High Amounts Of Heavy Metals Research Articles

Electrolytic recovery of lead in used lime leachate from municipal waste incinerator

The purification of municipal incinerator gases generates huge quantities of both fly ashes and used lime, containing high amount of heavy metals (Pb, Cd, Zn and Hg). The used lime is mainly contaminated by Pb and often considered as hazardous waste. This paper is related to a laboratory study on the performance of electrochemical techniques used to recover Pb from leachate produced during used lime decontamination. Two types of electrolytic units (monopolar and bipolar electrode cells) using different electrode materials were studied. Effectiveness was measured in terms of energy consumed, weight of residue sludge produced and reduction in Pb concentration. Results showed that the best performances for Pb removal (in terms of effectiveness and cost) were obtained by initially adjusting the pH of UL leachate to pH 7.5–8.5 with sulphuric acid followed by electrochemical treatment using bipolar electrode (mild steel) system operated at current intensity of 1.5 A through only 5 min. The yield of Pb removal was 98.8 ± 1.3% and an amount of 4.9 ± 1.3 kg trt −1 of metallic sludge was produced. The optimal conditions determined for Pb recovery involved a total cost of CAN$ 1.66 t −1 of dry residue treated, including acid consumption, energy consumption and metallic sludge disposal.

Effects of heavy metal pollution on red wood ant ( Formica s. str.) populations

We studied the species composition, mound population densities, relative abundance and colony sizes of red wood ants along a well known air pollution gradient of a copper smelter in Southwest Finland. The dominant species, Formica aquilonia, was further studied for heavy metal (Al, Cu, Cd, Ni, Zn, As, Pb, Hg) levels and morphological characters (body mass, head width, labial gland disease) of workers. We found five species belonging to Formica s. str., and two of them showed changes in their relative abundance, which could not be explained by natural habitat differences. Nest mound volumes were 34% smaller in the polluted area, suggesting that smaller colonies can be maintained there. The heavy metal levels in F. aquilonia workers were higher in the polluted area for all metals, except Hg. The largest relative differences between the study areas (polluted/unpolluted) were found for As (4.1), Ni (2.4), Cu (2.1) and Pb (1.8). Morphological characters of workers were not related to the heavy metal levels. Our data showed that red wood ants can tolerate relatively high amounts of heavy metals and maintain reproducing colonies even in a heavily polluted area, but on the basis of smaller colony sizes, pollution stress may also cause trade-offs in reproduction.

Nitrogen release during high temperature pyrolysis of coals and catalytic role of calcium in N 2 formation : Tsubouchi, N. and Ohtsuka, Y. Fuel, 2002, 81, (18), 2335–2342

The term “hyperaccumulator” describes a number of plants that belong to distantly related families, but share the ability to grow on metalliferous soils and to accumulate extraordinarily high amounts of heavy metals in the aerial organs, far in excess of the levels found in the majority of species, without suffering phytotoxic effects. Three basic hallmarks distinguish hyperaccumulators from related non-hyperaccumulating taxa: a strongly enhanced rate of heavy metal uptake, a faster root-to-shoot translocation and a greater ability to detoxify and sequester heavy metals in leaves. An interesting breakthrough that has emerged from comparative physiological and molecular analyses of hyperaccumulators and related non-hyperaccumulators is that most key steps of hyperaccumulation rely on different regulation and expression of genes found in both kinds of plants. In particular, a determinant role in driving the uptake, translocation to leaves and, finally, sequestration in vacuoles or cell walls of great amounts of heavy metals, is played in hyperaccumulators by constitutive overexpression of genes encoding transmembrane transporters, such as members of ZIP, HMA, MATE, YSL and MTP families. Among the hypotheses proposed to explain the function of hyperaccumulation, most evidence has supported the “elemental defence” hypothesis, which states that plants hyperaccumulate heavy metals as a defence mechanism against natural enemies, such as herbivores. According to the more recent hypothesis of “joint effects”, heavy metals can operate in concert with organic defensive compounds leading to enhanced plant defence overall.Heavy metal contaminated soils pose an increasing problem to human and animal health. Using plants that hyperaccumulate specific metals in cleanup efforts appeared over the last 20 years. Metal accumulating species can be used for phytoremediation (removal of contaminant from soils) or phytomining (growing plants to harvest the metals). In addition, as many of the metals that can be hyperaccumulated are also essential nutrients, food fortification and phytoremediation might be considered two sides of the same coin. An overview of literature discussing the phytoremediation capacity of hyperaccumulators to clean up soils contaminated with heavy metals and the possibility of using these plants in phytomining is presented.

Influence of nickel-contaminated soils on fenugreek ( Trigonella corniculata L.) growth and mineral composition

Leafy vegetables accumulate higher amount of heavy metals like nickel (Ni) due to their more leafy vegetative growth. Therefore, a screenhouse experiment was conducted using an alkaline sandy loam soil equilibrated with graded levels of Ni (0, 10, 20, 30, 40, 50, 60, 70, 80, 90, 100, 150, 200, 250 and 300 mg kg −1 soil) to assess the Ni accumulation pattern and its influence on growth and micronutrient distribution in fenugreek plants. Green as well as the dry matter yields of fenugreek increased slightly up to 20 g Ni kg −1 soil but decreased significantly with the application ≥40 mg Ni kg −1 soil. Crops showed characteristic toxicity symptoms of interveinal chlorosis in pots receiving ≥40 mg Ni kg −1 soil. While the total content of Ni in the plant tissues increased consistently with increasing rates of applied Ni, the roots accumulated much higher amount of this element compared to the shoot. The content of Fe in plants showed an increase whereas that of Cu and Zn experienced a decrease with the rise in the applied Ni.

EFFECTS OF HIGH TEMPERATURE MELTING ON FRACTIONATION OF HEAVY METALS IN SEWAGE SLUDGE

ABSTRACT Sewage sludge from aerobic treatment plant was found to contain high amounts of heavy metals. Research was carried out to investigate the speciation and leaching behavior of heavy metals when using high temperature melting technology for treatment. This was achieved by conducting a sequential chemical extraction procedure and EP-TOX leaching test. The thermal treatment led to increased shift of metals from organic fraction to residual fraction, indicating that the thermal treatment caused metals in sewage sludge to become stable. Furthermore, results from leaching test revealed that metals were not leached from the final product after thermal treatment and this was verified using US EPA standard limits. Results from this study indicated that melting technology could convert the sludge to product that can be either reused or landfilled without an adverse environmental impact.

INFLUENCE OF SOME SOIL CHARACTERISTICS ON HEAVY METAL CONTENT IN HYPERICUM PERFORATUM L. AND ACHILLEA MILLEFOLIUM L.

INFLUENCE OF SOME SOIL CHARACTERISTICS ON HEAVY METAL CONTENT IN HYPERICUM PERFORATUM L. AND ACHILLEA MILLEFOLIUM L.

Characteristics of contaminant release from lake sediment under different salinity and redox conditions

A laboratory-scale reactor containing the lake sediment obtained from two regional sites, mainly affected by live-stock wastewater and industrial wastewater, respectively, was tested for the amount of contaminants (i.e., organics, nutrients, and heavy metals) released from the sediment, under different salinity (freshwater vs. seawater) and redox (oxic vs. anoxic) conditions. Results showed that the amounts of released contaminants in freshwater were higher (e.g., up to 11.6-fold for Cd) than those in seawater, resulting from the increased saturation concentration toward the overlying water due to the relatively lower ionic strength in freshwater. On the other hand, the released amounts under the anoxic condition were higher (e.g., up to 2.9-fold for NH 4 + −N in livestock wastewater affecting regions) than those under the oxic condition, due to the increased amount resulted from the formation of reduced environment in overlying water under the anoxic condition. A the contaminant release proceeds through pore water in sediment under this reduced condition, the sediment it self can act as an area pollution source, resulting in a gradual deterioration of water quality pollution in lower water layers. In general, the release rates of organics and nutrients were higher than those of heavy metals. In addition, the livestock waste-water affecting regions showed high amounts of organics and nutrients released, whereas the industrial wastewater affecting regions showed high amounts of heavy metals released, due to the regional characteristics such as high content of specific components within pore water. In case of heavy metals, the release rates were in the order of Mn>Zn>Cu>Pb>Cd. Among all the conditions tested, the anoxic/freshwater condition showed the highest release of contaminants, whereas the anoxic/seawater condition showed the lowest release.

29Si, 27Al and 23Na solid-state nuclear magnetic resonance studies of combustion-generated ash

Combustion-generated ash was synthesized, heated and analyzed by solid-state nuclear magnetic resonance spectroscopy with magic angle spinning (NMR–MAS). The structural information obtained from this study indicates that the ash contains different magnetic resonance environments for Al, Si and Na after combustion. The final ash material contains a major amorphous aluminosilicate glass phase with mullite and corundum crystals. 29Si NMR spectra showed a single peak at −110.5 ppm ( δ) for the initial powder sample due to SiO 2. When the sample was heated to 1500°C the peak shifts to lower field ( δ=−99 ppm) due to the formation of aluminosilicate amorphous glass containing alkali or alkaline earth metals. The 27Al NMR spectra of the initial sample gives a single peak at 10.1 ppm due to the AlO 6 (octahedral group) present in the Al 2O 3. When the sample is heated to 1500°C, a new peak appeared at 50 ppm due to the formation of AlO 4 tetrahedral represent the mullite and aluminosilicate compounds. The 23Na NMR spectra of both the initial and the heated samples (at 1500°C) give rise to a single peak at −14.3 and −28.7 ppm, respectively. The sharp peak at −14.3 ppm is contributed from the crystalline Na 2O and the broad peak around −28.7 ppm is due to the Na + present to compensate SiO − present in the amorphous aluminosilicate glass material. The presence of low amounts of heavy metals Cr (2800 ppm), Cd (2700 ppm) and Pb (2800 ppm) in the ash generally does not show any influence on the 27Al, 29Si and 23Na solid-state NMR spectra. On the other hand, the ash sample containing higher amounts of heavy metals (Cd=14210 ppm, Cr=13120 ppm and Pb=13140 ppm) showed significant effect on the 27Al NMR spectra. The replacement of Al 3+ from its octahedral sites by Cr 3+ leads to the decrease in the intensity of the AlO 6 octahedral peak. The presence of Cr 3+, Cd 2+ and Pb 2+ in the aluminosilicate matrix exerts a deshielding effect on 29Si resonance and thus shifts δ to low-field. The results clearly indicate an interaction between the heavy metals and the ash matrix compounds.

Phytochelatin production in freshwater algae Stigeoclonium in response to heavy metals contained in mining water; effects of some environmental factors

Production of phytochelatins (PC) in two freshwater, filamentous green algae of the genus Stigeoclonium, in response to heavy metals contained in mining water was studied. Stigeoclonium sp. grown abundantly in ditches with the mining water (southern Poland) accumulated high amounts of heavy metals. The other studied alga Stigeoclonium tenue Kütz. was isolated from unpolluted lake water in the Netherlands. Both algae exposed to the heavy metal mixture (17 μM; mainly zinc) contained in the hard, alkaline (pH 8.2) mining water produced similar amounts of phytochelatins (PC 2 and PC 3): 500–600 nmol SH g −1 dry weight. After water acidification to pH 6.8, a >2-fold increase of the total phytochelatin level as well as the appearance of longer chain peptide PC 4 in the cells of both algae was observed. The concentration of labile forms of zinc in the acidified mining water was four times as high as that in the alkaline water. The heavy metal mixture (17 μM) in non-complexing solution of pH 6.8 caused a comparable phytochelatin production in both Stigeoclonium strains as the same mixture present in the acidified mining water. However, in the non-complexing solution of pH 8.2, the metal mixture induced in algae more PCs than at pH 6.8. A positive effect of bicarbonate enrichment in the solution on the PC production in S. tenue was also observed. Stigeoclonium sp. exposed to high concentrations (10 μM) of individual metals (Zn, Pb and Cd available as free cations) synthesised much higher amounts of phytochelatins (PC 2–PC 4) than in response to the metal mixture contained in the mining water. The order of PC induction by the studied metals in the Stigeoclonium sp. was Cd>Pb>Zn. Addition of suspended solid matter to the heavy metal solution resulted in essential quantitative changes in phytochelatins in algal cells; a considerable decrease of PC 2, PC 3 and PC 4 levels was observed. The PC production in algae of the genus Stigeoclonium exposed to the heavy metal mixture is discussed in the context of various metal bioavailability and the algal adaptation to complex aquatic environment.

Genotoxic effects after in vivo exposure of vegetable extracts containing heavy metals from the Dhapa area of Calcutta, India. I. Effects of cauliflower, spinach and radish

Several reports have indicated that the sewage-fed vegetables of the Dhapa area, near the city of Calcutta, contain a very high amount of heavy metals. Currently 800 ha of land is being utilised throughout the year to cultivate more than eight types of vegetables, with a production of about 147 tonnes per day. A major population of Calcutta consumes these vegetables grown in the Dhapa area. Recently there has been huge pressure on the State Government to ban vegetables grown in the Dhapa area for human consumption. For this reason, we have studied the genotoxic effects of some of the most commonly used vegetable extracts from the Dhapa area after in vivo acute exposure in mice as measured by chromosomal aberrations (CA) and sister chromatid exchanges (SCE) to find out the minimum threshold dose to induce CA and SCE. Three different concentrations of the three most commonly used vegetable extracts (cauliflower, spinach, radish) were fed by gavage to mice for the study of CA and SCE. A significant increase in CA was observed only at the highest concentration of all the vegetable extract-treated groups when compared with the solvent control. A significant increase in SCE were observed in the middle and high doses of spinach and only the high dose of cauliflower and radish extract-treated series when compared with distilled water control. The lowest dose was equivalent to approximately 1 kg of vegetables consumed by a human (60 kg body weight) in a day. The middle and high doses of each vegetable extract were much higher than the normal amount of vegetables that a human can consume per day. So the minimum dose for inducing SCE and CA was much higher than the amount a human can consume in a day. Therefore this study indicates that these vegetables are safe for human consumption up to a certain limit, and attention should be given to reducing the heavy metal contents in the soil and sewage of the Dhapa area to thus reduce the heavy metal concentrations in the vegetables.

Treatment of acid lignite mine flooding water by means of microbial sulfate reduction

During and after mining activities acidic waters containing high amounts of heavy metals and sulfate often occur. In addition to precipitation processes, water purification is also possible with the help of sulfate-reducing bacteria (SRB). A mixed culture of SRB was adapted to methanol as a cheap carbon source. In order to receive high sulfate-reduction rates immobilization on porous materials proved to be advantageous. Continuous laboratory experiments based on immobilized SRB were carried out with original water from a lignite mining site reaching sulfate-reducing rates up to 132 mg SO 4 2−/(l h). Based on these results a process for the treatment of such waters was designed. Heavy metals are removed by recycling sulfide containing effluent, excess sulfide can be oxidized to elemental sulfur by addition of hydrogen peroxide. The plant with a 3.9 m 3 bioreactor with immobilized SRB was constructed at the mine site. This pilot plant was operated successfully for some months. The removal of heavy metals was close to 100%, the pH of the acidic water increased from 3.0 to 6.9. The sulfate-reducing rate again reached 134 mg SO 4 2−/(l h). The production of sulfur from the excess sulfide is possible.

Adubação fosfatada e metais pesados em Latossolo cultivado com arroz

A avaliação da contaminação por metais pesados contidos nos fertilizantes tem atraído a atenção devido a um eventual efeito no ambiente. O objetivo do trabalho foi estudar a absorção de metais pesados presentes nos adubos fosfatados pelo arroz, utilizando-se uma metodologia de extração seqüencial passível de ser adaptada à análise de rotina. O delineamento experimental foi em blocos casualizados e utilizaram-se quatro fontes de P (superfosfato triplo, termofosfato magnesiano e fosfatos naturais da Carolina do Norte e de Arad) em três doses (50, 100 e 200 mg dm-3). Foram cultivadas plantas de arroz após o cultivo de Brachiaria decumbens e Centrosema pubescens em Latossolo Vermelho-Amarelo distrófico, em condições de casa-de-vegetação. A transferência de metais pesados (Cu, Mn, Cd, Ni, Zn) para o solo e para as plantas ocorreu de forma diferenciada para as doses e fontes utilizadas. Os adubos fosfatados não contribuíram de modo relevante para o aumento do teor de metais pesados no solo e nas plantas. Na extração seqüencial, o HCl 6 mol L-1 extraiu maior percentual de metais pesados do solo, seguido por Mehlich 1 e H2O, exceto para Zn.

Bioavailability of heavy metals in sewage sludge-amended Thai soils.

Plough and subsoil layers of two majoragricultural soil series, Rangsit and Thonburi, foundin Bangkok area of Thailand were studied fordetermining the bioavailability and solubilitybehavior of heavy metals (Cd, Cu, Zn, Mn, and Fe)following application of sewage sludge from awastewater treatment plant and a series of laboratoryexperiments. The soils contained low indigenous heavymetals while the sludge contained higher amounts ofheavy metals but in an acceptable range forapplication as plant nutrient source in agriculturalsoil. Applications of sewage sludge increased pH ofthe acid soil and available plant nutrients to thesoils. The heavy metal concentration levels in thesoils also increased. Most partitioned into easilymobile pools and later into sparingly mobile poolsfollowing 12 weeks of incubation time. Bioavailabilityforms of Cd in soil solution were low but that of Cu,Zn, and Mn remained elevated even at 12 weeks of thereaction time. Applied inorganic Zn depressed Cdsorption capacity of two soils studied but it had noeffect on Cd desorption.

Effect of Organic Materials on Partitioning, Extractability and Plant Uptake of Metals in an Alum Shale Soil

Soils developed on sulphide-bearing shale (alum shale) in Norway contain naturally high amount of heavy metals. We conducted a greenhouse pot experiment to study the effect of four rates (0, 2, 4, and 8%) and three sources (cow manure, pig manure and peat soil) of organic matter in partitioning and distribution, extractability and plant uptake of Cd, Cu, Ni and Zn in an alum shale soil. Sequential extraction scheme was used to determine the distribution patterns of metals in the soil. DTPA was used for extracting the metals from the soil. Wheat (Triticum aestivum) was used as a test crop to study the plant uptake of metals. The highest amount of Cd was present in the exchangeable fraction, irrespective of the rate and source of organic matter applied. Copper, Ni, and Zn, on the other hand, were present only in small quantities in this fraction. The largest fraction of Cu was associated with organic matter and the amounts present in the oxide, carbonate and exchangeable fractions were very small. Nickel and Zn were found mainly in the residual fraction. Increasing rates of cow and pig manure decreased the amounts of Cd and Ni associated with the exchangeable fraction whereas, the addition of peat soil at the same rate increased the amounts of these metals associated with this fraction. This effect of organic matter was primarily associated with the change in soil pH caused by different organic matter sources. The DTPA-extractable metals were decreased with increasing rates of organic matter application, irrespective of its source. Grain and straw yields of wheat were decreased with increasing rates of organic matter. The application of organic matter increased the Cu and Zn concentrations in both grain and straw. The concentration of all metals was lower in plants grown in the cow manure amended soil as compared to those grown in the soil amended with either pig manure or peat soil. These results sugggest that the source of organic matter was a determining factor for metal distribution in the soil and for metal uptake by plants. In this study cow manure slightly increased the soil pH and thus was more effective than either pig manure or peat soil in reducing the plant uptake of metals but in general the efficiency of the organic material in reducing heavy metal uptake was small.

Heavy metal uptake and chemical changes in the rhizosphere of Thlaspi caerulescens and Thlaspi ochroleucum grown in contaminated soils

Thlaspi caerulescens (J. and C. Presl) and Thlaspi ochroleucum (Boiss. ex Heldr) were grown in three different soils containing moderate to high amounts of heavy metals in a pot experiment, using a rhizobag technique. T. caerulescens accumulated significantly more Zn in the shoots than T. ochroleucum. The concentrations of Zn in the shoots of T. caerulescens ranged from 3100 to 8100 mg kg-1 dry matter (DM), but only from 800 to 1600 mg kg-1 DM in T. ochroleucum. Total uptake of Zn in the shoots of T. caerulescens was about 5 times that of T. ochroleucum. In contrast, the differences between the two species in the uptake of Cd, Cr, Cu, Ni and Pb were generally small. Concentrations of mobile Zn (extractable with 1M NH4NO3) in the rhizosphere and non-rhizosphere soils decreased considerably after growth of both plants, but the decreases were greater with T. caerulescens than with T. ochroleucum. The decreases in the mobile fraction accounted for less than 10% of the total Zn uptake by T. caerulescens indicating that this species was effective in mobilising Zn from less soluble fractions in the soils. The rhizosphere soils tended to have higher concentrations of mobile Zn than the non-rhizosphere soils, probably because of the lower pH in the rhizosphere. The pH in the rhizosphere soils was 0.2-0.4 units lower than that in the non-rhizosphere soils at the end of the experiment. However, there were no significant differences between the two species in the degree of rhizosphere acidification. The results suggest that T. caerulescens has potential for removing Zn from moderately to highly contaminated soils, but that this ability was not related to the pH changes in the rhizosphere.

Growth and mortality of nestling great tits (Parus major) and pied flycatchers (Ficedula hypoleuca) in a heavy metal pollution gradient.

We studied nestling growth, growth abnormalities, mortality and breeding success of two hole-nesting passerines, the great tit (Parus major) and the pied fly-catcher (Ficedula hypoleuca), at 14 study sites around a copper smelter complex in Harjavalta, south-west Finland in 1991-1993. The main pollutants in the area are heavy metals and sulphuric oxides. Exposure of birds to heavy metals was shown by measuring their faecal concentrations. Copper, nickel and lead contents of nestling faeces were high near the factory and decreased with distance away from the pollution source. F. hypoleuca nestlings suffered high mortality very close to the factory complex, but did relatively well at all other sites. Breeding success of P. major was below background levels up to 3-4 km from the pollution source and nestlings grew poorly close to the factory. Growth abnormalities of legs and wings in F. hypoleuca nestlings were significantly more common near the factory than farther away. In contrast, F. hypoleuca nestlings grew equally well at all distances. The poor breeding success of F. hypoleuca close to the factory complex is probably related to the high amount of heavy metals in its diet, and low availability of calcium-rich food items may enhance this effect. We suggest that the poor breeding success of P. major is related to habitat changes that have taken place around the factory. The different responses of these two bird species are probably due to their different diet. Our results show convincingly that species-specific differences in response should be carefully considered when planning schemes for air pollution monitoring.

Sludge-grown algae for culturing aquatic organisms: Part II. Sludge-grown algae as feeds for aquatic organisms

This project investigated the feasibility of using sewage sludge to culture microalgae (Chlorella-HKBU) and their subsequent usage as feeds for rearing different organisms. Part II of the project evaluated the results of applying the sludge-grown algae to feed Oreochromis mossambicus (fish), Macrobrachium hainenese (shrimp), and Moina macrocopa (cladocera). In general, the yields of the cultivated organisms were unsatisfactory when they were fed the sludge-grown algae directly. The body weights of O. mossambicus and M. macrocopa dropped 21% and 37%, respectively, although there was a slight increase (4.4%) in M. hainenese. However, when feeding the algal-fed cladocerans to fish and shrimp, the body weights of the fish and shrimp were increased 7% and 11% accordingly. Protein contents of the cultivated organisms were comparable to the control diet, although they contained a rather high amount of heavy metals. When comparing absolute heavy metal contents in the cultivated organisms, the following order was observed: alga > cladocera > shrimp, fish > sludge extracts. Bioelimination of heavy metals may account for the decreasing heavy metal concentrations in higher trophic organisms.

PH influence on selectivity and retention of heavy metals in some clay soils

The problem of varying species of heavy metals existing as individual species or in combination with each other in simulated contaminant leachates (solutions) is studied in relation to selectivity and retention in four different kinds of soil. The influence of pH on the retention characteristics is also examined. The results obtained from the heavy metals single-species and composite-species adsorption tests indicate that in evaluating the attenuation potential of the soil substrate (i.e., contaminant attenuation), account needs to be given to the sensitivity of the soil – heavy metals contaminant system to the pH of the leachate and the competitive effect between the heavy metals present in the leachate. A change in the soil solution pH results in a corresponding change of the dominant retention mechanism of heavy metals in the soils. At high pH values, precipitation mechanisms (e.g., precipitating as hydroxides and (or) as carbonates) dominate. As pH decreases, precipitation becomes less important, and cation exchange becomes dominant. High amounts of heavy metals are retained in the soils if the soil buffer capacity remains high enough to resist a change in pH. The selectivity order of heavy-metal retention in soils depends on the pH of soil solution. At soil solution pH values above 4 or 5, when precipitation prevails, the selectivity order obtained is given as Pb > Cu > Zn ≥ Cd, as demonstrated for the illite, montmorillonite, and natural clay soils. At lower soil solution pH values, the selectivity order obtained is given as Pb > Cd > Zn > Cu, as can be seen in the case of kaolinite and montmorillonite. Key words : heavy metals, retention, selectivity, preferential adsorption, precipitation.

Selective sequential extraction analysis of heavy-metal retention in soil

The selective sequential extraction method of analysis is used in this study to determine the distribution of heavy metals in some clay soils, to assist in evaluation of the role of the various clay soil solids (clay minerals, organics, amorphous materials, and carbonates) in heavy-metal retention capability as a function of acidity of the leachate. The chemical speciation model MINTEQ (metal speciation equilibrium model for surface and groundwater) is used to calculate the probable percent distribution of different species of heavy metals present in the leachate used. The selective sequential extraction method is based on the fact that different forms of heavy metals that are retained in soil (e.g., as oxides, hydroxides, carbonates, bound with organic matter) can be extracted selectively by using appropriate reagents. The results show that heavy metals can be retained in the four clay soils studied by several soil phases or mechanisms such as exchangeable, carbonate, hydroxide, and organic phases. The retention of heavy metals in any phase depends on soil solution pH, soil constituents, and the type of heavy metal. At high soil solution pH values, retention of heavy metal by precipitation mechanisms prevails, whereas at low soil solution pH, retention by cation exchange mechanisms becomes dominant. The results from the selective sequential extraction analysis support the conclusion of the significance of soil buffer capacity with regard to heavy-metal retention. The capacity of the soils to retain high amounts of heavy metals as they receive increasing amounts of acid (i.e., as the pH is reduced) depends directly on the soil initial pH values and on their buffer capacities. Key words : selective sequential analysis, exchangeable cations, heavy metals, equilibrium models, oxides.

Use of contaminated dredged sludge as a substratum for forest growth - case study

Preliminary research was done to assess the suitability of dredged sludge as a growing medium. On an experimental sludge site, consolidated and aged during 3 years, physical, chemical and biological environmental parameters were analysed. Cuttings of poplar clones were used to evaluate growing response, in comparison with identical clones on the nursery site. This study, conducted in order to attempt the potentiality of afforestation, affirms its intention. Afforestation seems to be possible. As a consequence, relatively high amounts of heavy metals will be introduced into the forest ecosystem.