Study of the biosorption of different heavy metal ions onto Kraft lignin

The ability of Kraft lignin, a waste product of paper production, for removing copper, zinc, cadmium and chromium ions from water was investigated. The studies were conducted by a batch method to determine equilibrium parameters. The adsorbed heavy metal ions followed the order: Cr(VI) ? Cd(II) > Cu(II) > Zn(II). The influence of other ions such as Ni(II), Cd(II) and Pb(II), on Cu(II) adsorption by Kraft lignin was evaluated. Obtained results support the idea that adsorption behaviour of heavy metal ions have to be perceived from the aspect of possible influence of interfering ion species.     

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.     

Role of the Ca-pectates on the accumulation of heavy metals in the root apoplasm

In order to better understand the processes that regulate the accumulation in the apoplasm of heavy metals and their mobilization by the plant metabolites it is essential to study the mechanisms that regulate the interactions between metal ions and pectins. In such a context, the sorption of Cd(II), Zn(II), Cu(II) and Pb(II) from single and multi-metal solutions, by a Ca-polygalacturonate gel with a degree of esterification of 18.0 (PGAM₁) and 65.5% (PGAM₂) was studied in the 3.0–6.0 pH range in the presence of CaCl₂ 2.5 mM. The sorption of Cr(III) from single metal solution was also considered. The results show that the amount of each metal ion sorbed increases with increasing the initial metal ion concentration and pH. The data from the single metal solution tests show that at pH 6.0 the affinity of the metal ions towards the PGAM₁ matrix follows the order: Cr(III) > Cu(II) ? Pb(II) ? Zn(II) ? Cd(II). The simultaneous sorption of the bivalent metal ions by the PGAM₁ gels indicates that Pb(II) is selectively sorbed. The FT-IR spectra show that the carboxylate groups are mainly responsible for the metal ion coordination. The ability of PGAM₂ to accumulate Cr(III), Cu(II), and Pb(II) was lower than that found in the PGAM₁ systems whereas the sorption of Zn(II) and Cd(II) was negligible.     

Biosorption of Heavy Metals from Wastewater by Biosolids

In a study where the removal of heavy metals from wastewater is the primary aim, the biosorption of heavy metals onto biosolids prepared as Pseudomonas aeruginosa immobilized onto granular activated carbon was investigated in batch and column systems. In the batch system, adsorption equilibriums of heavy metals were reached between 20 and 50 min, and the optimal dosage of biosolids was 0.3 g/L. The biosorption efficiencies were 84, 80, 79, 59 and 42 % for Cr(VI), Ni(II), Cu(II), Zn(II) and Cd(II) ions, respectively. The rate constants of biosorption and pore diffusion of heavy metals were 0.013–0.089 min^–1 and 0.026–0.690 min^–0.5. In the column systems, the biosorption efficiencies for all heavy metals increased up to 81–100 %. The affinity of biosorption for various metal ions towards biosolids was decreased in the order: Cr = Ni > Cu > Zn > Cd.     

Validation of an in vitro cytotoxicity test for four heavy metals using cell lines derived from a green sea turtle (<Emphasis Type="Italic">Chelonia mydas</Emphasis>)

Ten cell lines established from juvenile green sea turtles were tested and evaluated for their cytotoxic responses to four heavy metals: cadmium (Cd), chromium (Cr), zinc (Zn), and copper (Cu). Following a 24-h exposure to these metal salts at selected concentrations, test cells were comparatively characterized by morphology, viability, and proliferation. Experimental results indicated that all these metal salts were cytotoxic to these turtle cell lines at varied concentrations. Calculated 10% and 50% inhibitory concentration (IC₁₀ and IC₅₀) values revealed that the cytotoxicities of Cd and Cr were significantly more potent than the other two metal salts (p < 0.01). Comparative analysis of IC₁₀ values in these ten cell lines showed that turtle lung cells (GT-LG) are the most sensitive cell line to Cd, Cr, Zn, and Cu. Among these turtle cell lines, turtle liver cells (GT-LV) are more tolerant than other cells to Cd, Cr, and Zn, while GT-EYE cells are more tolerant to Cu, as determined by IC₅₀ values. Overall, GT-LG represents the most sensitive cells to heavy metal contamination and may be used for initial environmental monitoring, while the highly tolerant nature of GT-LV and GT-EYE cells to the tested heavy metals suggest their potential use as an emergency last-resort indicator of potential metal-related adverse effect on human health.     

Metal ion interaction with a novel anthracene pendant-armed fluorescent molecular probe. Synthesis, characterization, and fluorescence studies

A new scorpionate system (L) containing an emissive anthracene pendant arm, derived of O¹,O⁷-bis(2-formylphenyl)-1,4,7-trioxaheptane and tren, has been synthesized and characterized. The sensing capability of L towards a range of metal ions has been studied. Protonation and complexation studies, using UV-Vis and fluorescent emission measurements, have been performed with alkaline and alkaline earth metal ions (M = Na(I), K(I), Li(I), Ca(II), Mg(II)), as well as transition and post-transition metal ions (M = Cr(III), Cu(II) and Zn(II), Cd(II), Hg(II) and Al(III)). An increase in the fluorescence emission (CHEF effect) was observed in methanol and in methanol/water mixtures in the presence of Cd(II) (5.0-fold), Zn(II) (4.5-fold), Cr(III) (2.0-fold) and Al(III) (1.8-fold); these results suggest a notable sensing ability of this new N₃O₄ ligand for these metals; these experiments were also performed in the presence of large amounts of alkaline and alkaline earth metal ions.     

Interaction of Heavy Metals in Multimetal Biosorption by Galerina vittiformis from Soil

ABSTRACT Soil heavy metal contamination, a major threat due to industrialization, can be tackled by an efficient and economical process called bioremediation. Mushrooms are employed to accumulate heavy metals from soil due to their high metal accumulation potential and better adaptability. The bioaccumulation potential of Galerina vittiformis was already reported for individual metals. At natural conditions, since soil consists of more than one polluting metal, more focus has to be given to multimetal systems. In this study, multimetal accumulation potential was analyzed using central composite design, and the responses obtained were analyzed using response surface methodology. Heavy metals such as Cu(II), Cd(II), Cr(VI), Pb(II), and Zn(II) were subjected to biosorption at 10–250 mg/kg concentrations along with pH 5–8. The results showed that the preference of the organism for the five metals under study was in the order Pb(II) > Zn(II) > Cd(II) > Cu(II) > Cr(VI) at pH 6.5 under multimetal condition. The study also indicates that the metal interaction pattern in multimetal interaction is a property of their ionic radii. The response surface methodology clearly explains the effect of interaction of heavy metals on the accumulation potential of the organism using three-dimensional response plots. The present work suggests that the fungus Galerina vittiformis could be employed as a low-cost metal removal agent from heavy metal–polluted soil.     

Effective bioremoval of reactive dye and heavy metals by Aspergillus versicolor

In this study, bioaccumulation of heavy metal and dye by Aspergillus versicolor was investigated. Optimum pH values of the maximum heavy metal bioaccumulation was found as 6 for 50 mg/L Cr(VI), Ni(II) and 5 for Cu(II) ions with the 99.89%, 30.05% and 29.06% removal yield, respectively. The bioremoval of the dye up to 800 mg/L at pH 5 and 6 was investigated and 27.15% and 28.95% removal rates were measured respectively. The presence of Cr(VI) with dye, decreased the uptake yield for both pollutants. In the medium with Cu(II) and dye, dye removal was not affected by Cu(II), but Cu(II) removal rate increased from 29.06% to 37.91% by the existence of the dye. When Ni(II) and dye were combined, neither pollutant affected the other’s removal yield. These results indicate that the isolated A. versicolor strain deserves attention as a promising bioaccumulator of heavy metal ions and reactive dyes in wastewater effluents.     

Adsorptive Removal and Recovery of U(VI), Cu(II), Zn(II), and Co(II) from Water and Industry Effluents

Tamarind fruit shell (TFS) was converted to a cation exchanger (PGTFS-SP-COOH) having a carboxylate functional group at the chain end by grafting poly(hydroxyethylmethacrylate) onto TFS (a lignocellulosic residue) using potassium peroxydisulfate-sodium thiosulfate redox initiator, and in the presence of N, N ′-methylenebisacrylamide as a cross-linking agent, followed by functionalization. The chemical modification was investigated using Fourier transform infrared (FTIR), X-ray diffraction (XRD), and potentiometric titrations. The feasibility of PGTFS-SP-COOH for the removal of heavy metals such as U(VI), Cu(II), Zn(II), and Co(II) ions from aqueous solutions was investigated by batch process. The optimum pH range for the removal of meal ions was found to be 6.0. For all the metal ions, equilibrium was attained within 2 h. The kinetic and isotherm data, obtained at optimum pH value 6.0, could be fitted with pseudo-second-order equation and Sips isotherm model, respectively. The Sips maximum adsorption capacity for U(VI), Cu(II), Zn(II), and Co(II) ions at 30°C was found to be 100.79, 65.69, 65.97, and 58. 81 mg/g, respectively. Increase of ionic strength decreased the metal ion adsorption. Different wastewater samples were treated with PGTFS-SP-COOH to demonstrate its efficiency in removing metal ions from wastewater. The adsorbed metal ions on PGTFS-SP-COOH can be recovered by treating with 1.0 M NaCl + 0.5 M HCl for U(VI) ions and 0.2 M HCl for Cu(II), Co(II), and Zn(II) ions. Four adsorption/desorption cycles were performed without significant decrease in removal capacity. The results showed that PGTFS-SP-COOH developed in this study exhibited considerable adsorption potential for the removal of U(VI), Cu(II), Zn(II), and Co(II) ions from water and wastewaters.     

METAL‐INDUCED REACTIVE OXYGEN SPECIES PRODUCTION IN CHLAMYDOMONAS REINHARDTII (CHLOROPHYCEAE)1

Toxic effects of metals appear to be partly related to the production of reactive oxygen species (ROS), which can cause oxidative damage to cells. The ability of several redox active metals [Fe(III), Cu(II), Ag(I), Cr(III), Cr(VI)], nonredox active metals [Pb(II), Cd(II), Zn(II)], and the metalloid As(III) and As(V) to produce ROS at environmentally relevant metal concentrations was assessed. Cells of the freshwater alga Chlamydomonas reinhardtii P. A. Dang. were exposed to various metal concentrations for 2.5 h. Intracellular ROS accumulation was detected using an oxidation‐sensitive reporter dye, 5‐(and‐6)‐carboxy‐2′,7′‐dihydrodifluorofluorescein diacetate (H₂DFFDA), and changes in the fluorescence signal were quantified by flow cytometry (FCM). In almost all cases, low concentrations of both redox and nonredox active metals enhanced intracellular ROS levels. The hierarchy of maximal ROS induction indicated by the increased number of stained cells compared to the control sample was as follows: Pb(II) > Fe(III) > Cd(II) > Ag(I) > Cu(II) > As(V) > Cr(VI) > Zn(II). As(III) and Cr(III) had no detectable effect. The effective free metal ion concentrations ranged from 10^?6 to 10^?9 M, except in the case of Fe(III), which was effective at 10^?18 M. These metal concentrations did not affect algal photosynthesis. Therefore, a slightly enhanced ROS production is a general and early response to elevated, environmentally relevant metal concentrations.     

Effect of Zn(II) on the reduction and accumulation of Cr(VI) by <Emphasis Type="Italic">Arthrobacter</Emphasis> species

Natural habitats are often characterized by the coexistence of Zn and Cr. This study assessed the potential of two Gram-positive, Cr(VI)-reducing, aerobic bacterial strains belonging to Arthrobacter genera, which were isolated from basalt samples taken from the most polluted region of the Republic of Georgia, to remediate Cr(VI) in environments in the presence of Zn(II). Our batch experiments revealed that the addition of Zn(II) to the tested bacterial cells significantly enhanced the accumulation of Cr. According to electron spin resonance (ESR) measurements, the presence of Zn(II) ions did not change the nature of Cr(V) and Cr(III) complexes generated during the microbial reduction of Cr(VI). The efficiency of Cr(VI) reduction also remained unchanged after the addition of 50 mg/l of Zn(II) to the bacterial cells. However, at high concentrations of Zn(II) (higher than 200 mg/l), the transformation of Cr(VI) to Cr(V) and Cr(III) complexes decreases significantly. In addition, it was shown that the accumulation pattern of Zn in the tested bacterial species in the presence of 100 mg/l of Cr(VI) fits the Langmuir–Freundlich model well. The two tested bacterial strains exhibited different characteristics of Zn accumulation.     

Heavy metal tolerance in marine strains of Yarrowia lipolytica

Heavy metal tolerance of two marine strains of Yarrowia lipolytica was tested on solid yeast extract peptone dextrose agar plates. Based on minimum inhibitory concentration esteems, it is inferred that the two strains of Y. lipolytica were tolerant to heavy metals such as Pb(II), Cr(III), Zn(II), Cu(II), As(V), and Ni(II) ions. The impact of various heavy metal concentrations on the growth kinetics of Y. lipolytica was likewise assessed. With increased heavy metal concentration, the specific growth rate was reduced with delayed doubling time. Furthermore, biofilm development of both yeasts on the glass surfaces and in microtitre plates was assessed in presence of different heavy metals. In microtitre plates, a short lag phase of biofilm formation was noticed without the addition of heavy metals in yeast nitrogen base liquid media. A lag phase was extended over increasing metal concentrations of media. Heavy metals like Cr(VI), Cd(II), and As(V) are contrastingly influenced on biofilms’ formation of microtitre plates. Other heavy metals did not much influence on biofilms development. Thus, biofilm formation is a strategy of Y. lipolytica under stress of heavy metals has significance in bioremediation process for recovery of heavy metals from contaminated environment.

     

On the possible roles of N-terminal His-rich domains of Cu,Zn SODs of some Gram-negative bacteria

The Cu,Zn superoxide dismutases (Cu,Zn SOD) isolated from some Gram-negative bacteria possess a His-rich N-terminal metal binding extension. The N-terminal domain of Haemophilus ducreyi Cu,Zn SOD has been previously proposed to play a copper(II)-, and may be a zinc(II)-chaperoning role under metal ion starvation, and to behave as a temporary (low activity) superoxide dismutating center if copper(II) is available. The N-terminal extension of Cu,Zn SOD from Actinobacillus pleuropneumoniae starts with an analogous sequence (HxDHxH), but contains considerably fewer metal binding sites. In order to study the possibility of the generalization of the above mentioned functions over all Gram-negative bacteria possessing His-rich N-terminal extension, here we report thermodynamic and solution structural analysis of the copper(II) and zinc(II) complexes of a peptide corresponding to the first eight amino acids (HADHDHKK-NH₂, L) of the enzyme isolated from A. pleuropneumoniae. In equimolar solutions of Cu(II)/Zn(II) and the peptide the MH₂L complexes are dominant in the neutral pH-range. L has extraordinary copper(II) sequestering capacity (K_D,Cu = 7.4 × 10^− 13 M at pH 7.4), which is provided only by non-amide (side chain) donors. The central ion in CuH₂L is coordinated by four nitrogens {NH₂,3N_im} in the equatorial plane. In ZnH₂L the peptide binds to zinc(II) through a {NH₂,2N_im,COO⁻} donor set, and its zinc binding affinity is relatively modest (K_D,Zn = 4.8 × 10^− 7 M at pH 7.4). Consequently, the presented data do support a general chaperoning role of the N-terminal His-rich region of Gram-negative bacteria in copper(II) uptake, but do not confirm similar function for zinc(II). Interestingly, the complex CuH₂L has very high SOD-like activity, which may further support the multifunctional role of the copper(II)-bound N-terminal His-rich domain of Cu,Zn SODs of Gram-negative bacteria. The proposed structure for the MH₂L complexes has been verified by semiempirical quantum chemical calculations (PM6), too.     

Metal-induced inhibition of anaerobic metabolism of volatile fatty acids and hydrogen

The effects of copper (Cu), chromium (Cr), cadmium (Cd), lead (Pb) and zinc (Zn) on the biotransformation of organic acids (acetate, propionate and butyrate) and H₂ were assessed in serum-bottle microcosms. Experiments were performed over a range of metal concentrations (20–200 mg/1) using biomass from an anaerobic bioreactor fed continuously with ethanol distillery waste as inoculum. In general, the added metals inhibited the biotransformation of organic acids with increasing metal concentration. However, the extent of inhibition varied for the different biotransformations and for the different metals tested. For example, the concentration of CuCl₂ effecting a 50% reduction in the rate constant for biotransformation of acetate, propionate and butyrate was 60, 75 and 30 mg/1, respectively. Cu and Cr (VI) were the most inhibitory metals in organic acid transformation, whereas Pb was the least toxic. The rate of biotransformation of acetate was reduced by half at Cu and Cr concentrations of 60 and 40 gm/1 respectively, whereas Cd, Pb, and Zn concentrations of 160 to 200 mg/l had little effect. The activities of hydrogenotrophic methanogens were much less affected by the same metals and metal concentrations.     

A fluorescent ligand rationally designed to be selective for zinc(II) over larger metal ions. The structures of the zinc(II) and cadmium(II) complexes of N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine

The metal ion coordinating properties of the ligands N,N-bis(2-methylquinoline)-2-(2-aminoethyl)pyridine (DQPEA) and N,N-bis(2-methylquinoline)-2-(2-aminomethyl)pyridine (DQPMA) are presented. DQPEA and DQPMA differ only in that DQPEA forms six-membered chelate rings that involve the pyridyl group, whereas DQPMA forms analogous five-membered chelate rings.These two ligands illustrate the application of a ligand design principle, which states that increase of chelate ring size in a ligand will result in increase in selectivity for smaller relative to larger metal ions. The formation constants (log K₁) of DQPEA and DQPMA with Ni(II), Cu(II), Zn(II), Cd(II) and Pb(II) are reported. As expected from the applied ligand design principle, small metal ions such as Ni(II) and Zn(II) show increases in log K₁ with DQPEA (six-membered chelate ring) relative to DQPMA (five-membered chelate ring), while large metal ions such as Cd(II) and Pb(II) show decreases in log K₁ when the chelate ring increases in size. In order to further understand the steric origin of the destabilization of complexes of metal ions of differing sizes by the six-membered chelate ring of DQPEA, the structures of [Zn(DQPEA)H₂O](ClO₄)₂ (1) [triclinic, , a = 9.2906(10), b = 10.3943(10), c = 17.3880(18) Å, α = 82.748(7)°, β = 88.519(7)°, γ = 66.957(6)°, Z = 4, R = 0.073] and [Cd(DQPEA)(NO₃)₂] (2) [monoclinic, C2/c, a = 22.160(3), b = 15.9444(18), c = 16.6962(18) Å, β = 119.780(3)°, Z = 8, R = 0.0425] are reported. The Zn in (1) is five-coordinate, with a water molecule completing the coordination sphere. The Cd(II) in (2) is six-coordinate, with two unidentate nitrates coordinated to the Cd. It is found that the bonds to the quinaldine nitrogens in the DQPEA complexes are considerably stretched as compared to those of analogous TPyA (tri(pyridylmethyl)amine) complexes, which effect is attributed to the greater steric crowding in the DQPEA complexes. The structures are analyzed for indications of the origins of the destabilization of the complex of the large Cd(II) ion relative to the smaller Zn(II) ion. A possible cause is the greater distortion of the six-membered chelate ring in (2) than in (1), as evidenced by torsion angles that are further away from the ideal values in (2) than in (1). Fluorescence properties of the DQPMA and DQPEA complexes of Zn(II) and Cd(II) are reported. It is found that the DQPEA complex of Zn(II) has increased fluorescence intensity compared to the DQPMA complex, while for the Cd(II) complex the opposite is found. This is related to the greater strain in the six-membered chelate ring of the Cd(II) DQPEA complex as compared to the Zn(II) complex, with resulting poorer overlap in the Cd-N bond, and hence greater ability to quench the fluorescence in the Cd(II) complex.     

Variations in the coordination environment of Co, Cu and Zn complexes prepared from a tridentate (imino)pyridine ligand and their structural comparisons

The variations in the coordination environment of Co(II), Cu(II) and Zn(II) complexes with the neutral, tridentate ligand bis[1-(cyclohexylimino)ethyl]pyridine (BCIP) are reported. Analogous syntheses were carried out utilizing either the M(BF₄)₂ · xH₂O or MCl₂ · xH₂O metal salts (where M = Co(II), Cu(II) or Zn(II)) with one equivalent of BCIP. When the hydrated metal starting material was used, cationic, octahedral complexes of the type [M(BCIP)₂]²⁺ were isolated as the tetrafluoroborate salt (4, 5). Conversely, when the hydrated chloride metal salt was used as the starting material, only neutral, pentacoordinate [M(BCIP)Cl₂] complexes (1-3) formed. All complexes were characterized by X-ray diffraction studies. The three complexes that are five coordinate have distortions due mainly to the pyridine di-imine bite angle. The [Cu(BCIP)Cl₂] (2) also exhibits deviations in the Cu(II)-Cl bond distances with values of 2.4242(9) and 2.2505(9) Å, which are not seen in the analogous Zn(II) and Co(II) structures. Similarly, the two six coordinate complexes (5, 6) are also altered by the ligand frame bite angle giving rise to distorted octahedral geometries in each complex. The [Cu(BCIP)₂](BF₄)₂ (6) also exhibits Cu(II)-N_imine bond lengths that are on average 0.14 Å longer than those found in the analogous 5 coordinate complex, [Cu(BCIP)Cl₂]. In addition to X-ray analysis, all complexes were also characterized by UV/Vis and IR spectroscopy with ¹H NMR spectroscopy being used for the analysis of the Zn(II) analogue (3).     

Chitin nanofibrils for rapid and efficient removal of metal ions from water system

Joint mechanical defibrillation was successfully used to downsize chitin micro-particles (CMP) into nanofibrils without changing its chemical or crystalline structure. The fine chitin nanofibrils (CNF) bearing width of about 50 nm and length of more than 1 μm were then developed as heavy metal ion sorbents. The uptake performance of CNF dependent on pH, ionic concentration, time, and temperature was investigated. Results show that fixation amount of Cd(II), Ni(II), Cu(II), Zn(II), Pb(II), Cr(III) on CNF was up to 2.94, 2.30, 2.22, 2.06, 1.46, and 0.31 mmol/g, respectively, much higher than CMP due to high specific surface area and widely distributed pores of CNF. Adsorption kinetics of CMP and CNF followed pseudo-second-order model and Freundlich isotherm although CNF exhibited higher rate constant and sorption capacity than that of CMP. The defibrillated CNF is renewable, feasible, easily recyclable, and is thought as good candidate for heavy metal ion treatment due to their low sorption energy, rapid and efficient uptake capacity.     

Anaerobic digestion of cattail with rumen culture in the presence of heavy metals

The anaerobic digestion of cattail by rumen cultures in the presence of Cu(II), Cd(II) or Cr(VI) was investigated in this study. Three cases were respectively observed for the different metal dosages: promoted cattail degradation and methane production at a low heavy metal concentration, e.g., Cu(II) 2.4 mg/l, Cd(II) 1.6 mg/l, Cr(VI) 4.0 mg/l; reduced cattail degradation efficiency and methane production at a middle metal level; a severe inhibition to the cattail degradation at a high heavy metal dosage. The inhibition kinetics of Cu(II) on the digestion of cattail by rumen cultures was also analyzed and a simplified Andrews equation was used to describe such an inhibition. The inhibition constants for Cu(II) on the degradation of cattail, production of volatile fatty acids and formation of methane were estimated as 7.4, 9.5 and 6.4 mg/l, respectively. Comparative experimental results suggest that the order of toxicity degree of the tested metals on the rumen cultures was: Cd(II) > Cu(II) > Cr(VI).     

Tailoring size and structural distortion of Fe3O4 nanoparticles for the purification of contaminated water

Fe₃O₄ magnetic nanoparticles with different particle sizes were synthesized using two methods, i.e., a co-precipitation process and a polyol process, respectively. The atomic pair distribution analyses from the high-energy X-ray scattering data and TEM observations show that the two kinds of nanoparticles have different sizes and structural distortions. An average particle size of 6–8 nm with a narrow size distribution was observed for the nanoparticles prepared with the co-precipitation method. Magnetic measurements show that those particles are in ferromagnetic state with a saturation magnetization of 74.3 emu g⁻¹. For the particles synthesized with the polyol process, a mean diameter of 18–35 nm was observed with a saturation magnetization of 78.2 emu g⁻¹. Although both kinds of nanoparticles are well crystallized, an obviously higher structural distortion is evidenced for the co-precipitation processed nanoparticles. The synthesized Fe₃O₄ particles with different mean particle size were used for treating the wastewater contaminated with the metal ions, such as Ni(II), Cu(II), Cd(II) and Cr(VI). It is found that the adsorption capacity of Fe₃O₄ particles increased with decreasing the particle size or increasing the surface area. While the particle size was decreased to 8 nm, the Fe₃O₄ particles can absorb almost all of the above-mentioned metal ions in the contaminated water with the adsorption capacity of 34.93 mg/g, which is ∼7 times higher than that using the coarse particles. We attribute the extremely high adsorption capacity to the highly-distorted surface.     

Ecophysiological responses of the mangrove Avicennia marina to trace metal contamination

Growth responses of Avicennia marina seedlings to contamination by different concentrations of two essential (Cu, Zn) and two non-essential (Pb, Hg) trace metals were studied under glasshouse conditions. We tested the hypothesis that soil retention and root ultrafiltration would exclude most of the trace metals, and that those that are absorbed and translocated to the shoots would interfere with plant performance and be excreted via leaf salt glands. One-month-old seedlings were subjected to Cu, Zn, Pb and Hg at concentrations of 0, 40, 80, 120 and 160 μg g⁻¹ sediment for 12 months in a randomized complete block design (n = 6). Photosynthesis was measured at the end of 12 months of trace metal exposure with a portable gas exchange system and chlorophyll fluorescence with a pulse-modulated fluorometer. After morphometric measurements, plants were harvested and analyzed for Cu, Zn, Pb and Hg by atomic absorption spectroscopy. Total dry biomass decreased with increasing trace metal concentration for all metals. In the 160 μg g⁻¹ Cu, Zn, Hg and Pb treatments, total biomass was significantly lower than the control value by 43%, 37%, 42% and 40%, respectively. Decreases in plant height and number of leaves followed trends similar to those for total biomass and ranged from 37% to 60%, compared to the controls. Decreases in chlorophyll content in the trace metal treatments ranged from 50% to 58% compared to the control. Carbon dioxide exchange, quantum yield of photosystem II (PSII), electron transport rate (ETR) through PSII and photosynthetic efficiency of PSII (F_v/F_m) were highest in the control treatment and decreased with increasing trace metal concentrations. Decreases in CO₂ exchange in the 160 μg g⁻¹ treatments for all trace metals ranged from 50% to 60%. Concentrations of all trace metals in plant organs increased with increasing metal concentrations and were higher in roots than in shoots, with concentrations of Cu and Zn being considerably higher than those of Hg and Pb. Qualitative elemental analyses and X-ray mapping of crystalline deposits over the glands at the leaf surfaces indicated that Cu and Zn were excreted from the salt glands, while Hg and Pb were absent, at least being below the limits of detection. These results demonstrate that growth processes are sensitive to trace metals and therefore can be considered as a cost of metal tolerance, but salt glands of this mangrove species do contribute eliminating at least part of physiologically essential trace metals if taken up in excess.