Mn Oxide Fractions Research Articles

Quantitative speciation of heavy metals in soil and crops of agricultural fields of Islamabad, Pakistan

Two root crops: carrot (Daucus carota) and spring onion (Allium fistulosum) and soil samples were selected from the agricultural fields located near Islamabad, Pakistan to determine their elemental content. Field soil speciation of the two crops was also carried out to analyse the correlation of the elements in field crop and soil. Concentrations of selected elements were evaluated in the leaf, stem, root and flowering part of the crops using flame atomic absorption spectrophotometry. The results showed that elements are mostly concentrated in soil rather than crop parts following the sequence Zn>Cu>Pb>Ni>Cr>Cd. Furthermore, soil speciation showed that Ni and Cr are more prevalent in the Fe–Mn oxide fraction, Zn and Cd as the carbonate bound fraction and Cu is found in the organic bound form. However, concentrations of Pb are similar across the carbonate, Fe–Mn oxide and organic bound fractions. The highest average concentration of Zn is found as the carbonate bound fraction (2.09 ± 0.005 mg kg−1) and Cu as the organic bound (1.51 ± 0.029 mg kg−1) in soil samples taken from the agricultural field of Daucus carota.

Assessment of heavy metal speciation in soils impacted with crude oil in the Niger Delta, Nigeria

Chemical fractionation of Cd, Cu, Pb, Ni, Cr, Zn and Mn in soils that had received a significant impact of crude oil spillage in the Niger Delta, Nigeria was studied using a sequential chemical extraction method. The results revealed that significant amounts of the metals (Cd, Cu, Pb, Ni, Cr, Zn and Mn) were found in the most labile fractions as compared to the control site. On average, Ni, Cr and Zn were mostly associated with the residual fraction; Pb and Mn with the Fe–Mn oxides; Cu with the organic fraction and Cd with the exchangeable fraction. Among the non-residual fractions, metals were mostly associated with the Fe–Mn oxides fraction. The mobility factors of these metals were higher at the impacted sites as compared with the control site. High mobility of the metals in the impacted soils was associated with the oil spillage, since exogenous metals are usually weakly bound to soil particles. The mobility factors for the metals follow the order: Cd>Zn>Pb>Ni>Mn>Cu>Cr.

Antimony distribution and mobility in rivers around the world's largest antimony mine of Xikuangshan, Hunan Province, China

Mining and smelting activities of the world largest Antimony (Sb) mine which is located at Xikuangshan area of Hunan Province, China, constitute important sources of Sb pollution throughout the rivers in or around the mine. Water samples show high levels of Sb (2–6384 µg/l) relative to the average concentration of the world rivers (1 µg/l) and it occurs mainly in oxidized form. Sb has a higher affinity for the particulate phase than for the aqueous phase. Its contents in sediments decreased along with the distance from the mine (from 7316 to 57 mg/kg) and had good correlation relationships ( p < 0.001) with porewaters. In addition to the major pools in the Fe–Mn oxide (22.2–66.4%) and residual fractions (5.66–53.5%), Sb was relatively abundant in strongly adsorbed fraction. Laboratory experiments of the contaminated sediments show that with increasing amounts of Sb in the sediment, an increasing amount of Sb was leached and went into solution. Although Sb(V) was the predominant form, the release of Sb(III) in oxic conditions was also observed during laboratory experiments. And the amount of Sb released into solution was higher in anaerobic conditions than in oxygenated water.

Speciation Analysis of Heavy Metals of Core Amuta Sediments in Lianhua Lake

The BCR-SEP method was used to determine the binding forms of heavy metals in Amuta Lake(AMT) in this paper. The chemical forms of heavy metals, namely extractable fractions or valid fractions, including exchangeable-carbonate fraction, Fe-Mn oxide fraction and Organic-sulfide fraction .The results of the partitioning study indicated that in the core AMT sediments, Cr, Fe and Ni are mainly associated with the residue fraction, Cu is mainly concentrated in the Fe–Mn oxide fractions and residue fraction, Mn is concentrated in the exchangeable-carbonate fraction and residue fraction. Zn is concentrated in organic-sulfide fraction and residue fraction.

Different spontaneous plant communities in Sanmen Pb/Zn mine tailing and their effects on mine tailing physico-chemical properties

Different plant communities have established spontaneously on Sanmen Pb/Zn mine tailing. The site was inspected and four different plant communities were identified according to their species composition. To understand the effects of different communities on mine tailing physico-chemical properties, a community survey was carried out in Sanmen Pb/Zn mine tailing, and the physico-chemical properties and heavy metal (Cu, Pb, Cd and Zn) distribution of mine tailings were determined. Results showed that there were four types of communities (I, II, III and IV) in Sanmen Pb/Zn mine tailing. From community I to IV, the number of plant species and community characteristics (aboveground biomass, underground biomass, coverage and height) consistently increased. Moreover, the nutrient pool and physico-chemical properties of mine tailing consistently reestablished from community I to IV, while the total heavy metal content consistently decreased. The contents of residual fractions, Fe–Mn oxide fractions for Pb, Zn, Cu and Cd and exchangeable fractions for Pb and Zn also consistently decreased. However, the contents of organically bound fraction had no obvious change from community I to IV. Moreover, the contents of Cu organically bound fraction reversely increased. Results demonstrate that communities I, II, III and IV should be a progressive community succession. Moreover, along with the progressive community succession, phytostabilization and phytoextraction of mine tailings are more and more effective.

Redistribution of cadmium, copper, lead, nickel, and zinc among soil fractions in a contaminated calcareous soil after application of nitrogen fertilizers

AbstractThis study was conducted to evaluate the redistribution of the heavy metals Cd, Cu, Pb, Ni, and Zn among different soil fractions by N fertilizers. In a lab experiment, soil columns were leached with distilled water, KNO3, NaNO3, NH4NO3, or Ca(NO3)2 · 4H2O. After leaching, soil samples were sequentially extracted for exchangeable (EXCH), carbonate (CARB), organic‐matter (OM), Mn oxide (MNO), Fe oxide (FEO), and residual (RES) fractions. Distilled water significantly increased the concentrations of Cd and Ni in EXCH fraction, while concentration of Cu and Zn did not change significantly. Application of KNO3, NaNO3, NH4NO3, or Ca(NO3)2 · 4H2O significantly increased the concentrations of Cd and Zn in EXCH fraction, while concentration of Pb and Ni was decreased. Application of all fertilizers caused an increase of Cu in the OM fraction. Moreover, leaching with these solutions significantly increased Cd [except in Ca(NO3)2 · 4H2O], Cu, and Zn concentrations in the CARB fraction, while Pb and Ni concentrations were decreased. With application of all leaching solutions, Zn in the EXCH, CARB, FEO, and MNO fractions was significantly increased, while Zn in the OM fraction did not change. The mobility index indicated that Ca(NO3)2 · 4H2O increased the mobility of Cd, Cu, and Zn in the soil, whereas NaNO3 decreased the mobility of Pb and Ni in the soil. The mobility index of Pb decreased by all leaching solutions. Thus, these results suggest that applying N fertilizers may change heavy‐metal fractions in contaminated calcareous soil and possibly enhance metal mobility and that N‐fertilization management therefore may need modification.

Lead fractionation and bioaccessibility in contaminated soils with variable chemical properties

The hazard imposed by trace elements within soils is dependent on soil properties and the relative distribution of metal species. Hence, a greenhouse column study was conducted to investigate the geochemical speciation and bioaccessibility of lead (Pb) as a function of soil properties. Four different soil types (Immokalee, Belle Glade, Tobosa and Millhopper series) varying in physico-chemical properties were selected and amended with Pb as Pb(NO3) at 400, 800, and 1,200 mg kg−1. A sequential extraction was employed to define the reactive metal pool, which was correlated with Pb bio-accessibility as determined by the physiologically based extraction test. Results show that Pb was mainly distributed in soluble+exchangeable phase in Immokallee (82%) and Millhopper (45%) series, and carbonate and Fe+Mn oxide fractions in Belle Glade (14–74%) and Tobosa (31–64%) series at time zero. With soil aging, Pb underwent chemical transformations in the soils and the majority of added Pb was associated with Fe+Mn oxide fraction (64–81%). Also, Pb bioaccessibility varied widely as a function of soil type and soil aging. Gastric phase (IVG-S) extracted 34–81% and 29–75% and the absorbed intestinal phase (IVG-AI) extracted 12–79% and 12–45% of amended Pb in all the soils at time zero and 6 months, respectively. Among soil types, Tobosa and Belle Glade showed reduced bioaccessibility relative to Immokalee and Millhopper. Statistical analysis revealed that the IVG-S Pb decreases as soil organic matter and cation exchange capacity (CEC) increases and total P decreases. While the Mehlich extractable P and Ca+Mg, total Fe+Al and organic matter predicted the Pb in an intestinal system.

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

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

Rationale of lead immobilization by ball milling in synthetic soils and remediation of heavy metals contaminated tailings

In this work, the use of mechanical milling for the remediation of heavy metals in synthetic soils and tailings sampled from the mining area of “Barraxiutta”, SW of Sardinia, Italy is investigated. Specifically, Pb(II) contaminated synthetic soils of sandy, bentonitic and kaolinitic type are taken into account following the results obtained in previous works. Suitable sequential extraction procedures have been performed on both untreated and treated synthetic soils. It is found that mechanical loads which occur during collisions among milling media and soils are able to modify the distribution of Pb(II) onto the different solid fractions of contaminated synthetic soils. Specifically, for sandy soils the milling treatment induces a significant increase in Pb(II) content in the Fe–Mn oxides fraction. On the other hand, for bentonitic and kaolinitic soils, Pb(II) content in both carbonate and Fe–Mn oxide fractions is augmented after treatment. Such phenomena may contribute to Pb(II) immobilization efficiency since the heavy metal trans-speciation occurs in favor of fractions characterized by stronger bonds and lower solubility. As for the heavy metals contaminated tailings, their immobilization is obtained using both ball and attrition milling devices under specific ball to powder ratio values. The degree of metals immobilization is evaluated by analyzing the corresponding leachable fraction obtained through the Synthetic Precipitation Leaching Procedure (SPLP) proposed by EPA. X-ray diffraction and granulometric analyses revealed no significant alterations of the intrinsic character of the tailings after milling except for a relatively small increase in particles size. The increase in immobilization efficiency when tailings are mechanically treated may be due to specific phenomena induced during milling such as entrapment of heavy metals into aggregates, solid diffusion of metals into the crystalline reticulum of soil particles, the formation of new fresh surfaces onto which heavy metals may be irreversibly adsorbed as well as metal trans-speciation onto tailings fractions characterized by stronger bonds and lower solubility.

Investigation of the transport and fate of Pb, Cd, Cr(VI) and As(V) in soil zones derived from moderately contaminated farmland in Northeast, China

Some farmland in Shenyang had been irrigated with industrial wastewater since 1962. Although wastewater irrigation was ceased in 1992, soil had been heavily polluted by heavy metals, especially by Cd. For better understanding processes of soil-heavy metal interactions, in particular, the mobility and retention mechanism of heavy metal in soil, a study on the transport and fate of heavy metals in soil zones from Shenyang suburb was carried out by column leaching tests in laboratory. Breakthrough curves of Pb, Cd, Cr(VI) and As(V) fitted by Thomas model and Yoon–Nelson model. The results of fitted breakthrough curves showed that transport rates of the four heavy metals in the soil zones followed the order: Cr(VI) > As(V) > Cd > Pb, which indicated that Cr(VI) was much more mobile, and Pb was comparatively unmovable. Cr in effluents and As were almost entirely Cr(VI) and As(V), respectively, and no Cr(III) and As(III) was ever detected during the leaching tests. The contents of Pb, Cd, Cr and As in leached soils decreased in the order of Pb > Cd > Cr > As, which suggested that adsorption ability of soil to Pb was greatest and to As was least. The methods of selective sequential extraction and solvent extraction were used to determine the fractions of Pb, Cd, Cr, As and the valent states of Cr, As [Cr(VI) or Cr(III), As(V) or As(III)] in original soils and in leached soils. After leaching tests, the relative and absolute concentrations of exchangeable, carbonate, Fe–Mn oxide and organic fraction of each element were all increased, which enhanced the potential mobility and risk of Pb, Cd, Cr and As to soil/groundwater system. The relative concentrations of Cr(III) and As(III) in different depth of the soil zones after leaching tests were increased by about 6.0% and 5.6%, respectively. Cr(III) and As(III) tended to be adsorbed by soils, which reduced the mobility of them into groundwater.

The immobilization of heavy metals in biosolids using phosphate amendments—Comparison of EPA (6010 and 3051) and selective sequential extraction methods

Biosolids are organic by-products from wastewater treatment plants that contain valuable nutrients but also represent a pollution problem. The amount of heavy metals in biosolids at high concentrations prevents their use as fertilizers. The aim of the present study is to immobilize heavy metals in biosolids using phosphate amendments. Analytical-grade potassium dihydrogenphosphate (KH 2PO 4) was used as the source of phosphate, and its ability to reduce heavy metals in biosolids (200 g) was evaluated according to five additional phosphate quantities: Control (C) (without phosphate), P1 (1.45 g), P2 (2.9 g), P3 (5.8 g), P4 (10.15 g), and P5 (14.5 g). The effect of phosphate treatments on metal extractability was evaluated using the selective sequential extraction (SSE) method, and total metal concentrations were analyzed by the (US Environmental Protection Agency) EPA 6010 and EPA 3051 methods. The total and extractable level of metals showed that Cu, Zn and Pb were the predominant elements in the biosolids analyzed in this study (control). SSE results showed that, on average, over 80% of the total metals present in the biosolids were found in the organic (F4) and residual (F5) fractions for Cu and Zn; Fe–Mn oxide (F3), organic (F4) and residual (F5) fractions for Cd; exchangeable (F1) and residual (F5) fractions for Pb; and exchangeable (F1), organic (F4) and residual (F5) fractions for Ni. The addition of phosphate substantially decreased the amount of metals (Cu, Zn, Cd, Pb, and Ni) in biosolids after a 10-day period; however, the amount of removal varied between the examined analytical techniques.

Study on effective species of heavy metals in lacustrine sediment core from Xijiu Lake, Taihu Lake catchment, China

The BCR sequential extraction procedure is applied to probe into the speciation distribution of heavy metals (Cd, Cr, Zn, Cu and Pb) in lake sediments of Core XJ2 in Xijiu Lake, Taihu Lake catchment, China. The results showed that the effective species concentration of this five heavy metal elements increased obviously during the past century, the proportions of organic/sulphide fractions of Zn, Cu and Pb decreased while the Fe–Mn oxide fractions increased, and the proportion of Fe–Mn oxide fractions of Cd decreased while the exchangeable and carbonate fractions increased. The concentrations of exchangeable and carbonate fractions of these five elements were increased in the past century, especially the proportions of these fractions of Cd, Zn, Cu and Pb increased prominently. These changes could be attributed to the anthropogenic pollution. Since the changes of the heavy metal concentrations were corresponding to the history of human activities, especially the industry development, within the catchment.

Induced reduction of the potential leachability of As, Cd and Tl in an element-spiked acid soil by the application of industrial by-products

A series of incubation and leaching experiments were performed to assess the feasibility of two industrial by-products (phosphogypsum —PG— and sugar foam —SF—, rich in gypsum and calcium carbonate, respectively) to reduce the potential leachability of As, Cd, and Tl in an acidic soil. The effectiveness of the treatments (SF and PG + SF) was evaluated in response to the addition of a chelating agent (DTPA solution) or weak acidification (acetic acid at pH 4.93, TCLP solution) and the resulting sorption mechanisms as a function of treatment was estimated through the application of a sequential extraction procedure. Both amendments induced a significant increment in the soil retention capacity of the three elements. The subsequent leaching tests indicated that those columns treated with SF and PG + SF significantly reduced the amount of element leached regardless the experiments were performed with DTPA or an acidifying solution. The results of the sequential extraction procedure revealed that amending contaminated soils with both SF and PG + SF results in a redistribution of the three toxic elements from soluble and exchangeable pools (FI) to the Al, Fe and Mn (hydr)oxide (FII) fraction Overall, the addition of these amendments to an acid soil contaminated with As, Cd, and Tl reduced their mobility and potential leachability.

Fractionation and Distribution of Copper and Zinc in Calcareous Soils of Igarra, Nigeria

The experiment was conducted to fractionate Cu and Zn into the exchangeable, carbonate, Fe- Mn Oxide, organic and residual fractions within 0-30, 30-60 and 60-90 cm soil depths of calcareous soils of Igarra. The results obtained indicated that mean concentration of copper was highest in the Fe/Mn oxide fraction (3.68 mg kg-1) followed by the carbonate (1.93 mg kg-1) and exchangeable fractions (1.28 mg kg-1) respectively. Hence, the distribution trend of Cu in the various fractions was in the order Fe/Mn oxide > carbonate > residual > organic. On the other hand, the amount of Zn increased with depth in the exchangeable fraction with a relatively high concentration of 9.13 mg Kg-1. However, the highest amount of Zn (12.15 mg Kg-1) was obtained in the Fe/Mn oxide fraction. Zn occurrence in other fractions decreased in the following order: Fe/Mn oxide fraction > organic > carbonate > exchangeable. The present assessment of the forms and distribution of Cu and Zn in the soil showed that higher concentration of these metals in the Fe/Mn oxide fraction suggest unavailability or low supply of these metals for possible plant uptake in the short term.

The distribution and phytoavailability of heavy metal fractions in rhizosphere soils of Paulowniu fortunei (seem) Hems near a Pb/Zn smelter in Guangdong, PR China

In order to understand the change of soil environment induced by re-vegetation, the physico-chemical properties, heavy metal (Cu, Pb, Cd and Zn) distribution and bioavailability was investigated in four different sites with different re-vegetation time. Results showed that soil physico-chemical properties and total content of heavy metals consistently increased with the re-vegetation time. The proportions of carbonate, Fe–Mn oxide and organically bound fractions in the rhizosphere soils were higher than those in the bulk soils. However, the proportions of exchangeable and residual fractions were less. The pH, electrical conductivity (EC) and organic matter (OM) were the most important factors affecting the distribution of heavy metal fraction. The exchangeable and organically bound fractions were easily available for Paulownia fortunei, but carbonate, Fe–Mn oxide and residual fractions were not. The correlation analysis indicated that the heavy metal contents in roots were generally and significantly correlated with total metal contents and metal contents bound to different fractions, thus might be better indicators of heavy metals bioavailability in soil than those in aboveground tissues.

Chemical properties of heavy metals in typical hospital waste incinerator ashes in China.

Incineration has become the main mechanism for hospital waste (HW) disposal in China after the outbreak of Severe Acute Respiratory Syndrome (SARS) in 2003. However, little information is available on the chemical properties of the resulting ashes. In the present study, 22 HW ash samples, including 14 samples of bottom ash and eight samples of fly ash, were collected from four typical HW incineration plants located across China. Chemical analysis indicated that the HW ashes contained large amounts of metal salts of Al, Ca, Fe, K, Mg, Na with a concentration range of 1.8–315 g kg−1. Furthermore, the ashes contained high concentrations of heavy metals such as Ag, As, Ba, Bi, Cd, Cr, Cu, Mn, Ni, Pb, Ti, Sb, Sn, Sr, Zn with a vast range of 1.1–121,411 mg kg−1, with higher concentrations found in the fly ash samples. Sequential extraction results showed that Ba, Cr, Ni and Sn are present in the residual fraction, while Cd existed in the exchangeable and carbonate fractions. As, Mn, Zn existed in the Fe–Mn oxide fraction, Pb was present in the Fe–Mn oxide and residual fractions, and Cu was present in the organic matter fraction. Furthermore, toxicity characteristic leaching procedure (TCLP) results indicated that leached amounts of Cd, Cu and Pb from almost all fly ash samples exceeded the USEPA regulated levels. A comparison between the HW ashes and municipal solid waste (MSW) ash showed that both HW bottom ash and fly ash contained higher concentrations of Ag, As, Bi, Cd, Cr, Cu, Pb, Ti, and Zn. This research provides critical information for appropriate HW incineration ash management plans.

Source Identification and Speciation of Metals in the Topsoil of the Khli Ti Watershed, Thailand

The enrichment factor, multivariate analysis and metal speciation studies were used to identify degree, source and dispersal of metal contamination in Khli Ti watershed, Thailand. Topsoil samples were collected throughout the watershed, analyzed for total metal concentration. Sequential extraction was also carried out to determine geochemical phases of metals which were identified as exchangeable and bound to carbonates, Fe–Mn oxides, organic matter and residuals. Soil characteristics including pH, total organic carbon, redox potential, cation exchange capacity and texture were also analyzed. Principal component analysis yielded three metal groups which explained 83% of the variance. The concentrations of metals which were derived from lithogenic origin, such as Co, Cr, Fe, Ni and V were in natural background levels and were mostly bound to the residual phase. The remaining elements (i.e. Ba, Cd, Cu, Pb, Sb and Zn) were associated with the contamination from previous activities of the Pb-ore concentrator and Zn–Pb mining. Anthropogenic contamination mainly increased Pb and Zn bound to Fe–Mn oxides at the expense of residual fraction. Even though low exchangeable Pb contents in Khli Ti soils indicated low availability to plants, Pb bound to Fe–Mn oxides fraction might increase its mobility under reducing conditions.

Distribution and variability of redox zones controlling spatial variability of arsenic in the Mississippi River Valley alluvial aquifer, southeastern Arkansas

Twenty one of 118 irrigation water wells in the shallow (25–30 m thick) Mississippi River Valley alluvial aquifer in the Bayou Bartholomew watershed, southeastern Arkansas had arsenic (As) concentrations (<0.5 to 77 µg/L) exceeding 10 µg/L. Sediment and groundwater samples were collected and analyzed from the sites of the highest, median, and lowest concentrations of As in groundwater in the alluvial aquifers located at Jefferson County, Arkansas. A traditional five-step sequential extraction was performed to differentiate the exchangeable, carbonate, amorphous Fe and Mn oxide, organic, and hot HNO3-leachable fraction of As and other compounds in sediments. The Chao reagent (0.25 M hydroxylamine hydrochloride in 0.25 M HCl) removes amorphous Fe and Mn oxides and oxyhydroxides (present as coatings on grains and amorphous minerals) by reductive dissolution and is a measure of reducible Fe and Mn in sediments. The hot HNO3 extraction removes mostly crystalline metal oxides and all other labile forms of As. Significant total As (20%) is complexed with amorphous Fe and Mn oxides in sediments. Arsenic abundance is not significant in carbonates or organic matter. Significant (40–70 µg/kg) exchangeable As is only present at shallow depth (0–1 m below ground surface). Arsenic is positively correlated to Fe extracted by Chao reagent (r=0.83) and hot HNO3 (r=0.85). Arsenic extracted by Chao reagent decreases significantly with depth as compared to As extracted by hot HNO3. Fe (II)/Fe (the ratio of Fe concentration in the extracts of Chao reagent and hot HNO3) is positively correlated (r=0.76) to As extracted from Chao reagent. Although Fe (II)/Fe increases with depth, the relative abundance of reducible Fe decreases noticeably with depth. The amount of reducible Fe, as well as As complexed to amorphous Fe and Mn oxides and oxyhydroxides decreases with depth. Possible explanations for the decrease in reducible Fe and its complexed As with depth include historic flushing of As and Fe from hydrous ferric oxides (HFO) by microbially-mediated reductive dissolution and aging of HFO to crystalline phases. Hydrogeochemical data suggests that the groundwater in the area falls in the mildly reducing (suboxic) to relatively highly reducing (anoxic) zone, and points to reductive dissolution of HFO as the dominant As release mechanism. Spatial variability of gypsum solubility and simultaneous SO42− reduction with co-precipitation of As and sulfide is an important limiting process controlling the concentration of As in groundwater in the area.

Chemical fractionation and translocation of heavy metals in Canna indica L. grown on industrial waste amended soil

A pot experiment was carried out to assess the effect of different amendments of industrial sludge on the growth of Canna indica L. as well as the translocation potential of heavy metals of this plant. The accumulation of metals (Cr, Fe, Cd, Cu, Ni, Zn, Mn and Pb) in different parts of C. indica L. grown on industrial sludge-amended soil increased with time and increasing doses of sludge amendments. Sequential extraction method was followed to estimate the different fractions of heavy metals in sludge-amended soils collected from different periods of this study. The results showed that Mn, Zn, Cd, Cr and Pb were mostly associated with Fe–Mn oxide fraction in all amendments, whereas, Ni was mostly found in residual (RES) fraction. Cu and Fe were found to be higher in organically bounded form (OM) and RES fraction. The metal concentration in C. indica L. after 90 days of experiment started, was in the order of Fe > Cr > Mn > Zn > Ni > Cu > Cd > Pb and the metal translocation was found lesser in shoot. With the increasing percentage of sludge amendments in soil the metal concentrations increased in different parts of plants. Overall, the plant C. indica L. was found to be well adapted in industrial sludge amendments and it may be recommended that this plant was found suitable for phytoremediation of most of the studied metals.

Metal fractionation in soil profiles at automobile mechanic waste dumps

Soil profiles at five automobile mechanic waste dumps in Port-Harcourt, Nigeria were investigated to assess the spatial distribution, chemical speciation, and likely mobility of Cd, Cu, Pb, Zn, Cr and Ni in the soil as a function of the soil properties. A sequential fractionation protocol was used that generated six different fractions into which soil metal could partition. Cadmium was associated with non-residual fractions at surface horizons, but at lower depths it was in the residual fractions. Copper and Cr partitioned into organic and residual fractions, while Pb was associated with an Fe-Mn oxide fraction and the residual fractions. Zinc in surface horizons partitioned into an Fe-Mn oxide fraction and a fraction that captured carbonate-bound species, but in subsurface horizons, it was mainly in the residual fractions. Ni was predominantly found in the residual fractions. Mobility factors were calculated, and their values tended to decrease with increasing profile depth, indicating that these metals are relatively mobile in the surface horizons compared the subsurface except for chromium in the 15-30 cm depths. The mobility factors for the heavy metals follow the order: Cd > Zn > Pb > Cu > Cr > Ni. The results suggest that there is serious contamination hazard with Cd, Pb, and Zn in the soil profiles.