Removal of chromium on Polyalthia longifolia leaves biomass

Adsorption is an environmental friendly process for removal and/or recovery of heavy metals from wastewater. In recent years, it has been substantiated as a popular technique to treat industrial waste effluents, with significant advantages. In this work, batchwise removal of chromium (III) ions from water by Polyalthia longifolia leaves was studied as a function of adsorbent dose, pH, contact time, and agitation speed. Surface characteristics of the leaves were evaluated by recording IR spectra. The Langmuir, Freundlich, and Temkin adsorption isotherms were employed to explain the sorption process. It was found that one gram of leaves can remove 1.87 mg of trivalent chromium when working at pH 3.0. It has been concluded that Polyalthia longifolia leaves can be used as cost-effective and benign adsorbents for removal of Cr(III) ions from wastewater.     

Chromium(III) hydrolytic oligomers: their relevance to protein binding

The nature of chromium(III) complexes has been found to show a profound influence in its interaction with collagen. The hydrothermal stability of rat tail tendon (RTT) fibres treated with dimeric, trimeric and tetrameric species of chromium(III) has been found to be 102, 87 and 68 degrees C, while that of native RTT is 62 degrees C. This shows that the efficiency of crosslinking of collagen by chromium(III) species is dimeric > trimeric > tetrameric. This order of stabilisation is again confirmed by cyanogen bromide (CNBr) cleavage of RTT collagen treated with dimeric, trimeric and tetrameric chromium(III) species. CNBr has been found to cleave the collagen treated with tetrameric chromium(III) species extensively. On the other hand, dimer-treated collagen does not undergo any cleavage on CNBr treatment. The equilibrium constants for the reaction of a nucleophile like NCS(-) to the dimeric, trimeric and tetrameric species of chromium(III) have been found to be 15.7+/-0.1, 14.6+/-0.1 and 1.2+/-0.1 M(-1), respectively. These equilibrium constant values reflect the relative thermodynamic stability of the chromium(III) species-nucleophile complex. The low stabilising effect of the tetrameric species can be traced to its low thermodynamic affinity for nucleophiles.     

Effect of organic Cr(III) complexes on chromium speciation

Abstract

Chromium speciation in the presence of organic chromium(III) complexes was investigated using solid-phase extraction. The adsorptions of Cr(VI) and Cr(III) on alumina and pumice powder were studied. Maximum sorption of Cr(VI) was obtained by alumina (90.22%), while Cr(III) was highly adsorbed onto pumice powder (86.65%). This result shows that pumice may be a new and promising adsorbent for Cr(III). The experimental equilibrium data for Cr(VI) adsorption onto alumina and Cr(III) sorption onto pumice were analysed using Langmuir and Freundlich isotherms. The separation and adsorption of Cr(VI), Cr(III) and five organic chromium(III) complexes onto pumice and alumina at different pH values were evaluated. Ethylenediaminetetraacetate (EDTA), oxalate, citrate, glycine, alanine and 8-hydroxyqinoline were used as ligands. Sorption of alanine and ethylenediaminetetraacetate complexes was higher onto alumina than pumice at pH>3. The enhancement of adsorption of chromium(III) complexes onto pumice was achieved by surface modification of pumice using a surfactant, namely hexadecyltrimethylammoniumbromür (HDTMA). The presence of surfactant enhanced the adsorption of Cr(III) citrate, oxalate, glycine and 8-hydroxyquinoline complexes onto pumice. However, the adsorption of EDTA and alanine complexes decreased, with ratio of 13.40% and 4.00% respectively. Here we demonstrate that chromium speciation methods depending on adsorption onto various adsorbents including alumina may lead erroneous results. Analytical measurements were performed by flame AAS, data were obtained by standard addition method.     

Effect of Rhamnolipids on Chromium-Contaminated Kaolinite

Hexavalent chromium Cr(VI) is a common environmental pollutant that is treated by its reduction to the trivalent form Cr(III). The latter can be re-oxidized to the toxic form, Cr(VI), under specific conditions. A study was conducted on the removal of Cr(III) to eliminate the hazard imposed by its presence in soil as there has been some evidence that organic compounds can decrease its sorption. The effect of addition of negatively-charged biosurfactants (rhamnolipids) on chromium contaminated kaolinite was studied. Results showed that the rhamnolipids have the capability of extracting 25% portion of the stable form of chromium, Cr(III), from the kaolinite, under optimal conditions. The removal of hexavalent chromium was also enhanced compared to water by a factor of 2 using a solution of rhamnolipids. Results from the sequential extraction procedure showed that rhamnolipids remove Cr(III) mainly from the carbonate and oxide/hydroxide portions of the kaolinite. The rhamnolipids had also the capability of reducing close to 100% of the extracted Cr(VI) to Cr(III) over a period of 24 days. This study indicated that rhamnolipids could be beneficial for the removal or long–term conversion of chromium Cr(VI) to Cr(III).     

Chromium (VI) uptake by grape stalks wastes encapsulated in calcium alginate beads: equilibrium and kinetics studies

Abstract

The removal of hexavalent chromium from aqueous solution using grape stalks wastes encapsulated in calcium alginate (GS–CA) beads was investigated. Cr(VI) sorption kinetics were evaluated as a function of chromium initial concentration and grape stalks (GS) content in the calcium alginate (CA) beads. The process follows pseudo second-order kinetics. Transport properties of hexavalent chromium on GS–CA beads was characterised by calculating chromium diffusion coefficient using the Linear Absorption Model (LAM). Langmuir isotherms, at pH 3.0 were used to describe sorption equilibrium data as a function of GS percentage in the CAbeads. Maximum uptake obtained was 86.42 mmol of Cr(VI) per L of wet sorbent volume. Results indicated that both kinetic and equilibrium models describe adequately the adsorption process.     

The use of flocculating brewer's yeast for Cr(III) and Pb(II) removal from residual wastewaters

The use of inexpensive biosorbents to sequester heavy metals from aqueous solutions, is one of the most promising technologies being developed to remove these toxic contaminants from wastewaters. Considering this challenge, the viability of Cr(III) and Pb(II) removal from aqueous solutions using a flocculating brewer's yeast residual biomass from a Portuguese brewing industry was studied. The influence of physicochemical factors such as medium pH, biomass concentration and the presence of a co-ion was characterised. Metal uptake kinetics and equilibrium were also analysed, considering different incubation temperatures. For both metals, uptake increased with medium pH, being maximal at 5.0. Optimal biomass concentration for the biosorption process was determined to be 4.5?g dry weight/l. In chromium and lead mixture solutions, competition for yeast binding sites was observed between the two metals, this competition being pH dependent. Yeast biomass showed higher selectivity and uptake capacity to lead. Chromium uptake kinetic was characterised as having a rapid initial step, followed by a slower one. Langmuir model describes well chromium uptake equilibrium. Lead uptake kinetics suggested the presence of mechanisms other than biosorption, possibly including its precipitation.     

Impact of fluorides on the removal of heavy metals from an electroplating effluent using a flocculent brewer’s yeast strain of Saccharomyces cerevisiae

Abstract

Besides several toxic heavy metals, electroplating effluents can have in solution different cations and anions, which may influence heavy metals removal by the biomass. Among them, fluorides are commonly used in the electroplating industries and thus can be found in the respective wastewaters. In the present work, the effect of the presence of fluorides in the efficiency of chromium(III), copper(II) and nickel(II) removal, from an effluent, by heat-inactivated cells of a brewing flocculent strain of Saccharomyces cerevisiae was evaluated. The presence of fluorides severely decreased (>60%) the removal of chromium(III) by yeast biomass. This effect impaired the effective treatment of the effluent according to the US Environmental Protection Agency and the Portuguese law; conversely, a higher removal of copper(II) and nickel(II) was observed. This behaviour can be understood by metal speciation. In the presence of fluorides, chromium(III) was mainly complexed, becoming unavailable for yeast accumulation; this effect decreased the efficiency of chromium(III) removal. Thus, in the presence of fluorides, less chromium(III) is associated with biomass and consequently more yeast binding sites remain available for the uptake of other metals present in solution. This fact explains the increase of copper(II) and nickel(II) removal in the presence of fluorides.     

Chromium removal from a real tanning effluent by autochthonous and allochthonous fungi

Heavy metals represent an important ecological and health hazard due to their toxic effects and their accumulation throughout the food chain. Conventional techniques commonly applied to recover chromium from tanning wastewaters have several disadvantages whereas biosorption has good metal removal performance from large volume of effluents. To date most studies about chromium biosorption have been performed on simulated effluents bypassing the problems due to organic or inorganic ligands present in real industrial wastewaters that may sequestrate the Cr(III) ions. In the present study a tanning effluent was characterized from a mycological point of view and different fungal biomasses were tested for the removal of Cr(III) from the same tanning effluent in which, after the conventional treatments, Cr(III) amount was very low but not enough to guarantee the good quality of the receptor water river. The experiments gave rise to promising results with a percentage of removed Cr(III) up to 40%. Moreover, to elucidate the mechanisms involved in biosorption process, the same biomasses were tested for Cr(III) removal from synthetic aqueous solutions at different Cr(III) concentrations.     

Molecular basis of chromium insulin interactions

The physiological role of chromium (III) in diabetes mellitus has been an area of inconclusive research for many years. It is of great interest to explore the interactions made by chromium (III) to get a better insight into their role in glucose metabolism. To understand the molecular basis of chromium action we have carried out spectroscopic and crystallographic investigations on the binding of Cr(III)-Salen with insulin, as Cr(III)-Salen is reported to result in the enhancement of insulin activity. The Cr(III)-insulin complex formation has been characterised at two pHs, viz., 3.5 and 9.0 using UV-Vis and fluorescence studies. The crystallographic analysis of Cr(III)-Salen soaked cubic insulin crystals, using anomalous difference Fourier method, revealed B21 Glu to be the binding site for chromium (III).     

A study of the interaction of Cr(III) complexes and their selective binding with B-DNA: a molecular modeling approach

Molecular modeling and energy minimisation calculations have been used to investigate the interaction of chromium(III) complexes in different ligand environments with various sequences of B-DNA. The complexes are [Cr(salen)(H(2)O)(2)](+); salen denotes 1, 2 bis-salicylideneaminoethane, [Cr(salprn)(H(2)O)(2)](+); salprn denotes 1, 3 bis- salicylideneaminopropane, [Cr(phen)(3)](3+); phen denotes 1, 10 phenanthroline and [Cr(en)(3)](3+); en denotes ethylenediamine. All the chromium(III) complexes are interacted with the minor groove and major groove of d(AT)(12), d(CGCGAATTCGCG)(2) and d(GC)(12) sequences of DNA. The binding energy and hydrogen bond parameters of DNA-Cr complex adduct in both the groove have been determined using molecular mechanics approach. The binding energy and formation of hydrogen bonds between chromium(III) complex and DNA has shown that all complexes of chromium(III) prefer minor groove interaction as the favourable binding mode.     

Protein degradation by peroxide catalyzed by chromium (III): role of coordinated ligand

In order to understand the role of coordinated ligands in controlling the biotoxicity of chromium (III), interactions of three types of chromium (III) complexes viz. trans-diaquo [1,2 bis (salicyledeneamino) ethane chromium (III) perchlorate, [(Cr(salen)(H(2)O)(2)](ClO(4)); tris (ethylenediamine) chromium (III) chloride, [Cr(en)(3)]Cl(3), and monosodium ethylene diamine tetraacetato monoaquo chromiate (III), [Cr(EDTA)(H(2)O)]Na with BSA has been investigated. Spectroscopic and equilibrium dialysis studies show that the two cationic complexes Cr(salen)(H(2)O)(+)(2) and Cr(en)(3+)(3) bind to the protein with a protein-metal ratio of 1:8 and 1:4. The anionic complex Cr(EDTA)(H(2)O)(-) binds to the protein with a protein-metal ratio of 1:2. The binding constant K(b) as estimated from the fluorescence quenching studies has been found to be 7.6 +/- 0.4 x 10(3) M(-1), 3.1 +/- 0.2 x 10(2) M(-1), and 1.8 +/- 0.2 x 10(2) M(-1) for Cr(salen)(H(2)O)(+)(2), Cr(en)(3+)(3), and Cr(EDTA)(H(2)O)(-) respectively indicating that the thermodynamic stability of protein-chromium complex is Cr(salen)(H(2)O)(+)(2) > Cr(en)(3+)(3) approximately Cr(EDTA)(H(2)O)(-). The complexes Cr(salen)(H(2)O)(+)(2) and Cr(EDTA)(H(2)O)(-) in the presence of hydrogen peroxide have been found to bring about protein degradation, whereas Cr(en)(3+)(3) does not bring about any protein damage. This clearly shows that the nature of the chromium (III) complex plays a major role in the biotoxicity of chromium (III).     

Cellulose derivative-hyaluronic acid-based microporous hydrogels cross-linked through divinyl sulfone (DVS) to modulate equilibrium sorption capacity and network stability

The aim of this work is to obtain a chemically cross-linked hydrogel from hyaluronic acid and cellulose derivatives that exhibits sensitivity to variation of the composition of the external absorbing medium and an equilibrium sorption capacity higher than a common hyaluronic acid-based hydrogel, in view of its potential use in prevention of postsurgical soft tissue adhesion. This has been achieved by chemical stabilization of hyaluronic acid (HA) and cellulose derivatives, hydroxyethylcellulose (HEC) and carboxymethylcellulose (CMCNa) through the difunctional cross-linker divinyl sulfone. Significant increase in sorption capacity, both in water and in water solutions at different ionic strength, has been observed for these samples in comparison with hydrogels obtained through chemical stabilization of hyaluronic acid. Moreover, different dehydration procedures adopted for the xerogel synthesis have been used, which resulted in a modulation of the equilibrium sorption capacity. Hyaluronic acid stability has been confirmed by means of NMR analysis.     

Concurrent sorption of Ni2+ and Cu2+ by Chlorella vulgaris from a binary metal solution

Kinetics and capacity of Ni2+ and Cu2+ sorption by Chlorella vulgaris were studied using single and binary metal solutions at various concentrations of these metal ions. The second-order rate law best described the kinetics of metal sorption from both single and binary metal systems. C. vulgaris preferentially sorbed Cu2+ over Ni2+ in the binary system. In comparison to the single metal system, the amounts of Ni2+ and Cu2+ sorbed at equilibrium (qe) were respectively 73% and 25%, and the initial rate of sorption (h) was ca. 50% in the case of the binary metal system. The test metals inhibited sorption of each other, thereby indicating competition between Ni2+ and Cu2+ for sorption onto non-specific binding sites. The present study showed that C. vulgaris has specific as well as non-specific sites for the binding of Ni2+ and Cu2+. Participation of these sites for sorption depended on the ratio of Ni2+ and CU2+ in solution. The maximum metal sorption capacity of C. vulgaris was 6.75 mmol g(-1) from the binary metal solution at the tested biomass concentration (100 mg dry weight l(-1)). Total metal sorption was enhanced with increasing total concentration of both the metals up to 1.6 mM, beyond which a decrease occurred. Two-dimensional contour plots were successfully used for the first time for the evaluation of metal sorption potential.     

Preparation of Modified Chitin for the Removal of Chromium(VI)

Chitin was chemically modified into various forms for enhancing chromium sorption. The modified forms of chitin, viz., protonated chitin (PC), carboxylated chitin (CC), and grafted chitin (GC), possessed enhanced chromium sorption capacities (SCs) of 2812, 3010, and 3770 mg/kg, respectively, than the raw chitin (C), which showed the SC of 2316 mg/kg. The sorption experiments were carried out in batch mode to optimize various influencing parameters, viz., contact time, pH, common ions, and temperature. The sorbents were characterized by Fourier transform infrared (FTIR) spectroscopy and scanning electron microscopy (SEM). The modified forms of chitin removes chromium by means of electrostatic adsorption coupled reduction and complexation. The adsorption data were fitted with Freundlich and Langmuir isotherms. The calculated values of thermodynamic parameters indicate the nature of chromium sorption. The dynamic studies demonstrated that the sorption process follows pseudo-second-order and intraparticle diffusion models. The suitability of these modified chitin has been tested with field sample collected from a nearby industrial area.     

Column study on the adsorption of Cr(III) and Cr(VI) using Pumice, Yarikkaya brown coal, Chelex-100 and Lewatit MP 62

In the present study, adsorption of Cr(III) and Cr(VI) on Pumice (Pmc), Yarikkaya (YK) brown coal, Chelex-100, and Lewatit MP 62 is examined at room temperature and at initial chromium concentration of 1.0 x 10(-3) mol/L. Column method was carried out as a function of pH, concentration of Cr(III) and Cr(VI) ions, volume of samples and flow rate. The experimental data were evaluated by Freundlich and Langmuir isotherm models. The dynamic breakthrough capacities of the adsorbents for Cr(III) and Cr(VI) were calculated. The maximum chromium sorption occurred at 5 mL/min flow rate and 25 mL volume for all adsorbents. The results showed that the two readily available adsorbents namely Pmc and YK, were suitable for removing chromium from aqueous solution.     

Metals sorption from aqueous solutions by Kluyveromyces marxianus: Process optimization,equilibrium modeling and chemical characterization

The dead Kluyveromyces marxianus biomass, a fermentation industry waste, was used to explore its sorption potential for lead, mercury, arsenic, cobalt, and cadmium as a function of pH, biosorbent dosage, contact time, agitation speed, and initial metal concentration. The equilibrium data fitted the Langmuir model better for cobalt and cadmium, but Freundlich isotherm for all metals tested. At equilibrium, the maximum uptake capacity (Qmax) was highest for lead followed by mercury, arsenic, cobalt, and cadmium. The RL values ranged between 0–1, indicating favorable sorption of all test metals by the biosorbent. The maximum Kf value of Pb showed its efficient removal from the solution. However, multi-metal analysis depicted that sorption of all metals decreased except Pb. The potentiometric titration of biosorbent revealed the presence of functional groups viz. amines, carboxylic acids, phosphates, and sulfhydryl group involved in heavy metal sorption. The extent of contribution of functional groups and lipids to biosorption was in the order: carboxylic>lipids>amines>phosphates. Blocking of sulfhydryl group did not have any significant effect on metal sorption.     

Isolation of a novel chromium(III) binding protein from bovine liver tissue after chromium(VI) exposure

In the ongoing investigation into the biological importance and toxicity issues surrounding the bioinorganic chemistry of chromium, the accepted literature procedure for the isolation of the biological form of chromium, low molecular weight chromium binding protein (LMWCr) or chromodulin, was investigated for its specificity. When chromium(VI) is added to bovine liver homogenate, results presented here indicate at least four chromium(III) binding peptides and proteins are produced and that the process is non-specific for the isolation of LMWCr. A novel trivalent chromium containing protein (1) has been isolated to purity and initial characterization is reported here. Chromium(III) identification was determined by optical spectroscopy and diphenylcarbazide testing. This chromium binding protein has a molecular weight of 15.6kDa, which was determined from both gel-electrophoresis and mass spectrometry. The protein is comprised primarily of Asx, Glx, His, Gly/Thr, Ala, and Lys in a 1.00:2.51:0.37:2.09:0.39:1.17 ratio and is anionic at pH 7.4. In addition, the protein binds approximately 2.5 chromium(III) ions per molecule.     

Preparation and conformational characterization of Cr(III) hemoglobin

Chromium(III) substituted hemoglobin has been prepared. Circular dichroism spectra in the UV region have been recorded in the presence and absence of the allosteric affector inositol hexaphosphate. The reactivity with bromthymol blue and p-mercuribenzoate has been measured. All data indicate a T state (or T state-like) structure, whereas an R structure would be expected from the chromium stereochemistry. Similarities to cobalt(III) hemoglobin suggest that the chromium derivative also exists as an internal hemichrome. Thus, despite major tertiary structure differences, “denatured” hemichromes may have a quaternary structure quite similar to deoxyhemoglobin.     

Interaction of chromium(III) complexes with model lipid bilayers: implications on cellular uptake

To understand molecular cytotoxicity of chromium(III) and how it affects the stability of biological membranes, studies on the interaction of chromium(III) complexes aquapentaminechromium complex (complex I) and trans- [Cr(5-methoxysalcyclohex) (H(2)O) (2)] ClO(4) (complex II) with model biomembranes have been carried out. Langmuir films of dimyristoylphosphatidylcholine (DMPC), dipalmitoylphosphatidic acid (DPPA), dioctadecyldimethylammoniumbromide (DOMA) at air/water interface interacting with the chromium(III) complexes have been characterized using the surface pressure-molecular area (π-A) isotherms. Initial surface pressures changes for the two complexes show that the chromium(III) complexes inserted in the Langmuir films and complex I interacted strongly compared to complex II. Supported bilayers (SB) of the lipids on solid substrates formed by hydrating their Langmuir-Blodgett films (LB films) have been characterized using linear dichroic spectra, low angle X-ray diffraction and steady state fluorescence anisotropy. Depending on the geometry of the ligands and concentration, the complexes either insert in the alkyl or in the head group region of the SB and sometimes in both regions. The Supported lipid bilayers are well-layered and at low concentration, the metal complexes are incorporated near the head group region. Order and increase in lamellar spacing show stronger interaction of complex I with the lipids compared with complex II. This study provides some insights into the mechanism of chromium(III) toxicity and uptake of chromium(III) by the cells.     

Chromium accumulation and toxicity in aquatic vascular plants

Chromium poisoning among leather tanners has long been known. The workers have been found to suffer from ulcers, allergic dermatitis, lung cancer, and liver necrosis due to prolonged contact with chromium salts. One of the highly catastrophic incidences of lung cancer as a result of inhaling dust containing Cr (VI) was reported in 1960 from the Kiryama factory of the Nippon-Denko concern on the island of Hokkaido, Japan. Pollution of water resources, both surface and underground, by indiscriminate discharge of spent wastes of chromium-based industries has become a serious global concern, for it has created an acute scarcity of safe drinking water in many countries. In August 1975 it was observed that underground drinking water in Tokyo near the chromium (VI))-containing spoil heaps contained more than 2000 times the permissible limit of chromium. In Ludhiana and Chennai, India, chromium levels in underground water have been recorded at more than 12 mg/L and 550–1500 ppm/L, respectively. Chromium is widely distributed in nature, occupying 21st position in the index of most commonly occurring elements in the earth’s crust. Chromium occurs in nature in the form of a compound (chromium + oxygen + iron) known as “chromite.” The geographical distribution of chromite mines is uneven. Over 95% of economically viable chromite ores are situated in the southern part of Africa. Its annual global production is ca. 9 million tons, mainly mined in the former Soviet Union, Albania, and Africa. In India, over 90% of chromite deposits are located in Sukinda Valley of Orissa. Chromium occurs in several oxidation states, ranging from Cr²⁺ to Cr⁶⁺, with trivalent and hexavalent states being the most stable and common in the terrestrial environment. Chromium (III) is used for leather tanning because it forms stable complexes with amino groups in organic material. In the presence of excessive oxygen, chromium (III) oxidizes into Cr (VI), which is highly toxic and more soluble in water than are other forms. Chromium (VI) can easily cross the cell membrane, whereas the phosphate-sulphate carrier also transports the chromite anions. On the other hand, Cr (III) does not utilize any specific membrane carrier and hence enters into the cell through simple diffusion. The diffusion is possible only after the formation of appropriate lipophilic ligands. Use of chromium as industrial material was discovered only 100 years ago. It was used for the first time in the production of corrosion-resistant steel (stainless steel) and coatings. Subsequently, chromium was widely deployed in various industries; namely, electroplating, dyes and pigments, textiles, photography, and wood processing. The tanning industry is one of the major users of chromium (III) salts. During leather processing the conversion of putrefactive proteinaceous matter, skin, into non-putricible is carried out by the treatment of chromium sulphate solution. According to an estimate, ca. 32 tons of chromium sulphate salts are used annually in Indian tanneries. As a result of unplanned disposal of spent tannery wastes, ca. 2000–3200 tons of chromium as element escapes into the environment. This has raised severe ecological concern and reduced the forest cover considerably. Aquatic vascular plants play an important role in the uptake, storage, and recycling of metals. The uptake of metals depends on the chemical form present in the system and on the life form of the macrophytes (floating, free floating, well rooted, or rootless). The free-floating species (Eichhornia, Lemna, Pistia) absorb elements through the roots/leaves, whereas the rootless speciesCeratophyllum demersum absorbs mainly through the finally divided leaves. Submerged species showed higher chromium accumulation than do floating and emergent ones. The order is:Elodea canadensis > Lagarosiphon major > Potamogeton crispes > Trapa natans > Phragmitis communis. Roots of water hyacinth (Eichhornia crassipes) showed an accumulation of 18.92 μmol (g dry tissue wt^-1) Cr. AlthoughCeratophyllum demersum andHydrodictyon reticulatum showed lower levels of chromium accumulation, their bioconcentration factor values were very high. Floating-species duckweeds (Lemna, Spirodela) are potential accumulators of heavy metals. They have bioconcentrated Fe and Cu, as high as 78 times their concentration in wastewater. Duckweeds have also shown the ability to accumulate chromium substantially. Although duckweeds attain higher concentrations of chromium in their tissues than do other macrophytes, their bioconcentration factor (BCF) values were much lower than those reported in other aquatic species. A moderate accumulation of chromium has been found in emergent species. Plants ofScirpus validatus andCyperus esculentus accumulated 0.55 kg and 0.73 kg^-1 Cr, respectively. InBacopa monnieri andScirpus lacustris accumulations of 1600 and 739 μg g^-1 dw Cr, respectively, have been reported when exposed to 5 mg L^-1 Cr for 168 hours in solution culture. The accumulation of Cr was greater in the root than the shoot. Higher accumulations of chromium in roots and least in shoots of emergent species have also been recorded. Phytotoxicity of chromium in aquatic environment has not been studied in detail. The mechanism of injury in terms of ultrastructural organization, biochemical changes, and metabolic regulations has not been elucidated. It has been pointed out that while considering the toxicity of heavy metals, a distinction should be made between elements essential to plants and metals that have no proven beneficial biochemical effects. For example, an increased level of chromium may actually stimulate growth without being essential for any metabolic process. In aquatic species—namely,Myriophyllum spicatum— the maximum increase in shoot length was found at 50 μgl^-1 Cr. Higher concentrations up to 1000 μ gl^-1 caused an almost linear reduction both in shoot weight and length. Duckweeds showed relatively greater tolerance to chromium. However, an inhibition of growth inSpirodela andLemna was found at 0.02 mM and 0.00002 mM Cr concentrations, respectively. Mortality ofL. aequinoctialis was found at 0.005 mM Cr and higher concentrations. The effective chromium concentrations (EC-50) for some aquatic species have been reported as follows:Lemna minor, 5.0 mg L^-1, 14 days EC;L. Paucicostata, 1.0 mg L-¹, 20 days EC;Myriophyllum spicatum, 1.9 mg L^-1, 32 days EC; andSpirodela polyrrhiza, 50 mg L^-1, 14 days EC. Chromium toxicity on biochemical parameters showed a reduction in photosynthetic rate at 50 μgl^-1 Cr inMyriophyllum spicatum. Decrease in chlorophyll and protein contents were also recorded inNajas indica, Vallisneria spiralis, andAlternanthera sessilis with an increase in chromium concentration. InLimnanthemum cristatum, a slight reduction in chlorophyll and almost no change in control were found due to chromium toxicity. Submerged species (Ceratophyllum demersum, Vallisneria spiralis) and an emergent one (Alternanthera sessilis) showed decreases in chlorophyll as well as in protein contents when treated with chromium. Chromium-induced morphological and ultrastructural changes have been reported in several aquatic vascular plants: InLemna minor andCeratophyllum demersum, chromium-induced changes in chloroplast fine structure disorganized thylakoids with loss of grain and caused formation of many vesicles in the chloroplast. Chromium (VI) has caused stunting and browning of roots produced from the chromium-treated excised leaves ofLimnanthemum cristatum. At 226 μg/g Cr dry wt leaf tissue concentration, development of brown coloration in the hydathodes of juvenile leaves ofLimnanthemum cristatum is a characteristic chromiuminduced alteration. Aquatic vascular plants and algae may serve as effective bioindicators in respect to metals in aquatic environments. Chromium-induced morphological and ultrastructural changes inLimnanthemum cristatum have significant indicator values and could be used for assessing the level of chromium in ambient water.Wolffia globosa, a rootless duckweed, showed substantial chromium accumulation and high concentration factor (BCF) value at very low ambient chromium concentrations, suggesting its feasibility in detecting chromium pollution in water resources. Methylene blue-stained cells ofScenedesmus acutus become uniformly dark blue during chromium (VI) treatment. This may serve as an indicator of chromium pollution.