Mechanism of enrichment of trace metals on fine sludges collected from filtration plants

Fine sludges were collected from five filtration plants, and the partitioning of ten metals (Ag, Cd, Mn, Zn, Pb, Cu, Sn, Co, Ni, and Fe) in them was determined by selective leaching techniques. (1) The available amounts, which shows the total of each metal leached between 1 M CH₃COONH₄ and 30 percent H₂O₂, for Ag, Cd and Mn, ranged from 51 to 98 percent for five sludges. (2) The available amounts for Zn, Pb, Cu, and Sn were 47–92 percent for five sludges. (3) The most important fraction for Co, Ni, and Fe, except the Inagawa sludge, which is markedly polluted by organic matter, was the crystalline particle. Therefore, the above metals, except Co, Ni, and Fe, are thought to be enriched on ion-exchangeable sites, organic matter, hydrous Fe/Mn oxides, and sulfides in fine sludges.     

云浮黄铁矿利用过程中微量毒害元素的环境化学活动性

为了解云浮黄铁矿利用过程中微量毒害元素的环境地球化学行为，客观评价它们对环境质量的影响，利用元素结合形态的连续提取实验方法，分析了云浮黄铁矿及其工业废渣中Co,Ni,Cu,Zn,As,Se,Cd,Sn,Sb,Pb和Tl等11种毒害元素的形态及化学活动性。结果表明，黄铁矿中大部分微量毒害元素都有着极强的化学活动性，各元素活动态浸出比例依次为Co96.3%,Se91.9%,Cu90.3%,Cd90.0%,Pb89.7%,Zn88.6%,Sb82.5%,Ni80.6%，Sn70%,Tl55.1%和As31.9％，元素As和Tl主要赋存于硫化物和硅酸盐矿物相中，另有少量的Cu,Pb和Sb可能赋存于碳酸盐矿物相中，其他元素则主要赋存于硫化物矿物相中。与黄铁矿相比，飞灰和灰渣中各元素可交换态和碳酸盐结合态所占的比例明显减少。废渣中各元素的化学活动性表现出很大的差别，其中Cu,Zn和Cd的化学活动性最强，活性态浸出比例在90％以上；其次是Co,Ni,Se,Pb和Tl，浸出比例在50％左右；Sb,As和Sn的稳定性较高，浸出比例分别为1％、5％和14％左右；飞灰中微量毒害元素的活动性均高于灰渣。     

Heavy metal geochemistry and mineral magnetic characterization of urban soil in Xuzhou,China

In the present study, the enrichment, availability, speciation of heavy metals including Pb, Zn, Cu, Cd, Ni and Sb and magnetic properties of urban soils of Xuzhou (China) were investigated. All analyzed metals showed elevated concentrations compared to local background concentrations. Cadmium and Sb are the metals most enriched in the analyzed area, presenting enrichment factor, on average, of 16.5 and 8.3, respectively. By self-organizing map in combination with diagnostic ratios, the source of Sb, Cd, Cu and Pb in soils might be mainly from traffic emissions. Sequential extractions indicate that metals were primarily associated with the reducible fraction with the exception of Ni. The order of extraction efficiency of various metals was SBET (simplified physiologically based extraction test) > DTPA (diethylenetriaminepentaacetic acid) > CaCl₂. The magnetic results show that soil samples were dominated by a strong ferrimagnetic mineral component with multi- and single-domain magnetic grains. Only CaCl₂ extractable Sb was found to show significant correlations with χlf and SIRM. For both DTPA and SBET extractions, all metals investigated showed significant associations with both χlf and SIRM (saturation isothermal remanent magnetization).     

Background levels and baseline values of available heavy metals in Mediterranean greenhouse soils (Spain)

This study determines extractable levels of Cd, Cu, Pb, Zn, Ni and Co in western Almería (Spain) greenhouse surface soil horizons using EDTA solution, which is identified as the fraction available for organisms and plants. It also establishes background levels, geochemical baseline concentration and reference values (RV), and investigates the possible relationships between soil properties and elemental concentrations. The results show that the soil concentration of these extractable heavy metals was high as those reported by other authors for Spanish agricultural soils. The available RV concentrations obtained (mg kg⁻¹) were: Cd 0.17, Cu 1.6, Pb 13.8, Zn 5.0 Ni 1.7 and Co 2.9. Using the upper baseline criterion, 95% of greenhouse soils present a relatively higher content of extractable heavy metals given their Cd and Cu concentration. Significant correlations between total and EDTA-extractable metal levels were found for Zn, Pb, Cu, Cd and Ni. Soil properties also related to heavy metals content, suggesting that Cd, Cu, Pb and Zn are of similar origin and relate to anthropic activities, and implies the same interactions and/or relationships among these metals.     

A GIS-based approach for detecting pollution sources and bioavailability of metals in coastal and marine sediments of Chabahar Bay,SE Iran

Chabahar Bay in SE of Iran is a shallow semi-enclosed environment affected by anthropogenic activities. In this paper, 19 sediment samples were collected and concentration of selected metals (Cu, Pb, Zn, Cd, Ni, Cr, Co, V and Fe) was determined using ICP-MS analytical method. Sediment samples from five stations were also selected for sequential extraction analysis and concentration of metals in each fraction was determined using ICP-OES. In order to investigate the environmental quality of Chabahar Bay, geographic information system (GIS) along with geochemical data, environmental indices and statistical analyses were used. Calculated contamination degree (C_d) revealed that most contaminated stations (Ch3, S1 and S3) are located SE of Chabahar Bay and contamination decreases in a NW direction. The S9 station, west of the bay, is also contaminated. High organic matter (OM) content in the sediments is most likely the result of fuel and sewage discharge from fishing vessels along with discharge of fishing leftovers. Significant correlation coefficient among OM, Fe, Cu, Pb, Zn and Cd seemingly reflects the importance of the role that OM and Fe oxy-hydroxides play in the metals mobility. The results of hierarchical cluster analysis (HCA), computed correlation coefficient and sequential extraction analysis suggest that Cu, Pb, Zn and Cd probably come from antifouling and sea vessel paints, while Ni, Cr, Co, V and Fe are most likely contributed by ophiolitic formations located north of the bay and/or deep sea sediments. Average individual contamination factors (ICFs) indicated that the highest health hazard from the bay is posed by Cu, Pb and Zn.     

Heavy metals in Xuzhou urban roadside topsoils (China): magnetic characterization and enrichment mechanism

Heavy metal contamination is prevalent in urban areas where soil represents a significant sink. Urban topsoil samples were collected and metal concentrations including Pb, Zn, Cu, Cd, Ni and Co were measured by inductively coupled plasma mass spectrometry. All analyzed metals showed elevated concentrations compared to local background concentrations with the exception of Co. Cadmium was the metal most enriched in the analyzed area, presenting enrichment factor, on average, of 16.5. Mineral magnetic concentration parameters (χlf and SIRM) exhibited significant relationships with Pb, Zn, Cu and Cd, respectively. Zinc, Co and Ni exhibited a substantial build-up in the finest particles (<28 μm). Enrichment was positively correlated with carbonate complexation constants (but not bulk solubility products) and suggests that the dominant mechanism controlling metal enrichment in these samples is a precipitation of carbonate surfaces that subsequently adsorb metals.     

Distribution and immobilization of heavy metals in Pliocene aquifer sediments in Wadi El Natrun depression, Western Desert

The Pliocene aquifer receives inflow of Miocene and Pleistocene aquifer waters in Wadi El Natrun depression. The aquifer also receives inflow from the agricultural activity and septic tanks. Nine sediment samples were collected from the Pliocene aquifer in Wadi E1 Natrun. Heavy metal (Cu, Sr, Zn, Mn, Fe, Al, Ba, Cr, Ni, V, Cd, Co, Mo, and Pb) concentrations of Pliocene aquifer sediments were investigated in bulk, sand, and mud fractions. The determination of extractable trace metals (Cu, Zn, Fe, Mn, and Pb) in Pliocene aquifer sediments using sequential extraction procedure (four steps) has been performed in order to study environmental pathways (e.g., mobility of metals, bounding states). These employ a series of successively stronger chemical leaching reagents which nominally target the different compositional fractions. By analyzing the liquid leachates and the residual solid components, it is possible to determine not only the type and concentration of metals retained in each phase but also their potential ecological significance. Cu, Sr, Zn, Mn, Fe, and Al concentrations are higher in finer sediments than in coarser sediments, while Ba, Cr, Ni, V, Cd, Co, Mo, and Pb are enriched in the coarser fraction. The differences in relative concentrations are attributed to intense anthropogenic inputs from different sources. Heavy metal concentrations are higher than global average concentrations in sandstone, USEPA guidelines, and other local and international aquifer sediments. The order of trace elements in the bulk Pliocene aquifer sediments, from high to low concentrations, is Fe?>?Al?>?Mn?>?Cr?>?Zn?>?Cu?>?Ni?>?V?>?Sr?>?Ba?>?Pb?>?Mo?>?Cd?>?Co. The Pliocene aquifer sediments are highly contaminated for most toxic metals, except Pb and Co which have moderate contamination. The active soluble (F0) and exchangeable (F1) phases are represented by high concentrations of Cu, Zn, Fe, and Mn and relatively higher concentrations of Pb and Cd. This may be due to the increase of silt and clay fractions (mud) in sediments, which act as an adsorbent, retaining metals through ion exchange and other processes. The order of mobility of heavy metals in this phase is found to be Pb?>?Cd?>?Zn?>?Cu?>?Fe?>?Mn. The values of the active phase of most heavy metals are relatively high, indicating that Pliocene sediments are potentially a major sink for heavy metals characterized by high mobility and bioavailability. Fe–Mn oxyhydroxide phase is the most important fraction among labile fractions and represents 22% for Cd, 20% for Fe, 11% for Zn, 8% for Cu, 5% for Pb, and 3% for Mn. The organic matter-bound fraction contains 80% of Mn, 72% of Cu, 68% of Zn, 60% of Fe, 35% of Pb, and 30% of Cd (as mean). Summarizing the sequential extraction, a very good immobilization of the heavy metals by the organic matter-bound fraction is followed by the carbonate-exchangeable-bound fraction. The mobility of the Cd metal in the active and Fe–Mn oxyhydroxide phases is the highest, while the Mn metal had the lowest mobility.     

Geochemistry of trace metals associated with reduced sulfur in freshwater sediments

Porewater concentration profiles were determined for Fe, trace elements (As, Cd, Co, Cu, Mn, Ni, Pb, Zn), sulfide, SO₄ and pH in two Canadian Shield lakes (Chevreuil and Clearwater). Profiles of pyrite, sedimentary trace elements associated with pyrite and AVS were also obtained at the same sites. Thermodynamic calculations are used, for the anoxic porewaters where sulfide was measured, to characterize diagenetic processes involving sulfide and trace elements and to illustrate the importance of sulfide, and possibly polysulfides and thiols, in binding trace elements. The ion activity products (IAP) of Fe sulfide agree with the solubility products (K_s) of greigite or mackinawite. For Co, Ni and Zn, IAP values are close to the K_S values of their sulfide precipitates; for Cu and Pb, IAP/K_s indicate large oversaturations, which can be explained by the presence of other ligands (not measured) such as polysulfides (Cu) and thiols (Pb). Cobalt, Cu, Ni and Zn porewater profiles generally display a decrease in concentration with increasing ΣH₂S, as expected for transition metals, whereas Cd, Pb and Zn show an increase (mobilisation). The results suggest that removal of trace elements from anoxic porewaters occurs by coprecipitation (As and Mn) with FeS(s) and/or adsorption (As and Mn) on FeS(s), and by formation of discrete solid sulfides (Cd, Cu, Ni, Pb, Zn and Co). Reactive Fe is extensively sulfidized (51–65%) in both lakes, mostly as pyrite, but also as AVS. Similarities between As, Co, Cu and Ni to Fe ratios in pyrite and their corresponding mean diffusive flux ratios suggest that pyrite is an important sink at depth for these trace elements. High molar ratios of trace elements to Fe in pyrite from Clearwater Lake correspond chronologically to the onset of smelting activities. AVS can be an important reservoir of reactive As, Cd and Ni and, to a lesser extent, of Co, Cu and Pb. Overall, the trace elements most extensively sulfidized were Ni, Cd and As (maximum of 100%, 81% and 49% of the reactive fraction, respectively), whereas Co, Cu, Mn, Pb and Zn were only moderately sulfidized (11–16%).     

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.     

Trace metals in Antarctic ecosystems: Results from the Larsemann Hills,East Antarctica

Sediments, mosses and algae, collected from lake catchments of the Larsemann Hills, East Antarctica, were analysed to establish baseline levels of trace metals (Ag, As, Cd, Co, Cr, Cu, Ni, Sb, Pb, Se, V and Zn), and to quantify the extent of trace metal pollution in the area. Both impacted and non-impacted sites were included in the study. Four different leaching solutions (1 M MgCl₂, 1 M CH₃COONH₄, 1 M NH₄NO₃, and 0.3 N HCl) were tested on the fine fraction (<63 μm) of the sediments to extract the mobile fraction of trace metals derived from human impact and from weathering of basement lithologies. Results of these tests indicate that dilute HCl partly dissolves primary minerals present in the sediment, thus leading to an overestimate of the mobile trace metal fraction. Concentrations of trace metals released using the other 3 procedures indicate negligible levels of anthropogenic contribution to the trace metal budget. Data derived from this study and a thorough characterisation of the site allowed the authors to define natural baseline levels of trace metals in sediments, mosses and algae, and their spatial variability across the area. The results show that, with a few notable exceptions, human activities at the research stations have contributed negligible levels (lower than natural variability) of trace metals to the Larsemann Hills ecosystem. This study further demonstrates that anthropogenic sources of trace metals can be correctly identified and quantified only if natural baselines, their variability, and processes controlling the mobility of trace metals in the ecosystem, have been fully characterised.     

High-resolution profiles of trace metals assessed by DGT techniques in lake sediment porewaters

The technique of diffusive gradients in thin films (DGT) was applied to obtain high-resolution vertical profiles of trace metals in sediment porewater of a eutrophic lake, Lake Chaohu. All sampling sediments were under anaerobic conditions with Eh values below 0, the redox potential profile in M4 was relatively stable, and higher Eh values in M4 than that in M1 were observed due to hydrodynamic effects. Fe, Mn and As exhibited closely corresponding profiles due to the co-release of Fe and Mn oxides and the reduction of As. Higher Fe and Mn concentrations and lower As concentrations were observed in M1 of the western half-lake than those in M4 of the eastern half-lake due to different sources and metal contamination levels in the two regions. Cu and Zn showed increasing concentrations similar to Mn and Fe at 1–2 cm depth of sediments, while DGT measured Co, Ni, Cd and Pb concentrations decreased down to 3–4 cm in the profiles. Co, Ni, Cu, Zn, Cd and Pb showed insignificant regional concentration variances in the western and eastern half-lakes. According to the R(C _DGT/C _{centrifugation}) values, the rank order of metal labilities decrease as follows: Fe (>1) > Cu, Pb, Zn (>0.9) > Co, Ni, Cd (>0.3) > Mn, As (>0.1).     

Analysis of a weathered profile on sulfide mineralization at Mugga Mugga, Western Australia

The mineralogy and geochemistry of the massive pyrite-pyrrhotite mineralization, which contains minor magnetite, sphalerite and galena, the weathered profile and surface gossan at Mugga Mugga in Western Australia have been examined. Reactions between amphibolite wall rocks and acid waters from the oxidation of the iron sulfides have resulted in distinct mineralogical zonation of the weathered profile which is further modified near the surface by lateritization. At the base of the weathered zone an opaline chert (Opal-CT) has been precipitated from fluctuations of the water table. A gossanous zone from 25.14–68.80 m with boxworks after massive pyrite is modified by abundant kaolinite, dickite and an alunite-type mineral derived from amphibolite wall rocks, while above 25.14 m both plinthite and mottled clay zones of a laterite profile are evident. Some characteristics of a mature gossan profile – sulfate-phosphate-arsenate near the base, a carbonate zone higher in the profile, and an oxide zone near the surface – overprint the gross zonation.At the interface between sulfide and weathered rock Mg, Ca, K, S, Zn, Cd, Hg, Ba are depleted, As, Sb, Mo, Cr and V contents increase and in the weathered zone, SiO₂, TiO₂, P₂O₅, SO₃, Pb, Zn, Hg, Sb, Co, Ni, W, Ba, Sr and Zr decrease up the profile whilst Al₂O₃, Fe₂O₃, CO₂, Cu and As increase. Of the elements associated with the massive pyrite (Pb, Zn, Cu, Ag, As, Cd, Hg, Sb, Co, Ni) anomalous concentrations of Pb, Cu, Ag, As and Sb occur in the surface gossan despite the possibility of complete leaching by highly acidic solutions. These anomalies are similar to those found in gossans over pyrite mineralization elsewhere in the Yilgarn Block.     

Geochemical characteristics of water and sediment from the Dal Lake, Kashmir Himalaya: constraints on weathering and anthropogenic activity

Two hundred and forty water samples (in four seasons) and seventeen sediment samples have been analyzed to monitor the natural and anthropogenic influences on the water and sediment chemistry of the Dal Lake, Kashmir Himalaya. The scatter diagrams [(Ca+Mg)/total cations (TZ⁺), (Ca+Mg)/HCO₃, (Ca+Mg)/(HCO₃₊SO₄), (Na+K)/TZ⁺; (Ca+Mg)/(Na+K)] and the geological map of the study area suggest predominance of carbonate and silicate weathering. Lower pH and high total dissolved solids, electrical conductivity and values in the Gagribal basin and in some patches of other basins reflect anthropogenic inputs in the form of sewage from surrounding population, houseboats, hotels, etc. The Dal Lake is characterized by high chemical index of alteration (CIA: 87–95), reflecting extreme weathering of the catchment area. Relative to the average carbonates, the lakebed sediments are enriched in Al, Ti, Zn, Cu and Co and depleted in Ni and Mn. Compared to the post-Archean Shale the sediments have higher Al, Zn and Cu contents and lower Ni and Co. There are distinct positive anomalies of Al, Mn, Zn and Cu and negative anomalies of Ni and Pb with respect to the upper continental crust. Geoaccumulation index (I _geo) and the US Environmental Protection Agency sediment quality standards indicate that the Gagribal basin and some patches of the Nagin basin are polluted with respect to Zn, Cu and Pb. These data suggest that the Dal Lake is characterized by differential natural and anthropogenic influences.     

Chemical fractionation of transition elements in Pacific pelagic sediments

Partitioning of transition elements in Pacific pelagic sediments (35 samples) was performed by sequential chemical leaching with barium chloride/triethanolamine (easily extractable fraction), acidic cation exchange resin (carbonate phases), and hydroxylamine hydrochloride and dilute hydrochloric acid solutions (hydrous oxides). Residual metal percentages are highest in red-brown clays and siliceous ooze, intermediate in calcareous materials and low in micronodules (2 samples, > 125 μm): residual metal contents seem to be controlled predominantly by the rate of admixture of volcanoclastic materials. At higher bulk metal concentrations, the non-residual fractions of Mn, Cu, Ni and Zn generally increase both in red-brown pelagic clays and in siliceous ooze. Mn, Ni, and Co concentrations are mainly associated with the easily reducible fraction (0.1 M NH₂OH·HCl), whereas Fe, Cu, and Zn exhibit higher percentages in the hydrochloric acid soluble fractions (0.3 M HCl); Zn and Cu are associated to some extent with the carbonate phase, copper with the easily extractable fraction.     

Selective chemical extraction of heavy metals in tailings and soils contaminated by mining activity: Environmental implications

Total concentrations of chemical elements in soils may not be enough to understand the mobility and bioavailability of the elements. It is important to characterise the degree of association of chemical elements in different physical and chemical phases of soil. Another geochemical characterisation methodology is to apply sequential selective chemical extraction techniques. A seven-step sequential extraction procedure was used to investigate the mobility and retention behaviour of Al, Fe, Mn, Cu, Zn, Pb, Cr, Co, Ni, Mo, Cd, Bi, Sn, W, Ag, As and U in specific physical–chemical and mineral phases in mine tailings and soils in the surroundings of the abandoned Ervedosa mine. The soil geochemical data show anomalies associated with mineralised veins or influenced by mining. Beyond the tailings, the highest recorded concentrations for most elements are in soils situated in mineralised areas or under the influence of tailings. The application of principal components analysis allowed recognition of (a) element associations according to their geochemical behaviour and (b) distinction between samples representing local geochemical background and samples representing contamination. Some metal cations (Mn, Cd, Cu, Zn, Co, Cr, Ni) showed important enrichment in the most mobilisable and bioavailable (i.e., water-soluble and exchangeable) fractions due likely to the acidic conditions in the area. In contrast, oxy-anions such as Mo and As showed lower mobility because of adsorption to Fe oxy-hydroxides. The residual fraction comprised largest proportions of Sn and Al and to a lesser extent Zn, Pb, Ni, Cr, Bi, W, and Ag, which are also present at low concentrations in the bioavailable fractions. The elements in secondary mineral phases (mainly Fe, Mn, Cu, Zn, Cd, Pb, W, Bi, Mo, Cr, Ni, Co, As and U) as well as in organic matter and sulphides are temporarily withheld, suggesting that they may be released to the environment by changes in physico-chemical conditions.     

Enrichment pattern of leachable trace metals in roadside soils of Miri City,Eastern Malaysia

This article presents the results on distribution and enrichment pattern of acid-leachable trace metals (ALTMs) from roadside soil of Miri city, Sarawak, East Malaysia. The city is one of the fastest developing in the Malaysian region with huge petroleum resources. ALTMs Fe, Mn, Cr, Cu, Ni, Co, Pb, Zn and Cd along with organic carbon and carbonates (CaCO₃) were analyzed in 37 soil sediments collected from roadside. The enrichment of ALTMs [especially Cu (0.4–13.1 μg g^?1), Zn (9.3–70.7 μg g^?1), Pb (13.8–99.1 μg g^?1)] in the roadside soils indicate that these metals are mainly derived from sources related to traffic exhausts, forest fires and oil refineries. The comparative study and enrichment pattern of elements indicates that Mn, Cu, Zn and Pb are enriched multi-fold than the unpolluted soil and Ni, Pb, Cd in some samples compared to Sediment Quality Guidelines like Lowest Effect Level (LEL) and Effects Range Low (ERL) in the region which is mainly due to the recent industrial developments in the region.     

Multivariate statistical techniques for evaluating and identifying the environmental significance of heavy metal contamination in sediments of the Yangtze River, China

The concentrations of heavy metals (Cr, Co, Ni, Cu, Zn, Pb, Cd, As, Hg, and Fe) in sediments of the Yangtze River, China, were investigated to evaluate levels of contamination and their potential sources. The lowest heavy metal concentrations were found in the source regions of the river basin. Relatively high concentrations of metals, except Cr, were found in the Sichuan Basin, and the highest concentrations were in the Xiangjiang and Shun’anhe rivers. All concentrations, except Ni, were higher than global averages. Principal component analysis and hierarchical cluster analysis showed that Zn, Pb, As, Hg, and Cd were derived mainly from the exploitation of various multi-metal minerals, industrial wastewater, and domestic sewage. Cu, Co, and Fe were derived mainly from natural weathering (erosion). Cr and Ni were derived mainly from agricultural activities, municipal and industrial wastewater. Sediment pollution was assessed using the geoaccumulation index (I _geo) and enrichment factor (EF). Among the ten heavy metals assessed, Cd and Pb had the highest I _geo values, followed by Cu, As, Zn, and Hg. The I _geo values of Fe, Cr, Co, and Ni were <0 in all sediments. EF provided similar information to I _geo: no enrichment was found for Cr, Co, and Ni. Cu, Zn, As, and Hg were relatively enriched at some sites while Cd and Pb showed significant enrichment.     

Distribution,enrichment and sources of trace metals in the topsoil in the vicinity of a steel wire plant along the Silk Road economic belt,northwest China

The West Development Program, initiated in 2000 by the central government of China, has attracted huge investments in the arid and semiarid regions of northwest China. As a consequence of this development, environmental pollution and ecological degradation have been widely reported. The Silk Road economic belt proposed by China promotes further economic development in the regions, but rational planning and regular monitoring are essential to minimize any additional negative impacts of the anthropogenic activities. This article reports an investigation on the distribution, enrichment and sources of trace metals in the topsoil in and around the Ningxia Hengli Steel Wire Plant (HSWP) situated along the Silk Road economic belt. The concentrations of Cd, Pb, Cr, Cu, Zn, Ni, Mn, V and Co in the surface soils of the study area vary, respectively, in the following ranges: 0.083–18.600, 21.9–2681.0, 58.0–100.0, 14.6–169.9, 59.0–4207.3, 19.3–40.8, 411–711, 55.2–76.6 and 7.46–25.21 mg/kg. The concentrations of Cd, Pb, Cr, Cu, Zn and Co are significantly higher than their local background values. Pollution levels of these trace metals in the surface soils were assessed using contamination index (C _f ⁱ ), geo-accumulation index (I _geo), modified contamination degree (mC _d) and pollution load index. The potential ecological risks caused by the metal pollution were assessed by means of potential ecological risk factor (E _f ⁱ ) and potential ecological risk index. The Spearman correlation and cluster analysis were applied to determine the contamination sources. The HSWP zone, associated with very high potential ecological risk caused by Pb and Cd, is more seriously contaminated by trace metals than the residential zone. This study indicates that Cd, Pb, Cu, Zn and Co mainly originate from industrial pollution, whereas Cr, Mn, Ni and V result from both industrial activities and natural processes.     

Transport and sediment–water partitioning of trace metals in acid mine drainage: an example from the abandoned Kwangyang Au–Ag mine area, South Korea

Transport and sediment–water partitioning of trace metals (Cr, Co, Fe, Pb, Cu, Ni, Zn, Cd) in acid mine drainage were studied in two creeks in the Kwangyang Au–Ag mine area, southern part of Korea. Chemical analysis of stream waters and the weak acid (0.1 N HCl) extraction, strong acid (HF–HNO₃–HClO₄) extraction, and sequential extraction of stream sediments were performed. Heavy metal pollution of sediments was higher in Chonam-ri creek than in Sagok-ri creek, because there is a larger source of base metal sulfides in the ores and waste dump upstream of Chonam-ri creek. The sediment–water distribution coefficients (K _d) for metals in both creeks were dependent on the water pH and decreased in the order Pb ≈ Al > Cu > Mn > Zn > Co > Ni ≈ Cd. K _d values for Al, Cu and Zn were very sensitive to changes in pH. The results of sequential extraction indicated that among non-residual fractions, Fe–Mn oxides are most important for retaining trace metals in the sediments. Therefore, the precipitation of Fe(–Mn) oxides due to pH increase in downstream sites plays an important role in regulating the concentrations of dissolved trace metals in both creeks. For Al, Co, Cu, Mn, Pb and Zn, the metal concentrations determined by 0.1 N HCl extraction (Korean Standard Method for Soil Pollution) were almost identical to the cumulative concentrations determined for the first three weakly-bound fractions (exchangeable + bound to carbonates + bound to Fe–Mn oxides) in the sequential extraction procedure. This suggests that 0.1 N HCl extraction can be effectively used to assess the environmentally available and/or bioavailable forms of trace metals in natural stream sediments.     

Trace metal occurrence in a mineralised and a non-mineralised spodosol in northern Sweden

In order to determine the metal-bearing phases with special emphasis on Cu, a sequential extraction has been carried out on seven soil samples from a sulphide-bearing spodosol profile in Liikavaara Östra, close to the Aitik Copper Mine in northern Sweden. A reference spodosol profile with very low abundances of sulphides located far from anthropogenic emissions was also studied. Five fractions were selected for the extraction: (I) CH₃COONa-extractable (exchangeable/adsorbed/carbonate); (II) Na₄P₂O₇-extractable (labile organics); (III) 0.25 M NH₂OH·HCl-extractable (amorphous Fe oxyhydroxides/Mn oxides); (IV) 1 M NH₂OH·HCl-extractable (crystalline Fe oxides); and (V) KClO₃/HCl-extractable (organics and sulphides). The distribution of trace elements (Co, Cr, Cu, Ni, Pb and Zn) in the profile in Liikavaara Östra is different from that in the reference profile. Possible explanations for these differences are (i) the presence of sulphides in the soil, (ii) atmospheric deposition of dust derived from mining activities at the Aitik Copper Mine, and (iii) mineralogical heterogeneities inherited from the deposition of the till. There is no straightforward correlation between the amount of the extracted phases and the metal extractability in the soils. This fact indicates that other factors are important for the retention of trace metals as well. The data presented in this study suggest that Co, Cr and Ni, to a fairly large extent, are associated with the organic matter in the B-horizon in both profiles, while in the C-horizon in Liikavaara Östra, sulphides are probably the more important carriers of these elements. For Co and Ni, Fe oxyhydroxides seem to be important. Most of the Cr occurred in the residual remaining after the leaching procedure. Copper and Zn seem to be associated with the organic matter to some extent in the B-horizon. The concentration of Cu in the C-horizon in Liikavaara Östra is high (2310 ppm), but only a very small fraction is likely to be hosted by sulphides. It is concluded that the major part of Cu in the C-horizon and a prominent fraction in the B-horizon in Liikavaara Östra are associated with some secondary phase that is extractable during extractions III and IV. Possible candidates for this phase are goethite and inclusions of native Cu in weathered biotite.