values of 16.58–24.77 MJ/kg and 16.68–24.10 MJ/kg, respectively. The changes of physicochemical properties of the charcoal was evaluated by many spectroscopies, contact angle determination, and combustion test. Hemicelluloses were not detected for the torrefaction under the hard conditions. As the severity increased, C concentration raised while H and O concentrations reduced. Combustion test showed that the burnout temperature of charcoal declined with the elevation of reaction temperature, and torrefaction at a high temperature shortened the time for the whole combustion process. Base on the data, torrefaction at 260 °C under carbon dioxide was recommended for the torrefaction of corncob. [ABSTRACT FROM AUTHOR]

Background: Glutathione peroxidase (GPX) 4 and selenoprotein P (SELENOP) are abundant, and several variants are expressed in the testis.Objective: We determined the effects of dietary selenium deficiency or excess on sperm quality and expressions of GPX4 and SELENOP variants in rat testis and liver.Methods: After weaning, male Sprague-Dawley rats were fed a Se-deficient basal diet (BD) for 5 wk until they were 9 wk old [mean ± SEM body weight (BW) = 256 ± 5 g]. They were then fed the BD diet alone (deficient) or with 0.25 (adequate), 3 (excess), or 5 (excess) mg Se/kg for 4 wk. Testis, liver, blood, and semen were collected to assay for selenoprotein mRNA and protein abundances, selenium concentration, GPX activity, 8-hydroxy-deoxyguanosine concentration, and sperm quality.Results: Dietary selenium supplementations elevated (P < 0.05) tissue selenium concentrations and GPX activities. Compared with those fed BD + 0.25 mg Se/kg, rats fed BD showed lower (P < 0.05) BW gain (86%) and sperm density (57%) but higher (P < 0.05) plasma 8-hydroxy-deoxyguanosine concentrations (189%), and nonprogressive sperm motility (4.4-fold). Likewise, rats fed BD + 5 mg Se/kg had (P = 0.06) lower BW gain and higher (1.9-fold) sperm deformity rates than those in the selenium-adequate group. Compared with the selenium-adequate group, dietary selenium deficiency (BD) or excess (BD + 3 or 5 mg Se/kg) resulted in 45-77% lower (P < 0.05) nuclear Gpx4 (nGpx4) mRNA abundance in the testis. Rats fed BD had lower (P < 0.05) mRNA levels of 2 Selenop variants in both testis and liver than those in the other groups. Testicular SELENOP was 155-170% higher (P < 0.05) in rats fed BD + 5 mg Se/kg and hepatic c/mGPX4 was 13-15% lower (P < 0.05) in rats fed BD than in the other groups.Conclusions: The mRNA abundance of rat testicular nGPX4 responded to dietary selenium concentrations in similar ways to sperm parameters and may be used as a sensitive marker to assess appropriate Se status for male function. [ABSTRACT FROM AUTHOR]

The failure mode of rolling bearings is closely related to its operating conditions. In this study, a batch of rolling bearings, which have failed after a certain service period under oil-air lubrication, were collected and the failure modes of the bearings were analyzed. A statistical analysis showed that abrasion and not fatigue is the main failure mode of the collected bearings. The main failure mode for the inner and outer rings of rolling bearings in oil-air lubrication was abrasion, burn-up, corrosion, fatigue and indentation respectively. The causes of abrasion, burn-up, fatigue, indentation and corrosion failure mode were analyzed by visual inspection and the elemental composition of the raceway material of the failed bearings was analyzed by energy-dispersive X-ray spectroscopy. The domination of abrasion failure mode in rolling bearing under oil-air lubrication might be due to the existence of haze particles in the lubrication air. [ABSTRACT FROM AUTHOR]

Background: The involvement of cytochrome P450 (CYP450) isozymes and the selenogenome in selenium-mediated protection against aflatoxin B1 (AFB1)-induced adverse effects in broilers remains unclear.Objective: This study was designed first to determine whether selenium could reduce AFB1-induced hepatotoxic effects and then to determine whether these effects were due to changes in the CYP450 isozymes and selenogenome expression in the liver of chicks.Methods: Male avian broilers (aged 120 d) were allocated to 4 groups with 5 replicates of 6 birds to be included in a 2-by-2 factorial trial in which the main factors included supplementation of AFB1 (<5 compared with 100 μg/kg) and selenium (0.2 compared with 0.5 mg/kg) in a corn/soybean-based diet for 4 wk. Serum biochemistry, hepatic histology, and mRNA and/or activities of hepatic antioxidant enzymes, CYP450 isozymes, and 26 selenoproteins were analyzed at week 2 and/or 4.Results: Administration of AFB1 induced liver injury, decreasing (P < 0.05) total protein and albumin concentrations by 33.3-43.8% and increasing (P < 0.05) alanine aminotransferase and aspartate aminotransferase activities by 26.0-33.8% in serum, and induced hepatic necrosis and bile duct hyperplasia at week 2. AFB1 also decreased (P < 0.05) hepatic activities of glutathione peroxidase (GPX), thioredoxin reductase (TXNRD), and catalase, and the glutathione concentration by 13.1-59.9% and increased (P < 0.05) malondialdehyde, 8-hydroxydeoxyguanosine and exo-AFB1-8,9-epoxide (AFBO) DNA concentrations by 17.9-1200%. In addition, the mRNA and activity of enzymes responsible for the bioactivation of AFB1 into AFBO, which included CYP450 A1, 1A2, 2A6, and 3A4, were significantly induced (P < 0.05) by 29.2-271% in liver microsomes after 2-wk exposure to AFB1. These alterations induced by AFB1 were prevented by selenium supplementation. Dietary selenium supplementation increased (P < 0.05) mRNA and/or activities of 6 selenoprotein genes (Gpx3, Txnrd1, Txnrd2, Txnrd3, iodothyronine deiodinase 2, and selenoprotein N) in the liver of AFB1-treated groups at week 2.Conclusions: Dietary selenium protected chicks from AFB1-induced liver injury, potentially through the synergistic actions of inhibition of the pivotal CYP450 isozyme-mediated activation of AFB1 to toxic AFBO, and increased antioxidant capacities by upregulation of selenoprotein genes coding for antioxidant proteins. [ABSTRACT FROM AUTHOR]

Torrefaction of bamboo was performed in a horizontal tubular reactor under nitrogen atmosphere at 220, 240, 260, and 280 °C for 10, 30, and 60 min, respectively. It was found that with an increase of the severity of torrefaction, the mass yield and energy yield decreased while the high heating value increased. Due to the release of hydroxyl groups, the torrefied bamboo became more hydrophobic and the maximum content of absorbed moisture was reduced by 53.89%. The elemental components of torrefied bamboo tended to that of coal since carbon content was enriched with the increase of torrefaction severity. The removal of hemicelluloses and the enrichment of lignin produced samples with more uniform quality. This study suggested that torrefaction of bamboo under nitrogen produced a good feedstock for the application in burning. [ABSTRACT FROM AUTHOR]

Besides mediating the viral entry process, the human immunodeficiency virus (HIV-1) envelope protein gp41 can bind to many host cell components and regulate cell functions. Using a yeast two-hybrid system, we screened a human bone marrow cDNA library and identified a novel gp41-binding protein, CD74 (the MHC class II-associated invariant chain). Here, we report possible biological effects mediated by interaction between gp41 and CD74. We found that HIV-1 gp41 could bind directly to host CD74 in HIV-1-infected cells, and the peptide 6358 derived from gp41 loop region (aa 597-611) could effectively block the gp41-CD74 interaction. As a result of this binding, recombinant soluble gp41 and gp41 peptide 6358 activated the CD74-mediated ERK/MAPK pathway and significantly enhanced HIV-1 infection in vitro. Conversely, the enhancing effect could be suppressed by the recombinant CD74 extracellular domain. These results reveal a novel mechanism underlying gp41 mediation of HIV-1 infection and replication. [ABSTRACT FROM AUTHOR]

Abstract: This paper presents a new mesh simplification algorithm based on stochastic sampling driving by local geometric feature. First, local geometric feature value of each triangle was computed and the selection probability of the triangle was acquired according to the probability distribution function. Then, the selection triangles were collapsed and new vertices were generated by minimization volume change between the original mesh and the simplify mesh. The experiment results show that mesh models were simplified and the volume was kept while the detail feature was preserved. [Copyright &y& Elsevier]

Abstract: Worldwide contamination of arsenic in aquatic systems requires the development of a cost-effective, in situ phytoremediation technology. Hydrilla verticillata (L.f.) Royle, a submerged macrophyte widely distributed throughout the world, has the potential to effectively remove heavy metals from water. In order to understand the potential of H. verticillata for As phytofiltration and its impacts on As cycling in the water system, we investigated As accumulation, speciation and translocation in H. verticillata plants. Plant shoots showed a significant accumulation of As, with a maximum of >700μgg−1 dry weight (DW) after exposure to 20μM arsenate [As(V)] or arsenite [As(III)] for 4d, with no significant differences between the As(V) and As(III) treatments (P> 0.05). In addition, results of an in planta transport experiment showed that, after exposure of root and shoot to 2μM As(V) and As(III) for 4d, the bioconcentration factor (BCF) in roots for As(V) was almost twofold than that of As(III). Higher As BCFs in roots compared to shoots was also observed. Arsenic accumulated primarily in the cell walls of root cells (>73% of the total As in roots) and in the soluble parts of leaves (>60% of the total As in leaves). Regardless of the form of As supplied [As(III) or As(V)], As(V) was the dominant form in roots and As(III) was the dominant form in leaves. Further, basipetal translocation of As in this plant (⩾17%) was markedly higher than acropetal translocation (⩽3%). Because of accumulation of As in the shoot and immobilization of As below ground in roots, H. verticillata is a potential As phytofiltrator for bioremediation. [Copyright &y& Elsevier]

Abstract: We present necessary and sufficient conditions for the existence of a positive solution to the system of adjointable operator equations over Hilbert -modules. We also derive a representation for a general positive solution to this system when the solvability conditions are satisfied. The results of this paper extend some known results in the literature. [ABSTRACT FROM AUTHOR]

Expression and function of selenoproteins in endocrine tissues remain unclear, largely due to limited sample availability. Pigs have a greater metabolic similarity and tissue size than rodents as a model of humans for that purpose. We conducted 2 experiments: 1) we cloned 5 novel porcine selenoprotein genes; and 2) we compared the effects of dietary selenium (Se) on mRNA levels of 12 selenoproteins, activities of 4 antioxidant enzymes, and Se concentrations in testis, thyroid, and pituitary with those in liver of pigs. In Experiment 1, porcine Gpx2, Sephs2, Sep15, Sepn1, and Sepp1 were cloned and demonstrated 84-94% of coding sequence homology to human genes. In Experiment 2, weanling male pigs (n = 30) were fed a Se-deficient 10.02 mg Se/kg) diet added with 0, 0.3, or 3.0 mg Se/kg as Se-enriched yeast for 8 wk. Although dietary Se resulted in dose-dependent increases (P< 0.05) in Se concentrations and GPX activities in all 4 tissues, it did not affect the mRNA levels of any selenoprotein gene in thyroid or pituitary. Testis mRNA levels of Txnrd1 and Sep15 were decreased (P< 0.05) by increasing dietary Se from 0.3 to 3.0 mg/kg. Comparatively, expressions of Gpx2, Gpx4, Dio3, and Sep15 were high in pituitary and Dio1, Sepp1, Sephs2, and Gpx1 were high in liver. In conclusion, the mANA abundances of the 12 selenoprotein genes in thyroid and pituitary of young pigs were resistant to dietary Se deficiency or excess. [ABSTRACT FROM AUTHOR]

Abstract: A designed asymmetric hybrid electrochemical capacitor was presented where NiO and Ru0.35V0.65O2 as the positive and negative electrode, respectively, both stored charge through reversible faradic pseudocapacitive reactions of the anions (OH−) with electroactive materials. And the two electrodes had been individually tested in 1M KOH aqueous electrolyte to define the adequate balance of the active materials in the hybrid system as well as the working voltage of the capacitor based on them. The electrochemical tests demonstrated that the maximum specific capacitance and energy density of the asymmetric hybrid electrochemical capacitor were 102.6Fg−1 and 41.2Whkg−1, respectively, delivered at a current density of 7.5Acm−2. And the specific energy density decreased to 23.0Whkg−1 when the specific power density increased up to 1416.7Wkg−1. The hybrid electrochemical capacitor also exhibited a good electrochemical stability with 83.5% of the initial capacitance over consecutive 1500 cycle numbers. [Copyright &y& Elsevier]

Abstract: SnO2/TiO2 nanotubes composite photocatalysts with different SnO2 contents were successfully synthesized by means of a simple solvothermal process. The synthesized products were characterized physically by X-ray diffraction (XRD) and high-resolution transmission electron microscope (HRTEM). The composite photocatalysts can not only make the target pollutant, methylene blue (MB), adsorbed at a high concentration level around the surface of the composites but also decrease the recombination rate of electron–hole pairs so as to achieve good photocatalytic performance. The effect of SnO2 contents on the photocatalytic activities of the composites was also investigated. The results showed that the SnO2/TiO2 nanotubes composite photocatalyst with 5wt.% SnO2 loading had the highest photocatalytic efficiency. [Copyright &y& Elsevier]

Abstract: Sunlight-driven photocatalyst Bi38ZnO58 was synthesized by a solid-state reaction method. The synthesized product was characterized physically by X-ray diffraction (XRD), scanning electron microscopy (SEM) and transmission electron microscopy (TEM). The photocatalytic degradation of methylene blue was evaluated by spectrophotometric analysis; meanwhile, the possible pathway of the photocatalytic reaction also has been studied. In addition, the band edge position of Bi38ZnO58 was roughly calculated according to the electronegativity of the constituent atoms, and the calculation result further confirms the strong oxidative property of the photocatalyst under the sunlight irradiation. [Copyright &y& Elsevier]

Previous studies on azoospermia or oligozoospermia induced by heat stress or high doses of testosterone mainly focused on germ cell apoptosis; no data regarding their possible effect on spermatogonia mitosis are available. We have established unilateral cryptorchid and testosterone undecanoate (TU)-treated monkey models and examined expression of P16(INK4a) in the testis to look at its possible role in azoospermia or oligozoospermia induced by the heat stress or the TU treatment. The results showed that both heat stress and TU were capable of inducing expression of P16(INK4a) mainly in spermatogonia and other types of germ cells as well as Sertoli cells at the later stage of germ cell apoptosis, namely on Day 10 after operation or on Day 60 after TU injection. It is, therefore, suggested for the first time that P16(INK4a) protein may inhibit the spermatogonia mitosis in the testis at the later stage of the germ cell apoptosis, resulting in arrest of spermatogenesis. [ABSTRACT FROM AUTHOR]

Previous studies on azoospermia or oligozoospermia induced by heat stress or high doses of testosterone mainly focused on germ cell apoptosis; no data regarding their possible effect on spermatogonia mitosis are available. We have established unilateral cryptorchid and testosterone undecanoate (TU)-treated monkey models and examined expression of P16INK4a in the testis to look at its possible role in azoospermia or oligozoospermia induced by the heat stress or the TU treatment. The results showed that both heat stress and TU were capable of inducing expression of P16INK4a mainly in spermatogonia and other types of germ cells as well as Sertoli cells at the later stage of germ cell apoptosis, namely on Day 10 after operation or on Day 60 after TU injection. It is, therefore, suggested for the first time that P16INK4a protein may inhibit the spermatogonia mitosis in the testis at the later stage of the germ cell apoptosis, resulting in arrest of spermatogenesis. [Copyright &y& Elsevier]

Two typical lignocelluloses, pine and poplar, were torrefied in a tubular reactor under carbon dioxide medium at temperatures ranging from 220 to 340 °C. The effect of torrefaction temperature on the structure and properties of the chars obtained was investigated to evaluate their fuel applications. As the temperature raised from 220 to 340 °C, the mass yield decreased from 96.7% to 48.7% for pine, and from 97.1% to 43.8% for poplar. The higher heating value of the torrefied pine increased to 25.6 MJ/kg for the sample torrefied at 340 °C. An increase in reaction temperature resulted in a decrease in the contents of cellulose and hemicelluloses but notable increase of the content of lignin, especially for the sample subjected to the strongest torrefaction. The variation of C, H, and O contents of the samples after torrefaction suggested that a high temperature promoted the dehydration and deacetylation reactions. Thermal analysis indicated that the combustion activity of the sample was improved to a level of lignite after torrefaction. The hydrophobicity of lignocelluloses was notably increased with increased torrefaction severity, suggesting the prepared samples are good feedstocks for further processing. [ABSTRACT FROM AUTHOR]

Bamboo ( Phyllostachys sulphurea (Carr.) A. et C. Riv.) was torrefied at temperatures ranging from 280 to 340 °C and holding times between 10 and 90 min. The changes of mass yield, high heating value, and energy yield were investigated. The variations of the chemical components were depicted in Ross diagram and the alterations of H/C and O/C were plotted in van Krevelen diagram. The structural changes of the torrefied bamboo were studied by Fourier transform infrared and nuclear magnetic resonance spectroscopies and the morphology was examined by scanning electron microscopy. Results indicated that a high temperature and long holding time produced the torrefied sample with low mass and energy yields. The lignin mass fraction increased due to the transformation of carbohydrate degradation products when the torrefaction severity increased. Only a minor amount of cellulose was detected (0.15%) when torrefied at 320 °C and a higher temperature of 340 °C resulted in the complete removal of carbohydrates. The torrefaction at 340 °C and holding time of 60 min produced solid products with H/C and O/C ratios lower than those of lignite. Less water and hydrogen bonding sites were presented in heavy torrefied bamboo resulted from the degradation of both cellulose and hemicelluloses. With the increase of temperature, aliphaticity decreased but aromaticity increased due to the deoxygenation and dehydration reactions. The mass fraction of absorbed moisture of bamboo decreased with the increase of torrefaction temperature and prolongation of holding time. [ABSTRACT FROM AUTHOR]

Highlights: [•] Heterotrophic biofilm can use electrode as electron donor for denitrification. [•] High pH suppressed the activities of reductases involving in denitrification. [•] Low potential reduced the electron supply for denitrification processes. [Copyright &y& Elsevier]

Abstract: A comprehensive understanding of the uptake, tolerance and transport of heavy metals in the wetland system through aquatic plants will be essential for the development of phytoremediation technologies. Copper accumulation and translocation of a submersed macrophyte Hydrilla verticillata (L.f.) Royle were investigated. Plant shoots showed a significant accumulation of Cu with a maximum of 30830mg Cukg−1 dry weight after exposed to 4000μgL−1 Cu for 4d. Both roots and shoots can directly take up Cu from solution and Cu mainly accumulated in cell wall fractions. Moreover, H. verticillata predominantly accumulated Cu through shoots from the aqueous solutions because of the higher weights and bioaccumulation factors of shoots than those of roots. Acropetal translocation of Cu in the plant is higher than the basipetal translocation, which implies that upward translocation of Cu is mainly via the xylem and downward translocation is mainly through the phloem. These findings contribute to the application of submerged aquatic plants to copper removal from moderately contaminated waters. [ABSTRACT FROM AUTHOR]

Tannin (complex polyphenol) is commonly obtained from the bark and fruits. Its ortho-phenolic hydroxyl groups can adsorb heavy metal ions from wastewater by chelation. However, the adsorption performance to heavy metals (especially Pb) of the tannin-based materials is unsatisfactory. Herein, the tannin-reduced graphene aerogel (TRGA) was prepared by a one-step method for Pb(II) and Cd(II) adsorption. Results indicated that TRGA with a three-dimensional porous structure, low density, large specific surface area (122.2 m2/g) and high porosity, can facilitate the adsorption of metal ions. The maximum Pb(II) adsorption capacity of TRGA reached 803.84 mg/g at pH 4, which was much higher than that of precious tannin based adsorbents. Besides, the maximum adsorption capacity for Cd(II) is 395.80 mg/g at pH 4 when the optimal initial concentration of Cd(II) is 160 mg/L. Overall, the high capability and large efficiency of TRGA display widespread potentials for heavy metals adsorption. [Display omitted] • 3D porous TRGA was synthesized by one-step hydrothermal treatment. • TRGA showed quite low density so that it can be raised by a petal. • The adsorption capacity on Pb (II) and Cd (II) of TRGA were optimized. • TRGA might be utilized as a competitive adsorbent for Pb (II) and Cd (II) removal. [ABSTRACT FROM AUTHOR]

Abstract: Effects of chitosan on a submersed plant, Hydrilla verticillata, were investigated. Results indicated that H. verricillata could prevent ultrastructure phytotoxicities and oxidativereaction from polluted water with high chemical oxygen demand (COD). Superoxide dismutase (SOD) activity and malondialdehyde (MDA) contents in H. verticillata treated with 0.1% chitosan in wastewater increased with high COD (980 mg/L) and decreased with low COD (63 mg/L), respectively. Ultrastructural analysis showed that the stroma and grana of chloroplast basically remained normal. However, plant cells from the control experiment (untreated with chitosan) were vacuolated and the cell interval increased. The relict of protoplast moved to the center, with cells tending to disjoint. Our findings indicate that wastewater with high COD concentration can cause a substantial damage to submersed plant, nevertheless, chitosan probably could alleviate the membrane lipid peroxidization and ultrastructure phytotoxicities, and protect plant cells from stress of high COD concentration polluted water. [Copyright &y& Elsevier]