Uptake of 203Hg++ and 115 mCd++ by Chlamydomonas reinhardi under various conditions

The uptake of radioactively labeled mercury and cadmium ions by living and dead cells of Chlamydomonas reinhardi WT⁺ was measured at 25 °C under minimal and optimal conditions (dark/nitrogen or light/air, respectively). In each case, incorporation was completely independent of external energy. Living and dead cells incorporated almost the same amount of the added heavy metal ions; after about 4 to 8 hours, saturation was obtained. Furthermore, the distribution of mercury in the system of algea/culture medium/gas phase and the amount of mercury and cadmium adsorbed by cells were studied.     

Fate of cadmium in Elodea canadensis

Elodea canadensis is a submersed macrophytes, widely distributed in stormwater treatment ponds and able to remove heavy metals from water. This study examines the Cd uptake, translocation, and efflux patterns in Elodea. Several experiments were set up in a climate chamber. To study the root and shoot Cd uptake, living and dead roots and shoots were treated with (109)Cd in one- and two-compartment systems. Furthermore, to examine Cd translocation and distribution, either roots or shoots were treated with (109)Cd. Finally, the efflux of Cd from roots and shoots, respectively, to the external solution was studied after loading whole plants with (109)Cd. Results from the two compartment studies show that Cd is accumulated via direct uptake by both roots and shoots of Elodea. The Cd accumulation proved not to be metabolically dependent in Elodea, and the apoplastic uptake in particular was decreased by Cd pretreatment. In one week, up to 23% of the root uptake was translocated to the shoots, while about 2% of the Cd accumulated by shoots was translocated to the roots. Thus, slight dispersion of Cd is possible, while metal immobilization will not be directly mediated via the Elodea plant. The efflux experiment proved that both shoots of dead plants and roots of living plants had a faster efflux than did shoots of living plants. This information is relevant for an understanding of the fate of Cd in stormwater treatment ponds with Elodea.     

Municipal landfill leachate treatment for metal removal using water hyacinth in a floating aquatic system.

Experiments were carried out to investigate the ability of water hyacinth (Eichhornia crassipes) to remove five heavy metals (cadmium, chromium, copper, nickel, and lead) commonly found in leachate. All experiments were conducted in batch reactors in a greenhouse. It was found that living biomass of water hyacinth was a good accumulator for copper, chromium, and cadmium. The plants accumulated copper, chromium, and cadmium up to 0.96, 0.83, and 0.50%, respectively, of their dry root mass. However, lead and nickel were poorly accumulated in water hyacinth. Also, nonliving biomass of water hyacinth dry roots showed ability to accumulate all metals, except Cr(VI), which was added in anionic form. The highest total metal sorption by nonliving dry water hyacinth roots was found to take place at pH 6.4. The current research demonstrates the potential of using water hyacinth for the treatment of landfill leachate containing heavy metals.     

Tolerance and uptake of heavy metals by Trichoderma atroviride isolated from sludge

A strain of Trichoderma atroviride, isolated from sewage sludge obtained from a water treatment plant located in Madrid (Spain), has been studied for tolerance to heavy metals (copper, zinc and cadmium) and for its capacities to uptake these metals. It was found that this fungus is capable of surviving high metal concentrations, apparently as a result of the natural selection of resistant cells. Also, growth and metal uptake have been assayed in samples where the fungus was cultured in the presence of a single metal and in the presence of a combination of two or three cations, where additive and synergistic interactions were observed. Finally, metal uptake by this strain has been studied under different nutritional conditions. It was found that the highest values of metals removal were achieved for autolysed mycelia while the lowest levels were observed in the presence of glucose.     

Bioconcentration of cadmium in water hyacinth (Eichhornia crassipes) in relation to thiol group content

To study the bioconcentration of cadmium in water hyacinth, the plants were exposed to water containing 2 microg Cd2+/ml for extended periods of time. Three strains from several exposures during a 30-day period were sampled for the analyses of cadmium and thiol group. The data showed that the plant concentrates cadmium mainly in the roots and that the cadmium uptake is proportional to the increase of the thiol group content. The latter suggests the possibility of using the thiol group content to assess the bioconcentration of heavy metal ions in water hyacinth and as a general parameter for monitoring the heavy metal pollution of water. A simple two-compartmental model was used to simulate the kinetics of cadmium uptake. The calculated bioconcentration factor matches the one derived directly from experimental data, indicating the adequacy of the model.     

Cadmium uptake and translocation in tumbleweed (Salsola kali), a potential Cd-hyperaccumulator desert plant species: ICP/OES and XAS studies

Cadmium is a heavy metal, which, even at low concentrations, can be highly toxic to the growth and development of both plants and animals. Plant species vary extensively in their tolerance to excess cadmium in a growth medium and very few cadmium-tolerant species have been identified. In this study, tumbleweed plants (Salsola kali) grown in an agar-based medium with 20 mgl(-1) of Cd(II) did not show phytotoxicity, and their roots had the most biomass (4.5 mg) (P < 0.05) compared to the control plants (2.7 mg) as well as other treated plants. These plants accumulated 2696, 2075, and 2016 mg Cd kg(-1) of dry roots, stems, and leaves, respectively. The results suggest that there is no restricted cadmium movement in tumbleweed plants. In addition, the amount of Cd found in the dry leaf tissue suggests that tumbleweed could be considered as potential cadmium hyperaccumulating species. X-ray absorption spectroscopy studies demonstrated that in roots, cadmium was bound to oxygen while in stems and leaves, the metal was attached to oxygen and sulfur groups. This might imply that some small organic acids are responsible for Cd transport from roots to stems and leaves. In addition, it might be possible that the plant synthesizes phytochelatins in the stems, later coordinating the absorbed cadmium for transport and storage in cell structures. Thus, it is possible that in the leaves, Cd either exists as a Cd-phytochelatin complex or bound to cell wall structures. Current studies are being performed in order to elucidate the proposed hypothesis.     

In situ cadmium reclamation by freshwater bivalve Lamellidens marginalis from an industrial pollutant-fed river canal

The biofilter potential of the freshwater bivalve, Lamellidens marginalis was examined in cage experiments conducted in a river canal (Ichhapore, 24-Parganas, West Bengal, India) receiving industrial effluents from steel and metal factories as well as from an ordinance factory. Cadmium is one of the major contaminants in this river canal. Lamellidens collected from pollution free natural ponds, were sorted into three size groups (large: 59+/-3.2 g, 10+/-2.3 cm; medium: 30+/-2 g, 6+/-1.7 cm and small: 13+/-1.5 g, 4+/-1.2 cm) were held in cages at three different sites along a cadmium concentration gradient. Concentrations of cadmium were measured from water, sediment and different tissues of Lamellidens at weekly intervals using atomic absorption spectrophotometric methods. Cadmium uptake by Lamellidens in all media were highly concentration dependent in both summer and winter months. For all three size groups, cadmium uptake was maximum in the gills at the beginning of experiment, and liver at the later phase. Cadmium uptake was maximum in the small bivalves and minimum in the large bivalves groups. Cadmium uptake was 11-67% higher during summer than during the monsoon season for all tissues and size groups. Estimation of concentration factor revealed that tissues were saturated with cadmium during the 13-14th week after Lamellidens introduction during summer, but remained unsaturated during the monsoon season. It is concluded that Lamellidens might be considered as an efficient biofilter for reclamation of aquatic environment having sub-lethal concentrations of cadmium.     

Factors controlling the bioaccumulation of mercury and methylmercury by the estuarine amphipod Leptocheirus plumulosus

The bioaccumulation of inorganic mercury (HgI) and monomethylmercury (MMHg) by benthic organisms and subsequent trophic transfer couples the benthic and pelagic realms of aquatic systems and provides a mechanism for transfer of sedimentary contaminants to aquatic food chains. Experiments were performed to investigate the bioavailability and bioaccumulation of particle-associated HgI and MMHg by the estuarine amphipod Leptocheirus plumulosus to further understand the controls on bioaccumulation by benthic organisms. HgI and MMHg are particle reactive and have a strong affinity for organic matter, a potential food source for amphipods. Microcosm laboratory experiments were performed to determine the effects of organic matter on Hg bioaccumulation and to determine the major route of Hg uptake (i.e. sediment ingestion, uptake from water/porewater, or uptake from 'food'). Amphipods living in organic-rich sediment spiked with Hg accumulated less Hg than those living in sediments with a lower organic matter content. Feeding had a significant impact on the amount of HgI and MMHg accumulated. Similarly, amphipods living in water with little organic matter accumulated more Hg than those living in water with a greater percentage of organic matter. MMHg was more readily available for uptake than HgI. Experimental results, coupled with results from a bioaccumulation model, suggest that accumulation of HgI and MMHg from sediment cannot be accurately predicted based solely on the total Hg, or even the MMHg, concentration of the sediment, and sediment-based bioaccumulation factors. All routes of exposure need to be considered in determining the accumulation of HgI and MMHg from sediment to benthic invertebrates.     

Biosorption of cadmium and copper contaminated water by Scenedesmus abundans

Experiments were conducted comparing the individual removals of cadmium and copper from water via biosorption using Scenedesmus abundans, a common green algae, to removal in a multi-component system to determine competitive effects, if any, between the metals. The goal was to characterize the biological treatment of water contaminated with heavy metals using live aquatic species. In addition, experiments were performed to measure cell viability as a function of metal concentration and also to compare metal removal using living species to that using nonliving ones. It was shown that, while both living and nonliving S. abundans removed cadmium and copper from water, living algae significantly outperformed nonliving algae. Further, in characterizing biosorption by three concentrations of live S. abundans, capacity curves were created comparing the metal biosorbed per mass algae to the initial metal concentration in solution. The algae concentration was not a factor in the biosorption of either metal individually, such that the capacity of the algae for the metal increased with decreasing algae concentration. At the lowest algae concentration considered, competitive effects were observed at copper and cadmium concentrations above 4 mg/l each. At the highest algae concentration considered, no competitive effects were observed in the range of cadmium and copper concentrations studied (1-7 mg/l). It was concluded that biological treatment of heavy metal contaminated water is possible and that at adequately high algae concentrations, multi-component metal systems can be remediated to the same level as individual metals.     

Metabolic rate and uptake and loss of cadmium from food by the fish Noemacheilus barbatulus L. (stone loach)

Fish, Noemacheilus barbatulus (stone loach), of different body weights were used to study rates of uptake and loss of cadmium during and after dietary exposure. Fish were kept singly in a continuous-flow system, and fed tubificid worms. The worms had a range of cadmium levels, but all levels were below that needed to cause acute lethal toxicity in the fish. Body weight affected both the maintenance ration and the amount of food consumed ad libitum, but the exponent for body weight (0.78+/-0.04), relating body weight to food consumption, was unaffected by either temperature or the size of feeding ration. The cadmium content of the worms did not affect the size of the maintenance ration. Metal burden in fish changed rapidly both during and after exposure. After exposure, the cadmium burden of starved fish usually declined more rapidly than in fed fish. A 58-fold increase in cadmium content in the food produced a 28% increase of body burden in the fish, and there was no evidence for biomagnification. Maintenance ration and ration ad libitum and rates of uptake and loss of cadmium increased with temperature within the range 8-18 degrees C, but exposure to cadmium at 16 degrees C yielded a higher asymptotic body burden than either 8 degrees C or 18 degrees C. Rate constants for loss of cadmium after exposure appear to be lower than for loss during exposure. Rates of uptake and loss of cadmium vary with metabolic rate. A maximum in the rate of oxygen consumption was measured at 16 degrees C, above which the rate dropped, presumably due to stress. The exponent for body weight was unaffected by activity or temperature. Body weight of fish appeared to affect both the rates of uptake and loss of cadmium, and feeding rations and respiration to the same extent: body weight exponents were not dissimilar.     

Zinc-copper interaction affecting plant growth on a metal-contaminated soil

In order to assess the effects of metal interactions on plant growth, a greenhouse experiment was conducted, in which spring barley was grown for 48 days in a soil to which cadmium, copper, lead and zinc were added singly and in combination. Plant growth was measured as shoot and root dry matter production. At the end of the experiment the plant material was analysed for metal uptake and the soil was extracted with CaCl(2) solution, to measure the plant-available metal content. The most consistent effect on plant growth was an interaction between copper and zinc, which was also important in determining uptake of these metals and the amounts extractable with CaCl(2) solution. An analysis of the underlying mechanism led to the conclusion that the growth of barley was controlled principally by the amount of plant-available zinc, which depended on the amounts of both added zinc and added copper. The effect of the added copper was to increase the toxicity of the added zinc.     

Unterschiedliche Aufnahme von Cadmium in Saccharomyces- BZW. Rhodotorula-Zellen

The uptake of Cadmium-115m in two strains of Saccharomyces and one strain of Rhodotorula cells was measured in the presence and absence of glucose.It was shown that the uptake of cadmium in the absence of glucose is about the same in all three strains.In the presence of glucose one can find an about ten fold higher uptake in Saccharomyces than in Rhodotorula cells.It was concluded from these and other results than cadmium is transported in Rhodotorula cells by diffussion, in Saccharomyces cells by an energy-dependent transport system.These results declare the great difference of the sensitivity of these strains against cadmium and correct a misinterpretation in an earlier publication (1).     

The fate of trace metals during the metamorphosis of chironomids (diptera, chironomidae)

The fate of the trace metals zinc, cadmium and copper during the metamorphosis of chironomids was studied under field and experimental conditions. Field observations demonstrated a significant decrease in the trace metal body burden of larvae and imagines of Stictochironomus histrio Fabricius. No such difference were noted between successive developmental stages of Chironomus anthracinus Zett. The exuviae of both species contained small amounts of trace metals. Experiments, in which larvae of S. histrio and C. riparius Meigen were individually exposed, showed that larvae of both species accumulated substantial amounts of zinc and cadmium. For these metals, a transfer to pupae and imagines occurred. However, pupae had a lower body burden than larvae, and imagines a lower body burden than the pupae. Copper was also accumulated in the larvae, but it was excreted almost completely before the pupal stage. Elimination pathways of the trace metals during metamorphosis and the ecotoxicological consequences of trace metal transfer are discussed.     

Cadmium effects on the fitness-related traits and antioxidative defense of Lymantria dispar L. larvae

Cadmium, like many other pollutants, is nondegradable and can be accumulated by Lymantria dispar at a level that affects fitness components, physiology, and development, which could indicate presence of environment pollution by heavy metals. The cadmium effect on fitness-related traits in the third, fourth, fifth, and sixth instar of L. dispar L. was determined. Furthermore, activities of the following antioxidative defense components after the larvae had been fed on the artificial cadmium-supplemented diet (50 μg Cd/g dry food) were assessed: superoxide dismutase (SOD), catalase (CAT), ascorbate peroxidase (APOX), total glutathione amount (GSH), glutathione-S-transferase (GST), glutathione reductase (GR), and the amount of free sulfhydryl (SH) groups. Statistically significant delay of development in the fourth, fifth, and sixth instar and decrease of the larval mass in the third and fourth instar were estimated after the exposure to cadmium through food in comparison to the control. There were no changes in SOD activity of cadmium-treated larvae. Significantly lower CAT, APOX, and GR activities were recorded in the third, fifth, and in the third instar, respectively. At the same time, higher activity was recorded in the sixth instar, while GST activity was higher in the third. GSH content was significantly lower during all instars after treatment but the amount of SH groups was higher in older larvae. The strategy of antioxidative defense and the adjustment or modulation of fitness-related traits in presence of cadmium was dependent on the age of larvae in L. dispar, which might be used in early metal risk assessment in Lepidoptera and other insects.     

Characteristics of different molecular weight fractions of organic matter in landfill leachate and their role in soil sorption of heavy metals.

We have characterised two kinds of municipal landfill leachates derived from 'old' and 'young' municipal waste landfills on the basis of the molecular weight distribution of the constituents, taking into account that the great variety of leachate constituents prevents any evaluation of the fate and of the role played by each component in the environmental impact. In the sample S1 (old leachate), the constituents were distributed over a wider range of molecular weights; high molecular weight fractions were present. In sample S2 (young leachate), the fractions are actually narrower at the lower molecular weights. The high molecular weight fractions of old leachates are found to be complex structures formed by condensed nuclei of carbons substituted by functional groups containing nitrogen, sulphur and oxygen atoms; the low molecular weight fractions of leachates are, instead, characterised by linear chains substituted by oxygenated functional groups such as carboxyl and/or alcoholic groups. After characterising each fraction we studied the role played by these fractions in the soil's capability for retaining heavy metals [copper (Cu) and cadmium(Cd)]. The Cd uptake increases only on the soil treated with sample S1 characterised by a higher pH value and by the presence of high molecular weight fractions. The Cu uptake also increases on the soil treated with sample S2, characterised by the sole presence of low molecular weight fractions. On the other hand, the metal adsorption tests performed on soil treated with the single fractions show that the amount of Cu and Cd retained by soil treated with the high molecular weight fractions of sample does not increase after 72 h of treatment and that the amount of Cu retained by the low molecular weight fractions of sample S1 and by the fractions of sample S2 increases, but does not justify the amount retained by soil treated with the total leachates.     

Metal uptake capacity of modified Saccharomyces pastorianus biomass from different types of solution

In this paper, we investigate the effect of different biomass pretreatments on metal ion uptake by various biosorbents. Heat-treated as well as caustic-treated and ground biomass of Saccharomyces pastorianus was used to remove copper, lead and cadmium from various solutions. Untreated yeast was used as the control sample. The effect of yeast modification on sorption capacity depended on the different types of heavy metal ions and whether they were in single- or multi-component solutions. The highest uptake of copper and lead from a single-metal solution was obtained from heat-treated cells. Ground biomass was the most efficient at cadmium removal. However, the sorption capacity of the modified biomass did not improve when metal ions were removed from multi-component solutions. Indeed, the results in this paper show that optimizing metal removal from single-cation solutions can lead to decreased sorption capacity in multi-component solutions. Therefore, while adjusting the procedure of biomass modification, not only the nature of the metal ion being sorbed but also the chemical composition of the metal ion solution should be taken into account.     

The influence of humic acids on the phytoextraction of cadmium from soil

Cadmium poses a major environmental and human health threat because of its constant release through anthropogenic activities. A need, therefore, exists for cost-effective remediation procedures. Phytoremediation, the use of plants to extract contaminants from soils and groundwater, has revealed great potential. However, it is limited by the fact that plants need time, nutrient supply and, moreover, have a limited metal uptake capacity. Synthetic chelators have shown positive effects in enhancing heavy metal extraction through phytoremediation, but they have also revealed a vast number of negative side-effects. The objective of this research was to investigate the use of humic acids as an alternative to synthetic chelators. Humic acids were applied to a cadmium-contaminated soil at various dosages, and the uptake of cadmium into Nicotiana tabacum SR-1 was determined in relation to the amounts of total and bioavailable cadmium in the soil. It was found that the theoretical bioavailability of cadmium, as determined by diethylenetriaminepentaacetic acid (DTPA) extraction, did not change, but its plant uptake was enhanced significantly, in some cases up to 65%. Humic acids added at a rate of 2 g kg(-1) soil increased the cadmium concentration in the shoots from 30.9 to 39.9 mg kg(-1). A possible reason for this enhancement is the decrease in pH, resulting in higher cadmium availability. Another possibility taken into account is that plants may take up cadmium complexes with humic acid fragments, which result from microbiological degradation or, self-dissociation.     

Cadmium and methylmercury bioaccumulation by nymphs of the burrowing mayflyHexagenia rigida from the water column and sediment

Based on a three compartment microcosm-water column, natural sediment,Hexagenia rigida nymphs-an experimental study was set up to compare cadmium (Cd) and methylmercury (MeHg) bioaccumulation by a burrowing mayfly species, after exposure via the water column or the sediment as initial contamination sources. Results from a wide concentration range for each exposure condition revealed very marked differences between the two metals: MeHg was readily accumulated from the two contamination sources, leading to important metal concentrations in the nymphs after the 2 weeks’ exposure; Cd bioaccumulation, on the other hand, was negligible when the metal was added to the water compartment, even though significant transfers were observed from the sediment source. The average Cd concentrations in the nymphs were proportional to the sediment contamination levels. Turbidity measurements in the water column, reflecting the bioturbation activity of the nymphs, revealed that the effect of Cd was significant, but only when the metal was initially added to the sediment. The results are discussed according to the uptake routes and the structural and functional properties of the biological barriers involved (gills and gut).     

Heavy metal concentrations in soil and earthworms in a floodplain grassland

We determined accumulated heavy metal concentrations (Cd, Pb, Cu, Zn) of earthworms in moderately contaminated floodplain soils. Both soil and mature earthworms were sampled before and after flooding and earthworm species were identified to understand species specific differences in bioconcentration. Accumulated metal concentrations in floodplain earthworms differed before and after flooding. Differences in uptake and elimination mechanisms, in food choice and living habitat of the different earthworm species and changes in speciation of the heavy metals are possible causes for this observation. Regression equations taken from literature, that relate metal accumulation by earthworms in floodplains as a function of metal concentration in soil, performed well when all species specific data were combined in an average accumulation, but did not address differences in accumulation between earthworm species.     

The marine macroalga Cystoseira baccata as biosorbent for cadmium(II) and lead(II) removal: kinetic and equilibrium studies

This work reports kinetic and equilibrium studies of cadmium(II) and lead(II) adsorption by the brown seaweed Cystoseira baccata. Kinetic experiments demonstrated rapid metal uptake. Kinetic data were satisfactorily described by a pseudo-second order chemical sorption process. Temperature change from 15 to 45 degrees C showed small variation on kinetic parameters. Langmuir-Freundlich equation was selected to describe the metal isotherms and the proton binding in acid-base titrations. The maximum metal uptake values were around 0.9 mmol g(-1) (101 and 186 mg g(-1) for cadmium(II) and lead(II), respectively) at pH 4.5 (raw biomass), while the number of weak acid groups were 2.2 mmol g(-1) and their proton binding constant, K(H), 10(3.67) (protonated biomass). FTIR analysis confirmed the participation of carboxyl groups in metal uptake. The metal sorption was found to increase with the solution pH reaching a plateau above pH 4. Calcium and sodium nitrate salts in solution were found to affect considerably the metal biosorption.