Phytoremediation Potential of Duckweed (Lemna minor L.) On Steel Wastewater

An eco-friendly and cost effective technique- phytoremediation was used to remediate contaminants from waste water. This study demonstrated that phytoremediation ability of duckweed (Lemna minor L.) to remove chloride, sulphate from Biological Oxygen Treatment (BOT) waste water of coke oven plant. The BOT water quality was assessed by analyzing physico-biochemical characters – pH, Biological oxygen demand (BOD), Chemical oxygen demand (COD), total dissolved solids (TDS) and elemental concentration. It was observed that an increase in pH value indicated an improvement of water quality. The experimental results showed that, duckweed effectively removed 30% chloride, 16% sulphate and 14% TDS from BOT waste water, which suggested its ability in phytoremediation for removal of chloride and sulphate from BOT waste water. A maximum increase of 30% relative growth rate of duckweed was achieved after 21 days of experiment. Thus, it was concluded that duckweed, an aquatic plant, can be considered for treatment of the effluent discharged from the coke oven plant.     

Effects of sodium dodecyl sulphate on the aquatic macrophytes Azolla and Lemna

Abstract

In this work, we determined the tolerance to sodium dodecyl sulphate (SDS) of Azolla filiculoides and of Lemna minor. The presence of the detergent in the media affected growth more than the chlorophyll content. On the basis of the effect indices, Lemna is more tolerant to SDS than Azolla. The fern had a better capacity, compared with duckweed, to remove and accumulate the pollutant.     

Cadmium Removal by Lemna minor and Spirodela polyrhiza

The present study investigates the ability of two genus of duckweed (Lemna minor and Spirodela polyrhiza) to phytoremediate cadmium from aqueous solution. Duckweed was exposed to six different cadmium concentrations, such as, 0.5, 1.0, 1.5, 2.0, 2.5, and 3.0 mg/L and the experiment was continued for 22 days. Water samples were collected periodically for estimation of residual cadmium content in aqueous solution. At the end of treatment period plant samples were collected and accumulated cadmium content was measured. Cadmium toxicity was observed through relative growth factor and changes in chlorophyll content. Experimental results showed that Lemna minor and Spirodela polyrhiza were capable of removing 42–78% and 52–75% cadmium from media depending upon initial cadmium concentrations. Cadmium was removed following pseudo second order kinetic model. Maximum cadmium accumulation in Lemna minor was 4734.56 mg/kg at 2 mg/L initial cadmium concentration and 7711.00 mg/kg in Spirodela polyrhiza at 3 mg/L initial cadmium concentration at the end of treatment period. Conversely in both cases maximum bio-concentration factor obtained at lowest initial cadmium concentrations, i.e., 0.5 mg/L, were 3295.61 and 4752.00 for Lemna minor and Spirodela polyrhiza respectively. The present study revealed that both Lemna minor and Spirodela polyrhiza was potential cadmium accumulator.     

Arsenic Uptake by Lemna minor in Hydroponic System

Arsenic is hazardous and causes several ill effects on human beings. Phytoremediation is the use of aquatic plants for the removal of toxic pollutants from external media. In the present research work, the removal efficiency as well as the arsenic uptake capacity of duckweed Lemna minor has been studied. Arsenic concentration in water samples and plant biomass were determined by AAS. The relative growth factor of Lemna minor was determined. The duckweed had potential to remove as well as uptake arsenic from the aqueous medium. Maximum removal of more than 70% arsenic was achieved at initial concentration of 0.5 mg/l arsenic on 15th day of experimental period of 22 days. Removal percentage was found to decrease with the increase in initial concentration. From BCF value, Lemna minor was found to be a hyperaccumulator of arsenic at initial concentration of 0.5 mg/L, such that accumulation decreased with increase in initial arsenic concentration.     

Evaluation of heat shock protein 70 as a biomarker of environmental stress in Fucus serratus and Lemna minor

Heat shock proteins (Hsps) are known to be induced in response to short-term stress. The present study aimed to evaluate the potential of Hsp70 as a biomarker of stress produced by increased temperature, osmotic pressure, and exposure to cadmium and sodium chloride in marine macroalgae and fresh water plant species. An indirect competitive enzyme-linked immunosorbent assay (IC-ELISA) was developed with a working range of 0.025–10 μg?ml^?1 using a monoclonal antibody raised against purified Hsp70 of Phaseolus aureus (mung bean). Fucus serratus (toothed wrack), Chondrus crispus (Stackhouse or Carrageen moss), Ulva lactuca (sea lettuce) and Lemna minor (common duckweed) sample extracts were stressed for up to 24 h and then tested in the IC-ELISA. The presence of Hsp70 and cross-reactivity of the monoclonal antibody was confirmed by Western blot. The heat shock response was confirmed in each species using a 2-h 42°C treatment. Following heat shock, Hsp70 concentrations increased to a peak at 2 h (F. serratus) or 4 h (L. minor), after which concentrations decreased. Osmotic and cadmium stresses also resulted in elevated Hsp70 concentrations in samples of F. serratus and L. minor when compared with unstressed controls. In both, osmotic and metal stress, the production of Hsp70 increased to a maximum and subsequently decreased as the stressor levels increased. Results suggest that Hsp70 IC-ELISA could potentially be applied to the detection of stress in these aquatic species, although it would probably be most effective when used in conjunction with other measurements to provide a stressor-specific biomarker profile or fingerprint.     

Allozymic and morphometric variation inLemna minor (Lemnaceae)

Allozymic and morphometric variation was studied in 28 clones ofLemna minor. This variation was compared with the corresponding variation in four clones ofLemna gibba and four clones ofSpirodela polyrrhiza. A high level of allozymic variation was observed among the clones, despite having been grown under uniform laboratory conditions for several years and despite its quasi-exclusive clonal means of propagation. Based on degree of allozymic similarity,Spirodela polyrrhiza was distinguished from the twoLemna species but the latter species were genetically indistinguishable. Allozymic similarity among clones ofLemna minor was not related to morphometric similarity, nor was it related to the degree of geographic separation or climatic similarity of their sites of origin. The results suggest that allozymic variation among these clones ofLemna minor may be largely neutral and not a consequence of differential selection.     

Isotherm and kinetic modelling of Toluidine Blue (TB) removal from aqueous solution using Lemna minor

The aim of this study was to investigate the ability of Lemna minor for Toluidine Blue (TB) removal. Influence of the initial concentration over the removal process was considered. Experimental data have been analyzed using Langmuir, Freundlich, Dubinin–Radushkevich (D–R), and Elovich isotherm models. In addition, several kinetic models, pseudo-first-, pseudo-second-order, intraparticle and film diffusion models were considered. Langmuir and Freundlich isotherm suggested a favorable adsorption of TB by Lemna minor plants. From the D–R the mean free energy was calculated to be 11.18 kJ/mol, which indicates that TB adsorption was characterized by a chemisorption process. Kinetic studies showed that liquid film diffusion plays an important role during the process. Adsorption capacities of up to 26.69 mg/g and a high capacity of adaptation indicated that phytoremediation using Lemna minor could be a valuable alternative for dyes removal from wastewaters.     

Bioremoval of Aqueous Lead Using Lemna Minor

The aquatic plant Lemna minor (duckweed) was examined for its ability to sorb soluble lead from water under laboratory conditions. The use of biomass as a sorption medium provides a simple alternative separation technology. Laboratory-scale (700-mL) batch reactors containing soil-based sediments were used to expose L. minor to concentrations of 0.0, 5.0, and 10.0 mg/L of lead for 7 d. Overall removal amounts of 95% were observed, with 85% removal occurring within the first day. A sorption process model was developed based on a mass balance and a power law rate of sorption equation.     

Effets physiologiques de ľ atrazine à doses sublétales sur Lemna minor, VII. Incorporation ďacétate-l,2-[14C] dans les groupes de lipides et leurs acides gras

Physiological effects of sublethal doses of atrazine on Lemna minor. VII. 1,2-[¹⁴C] acetate incorporation into the groups of lipids and their fatty acids. The lipids and the fatty acids of ten-day old duckweed (Lemna minor L.), cultivated aseptically in mineral solution containing sublethal concentrations of 0,10 and 0,50 ppm (0.46 and 2.3 μM, respectively) of atrazine, were analyzed by thin-layer chromatography and gas-liquid radiochromatography after 1,2-[¹⁴C] acetate feeding. Sublethal concentrations of atrazine increased the incorporation of radioactivity in total lipids, diacylgalactosylglycerol (DGG), diacyldigalactosylglycerol (DDG), sul-folipids (SL), phosphatidylglycerol (PG), diacylglycerol (DAG) and triacylglycerol + steroll esters (TAG+SE). The incorporation of acetate-1,2-[¹⁴C] decreased in phos-phatidylcholine (PC) and in phosphatidylethanolamine (PE) in the presence of atrazine. The radioactivity increased in total Transic-hexadecenoic, linoleic and α -linolenic acids while it decreased in the other fatty acids. This indicates that the sublethal concentrations of atrazine stimulate the desaturation of fatty acids of L. minor. The radioactivity was strongly incorporated in the α -linolenic acid of DGG in the presence of atrazine. The specific radioactivity of α-linolenic acid was greater in DAG than in PG > TAG + SE > PC > PE > DGG > SL > DDG and it increased in all groupd of lipids analyzed under the influence of sublethal doses of atrazine. The labelling of Translchexadecenoic acid of PG and its specific radioactivity increased in the presence of atrazine. These changes suggest that the sublethal concentrations of atrazine stimulate especially the lipid metabolism of the chloroplasts of L. minor and they could explain the increase in the number of grana per chloroplast in treated L. minor. The results are discussed in relation to the biosynthesis of galactolipids.     

Aquatic plant bioassays used in the assessment of water quality in German rivers

A novel aquatic bioassay with Lemna minor (duckweed), a representative of higher plants, was applied to pore waters (interstitial waters) from river sediments. The results have been used for the ecotoxicological assessment of sediments in several German rivers. The aim of the present study is to demonstrate the usefulness of a macrophyte bioassay, as a supplement to the standardised algae bioassays, with regard to the ecotoxicological assessment of aquatic systems. Results relating to the development of a sediment contact test (using the whole sediment) with Lemna minor are also presented.     

Investigations on Cytokinins. III. Cytokinin Activity in Lemna minor tRNA Hydrolysates

tRNA was extracted from Lemna minor, grown on a cytokinin free medium. Alkaline hydrolysates of the tRNA were active in three cytokinin bioassays: mobilization test, tissue culture and growth of Lemna cultures. Some observations on the growth of Lemna as a bioassay for cytokinins, are given.     

The Effect of Drugs on the Growth of Lemna minor C.

Lemna minor fronds were grown for periods of between 90 and190 days in nutrient solutions to which non-lethal doses ofone of the following drugs were added: sodium nitrite, sodiumazide, brilliant green, proflavine, propamidine isethionate,and dinitrobutyl phenol. Over these periods there was no signof any increase in the growth-rate with time, such as mightbe expected if Lemna showed adaptation to drugs similar to thatfound in micro-organisms. ‘Changeover’ experimentsshowed that the growth-rate of fronds in a drug solution wasgenerally less if they had been previously exposed to that drugthan if they had not. The sensitivity of the fronds, inducedby growth in solutions containing sodium nitrite, persistedover five to six generations of growth in nitrite-free solutions.     

Heavy-metal (Zn,Cd) tolerance in selected clones of duck weed (Lemna minor)

Cryo-microprobe analysis of quench-frozen fronds of a Zn-tolerant clone of Lemna minor exposed to a high level of Zn (300 μM) showed the presence of cellular deposits consisting of Zn, Mg, K and P or Zn, K and P (Zn phytate). The same Zn-tolerant clone of Lemna minor, when exposed to a high level of Cd (30 μM), showed the presence of globular deposits consisting of Cd, K and P in mature fronds, but the immature cells of the enclosed daughter fronds contained relatively large deposits with Cd and S as the main components (Cd-phytochelatin?). Selection for Zn tolerance in a population of Lemna minor was easily achieved but selection for Cd tolerance has so far not been successful. The Zn-tolerant clone also tolerates high levels of phosphate.     

PHYTOCHROME CONTROL OF ROOT GROWTH RATE IN LEMNA SPECIES

Root growth rate was studied in Lemna gibba L. (strains Gl and G3) and L. minor L. in relation to low energy red and far-red light treatments. Far-red treatments inhibited growth rate; inhibition was abolished upon subsequent treatment with red light. These effects can be observed after an 18-hr growth period. This red/far-red photoreversible response suggests that root growth in L. gibba L. and L. minor L. is under phytochrome control.     

Is protein degradation correlated with either the charge or size of Lemna proteins?

Evidence is presented that the organelles of Lemna minor do not degrade as functional units. The proteins of Lemna show wide differences in their rates of degradation and ribulose bisphosphate carboxylase (EC 4.1.1.39) has a particularly slow rate of degradation. Contrary to some earlier evidence, we found no correlation between the rate of soluble-protein degradation and either charge or size of proteins. We could find no correlation between protein degradation and subunit size in any of the organelles of Lemna.Abbreviations FPLC fast protein liquid chromatography - PAGE polyacrylamide gel electrophoresis - RuBPCase ribulose-1,5-bisphosphate carboxylase - SDS sodium dodecylsulphate - Tris 2-amino-2-(hydroxymethyl)-1,3-propanediol     

Sublethal Toxicity Testing of Canadian Metal Mining Effluents: National Trends and Site-Specific Uses

As part of the Canadian Environmental Effects Monitoring program under the National Metal Mining Effluent Regulation, there is a requirement to conduct sublethal toxicity tests twice per year for the first three years. These first three years (2003 to 2005) were considered a period of initial monitoring and resulted in test endpoints for each of the required standardized methods on a fish, an aquatic plant, an invertebrate, and an algal species. On a national level (based on 1648 valid results), the test from most to least sensitive was: the inhibition of reproduction with Ceriodaphnia dubia, the growth inhibition (frond number) with Lemna minor, the inhibition of cell yield with Pseudokirchneriella subcapitata, the growth inhibition (dry weight) with Lemna minor, the growth inhibition of fathead minnows, and the effect on embryo viability with rainbow trout. This sensitivity ranking changed when tests were further evaluated on a geographical region and mine-type basis (e.g., base metal, precious metal, uranium, iron ore). Site-specific examples show how sublethal toxicity data are being used to track changes in effluent quality, choosing a final discharge point, monitoring multiple discharges to the same watercourse, and to identify study design weaknesses by comparing laboratory results to field survey conclusions.     

Real-time in vivo visualization of oxidative stress in duckweed (Lemna minor L.)

An experimental set-up which enabled non-invasive, real-time reactive oxygen species (ROS) visualization on a whole plant level was constructed. In the test organism, Lemna minor L. (common duckweed), apoplastic and symplastic oxidative stress was evaluated by exposure to menadione (50 μM), menadione (50 μM) + ascorbate (100 μM) or neither for control. Menadione (50 μM) caused a statistically significant increase in H₂DCFDA fluorescence in the apoplast after 60 minutes of exposure. The addition of ascorbate (100 μM) in the test medium significantly decreased apoplastic oxidative stress. 50 μM menadione caused an increase in symplastic H₂DCFDA fluorescence in 57% of fronds. The exposure of L. minor plants to both menadione and ascorbate decreased the rate of fluorescence intensity accumulation in the symplast to control levels. The method has proven to be quick and straightforward and could be applied to a range of chemicals in various physiological and toxicological plant studies. The advantages of the set-up and different possible artefacts are discussed.     

Metabolic responses of Lemna minor to lead ions I. Growth, chlorophyll level and activity of fermentative enzymes

Duckweed Lemna minor L. was grown on Wang culture medium supplemented with lead ions for 24 hours. Metal was tested at 1.5, 3 and 6 mg·dm⁻³ concentrations. The growth of Lemna minor was inhibited by lead ions, but the dry to fresh weight ratio increased as the concentration of Pb²⁺ in the medium increased. With increased concentrations of Pb ions, the contents of chlorophyll a and chlorophyll b in roots and fronds were correspondingly lower in comparision with the control. The effect of lead upon activities of some glycolitic and fermentative enzymes in roots of duckweed was examined. The activity of pyruvate kinase decreased with increasing lead concentrations, but cytosolic malate dehydrogenase behaved in an opposite manner. The lowest concentration of Pb stimulated alcohol dehydrogenase; phosphoenolopyruvate carboxylase activity was maintained at relatively constant values at all tested lead concentrations.     

Genetic transformation of duckweed Lemna gibba and Lemna minor

Summary We developed efficient genetic transformation protocols for two species of duckweed, Lemna gibba (G3) and Lemna minor (8627 and 8744), using Agrobacterium-mediated gene transfer. Partially differentiated nodules were co-cultivated with Agrobacterium tumefaciens harboring a binary vector containing β-glucuronidase and nptII expression cassettes. Transformed cells were selected and allowed to grow into nodules in the presence of kanamycin. Transgenic duckweed fronds were regenerated from selected nodules. We demonstrated that transgenic duckweed could be regenerated within 3 mo. after Agrobacterium-mediated transformation of nodules. Furthermore, we developed a method for transforming L. minor 8627 in 6 wk. These transformation protocols will facilitate genetic engineering of duckweed, ideal plants for bioremediation and large-scale industrial production of biomass and recombinant proteins.     

The control of glutamine synthetase level in Lemna minor L.

Summary The specific activity of glutamine synthetase (E.C. 6.3.1.2) of Lemna minor L. is markedly reduced when either ammonium ions or glutamine are present in the growth medium. Combinations of 5 mM ammonia and 5 mM glutamic acid or 5 mM ammonia and 5 mM glutamine as nitrogen source, lead to a 4–5 fold reduction of the maximum activity measurable on 5 mM -aminobutyric acid. Analyses of the soluble pool of nitrogen indicate that the reduction in enzyme level is associated with an increase in the pool of glutamine. There is an inverse correlation between the apparent rate of synthesis of glutamine synthetase and the intracellular concentration of glutamine, and this relationship suggests that the glutamine synthetase of Lemna minor is subject to end product repression by the endogenous pool of glutamine.