A nature-based closed-loop wastewater treatment system at vehicle-washing facilities: From linear to circular economy

Pakistan, among the top five most water-stressed nations globally, grapples with water scarcity owing to inadequate treatment infrastructure and groundwater overextraction. We demonstrate a successful nature-based closed-loop system to treat wastewater from urban vehicle-washing facilities, previously reliant on groundwater. An eco-friendly integrated system containing floating treatment wetlands (FTWs), subsurface flow constructed wetlands (SSF-CWs), and sand filtration (SF) was designed and installed at three vehicle-washing facilities for wastewater treatment and reuse in a loop. While the system is still operational after years, a consistent and significant reduction in water quality indicators is recorded, successfully meeting the national environmental quality standards of Pakistan. By reducing per unit water treatment costs to as low as $0.0163/m³ and achieving payback periods under a year, the embrace of these closed-loop strategies vividly underscores the imperative of transitioning to a circular economy in the domains of wastewater treatment and resource conservation.

Operational parameters optimization for remediation of crude oil-polluted water in floating treatment wetlands using response surface methodology

The application of floating treatment wetlands (FTWs) is an innovative nature-based solution for the remediation of polluted water. The rational improvement of water treatment via FTWs is typically based on multifactorial experiments which are labor-intensive and time-consuming. Here, we used the response surface methodology (RSM) for the optimization of FTW's operational parameters for the remediation of water polluted by crude oil. The central composite design (CCD) of RSM was used to generate the experimental layout for testing the effect of the variables hydrocarbon, nutrient, and surfactant concentrations, aeration, and retention time on the hydrocarbon removal in 50 different FTW test systems planted with the common reed, Phragmites australis. The results from these FTW were used to formulate a mathematical model in which the computational data strongly correlated with the experimental results. The operational parameters were further optimized via modeling prediction plus experimental validation in test FTW systems. In the FTW with optimized parameters, there was a 95% attenuation of the hydrocarbon concentration, which was very close to the 98% attenuation predicted by the model. The cost-effectiveness ratio showed a reduction of the treatment cost up to $0.048/liter of wastewater. The approach showed that RSM is a useful strategy for designing FTW experiments and optimizing operational parameters.

Proton pump inhibitors and histamine-2 receptor antagonists on the risk of pancreatic cancer: a systematic review and meta-analysis

BACKGROUND

Proton pump inhibitors (PPI) and histamine-2 receptor antagonists (H2RA) have been widely used for multiple purposes. Recent studies have suggested an association between these medications and the risk of pancreatic cancer. However, the results have been inconclusive.

AIM

We, therefore, conducted a study to assess the risk of developing pancreatic cancer in patients who used PPI and H2RA.

DESIGN

A systematic review and meta-analysis.

METHODS

A literature search was performed using MEDLINE and EMBASE databases from inception through February 2019. Studies that reported risk ratio comparing the risk of pancreatic cancer in patients who received PPI or H2RA versus those who did not receive treatments were included. Pooled risk ratios (RR) and 95% confidence intervals (CI) were calculated using a random-effect generic inverse variance method. Sensitivity analysis, excluding one study at a time, was performed.

RESULTS

After screening abstracts from the searching methods, seven studies (six case-control studies and one cohort study) were included in the analysis with total 546 199 participants. Compared to patients who did not take medications, the pooled RR of developing pancreatic cancer in patients receiving PPI and H2RA were 1.73 (95% CI: 1.16-2.57) and 1.26 (95% CI: 1.02-1.57), respectively. However, the sensitivity analysis of PPI changed the pooled RR to 1.87 (95% CI: 1.00-3.51) after a study was dropped out. Likewise, H2RA sensitivity analysis also resulted in non-significant pooled RR.

CONCLUSIONS

This meta-analysis did not find the strong evidence for the associations between the use of PPI and H2RA and pancreatic cancer.

Contrasting Responses to Stress Displayed by Tobacco Overexpressing an Algal Plastid Terminal Oxidase in the Chloroplast

The plastid terminal oxidase (PTOX) - an interfacial diiron carboxylate protein found in the thylakoid membranes of chloroplasts - oxidizes plastoquinol and reduces molecular oxygen to water. It is believed to play a physiologically important role in the response of some plant species to light and salt (NaCl) stress by diverting excess electrons to oxygen thereby protecting photosystem II (PSII) from photodamage. PTOX is therefore a candidate for engineering stress tolerance in crop plants. Previously, we used chloroplast transformation technology to over express PTOX1 from the green alga Chlamydomonas reinhardtii in tobacco (generating line Nt-PTOX-OE). Contrary to expectation, growth of Nt-PTOX-OE plants was more sensitive to light stress. Here we have examined in detail the effects of PTOX1 on photosynthesis in Nt-PTOX-OE tobacco plants grown at two different light intensities. Under 'low light' (50 μmol photons m^-2 s^-1) conditions, Nt-PTOX-OE and WT plants showed similar photosynthetic activities. In contrast, under 'high light' (125 μmol photons m^-2 s^-1) conditions, Nt-PTOX-OE showed less PSII activity than WT while photosystem I (PSI) activity was unaffected. Nt-PTOX-OE grown under high light also failed to increase the chlorophyll a/b ratio and the maximum rate of CO₂ assimilation compared to low-light grown plants, suggesting a defect in acclimation. In contrast, Nt-PTOX-OE plants showed much better germination, root length, and shoot biomass accumulation than WT when exposed to high levels of NaCl and showed better recovery and less chlorophyll bleaching after NaCl stress when grown hydroponically. Overall, our results strengthen the link between PTOX and the resistance of plants to salt stress.

Assessment of potential dietary toxicity and arsenic accumulation in two contrasting rice genotypes: Effect of soil amendments

High concentration of arsenic (As) in rice is a serious problem worldwide. Pot experiments were conducted to assess the potential dietary toxicity of arsenic and effect of various soil amendments on arsenic accumulation in rice grains. Two basmati rice genotypes were used to conduct pot experiments using various levels of arsenic (10, 25, 50 and 100 mg kg^-1 soil). In addition, plants were exposed to soil collected from a well documented arsenic contaminated site. Contrasting results for growth, yield and grain arsenic concentration were obtained for basmati-385 (Bas-385), exhibiting tolerance (56% yield improvement at 10 mg As kg^-1), while genotype BR-1 showed 18% yield decline under same conditions. Furthermore, application of soil amendments such as iron (Fe), phosphate (PO₄) and farmyard manure (FYM) at 50 mg kg^-1, 80 kg ha^-1 and 10 t ha^-1, respectively improved the plant height and biomass in both genotypes. Accumulation of arsenic in rice grain followed a linear trend in BR-1 whereas a parabolic relationship was observed in Bas-385. Both genotypes exhibited a positive response to iron sulfate amendment with significant reduction in grain arsenic concentrations. Regression analysis gave soil arsenic threshold values of 12 mg kg^-1 in Bas-385 and 10 mg kg^-1 in BR-1 for potential dietary toxicity. This study suggests that genotype Bas-385 can be used for safe rice production in areas with soil arsenic contamination up to 12 mg kg^-1 and that appropriate dose of iron sulfate for soil amendment can be used effectively to reduce translocation of arsenic to rice grain.

Glucose dehydrogenase gene containing phosphobacteria for biofortification of Phosphorus with growth promotion of rice

Phosphorus (P) is an essential plant nutrient, but often limited in soils for plant uptake. A major economic constraint in the rice production is excessive use of chemical fertilizers to meet the P requirement. Bioaugmentation of phosphate solubilizing rhizobacteria (PSB) can be used as promising alternative. In the present study 11 mineral PSB were isolated from Basmati rice growing areas of Pakistan. In broth medium, PSB solubilized tricalcium phosphate (27-354 μg mL^-1) with concomitant decrease in pH up to 3.6 due to the production of different organic acids, predominantly gluconic acid. Of these, 4 strains also have ability to mineralize phytate (245-412 μg mL^-1). Principle component analysis showed that the gluconic acid producing PSB strains (Acinetobacter sp. MR5 and Pseudomonas sp. MR7) have pronounced effect on grain yield (up to 55%), plant P (up to 67%) and soil available P (up to 67%), with 20% reduced fertilization. For simultaneous validation of gluconic acid production by MR5 and MR7 through PCR, new specific primers were designed to amplify gcd, pqqE, pqqC genes responsible for glucose dehydrogenase (gcd) mediated phosphate solubilization. These findings for the first time demonstrated Acinetobacter soli as potent P solubilizer for rice and expands our knowledge about genus specific pqq and gcd primers. These two gcd containing PSB Acinetobacter sp. MR5 (DSM 106631) and Pseudomonas sp. MR7 (DSM 106634) submitted to German culture collection (DSMZ), serve as global valuable pool to significantly increase the P uptake, growth and yield of Basmati rice with decreased dependence on chemical fertilizer in P deficit agricultural soils.

Pb-induced phytotoxicity in para grass (Brachiaria mutica) and Castorbean (Ricinus communis L.): Antioxidant and ultrastructural studies

Hydroponics experiment was conducted to investigate the effects of different levels of Pb on Para Grass (Brachiaria mutica) and Castorbean (Ricinus communis L). Generally, Para Grass exhibited higher tolerance to excessive concentrations of Pb in nutrient solution, whereas a consistent decline was observed in growth of Castorbean plants exposed to similar Pb levels. Malondialdehyde (MDA) and H₂O₂ contents exhibited contrasting results with a general decrease in Para Grass and a linear increase in case of Castorbean. In both species a decrease was noticed in the activities of superoxide dismutase (SOD) and guaiacol peroxidase (G-POD) while catalase (CAT) activity was significantly increased. Ultrastructural studies revealed increased starch grains and adversely affected thylakoid membranes in chloroplasts of leaf cells of plants treated with 500 μM Pb. Photosynthetic parameters such as CO₂ assimilation rate, stomatal conductance (gs) and transpiration rate (E) decreased in both plant species under different levels of Pb. Maximum concentrations of Pb in shoots of Para Grass and Castorbean were 1.29 and 0.352 g kg^-1, respectively while in roots maximum values were 8.88 and 49.86 g kg^-1, respectively. The high concentrations of Pb (about 5%) in the roots of Castorbean plants suggest its possible role in the phytoremediation/rhizofiltration of Pb contaminated water.

Arsenic removal by Japanese oak wood biochar in aqueous solutions and well water: Investigating arsenic fate using integrated spectroscopic and microscopic techniques

In this study, we examined the sorption of arsenite (As(III)) and arsenate (As(V)) to Japanese oak wood-derived biochar (OW-BC) in aqueous solutions, and determined its efficiency to remove As from As-contaminated well water. Results revealed that, among the four sorption isotherm models, Langmuir model showed the best fit to describe As(III) and As(V) sorption on OW-BC, with slightly greater sorption affinity for As(V) compared to As(III) (Q_L=3.89 and 3.16mgg^-1; R²=0.91 and 0.85, respectively). Sorption edge experiments indicated that the maximum As removal was 81% and 84% for As(III)- and As(V)-OW-BC systems at pH7 and 6, respectively, which decreased above these pH values (76-69% and 80-58%). Surface functional groups, notably OH, COOH, CO, CH₃, were involved in As sequestration by OW-BC, suggesting the surface complexation/precipitation and/or electrostatic interaction of As on OW-BC surface. Arsenic K-edge X-ray absorption near edge structure (XANES) spectroscopy indicated that 36% of the added As(III) was partially oxidized to As(V) in the As(III) sorption experiment, and in As(V) sorption experiment, 48% of As(V) was, albeit incompletely, reduced to As(III) on OW-BC surface. Application of OW-BC to As-contaminated well water (As: 27-144μgL^-1; n=10) displayed that 92 to 100% of As was depleted despite in the presence of co-occurring competing anions (e.g., SO₄^2-, CO₃^2-, PO₄^3-). This study shows that OW-BC has a great potential to remove As from solution and drinking (well) water. Overall, the combination of macroscopic sorption data and integrated spectroscopic and microscopic techniques highlight that the fate of As on biochar involves complex redox transformation and association with surface functional moieties in aquatic systems, thereby providing crucial information required for implication of biochar in environmental remediation programs.

Cadmium-induced oxidative stress, response of antioxidants and detection of intracellular cadmium in organs of moso bamboo (Phyllostachys pubescens) seedlings

Moso bamboo (Phyllostachys pubescens (Pradelle) Mazel ex J.Houz.) is recognized as a potential phytoremediation plant due to its huge biomass and high tolerance to environmental stresses. The objectives of this study were to investigate mechanism related to cadmium (Cd) tolerance and to evaluate Cd accumulation capacity of moso bamboo. The results of the pot experiment showed that Cd accumulation by bamboo increased with increasing the Cd levels in soil and the values in stem ranged from 28.51 to 132.13 mg kg(-1). Meanwhile chlorophyll in leaves and total biomass showed a decreasing trend. The bioaccumulation factors (BAF) for roots and stem in all the treatments were more than 1.0 and the translocation factor (TF) ranged from 0.70 to 1.06. In hydroponics experiment, the concentrations of malondialdehyde (MDA) in the leaves were significantly increased in Cd treated plants as compared with control. The activities of superoxide dismutase (SOD) and peroxidase (POD) were enhanced at initial stage and then decreased consistently with the increase of Cd addition. The proline concentrations were also increased due to the presence of Cd, particularly at 25 μM Cd treatment. According to TEM-EDX analysis, the cytoplasm was the main site for accumulation of Cd in moso bamboo. On the basis of overall results, it is suggested that moso bamboo could be successfully used for the remediation of low Cd (no more than 5 mg kg(-1)) contaminated soils.

Biochemical mechanisms of signaling: perspectives in plants under arsenic stress

Plants are the ultimate food source for humans, either directly or indirectly. Being sessile in nature, they are exposed to various biotic and abiotic stresses because of changing climate that adversely effects their growth and development. Contamination of heavy metals is one of the major abiotic stresses because of anthropogenic as well as natural factors which lead to increased toxicity and accumulation in plants. Arsenic is a naturally occurring metalloid toxin present in the earth crust. Due to its presence in terrestrial and aquatic environments, it effects the growth of plants. Plants can tolerate arsenic using several mechanisms like phytochelation, vacuole sequestration and activation of antioxidant defense systems. Several signaling mechanisms have evolved in plants that involve the use of proteins, calcium ions, hormones, reactive oxygen species and nitric oxide as signaling molecules to cope with arsenic toxicity. These mechanisms facilitate plants to survive under metal stress by activating their defense systems. The pathways by which these stress signals are perceived and responded is an unexplored area of research and there are lots of gaps still to be filled. A good understanding of these signaling pathways can help in raising the plants which can perform better in arsenic contaminated soil and water. In order to increase the survival of plants in contaminated areas there is a strong need to identify suitable gene targets that can be modified according to needs of the stakeholders using various biotechnological techniques. This review focuses on the signaling mechanisms of plants grown under arsenic stress and will give an insight of the different sensory systems in plants. Furthermore, it provides the knowledge about several pathways that can be exploited to develop plant cultivars which are resistant to arsenic stress or can reduce its uptake to minimize the risk of arsenic toxicity through food chain thus ensuring food security.

Lead accumulation and tolerance of Moso bamboo (Phyllostachys pubescens) seedlings: applications of phytoremediation

A hydroponics experiment was aimed at identifying the lead (Pb) tolerance and phytoremediation potential of Moso bamboo (Phyllostachys pubescens) seedlings grown under different Pb treatments. Experimental results indicated that at the highest Pb concentration (400 μmol/L), the growth of bamboo seedlings was inhibited and Pb concentrations in leaves, stems, and roots reached the maximum of 148.8, 482.2, and 4282.8 mg/kg, respectively. Scanning electron microscopy revealed that the excessive Pb caused decreased stomatal opening, formation of abundant inclusions in roots, and just a few inclusions in stems. The ultrastructural analysis using transmission electron microscopy revealed that the addition of excessive Pb caused abnormally shaped chloroplasts, disappearance of endoplasmic reticulum, shrinkage of nucleus and nucleolus, and loss of thylakoid membranes. Although ultrastructural analysis revealed some internal damage, even the plants exposed to 400 µmol/L Pb survived and no visual Pb toxicity symptoms such as necrosis and chlorosis were observed in these plants. Even at the highest Pb treatment, no significant difference was observed for the dry weight of stem compared with controls. It is suggested that use of Moso bamboo as an experimental material provides a new perspective for remediation of heavy metal contaminated soil owing to its high metal tolerance and greater biomass.

Enhanced degradation of textile effluent in constructed wetland system using Typha domingensis and textile effluent-degrading endophytic bacteria

Textile effluent is one of the main contributors of water pollution and it adversely affects fauna and flora. Constructed wetland is a promising approach to remediate the industrial effluent. The detoxification of industrial effluent in a constructed wetland system may be enhanced by applying beneficial bacteria that are able to degrade contaminants present in industrial effluent. The aim of this study was to evaluate the influence of inoculation of textile effluent-degrading endophytic bacteria on the detoxification of textile effluent in a vertical flow constructed wetland reactor. A wetland plant, Typha domingensis, was vegetated in reactor and inoculated with two endophytic bacterial strains, Microbacterium arborescens TYSI04 and Bacillus pumilus PIRI30. These strains possessed textile effluent-degrading and plant growth-promoting activities. Results indicated that bacterial inoculation improved plant growth, textile effluent degradation and mutagenicity reduction and were correlated with the population of textile effluent-degrading bacteria in the rhizosphere and endosphere of T. domingensis. Bacterial inoculation enhanced textile effluent-degrading bacterial population in rhizosphere, root and shoot of T. domingensis. Significant reductions in COD (79%), BOD (77%) TDS (59%) and TSS (27%) were observed by the combined use of plants and bacteria within 72 h. The resultant effluent meets the wastewater discharge standards of Pakistan and can be discharged into the environment without any risks. This study revealed that the combined use of plant and endophytic bacteria is one of the approaches to enhance textile effluent degradation in a constructed wetland system.

Enhanced remediation of chlorpyrifos from soil using ryegrass (Lollium multiflorum) and chlorpyrifos-degrading bacterium Bacillus pumilus C2A1

The combined use of plants and associated microorganisms has great potential for remediating soil contaminated with organic compounds such as pesticides. The objective of this study was to determine whether the bacterial inoculation influences plant growth promotion and chlorpyrifos (CP) degradation and accumulation in different parts of the plant. Ryegrass was grown in soil spiked with CP and inoculated with a pesticide degrading bacterial strain Bacillus pumilus C2A1. Inoculation generally had a beneficial effect on CP degradation and plant biomass production, highest CP degradation (97%) was observed after 45 days of inoculation. Furthermore, inoculated strain efficiently colonized in the rhizosphere of inoculated plant and enhanced CP and its primary metabolite 3,5,6-trichloro-2-pyridinol (TCP) degradation. There was significantly less CP accumulation in roots and shoots of inoculated plants as compared to uninoculated plants. The results show the effectiveness of inoculated exogenous bacteria to boost the remediation of CP contaminated sites and decrease levels of toxic pesticide residues in crop plants.

Effect of Pb toxicity on the growth and physiology of two ecotypes of Elsholtzia argyi and its alleviation by Zn

Hydroponics experiments were conducted to underpin the nature of interactions between Zn, an essential micronutrient and Pb, a nonessential element on plant growth and root morphology, as well as antioxidant adaptation in mined ecotype (ME) and nonmined ecotype (NME) of Elsholtzia argyi. Plants were exposed to 50 μM Pb having normal Zn (0.5 μM), and two other treatments of the same Pb with low (0.05 μM) and high (20 μM) Zn, respectively for 12 days. Application of Pb with normal Zn caused adverse effects on the overall growth and antioxidant capacity of both ecotypes, however; effects were more pronounced in NME. The addition of high Zn along with Pb improved the growth and antioxidant capacity of both the ecotypes, while low Zn failed to show significant changes in NME plants; however slightly aggravated the Pb toxicity in the plants of ME. Zinc antagonized Pb concentrations in root and stem of both ecotypes and leaf of ME, while no significant differences were noted in Pb concentrations of NME leaf. It is suggested that in E. argyi, mechanisms of Pb and Zn uptake and translocation as well as their interactions within the plant cell may be different for both ecotypes and need to be further investigated.

Rhizosphere characteristics of zinc hyperaccumulator Sedum alfredii involved in zinc accumulation

A hyperaccumulating ecotype (HE) and a non-hyperaccumulating ecotype (NHE) of Sedum alfredii were grown in a pot experiment to investigate the chemical characteristics of the rhizosphere. The results indicated that HE accumulated more Zn in the shoot than NHE after growing in both heavily and slightly polluted soil. The water soluble Zn and mobile Zn (extractable with 1M NH(4)NO(3)) fraction in both rhizosphere and bulk soils decreased considerably after growth of HE compared to NHE. However, the decreases in mobile fraction accounted for less than 8.5% of the total Zn uptake by HE indicating that HE was effective in mobilizing Zn from the non-mobile fractions. Zinc-induced root exudates reduced the soil pH (by 0.6-0.8 units) and increased dissolved organic carbon concentrations in the rhizosphere of HE compared to the bulk soil. The dissolved organic matter (DOM) from the rhizosphere of HE showed greater (1.7-2.5 times) extracting ability of Zn from various Zn minerals than those of NHE-DOM (P<0.05). Results from this study suggests that rhizosphere acidification and the exudation of high amounts of DOM with great metal extracting ability might be two important mechanisms by which HE S. alfredii is involved in activating metal in the rhizosphere.

Effects of zinc and cadmium interactions on root morphology and metal translocation in a hyperaccumulating species under hydroponic conditions

Effects of zinc (Zn) and cadmium (Cd) interactions on root morphology and metal translocation in the hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) of S. alfredii were investigated under hydroponic conditions. Specific root lengths (SRL), specific root surface areas (SRA) and specific root volumes (SRV) of the HE increased significantly when plant were treated with 500 microM Zn or 100 microM Cd+500 microM Zn, whereas these root parameters were significantly decreased for the NHE when plant were treated with 100 microM Cd, 500 microM Zn or 100 microM Cd+500 microM Zn. SRL and SRA of the HE were mainly constituted by roots with diameter between 0.2-0.4mm (diameter class 3 and 4) which were significantly increased in treatment of 500 microM Zn or 100 microM Cd+500 microM Zn, whereas in the NHE, metal treatments caused a significant decrease in SRL and SRA of the finest diameter class root (diameter between 0.1-0.3mm). The HE of S. alfredii could maintain a fine, widely branched root system under contaminated conditions compared with the NHE. Relative root growth, net Cd uptake and translocation rate in the HE were significantly increased by adding 500 microM Zn, as compared with the second growth period, where 100 microM Cd was supplied alone. Cadmium and Zn concentrations in the shoots of the HE were 12-16 times and 22-27 times higher than those of the NHE under 100 microM Cd+500 microM Zn combined treatment. These results indicate strong positive interactions of Zn and Cd occurred in the HE under 100 microM Cd+500 microM Zn treatment and Cd uptake and translocation was enhanced by adding 500 microM Zn.

The effect of EDDS addition on the phytoextraction efficiency from Pb contaminated soil by Sedum alfredii Hance

Present study reports the results of three pot experiments, conducted to investigate the chelate-assisted phytoextraction of Pb contaminated soils. The optimum phytoextraction was observed when 2.5mM ethylene diamine disuccinic acid (EDDS) was added in single dosage for 14 days to low Pb soil (treated with 400 mg kg(-1)soil). On the contrary, for high Pb soil (treated with 1200 mg kg(-1)soil), 5mM EDDS concentration in single dosage for 10 days produced better results. Post-harvest effects of EDDS on the concentrations of available Pb and dissolved organic carbon (DOC) were significantly higher as compared with check (CK i.e. without EDDS addition), and consequently decreased with the passage of time. Our results suggested that chelate-assisted phytoextraction was more suitable for slightly contaminated soils.

Isolation of Ochrobactrum sp.QZ2 from sulfide and nitrite treatment system

A bacterial strain QZ2 was isolated from sludge of anoxic sulfide-oxidizing (ASO) reactor. Based on 16S rDNA sequence analysis and morphology, the isolate was identified as Ochrobactrum sp. QZ2. The strain was facultative chemolithotroph, able of using sulfide to reduce nitrite anaerobically. It produced either elemental sulfur or sulfate as the product of sulfide oxidation, depending on the initial sulfide and nitrite concentrations. The optimum growth pH and temperature for Ochrobactrum sp. QZ2 were found as 6.5-7.0 and 30 degrees C, respectively. The specific growth rate (micro) was found as 0.06 h(-1) with a doubling time of 19.75h; the growth seemed more sensitive to highly alkaline pH. Ochrobactrum sp. QZ2 catalyzed sulfide oxidation to sulfate was more sensitive to sulfide compared with nitrite as indicated by IC(50) values for sulfide and nitrite utilization implying that isolate was relatively more tolerant to nitrite. The comparison of physiology of Ochrobactrum sp. QZ2 with those of other known sulfide-oxidizing bacteria suggested that the present isolate resembled to Ochrobactrum anthropi in its denitrification ability.

Ultrastructural changes, zinc hyperaccumulation and its relation with antioxidants in two ecotypes of Sedum alfredii Hance

Zn phytotoxicity and its possible detoxifying responses in two ecotypes of Sedum alfredii Hance, i.e. hyperaccumulating ecotype (HE) and non-hyperaccumulating ecotype (NHE) were investigated. HE grew better with high Zn concentrations of 29.11gkg(-1) DW in shoots when exposed to 500microM Zn2+. Toxicity symptoms caused by Zn in root cells of both ecotypes mainly included plasmolysis, disruption of plasma membranes and increased cell vacuolation. At high supplied Zn concentration, chloroplasts suffered from structural disorganization in both ecotypes. Zn-induced hydrogen peroxide (H2O2) and superoxide radical (O(2)-) productions in leaves were determined by a histochemical method, which revealed that Zn stress may have involved NADPH oxidase, protein phosphatases and intracellular Ca2+ to activate the reactive oxygen species production. Inhibition of glutathione synthesis may have led to increased H2O2 and O(2)- accumulations in leaves of HE. In response to higher Zn concentrations, ascorbic acid significantly increased in both ecotypes and levels of glutathione increased in both leaves and roots of HE and in roots of NHE without any change in the leaves of NHE. The enzymatic activities like those of superoxide dismutase (SOD, EC 1.15.1.1), catalase (CAT, EC 1.11.1.6), guaiacol peroxidase (GPX, EC 1.11.1.7), ascorbate peroxidase (APX, EC 1.11.1.11), dehydroascorbate reductase (DHAR, EC 1.8.5.1), and glutathione reductase (GR, EC 1.6.4.2) in leaves of HE were all enhanced at supplied Zn concentration of 500microM, which may account for its better growth.

Effects of cadmium on ultrastructure and antioxidative defense system in hyperaccumulator and non-hyperaccumulator ecotypes of Sedum alfredii Hance

Plant growth, ultrastructural and antioxidant adaptations and glutathione biosynthesis in Cd-hyperaccumulating ecotype Sedum alfredii Hance (HE) countering high Cd environment were investigated and compared with its non Cd-hyperaccumulating ecotype (NHE). Cadmium exposure resulted in significant ultrastructural changes in root meristem and leaf mesophyll cells of S. alfredii, but damage was more pronounced in NHE even when Cd concentrations were one-tenth of those applied to HE. Cadmium stress damaged chloroplasts causing imbalanced lamellae formation coupled with early leaf senescence. Histochemical results revealed that glutathione (GSH) biosynthesis inhibition led to overproduction of hydrogen peroxide (H(2)O(2)) and superoxide radical (O(2)(*-)) in HE but not in NHE. Differences were noted in both HE and NHE for catalase (CAT), guaiacol peroxidase (GPX), ascorbate peroxidase (APX) and glutathione reductase (GR) activities under various Cd stress levels. No relationship was found between antioxidative defense capacity including activities of superoxide dismutase (SOD), CAT, GPX, APX and GR as well as ascorbic acid (AsA) contents and Cd tolerance in the two ecotypes of S. alfredii. The GSH biosynthesis induction in root and shoot exposed to elevated Cd conditions may be involved in Cd tolerance and hyperaccumulation in HE of S. alfredii H.

Response of antioxidant enzymes, ascorbate and glutathione metabolism towards cadmium in hyperaccumulator and nonhyperaccumulator ecotypes of Sedum alfredii H

Hydroponics studies were conducted to investigate the antioxidant adaptations, ascorbate and glutathione metabolism in hyperaccumulating ecotype of Sedum alfredii (HE) exposed to high Cd environment, when compared with its nonhyperaccumulating ecotype (NHE). Exposure to Cd induced a burst of oxidative stress in both ecotypes which was evident by the sharp increase in hydrogen peroxide (H(2)O(2)) contents and lipid peroxidation. Buthionine sulfoximine (BSO), an inhibitor of glutathione (GSH) synthesis, did not affect H(2)O(2) concentrations as well as growth of both ecotypes in the absence of Cd. However, compared with Cd application alone, BSO combined with Cd treatment caused a substantial augmentation of H(2)O(2) accumulation accompanied by a reduction in Cd concentrations in roots and leaves of HE at the end of treatment, which may rule out the possibility that GSH biosynthesis may play an important role as a signal of the stress regulation. No efficient and superior enzymatic antioxidant defense mechanisms against Cd-imposed oxidative stress existed in both NHE and HE, but the essential nonenzymatic components like ascorbic acid (AsA) and GSH played a prominent role in tolerance against Cd. Cadmium stimulated a notable rise in AsA concentration in both ecotypes soon after the application of treatment. A preferential Cd-stress response in HE was suggested to changes in the GSH pool, where acclimation was marked by increased GSH concentrations.

Optimization of chelator-assisted phytoextraction, using EDTA, lead and Sedum alfredii Hance as a model system

Pot and leaching column experiments were conducted to optimize chelator-assisted phytoextraction of lead (Pb) from contaminated soils. Optimum phytoextraction occurred at added EDTA concentration of 5 mM in single dose for 10 days in low Pb soil (treated with 400 mg kg(-1) soil), while it would be better for high Pb soil (treated with 1,200 mg kg(-1) soil) with five intermittent doses of 10 mM EDTA for 7 days. Combined with column experiment, it could be inferred that chelator-assisted phytoextraction is more suitable for the slightly contaminated soils.

Effect of Pb toxicity on leaf growth, physiology and ultrastructure in the two ecotypes of Elsholtzia argyi

Hydroponics experiments were conducted to study the effects of Pb on mined ecotype (ME) and non-mined ecotype (NME) of Elsholtzia argyi from Pb/Cu mining and the non-contaminated agricultural areas, respectively. The results showed that at 200 microM Pb treatment, although concentrations of Pb in leaves and stem of the ME were 2.6 and 4.5 times higher than those of the NME, these plants exhibited higher tolerance to excessive levels of Pb in the growth medium. In both the ecotypes, Pb caused inhibition of leaf growth and photosynthesis, and induced the membrane damage which was more obvious in the NME. Pb treatment decreased the activities of superoxide dismutase (SOD) and guaiacol peroxidase (G-POD) while activity of catalase (CAT) and levels of total soluble proteins (TSP), ascorbic acid (AsA) and glutathione (GSH) were significantly induced after Pb exposure, however, increase was sharp in the ME plants. Leaf ultrastructural analysis of the spongy mesophyll cells revealed that the excessive Pb concentrations caused adverse effects on chloroplast ultrastructure of both ecotypes whereby internal damage was more severe in NME. The higher tolerance to Pb displayed by ME is mainly attributed to maintenance of its leaf growth and physiology, induction of GSH and integrity of cell organelles especially chloroplast ultrastructure.

Comparison of synthetic chelators and low molecular weight organic acids in enhancing phytoextraction of heavy metals by two ecotypes of Sedum alfredii Hance

Lab scale and pot experiments were conducted to compare the effects of synthetic chelators and low molecular weight organic acids (LMWOA) on the phytoextraction of multi-contaminated soils by two ecotypes of Sedum alfredii Hance. Through lab scale experiments, the treatment dosage of 5 and 10 mM for synthetic chelators and LMWOA, respectively, and the treatment time of 10 days were selected for pot experiment. In pot experiment, the hyperaccumulating ecotype (HE) was found more tolerant to the metal toxicity compared with the non-hyperaccumulating ecotype (NHE). EDTA for Pb, EDDS for Cu, and DTPA for Cu and Cd were found more effective to enhance heavy metal accumulation in the shoots of S. alfredii Hance. Compared with synthetic chelators, the phytoextraction ability of LMWOA was lesser. Considering the strong post-harvest effects of synthetic chelators, it is suggested that higher dosage of LMWOA could be practiced during phytoextraction, and some additional measures could also be taken to lower the potential environmental risks of synthetic chelators in the future studies.

Effect of pH on anoxic sulfide oxidizing reactor performance

The effects of pH on the performance of anoxic sulfide oxidizing (ASO) reactor were evaluated. Performance was investigated under various operational conditions at influent pH range of 4-11. At the influent pH of 7-7.5 during loading tests and HRT tests, the sulfide oxidation was partial. In general, the amount of sulfate formed decreased with the increasing sulfide and nitrite loadings. The bacterial communities in ASO reactors were more sensitive to acidic pH compared with alkaline pH, as nitrite and sulfide removal rates dropped significantly when exposed to acidic pH 3. High dissolved bisulfide ions, nitrite and excess of sulfate (>300 mg/L) might have inhibited the sulfide oxidation under highly acidic and alkaline conditions in the ASO reactor. Based on sulfide and nitrite removal efficiencies, the ASO reactor can be operated in a wide range of pH, i.e. 5-11.

Quantitative comparison of stability of ANAMMOX process in different reactor configurations

A new stability evaluating system for ANAMMOX comprising three instability indices i.e. coefficient of variation ratio, coefficient of range ratio and coefficient of regression function derivative was established. Three lab-scale ANAMMOX reactors viz upflow anaerobic sludge blanket (UASB) reactor, upflow stationary fixed film (USFF) reactor and anaerobic sequencing batch reactor (ASBR) were compared for their stability based on the established criterion against the hydraulic and substrate concentration shocks. The results showed that all ANAMMOX reactors under investigation were more tolerant to the hydraulic shock than substrate concentration shock. The UASB reactor was the most stable reactor configuration towards substrate concentration shock, followed by the USFF reactor and ASBR. However, the ASBR proved the most tolerant to hydraulic shock, followed by the UASB reactor and USFF reactor. In terms of stability, UASB reactor was more suitable configuration compared with USFF reactor. The instability indices proved to be effective and explicit for the evaluation of ANAMMOX systems.

Phosphate removal from solution using steel slag through magnetic separation

Steel slag with magnetic separation was used to remove phosphate from aqueous solutions. The influence of adsorbent dose, pH, and temperature on phosphate removal was investigated in a series of batch experiments. Phosphate removal increased with the increasing temperature, adsorbent dose and decreased with increasing initial phosphate concentrations, while it was at its peak at pH of 5.5. The phosphate removal predominantly occurred through ion exchange. The specific surface area of the steel slag was 2.09m2/g. The adsorption of phosphate followed both Langmuir and Freundlich isotherms. The maximum adsorption capacity of the steel slag was 5.3mgP/g. The removal rates of total phosphorus (TP) and dissolved phosphorus (DP) from secondary effluents were 62-79% and 71-82%, respectively. Due to their low cost and high capability, it was concluded that the steel slag may be an efficient adsorbent to remove phosphate both from solution and wastewater.

Lead induced changes in the growth and antioxidant metabolism of the lead accumulating and non-accumulating ecotypes of Sedum alfredii

The phytotoxicity and antioxidative adaptations of lead (Pb) accumulating ecotype (AE) and non-accumulating ecotype (NAE) of Sedum alfredii Hance were investigated under different Pb treatments involving 0, 0.02 mmol/L Pb, 0.1 mmol/L Pb and 0.1 mmol/L Pb/0.1 mmol/L ethylenediaminetetraacetic acid (EDTA) for 6 days. With the increasing Pb level, the Pb concentration in the shoots of AE plants enhanced accordingly, and EDTA supply helped 51% of Pb translocation to shoots of AE compared with those treated with 0.1 mmol/L Pb alone. Moreover, the presence of EDTA alleviated Pb phytotoxicity through changes in plant biomass, root morphology and chlorophyll contents. Lead toxicity induced hydrogen peroxide (H2O2) accumulation and lipid peroxidation in both ecotypes of S. alfredii. The activities of superoxide dismutase (SOD), guaiacol peroxidase (G-POD), ascorbate peroxidase, and dehydroascorbate reductase elevated in both leaves and roots of AE as well as in leaves of NAE with the increasing Pb levels, but SOD and G-POD declined in roots of NAE. Enhancement in glutathione reductase activity was only detected in roots of NAE while a depression in catalase activity was recorded in the leaves of NAE. A significant enhancement in glutathione and ascorbic acid (AsA)levels occurred in both ecotypes exposed to Pb and Pb/EDTA treatment compared with the control, however, the differences between these two treatments were insignificant. The dehydroascorbate (DHA) contents in roots of both ecotypes were 1.41 to 11.22-fold higher than those in leaves, whereas the ratios of AsA to DHA (1.38 to 6.84) in leaves altering more to the reduced AsA form were much higher than those in roots. These results suggested that antioxidative enzymes and antioxidants play an important role in counteracting Pb stress in S. alfredii.

Effect of Pb toxicity on root morphology, physiology and ultrastructure in the two ecotypes of Elsholtzia argyi

Seed germination and hydroponics experiments were conducted to underpin the effects of Pb on mined ecotype (ME) and non-mined ecotype (NME) of Elsholtzia argyi from Pb/Cu mining areas and the non-contaminated agricultural areas, respectively. In both experiments, ME exhibited higher tolerance to excessive levels of Pb in the growth medium. Various Pb treatments caused a stimulatory effect on seed germination of both the ecotypes. Concentrations of Pb in the leaves and the stem of the ME were 2.6 and 4.5 times respectively higher than those of the NME when plants were supplied with Pb level of 200microM. Pb posed adverse effects on root morphological organization and root activity of both the ecotypes but decrease was not sharp and root activity was recovered in ME plants. Root ultrastructural studies revealed that in ME, Pb was detected as fine particles dispersed throughout the cell membrane and cell wall fraction, whereas most of the Pb was found as large aggregates deposited in the cell walls of NME plants. Comparatively better growth, higher tolerance and accumulation of Pb expressed by ME plants is mainly attributed to the maintenance of its root growth and activity as well as integrity of cell organelles.