Large Amounts Of Heavy Metals Research Articles

Modeling zinc regulation in small mammals

Due to large zinc discharges into the global environment, both terrestrial and aquatic environments have been polluted with zinc. The embanked floodplains of the lower Rhine River in the Netherlands contain large amounts of heavy metals, including zinc. These large amounts of heavy metals may pose risks to flora and fauna by accumulation in food webs, and risk assessment may be required. However, toxicokinetic models for zinc metabolism in mammalian wildlife species are currently lacking. The present study describes the development of a zinc kinetics model that predicts internal zinc concentrations in small mammals by modeling zinc absorption and excretion dependent on the dietary zinc intake using adapted Michaelis-Menten equations. The equations were parameterized based on experimental data reported in the scientific literature. Within the dietary zinc range of 3 to 104 mg/kg dry weight, the model predicts internal zinc concentrations and shows that the internal zinc is regulated within this range. Outside this range, the model could not be calibrated due to a lack of data. Validation of the model with four small mammal species living in an embanked floodplain along a distributary of the Rhine River illustrated that the model predicts internal zinc concentrations differing up to a factor of 1.6 (Common shrew) to 1.7 (Common vole) from field measurements.

Use of fly ash, phosphogypsum and red mud as a liner material for the disposal of hazardous zinc leach residue waste

Increasing amounts of residues and waste materials coming from industrial activities in different processes have become an increasingly urgent problem for the future. The release of large quantities of heavy metals into the environment has resulted in a number of environmental problems. The present study investigated the safe disposal of the zinc leach residue waste using industrial residues such as fly ash, phosphogypsum and red mud. In the study, leachability of heavy metals from the zinc leach residue has been evaluated by mine water leaching procedure (MWLP) and toxicity characteristic leaching procedure (TCLP). Zinc removal from leachate was studied using fly ash, phosphogypsum and red mud. The adsorption capacities and adsorption efficiencies were determined. The adsorption rate data was analyzed according to the pseudo-second-order kinetic, Elovich kinetic and intra-particle diffusion kinetic models. The pseudo-second-order kinetic was the best fit kinetic model for the experimental data. The results show that addition of fly ash, phosphogypsum and red mud to the zinc leach residue drastically reduces the heavy metal content in the leachate and could be used as liner materials.

Typical pollutants in bottom ashes from a typical medical waste incinerator.

Incineration of medical waste (MW) is an important alternative way for disposal of this type of hazardous waste, especially in China because of the outbreak of severe acute respiratory syndromes (SARs) in 2003. Thus, far, fly ash has received much attention but less attention has been paid to bottom ash. In this study, bottom ash samples were collected from a typical MW incinerator, and typical pollutants including heavy metals and polycyclic aromatic hydrocarbons (PAHs) in the ash were examined. X-ray fluorescence spectroscopy results indicated that CaO, SiO2 and Al2O3 were the main components of the bottom ash. Inductively coupled plasma-optical emission spectroscopy showed that the ash contained large amounts of heavy metals, including Zn, Ti, Ba, Cu, Pb, Mn, Cr, Ni and Sn. Most of the heavy metals (e.g., Ba, Cr, Ni, and Sn) presented in the residual fraction; whereas Mn, Pb and Zn presented in Fe–Mn oxides fraction, and Cu in organic-matter fraction. Toxicity characteristic leaching procedure tests indicated that the leached amounts of heavy metals were well below the limits. The sum of 16 US EPA priority PAHs (ΣPAHs) varied from 10.30 to 38.14 mg kg−1, and the total amounts of carcinogenic PAHs ranged between 4.09 and 16.95 mg kg−1, exceeding the limits regulated by several countries. This research provides basic information for the evaluation of the environmental risk of MW incinerator bottom ash.

Simultaneous removal of Cu, Mn and Zn from drinking water with the use of clinoptilolite and its Fe-modified form

Zeolites have been widely used in water treatment and especially clinoptilolite, due to its low cost and high abundance. It has large cation-exchange capacity and is capable of removing large quantities of heavy metals from contaminated water samples. By loading the surface of clinoptilolite with amorphous Fe-oxide species, a total improvement in adsorption capacity could be achieved. Thus, the Clin–Fe oxide system is capable of adsorbing significantly higher heavy metal concentrations than untreated clinoptilolite with simultaneous noticeable decrease in water hardness. Batch adsorption experiments have shown that Clin–Fe system has very large Cu, Zn and Mn adsorption capacity and for most of the cases the treated water samples were suitable for human consumption or agricultural use. New experiments were conducted to study the effectiveness of clinoptilolite and of the Clin–Fe system in removal of Cu, Mn, Zn, present simultaneously in water samples, so that the study of metal–sorbent chemical behavior and of the adsorption selectivity would be feasible. Desorption of metals was also examined and an integrated approach of the effectiveness of such materials in drinking water treatment is presented.

Implications of metal accumulation mechanisms to phytoremediation

Trace elements (heavy metals and metalloids) are important environmental pollutants, and many of them are toxic even at very low concentrations. Pollution of the biosphere with trace elements has accelerated dramatically since the Industrial Revolution. Primary sources are the burning of fossil fuels, mining and smelting of metalliferous ores, municipal wastes, agrochemicals, and sewage. In addition, natural mineral deposits containing particularly large quantities of heavy metals are found in many regions. These areas often support characteristic plant species thriving in metal-enriched environments. Whereas many species avoid the uptake of heavy metals from these soils, some of them can accumulate significantly high concentrations of toxic metals, to levels which by far exceed the soil levels. The natural phenomenon of heavy metal tolerance has enhanced the interest of plant ecologists, plant physiologists, and plant biologists to investigate the physiology and genetics of metal tolerance in specialized hyperaccumulator plants such as Arabidopsis halleri and Thlaspi caerulescens. In this review, we describe recent advances in understanding the genetic and molecular basis of metal tolerance in plants with special reference to transcriptomics of heavy metal accumulator plants and the identification of functional genes implied in tolerance and detoxification. Plants are susceptible to heavy metal toxicity and respond to avoid detrimental effects in a variety of different ways. The toxic dose depends on the type of ion, ion concentration, plant species, and stage of plant growth. Tolerance to metals is based on multiple mechanisms such as cell wall binding, active transport of ions into the vacuole, and formation of complexes with organic acids or peptides. One of the most important mechanisms for metal detoxification in plants appears to be chelation of metals by low-molecular-weight proteins such as metallothioneins and peptide ligands, the phytochelatins. For example, glutathione (GSH), a precursor of phytochelatin synthesis, plays a key role not only in metal detoxification but also in protecting plant cells from other environmental stresses including intrinsic oxidative stress reactions. In the last decade, tremendous developments in molecular biology and success of genomics have highly encouraged studies in molecular genetics, mainly transcriptomics, to identify functional genes implied in metal tolerance in plants, largely belonging to the metal homeostasis network. Analyzing the genetics of metal accumulation in these accumulator plants has been greatly enhanced through the wealth of tools and the resources developed for the study of the model plant Arabidopsis thaliana such as transcript profiling platforms, protein and metabolite profiling, tools depending on RNA interference (RNAi), and collections of insertion line mutants. To understand the genetics of metal accumulation and adaptation, the vast arsenal of resources developed in A. thaliana could be extended to one of its closest relatives that display the highest level of adaptation to high metal environments such as A. halleri and T. caerulescens. This review paper deals with the mechanisms of heavy metal accumulation and tolerance in plants. Detailed information has been provided for metal transporters, metal chelation, and oxidative stress in metal-tolerant plants. Advances in phytoremediation technologies and the importance of metal accumulator plants and strategies for exploring these immense and valuable genetic and biological resources for phytoremediation are discussed. A number of species within the Brassicaceae family have been identified as metal accumulators. To understand fully the genetics of metal accumulation, the vast genetic resources developed in A. thaliana must be extended to other metal accumulator species that display traits absent in this model species. A. thaliana microarray chips could be used to identify differentially expressed genes in metal accumulator plants in Brassicaceae. The integration of resources obtained from model and wild species of the Brassicaceae family will be of utmost importance, bringing most of the diverse fields of plant biology together such as functional genomics, population genetics, phylogenetics, and ecology. Further development of phytoremediation requires an integrated multidisciplinary research effort that combines plant biology, genetic engineering, soil chemistry, soil microbiology, as well as agricultural and environmental engineering.

Contamination profiles of heavy metals, organochlorine pesticides, polycyclic aromatic hydrocarbons and alkylphenols in sediment and oyster collected from marsh/estuarine Savannah GA, USA

Inorganic compounds from natural and anthropogenic sources continuously enter the aquatic ecosystem where they pose a serious threat because of their toxicity, long time persistence, bioaccumulation, and biomagnification in the food chain (Papagiannis et al., 2004). Increased industrialization and agricultural activities contribute to their elevated levels in natural waters (Wahlberg et al., 2001). Aquatic animals accumulate large quantities of these xenobiotics, and the accumulation depends up on the intake and elimination from their body (Karadede et al., 2004). Among different aquatic organisms; clams, oysters and mussels, accumulate large quantities of heavy metals due to their habitat and feeding nature. Inorganic compounds such as heavy metals are shown to have a multitude of toxic effects such as acute syndrome and neurotoxic effects (that ultimately cause disease in brain, kidney, skin cancer, etc.). Organochlorine compounds (OCs) such as polychlorinated biphenyls (PCBs) and organochlorine pesticides (OCPs) such as hexachlorocyclohexane isomers (HCHs), chlordane compounds (CHLs), DDT and its derivatives, as well as hexachlorobenzene (HCB) have been detected in sediments and sediment-dwelling organisms from several countries (Tanabe et al., 1982; Haynes et al., 2000; Guruge and Tanabe, 2001; Loganathan et al., 2001; Senthil Kumar et al., 1999, 2001; Fillmann et al., 2002; Menone et al., 2007; Sajwan et al., 2007). Despite a 1970s ban on use of PCBs and DDTs in the USA, these compounds are ubiquitous and persistent in various environmental media and biota. Organochlorines have been reported to cause a variety of adverse effects including hormone dependent cancers, compromised reproductive fitness, and abnormal reproductive system development in wildlife and humans (Giesy and Kannan, 1998), thus they remain a cause for significant concern. Therefore, monitoring of fish and shellfish in an aquatic environment serves as an important indicator of the water quality in a given ecosystem (Fairey et al., 1997). Polycyclic aromatic hydrocarbons (PAHs) are a group of common environmental contaminants. PAHs originate from anthropogenic sources such as waste incineration, coal gasification, accidental oil spills, as well as natural processes such as fossil fuel and wood combustion (Asikainen et al., 2002; Law et al., 2002; Koh et al., 2004; The objective of BASELINE is to publish short communications on different aspects of pollution of the marine environment. Only those papers which clearly identify the quality of the data will be considered for publication. Contributors to Baseline should refer to ‘Baseline—The New Format and Content’ (Mar. Pollut. Bull. 42, 703–704).

Chenopodium: a prospective plant for phytoextraction

Leaf samples were collected from 40 accessions of Chenopodium spp. and assessed for six heavy metals (Fe, Zn, Cu, Ni, Cr and Cd) accumulation to explore the use of Chenopodium for phytoextraction of heavy metals. The results suggest that Chenopodium spp. have the ability to accumulate large quantities of heavy metals in the leaf tissues even when they are present in low concentrations in the soil. C. quinoa is a better accumulator of Ni, Cr and Cd than the rest of the species, while C. album accessions are good copper accumulators. Bioconcentration factor for chromium ranged from 0.36 (C. album “Chandanbathua”) to 6.57 (C. quinoa Ames 13719) with 13 accessions of C. quinoa scoring above the mean value. High heritability coupled with high genetic advance was recorded for Ni, Cr and Cd, which indicated a major role of additive gene action in the inheritance of these characters. Zinc showed significant positive association with iron (0.351**), nickel (0.659**), chromium (0.743**) and cadmium (0.288**). Nickel was significantly and negatively associated with copper (−0.663**), while it was positively and significantly correlated with chromium (0.682**) and cadmium (0.461**). Considering the accumulation efficiency of Chenopodium spp. with respect to heavy metals, this genus should be further explored for decontamination of metal polluted soils, with plant breeding playing an important role in evolving new plant types with higher capacity of heavy metal accumulation.

Heavy metals in coastal wetland sediments of the Pearl River Estuary, China

Sediment quality in coastal wetlands of the Pearl River Estuary was concerned since the wetlands were used for land reclamation, aquaculture and wildlife protection, and meanwhile served as one of the main ultimate sinks for large amount of heavy metals discharged from the rapidly developing Pearl River Delta. Total concentrations of heavy metal, such as Zn, Ni, Cr, Cu, Pb, and Cd, and their chemical speciation were investigated. Results showed that the sediments were significantly contaminated by Cd, Zn and Ni with concentration ranges of 2.79–4.65, 239.4–345.7 and 24.8–122.1 mg/kg, respectively. A major portion (34.6–46.8%) of Pb, Cd, and Zn was strongly associated with exchangeable fractions, while Cu, Ni and Cr were predominantly associated with organic fractions, residual, and Fe–Mn oxide. Cd and Zn would be the main potential risk and the sediment quality is no longer meeting the demand of the current wetland utilization strategies.

Potential of Borago officinalis, Sinapis alba L. and Phacelia boratus for Phytoextraction of Cd and Pb from Soil

Heavy metal phytoextraction is a soil remediation technique, which makes use of plants in removing contamination from soil. The plants must thus be tolerant to heavy metals, adaptable to soil and climate characteristics, and able to take up large amounts of heavy metals. Most of the high biomass productive plants such as, maize, oat and sunflower are plants, which do not grow in cold climates or need intensive care. In this study three “weed” plants, Borago officinalis; Sinapis alba L. and Phacelia boratus were investigated for their ability to tolerate and accumulate high amounts of Cd and Pb. Pot experiments were performed with soil containing Cd and Pb at concentrations of up to 180 mg kg−1 and 2,400 mg kg−1 respectively. All three plants showed high levels of tolerance. Borago officinalis; and Sinapis alba L. accumulated 109 mg kg−1 and 123 mg kg−1 Cd, respectively at the highest Cd spiked soil concentration. Phacelia boratus reached a Cd concentration of 42 mg kg−1 at a Cd soil concentration of 100 mg kg−1. In the case of Pb, B. officinalis and S. alba L. displayed Pb concentrations of 25 mg kg−1 and 29 mg kg−1, respectively at the highest Pb spiked soil concentration. Although the Pb uptake in P. boratus reached up to 57 mg kg−1 at a Pb spiked soil concentration of 1,200 mg kg−1, it is not suitable for phytoextraction because of its too low biomass.

Enhancing the use of waste activated sludge as bio-fuel through selectively reducing its heavy metal content

Power plant or cement kiln co-incineration are important disposal routes for the large amounts of waste activated sludge (WAS) which are generated annually. The presence of significant amounts of heavy metals in the sludge however poses serious problems since they are partly emitted with the flue gases (and collected in the flue gas dedusting) and partly incorporated in the ashes of the incinerator: in both cases, the disposal or reuse of the fly ash and bottom ashes can be jeopardized since subsequent leaching in landfill disposal can occur, or their “pozzolanic” incorporation in cement cannot be applied. The present paper studies some physicochemical methods for reducing the heavy metal content of WAS. The used techniques include acid and alkaline thermal hydrolysis and Fenton's peroxidation. By degrading the extracellular polymeric substances, binding sites for a large amount of heavy metals, the latter are released into the sludge water. The behaviour of several heavy metals (Cd, Cr, Cu, Hg, Pb, Ni, Zn) was assessed in laboratory tests. Results of these show a significant reduction of most heavy metals.

Relationships between heavy metals and iron oxides, fulvic acids, particle size fractions in urban roadside soils

Urban roadside soils are the “recipients” of large amounts of heavy metals from a variety of sources including vehicle emissions, coal burning waste and other activities. The behavior of heavy metals in urban roadside soils depends on the occurrence as well as the total amount. Accordingly, knowledge of the interactions between heavy metals and other constituents in the soil is required to judge their environmental impact. In this study, correlations of heavy metal concentrations (Pb, Zn, Cu, Ag, Se, Ni, Cr and Ba) to iron extracted using dithionite–citrate–bicarbonate (DCB) buffer (FeDCB), fulvic acids and particle size fractions were examined from the Xuzhou urban roadside soils. Heavy metals except for Cr and fulvic acids had a positive significant correlation with FeDCB, indicating these metals and fulvic acids are principally associated with the surfaces of iron oxides of the soils. Significant positive correlations were also found between the contents of fulvic acids and heavy metals, showing these heavy metals (especially for Cu, Ni and Cr) form stable complexes with fulvic acids. Such finding is of importance with regard to the increased mobilization of heavy metals, e.g., into freshwater ecosystems. Ag, Se and Cr are independent of particle size fractions because of their low concentrations of Ag and Se in the studied soils. Pb, Zn, Cu, Ba and Ag are mainly enriched in the finer soil particles (especially <16 μm).

Heavy Metals Pollution of the Atlantic Marine Environment by the Moroccan Phosphate Industry, as Observed through their Bioaccumulation in Ulva Lactuca

The Moroccan phosphate industry releases large amounts of heavy metals in the Atlantic Ocean in the surroundings of two places: Safi and Jorf Lasfar. The major waste, called phosphogypsum and composed of calcium sulphate and other additional salts, is introduced into sea water in particulate form. After dissolution of the particles, heavy metal concentrations can be influenced near the release point. Two multi-element analytical techniques were used to measure 47 element concentrations in various materials involved in the study of the phosphate pollution: Inductively Coupled Plasma Mass Spectrometry (ICPMS) and instrumental neutron activation analysis (INAA). At first, phosphate and phosphogypsum were characterized in order to recognize the overall features of the heavy metal pollution source. From the yearly amount of phosphogypsum produced by the Moroccan industry and the element concentrations in phosphogypsum, it has been possible to estimate a yearly flux of heavy metals introduced in the Atlantic Ocean. Algae were used as bio-accumulator materials of heavy metals in the marine environment, in the region of Jorf Lasfar, in order to significantly reveal the signal of the heavy metal pollution. Ulva lactuca Linnaeus was selected to assess heavy metal pollution around the waste release point. Accumulation factors were determined for 47 elements in U. lactuca, by comparing mean concentrations obtained in algae collected in non-polluted sites (background sites) and an average sea water concentration given in the literature. The ratio between the concentration in U. lactuca, collected in a polluted site to the background concentration in U. lactuca, was determined, giving an estimate of the pollution factor for the same elements by the phosphate industry. The decrease of the pollution due to the dilution in the sea water was observed as far as 6 km southward of the release point. A specific variation was observed for lead and its isotopic composition, denoting that the phosphate industry is not the only pollution source in this region. Natural processes were likely involved to induce the lead concentrations variations along the littoral.

Distribution of copper, zinc, lead and cadmium concentrations in stream sediments from the Mapocho River in Santiago, Chile

The Mapocho river, which crosses downtown Santiago, is one of the most important rivers in contact with a population of about six million inhabitants. Anthropogenic activities, industrialization, farming activities, transport, urbanization, animal and human excretions, domestic wastes and copper mining have affected the river, contaminating it and its sediments with heavy metals. Concentration and distribution of Cu, Zn, Pb and Cd were studied with the purpose of determining their bioavailability and their relation with the characteristics of the sediments. Freshly deposited seasonal sediments were collected from 0–8 cm depths from 6 locations (S 1 to S 6) along the 30-km long channel length, in the four seasons of year on the following dates: May 2001 (D 1, autumn); August 2001 (D 2, winter); October 2001 (D 3, spring) and January 2002 (D 4, summer). The dried samples were sifted to obtain the < 63-μm sediment fraction, since it has been shown that large amounts of heavy metals are bound in the fine-grained fraction of the sediment. Cu and Zn were analyzed by atomic absorption spectrophotometry and Pb and Cd by square wave anodic stripping voltammetry. The highest concentrations of Cu (2850 μg g − 1 ) were found in the northern part of the river (S 1, average D 1–D 4), near the mountains and a copper mine, and then decreased downstream to 209 μg g − 1 (S 6). Total Zn showed an irregular variation, with higher values at S 1 (1290 μg g − 1 ) and high values in some winter sampling (1384 μg g − 1 S 4, S 5–D 2). Pb showed different trends, increasing from S 1 to S 6 (17 to 61 μg g − 1 ), with the highest values in the summer samples (83 μg g − 1 , S 4–S 6, D 4), and total Cd increased slightly from mean values of 0.2 and 0.5 μg g − 1 . Partition into five fractions was made using Tessier's analytical sequential extraction technique; the residue was treated with aqua regia for recovery studies, although this step is not part of the Tessier procedure. The results show that Cu, Zn and Pb in the sediments were dependent on the sampling places along the river, and variation in two years was low (D 1–D 4). The highest values of total organic matter, carbonate and conductivity were found in S 6, which has the smallest size particles, while at S 1 the sediments were predominantly sand and contain larger amounts of silica. Cu associated with carbonate decreased gradually from 58% (1771 μg g − 1 , S 1) to 16% (32 μg g − 1 , S 6); Cu bonded to reducible fraction was almost constant (33% to 37%), and Cu associated with oxidizable fraction increased from 7% (S 1) to 34% (S 6), but copper content was lower (214 to 68 μg g − 1 ). Zn had a similar fractionation profile. However, Pb bound to oxidizable fraction did not show significant percent variation along the river (20% to 19%), but the amount bounded was 4 to 12 μg g − 1 . The residual fraction increased from 24% to 41% (5 to 25 μg g − 1 , S 1 to S 6). The distribution of Cd in the sediment was almost independent of the sampling stations and was bound to carbonate, reducible and residual fraction in similar proportion. Cu and Zn at S 1 were mainly bound to carbonates and reducible phases with 91% and 73% (2779 and 965 μg g − 1 , respectively), and with a change in the pH and/or the redox potential of the sediment–water system, these contaminants could easily enter the food chain. In S 6 the amount of Cu and Zn in these phases was 50% and 53% (100 to 313 μg g − 1 , respectively).

High exposure of Chinese mercury mine workers to elemental mercury vapor and their increased hair methylmercury levels: A preliminary report

Environmental impact resulting from mining activities is serious and ubiquitous all over the world, and it has become one of the important aspects in environmental geochemistry. The environment was seriously damaged by wastes from historical zinc smelting in Northwest Guizhou. The geochemical distributions of Pb and Zn in the different grain-size fractions of wastes indicate that the coarser particles show similar or even higher heavy metal concentrations than finer ones in the samples, although the concentrations of heavy metals tend generally to increase as the size fractions get finer. The heavy metal contents are very high, with maximum values of 31631, 57178, 2367 and 311.5 mg/kg for Pb, Zn, Cu and Cd, respectively. It is also shown that the residual fraction of Pb is less than that of Zn, accounting for 0.39%--15.75% and 14.3%--46.2%, respectively, of the total, and this is likely relative to Zn-silicate minerals formed from smelting. Although the relative partitioning of Pb and Zn is very low (0.03%-1.3.% for Pb; 0.03% --3.3% for Zn), the exchangeable fraction of the waste contains large amounts of heavy metals (1.5%--385 p,g/g for Pb; 3--590 ~tg/g for Zn). Heavy metals in exchangeable forms have the highest solubility to give the highest potential bioavailability in contrast to other chemical forms. Mineralogical study indicates that the wastes were found to be highly heterogeneous materials, dominated by quartz, feldspar, carbonatite, iron or/and aluminum vitric compounds and a few secondary mineral phases, and their contents vary with the type of smelting wastes. The secondary minerals formed from smelting and sequentially weathering are the major chemical phase for heavy metals. Complex composition of many phases and substitution of elements suggested that many of the phases were found to be non-stoichiometric compounds. Pb was found to be the main Pb phase in the wastes by precipitation or/and adsorption. The species Zn is more complex in the form of occurrence than Pb, and Zn-bearing minerals include willemite, tephrowillemite and zinalsite, and occasionally Zn can be found in the wastes, and this is a possible reason why the relative partitioning of Zn in residue fraction is higher than that of Pb. The natural releasing processes of Pb, Zn and Cd in the wastes can be primely described with minus-exponent equation and with prolongation of piling time, the contents of these heavy metals in the wastes decrease gradually. They are hazardous to environment because of their high total contents and long-time release.

Heavy Metal Adsorption by Montmorillonites Modified with Natural Organic Cations

Agricultural and industrial pollution release large amounts of heavy metals into the atmosphere, surface water, soil, and plants. The protection and restoration of soils and water contaminated with heavy metals generate a great need to develop efficient adsorbents for these pollutants. This study reports the adsorption of Pb(II) and Hg(II) by two reference montmorillonites, Wyoming (SWy‐2) and Arizona (SAz‐1), that were pretreated with various natural organic cations containing different functional groups (L‐carnitine, L‐cysteine ethyl ester, L‐cystine dimethyl ester, and thiamine cations) and with synthetic, nonfunctionalized organic cations (hexadecyltrimethylammonium [HDTMA] and phenyltrimethylammonium [PTMA] cations). Most of the organoclays adsorbed less Pb(II) than the untreated montmorillonites, with the exception of the L‐carnitine–treated montmorillonites. The carboxyl functional group on L‐carnitine was apparently effective for complexing Pb. In contrast, Hg(II) adsorption was greatly increased by several of the organic cation pretreatments. Sulfur‐containing organic functional groups enhanced Hg(II) adsorption. The synthetic organic cations PTMA and HDTMA suppressed adsorption of Pb(II) and Hg(II) because these organic cations competed with the metals for adsorption sites on the clay surfaces and lack organic functional groups capable of interacting with the heavy metals. These findings are consistent with prior understanding of organic functional group‐metal complexation reactions but go further by demonstrating that organoclays can be selectively functionalized with natural organic cations to enhance their affinity for heavy metals.

Electrochemical degradation of aqueous phenols using graphite electrode in a divided electrolytic cell

Untreated industrial effluents invariably contain large amounts of heavy metals and organics. This paper reports the electrochemical oxidation of synthetic water containing 200 ppm of phenol. Studies have been carried out in a compartmentalized cell using platinum (cathode) and graphite (anode). Electrolysis has been done for 40 h at constant applied potential of 5 V in different electrolytes, such as, NaCl (aq), NaOH (aq) and a mixture containing both NaCl (aq) and NaOH (aq) as the anolyte and acid as the catholyte. Phenol concentration decreased from the initial value of 200 to about 10 ppm.; the corresponding COD values, respectively, are ∼400 to ∼100 ppm. The reaction goes through chloro-compounds as intermediates before being mineralized. The carbon anode seems to be passivated with a thin layer of poly-phenol. A concomitant amount of hydrogen is generated during the electrolytic degradation of phenol.

Elimination of Heavy Metals from Leachates by Membrane Electrolysis

AbstractThe elimination of heavy metals from bioleaching process waters (leachates) by electrolysis was studied in the anode and cathode region of a membrane electrolysis cell at current densities of 5–20 mA/cm2 using various electrode materials. The leaching waters containing a wide range of dissolved heavy metals, were high in sulfate, and had pH values of approx. 3. In preliminary tests using a rotating disc electrode the current density‐potential curve (CPK) was recorded at a rotation velocity of 0, 1000 and 2000 rpm and a scan rate of 10 mV/s in order to collect information on the influence of transport processes on the electrochemical processes taking place at the electrodes. The electrochemical deposition‐dissolution processes at the cathode are strongly dependent on the hydrodynamics. Detailed examination of the anodic oxidation of dissolved Mn(II) indicated that the manganese dioxide which formed adhered well to the electrode surface but in the cathodic return run it was again reduced. Electrode pairs of high‐grade steel, lead and coal as well as material combinations were used to investigate heavy metal elimination in a membrane electrolysis cell. Using high‐grade steel, lead and carbon electrode pairs, the reduction and deposition of Cu, Zn, Cr, Ni and some Cd in metallic or hydroxide form were observed in an order of 10–40 % in the cathode chamber. The dominant process in the anode chamber was the precipitation of manganese dioxide owing to the oxidation of dissolved Mn(II). Large amounts of heavy metals were co‐precipitated by adsorption onto the insoluble MnO2. High‐grade steel and to some extent lead anodes were dissolved and hence were proven unsuitable as an anode material. These findings were largely confirmed by experiments using combination electrodes of coal and platinized titanium as an anode material and steel as a cathode material. With both electrode combinations and current densities of 5 or 10 mA/cm2, in the cathode region low depositions of 10–20 % Cd, 2–10% Mn, 5–20 % Zn, 1–20 % Co and 5–15 % Ni were measured. By contrast, the elimination of other metals was substantially larger: Fe 40 –60 %, Cu 20–40 %, and Cr 40–60 %. In the anode region the removal of heavy metals was in the order of 30–50%, with Mn being as high as 80 %. The anode materials exhibit good resistance at the current densities tested. The precipitates deposited in both electrode regions contained as main components Al with 10–20 %, Mg with approximately 10 %, and SO4 with 5–20 %. The solid material in the cathode chamber consisted of relatively high proportions of Zn and Mn. Calcium in the solids indicated the co‐precipitation of calcium sulfate. The main components in the solids of the anode chamber were Mn in the form of pyrolusite, Al as basic sulfate, and Mg. The results indicate that electrochemical metal separation in the membrane electrolysis cell can represent a practical alternative to the metal separation by alkalization. Regarding the main heavy metals Zn, Mn and Ni in the process water, combination electrodes using steel as a cathode material and coal or platinized titanium as an anode material proved to be suitable for eliminating the heavy metals from the aqueous phase. However, for practical application, further work is necessary to improve the efficiency, applicability and costs of the process.

Influence of temperature and salinity on heavy metal uptake by submersed plants

Submersed plants can be useful in reducing heavy metal concentrations in stormwater, since they can accumulate large amounts of heavy metals in their shoots. To investigate the effects of water temperature and salinity on the metal uptake of two submersed plant species, Elodea canadensis (Michx.) and Potamogeton natans (L.), these plants were grown in the presence of Cu, Zn, Cd, and Pb at 5, 11, and 20 °C in combination with salinities of 0, 0.5, and 5‰. The metal concentrations in the plant tissue increased with increasing temperature in both species; the exception was the concentration of Pb in Elodea, which increased with decreasing salinity. Metal concentrations at high temperature or low salinity were up to twice those found at low temperature or high salinity. Plant biomass affected the metal uptake, with low biomass plants having higher metal concentrations than did high biomass plants.

The fertilizing effect of compost and biogas residues from source separated household waste

In Sweden, deposition of organic waste will be prohibited in the year 2005. Instead, the waste will be either incinerated or source separated, processed (composted or anaerobically digested) and recycled back to arable land. In order to evaluate the biologically processed waste products as fertilizers, a field experiment was initiated in Sweden in the autumn of 1998. The main focus of the experiment was to compare compost (C) from source-separated domestic waste with biogas residues (BR) from source-separated domestic waste. Each fertilizer was applied in two combinations: in treatments C50 and BR50, 50 kg N/ha/year originates from the waste and 50 kg N/ha/year from mineral nitrogen fertilizer, while in C100 and BR100, the organic wastes were the only plant nutrient sources (100 kg N/ha/year). Mineral fertilizer (NPS100) and unamended were used as controls. Generally pure mineral fertilizers resulted in the highest yield, while control without nitrogen generated the lowest yield. A combination of organic fertilizer and mineral fertilizer resulted in higher yield compared with applying sole organic fertilizer. Total mineral N in the fertilizer was generally the best overall predictor/regressor for grain yield, total nitrogen yield and apparent bioavailable nitrogen. Application of biogas residue resulted in higher yield and grain quality than compost. The higher concentration of nitrogen in oats suggested that oats is a better choice when using compost as a fertilizer. In conclusion, compost and anaerobic biogas residues should not be used as sole fertilizers. Compost should be complemented with mineral N and the biogas residues with P. If compensation for the low content of mineral N in compost is made by a higher application rate, large amounts of heavy metals might be applied along with the compost.

Effects of heavy metal exposure on the condition and health of nestlings of the great tit (Parus major), a small songbird species

In this study we examined the possible effects of heavy metal exposure on the condition and health of great tit nestlings (Parus major) at four study sites along a pollution gradient near a large non-ferrous smelter in Belgium during three consecutive breeding seasons. Our results showed that nestlings were indeed exposed to large amounts of heavy metals. Excrements contained significantly higher concentrations of several heavy metals (silver, arsenic, cadmium, mercury, lead) near the pollution source than at study sites farther away. When taking into account the number of young in the nest at the time of sampling, nestling body mass and condition were significantly reduced at the most polluted site. Nestlings at the two most polluted sites fledged significantly later than at the least polluted site. We also observed growth abnormalities of the legs near the pollution source. Tarsus length, wing length and haematocrit values did not differ significantly among study sites.