Fe-Mn Oxide Fraction Research Articles

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.

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.

Heavy metals in an impacted wetland system: A typical case from southwestern China

Historical zinc smelting in Hezhang, southwestern China, has resulted in significant heavy metal contamination of the surrounding ecosystems. The Caohai wetland system, which is an important national nature reserve close to the Hezhang zinc smelting area, was investigated in the present study. Results showed that sediments from the Caohai wetland system have been seriously contaminated by Cd, Pb and Zn with the highest concentrations in the surface sediments being up to 71, 160 and 1200 μg g − 1 , respectively. The heavy metals in the sediments were strongly associated with the organic/sulphide and residual fractions. A more oxidized condition induced by aquatic plants tended to cause the Cd, Pb and Zn bound to the Fe–Mn oxide fraction to become more dominant. Pb isotopic compositions in the sediments indicated that the inventories of Pb in the Caohai wetland sediments were mainly derived from the historical zinc smelting in the Hezhang area, although other anthropogenic sources, such as the gasoline Pb, also made a substantial contribution to the Pb in the sediments. Heavy metal contamination in aquatic plants was also studied and the results indicated that heavy metals accumulated by plants may pose a potential threat to the higher trophic-level organisms, including humans.

Interaction between cadmium, lead and potassium fertilizer (K2SO4) in a soil-plant system

A pot experiment was conducted to examine the influence of potassium (K) fertilizer (K(2)SO(4)) application on the phytoavailability and speciation distribution of cadmium (Cd) and lead (Pb) in soil. Spring wheat (Triticum aestivum L.) was selected as the test plant. There were seven treatments including single and combined contamination of Cd and Pb. CdCl(2).2.5 H(2)O and Pb(NO(3))(2) were added to the soil at the following dosages: Cd + Pb = 0.00 + 0.00, 5.00 + 0.00, 25.0 + 0.00, 0.00 + 500, 0.00 + 1000, 5.00 + 500 and 25.0 + 1000 mg kg(-1), denoted by CK, T1, T2, T3, T4, T5 and T6, respectively. The K fertilizer had five levels: 0.00, 50.0, 100, 200 and 400 mg K(2)O kg(-1) soil, denoted by K0, K1, K2, K3 and K4, respectively. The results showed that the K fertilizer promoted the dry weight (DW) of wheat in all treatments and alleviated the contamination by Cd and Pb. The application of K(2)SO(4) reduced the uptake of Cd in different parts including roots, haulms and grains of wheat; the optimum dosage was the K2 level. K supply resulted in a significant (P < 0.05) decrease in the soluble plus exchangeable (SE) fraction of Cd and there was a negative correlation (not significant, P > 0.05) between the levels of K and the SE fraction of Cd in soil. The application of the K fertilizer could obviously restrain the uptake of Pb by wheat and there were significant (P < 0.05) negative correlations between the concentrations of Pb in grains and the levels of K in soil. K supply resulted in a decrease in the SE fraction of Pb (except the K1 level) from the K0 to K4 levels. At the same time, the application of the K fertilizer induced a significant (P < 0.05) decrease in the weakly specifically adsorbed (WSA) fraction of Pb and a significant (P < 0.05) increase in the bound to Fe-Mn oxides (OX) fraction of Pb. At different K levels, the concentration of Pb in the roots, haulms and grains had a positive correlation with the SE (not significant, P > 0.05) and WSA (significant, P < 0.05) fractions of Pb in the soil. All the K application levels in this experiment reduced the phytoavailability of Cd and Pb. Thus, it is feasible to apply K fertilizer (K(2)SO(4)) to alleviate contamination by Cd and/or Pb in soil. Moreover, the level of K application should be considered to obtain an optimal effect with the minimum dosage.

Leaching Characteristics of Heavy Metals and As from Two Urban Roadside Soils

The leaching tests, including the Toxicity Characteristic Leaching Procedure (TCLP), EDTA extraction and BCR sequential extractions before and after EDTA treatments, were performed on two specific soils to elucidate heavy metal-associated mineral fractions and general leachability. The TCLP illustrated the low leachability of heavy metals in soils from two sites. EDTA is a strong chelator and therefore had higher extraction efficiency compared to that of TCLP. The lower extraction percentages by EDTA for As and Sb were found compared to the other heavy metals derived from anthropogenic sources. Sequential extractions showed that the importance of acid-extractable, organically-bound and Fe-Mn oxide fractions was identified for anthropogenic heavy metals with the exception of As and Ni while the importance of residual fraction was identified for endogenous metals. Changes in sequential fractions of heavy metals after leaching with EDTA are very complex and it is difficult to generalize on which fraction was more mobile than the others. These combined results are helpful in elucidating the association of heavy metals to soil fractions and the mobility characteristics of heavy metals under certain environmental conditions.

Speciation and mobility of heavy metals in mud in coastal reclamation areas in Shenzhen, China

Coastal reclamation has been carried out along the coastal areas near Shenzhen, China in a large scale since 1980s by dumping fill materials over the marine mud at the sea bottom. Usually the area to be reclaimed is drained first and some of the mud is air-dried for a few weeks before it is buried by fill. After reclamation, the terrestrial groundwater, which is relatively acidic and with high dissolved oxygen, gradually displaces the seawater, which is alkaline with high salinity. The changes in the burial conditions of mud and the properties of the pore water in the mud may induce the release of some heavy metals into the mud. Field survey confirms that the pH and salinity of the groundwater in the reclamation site are much lower than the seawater. Chemical analyses of mud and groundwater samples collected from the reclamation sites reclaimed in different years indicate that most of the heavy metals in the mud decrease gradually with time, but the heavy metals in the groundwater are increased. The release of heavy metals into pore water due to reactivation of heavy metals in the mud is of environmental concern. To understand why some of the heavy metals can be released from the mud more easily than others, a sequential extraction method was used to study the operationally determined chemical forms of five heavy metals (Cu, Ni, Pb, Zn, and Cd) in the mud samples. Heavy metals can be presented in five chemical forms: exchangeable, carbonate, Fe–Mn oxide, organic, and residual. Ni and Pb were mainly associated with the Fe–Mn oxide fraction and carbonate fraction; Zn was mainly associated with organic fraction and Fe–Mn oxide fraction, while Cu and Cd were associated with organic fraction and carbonate fraction, respectively. If the residual fraction can be considered as an inert phase of the metal that cannot be mobilized, it is the other four forms of heavy metal that cause the noticeable changes in the concentration of heavy metals in the mud. On the basis of the speciation of heavy metals, the mobility of metals have the following order: Pb (36.63%) > Cu (31.11%) > Zn (20.49%) > Ni (18.37%) > Cd (13.46%). The measured metal mobility fits reasonably well with the degree of concentration reduction of the metals with time of burial observed in the reclamation site.

Chemical speciation of heavy metals in the Ase River sediment, Niger Delta, Nigeria

The speciation patterns of heavy metals were assessed with a view to providing information on the bioavailability of metals in the sediment matrix. The results indicate that cadmium is speciated into residual and readily exchangeable forms, while copper speciated into organic bound, residual and Fe–Mn oxide fractions: lead into Fe–Mn oxide, organic and residual fractions; chromium into Fe–Mn oxide, organic and residual fractions; nickel into residual and organic bound fraction; zinc into residual Fe–Mn oxide and carbonate fractions; iron and manganese into Fe–Mn oxide, residual and easily exchangeable fractions. The speciation pattern gave a general picture that the majority of the metals exist either in the organic, or Fe–Mn oxide and residual fractions except for cadmium. It implies that metals that are predominantly in the Fe–Mn oxide and organic fractions can only be remobilised under conditions that change the redox potential of the sediment. There are significant spatial and temporal variations in the speciation patterns of heavy metals in river sediment.

Chemical fractions of heavy metals of sediments in Meiliang Bay, Lake Taihu and tracing for its pollution history

本文以梅梁湾沉积物中的重金属元素为研究对象, 利用五步连续提取的方法将梅梁湾沉积物中的重金属元素分水溶态、可交换态、碳酸盐结合态、铁锰氧化物结合态、有机物结合态和残留态六种相态。应用²¹⁰Pb、¹³⁷Cs定年法相结合, 通过对百年沉积物的连续提取及元素富集系数的分析, 得到重金属元素在不同相态中的含量随时间的变化。与历史时期人类活动相比较, 重建了自19世纪末期到2000年的人类活动影响流域环境的历史, 证实了重金属元素含量变化主要受人类活动的强度和方式制约。具明显影响的人类活动分三个时段, 其中最为严重的时段是自1977年至今。与无锡历年工业产值变化的对比分析表明, 各相态中重金属含量的相似变化记录了梅梁湾受湖湾沿岸居民的经济生产活动影响, 污染程度日益加剧, 且工业废污水中重金属主要以铁锰氧化物结合态进入太湖生态系统中。;The concentrations of heavy metals in different Chemical fractious of sediments collected from the Meiliang Bay, Lake Taihu, were measured. Sequential extraction method was used to gain the concentrations of sedi-ment-bound heavy metals in six fractions, i.e., soluble, exchangeable, bound to carbonates, bound to Fe-Mn oxides , bound to organic matter, and residual. By use of ²¹⁰Pb and ¹³⁷Cs activities to obtain age of sediments, temporal variations of heavy metals in different fractions and their enrichment factors were shown. Among them, variations of heavy metal concentration in Fe-Mn oxides fraction of the sediments can be used to reflect contaminant input by human activities. On the basis of our data, the history of catchment human activities was divided into three periods, among which the most heavily affected by human activity was from 1977 A. D. to present. By comparing the concentrations of heavy metals in Fe-Mn oxides fraction with historical industrial product values of Wuxi City, their similar trends suggest that the increasingly environmental pollution is due to a fast development of industries a-round northern Taihu region, further indicating that heavy metals was mainly as a form of bound to Fe-Mn oxides into the Lake Taihu ecosystem.

Phytoextraction capacity of the plants growing on tannery sludge dumping sites

The study was undertaken to assess the phytoremediation potential of four plants ( Sida acuta, Ricinus communis, Calotropis procera, Cassia fistula) growing at a tannery sludge disposal site. Results showed that maximum amount of K, Fe and Ni was associated with residual fraction, whereas, Zn, Mn, Cr, Pb, Cd and Co was found in Fe–Mn oxide fraction. Cu and Na were mostly associated with organic matter and carbonate fraction, respectively. The results demonstrated that the levels of accumulation of metals was found high in all the studied plants and followed the order; C. procera > S. acuta > R. communis = C. fistula. The principal components analysis (PCA) revealed that translocation behavior of Cu, Zn and Mn, Cr were found similar in the plants. Correlation analysis between metal accumulation in the plants with DTPA extractable metals emphasized that S. acuta and C. fistula provide better value of correlation for most of the tested metals. The values of transfer factor were also found high for most of the tested metals in the plants of S. acuta. Overall, the plants of S. acuta and C. fistula were found suitable for the decontamination of most of the metals from tannery waste contaminated sites.

Anthropogenic Pb accumulation in forest soils from Lake Clair watershed: Duchesnay experimental forest (Québec, Canada)

Mineral soil horizons (Ae, Bhf1, Bhf2, Bf, BC and C) were carefully collected from two podzolic soil profiles in the Lake Clair watershed (Québec) in order to assess anthropogenic trace metal accumulation. Petrographic and selective analyses were performed to establish the soil mineralogy and properties. Furthermore, a complete sequential extraction procedure has been applied to help understanding the complex chemical speciation of Pb in forest soils. Chemical speciation of Pb showed a strong vertical gradient: 85% of this metal is mainly partitioned in refractory minerals in the C-horizon whereas in the upper Bhf1 and Ae-horizons, less than 50% of Pb is associated with this fraction. In the Ae-horizon, for example, 35%, 30% and 12% of total Pb, respectively, is associated with the exchangeable, labile organic matter and amorphous Fe-Mn oxides fractions. The distribution of Pb and Cr in the studied forest soils mainly reflects progressive contamination of the watershed by anthropogenic atmospheric sources. The anthropogenic source is indicated by elevated Cr and Pb concentrations in the topsoil (Bhf and Ae) horizons and by strong negative correlation between 206Pb/ 207Pb ratios and total Pb concentrations. According to these isotopic values, penetration of anthropogenic Pb does not exceed 10 cm in both soil profiles. Below this depth, both Pb concentrations and isotopic ratios remain nearly constant and similar to values observed in pre-anthropogenic sediments from Lake Clair. These values are interpreted as the natural geochemical backgrounds of the watershed. Based on that behaviour, calculated anthropogenic Pb net inputs amounted to between 1.24 and 1.8 g/m 2.

Metal distribution in road dust samples collected in an urban area close to a petrochemical plant at Gela, Sicily

Eight samples of road dust were collected from three different localities (industrial, urban, peripheral) of the town of Gela (Italy) to characterize their chemical composition and to assess (a) the influence of the petrochemical plant and the urban traffic on the trace element content in different grain-size fractions of street dust and (b) the solid-phase speciation of the analysed metal using sequential extraction. The samples were sieved into six particle size ranges: 500–250, 250–125, 125–63, 63–40, 40–20 and <20 μm and then analysed for 15 trace elements by ICP-MS. Sequential extraction of metals was performed on each subsample. A principal component analysis was also carried out to define the possible origin of metals in dusts. A comparison was made between the trace metal concentrations in road dust and those in main local outcropping rocks. The obtained results, indicate, that the road dust samples contain non-soil-derived elements, whose primary contributors appear to be vehicular traffic and the nearby petrochemical plant. Traffic appears to be responsible for the high levels of Ba, Cu, Cr, Mo, Pb, Sb and Zn. High concentrations of Ni, V and, partly, Ba and Cr were associated with emissions from the petrochemical plant. With respect to the local background, Sb was the most highly enriched trace element in the road dusts. Results of sequential extraction analysis show that most metals are mainly distributed in the non-residual fractions and particularly in the organic/sulphide and Fe–Mn oxides fractions. They also point to superficial adsorption as an important transfer mechanism of trace metals from their sources to the environment.

Partitioning and mobility of trace metals in the Blesbokspruit: Impact assessment of dewatering of mine waters in the East Rand, South Africa

A suite of trace metals was analyzed in water and sediment samples from the Blesbokspruit, a Ramsar certified riparian wetland, to assess the impact of mining on the sediment quality and the fate of trace metals in the environment. Limited mobility of trace metals was observed primarily because of their high partition coefficient in alkaline waters. Nickel was most mobile with a mean K d of 10 3.28 L kg −1 whereas Zr was least mobile with a mean K d of 10 5.47 L kg −1. The overall trace metal mobility sequence, derived for the Blesbokspruit, in increasing order, is: Zr < Cr < Pb < Ba < V < Cu < Zn < Sr < Mn < U < Mo < Co < Ni. Once removed from the solution, most trace metals were preferentially associated with the carbonate and Fe–Mn oxide fraction followed by the exchangeable fraction of the sediments. Organic C played a limited role in trace metal uptake. Only Cu was primarily associated with the organic fraction whereas Ti and Zr were mostly found in the residual fraction. Compared to their regional background, Au and Ag were most enriched, at times by a factor of 20–400, in the sediments. Significant enrichment of U, Hg, V, Cr, Co, Cu and Zn was also observed in the sediments. The calculated geoaccumulation indices suggest that the sediments are very lightly to lightly polluted with respect to most trace metals and highly polluted with respect to Au and Ag. The metal pollution index (MPI) for the 20 sampled sites varied between 2.9 and 45.7. The highest MPI values were found at sites that were close to tailings dams. Sediment eco-toxicity was quantified by calculating the sediment quality guideline index (SQG-I). The calculated SQG-I values (0.09–0.69) suggest that the sediments at the study area have low to moderate potential for eco-toxicity.

Speciation distribution of Cd, Pb, Cu, and Zn in contaminated Phaeozem in north-east China using single and sequential extraction procedures

Knowledge of the total content of trace metals is not enough to fully assess the environmental impact of polluted soils. For this reason, the determination of metal speciation in soil is important to evaluate its mobilisation capacity and behaviour in the environment. The sequential extraction procedure was used to separate 4 heavy metals (Cd, Pb, Cu, Zn) from contaminated Phaeozem in north-east China into 5 operationally defined geochemical species: exchangeable, bound to carbonates, bound to Fe–Mn oxides, bound to organic matter, and residues. Neutral salts, dilute acids, and chelating reagents were used as single extractants for the functionally defined speciation. In the sequential extraction, the residual fraction was the most abundant pool for Pb, Cu, and Zn. A major portion (40–84%) of Pb, Cu, and Zn was associated with the residue. The speciation distribution of Pb, Cu, and Zn in the surface samples was similar to that in the subsurface, with residues &gt; bound to organic matter &gt; bound to Fe–Mn oxides &gt; bound to carbonates &gt; exchangeable. A significant amount (32–47%) of Cd persisted in the potential availability of the exchangeable fraction. The main part of Cd fractionation in the surface soil samples comprised exchangeable, carbonate, and Fe–Mn oxide fractions, whereas in the subsurface it comprised the residual and exchangeable phases. EDTA can be regarded as an extractant for assessing the plant-available species of Cd, Cu, and Zn; NH4Cl released electrostatically weakly bound metals and was used to estimate the mobile species. Assuming that metal mobility and bioavailability are related to their solubility and the contents in typical plants in the contaminated Phaeozem, Cd would be the main potential risk to animal health and groundwater safety in the area.

Geochemical fractionation of heavy metals in sediments of the Tapi estuary

Sequential extraction was used to study the operationally determined chemical forms of Co, Cr, Cu, Ni, Pb and Zn and their spatial distribution in the sediments of the Tapi estuary. It was found that oxidizable binding fraction was the most important phase for binding of all metals followed by Fe-Mn oxide and carbonate fractions. Zn bound to the Fe-Mn oxide fraction had a significant relationship with reducible Mn and reducible Fe concentrations suggesting that Fe-Mn oxides may be the main carriers of Zn from the fluvial environment to the estuarine body. The Zn bound to the Fe-Mn oxides and Cu bound to the oxidizable fraction showed a general distinctive decrease from the middle of the estuary (ES-3) to sea mouth (ES-5) and from upstream ES-2 to the mouth of the estuary (ES-2). Zn, Pb, and Cr were not correlated with bottom layers and had a high enrichment factor (up to 60 times) representing the influence of anthropogenic activities and thus are the main precursors of metal pollution. The average Igeo of six metals in the sediments from the middle of the estuary is 3.67 and is larger than the estuary mouth (1.24) and seaside sampling locations (2.33). This suggests that the middle of the estuary is strongly contaminated with heavy metals. Interestingly higher enrichment in the sediments is not linearly related to toxicity response factor which may be due to metal immobilization.

Fractionation and Sequential Extraction of Heavy Metals in the Soil of Scrapyard of Discarded Vehicles

Chemical and physical size fractionation of heavy metals were carried out on 20 soil samples from the scrap yard area. Tessier method was used in sequential extraction. Cadmium showed the highest levels among the other elements studied in the exchangeable fraction (about 33%), while other elements showed low levels in this fraction (> or =1%). Lead and manganese were mostly found in the Fe-Mn oxide fraction, zinc and iron were mostly in residual fraction, while copper was mostly found in the organic fraction of the soil. Soil samples were size-fractionated into four sizes: 1000-500, 500-125, 125-53, and less than 53 microm. The highest levels of Fe, Cu, Pb, Mn, and Cd were found in the medium fraction (500-125 mum), while zinc showed its highest levels in the fine fraction (125-53 microm). The order of heavy metal load in the size fractions was found to be medium > fine > coarse > silt for Fe, Mn, Cu, Pb, and Cd, where it was found as fine > medium > coarse > silt for zinc.

Chemical fractionation and heavy metal accumulation in the plant of Sesamum indicum (L.) var. T55 grown on soil amended with tannery sludge: Selection of single extractants

A pot experiment was carried out to study the single and sequential extractions of metals in different tannery sludge amendment and the potential of the plant of Sesamum indicum L. var. T55 (sesame) for the removal of metals from tannery waste contaminated site. The metal extraction efficiency obtained with each extractants was slightly different and follow the order; EDTA > DTPA > NH 4NO 3 > NaNO 3 > CaCl 2. The correlation analysis between extractable metals in the different amendments of sludge and metal accumulation in the plant (lower and upper parts) showed better correlation for most of the tested metals with EDTA extraction. In this study, a sequential extraction technique was applied on different amendments of tannery sludge. The results showed that Mn, Zn, Cr and Cd were mostly associated with Fe–Mn oxide fraction in most of the amendments, K and Ni was found in residual (RES) fraction, Fe and Cu was bound with organic matter (OM) and RES fractions and Na was associated with carbonate (CAR) fraction. The metal accumulation after 60 d of growth of the plant was found in the order of K > Na > Fe > Zn > Cr > Mn > Cu > Pb > Ni > Cd and its translocation was found less in upper part. The accumulation of toxic metals (Cr, Ni and Cd) in the plants was found to increase with increase in sludge ratio, in contrast, the accumulation of Pb decreased. In view of growth parameters and metal accumulation in the plant, it was observed that lower amendments (25%) of tannery sludge were found suitable for the phytoremediation of most of the studied metals.

Remediation of Metal-Contaminated Soil by an Integrated Soil Washing-Electrolysis Process

Chelating agents such as EDTA and DTPA are often used to remove metals from soil. However, their toxicity, bio-recalcitrance, and problems with recovery of heavy metal and chelating agents severely limit their applications. A biodegradable chelating agent, LED3A, and two surfactants, SDS and Triton X 100, were evaluated as potential alternatives for remediation of metal-contaminated soil. LED3A alone only removed 40% of cadmium the addition of surfactant significantly enhanced its cadmium removal capacity up to 80% for a wide range of pH (5 to 11). The enhancement increased with both surfactant concentrations and LED3A concentrations. Because LED3A had a much higher removal capacity for copper, the synergistic effect of surfactant-LED3A mixture was less obvious. Sequential extraction analysis indicated that the LED3A not only removed copper from carbonate and Fe-Mn oxide fraction, but also from organic fractions. A three-dimension electrolysis reactor could effectively recover both metals and LED3A-SDS within thirty minutes. The combined soil washing by LED3A-surfactants and electrolysis provides a potential approach for remediation of copper- and cadmium-contaminated soils.

Sequential extractions on mine tailings samples after and before bioassays: implications on the speciation of metals during microbial re-colonization

Mine tailings may be remediated using metal tolerant microorganisms as they may solve the limiting conditions for healthy development of plants (i.e., low organic mater content and poor physical conditions). The aim of this study was to investigate the consequences of microbial colonization on the chemical speciation of trace metals. Surface samples from the Valenciana mine tailings (Guanajuato, Mexico) were used for long-term bioassays (BA), which consisted in the promotion of microorganisms, development on tailings material under stable laboratory conditions (humidity, temperature, and light exposure). A five-step sequential extraction method (exchangeable, carbonate/specifically adsorbed, Fe–Mn oxides, organic matter (OM)/sulfide, and residual fractions) was performed before and after BA. Extraction solutions and leachates were analyzed by inductively coupled plasma-mass spectrometry. OM content, cationic exchange capacity, and pH values were also assessed before and after BA. The results indicate that trace elements are generally present in nonresidual fractions, mainly in the Fe–Mn oxides fraction. The concentration of total Zn, As, Se, Pb, and exchangeable Cu and Pb is above the recommendable limits for soils. Despite the high bioavailability of the former elements, biofilms successfully colonized the tailing samples during the BA. Cyanobacteria and green algae, heterotrophic fungi, aerobic bacteria, and anaerobic bacteria composed the developed biofilms. Chemical controls of trace elements could be attributed to absorption onto inorganic complexes (carbonates, metal oxides), while biofilm occurrence seems to enhance complexation and immobilization of Cr, Ni, Cu, Zn, As, and Pb. The biofilm developed does not increase the bioavailable forms and the leaching of the trace elements, but significantly improves the OM contents (natural fertilization). The results suggest that biofilms are useful during the first steps of the mine tailings remediation.

Solid-Phase Chemical Fractionation of Selected Trace Metals in Some Northern Kentucky Soils

The fractionation and distribution with depth of Cd, Cr, Cu, Ni, Pb, and Zn in 26 soils of Northern Kentucky were determined through a sequential extraction procedure in response to environmental concerns about increasing anthropogenic inputs in a fast-paced, urbanizing area. The selected sites have not received any biosolid- or industrial-waste applications. Average total concentrations per metal in soil profiles derived from alluvial, glacial till, and residual materials ranged from 0.43 to 56.00 mg kg−1 in the sequence Zn > Ni > Pb > Cr > Cu > Cd, suggesting relatively small anthropogenic inputs. The distribution of Cu, Cr, Ni, and Zn increased with soil depth, whereas Cd and Pb remained stable, indicating a strong geological or pedogenic influence. Residual forms were most important for the retention of Cu, Zn, and Ni. Cadmium and Pb exhibited a strong affinity for the Fe-Mn oxide fraction, while Cr showed the strongest association with the organic fraction. In terms of metal mobility and toxicity potential inferred from metal concentrations in labile fractions, Cd posed the greatest risk, followed by Cr ∼ Pb > Ni > Zn > Cu. Soil pH, OM, and clay content were the most important parameters explaining the partitioning of metals in labile and residual fractions, emphasizing the importance of metal fractionation in soil management decisions. Alluvial soils generally contained the highest total and labile metal concentrations, suggesting potential metal enrichment through anthropogenic additions and depositional processes. These environments exhibit the highest risk for metal mobilization due to drastic changes in redox conditions, which can destabilize existing metal retention pools.

Quick sequential procedure for speciation analysis of heavy metals in soils by supersonic extraction

In order to improve the extraction efficiency and reduce the operation time, supersonic energy by means of supersonic bath was used to the modified Tessier sequential extraction for speciation analysis of heavy metals in soils. Extractable contents of Cu, Fe, Mn, Ni, Pb and Zn were measured by flame atomic absorption spectroscopy. The merit of the supersonic extraction (SE) applied to the modified Tessier, method is not only that the operation time for the first 4 fractions was reduced from ca 18 h to 8 h, comparing with conventional extraction (CE), but also the extraction efficiency was higher. There were no significant differences between the data obtained by the proposed method using supersonic extraction and the reference values of the standard reference materials of EES-2 and EES-3. The results for both of SE and CE in the soil samples were consistent. The extractable Cu, Ni and Zn in the sample No. 1 were mainly associated with the third fraction (Fe-Mn oxides fraction), and fourth fraction (organic matter fraction) in the sample No. 2. The extractable Fe and Mn were all mainly associated with the third fraction, and Pb the fourth fraction in both of the samples. The effects of varying concentrations of hydroxylamine hydrochloride on the extraction of metals were also studied.