Effects of long-term irrigation with treated wastewater. Part I: Evolution of soil physico-chemical properties

The long-term impact of irrigation on a Mediterranean sandy soil irrigated with Treated wastewater (TWW) since 1980 was evaluated. The main soil properties (CEC, pH, size distribution, exchangeable cations and chloride, hydraulic conductivity) as well as the organic matter and Cu, Cr and Pb speciation in an irrigated soil and a non-irrigated control soil at various soil depths were monitored and compared during a 2 years experiment. In this first part, the evolution of the physico-chemical soil properties was described. The irrigation with TWW was beneficial with regard to water and nutrient supplying. All the exchangeable cations other than K⁺ were higher in the irrigated soil than in the reference one. A part of the exchangeable cations was not fixed on the exchange complex but stored as labile salts or in concentrated soil solution. Despite the very sandy soil texture, both saturated and unsaturated hydraulic conductivity exhibited a significant diminution in the irrigated soil, but remained high enough to allow water percolation during rainy periods and subsequent leaching of accumulated salts, preventing soil salinization. In the irrigated soil, exchangeable sodium percentage (ESP) exhibited high values (20% on average) and the soil organic C was lower than in the reference. No significant effect was noticed on soil mineralogical composition due to irrigation.     

Speciation of heavy metals in electroplating industry sludge and wastewater residue using inductively coupled plasma

The speciation of metals in environmental samples is a critical factor in assessing the potential environmental impacts, before their disposal. The distribution and speciation of toxic heavy metals in plating wastewater residues and sludge was investigated for four samples using sequential extraction method. Tessier method was used to fractionate the metal content into exchangeable, acid extractable, reducible and oxidizable fractions. Residual and total metal contents were determined in aqua regia digest. The extracts were analysed for metals using inductively coupled plasma -atomic emission spectrometry. The bioavailable fraction (exchangeable and acid extractable fractions) is comprised less than the other forms. The oxidisable and reducible forms are dominants for all the four samples studied. The major metal constitute in the samples is iron, the wastewater residue contains (12.3 and 7.4 g/Kg respectively on dry basis) and the sludge contains (31.5 and 41.6 g /Kg) respectively. Cr concentration is higher in wastewater residue of second electroplating industry. The descending order of the average total metal contents for these four samples were Fe > Cr > Sn > Zn >Cu > Ni > Mn > Pb > Cd > Ag. Based on the average of absolute values for the four samples the highest bioavailability order of metals is Cr (39 %) in wastewater residues and Zn (32 %) in sludge samples. Metal recovery was good, with < 10 % difference between the total metal recovered through the extractant steps and the total metal determined using aqua regia extract.     

The effect of long-term soil irrigation by wastewater on organic matter, polycyclic aromatic hydrocarbons, and heavy metals evolution: case study of Zaouit Sousse (Tunisia)

Irrigation by treated wastewater (TWW) can pollute the soil by different organic and inorganic compounds. The pollution level can depend on the irrigation period, soil nature, and wastewater characteristics. Since 1989, the Zaouit Sousse area (central Tunisian) has been irrigated by treated wastewater. The irrigation period and the mineralogy of soil composition change from one locality to another in Zaouit Sousse area. In this work, we are interested in organic compounds, polycyclic aromatic hydrocarbons (PAHs), and heavy metals (HMs) evolution. One control soil (S1) and four irrigated areas soil (S2, S3, S4, and S5) were chosen. The soil samples differ by the irrigation period and soil characteristics. Total PAHs content in control soil was 66.2 ng?g^?1 and in irrigated areas were between 46.23 and 129.51 ng?g^?1. The PAHs content in irrigated soil, except S5 which has been irrigated with wastewater for 20 years and contains the highest clay fraction percent, decreased with the irrigation period (from 0 to 20 years). The microbial degradation may decrease the PAHs concentrations in the soil thanks to bacterium brought by TWW and the important soil permeability. Concentration of heavy metals ranged from 24 to 1,320 μg?L^?1. The HMs (Cu, Cr, Zn, Fe, Ni, Pb, and Cd) contents decreased with the irrigation period (from 10 to 20 years). So, following the PAHs aerobic bio-degradation, this organic compound discharges their absorbed heavy metals which leached to deeper levels. The Cr, Cu, Al, Zn, and Cd mobility depend on the clay yield too. However, the PAHs and Pb mobility are also related to humic substance quantities. Cr and Cu have affinities both to clay and humic substance quantities.     

金昌市铜镍矿区周围土壤中重金属的迁移特征

对金昌矿区不同区域土壤5~20 cm层中重金属各化学形态及活性态的迁移行为进行了研究,结果表明：土壤中重金属不同化学形态迁移率不同,弱酸提取态、可还原态、可氧化态和残渣态平均迁移率分别为0.13、0.51、0.30和0.54。重金属总量和活性态（包括弱酸提取态、可还原态、可氧化态）迁移率也表现出很大差异,尾矿区土壤Cr总量迁移率较高为0.65,而其活性态迁移率较低为0.26,Ni与Cr迁移特征完全相反,总量迁移率为0.26,而活性态迁移率为0.67;农田土壤中Pb总量迁移率低而活性态迁移率高,Ni与Zn特征相似,总量迁移率高而活性态迁移率相对较低;大棚地土壤中重金属迁移率均较低,Cu和Ni活性态几乎未发生向下迁移。可见,重金属的迁移与其化学形态分布关系密切,与重金属总量的迁移率相比,活性态迁移率能够更有效地反映出土壤中重金属的迁移特征和潜在危害性。     

Soil Cd,Cu, Pb and Zn contaminants around Mount Isa city,Queensland, Australia: Potential sources and risks to human health

This article investigates the relationship between soil Cd, Cu, Pb and Zn contaminants and the location and activities of the Pb–Zn–Ag and Cu mines at Mount Isa, Queensland, Australia. Analysis of the data focuses primarily on soil Pb distributions and concentrations because of their potential impact on children’s health. The Xstrata Mount Isa Mines lease (XMIM) is Australia’s leading emitter of numerous contaminants to the environment, including Cu and Pb, and the mining-related activities have been linked causally to the findings of a 2008 study that showed 11.3% of local children (12–60 months) have blood Pb levels >10 μg/dL. Queensland government authorities and Xstrata Mount Isa Mines Pty Ltd maintain that contaminants within environmental systems around Mount Isa are largely the result of near-surface mineralization. The evidence for whether the contamination is derived from XMIM or other possible sources, such as the natural weathering of ore-rich bedrock, is investigated using data from surface and subsurface soil chemistry, atmospheric modelling of metal contaminants from mining and smelting operations and local geological and associated geochemical studies. Sixty surface soil samples collected from sites adjacent to houses, parks and schools throughout Mount Isa city were analyzed for their total extractable Cd, Cu, Pb and Zn concentrations in the <2 mm to >180 μm (coarser) and <180 μm (finer) grain size fractions. Concentrations in the finer size fraction reveal a range of values: Cd – 0.7–12.5 ppm; Cu – 31–12,100 ppm; Pb – 8–5770 ppm; Zn – 26–11,100 ppm, with several samples exceeding Australian residential health investigation guidelines. Spatial analysis shows that surface soil metal concentrations are significantly higher within 2 km of XMIM compared to more distant samples, and that more than 1000 property lots are at risk of having detrimentally high soil Pb levels. Determination of metal concentrations in 49 samples from eight soil pits shows that surface samples (0–2 cm) are enriched significantly relative to those at depth (10–20 cm), suggesting an atmospheric depositional origin. AUSPLUME air dispersal modelling of Pb originating from the Cu and Pb smelter stacks and mine site fugitive sources confirms that Pb is deposited across the urban area, during periods of the year (∼20%/a) when the wind blows from the direction of XMIM towards the urban area and disperses dusts from the uncovered spoil and road surfaces, as well as from stack emission sources. Although there are some spatially restricted outcrops of Pb close to the surface in parts of the urban area, the Cu-ore body is ∼244 m below the surface. However, enriched and significantly correlated surface soil concentrations of Cu and Pb (Pearson correlation 0.879, p = 0.000) in and around the urban area of Mount Isa can only be explained by atmospheric transport and deposition of metals from the adjoining mining and smelting operations. The results from this study provide unequivocal evidence that both historic and ongoing emissions from XMIM are contaminating the urban environment. Given the ongoing Pb poisoning issues in Mount Isa children, it is clear that remediation, reductions in mine emissions and more stringent regulatory actions are warranted.     

Geochemical features of heavy metals in core sediments of northwestern Taihu Lake, China

Sequential core sediments from northwestern Taihu Lake in China were analyzed for grain size, organic carbon and heavy metal content. The sediments are composed of organic-poor clayey-fine silts. The chemical speciations of Cu, Fe, Mn, Ni, Pb, and Zn were also analyzed using the BCR sequential extraction procedure. Cu, Fe, Ni, and Zn are mainly associated with the residue fraction; Mn is concentrated mainly in exchangeable/carbonate fraction and residue fraction; and Pb mainly in Fe/Mn oxide fraction and organic/sulfide fraction. The exchangeable/carbonate fractions of Cu, Fe, Ni, Zn and Pb are lower. The fractions of Ni, Pb and Zn bound to the Fe/Mn oxide have significant correlations with reducible Mn; the organic/sulfide fractions of Cu, Mn, Ni, Pb, and Zn have significant correlations with TOC. The extractable fractions of Cu, Mn, Ni, Pb, and Zn are high at the top 4 cm of the core sediments as compared to those in the deeper layers, showing the anthropogenic input of heavy metals is due to rapid industrial development. The heavy metal pollution history of the sediments has been recorded since the late 1970s, determined by the result of ^137Cs dating.     

Speciation and potential remobilization of heavy metals in sediments of the Taihu Lake, China

The species of Cu, Pb, Zn, Cd and Cr in sediments of the Taihu Lake, China, have been analyzed using the sequential chemical extraction method. Variations in the chemical fractions of these metals and their geographic distributions have also been studied. For all five metals, the residual fraction is highest but the exchangeable fraction is lowest among all the fractions. Compared to other metals, Cd has the highest percentage in the exchangeable fraction, and Cr is associated mainly with the residual fraction. Cu in the organic fraction and Pb in the Fe-Mn fraction are the important species, whereas the lowest percentages are found for Cd in the organic fraction, Cu in the Fe-Mn oxide fraction and Pb in the carbonate fraction. With respect to spatial differences, the total contents in the non-residual fractions of the metals in bay sediments are found to be higher than those in other sediments. The fractions of Cd, Cu and Cr showed significant variations in different regions. The fractions of Pb and Zn, however, did not show significant variations in spatial distribution, suggesting different amounts and different paths of anthropogenic input for the metals. Comparisons of the metal speciation indicated that Cd might be the most bioavailable metal, followed by Pb.     

Particulate-associated potentially harmful elements in urban road dusts in Xi’an,China

Sixty five urban road dust samples were collected from different land use areas of ∼240 km² in Xi’an, China. The concentrations of Ag, As, Cr, Cu, Hg, Pb, Sb and Zn were determined to investigate potentially harmful element (PHE) contamination, distribution and possible sources. In addition, the concentrations in different size fractions were measured to assess their potential impact on human health. The highest concentrations were found in the fraction with particle diameters between 80 μm and 101 μm, the finest particles (<63 μm) were not the most important carriers for Ag, As, Cd, Cr, Cu, Hg, Pb and Zn. The percentages of these elements in particles with diameters less than 63 μm (PM₆₃) and less than 101 μm (PM₁₀₁) were in the range of 7–15%, and 30–55%, respectively. Three main factors influencing element distributions have been identified: (a) industrial activities; (b) prior agricultural land use; and (c) other activities commonly found in urban areas, such as traffic, coal combustion, waste dumping, and building construction/renovation. The highest concentrations were found in industrial areas for As (20 mg kg⁻¹), Cr (853 mg kg⁻¹), Cu (1071 mg kg⁻¹), Pb (3060 mg kg⁻¹) and Zn (2112 mg kg⁻¹), and in previous agricultural areas for Ag and Hg, indicating significant contributions from industrial activities and prior agricultural activities.     

Heavy metal distribution in karst soils from Croatia and Slovakia

With the use of the optimised three-step BCR sequential-extraction procedure it was possible to assess the mobility of selected elements in soil profiles from Croatian and Slovakian karst terrains. The soils in the Croatian karst were enriched in Cr, Ni, V, Mn, Cu, Cd and Mo, while soils from the Slovak Karst had high Pb and Zn concentrations. It was determined that the elements were most readily mobilised from the topsoil and the degree of mobility decreased with depth. Cr and Ni were mainly bound to the residual fraction, and Pb in the oxidisable fraction. Cu mobility was high in samples treated with agrochemicals throughout the soil profile.     

Distribution and chemical speciation of heavy metals in the surficial sediments of the Bak?r?ay and Gediz Rivers, Eastern Aegean

The pollution of aquatic ecosystem by heavy metals has assumed serious proportions due to their toxicity and accumulative behaviour. The toxicity and fate of the water borne metal is dependent on its chemical form and therefore quantification of the different forms of metal is more meaningful than the estimation of its total metal concentrations. A five-step sequential extraction procedure was applied for the determination of the distribution of seven elements (Pb, Cr, Cu, Mn, Zn, Ni, Fe) in sediment samples collected from Bakır?ay and Gediz Rivers. According to this study, the results of metals are mostly retained in the residual, oxidizable and reducible fractions. Based on the chemical distribution of metals, we found that Cr, Zn, Cu and Ni are the most non-mobile metals. Pb is the metal that showed the highest percentages in the residual and reducible fractions. Mn is present in the higher percentages in the reducible and carbonate fractions. However, Fe is present in the greatest percentages in the residual fraction, which implies that these metals are strongly linked to the sediments. The risk assessment code as applied to the present study shows that about 12.3–26.9 and 15.7–33.5% of manganese at most of the sites exist in carbonate fraction in the Bakır?ay and Gediz Rivers, respectively. Therefore, Mn comes under the medium risk category in the Bakır?ay and high-risk category in the Gediz River. Speciation pattern of Cu, Zn, Pb, Cr, Ni, Fe shows low to medium risk to aquatic environment health in both rivers.     

Metal geochemical and mineral magnetic characterization of the <2.5 μm fraction of urban soils in Xuzhou (China)

The concentrations of metals (Pb, Cu, Zn, Co, Ni, Fe and Mn) in the <2.5 μm fraction of surface soils (0–5 cm) from highly industrialized areas in Xuzhou (China) were determined. All analyzed metals with the exception of Mn and Co in the present study showed elevated concentrations in the <2.5 μm fraction of soils compared to background concentrations, particularly for Zn. Metal enrichment was positively correlated with carbonate complexation constants (but not bulk solubility products) as well as the first stability constants of metal-citrate, likely suggesting that both metal–organic complexation and/or precipitation of carbonate surfaces that subsequently adsorb metals are likely responsible for these metal enrichment on these samples. Sequential extraction analysis shows the metals Pb, Cu, Zn, Co and Mn were largely associated with the reducible fraction, whereas Ni was largely associated with the oxidisable fraction. Manganese is the only metal showing significant association with the exchangeable fraction (up to 33 %), suggesting that it may be the most susceptible metal to mobilization. Mineral magnetic analysis indicates that ferrimagnetic SSD + SP (stable single domain + superparamagnetic) minerals dominated the <2.5 μm fraction of Xuzhou surface soils. Lead, Cu and Zn were found to show significant correlations with χlf (p < 0.01), suggesting that magnetic technique might be beneficially used as a rapid and inexpensive method to estimate these metal contaminations in the <2.5 μm fraction of surface soils.     

Speciation Study of Cr in a Geochemical Reference Material Sediment Series Using Sequential Extraction and XANES Spectroscopy

Speciation of Cr in geochemical reference materials was characterised by sequential extraction and X‐ray absorption near‐edge structure (XANES) spectroscopy to identify Cr(III) resulting from the reduction of pollutant Cr(VI). Sequential extraction suggested that the amount of Cr associated with an acetic acid soluble fraction was low; Cr associated with a reducible phase and an oxidisable phase was extracted at 5–10% of the total Cr concentration, and the residual phase was found to be the dominant Cr‐containing fraction. Cr speciation in soil artificially doped with Cr(VI) and sediment samples collected from highly populated and industrialised areas was different from that in naturally occurring materials. Substantial Cr was extracted as a reducible phase (15–30%) and an oxidisable phase (30–60%) for these samples. Through subsequent XANES spectroscopy analysis, the reducible phase was explained by Cr bound to Fe hydroxide, while the oxidisable phase was a mixture of Cr bound to humic substances and Cr hydroxides. That is, Cr(VI) present as a contaminant in sediments and soils was reduced to Cr(III), which then bound to Fe hydroxide and humic substances, precipitating as a hydroxide. Thus, a combination of sequential extraction and XANES spectroscopy allows for effective identification and quantification of the chemical forms of Cr in sediments and soils.     

Copper Speciation in a Collection of Geochemical Reference Materials Using Sequential Extraction and Evaluation of the Validity Using XANES Spectroscopy

Copper speciation in a collection of Japanese geochemical reference materials (JSO‐1, JLk‐1, JSd‐1, ‐2, ‐3 and ‐4, JMs‐1 and JMs‐2) was achieved by sequential extraction and characterised using X‐ray absorption near‐edge structure spectroscopy. In the first step of the extraction, referred to as the acid fraction, between 1% and 20% total Cu within the reference materials was extracted. Such a result is typically accounted for by absorption of Cu onto clay minerals. However, the presence of Cu sulfate (an oxidation product of chalcopyrite) was observed in some of the stream sediments affected by mining activity (JSd‐2 and JSd‐3) instead. Copper was extracted in the reducible fraction (targeting Fe hydroxide and Mn oxide) (2–49% total Cu). Between 2% and 51% Cu was extracted in the oxidised fraction (targeting sulfides and organic matter). X‐ray absorption near‐edge structure spectroscopy clarified that the reducible fraction consisted of Cu bound to Fe hydroxide, whereas the oxidised fraction was a mixture of Cu bound to humic acid (HA) and Cu sulfide. In the oxidisable fraction, chalcopyrite was the predominant species identified in JSd‐2, and Cu bound to HA was the major species identified in JSO‐1 (a soil sample).     

Distribution and sequential extraction of some heavy metals in urban soils of Guiyang City,China

Sixty-two soil samples collected from different functional zones of Guiyang were analyzed for total concentrations and sequential extraction of Cr, Cu, Pb, Zn and Cd by ICP spectrometry. The average total concentrations ofCr, Cu, Pb, Zn and Cd in the soils of Guiyang were 92.9, 51.6, 44.1,139.3 and 0.28 mg/kg, respectively. The soils have been polluted by Cr, Cu, Pb, Zn and Cd to some extent in comparison with the background values of Guiyang. Significant differences were recognized in the concentrations of Cr, Cu, Pb, Zn and Cd in different functional zones. As for the sequential extraction, Cr, Cu and Zn were present mainly in the residual fraction, and Pb was present mainly in the oxidizable fraction. The reducible fraction of Cd accounts for 47.5%, and the residual fraction is lowest. The mobility and bioavailability of heavy metals follow the order of Cd〉Pb〉Cu〉Cr〉Zn.     

Distribution and enrichment of heavy metals in a sediment core from the Pearl River Estuary

A sediment core collected from coastal zone near the Qiao Island in the Pearl River Estuary was analyzed for total metal concentrations, chemical partitioning, and physico-chemical properties. Three vertical distribution patterns of the heavy metals in the sediment core were identified, respectively. The dominant binding phases for Cu, Pb, Cr, and Zn were the residual and Fe/Mn oxides fractions. Cd in all sediments was mainly associated with exchangeable fraction. Influences of total organic carbon content and cation exchange capacity on the total concentrations and fractions of almost all the metals were not evident, whereas sand content might play an important role in the distributions of residual phases of Cr, Cu, Pb, and Zn. In addition, sediment pH had also an important influence on the Fe/Mn oxides, organic/sulfide and residual fractions of Cr, Cu, and Zn. Contamination assessment on the heavy metals in the sediment core adopting Index of Geoaccumulation showed that Cr, V, Be, Se, Sn, and Tl were unpolluted, while Cu, Ni, Pb, Zn, Cd, and Co were polluted in different degrees throughout the core. It was remarkable that the various pollution levels of the metals from moderate (for Cu, Pb, and Zn) to strong (for Cd) were observed in the top 45 cm of the profiles. The relative decrease of the residual fraction in the upper 45 cm of the core is striking, especially for Zn and Cu, and, also for Pb, and Cr. The change in fraction distribution in the upper 45 cm, which is very much contrasting to the one at larger depths, confirms that the residual fraction is related to the natural origin of these metals, whereas in the upper part, the non-residual fractions (mainly the Fe/Mn oxides fraction) are increased due to pollution in the last decade. The possible sources for Cu, Pb, Zn, and Cd contaminations were attributed to the increasing municipal and industrial wastewater discharges, agricultural runoff, atmospheric inputs, and runoff from upstream mining or smelting activities, which may be associated with an accelerating growth of economy in the Pearl River Delta region in the past decade.     

Geochemical and mineral magnetic characterisation of urban sediment particulates,Manchester, UK

Urban sediments are part of a complex system in which particulates accumulate potentially toxic pollutants, ultimately posing a threat to urban water-bodies and public health. It is therefore important to recognise sources, signatures and pathways of urban particulates. Urban sediment samples were analysed from both inner and outer city road surfaces of Manchester, UK. High metal concentrations, coupled with the largely ferrimagnetic multi-domain (MD) mineral magnetic composition of the particulates, indicate inputs of anthropogenic origin, primarily particulates derived from automobiles, as being the dominant source to the urban sediment system. Iron and Pb concentrations show a clear spatial trend, whereby concentrations are enhanced in the inner city samples. Lead concentrations for inner and outer city samples average 354 and 185 μg g⁻¹, respectively. Iron concentrations for inner and outer city samples average 11302 and 6486 μg g⁻¹, respectively. Sequential extraction analysis shows the metals Mn, Fe, Zn and Pb are largely associated with the reducible fraction, whereas Cu is largely associated with the oxidisable fraction. Zinc is the only metal showing significant association with the exchangeable fraction (up to 33%), suggesting that it may be the most susceptible metal to mobilisation during runoff. Metal fractions identified as showing larger associations with the reducible and oxidisable fractions will continue to be vulnerable to mobilisation as a result of changes in ambient pH and/or redox conditions. Mineral magnetic concentration parameters, such as the saturation isothermal remanent magnetisation (SIRM), together with hysteresis parameters such as the coercive force and interparametric ratios (such as (B_o)_cr/H_c and IRM_-100mT/SIRM) show that ferrimagnetic MD minerals dominate the Manchester urban sediments. Average results for frequency-dependent susceptibility as a percentage (2%) suggest that the composition of these Manchester sediments is not dominated by soil-derived material, and therefore magnetically coarser, anthropogenically-derived material is dominant. Unlike Pb and Fe concentrations, mineral magnetic characteristics of the Manchester urban sediment samples exhibit no significant spatial variation.     

The mobility,bioavailability, and human bioaccessibility of trace metals in urban soils of Hong Kong

Trace metals in soils may pose risks to both ecosystem and human health, especially in an urban environment. However, only a fraction of the metal content in soil is mobile and/or available for biota uptake and human ingestion. Various environmental availabilities of trace metals (Cu, Pb and Zn) in topsoil from highly urbanized areas of Hong Kong to plants, organisms, and humans, as well as the leaching potential to groundwater were evaluated in the present study. Forty selected soil samples were extracted with 0.11 M acid acetic, 0.01 M calcium chloride, 0.005 M diethylenetriaminepentaacetic acid, and simplified physiologically based extraction tests (PBET) for the operationally defined mobilizable, effectively bioavailable, potentially bioavailable, and human bioaccessible metal fractions, respectively. The metals were generally in the order of Zn > Cu ∼ Pb for both mobility (24%, 7.6%, 6.7%) and effective bioavailability (2.8%, 0.9%, 0.6%), Pb (18%) > Cu (13%) > Zn (7.4%) for potential bioavailability, and Pb (59%) ∼ Cu (58%) > Zn (38%) for human bioaccessibility. Although the variations in the different available concentrations of metals could mostly be explained by total metal concentrations in soil, the regression model predictions were further improved by the incorporation of soil physicochemical properties (pH, OM, EC). The effectively bioavailable Zn and Pb were mostly related to soil pH. Anthropogenic Pb in urban soils tended to be environmentally available as indicated by Pb isotopic composition analysis. Combining various site-specific environmental availabilities might produce a more realistic estimation for the integrated ecological and human health risks of metal contamination in urban soils.     

贵阳城市土壤重金属元素形态分析

选取贵阳市62个代表性的表层土壤样品,分析了其重金属元素的含量和存在形态.结果表明,贵阳城市土壤中5种重金属元素(Cr、Cu、Pb、Zn和Cd)的含量较高,且变化较大.表层土壤中Cr、Cu、Zn主要以残渣态形式存在,Pb主要以可氧化态形式存在.Cd可还原态含量高达47.5%,残渣态含量最低,说明Cd较活泼,具有潜在的环境影响能力.     

Sorption of lead by phlogopite-rich mine tailings

The Pb sorption capacity of apatite ore mine tailings and its potential to act as a remediation agent in a Pb polluted areas were investigated. The tailings, originating from the Siilinjärvi carbonatite complex in Finland, consist mainly of phlogopite and calcite accompanied by apatite residues. The ability of the tailings to retain Pb from an aqueous solution was investigated using an isotherm technique. Furthermore, in a 3-month incubation experiment, uncontaminated mineral soil was amended with untreated tailings and with tailings artificially weathered with acid to increase the quantity of Al and Fe (hydr)oxides. Tailings of two particle-sizes (∅ > 0.2 mm and ∅ < 0.2 mm) somewhat differing in their mineralogical composition were investigated as separate amendments. All tailings materials were added to the soil in two dosages (5 g and 10 g of tailings per 125 g of soil). Following incubation, tailings-induced changes in the Pb sorption capacity of the soil were investigated with the isotherm technique. Finally, to investigate the distribution of sorbed Pb among various chemical pools, the soil samples amended with tailings were contaminated with Pb and then subjected to sequential fractionation analysis. The results revealed efficient removal of Pb from an aqueous solution by the tailings, presumably through precipitation and surface complexation mechanisms. Amending the soil with the tailings increased the mass-based maximum Pb sorption capacity from 10.8 mg kg⁻¹ of the control soil to 14–20.5 mg kg⁻¹ for the untreated tailings and to 32.1–72.1 mg kg⁻¹ for the acid-treated material. The tailings transferred Pb from the exchangeable pool to the non-extracted one and thereby substantially decreased its bioavailability. The material with a particle diameter of less than 0.2 mm had a higher mass-based Pb sorption capacity than the large-sized material. The results suggest that the tailings may potentially serve as an immobilizing agent in polluted areas.     

Total concentration,speciation and mobility of potentially toxic elements in soils around a mining area in central Iran

The current study was designed to investigate the extent and severity of contamination as well as the fractionation of potentially toxic elements (As, Cd, Cr, Cu, Pb, Zn, Ni) in minesoils and agricultural soils around a Pb–Zn mine in central Iran. For this purpose, 20 agricultural soils and eight minesoils were geochemically characterized. Results showed that minesoils contained elevated concentrations of As (12.9–254 mg kg⁻¹), Cd (1.2–55.1 mg kg⁻¹), Pb (137–6239 mg kg⁻¹) and Zn (516–48,889 mg kg⁻¹). The agricultural soils were also polluted by As (5.5–57.1 mg kg⁻¹), Cd (0.2–8.5 mg kg⁻¹), Pb (22–3451 mg kg⁻¹) and Zn (94–9907 mg kg⁻¹). The highest recorded concentrations for these elements were in soils influenced directly by tailing ponds. Chromium, Cu and Ni content in agricultural soils (with average value of 74.1, 34.6 and 50.7 mg kg⁻¹, respectively) were slightly higher than the minesoils (with average value of 54.5, 33.1 and 43.4 mg kg⁻¹, respectively). Sequential extraction data indicated that there were some differences between the speciation of PTEs in soil samples. In the agricultural soils, Zn and Cd were mainly associated with carbonate bound fraction, As and Pb with reducible fraction, Cu with oxidisable fraction and Cr and Ni with residual phase. With respect to mobility factor values, Zn and Cd in the agricultural soils have been found to be the most mobile while As mobility is negligible. Also, the mobility factor of As, Cd and Pb in agricultural soils adjoining tailing ponds was high. In minesoil sample Cd was most abundant in the carbonate form, whereas other studied elements were mainly present in the reducible and residual fractions; therefore, despite the high total concentrations of As, Pb and Zn in the minesoils, the environmental risk of these elements was low. Based on the obtained data, a portion of Cu, Cr and Ni input was from agricultural activities.