Effectivity of host-Rhizobium leguminosarum symbiosis in soils receiving sewage water containing heavy metals

Disposal of sewage water in cultivated soils often containing considerable amount of potentially toxic metals such as Cu, Zn, Ni, Cd, Pb and Cr can be beneficial or harmful to plant growth, rhizobial survival, nodulation and nitrogen fixation. Soil samples from 14 such locations were collected. Symbiotic effectivity of host-Rhizobium leguminosarum symbiosis in these soils was assessed. The total metal contents of Cd, Cu, Zn and Ni in all the 14 samples collected from farmer's fields receiving sewage water ranged between 1.3 and 6.7, 55.8-353.2, 356.0-1028.0 and 90.0-199.7 mg kg(-1) of soil, respectively. In Rohtak 1 soil, levels of Cd, Cu and Zn were highest while Ni was highest in Sonipat 2 soil. The content of available Cd, Cu, Zn and Ni in these soils ranged from 1.0-29.3; 6.2-47.0; 2.4-13.5, respectively, and was 2-9 percent of their total metal contents. All the N2 fixing parameters in pea and Egyptian clover were adversely affected by the presence of heavy metals. Available Cd and Cu contents significantly affected the N contents of pea and Egyptian clover plants, whereas Ni contents were negatively correlated with the plant biomass of pea and Egyptian clover.     

Effects of nitrogen on the activity of antioxidant enzymes and gene expression in leaves of Populus plants subjected to cadmium stress

The research aimed to verify the important physiological effect of nitrogen (N) on plants exposed to cadmium (Cd). The poplar plants were grown in a Hoagland nutrient solution and treated with extra N, Cd, and N + Cd. After treatment, plant growth and chlorophyll content were recorded. The oxidative stress, the activity of antioxidant enzymes, and the expression of related genes were also examined. The results indicated the plants treated with sole Cd presented obvious toxicity symptoms, i.e. growth inhibition, reactive oxygen species accumulation, and chlorophyll content decrement. However, when N was added to the plants under Cd stress, plant growth was enhanced, chlorophyll synthesis was promoted, and the oxidative stress was alleviated. Further, the expression of antioxidant enzymes genes was upregulated by N. The results indicated that N partially reversed the toxic effect of Cd on poplar plants, which can provide new methodology to enhance the phytoremediation technology for heavy metal pollution soil.     

茎瘤对长喙田菁在铅锌尾矿环境适应中的意义II 茎瘤对长喙田菁固氮和积累重金属的影响

 探讨茎瘤对长喙田菁(Sesbania rostrata)在铅锌矿尾矿、客土和纯土环境中结瘤、固氮和积累重金属的影响。结果表明：保留茎瘤使长喙田菁全株植物氮含量和单株植物氮积累量分别比去除茎瘤处理提高了12.4%～34.0%和43.3%～131.4%,且环境愈恶劣,这种作用愈为显著。同时,保留茎瘤处理显著抑制了长喙田菁根瘤的生长,同样表现出环境愈恶劣,抑制作用愈显著的趋势。因此,在尾矿环境胁迫下,长喙田菁更趋向于选择茎瘤作为固氮途径。由此可见,茎瘤对生长在铅锌尾矿环境中的长喙田菁获得氮素及支持其生长有着特别     

Effect of Cd,Zn, and Pb Compound Pollution on Celery in a Ferric Acrisol

A pot experiment with an orthogonal experimental design L₉(3⁴) was conducted to study the combined effects of Cd, Zn, and Pb on the growth and metal content of celery grown in a ferric acrisol. The uptake of Cd, Zn, and Pb by celery was not only affected by the individual elements, but also by combinations of the elements. The effect of coexisting elements on plant uptake of the heavy metals depended on the concentration ratios of the elements. There is a given ratio where a maximum antagonism or synergism effect occurs. The combinations of elements clearly affected the dry weight of celery and the heavy metal concentration in celery. The removal rate (the ratio of plant total uptake to the total metal content in soil) was in the order of Cd > Zn > Pb, with no obvious difference between the removal rate under single pollution and that under compound pollution.     

Assessment of willow (Salix sp.) as a woody heavy metal accumulator: field survey and in vivo X-ray analyses

Trees that accumulate metals are important plants for restoring contaminated soil because of their high biomass. In our previous study, we discovered that Salix miyabeana has the capability to take up high levels of Cd, and identified the several accumulation sites of the endogenous metals in the leaf parts of plants. To analyze the detailed localization of Cd in apoplastic and symplastic compartments in S. miyabeana, synchrotron radiation-based micro X-ray fluorescence (SR-μ-XRF) analysis and micro X-ray absorption near edge structure (μ-XANES) measurements were performed on beam line 37XU of the SPring-8 (Hyogo, Japan). The two-dimensional metal distribution of segments of young stems was obtained by μ-XRF with approximately 2 μm(2) X-ray beams and showed the predominant localization of Cd in the apoplastic region. μ-XANES analyses suggest that the apoplastic detoxification of Cd in willow depends on Cd-oxygen, but not on Cd-sulfur, interaction. S. miyabeana growing near an old mining site in Japan was then examined to evaluate the metal accumulating ability of this plant in the field. The metal concentration in the leaves of the plants was compared to that in the soil and enrichment factors (EFs) were calculated for Cu, Zn, Cd and Pb. Results showed efficient removal of Cd and Zn from the contaminated sites by the willow plants. In order to discuss the combined and long-term effect of multiple heavy metals on S. miyabeana grown in soil, variable-pressure scanning electron microscopy fitted with energy dispersive X-ray analysis (VPSEM-EDX) and SR-μ-XRF was used to characterize the serration of leaves. The combination of 2D elemental images revealed metal accumulation in the tip cells in serrations without any exudation of heavy metals from the hydathodes.     

Inorganic materials as ameliorants for soil remediation of metal toxicity to wild mustard (Sinapis arvensis L.)

The ameliorating effects of different inorganic materials were investigated on a soil originating from a zinc smelter dumping site contaminated by toxic metals. Wild mustard (Sinapis arvensis L.) was used as a test plant. The soil was amended with different doses of mining sludge, Perferric Red Latosol (LVj), steel shots, cyclonic ash, silifertil, and superphosphate. The most effective amendments improved plant growth with 45% and reduced metal uptake by over 70% in comparison to untreated soil. Reductions in availability as estimated by BaCl2-extractable metals reached up to 90% for Zn and 65% for Cd as compared to unamended soil. These reductions were associated with lower shoot and root metal contents. Shoot Zn content was reduced from 1,369 microg g(-1) in plants grown on untreated soil to 377 microg g(-1) when grown on cyclonic ash amended soil while Cd decreased from 267 to 44 microg g(-1) in steel shots amended soil. Superphosphate addition had no ameliorating effect. On the contrary, it increased BaCl2-extractable amounts of Zn. Considering all parameters we determined, steel shots, cyclonic ash and silifertil are the most promising for remediating metal contaminated soil in the tropics. Further studies evaluating impacts, cost-effectiveness and durability of effects will be conducted.     

Usage of sewage effluent in irrigation of some woody tree seedlings. Part 3: Swietenia mahagoni (L.) Jacq.

A pot experiment was investigated to study the effect of sewage irrigation treatments (primary and secondary effluents) compared with tap water on the growth and chemical constituents of mahogany seedlings (Swietenia mahagoni (L.) Jacq.) as well as soil chemical properties. The experiment was conducted at a greenhouse in the nursery of Timber Trees Research Department of Sabahia, Horticultural Research Station in Alexandria, Egypt, from June 2003 to December 2004 for three irrigation periods (6, 12 and 18 months). The sewage effluent waters were taken from oxidation ponds located in New Borg EL-Arab city and used directly for irrigation.The primary effluent treatment was superior than other treatments in improving the growth parameters (plant height, stem diameter, leaf area, leaves number, fresh and dry weights of leaves, shoots and roots and shoot/root ratio) and showed the highest concentration and total uptake of N, P, K, Cd, Ni, Pb and Fe in plant parts, followed by secondary effluent then tap water. The data revealed that soil salinity in terms of electrical conductivity of saturated paste (EC), CaCO₃%, organic matter% and soluble anions and cations were influenced significantly by primary or secondary effluent treatment. The data also showed that the use of sewage effluent for irrigation increased N, P, K and DTPA-extractable-heavy metals (Cd, Cu, Ni, Pb, Fe, Mn and Zn). The effects of sewage effluent on growth parameters and elements content in plant parts and treated soil were more pronounced as water treatments were used for long period.The results suggested that the use of sewage effluent in irrigating mahogany trees grown on calcareous sandy loam soil was an important agriculture practice for improving soil properties, increasing fuel and timber production, and is an economic and safe way to dispose wastewaters.     

Response of Thlaspi caerulescens to nitrogen, phosphorus and sulfur fertilisation

The main limiting factor for cleaning-up contaminated soils with hyperaccumulator plants is the low production of aerial biomass and the number of successive crops needed to reach the objective of remediation. The aim of this study was to contribute to the determination of a fertilisation strategy to optimise soil metal phytoextraction by Thlaspi caerulescens. A pot experiment was conducted on an agricultural soil and on a contaminated soil from the vicinity of a former Pb/Zn smelter. The nitrogen (N) treatment consisted of 4 levels (0, 11, 21.5 and 31 mg N kg(-1) dry soil (DS)) added as NH4NO3. The highest N treatment was combined with 4 levels of phosphorus (P) (0, 20, 40 and 80 mg P kg(-1) DS as KH2PO4) and sulfur (S) additions (0, 10, 20 and 30 mg S kg(-1) DS as MgSO4). The highest N fertilisation contributed significantly to enhance biomass production of T. caerulescens and to decrease the concentration of Cd and Zn in the biomass. At constant N addition, P supply did not affect metal extraction by T. caerulescens but negatively affected plant health. Sulfur supply slightly increased phytoextraction of Cd. Our results show that N and S fertilisation might interact but further investigations on the effect of such interaction on Cd extraction efficiency are needed.     

Effects of atmospheric deposition,soil pH and acidification on heavy metal contents in soils and vegetation of semi-natural ecosystems at Rothamsted Experimental Station,UK

The effects of acidification on the soil chemistry and plant availability of the metals Pb, Cd, Zn, Cu, Mn and Ni in new and archived soil and plant samples taken from the >100-year-old experiments on natural woodland regeneration (Geescroft and Broadbalk Wildernesses) and a hay meadow (Park Grass) at Rothamsted Experimental Station are examined. We measured a significant input of metals from atmospheric deposition, enhanced under woodland by 33% (Ni) to 259% (Zn); Pb deposition was greatly influenced by vehicle emissions and the introduction of Pb in petrol. The build up of metals by long-term deposition was influenced by acidification, mobilization and leaching, but leaching, generally, only occurred in soils at pH<4. Mn and Cd were most sensitive to soil acidity with effective mobilization occurring at pH 6.0–5.5 (0.01 M CaCl₂), followed by Zn, Ni and Cu at pH 5.5–5.0. Pb was not mobilized until pH<4.5. Acidification to pH 4 mobilized 60–90% of total soil Cd but this was adsorbed onto ion exchange surfaces and/or complexed with soil organic matter. This buffering effect of ion exchange surfaces and organic matter in soils down to pH 4 was generally reflected by all the metals investigated. For grassland the maximum accumulation of metals in herbage generally corresponded to a soil pH of 4.0. For woodland the concentration of Pb, Mn and Cd in oak saplings (Quercus robur) was 3-, 4- and 6-fold larger at pH 4 than at pH 7. Mature Oak trees contained 10 times more Mn, 4 times more Ni and 3 times more Cd in their leaves at pH 4 than at pH 7. At pH values <4.0 on grassland the metal content in herbage declined. Only for Mn and Zn did this reflect a decline in the plant available soil content attributed to long-term acid weathering and leaching. The chief cause was a long-term decline in plant species richness and the increased dominance of two acid-tolerant, metal-excluder species     

Proteomic analysis of Arabidopsis halleri shoots in response to the heavy metals cadmium and zinc and rhizosphere microorganisms

Arabidopsis halleri has the rare ability to colonize heavy metal‐polluted sites and is an emerging model for research on adaptation and metal hyperaccumulation. The aim of this study was to analyze the effect of plant–microbe interaction on the accumulation of cadmium (Cd) and zinc (Zn) in shoots of an ecotype of A. halleri grown in heavy metal‐contaminated soil and to compare the shoot proteome of plants grown solely in the presence of Cd and Zn or in the presence of these two metals and the autochthonous soil rhizosphere‐derived microorganisms. The results of this analysis emphasized the role of plant–microbe interaction in shoot metal accumulation. Differences in protein expression pattern, identified by a proteomic approach involving 2‐DE and MS, indicated a general upregulation of photosynthesis‐related proteins in plants exposed to metals and to metals plus microorganisms, suggesting that metal accumulation in shoots is an energy‐demanding process. The analysis also showed that proteins involved in plant defense mechanisms were downregulated indicating that heavy metals accumulation in leaves supplies a protection system and highlights a cross‐talk between heavy metal signaling and defense signaling.     

Plant Cd2+ and Zn2+ status effects on root and shoot heavy metal accumulation in Thlaspi caerulescens

* In this study we address the impact of changes in plant heavy metal, (i.e. zinc (Zn) and cadmium (Cd)) status on metal accumulation in the Zn/Cd hyperaccumulator, Thlaspi caerulescens. * Thlaspi caerulescens plants were grown hydroponically on both high and low Zn and Cd regimes and whole-shoot and -root metal accumulation, and root (109)Cd(2+) influx were determined. * High-Zn-grown (500 microm Zn) plants were found to be more Cd-tolerant than plants grown in standard Zn conditions (1 microm Zn). Furthermore, shoot Cd accumulation was significantly greater in the high-Zn-grown plants. A positive correlation was also found between shoot Zn accumulation and increased plant Cd status. Radiotracer (109)Cd root flux experiments demonstrated that high-Zn-grown plants maintained significantly higher root Cd(2+) influx than plants grown on 1 microm Zn. It was also found that both nickel (Ni) and copper (Cu) shoot accumulation were stimulated by high plant Zn status, while manganese (Mn) accumulation was not affected. * A speculative model is presented to explain these findings, suggesting that xylem loading may be one of the key sites responsible for the hyperaccumulation of Zn and Cd accumulation in Thlaspi caerulescens.     

南京市城乡公路蜀桧叶片中金属元素和氮、硫含量分析

通过对南京市城乡公路(城市干线、绕城公路和城郊公路)和相对清洁对照点植物园环境中土壤和蜀桧叶片中金属元素和N、S含量的测定,研究了环境元素在土壤植物大气之间的转移.结果表明,在城市干线、绕城公路和城郊公路环境中生长的蜀桧叶片中,10种金属元素中有Al、Fe、Mo、Zn、Cd、Pb、As和Cr含量明显超过对照点,其中尤以Al、Fe、Mo和Zn最显著.公路环境蜀桧叶片中,Fe、Zn和As在土壤植物间的相关性显著,说明蜀桧可能是Fe、Zn和As的良好指示植物;蜀桧叶片中Al、Mo、Cu、Pb、Cd和Cr在土壤植物间相关性不显著,说明公路环境中其含量较高可能是受大气污染的影响.城市干线和绕城公路蜀桧叶片中的N和S含量高于对照点,而城郊公路则接近对照.相关分析表明,公路土壤含N量在土壤植物间呈负相关,低于对照,含S量在土壤植物间呈正相关,高于对照.因此,公路环境蜀桧叶片中较高的N含量可能是汽车尾气排放的NOx影响的结果,而较高的S含量则主要来自土壤.     

Effects of Municipal Sewage Sludge Doses on the Chlorophyll Contents and Heavy Metal Concentration of Sugar Beet (Beta vulgaris var. saccharifera)

The present study was conducted to assess the suitability of sewage sludge amendment (SSA) in soil for Beta vulgaris var. saccharifera (sugar beet) by evaluating the heavy metal accumulation and physiological responses of plants grown at a 10%, 25%, and 50% sewage sludge amendment rate. The sewage sludge amendment was modified by the physicochemical properties of soil, thus increasing the availability of heavy metals in the soil and consequently increasing accumulation in plant parts. Cd, Pb, Ni, and Cu concentrations in roots were significantly higher in plants grown at 25% as compared to 50% SSA; however, Cr and Zn concentration was higher at 50% than 25% SSA. The concentrations of heavy metal showed a trend of Zn > Ni > Cu > Cr > Pb > Cd in roots and Zn > Cu > Ni > Cr > Pb > Cd in leaves. The only instance in which the chlorophyll content did not increase after the sewage sludge treatments was 50%. There were approximately 1.12-fold differences between the control and 50% sewage sludge application for chlorophyll content. The sewage sludge amendment led to a significant increase in Pb, Cr, Cd, Cu, Zn, and Ni concentrations of the soil. The heavy metal accumulation in the soil after the treatments did not exceed the limits for the land application of sewage sludge recommended by the US Environmental Protection Agency (US EPA). The increased concentration of heavy metals in the soil due to the sewage sludge amendment led to increases in heavy metal uptake and the leaf and root concentrations of Ni, Zn, Cd, Cu, Cr, Pb, and Zn in plants as compared to those grown on unamended soil. More accumulation occurred in roots and leaves than in shoots for most of the heavy metals. The concentrations of Cd, Cr, and Pb were more than the permissible limits of national standards in the edible portion of sugar beet grown on different sewage sludge amendment ratios. The study concludes that the sewage sludge amendment in the soil for growing sugar beet may not be a good option due to risk of contamination of Cr, Pb, and Cd.     

Effects of bacteria on enhanced metal uptake of the Cd/Zn-hyperaccumulating plant, Sedum alfredii

To investigate the effects of bacteria (Burkholderia cepacia) on metal uptake by the hyperaccumulating plant, Sedum alfredii, a hydroponic experiment with different concentrations of Cd and Zn was conducted. It was found that inoculation of bacteria on S. alfredii significantly enhanced plant growth (up to 110% with Zn treatment), P (up to 56.1% with Cd treatment), and metal uptake (up to 243% and 96.3% with Cd and Zn treatment, respectively) in shoots, tolerance index (up to 134% with Zn added treatment), and better translocation of metals (up to 296% and 135% with Cd and Zn treatment, respectively) from root to shoot. In the ampicillin added treatment with metal addition, stimulation of organic acid production (up to an increase of 133% of tartaric acid with Cd treatment) by roots of S. alfredii was observed. The secretion of organic acids appears to be a functional metal resistance mechanism that chelates the metal ions extracellularly, reducing their uptake and subsequent impacts on root physiological processes.     

The potential of Thlaspi caerulescens for phytoremediation of contaminated soils

Uptake of Cd, Zn, Pb and Mn by the hyperaccumulator Thlaspi caerulescens was studied by pot trials in plant growth units and in populations of wild plants growing over Pb/Zn base-metal mine wastes at Les Malines in the south of France. The pot trials utilised metal-contaminated soils from Auby in the Lille area. Zinc and Cd concentrations in wild plants averaged 1.16% and 0.16% (dry weight) respectively. The unfertilised biomass of the plants was 2.6 t/ha. A single fertilised crop with the above metal content could remove 60 kg of Zn and 8.4 kg Cd per hectare. Experiments with pot-grown and wild plants showed that metal concentrations (dry weight basis) were up to 1% Zn (4% Zn in the soil) and just over 0.1% Cd (0.02% Cd in the soil). The metal content of the plants was correlated strongly with the plant-available fraction in the soils as measured by extraction with ammonium acetate and was inversely correlated with pH. Bioaccumulation coefficients (plant/soil metal concentration quotients) were in general higher for Cd than for Zn except at low metal concentrations in the soil. There was a tendency for these coefficients to increase with decreasing metal concentrations in the soil. It is proposed that phytoremediation using Thlaspi caerulescens would be entirely feasible for low levels of Cd where only a single crop would be needed to halve a Cd content of 10 g/g in the soil. It will never be possible to remediate elevated Zn concentrations within an economic time frame (<10 yr) because of the lower bioaccumulation coefficient for this element coupled with the much higher Zn content of the soils.     

The Effect of NaCl on growth, N2 fixation (acetylene reduction), and percentage total nitrogen in Leucaena leucocephala (Leguminosae) var. K-8

Leucaena leucocephala var. K-8 is a fast-growing, tropical leguminous tree that has multiple economic uses. This study was conducted to evaluate the effect(s) of varying NaCl concentrations on growth, N(2) fixation, and percentage of total tissue nitrogen in different organs in L. leucocephala. Seeds were germinated and grown for 10 wk with a nitrogen-free fertilizer applied every 2 wk. At 10 wk, plants were treated for either 0, 7, 14, 21, or 28 wk with either deionized water (control), 0.00625 mol/L, 0.0125 mol/L, 0.025 mol/L, 0.05 mol/L, or 0.1 mol/L NaCl in addition to the fertilizer every 2 wk. Growth was measured as plant height, nodule number and mass, and dry tissue mass. N(2) fixation was measured by the acetylene reduction assay. Percentage of tissue nitrogen was determined using Kjeldahl analysis. In younger plants (7-wk treatment), major fluctuations in NaCl tolerance were observed in the different plant organs. As plants matured (14- and 21-wk treatment) NaCl concentrations of 0.025 mol/L and higher caused the greatest reduction in growth and tissue nitrogen. We conclude that NaCl concentrations of 0.025 mol/L and greater caused a major decrease in growth, N(2) fixation, and percentage of tissue nitrogen in L. leucocephala plants that were less than 1 yr old.     

Long-term field phytoextraction of zinc/cadmium contaminated soil by Sedum plumbizincicola under different agronomic strategies

In two long-term field experiments the zinc (Zn)/cadmium (Cd) hyperaccumulator Sedum plumbizincicola (S. plumbizincicola) was examined to optimize the phytoextraction of metal contaminated soil by two agronomic strategies of intercropping with maize (Zea mays) and plant densities. Soil total Zn and Cd concentrations decreased markedly after long-term phytoextraction. But shoot biomass and Cd and Zn concentrations showed no significant difference with increasing remediation time. In the intercropping experiment the phytoremediation efficiency in the treatment “S. plumbizincicola intercropped with maize” was higher than in S. plumbizincicola monocropping, and Cd concentrations of corn were below the maximum national limit. In the plant density experiment the phytoremediation efficiency increased with increasing plant density and 440,000 plants ha^?1 gave the maximum rate. These results indicated that S. plumbizincicola at an appropriate planting density and intercropped with maize can achieve high remediation efficiency to contaminated soil without affecting the cereal crop productivity. This cropping system combines adequate agricultural production with soil heavy metal phytoextraction.     

Siderophores mediate reduced and increased uptake of cadmium by Streptomyces tendae F4 and sunflower (Helianthus annuus), respectively

Aims: As a toxic metal, cadmium (Cd) affects microbial and plant metabolic processes, thereby potentially reducing the efficiency of microbe or plant‐mediated remediation of Cd‐polluted soil. The role of siderophores produced by Streptomyces tendae F4 in the uptake of Cd by bacteria and plant was investigated to gain insight into the influence of siderophores on Cd availability to micro‐organisms and plants. Methods and Results: The bacterium was cultured under siderophore‐inducing conditions in the presence of Cd. The kinetics of siderophore production and identification of the siderophores and their metal‐bound forms were performed using electrospray ionization mass spectrometry. Inductively coupled plasma spectroscopy was used to measure iron (Fe) and Cd contents in the bacterium and in sunflower plant grown in Cd‐amended soil. Siderophores significantly reduced the Cd uptake by the bacterium, while supplying it with iron. Bacterial culture filtrates containing three hydroxamate siderophores secreted by S. tendae F4 significantly promoted plant growth and enhanced uptake of Cd and Fe by the plant, relative to the control. Furthermore, application of siderophores caused slightly more Cd, but similar Fe uptake, compared with EDTA. Bioinoculation with Streptomyces caused a dramatic increase in plant Fe content, but resulted only in slight increase in plant Cd content. Conclusion: It is concluded that siderophores can help reduce toxic metal uptake in bacteria, while simultaneously facilitating the uptake of such metals by plants. Also, EDTA is not superior to hydroxamate siderophores in terms of metal solubilization for plant uptake. Significance and Impact of the Study: The study showed that microbial processes could indirectly influence the availability and amount of toxic metals taken up from the rhizosphere of plants. Furthermore, although EDTA is used for chelator‐enhanced phytoremediation, microbial siderophores would be ideal for this purpose.     

CO_2倍增对植物生长和土壤微生物生物量碳、氮的影响

关于大气ＣＯ２浓度倍增（即为７００μｍｏｌＣＯ２·ｍｏｌ－１空气）将对植物生长产生诸多影响,已有大量报道［１,２］。但ＣＯ２倍增对植物及所在土壤中微生物影响的研究甚少［３,４］。土壤微生物是陆地生态系统中最活跃的成分,担负着分解动植物残体的重要作用,...     

Phytoremediation of the toxic effluent generated during recovery of precious metals from polymetallic sea nodules

Recovery of metals from the polymetallic sea nodules at the pilot plant at National Metallurgical Laboratory, Jamshedpur, India has generated a highly toxic effluent. This effluent contains several metals like Mn, Cu, Zn, Fe, Pb, Cr, and Cd that pollute the neighboring water bodies when discharged. Hence detoxification of this effluent was practiced using two plants: Lemna minor and Azolla pinnata for 7 days. During investigation A. pinnata removed 96% of Mn, 97% of Cu, 98% of Zn, 70% of Fe, 96% of Pb, 93% of Cr, 78% of Cd, and was comparatively more effective than L. minor which removed 94% of Mn, 86% of Cu, 62% of Zn, 74% of Fe, 84% of Pb, 63% of Cr, 78% of Cd. During the 7 days of experiment chlorophyll content decreased by 51% and 59% in A. pinnata and L. minor respectively. Based on our findings we can suggest that these two plants have wide range of metal retention potentialities hence can be of routine use for purification of toxic effluents.