Conocarpus biochar as a soil amendment for reducing heavy metal availability and uptake by maize plants

The objective of this study was to assess the use of Concarpus biochar as a soil amendment for reducing heavy metal accessibility and uptake by maize plants (Zea mays L.). The impacts of biochar rates (0.0, 1.0, 3.0, and 5.0% w/w) and two soil moisture levels (75% and 100% of field capacity, FC) on immobilization and availability of Fe, Mn, Zn, Cd, Cu and Pb to maize plants as well as its application effects on soil pH, EC, bulk density, and moisture content were evaluated using heavy metal-contaminated soil collected from mining area. The biochar addition significantly decreased the bulk density and increased moisture content of soil. Applying biochar significantly reduced NH₄OAc- or AB-DTPA-extractable heavy metal concentrations of soils, indicating metal immobilization. Conocarpus biochar increased shoot dry biomass of maize plants by 54.5–102% at 75% FC and 133–266% at 100% FC. Moreover, applying biochar significantly reduced shoot heavy metal concentrations in maize plants (except for Fe at 75% FC) in response to increasing application rates, with a highest decrease of 51.3% and 60.5% for Mn, 28% and 21.2% for Zn, 60% and 29.5% for Cu, 53.2% and 47.2% for Cd at soil moisture levels of 75% FC and 100% FC, respectively. The results suggest that biochar may be effectively used as a soil amendment for heavy metal immobilization and in reducing its phytotoxicity.     

Biosorption of heavy metals by Bacillus thuringiensis strain OSM29 originating from industrial effluent contaminated north Indian soil

The study was navigated to examine the metal biosorbing ability of bacterial strain OSM29 recovered from rhizosphere of cauliflower grown in soil irrigated consistently with industrial effluents. The metal tolerant bacterial strain OSM29 was identified as Bacillus thuringiensis following 16S rRNA gene sequence analysis. In the presence of the varying concentrations (25–150 mgl⁻¹) of heavy metals, such as cadmium, chromium, copper, lead and nickel, the B. thuringiensis strain OSM29 showed an obvious metal removing potential. The effect of certain physico-chemical factors such as pH, initial metal concentration, and contact time on biosorption was also assessed. The optimum pH for nickel and chromium removal was 7, while for cadmium, copper and lead, it was 6. The optimal contact time was 30 min. for each metal at 32 ± 2 °C by strain OSM29. The biosorption capacity of the strain OSM29 for the metallic ions was highest for Ni (94%) which was followed by Cu (91.8%), while the lowest sorption by bacterial biomass was recorded for Cd (87%) at 25 mgl⁻¹ initial metal ion concentration. The regression coefficients obtained for heavy metals from the Freundlich and Langmuir models were significant. The surface chemical functional groups of B. thuringiensis biomass identified by Fourier transform infrared (FTIR) were amino, carboxyl, hydroxyl, and carbonyl groups, which may be involved in the biosorption of heavy metals. The biosorption ability of B. thuringiensis OSM29 varied with metals and was pH and metal concentration dependent. The biosorption of each metal was fairly rapid which could be an advantage for large scale treatment of contaminated sites.     

Sex allocation in aquatic ferns: The role of body size

Patterns of resource allocation reflect the plastic strategies that result from different selective pressures imposed by the environment. However, biomass allocation can be limited by architectural restrictions that change with the plant size. Our knowledge about sex allocation in heterosporous aquatic ferns remains scarce and studies on the reproductive strategies of these plants may yield valuable information regarding the evolutionary history of heterospory. Here, we investigate resources allocation, both in number and in biomass, to produce megasporangia and microsporangia among three species of Salvinia with different body sizes. Salvinia oblongifolia, S. auriculata and S. minima were collected in temporary ponds on the floodplain of the Pandeiros River in Brazil. We counted megasporangia and microsporangia, and measured their dry mass in each ramet. We also measured the total vegetative biomass and total reproductive biomass of each ramet in each species. Resource allocation to megasporangia production is associated with the specific body size of each species. However, the allocation for microsporangia production was higher in the species with intermediate size, which probably may be related to the drought event. The total reproductive biomass of each species was not dependent on the total vegetative biomass, but despite a similar reproductive effort, species differ on which sex is prioritized in the allocation process. Our results provide the first data about the processes underlying the sex allocation of Salvinia in the floodplains. The production of sori is size dependent in each Salvinia species and is shaped by drought, an intense selective pressure in temporary wet habitats.     

The application of a micro-algal/bacterial biofilter for the detoxification of copper and cadmium metal wastes

In the present study the potential of a biofilter containing a mixture of dried micro-algal/bacterial biomass for removing heavy metals (Cu²⁺, Cd²⁺) from dilute electroplating waste was tested. The biomass was produced in an artificial stream using the effluent of a municipal waste water treatment plant as a nutrient source, with the additional benefit of reducing phosphorus and nitrogen loadings. Baseline batch experiments determined that optimum adsorption for both metals (80–100%) were achieved with the deionized-H₂O conditioned biomass at initial pH 4.0. Other biosorption variables (contact time, initial metal concentration) were also tested. Biosorption data were fitted successfully by the Langmuir model and results showed a high affinity of the used biomass for both metals (q_max 18–31 mg metal/g.d.w). Flow-through column experiments containing Ca-alginate/biomass beads showed that metal adsorption depends also on flow-rate and volume of treated waste. Desorption of both metals with weak acids was very successful (95–100%) but the regeneration of the columns was not achieved due to the destabilization of beads.     

Sorption of heavy metals from electroplating effluent using immobilized biomass Trichoderma viride in a continuous packed-bed column

The sorption of heavy metals ions by immobilized Trichoderma viride biomass in a packed-bed column was studied. Fungal biomass T. viride was immobilized to Ca-alginate used for removal of Cr(VI), Ni(II) and Zn(II) ions from synthetic solutions and electroplating effluent. The experiments were conducted to study the effect of important design parameters such as bed height, flow rate and initial concentration of metal ions. The maximum sorption capacity was observed at flow rate 5 ml/min, bed height 20 cm and metal ions concentration 50 mg/L with immobilized biomass. Whereas, breakthrough time and saturation time decreased with increase flow rate and metal ions concentration and an inverse condition was found in bed height. The bed depth service time (BDST) Adams-Bohart model was used to analyze the experimental data. The regeneration efficiency was observed 40.1%, 75% and 53% for Cr(VI), Ni(II) and Zn(II) without any significant alteration in sorption capacity after 5th sorption-desorption cycles.     

Growth of a floating aquatic weed,Salvinia under standard conditions

1. Growth of the floating aquatic weed, Salvinia, in sterile culture was exponential for at least 2 weeks under standardized conditions.
2. Increase in light intensity or in CO₂ resulted in increases in growth rate, but did not extend the exponential period of growth.
3. This aquatic plant, like many others, discriminates against calcium relative to strontium.
4. In culture Salvinia exhibited luxury consumption of N and P.
5. Because of high C/N ratios, Salvinia may not be a favorable source of animal food, but might be useful in nutrient removal schemes.
6. In sterile culture, S. molesta produced fewer leaves than S. minima, but maintained a significant increase in leaf area and dry weight. This may be correlated with the ability of the first species to rapidly spread over tropical waterways.

     

Microbial biomass,respiration and diversity in ultramafic soils of West Dome,New Zealand

Ultramafic soils are colonised by plant communities adapted to naturally elevated heavy metal content but it is not known whether soil microbial communities are similarly adapted to heavy metals. We measured microbial properties of six ultramafic soils that ranged in heavy metal content to test whether microbial diversity would decrease and respiratory quotient (microbial respiration:biomass) increase due to the stress imposed by increasing metal content. Soil samples were collected from beneath Nothofagus solandri var. cliffortioides tall forest, tall Leptospermum scoparium shrubland, open Leptospermum scoparium shrubland, an open Leptospermum scoparium shrubland with the rare ultramafic endemic Celmisia spedenii, a mixed divaricate shrubland, and a red tussock (Chionochloa rubra) grassland on the Dun Mountain Ophiolite belt, New Zealand. Samples were analysed for catabolic evenness using the catabolic response profile technique, microbial biomass, microbial respiration, and soil properties (pH, total carbon, total nitrogen, magnesium and total or extractable chromium and nickel). The sites differed in base saturation, pH and concentrations of metals, particularly magnesium, chromium and nickel, properties that are a major determinant of the plant communities that develop. Microbial biomass and respiration, catabolic evenness (range of 19.1 to 22.7) and the respiratory quotient were not correlated to any of the measured soil chemical properties. Factor analysis of the respiratory responses showed that the microbial communities under each vegetation type were distinct. The second factor extracted was correlated to total carbon (r ²=0.62, P<0.01), basal respiration (r ²=0.55, P<0.01) and microbial biomass (r ²=0.65, P<0.01). Increasing metals concentrations had no direct impact on microbial diversity, biomass, respiration or community energetics. However, we suggest that metal concentrations may have exerted an indirect effect on the structure of the microbial communities through control of the vegetation community and litter inputs of carbon to the soil.     

Desarrollo de un bioadsorbente laminar con Phanerochaete chrysosporium hipertolerante al cadmio,al níquel y al plomo para el tratamiento de aguas

BackgroundThe use of basidiomycetes for metal removal is an alternative to traditional methods. In this, the biomass acts as a natural ionic exchanger removing metals from solution.ObjectiveTo develop a laminar biosorbent using a basidiomycete fungus resistant to high Cd, Ni and Pb concentrations.MethodsThe tolerance of Trametes versicolor, Pleurotus ostreatus and Phanerochaete chrysosporium was evaluated using increasing concentrations of the heavy metal salts, cadmium sulphate, lead acetate and nickel chloride. A biosorbent system was developed based on polyethylene sheets with a fungal biomass. It was evaluated in bubble columns using synthetic wastewater with the 3 metal salts at a rate of 300 mg/l. Finally, in a complementary experiment using shake flasks, the effect of a higher amount of biomass related to the metal removal efficiency was evaluated.ResultsP. chrysosporium strain was more tolerant to C₄H₆O₄Pb (10,000 mg/l), Cl₂Ni (300 mg/l) and CdSO₄·8H₂O (1,500 mg/l). In a reactor, under non-ligninolytic conditions, the fungus removed 69% of the chemical oxygen demand and produced enzymes such as LiP (0.01 U/l) and MnP (0.6 U/l.). An accumulation of metals in the wall was observed. By increasing the biomass to 1.6 (w/v), the metal biosorption was favored in the mixture (57% Pb, 74% Cd, and 98% Ni) and separately (95% Pb, 60% Cd, and 56% Ni). Competition between Ni and Pb by ligands of the wall was observed.ConclusionA novel laminar system based on P. chrysosporium viable biomass was developed. It has a large surface area and tolerance to high concentrations of Cd, Ni and Pb. It seems to be an alternative for the removal of metals from water.     

Metal biosorption by two cyanobacterial mats in relation to pH, biomass concentration, pretreatment and reuse

The pH-dependent metal sorption by Oscillatoria- and Phormidium-dominated mats was effectively expressed by the Hill function. The estimated Hill functions can fruitfully predict the amount of metal sorbed at a particular initial pH. Pretreatment of biomass with 0.1 mmol L⁻¹ HCl was more effective than pretreatment with CaCl₂, HNO₃, NaOH, and SDS in enhancing metal sorption ability of the biomass. Desorption of metal ions in the presence of 100 mmol L⁻¹ HCl from metal-loaded mat biomass was completed within 1 h. After six cycles of metal sorption/desorption, sorption decreased by 6-15%. Only 6% and 11% of the biomass derived from the Oscillatoria sp.- and Phormidium sp.-dominated mats was lost during the cycling. The cyanobacterial mats seem to have better potential than several biomass types for use in metal sorption from wastewaters as they are ubiquitous, self-immobilized, and have good reusability.     

Species specific plant-soil interactions influence plant distribution on serpentine soils

Where serpentine soils exist, variation in soil properties affects plant species distribution at both coarse and fine spatial scales. The New Idria (California, USA) serpentine mass has barren areas, supporting only sparse shrub and tree islands, adjacent to areas of densely-vegetated serpentine chaparral. To identify factors limiting growth on barren relative to vegetated serpentine soils, we analyzed soils from barren, shrub-island within barren, and vegetated areas and foliage from shrub-island and vegetated areas. We also grew Ceanothus cuneatus (native evergreen shrub), Achillea millefolium (native perennial forb), and Bromus madritensis ssp. rubens (invasive annual grass) in soils from barren and vegetated areas amended factorially with N, K, and Ca in a pot study. In well-watered pots, biomass was greater by 5-, 14-, and 33-fold for Ceanothus, Achillea, and Bromus, respectively, on vegetated-area-collected soils than on barren-collected soils, indicating a strong soil chemistry effect. Although field soil data suggested nutrient deficiency and not heavy metal toxicity, pot study plant data indicated otherwise for two of the three species. On barren-collected soils, only Ceanothus responded positively to added N and Ca and did not show greater foliar Mg or heavy metal (Fe, Ni, Cr, Co, Zn) concentrations than on vegetated-area-collected soils. Ceanothus maintained lower root Mg and heavy metal (Fe, Ni, Cr, Co) concentrations on barren soils and translocated less heavy metal (Fe, Ni, Cr, Co, Mn, Cu) from roots to foliage than Achillea and Bromus. Achillea and Bromus showed significant log-log biomass relationships with foliar Ca:Mg (+), Mg (-), and heavy metals (Fe, Ni, Cr, Co, Mn, Cu, Zn) (-), while Ceanothus showed relationships only with Ca:Mg (+) and Mg (-). The New Idria barren-vegetated pattern appears to be maintained by different factors for different species or functional types— low Ca:Mg ratios on barrens for all species tested, high heavy metal concentrations for Achillea and Bromus, and low macronutrient (N) concentrations for Ceanothus. Combined data from this and other studies suggest high heavy metal concentrations more strongly affect herbaceous than woody species, contributing to variation in species distribution on serpentine soils.     

Biosorption of Copper(II) by Live and Dried Biomass of the White Rot Fungi Phanerochaete chrysosporium and Funalia trogii

Biosorption is an innovative and alternative technology to remove heavy metal pollutants from aqueous solution using live, inactive and dead biomasses such as algae, bacteria and fungi. In this study, live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was applied as heavy metal adsorbent material. Biosorption of copper(II) cations in aqueous solution by live and dried biomass of Phanerochaete chrysosporium and Funalia trogii was investigated to study the effects of initial heavy metal concentration, pH, temperature, contact time, agitation rate and amount of fungus. Copper(II) was taken up quickly by fungal biomass (live or dried) during the first 15 min and the most important factor which affected the copper adsorption by live and dried biomass was the pH value. An initial pH of around 5.0 allowed for an optimum adsorption performance. Live biomass of two white rot fungi showed a high copper adsorption capacity compared with dried biomass. Copper(II) uptake was found to be independent of temperature in the range of 20–45 °C. The initial metal ion concentration (10–300 mg/L) significantly influenced the biosorption capacity of these fungi. The results indicate that a biosorption as high as 40–60 % by live and dried biomass can be obtained under optimum conditions.     

Assessment of heavy metal bioremediation potential of bacterial isolates from landfill soils

Indiscriminate disposal of wastes on landfills has led to increase in heavy metal contamination in landfill soils. However, the ability of the indigenous microorganisms to remediate the polluted environment can be of great influence in reclamation of such soils. The objectives of this study were to assess the bioremediation potential of the screened indigenous bacteria and evaluate the effects of carbon source and pH in the enhancement of the bioremediation process. Bacterial isolates from landfill sites were screened for their capability to utilize heavy metal (Cd and Pb). Nutrient Agar was supplemented with five different concentrations of each metal (25 to 600 mgL^-1). Viable counts of the isolates were taken four times at two days interval. Pseudomonas aeruginosa, Klebsiella edwardsii and Enterobacter cloacae were selected based on their tolerance to heavy metal for remediation process. Peptone broth was also supplemented using different concentrations of heavy metals. The remediation process was assessed by monitoring the growth of biomass using UV spectrophotometer at 600 nm and the residual heavy metal was evaluated after 8 days of incubation using AAS. Pseudomonas aeruginosa exhibited the highest bioremediation potential among the bacterial isolates with 58.80 and 33.67 remediation percentage in 50 mg Cd L^-1 and 300 mg Pb L^-1 . However, higher remediation percentage (79.87 and 92.41) was observed by Klebsiella edwardsii through addition of carbon source (5 g/L) and varying the pH (6) of the media in the heavy metal contaminated medium. The results of this study indicate that the effectiveness of the indigenous bacteria in remediation process can be enhanced through the addition of carbon source and increase pH for effective reclamation of contaminated soil.     

Chemical composition of the water fern,salvinia molesta,and its potential as feed source for ruminants

The chemical composition of the now widespread tropical aquatic fern Salvinia molestawas analysed with regard to its suitability as a source of forage for ruminants. Three different stages of plant growth collected in Kerala, India, were air dried, brought to Germany, and used for Weende analysis, detergent fibre analysis, and the determination of gross energy, amino acids, tannins, and minerals. The concentration of 12.4% crude protein in sand-corrected dry matter (DM) and of some other nutrients in Salviniais comparable to that in conventional forage. However, the high content of crude ash (17.3% in DM) and of lignin (13.7%) and the presence of tannins (0.93%) may reduce acceptance as well as digestibility and therefore restrict the use of Salviniaas a potential feed source for ruminants.     

Growth models for Salvinia molesta

Growth models have been developed using data from recent greenhouse studies on the effects of nitrogen, phosphorus and temperature on growth rates of Salvinia molesta Mitchell. Linear transformations were used for estimating Michaelis-Menten kinetic constants and a significant fit of the data was obtained. This has been confirmed by a comparison with field data. The growth models can be used for predicting the potential for Salvinia to remove nutrients from natural and polluted waters. Values thus obtained have a direct bearing on the design and costing of waste-water treatment ponds using Salvinia. Also, by predicting growth rates at particular temperatures and nutrient levels, the likelihood of successful control by biological agents can be assessed.     

Modelling of a single-staged bioseparation process for simultaneous removal of iron(III) and chromium(VI) by using Chlorella vulgaris

In this study, the competitive biosorption of iron(III) and chromium(VI) to Chlorella vulgaris from a binary metal mixture was investigated in a single-staged batch reactor as a function of V₀/X₀ (volume of solution containing heavy metal mixture/quantity of biosorbent) ratio and second metal ion concentration at pH 2. The obtained results showed that the increase in biomass quantity (or the decrease of V₀/X₀ ratio) with the addition of second metal ion affected the removed quantities of iron(III) or chromium(VI). The sorption phenomenon was expressed by the competitive, multi-component Langmuir adsorption isotherm and this expression was used for calculating each residual or adsorbed metal ion concentration at equilibrium (C_eq,i or C_ad,eq,i) at a constant V₀/X₀ ratio for a given combination of heavy metal ions in a single-staged batch reactor. Experimental C_eq,i and C_ad,eq,i values were compared to those calculated and graphically determined.     

The decline of Salvinia molesta on Lake Kariba

The floating fern,Salvinia molesta Mitch., underwent explosive growth following the creation of Lake Kariba in 1958. By 1962 this aquatic weed covered 22% of the Lake's surface but later declined to an apparently stable level of 10–15%. Coverage declined again in 1973 to 5% and by 1980 only about 1% of the lake was covered bySalvinia. This paper discusses the ecological context in which this decline took place and the role of the introduced neotropical grasshopper,Paulinia acuminata De Geer. This insect appears to have made a major contribution towards the decline ofSalvinia, but it is suggested that its effect was greatly enhanced by nutrient stress onSalvinia because of competition for nutrients between the floating weed and other ecosystem components. Nutrient supply to Lake Kariba is limited and the increasing requirements of submerged macrophyte, mussel and fish populations, which are all expanding probably reduced nutrient availability toSalvinia. Mussels and fish, with standing crops of 167 000t and 30 000t, respectively, are seen as particularly important nutrient reservoirs. It is concluded that the decline ofSalvinia in Kariba was part of the lake's maturation process and could possibly have occurred without the introduction ofPaulinia, but at a much slower rate.     

A new model for predicting time course toxicity of heavy metals based on Biotic Ligand Model (BLM)

A new model for predicting time course toxicity of heavy metals was developed by extending the effective ratio of biotic ligand binding with toxic heavy metals to the total biotic ligand for 50% of test organisms (f₅₀) derived by the Biotic Ligand Model (BLM). BLM has been well-known as a useful model for prediction of heavy metal toxicity. BLM can consider the effect of exposure conditions such as pH and Ca²⁺ on heavy metal toxicity. In addition to the exposure conditions, heavy metal toxicity is strongly dependent on exposure time. In this study, BLM is extended to predict time dependency of heavy metal toxicity by connecting with the concept of primary reaction. The model developed in this study also generates the estimation of the 50% effect concentration (EC₅₀) for toxicologically unknown organisms and heavy metals. Two toxicological and kinetic constants, f_50,0 and k, were derived from the initial value of f₅₀ (f_50,0) and a time constant (k) independent of time. The model developed in this study enables us to acquire information on the toxicity of heavy metals such as Cu, Cd and Co easily.     

Phytoremediation potential of vetiver grass irrigated with wastewater for treatment of metal contaminated soil

A field experiment was conducted to understand the potential of vetiver grass (Vetiveria zizanioides) in heavy metal uptake from the soil and wastewater. Four main irrigation treatments including T₁ (treated industrial wastewater), T₂ (1:1 ratio of municipal:industrial wastewater), T₃ (treated municipal wastewater) and T₄ (fresh water) were applied. Moreover, the effect of arbuscular mycorrhizal fungus (AMF), Glomus mosseae, on plant growth and heavy metal concentration was evaluated. Three main criteria including bioconcentration factor (BCF), translocation factor (TF) and heavy metal uptake were applied to assess the potential of vetiver grass in accumulation and translocation of heavy metals to aerial parts. The highest concentration of heavy metals was found in plant and soil irrigated with T₁ treatment followed by T₂, T₃ and the lowest concentrations were found in T₄ treatment. Irrigation with treated municipal wastewater led to a significant increase in plant biomass and heavy metal uptake compared to other treatments. In T₁ treatment (industrial wastewater), vetiver grass caused a significant decrease in Zn, Fe, Cu, Cd and Pb concentrations in soil as compared to no-plant treatment (without planting vetiver grass). Therefore, vetiver grass, irrigated with treated industrial wastewater, is a promising method for the development of urban and industrial green space.     

Jasmonic acid as modulator of lead toxicity in aquatic plant Wolffia arrhiza (Lemnaceae)

The present study was undertaken to test the influence of exogenously applied jasmonic acid (JA) upon the growth and metabolism of Wolffia arrhiza (Lemnaceae), the smallest vessel aquatic plant exposed to lead (Pb) stress. It was found, that JA acted in a concentration-dependent manner. Treatment with JA at the highest concentration 100 μM resulted in the enhancement of heavy metal toxicity leading to increase in metal biosorption and formation of lipid peroxides as well as decrease in fresh weight, chlorophyll a, carotenoid, monosaccharide and soluble protein content. In contrast, this phytohormone applied at 0.1 μM protected W. arrhiza fronds against Pb stress inhibiting heavy metal accumulation, restoring plant growth and primary metabolite level. Moreover, JA at 0.1 μM activated enzymatic (catalase, ascorbate peroxidase, NADH peroxidase) and non-enzymatic antioxidant (ascorbate, glutathione) system in W. arrhiza, and therefore, suppressed oxidative destruction of cellular components induced by heavy metal. The data suggest that JA plays an important role in the growth and metabolism of W. arrhiza exposed to abiotic stressor and its high adaptation ability to metal contamination of aquatic environment.     

Microrespirometric characterization of activated sludge inhibition by copper and zinc

We have developed a novel microrespirometric method to characterize the inhibitory effects due to heavy metals on activated sludge treatment. This method was based on pulse dynamic respirometry and involved the injection of several pulses of substrate and inhibitors, of increasing concentration. Furthermore, we evaluated the inhibitory effects of heavy metals (copper and zinc), substrate and biomass concentrations, and pH on activated sludge activity. While higher biomass concentrations counteracted the inhibitory effects of both copper and zinc, higher substrate concentrations predominantly augmented the inhibitory effect of copper but no significant change in inhibition by zinc was observed. pH had a clear but relatively small effect on inhibition, partially explained by thermodynamic speciation. We determined the key kinetic parameters; namely, the half saturation constant (K _S ) and the maximum oxygen uptake rate (OUR _max ). The results showed that higher heavy metal concentrations substantially decreased K _S and OUR _max suggesting that the inhibition was uncompetitive.