Concentrations and Pools of Heavy Metals in Urban Soils in Stockholm,Sweden

The concentrations of heavy metals (Cd, Cr, Cu, Hg, Ni, Pb andZn) and arsenic (As) were surveyed and the metal pools estimatedin soils in Stockholm Municipality. The sampling sites were distributed all over the entire municipality with a higher sampling density in the city centre. Soils were sampled to a maximum depth of 25 to 60 cm. Soil texture, total-C content, electrical conductivity and pH were analysed. Heavy metal concentrations were determined after wet digestion with boiling7 M HNO₃.The results showed a wide range in heavy metal concentrations, as well as in other soil properties. The city centre soils constituted a rather homogeneous group whereas outside this areano geographical zones could be distinguished. These soils were grouped based on present land use, i.e. undisturbed soils, public parks, wasteland (mainly former industrial areas), and roadside soils. The city centre and wasteland soils generally hadenhanced heavy metal concentrations to at least 30 cm depth compared to park soils outside the city centre and rural (arable)soils in the region, which were used to estimate background levels. For example, the mean Hg concentration was 0.9 (max 3.3)mg kg^-1 soil at 0–5 cm and 1.0 (max 2.9) at 30 cm depth in the city centre soils, while the background level was 0,04 mg kg^-1. Corresponding values for Pb were 104 (max 444) and135 (max 339) mg kg^-1, at 0–5 and 30 cm, respectively, while the background level was 17 mg kg^-1.The average soil pools (0–30 cm depth) of Cu, Pb and Zn were 21,38 and 58 g m^-2 respectively, which for Pb was 3–4 timeshigher and for Cu and Zn 1.5–2 times higher than the backgroundlevel. The total amount of accumulated metals (down to 30 cm)in the city centre soils (4.5^*10 ⁶ m² public gardens and green areas) was estimated at 80, 1.1, 120 and 40 t for Cu, Hg, Pb and Zn, respectively. The study showed (1) thatfrom a metal contamination point of view, more homogeneous soilgroups were obtained based on present land use than on geographicdistance to the city centre, (2) the importance of establishing a background level in order to quantify the degree of contamination, and (3) soil samples has to be taken below the surface layer (and deeper than 30 cm) in order to quantify theaccumulated metal pools in urban soils.     

Solubility and Potential Mobility of Heavy Metals in Two Contaminated Urban Soils from Stockholm,Sweden

The solubility and potential mobility of heavy metals (Cd, Cu,Hg, Pb and Zn) in two urban soils were studied by sequential andleaching extractions (rainwater). Compared to rural (arable) soils on similar parent material, the urban soils were highlycontaminated with Hg and Pb and to a lesser extent also with Cd,Cu and Zn. Metal concentrations in rainwater leachates were related to sequential extractions and metal levels reported fromStockholm groundwater. Cadmium and Zn in the soils were mainly recovered in easily extractable fractions, whereas Cu and Pb were complex bound. Concentrations of Pb in the residual fractionwere between two- and eightfold those in arable soils, indicatingthat the sequential extraction scheme did not reflect the solidphases affected by anthropogenic inputs. Cadmium and Zn conc. inthe rainwater leachates were within the range detected in Stockholm groundwater, while Cu and Pb conc. were higher, whichsuggests that Cu and Pb released from the surface soil were immobilised in deeper soil layers. In a soil highly contaminatedwith Hg, the Hg conc. in the leachate was above the median concentration, but still 50 times lower than the max concentration found in groundwater, indicating the possibilityof other sources. In conclusion, it proved difficult to quantitatively predict the mobility of metals in soils by sequential extractions.     

Changing of Lead and Cadmium Pools of Swedish Forest Soils

The aims of the paper are to; i)evaluate the rate and direction of present changesin lead (Pb) and cadmium (Cd) soil pools of Swedishforests; ii) discuss processes of importance forleaching of Pb and Cd in Swedish forest soils. Thepresently ongoing changes of Pb and Cd pools ofSwedish forest soils are evaluated by compilationof data from the literature and unpublishedsources. It is concluded that Cd pools arepresently decreasing in larger areas of Sweden. Therate of decrease is mainly determined by soilacidity status; Cd leaching is regulated by ionexchange with Ca²⁺, Mg²⁺, Al³⁺ andH⁺, and is higher in acid soils. The Pb poolsare presently increasing with 0.1 to 0.3 percentannually in the soil down to 0.5 meter. Pb isredistributed from the O horizon to the B horizon,most pronounced in spruce forests; the Pb pools ofthe O horizon are presently not increasing, but isslightly decreasing by 0.1 to 0.2 percent annually. The leaching of Pb in the soil is controlled byfactors regulating the solubility of organicmatter.     

Effect of nine years of animal waste deposition on profile distribution of heavy metals in Abeokuta,south-western Nigeria and its implication for environmental quality

Uncontrolled deposition of waste from animal farms is a common practice in south-western Nigeria, and the presence of heavy metals in soil constitutes environmental and health hazards by polluting the soil, ground water, adjoining streams and rivers. The study investigated the profile distribution of Mn, Pb, Cd, Zn, Fe, Cu, Ni and Cr in some tropical Alfisols in south-western Nigeria after nine years disposal of animal wastes. The amount of these metals in the soil horizons was high enough to cause health and phytotoxic risks. All the metals except Zn and Cr increased down the profile, while Mn, Pb, Cd, Fe, Cu and Ni accumulated at 80–120 cm depth. The increment of these metals at this depth over the top soil were 26%, 143%, 72%, 47%, 328% for Mn, Pb, Cd, Cu and Ni, respectively. It thus, shows their mobility and the possibility of polluting ground water. The Mn content at the poultry and cattle waste sites increased by 127% and 25%, respectively over the control, while that of cattle and swine dump site for Cd content were 9.82 and 15.63 mg kg^?1, respectively. Lead content also increased by 8.52 and 5.25 mg kg^?1, respectively.There was the accumulation of Zn and Cu at the swine dump site while the cattle dump site had the highest amounts of nickel and chromium. The least amount of Fe was recorded at the swine waste dump site. The reduction in organic matter with depths together with the reduced pH might have favored the mobility of the metals. The ranking of pollution among the sites was poultry > swine > cattle > sheep and could be due to the type of ration fed, the vaccination programmes, sanitation programmes and other management practices.     

Changes in cadmium mobility during composting and after soil application

The effect of twelve weeks of composting on the mobility and bioavailability of cadmium in six composts containing sewage sludge, wood chips and grass was studied, along with the cadmium immobilization capacity of compost. Two different soils were used and Cd accumulation measured in above-ground oat biomass (Avena sativa L.). Increasing pH appears to be an important cause of the observed decreases in available cadmium through the composting process. A pot experiment was performed with two different amounts of compost (9.6 and 28.8 g per kg of soil) added into Fluvisol with total Cd 0.255 mg kg^?1, and contaminated Cambisol with total Cd 6.16 mg kg^?1. Decrease of extractable Cd (0.01 mol l^?1 CaCl₂) was found in both soils after compost application. The higher amount of compost immobilized an exchangeable portion of Cd (0.11 mol l^?1 CH₃COOH extractable) in contaminated Cambisol unlike in light Fluvisol. The addition of a low amount of compost decreased the content of Cd in associated above-ground oat biomass grown in both soils, while a high amount of compost decreased the Cd content in oats only in the Cambisol.     

Water extraction with CO2 bubbling as pretreatment of melting-furnace fly ash for metal recovery

In Japan, melting-furnace fly ash (MFA) generated from ash melting and gasification/melting plants is considered an “urban mine” due to its high metal content. This study aimed to develop a novel approach to pretreating MFA for metal recovery. Water extraction with CO₂ bubbling was investigated because MFA mainly consists of water-soluble salts containing elements such as Cl, Ca, Na, and K. Instead of acid addition, CO₂ bubbling was applied to maintain the optimal pH for minimizing the release of target metal elements and maximizing the removal of undesirable elements during water extraction. The results revealed that CO₂ bubbling effectively decreased the release of Pb, Zn, and Cd into the treatment water. This was mainly due to coprecipitation with CaCO₃, which was primarily formed by the reaction of Ca²⁺ from the MFA with CO₃ ²⁻ from the CO₂ gas. The bubbling process also helped accelerate the removal of Cl from MFA. Furthermore, the study showed that it is possible to lower the water-to-solid ratio to 5 with only a slight reduction in water extraction effect. Finally, approximately four times the concentration of target metals (rare metals and Cu, Pb, and Zn) was achieved by removing 90% of Cl, 70%–90% of Na and K, and 30%–40% of Ca through water extraction with CO₂ bubbling, resulting in a concentration of target metals that was nearly equal to that of ore.     

Trace Metals in Different Crop/Cultivation Systems in Greece

Typical soils in Greece are neutral or alkaline and frequently are lime-rich, conditions that favour the accumulation of trace elements. The traditional use of metal-based fungicides in orchards and vineyards may have led to the accumulation of trace metals. Concentrations of Fe, Cu, Mn, Zn (aqua regia digestion) and some other soil parameters were measured in organically and conventionally cultivated soils (0–30 cm) from vineyards, olive groves and citrus groves of varying ages, and in uncultivated soils. Many vineyards and olive groves are situated in hilly or mountainous areas with sloping ground or terraces in contrastto citrus, which is cultivated in lower lying areas. Due to the difficulty of access, these crops often are cultivated extensively in both systems. Trace metal concentrations were found to lie withinthe ranges expected for the predominant soil types. Cu concentrations were relatively high (>100 mg kg^-1) in a few samples, but were not correlated with the age of the cultivation. A two-way ANOVA analysis showed larger differences in the mean concentrations of Cu, Mn and Zn between different crops (p≤ 0.001 for Cu, p≤ 0.05 for Zn, and p≤ 0.1 for Mn) than between different cultivation systems (no significant differences). The crop by cultivation interaction was not statistically significant for any metal (p > 0.8). Strong correlations (p≤ 0.001) were found between Fe, Mn and Zn and both clay concentration and CEC, although these relationshipswere not uniform throughout the different crop and cultivation systems. Concentrations of Cu were related to clay concentrations only for vineyards and to CEC only for citrus. Correlations were not found with organic matter or pH.     

TSP,PM<Subscript>10</Subscript> and health risk assessment for heavy metals (Cr,Ni, Cu,Zn, Cd,Pb) in the ambience of the production line for waste cathode ray tube recycling

Recently, a typical semi-automatic recycling line is proved to be a feasible method for resource recovery of raw material of waste CRTs. However, there are no relevant studies about health risk assessment of the particles and heavy metals diffused from this physical recycling process for CRTs. In this study, TSP, PM₁₀ and heavy metals (Cr, Ni, Cu, Zn, Cd and Pb) in the ambience of the workshop have been evaluated. The mean concentrations of TSP and PM₁₀ in the workshop were 481.5 and 316.9 μg/m³, respectively. Meanwhile, it can be seen that Zn (8.1 and 7.9 μg/m³, respectively) was the most enriched metal in TSP and PM₁₀, followed by Pb (3.2 and 3.0 μg/m³, respectively). Health risk assessment showed that the total hazard index was 3.29, exceeding the danger threshold. The health risk of different metals was Cr > Cd > Ni. In short, the research results show that mechanical–physical process for e-waste recycling do exist the pollutant mission. So the effective measures should be taken to reduce the harm of pollutants on the workers’ health.     

Zinc,lead, and cadmium tolerance and accumulation in Cistus libanotis,Cistus albidus,and Cistus salviifolius: Perspectives on phytoremediation

Heavy metal contamination is of particular concern for human health and the environment. Phytoremediation is an emerging cost‐effective strategy to remediate heavy metal contaminated soil. However, this technique is limited by the small number of plants that are tolerant to heavy metals and are also accumulators. This study assayed zinc, lead, and cadmium tolerance and accumulation in Cistus libanotis, Cistus albidus, and Cistus salviifolius. The plants were cultivated in hydroponic conditions and exposed to different concentrations of Pb(NO₃)₂ (100 and 200 µM), ZnSO₄ (100 and 200 µM), or CdCl₂ (10 and 20 µM) for 3 weeks. Plant biomass and metal accumulation in roots and aboveground parts varied greatly among the species. All three species appeared to be sensitive to Zn. However, C. albidus displayed strong tolerance to Pb and accumulated large quantities of Pb and Cd in its roots. C. libanotis accumulated large quantities of Pb and Cd in its aboveground parts. C. libanotis can thus be classified as a Pb and Cd accumulator species. The study results show that C. albidus is suitable for phytostabilization of Pb‐contaminated soils, while C. libanotis can be used for phytoextraction of both Pb and Cd.     

Treatment of urban stormwater for dissolved pollutants: A comparative study of natural organic filter media

Sorption capacities were evaluated for the dissolved stormwater (SW) pollutants onto two tree mulches and jute fiber. SW spiked with predetermined concentrations of copper (Cu), cadmium (Cd), hexavalent chromium (Cr ⁺⁶), lead (Pb), zinc (Zn), and benzo[a]pyrene (B[a]P), naphthalene (NP), fluoranthene (FA), 1,3‐dichlorobenzene (DCB), and butylbenzylphthalate (BBP) were used in this study. Each medium removed close to 100 percent of all the pollutants at the concentrations studied. Sorption capacities (μg/g) of the three organic media were in the order of jute > hardwood mulch > softwood mulch, and on a mole basis, both the heavy metals and the toxic organics were sorbed by the three media in an identical sequence: Cr ⁺⁶ > Cu, Zn > Cd > Pb; and NP > DCB > FA > B[a]P > BBP. Sorption capacities of the hardwood wood mulch and jute fiber for the pollutants were correlated with distinctive physical properties of the pollutants. © 2005 Wiley Periodicals, Inc.     

Removal of mixed contaminants by Fe0-based biobarrier in flow-through columns using recycled waste materials

The present study investigated the reactivity and ability of permeable reactive barriers [zero-valent iron (ZVI)-barrier plus biobarrier) to remove various contaminants (Cd, As, Zn, Cu, Mn, Cr, NO₃ ⁻, NH₄ ⁺, and COD_cr) from synthetic leachate. Two different reactive materials were used in this study, namely ZVI and autoclaved lightweight concrete (ALC). After 90 days of column operation, the contaminant profiles were determined along the length of the columns. The heavy metals were extensively removed in the bio-ALC and sequential barriers (ZVI plus bio-ALC), however the removal efficiencies for the heavy metals Zn and Cr in the ALC and bio-ALC barriers were comparatively low. Nitrate was completely removed (>99.9%) in the ALC, bio-ALC, and sequential barriers. More than 50% of the produced ammonium and organic materials were removed in the biologically reactive zone of the sequential barriers. The results of the present study suggest that sequential barriers are one of the best solutions for in situ remediation and that they can be applied to clean up the leachate released from landfills.     

Sludge earthworm composting technology by Eisenia fetida

Prior to vermicompost application to the soils, there is a need to determine the heavy metal concentrations in the final vermicomposts. Acute toxicity on Eisenia fetida for copper (Cu) and cadmium (Cd) were conducted by artificial soils tests. The dosage of interest is typically the median lethal concentration (LC₅₀) that will kill 50 % of the population of organisms within the test period. The dry artificial soil is pre-moistened 1 or 2 days before the test by adding deionized water to obtain approximately half of the required final water content of 40–60 % of the maximum water holding capacity. The 14-day LC₅₀ values (95 % confidence interval) for Cu and Cd were 530 (450–624) and 1118 (988–1265) mg kg^?1, respectively. The vermicomposting was designed to evaluate the effects of earthworm activity on heavy metals in sewage sludge. Compared with the sludge before vermicomposting by Eisenia fetida, the results are as follows: (1) water content, the pH value and organic matter content decreased, (2) total nitrogen content increased, total phosphorus content and total potassium content decreased, (3) available nitrogen concentration, available phosphorus content increased, and (4) the total content of five metals (Cu, Ni, Cd, Pb and Zn) decreased, and the bioaccumulation factor shows that vermicomposting can efficiently remove heavy metals. Therefore, it can be concluded that the soil use of sludge of the Wastewater Treatment Plant in Huaibei is feasible.     

Experimental evidence of colloids and nanoparticles presence from 25 waste leachates

The potential colloids release from a large panel of 25 solid industrial and municipal waste leachates, contaminated soil, contaminated sediments and landfill leachates was studied. Standardized leaching, cascade filtrations and measurement of element concentrations in the microfiltrate (MF) and ultrafiltrate (UF) fraction were used to easily detect colloids potentially released by waste. Precautions against CO₂ capture by alkaline leachates, or bacterial re-growth in leachates from wastes containing organic matter should be taken. Most of the colloidal particles were visible by transmission electron microscopy with energy dispersion spectrometry (TEM–EDS) if their elemental MF concentration is greater than 200 μg l^?1. If the samples are dried during the preparation for microscopy, neoformation of particles can occur from the soluble part of the element. Size distribution analysis measured by photon correlation spectroscopy (PCS) were frequently unvalid, particularly due to polydispersity and/or too low concentrations in the leachates. A low sensitivity device is required, and further improvement is desirable in that field. For some waste leachates, particles had a zeta potential strong enough to remain in suspension. Mn, As, Co, Pb, Sn, Zn had always a colloidal form (MF concentration/UF concentration > 1.5) and total organic carbon (TOC), Fe, P, Ba, Cr, Cu, Ni are partly colloidal for more than half of the samples). Nearly all the micro-pollutants (As, Ba, Co, Cr, Cu, Mo, Ni, Pb, Sb, Sn, V and Zn) were found at least once in colloidal form greater than 100 μg l^?1. In particular, the colloidal forms of Zn were always by far more concentrated than its dissolved form. The TEM–EDS method showed various particles, including manufactured nanoparticles (organic polymer, TiO₂, particles with Sr, La, Ce, Nd). All the waste had at least one element detected as colloidal. The solid waste leachates contained significant amount of colloids different in elemental composition from natural ones. The majority of the elements were in colloidal form for wastes of packaging (3), a steel slag, a sludge from hydrometallurgy, composts (2), a dredged sediment (#18), an As contaminated soil and two active landfill leachates.These results showed that cascade filtration and ICP elemental analysis seems valid methods in this field, and that electronic microscopy with elemental detection allows to identify particles. Particles can be formed from dissolved elements during TEM sample preparation and cross-checking with MF and UF composition by ICP is useful. The colloidal fraction of leachate of waste seems to be a significant source term, and should be taken into account in studies of emission and transfer of contaminants in the environment. Standardized cross-filtration method could be amended for the presence of colloids in waste leachates.     

Fate and behavior of metal(loid) contaminants in an organic matter-rich shooting range soil: Implications for remediation

This study investigates the fate and behavior of lead (Pb), copper (Cu), antimony (Sb), and arsenic (As) in a shooting range soil. The soil samples were collected from the surface (0–15 cm) and the subsurface (15–40 cm and 40–55 cm) of a grassy and wood chip covered impact area behind a firing position. Optical microscopy images indicate significant amounts of corroded bullet fragments and organic wood chips in the surface soil. Analysis by X-ray powder diffraction (XRPD) and scanning electron microscopy electron dispersive X-ray spectroscopy (SEM-EDS) showed that metallic Pb was transformed into lead oxides (litharge PbO and massicot PbO) and lead carbonates (hydrocerussite Pb₃(CO₃)₂(OH)₂, cerussite PbCO₃, and plumbonacrite Pb₅(CO₃)₃O(OH)₂). Rietveld quantification indicated the surface soil contained 14.1% metallic Pb, 17.9% hydrocerussite, 5.2% plumbonacrite, 5.9% litharge, and 3.9% massicot on a dry weight basis, or a total of 39.7% Pb, far in excess of lead concentrations typically found in US shooting range soils. Metallic Cu (bullet jacket material) appeared stable as no secondary minerals were detected in the surface soil. As and Sb concentrations were on the order of 1,057 mg/kg and 845 mg/kg respectively. The elevated soil pH coupled with high organic carbon content is thought to have caused downward migration of metals, especially for Pb, since 4,153 mg Pb/kg was observed at a depth of 55 cm. More than 60% of Pb was concentrated in the coarse soil (> 0.425 mm) fraction, suggesting soil clean-up possible by physical soil washing may be viable. The concentrations of Pb, As, and Sb in the toxicity characteristic leaching procedure (TCLP) extracts were 8,869 mg/L, 6.72 mg/L, and 6.42 mg/L respectively, were above the USEPA non-hazardous regulatory limit (As and Pb) of 5 mg/L. The elevated Sb and As concentrations draw concern because there is historically limited information concerning these metals at firing ranges and several values exceeded local soil cleanup criteria. As the high Pb concentrations appeared to be linked to the presence of organic-rich berm cover materials, the use of wood chips as berm cover to prevent soil erosion requires reconsideration as a shooting range management practice.     

重金属污染土壤生物毒性的发光菌法测定及评价

向土壤中人为投加重金属污染物,制备了重金属含量不同的一系列污染土壤,对土壤重金属浸提条件进行了探究,并应用明亮发光杆菌T3（Photobacterium phosphoreum T3）对单一Cu、Cd和Pb污染及Cu-Cd和Cu-Pb复合重金属污染土壤的生物毒性进行了测定。实验结果表明,土壤重金属的最佳浸提剂为0.1 mol/L HCl溶液,最佳浸提时间为2.0 h。在单一重金属污染条件下：Cu表现出低浓度促进生长、高浓度抑制生长的双重生物效应,而Cd和Pb则表现出浓度与生物毒性的正相关性;3种重金属污染土壤的毒性强弱顺序为Cd>Pb>Cu。在复合重金属污染条件下,由于重金属之间的相互作用,污染土壤的生物毒性增强。     

Mineralization and Transfer Processes of <Superscript>14</Superscript>C-labeled Pesticides in Outdoor Lysimeters

A recently designed two-chamber-lysimeter-test-system allows the detailed investigation of degradation, transport and transfer processes of ¹⁴C-labeled substances in soil–plant–atmosphere-systems under outdoor conditions. With this test system it is feasible to distinguish between ¹⁴C-emissions from soil surfaces and ¹⁴C-emissions from plant surfaces in soil monoliths under real environmental conditions. Special soil humidity sensors allow the measurement of soil water content near to the soil surface, in 1 and 5 cm depth. The behavior of organic chemicals can be followed for a whole vegetation period and a mass balance for the applied chemical can be established. Some selected results of the herbicides isoproturon and glyphosate – using the two-chamber-lysimeter-test-system – are presented to demonstrate its applicability for the identification and quantification of the processes that govern pesticide behavior in soil–plant-systems. Mineralization of ¹⁴C-isoproturon was very different in four different soils; the mineralization capacity of the soils ranged from 2 to 60%. Leaching of isoproturon in general was very low, but depending on the soil type and environmental conditions isoproturon and its metabolites could be leached via preferential flow, especially shortly after application. For the herbicide ¹⁴C-glyphosate no accumulation of residues in the soil and no leaching of the residues to deeper soil layers could be observed after three applications. Glyphosate was rapidly degraded to AMPA in the soil. Glyphosate and AMPA were accumulated in soy bean nodules.     

Distribution of Cd,Ck, Pb and Zn in Soil and Vegetation Compartments in Stands of Five Boreal Tree Species in N.E. Sweden

Concentrations and total quantity of cadmium (Cd), cupper (Cu),lead (Pb) and zink (Zn) were determined in biomass and soil compartments in a replicated tree species experiment with 27-yr-old stands growing on former farmland in N.E. Sweden. Sequentialextractions of soil samples were performed in order to estimate the exchangeable and an organically bound fraction of each element. The tree species included were Picea abies (L.)H. Karst., Pinus sylvestris L., Pinus contorta Dougl., Larix sibirica Ledeb., and Betula pendula Roth.Tree species influenced the rate of removal of Cu, Pb and Zn incase of stemwood harvesting, and of Cd, Cu and Zn in the case ofwhole-tree harvesting. B. pendula and P. abies had higher quantities and average concentrations of Zn in the biomass. For all species, >50% of the Zn in the stems was found in the bark. P. abies and L. sibirica had higher quantities of Cu in the biomass than the other species.P. abies and P. contorta had high quantities of Cd inthe biomass in relation to the other species. Branches and stembark contained high concentrations of Cd and Pb in relation to foliage and stemwood. Dead branches had especially high concentrations of Pb. The high accumulation rate of Zn in thebiomass of B. pendula was related to a low exchangeable amount of Zn in the A horizon. In the superficial centimeters ofthe A horizon, a depletion similar to that found for Zn was detected for Cu, whereas for Cd and Pb, no correlations were found between quantities of elements in the trees and element pools in the soil.     

Growth responses and metal accumulation capabilities of woody plants during the phytoremediation of tannery sludge

Five woody plants species (i.e. Terminalia arjuna, Prosopis juliflora, Populus alba, Eucalyptus tereticornis and Dendrocalamus strictus) were selected for phytoremediation and grow on tannery sludge dumps of Common Effluent Treatment Plant (CETP), Unnao (Uttar Pradesh), India. Concentration of toxic metals were observed high in the raw tannery sludge i.e. Fe-1667 > Cr-628 > Zn-592 > Pb-427 > Cu-354 > Mn-210 > Cd-125 > Ni-76 mg kg⁻¹ dw, respectively. Besides, physico-chemical properties of the raw sludge represented the toxic nature to human health and may pose numerous risks to local environment. The growth performances of woody plants were assessed in terms of various growth parameters such as height, diameter at breast height (DBH) and canopy area of plants. All the plant species have the capabilities to accumulate substantial amount of toxic metals in their tissues during the remediation. The ratio of accumulated metals in the plants were found in the order Fe > Cr > Mn > Pb > Zn > Cu > Cd > Ni and significant changes in physico-chemical parameters of tannery sludge were observed after treatment. All the woody plants indicated high bioconcentration factor for different metals in the order Fe > Cr > Mn > Ni > Cd > Pb > Zn > Cu. After one year of phytoremediation, the level of toxic metals were removed from tannery sludge up to Cr (70.22)%, Ni (59.21)%, Cd (58.4)%, Fe (49.75)%, Mn (30.95)%, Zn (22.80)%, Cu (20.46)% and Pb (14.05)%, respectively.     

Predicting the mobility of Zn, Fe, Cu, Pb, Cd from roasted sulfide (pyrite) residues—A case study of wastes from the sulfuric acid industry in Sweden

Leachates from roasted sulfide residues, which are the wastes from the production of sulfuric acid at Falun, Sweden, have low pH and high concentrations of Zn, Fe, and SO₄. The minerals are mainly hematite and maghemite and, because the various sulfides in the feed behave differently during the roasting process, the residual sulfides minerals are pyrrhotite and sphalerite. Oxidation of the residual sulfides contributes acidity, Zn, Fe, Cu, Cd, and sulfate to the effluents from the waste deposits. The dissolution of sphalerite is most likely accelerated in acid solution rich in Fe (III). The formation of Pb-sulfate coatings on galena may provides an armoring effect which slows the oxidation of the galena. Residual sulfides are source phases controlling long-term contaminant release. Other source minerals for Zn, Fe, Pb, Cu, Cd and SO₄ in the effluents are iron oxides which retained percentage quantities of SO₄, roast-derived alteration rims of Zn oxides on sphalerite, alterated silicates formed during the roasting process, and secondary minerals (e.g. Zn, Fe, Cu sulfates, iron hydroxides) that were precipitated by in-site oxidation in the waste dumps. The Zn, Fe, and Cu sulfates most likely control short-term changes in the chemistry of the leachate, while Pb concentration in the leachates may be controlled predominantly by Pb-release from the altered silicates. The mineralogical and geochemical data provide fundamental information essential for the remedial management of this type of industial waste.     

Regional Variability of Cd,Hg, Pb and C Concentrations in Different Horizons of Swedish Forest Soils

Contents of cadmium (Cd), mercury (Hg), lead (Pb) and carbon(C) in the O, B and C horizons of podzolized forest soils inSweden were surveyed. Concentrations and storage of Cd, Hg andPb in the O and B horizons were high in southern Sweden and gradually decreased towards the north, though with considerablelocal variability. This pattern reflects the influence of anthropogenic emissions of these metals, as well as the effectsof soil-forming processes. Parent till material, as representedby the C horizon concentration of the respective metal, accountedfor little of the variation in metal concentration in the O horizon. For Cd and Pb, the correlations were not significant orslightly negative (R² = 0.12 and 0.09 respectively) depending on region, while for Hg the correlation was not significant or slightly positive (R² = 0.03 and 0.08). Furthermore, parent till material accounted for more of the variation in metal concentrations in the B horizons in the northern part of Sweden than in the middle and southernmost parts, where the concentration of total carbon had more influence. The correlation between the metal concentrationsin the B and C horizon was strongest for Pb (R² = 0.63 and 0.36 in the two northernmost regions), lower for Cd (R² = 0.19 and 0.16) and not significant for Hg. For allsoil horizons, total C concentration accounted for much of thevariation in Hg concentration in particular (O-horizon R² = 0.15–0.69, B horizon R² = 0.36–0.50, C horizon R² = 0.23–0.50 and ns in one region). Ratios of metal concentrations between the B and C horizons were highest for Hg(maximum value of 30), indicating a relatively larger addition or retention of Hg compared to Cd and Pb (maximum value of 10)in the B horizon. This study indicate that factors other than parent material account for the large scale variation in O horizon concentrationsof metals but patterns correspond well with those of atmosphericdeposition of heavy metals and acidifying substances. Furthermore, the study highlights the importance of soil organicmatter and the intensity of pedogenic processes for the content and distribution of metals throughout the soil horizons.