Fraction Distribution Of Metals Research Articles

Immobilization of Cr3+, Cd2+, and Pb2+ added to calcareous soil amended with composted agro-industrial residues

The bioavailability of trace metals in soils poses a major threat to the environment, especially with massive mineral fertilizers added to increase plant yield. A plot experiment was conducted for the effectiveness evaluation of compost and vermicompost, recycled from agro-industrial wastes, in immobilizing chromium, cadmium, and lead added to calcareous soil (artificially contaminated). Moreover, immobilization efficiency was compared to the natural occurrence of these metals in the soil without metal addition (uncontaminated soil). In both soils, amendments and mineral fertilizers were applied at three different levels alone and combined to each other. The experimental design was arranged in factorial complete randomized blocks using contamination, organic and mineral fertilizer levels, and their combination as categorical factors. The distribution of metal fractions and their bioavailability in soils and bioaccumulation in wheat grains were evaluated. Soil alkalinity, the contents of soil organic carbon and nitrogen, available phosphorus, and soil micronutrients were significantly improved under vermicompost and compost compared to mineral fertilizer and control. Vermicompost was more effective than compost in reducing metals bioavailability in contaminated soils by increasing the immobilized organic fractions, but it regressed when combined with mineral fertilizers. The bioavailability of the naturally occurring metal levels in uncontaminated soil did not change significantly compared to contaminated soil. Likewise, wheat yield, plant biomass, and nutrient enrichment in wheat grains improved due to enhanced soil nutrient availability. These composted agro-industrial residues, by-products from food industries, can be classified as environmentally-friendly soil amendments for their great potential to enrich soil nutrients, reduce mineral fertilizer addition, enhance plant growth, and stabilize Cr, Cd, and Pb in contaminated calcareous soils under wheat plants.

Characterization of soil microbial community activity and structure for reducing available Cd by rice straw biochar and Bacillus cereus RC-1

The combination of biochar and specific bacteria has been widely applied to remediate Cadmium-contaminated soil. But little is known about how such composites affect the dynamic distribution of metal fractions. This process is accompanied by the alternations of soil properties and microbial community structures. Composite of rice straw biochar and Bacillus cereus RC-1 were applied to investigate its impacts on Cd alleviation and soil microbial diversity and structure. The bacterial/biochar composite treatment decreased the fraction of HOAc-extractable Cd by 38.82%, and increased residual Cd by 23.95% compared to the untreated control. Moreover, compared with the untreated control, the composite treatment significantly increased the soil pH by about 1.5 units, and the activities of catalase, urease and invertase enzymes were increased by 42.39%, 30.50% and 31.20%, respectively. Composite treatment increased soil bacterial and fungal alpha diversity, the relative abundance of Bacillus, Streptomyces, Arthrobacter, and Aspergillus species were also increased. Mantel test and correlation analysis indicated that the effects associated with fungal communities in influencing soil properties were lower than that those of bacterial communities by different treatment. Aggregated boosted tree (ABT) models analysis showed that soil chemical proprieties (as determined by SOM, CEC, AN, etc.,) contributed over 50% of the changes in bacterial and fungal communities by the composite treatment. The co-occurrence network results showed that all treatments enhanced the correlation between OUT groups and improved the possible relationships in the bacterial and fungal communities, especially the interrelationships between bacteria and fungi after the Cd fractions stabilized. These findings provide a new insight to optimal strategies for the remediation of Cd-contaminated soil.

Influence of Sediment Characteristics on Heavy Metal Fraction Distribution in the Water-Level Fluctuation Zone of the Three Gorges Reservoir Area, China

The concentrations and fractions of heavy metal in sediments at different altitudes in the water-level fluctuation zone (WLFZ) of the Three Gorges Reservoir (TGR) were determined. The Pearson correlation analysis was used to determine the differences between heavy metal fractions and physicochemical properties. The results showed that Cr and Cu were mainly horizontally and vertically distributed in the residual (RE) fractions with the highest stability and relatively low ecological risk. Pb and Zn were mainly in the Fe-Mn oxide-bound (Fe-Mn) fractions, which can be reduced to a bioavailable state when the redox potential decreased or the oxygen was severely depleted in the aquatic environment. There were significant differences in the heavy metal fractions and risks in sediment in the three different altitudes of the TGR. The physicochemical characteristics of the sediment indicated that the sediments in the low altitude area had rough forms and large pores. In addition, heavy metals at low altitudes were likely to be released into the water during antiseasonal water storage, causing secondary pollution, which greatly increased the mobility of heavy metals and ecological risks to the environment.

Fraction spatial distributions and ecological risk assessment of heavy metals in the sediments of Baiyangdian Lake

Baiyangdian Lake has been the ecological foundation of the Xiongan New Area, a newly developing economic zone in northern China since 2017, meaning that it is increasingly significant to recognize the contamination of the lake. In this work, the spatial distribution and ecological risk of heavy metals in the lake sediments were examined based on field investigation, multivariate statistical analyses and X-ray diffraction techniques (XRD). The results showed that the heavy metals in sediments pose moderate to high risks in most of the sample sites. The heavily contaminated sites presented more unstable chemical (exchangeable and reducible) fractions, and the ecological risk is highly sensitive to the exchangeable fraction in highly contaminative sites. The results of statistical analyses demonstrated that metal fractions were significantly correlated with physicochemical properties, and TP, TN and TOC exhibited a strong correlation with the exchangeable fraction of As, Cd, Pb and Zn. In contrast, Fe and Mn were weakly correlated with the fractions, which due to the high proportion of the nutrient elements in the sediment. Furthermore, the results from the XRD patterns demonstrated that the mineralogy phases of the various heavy metals contributed to the different chemical fractions. Those results demonstrated that further research on metal fraction distribution and influencing factors in the sediment should be implemented to ascertain the degree of toxicity to carry out effective strategies to remediate the lake sediment.

Fraction distribution and leaching behavior of heavy metals in dredged sediment disposal sites around Meiliang Bay, Lake Taihu (China).

The objectives of this study were to characterize the heavy metal contamination status of surface soils sampled at two dredged sediment land disposal sites (the Baimao and Kongwan landfills) in Meiliang Bay, Lake Taihu, China, as well as to investigate the effect on their leaching behaviors due to acid rain. Among all the metals, only the nickel content in the Baimao landfill was higher than the Chinese reference value, and all metal contents were below the limit values for agricultural soils. The fraction distribution of metals by sequential extraction was similar at both sites. Cadmium had a relatively high proportion of exchangeable-carbonate fractions, while the other metals were mainly classified as residue fractions. The metals released from soils by simulated rainwater comprised less than 1% of the total soil metal content, and the effect of acid rain on heavy metal release from dredged sediments in land disposal sites was found to be negligible at both sites. All results indicate no environmental concern for the land disposal of dredged sediments and support the feasibility of beneficially reusing dredged sediment soils as a supplement to agricultural soils.

Transformation of heavy metal fraction distribution in contaminated river sediment treated by chemical-enhanced washing

Mobility and toxicity of heavy metals in river sediments seldom relate to their total concentrations, but to a greater extent depend on their distribution of speciation fractions. Ex situ washing of dredged sediment can effectively reduce the total metal contents, but it may transform metals into more mobile species. This study investigated the changes of the metal fraction distribution and the mobility risk of chemical washed river sediment. Batch chemical-enhanced washing experiments with different agents, including inorganic acids and salt solutions, chelating agents, and oxidizing agents, were conducted on the heavy metal-contaminated sediment collected from Shenzhen River in South China. The removal of Cr, Cu, Pb, and Zn from the sediment was evaluated, and the corresponding changes of metal fraction distribution were examined by using a sequential extraction procedure. The mobility of the remaining metals in the washed sediment was assessed by leaching extractability and compared to those in the original sediment. The results showed that inorganic acid washing effectively removed the majority of heavy metals, but the transformation of Cr, Cu, and Pb from the reducible fraction to the acid-extractable fraction significantly enhanced the mobility of the remaining metals in the washed sediment. Chelating agents such as EDTA and EDDS could efficiently extract Pb and Zn from the sediment, but to a less extent with Cu and Cr. Chelating agents also reduced the relative portions of Cr, Cu, and Pb associated with reducible fraction. Cu and Cr extraction would require the use of oxidizing agents such as H2O2 and Na2S2O8 that reduced their relative portions associated with the oxidizable fraction. Citric acid was only effective for Cr removal through dissolution of Fe oxides/hydroxides into which Cr(III) incorporates. The feasibility of acid washing for sediment remediation should be reconsidered due to high mobility of residual metals, while H2O2 could be a promising additive for sediment remediation. However, a balance should be established between removing labile metal species and minimizing metal transformation.

Effect of drying on heavy metal fraction distribution in rice paddy soil.

An understanding of how redox conditions affect soil heavy metal fractions in rice paddies is important due to its implications for heavy metal mobility and plant uptake. Rice paddy soil samples routinely undergo oxidation prior to heavy metal analysis. Fraction distribution of Cu, Pb, Ni, and Cd from paddy soil with a wide pH range was investigated. Samples were both dried according to standard protocols and also preserved under anaerobic conditions through the sampling and analysis process and heavy metals were then sequentially extracted for the exchangeable and carbonate bound fraction (acid soluble fraction), iron and manganese oxide bound fraction (reducible fraction), organic bound fraction (oxidizable fraction), and residual fraction. Fractions were affected by redox conditions across all pH ranges. Drying decreased reducible fraction of all heavy metals. Curesidual fraction, Pboxidizable fraction, Cdresidual fraction, and Niresidual fraction increased by 25%, 33%, 35%, and >60%, respectively. Pbresidual fraction, Niacid soluble fraction, and Cdoxidizable fraction decreased 33%, 25%, and 15%, respectively. Drying paddy soil prior to heavy metal analysis overestimated Pb and underestimated Cu, Ni, and Cd. In future studies, samples should be stored after injecting N2 gas to maintain the redox potential of soil prior to heavy metal analysis, and investigate the correlation between heavy metal fraction distribution under field conditions and air-dried samples.

An assessment of heavy metal contamination in soils of fresh water aquifer system and evaluation of eco-toxicity by lithogenic implications

The chemistry of heavy metals in sediments with respect to bio-availability and chemical reactivity is regulated by pH, texture, and organic matter contents of the sediments and specific binding form and coupled reactivity of the metals within. To focus on the metal distribution (Fe, Mn, Pb, Cd, Zn, Co, Cu, and Cr) and behavior in a fresh water aquifer system along with the ecological toxicity parameters, a four-step sequential extraction method was applied on 18 Eastern Ghats' type sediments from fluorosis-hit Nayagarh district, India. Geo-accumulation index of metals in the sediments indicates that they are practically uncontaminated and/or less contaminated with and Fe, Mn, and Cu; contaminated to moderately contaminated with Pb, Zn, and Cr; and strongly contaminated with Cd. Rather, more than 80 % recovered Cd metal concentration in sediments constitute the labile fractions. Temporal clustering of metal fractions indicates transition metal fraction distribution claiming the sediment pH regulation. Similarly, base metal distribution accounts for organic carbon and soil conductivity due to their greater availability in exchangeable and sulfide fractions. Correlation analysis and factor analysis scores demonstrate lack of inter-relationship between transition group and base metal fractions. High fluoride concentration in ground water is associated with high sodium-bicarbonate-iron affinity with elevated pH values (i.e., >7.0) and high positive factor score with the total iron concentration in ground water.

Influence of soil washing with a chelator on subsequent chemical immobilization of heavy metals in a contaminated soil

To assess the influence of soil washing with a chelator on the chemical immobilization of heavy metals, batch experiments were performed on the fine fraction of a contaminated soil under various operating conditions. Results show that pre-washing with EDTA facilitated the chemical immobilization of Cu and Cr, while an opposite effect for Pb and Zn was observed, in particular when Ca(OH)(2) was added as the immobilizing agent. Metal fraction analyses of the soils indicate that soil washing can reduce the metal mobility by removing the labile fractions, while it may also destabilize some strongly bound fractions, reversely increasing the mobility and thus compromising the subsequent immobilization performance to some extents. To secure an effective combination of soil washing and chemical immobilization for the remediation of heavy metal-contaminated sites, a comprehensive study on metal fraction distribution in the soil is needed.

Time effect on the fractionation of heavy metals in soils

Time effect on the fractionation of Cu, Zn, Pb, and Cd in three typical Chinese soils was investigated. A total of 500 mg kg −1 of Cu, Zn, Pb and 2.5 mg kg −1 of Cd were added to soils as nitrates. Metals in the incubated soils were fractionated termly from 3 h to 8 weeks by the sequential extraction procedure, in which the metal fractions were experimentally defined as exchangeable, carbonate-, Fe–Mn oxide-, organic matter-bound and residual fractions. Results showed that the changes of Cu, Pb and Zn in fraction distribution were biphasic by an initial rapid step followed by a slow one. Metals in exchangeable fraction were increased in the first 3 h, and then decreased, such decreases could be simulated by a diffusion equation and the decrease rate followed the order Pb>Cu>Zn≫Cd. Metals bound to Fe–Mn oxides and organic matter increased consistently in the 8-week incubation. There were almost no changes for the metals in the residual fraction. After 3-h incubation most of Cd added to soils presented in the exchangeable fraction. The content of Cd in each fraction changed slightly in the 8-week incubation. Soil pH played an important role in metal fraction distribution patterns. Jiangxi soil, with low soil pH, tended to keep more metals added in exchangeable fraction and the changes of metals in each fraction were not as remarkable as in other two soils. High organic matter content resulted in the increased organic matter-bound fraction.

Characteristics of sediments from a stormwater management pond

Physical and chemical characteristics of bottom sediment from an on-stream stormwater pond were described by the depth of sediment accumulations, particle size distribution, water content, concentrations of total metals, and distribution of metal fractions determined by a sequential analysis. Except for a sand/gravel spit by the creek inflow, bottom sediments comprised silt and clay, with high water content (up to 80%, by volume), and accumulated at a rate of 0.02 m·yr−1 (bulk sediment depth). Sediments contained elevated levels of heavy metals, among which the levels of Cr, Cu and Pb caused the greatest environmental concerns. Furthermore, sequential analysis indicated that up to 70 - 90% of total metals in these sediment was in potentially mobile forms. Without further treatment, these sediments could not be reused in urban areas, nor readily disposed at municipal landfills.

Characteristics of sediments from a stormwater management pond

Physical and chemical characteristics of bottom sediment from an on-stream stormwater pond were described by the depth of sediment accumulations, particle size distribution, water content, concentrations of total metals, and distribution of metal fractions determined by a sequential analysis. Except for a sand/gravel spit by the creek inflow, bottom sediments comprised silt and clay, with high water content (up to 80%, by volume), and accumulated at a rate of 0.02 m·yr−1 (bulk sediment depth). Sediments contained elevated levels of heavy metals, among which the levels of Cr, Cu and Pb caused the greatest environmental concerns. Furthermore, sequential analysis indicated that up to 70 – 90% of total metals in these sediment was in potentially mobile forms. Without further treatment, these sediments could not be reused in urban areas, nor readily disposed at municipal landfills.