Use of sorption and extraction tests to predict the dynamics of the interaction of trace elements in agricultural soils contaminated by a mine tailing accident

Sporadic Pb accumulation by plants: Influence of soil biogeochemistry, microbial community and physiological mechanisms

Recent results revealed that considerable Pb accumulation in plants is possible under specific soil conditions that make Pb phytoavailable. In this review, the sources and transformations of Pb in soils, the interaction of Pb with bacteria and specifically the microbiota in the soil, factors and mechanisms of Pb uptake, translocation and accumulation in plants and Pb toxicity in living organisms are comprehensively elaborated. Specific adsorption and post-adsorption transformations of Pb in soil are the main mechanisms affecting the mobility, bioavailability, and toxicity of Pb. The adsorption ability of Pb largely depends on the composition and properties of soils and environmental conditions. Microbial impact on Pb mobility in soil and bioavailability as well as bacterial resistance to Pb are considered. Specific mechanisms conferring Pb-resistance, including Pb-efflux, siderophores, and EPS, have been identified. Pathways of Pb entry into plants as well as mechanisms of in planta Pb transport are poorly understood. Available evidence suggests the involvement of Ca transporters, organic acids and the phytochelatin pathway in Pb transport, mobility and detoxification, respectively.

Distribution and ecological risk assessment of heavy metals in sediments of Dajiuhu Lake Wetland in Shennongjia, China

The rapid development of modern society has resulted in discharge of large, heavy metal quantities into wetlands that have been continuously accumulating, causing severe pollution. Dajiuhu, located in the Shennongjia Forest District of Hubei Province in China, is a wetland of significant value internationally, serving as a model wetland ecosystem with heightened scientific research value. In this study, 27 surface sediment samples from nine sub-lakes in Dajiuhu were collected in August 2020. The concentrations of Cd, Cr, Cu, Ni, Pb, and Zn in the sediments were determined. The heavy metal occurrence and speciation characteristics were analyzed by an improved BCR (European Community Bureau of Reference) extraction method. Four methods were used to evaluate heavy metals' pollution degree and ecological risk. The possible source of heavy metals was inferred using correlation analysis and principal component analysis. The heavy metal content in the lake sediments of Dajiuhu wetland was from the highest to the lowest concentration as follows: Zn [Formula: see text] Cr [Formula: see text] Ni [Formula: see text] Pb [Formula: see text] Cu [Formula: see text] Cd. The average Cd content exceeded the national nature reserve threshold values, while the other heavy metals measured were below their respective threshold values. However, due to the occurrence of Pb and Cd in different forms, they still pose certain pollution and ecological risk to the lake wetlands. On the other hand, Zn, Cr, Ni, and Cu do not pose an ecological risk in the lakes of the Dajiuhu wetland. The spatial distribution of heavy metal content in the nine sub-lakes did vary significantly. Regarding the heavy metal sources in the lake sediments, Ni, Cr, and Cu originate from natural factors, and Cd and Pb have mainly anthropogenic origins. In contrast, Zn has both natural and anthropogenic origins. This study provides further insights into the study of heavy metal pollution in lake wetlands. It provides a framework and a direction for managing heavy metal pollution in the Dajiuhu wetland.

Effect of slow-released biomass alkaline amendments oyster shell on microecology in acidic heavy metal contaminated paddy soils

Soil ecosystem functions and microbial community structure were severely impaired with long-term cadmium (Cd) contamination and acidification. To investigate the effect of amendments on soil physiochemical parameters and soil micro-ecology in acidic Cd contaminated soil, this study was conducted in a pot experiment with the application of calcium amendments, oyster shell powders (OS) and limestone (LM). Each amendment applied at ratios of 1.0%, 3.0%, and 5.0% (w/w), respectively. The results showed that the application of amendments increased the soil pH by 2.10-2.88, the bioavailable Cd decreased by 12.49%-19.48%, and un-bioavailable Cd increased by 96.57%-200.7%. The OS increased the richness index (Chao and Ace increased by 13.23%-16.20% and 7.13%-47.63%), and LM increased the microbial diversity index (Shannon increased by 1.14%-8.72% and Simpson indexes decreased by 28.00%-63.61%). In LM groups, soil microbial communities were significantly altered with increasing application concentrations, the relative abundance of phylum Proteobacteria, Bacteroidota and Gemmatimonadota increased, while Firmicute, Actinobacteria, Chloroflexi decreased. In OS treatments, the soil microbial community structure was basically unchanged. The correlation analysis showed that pH, TN, TP, CEC, OM were the dominant factors affecting the microbial community. This study has shown that application of amendments could effectively reduce the Cd bioavailability in soil, but LM altered the soil microbial community structure, while OS maintained the soil microbiological structure.

Insight into functional microorganisms in wet–dry conversion to alleviate the toxicity of chromium fractions in red soil

Soil contamination with potentially toxic element such as chromium (Cr) poses a threat to the environment and human health. The environmental toxicity of Cr is related not only to the total Cr content but also to the distribution of Cr fractions. In this study, laboratory simulation experiments were conducted to explore the characteristics of Cr fractions and responses of the functional microbial community during dynamic leaching and static drying processes. The results showed that acid-soluble Cr and reducible Cr transformed into other relatively stable fractions under dry conditions, and ammonium nitrogen promoted the transformation. Nitrate-nitrogen was significantly positively correlated with Cr fractions in the wet stage (p < 0.05), while ammonium nitrogen showed the same relation in the dry process. Analysis of the microbial community showed that the bacterial and fungal genera Flavihumibacter, Altererythrobacter, Methylobacillus, Flavisolibacter, Lysobacter, and Cladosporium were related to the Cr fractions (acid-soluble Cr, reducible Cr, and oxidizable Cr) under wet conditions, while the microbial genera Ellin6067, MND1, and Ramlibacter were related to Cr fractions under dry conditions. Moreover, the proliferation of the functional microbial genera Methylobacillus, Ellin6067, and MND1 related to Cr fractions in the wet–dry conversion process alleviated the environmental toxicity of Cr. These findings provide useful information for the remediation of Cr-contaminated soils by monitoring the distribution fractions of Cr and the functional microbial community under wet–dry conditions.

Ecological and Health Risk Assessment of Heavy Metals in Soils from Recycled Lead Smelting Sites

In this study, 258 soil samples were collected to determine the total content and each speciation fraction of chromium (Cr), manganese (Mn), copper (Cu), zinc (Zn), cadmium (Cd), and lead (Pb) in the soil by inductively coupled plasma mass spectrometry (ICP-MS), and their potential ecological and human health risks were assessed using the geo-accumulation index (Igeo), risk assessment code (RAC), and health risk assessment. The results showed that: (1) The mean concentrations of heavy metals (HMs) (mg/kg) in the surface soil of the site were in the order of Pb (1921.77) > Mn (598.21) > Zn (162.29) > Cr (84.65) > Cu (15.16) > Cd (1.8), with the mean values of Cd and Pb exceeding the local background values by 164 and 725 times. (2) In the vertical direction, Cr, Mn, and Pb have no tendency to migrate downward; Cd and Zn demonstrate a strong ability to migrate. (3) The bioavailability of Cd is the highest in the surface soil, followed by Mn and Pb; in the soil below a depth of 0.5 m, the prevalent form of HMs is its residual state (F4). (4) The degree of Igeo pollution of each HMs is: Pb > Cd > Zn > Cr = Mn = Cu, where Pb pollutes the environment to an extremely contaminated level and Cd causes heavy pollution thereof. According to the RAC results, Cd in the surface soil poses a high risk to the environment, and Pb and Mn pose a moderate risk; meanwhile, with the increase of depth, the risk posed by Cd and Mn to the ecosystem shows a tendency to increase. Health risk evaluation indicated that respiratory intake was the main pathway affecting the carcinogenic risk (CR) and hazard quotient (HQ) of HMs, where Pb and Cr were the main hazard factors for non-CR and Cr was the main carcinogenic factor. This study can provide scientific guidance and technical support for soil risk control or remediation of HM-contaminated sites.

A synthetic health risk assessment based on geochemical equilibrium simulation and grid spatial interpolation for zinc (II) species

Soil heavy metal pollution has become a global issue involving environmental safety and human health risks. This paper quantified the sources of heavy metals by positive matrix factorization (PMF) model and explored the spatial distribution of heavy metals by means of grid scales, with an industrial site as the study area in Suzhou. The PMF identified four pollution sources of heavy metal in soil, and the quantitative results revealed that industrial activities (33.5%) contributed the most to heavy metals, followed by soil parent materials (30.8%) and agricultural activities (19.7%). Zinc (Zn) was screened out as the targeted metal (TM) through the potential ecological risk assessment, the metal species of which was simulated by the geochemical software PHREEQC. This research aimed to determine the dominant metal species of TM with high-risk levels to realize the transformation of toxic metal species. Herein, according to the morphological evolution of metal species, the activity and concentration of the Zn ion species were obtained for both carcinogenic and non-carcinogenic risk assessment. The evaluation of the optimized human health risk demonstrated that the associated health risk of Zn (II) ions depended predominantly on its metal speciation. Overall, the optimized carcinogenic and non-carcinogenic risk value of Zn₂S₃^2- for adults was 2.01E-04 and for children was 1.31, resulting in corresponding hazardous risk to humans, which accounted for high-risk levels of 61.5% and 58.5% for adults and children, respectively. The OHRA method can provide a reference for the decision-making of soil heavy metal pollution and remediation for specific heavy metals in polluted areas.

Effects of Fe-loaded biochar on the bioavailability of Arsenic and cadmium to lettuce growing in a mining contaminated soil

Arsenic (As) and cadmium (Cd) are two prominent metal contaminants in mining soil, threatening food and environmental safety. The effects of Fe-loaded biochar on the accumulation and translocation of As and Cd in a soil-lettuce system were investigated to evaluate the efficiency of Fe-loaded biochar in reducing As and Cd bioavailability. Application of Fe-loaded biochar at a rate of 0.5-1.5% decreased the concentrations of porewater As and Cd by 4.2-53.0% and -0.6-21.7%, respectively. The results of sequential extraction showed that Fe-loaded biochar can promote the transfer of As and Cd in soils from the available fraction to a relatively stable fraction, thus reducing the mobility and availability of As and Cd. The concentrations of As and Cd in lettuce shoots in the Fe-loaded biochar treatment were significantly decreased by 11.4-26.0% and 4.4-12.9% compared with those in the untreated soil, respectively. Fe-loaded biochar applied at a rate of 0.5-1.0% had no obvious effect on plant biomass, and the lowest weight of lettuce shoots and roots was observed in the treatment with Fe-loaded biochar applied at a rate of 1.5%, in which they were reduced by 12.9% and 18.0%, respectively. Overall, Fe-loaded biochar as a soil amendment was effective in simultaneously reducing As and Cd bioavailability in As and Cd co-contaminated soils, and an application rate lower than 1.5% is recommended to avoid significant decreases in plant growth.

Effects of UV-modified biochar derived from phytoremediation residue on Cd bioavailability and uptake in Coriandrum sativum L. in a Cd-contaminated soil

Biochar has been applied widely as an amendment in the remediation of contaminated soil to immobilize the heavy metals. However, the role of ultraviolet (UV) irradiation modified biochar derived from the residues of phytoremediation plants in the contaminated soil not investigated yet. In this study, the UV-modified biochars were obtained from Brassica napus L. and Lolium perenne L. by pyrolysis at 600 °C. They were applied in a pot experiment to investigate their effect on Cd bioavailability and uptake in Coriandrum sativum L. in a Cd-contaminated soil at four addition rate (0%, 0.2%, 0.4%, and 0.6%). The results showed that the Cd was effectively stabilized in the biochar with environmentally acceptable leaching toxicity. The specific surface area and carboxyl functional group of biochar were greatly increased after UV modification. The application of biochar progressively increased the soil pH and electrical conductivity (EC). Furthermore, the CaCl₂-extractable Cd was significantly reduced by 18.4-51.4% with biochar amendments. The concentration of Cd in shoots and roots was significantly reduced by biochars. In conclusion, the UV-modified biochar obtained from phytoremediation residue could effectively deal with hazardous waste and repair Cd-contaminated soil.

Defects and their behaviors in mineral dissolution under water environment: A review

Mineral dissolution is a spontaneous process that takes indispensible role in the determination of water quality in a specific water body. Deep insights into defects as a result of characterization technique development have greatly improved our understanding of their significances and behaviors in the dissolution within the mineral-water interface. Based on the progresses from previous decades, this review attempts to re-elaborate the molecular-scale process of dissolution. Material flow within the mineral/water interface is updated, with emphasis on the function of defect sites. A brief introduction of defect properties is presented, including the microscopic appearances and typical physicochemical characteristics. Feasible strategies that have been adopted to increase the defect abundance are inferred, which maybe enlightening for hydrometallurgy. The merits and drawbacks of the techniques that could be employed for the qualitative and quantitative determination of defect presence are introduced, although relatively satisfactory performances are noted. With the aid of these techniques, it is concluded that screw dislocation is the main defect type responsible for surface topography evolution as a result of dissolution. Finally, this review identifies the current knowledge gaps and future research needs for comprehensively identifying the significance of defects in mineral dissolution.

Pb speciation in rare earth minerals and use of entropy and fuzzy clustering methods to assess the migration capacity of Pb during mining activities

Ionic rare earth mining is of strategic importance in China; however, the heavy metal pollution it causes is of great concern, both at home and abroad. Data on Pb speciation at a rare earth mine were used to analyse the migration capacity of Pb during the process of ore leaching. The major factors thought to influence the migration capacity of Pb, including the clay mineral content, soil pH, oxidation-reduction potential, organic matter content, and cation exchange capacity (CEC), were quantified. Entropy and fuzzy clustering methods were used to identify the most predictive factors. The results showed that the clay mineral content of the soil exerts the strongest influence on the migration capacity of Pb in rare earth mines; the other factors demonstrated relatively weak influences on the transport processes. The results obtained from the classification of Pb per the potential migration index (PMI) approximated those obtained from fuzzy clustering, and the results of entropy analyses were consistent with those of fuzzy clustering. Thus, the methods upon which the proposed model is based are suitable for predicting the migration capacity of Pb in ore during the mining of ionic rare earth minerals.

Reduced arsenic availability and plant uptake and improved soil microbial diversity through combined addition of ferrihydrite and Trichoderma asperellum SM-12F1

Arsenic (As) accumulation in agricultural soils is prone to crop uptake, posing risk to human health. Passivation shows potential to inactivate soil labile As and lower crop As uptake but often contributes little to improving the microbiota in As-contaminated soils. Here, the combined addition of ferrihydrite and Trichoderma asperellum SM-12F1 as a potential future application for remediation of As-contaminated soil was studied via pot experiments. The results indicated that, compared with the control treatment, the combined addition of ferrihydrite and T. asperellum SM-12F1 significantly increased water spinach shoot and root biomass by 134 and 138%, respectively, and lowered As content in shoot and root by 37 and 34%, respectively. Soil available As decreased by 40% after the combined addition. The variances in soil pH and As fractionation and speciation were responsible for the changes in soil As availability. Importantly, the combined addition greatly increased the total phospholipid fatty acids (PLFAs) and gram-positive (G+), gram-negative (G-), actinobacterial, bacterial, fungal PLFAs by 114, 68, 276, 292, 133, and 626%, respectively, compared with the control treatment. Correspondingly, the soil enzyme activities closely associated with carbon, nitrogen, and phosphorus mineralization and antioxidant activity were improved. The combination of ferrihydrite and T. asperellum SM-12F1 in soils did not reduce their independent effects.

Soil-plant relationships and contamination by trace elements: A review of twenty years of experimentation and monitoring after the Aznalcóllar (SW Spain) mine accident

Soil contamination by trace elements (TE) is a major environmental problem and much research is done into its effects on ecosystems and human health, as well as into remediation techniques. The Aznalcóllar mine accident (April 1998) was a large-scale ecological and socio-economic catastrophe in the South of Spain. We present here a literature review that synthesizes the main results found during the research conducted at the affected area over the past 20years since the mine accident, focused on the soil-plant system. We review, in depth, information about the characterization of the mine slurry and contaminated soils, and of the TE monitoring, performed until the present time. The reclamation techniques included the removal of sludge and soil surface layer and use of soil amendments; we review the effects of different types of amendments at different spatial scales and their effectiveness with time. Monitoring of TE in soil and their transfer to plants (crops, herbs, shrubs, and trees) were evaluated to assess potential toxicity effects in the food web. The utility of some plants (accumulators) with regard to the biomonitoring of TE in the environment was also evaluated. On the other hand, retention of TE by plant roots and their associated microorganisms was used as a low-cost technique for TE stabilization and soil remediation. We also evaluate the experience acquired in making the Guadiamar Green Corridor a large-scale soil reclamation and phytoremediation case study.

Opportunities and challenges in the use of mineral nutrition for minimizing arsenic toxicity and accumulation in rice: A critical review

Growing rice on arsenic (As)-contaminated soil or irrigating with As-contaminated water leads to significant accumulation of As in grains. Moreover, rice accumulates more As into grains than other cereal crops. Thus, rice consumption has been identified as a major route of human exposure to As in many countries. Inorganic As species are carcinogenic and could pose a considerable health risk to humans even at low dietary concentration. Genotypic variation and concentration of nutrients such as iron, manganese, phosphate, sulfur and silicon are the two main factors that affect As accumulation in rice grains. Therefore, in addition to better growth and yield of plants, application of specific nutrients in optimum quantities offers an added benefit of decreasing As content in rice grains. These nutrient elements influence speciation of As in rhizosphere, compete with As for root uptake and interfere with As translocations to the shoot and ultimately accumulation in grains. This papers critically appraises the methods, forms and rate of application, mechanisms and extent of efficiency of different mineral nutrients in decreasing As accumulation in rice grains.

Factors controlling cadmium and lead activities in different parent material-derived soils from the Pearl River Basin

Labile metals in agricultural soils are available to crops and thus pose a great health risk for human beings. Therefore, factors influencing heavy metal activity are of interest to researchers. In this study, a total of 142 soil samples representing 5 typical parent materials in the Pearl River Basin (PRB), China were collected to investigate factors impacting the distribution of labile Cd and Pb in the soils. The results showed that the labile fractions accounted for 0.03%-14.7% for Cd and 0.01%-0.39% for Pb of the total metals, and the labile fractions were linearly correlated to their corresponding total contents. The step regression analyses suggested that the key factors impacting labile Cd and Pb varied in different parent material soils. Pb activity was highly sensitive to pH in alkaline limestone soils. The quartz sand remained in granite-produced soils enhanced Cd activity. And dissolved organic matter (DOM) compositions considerably influenced Cd and Pb activities in sand shale, diluvium, and alluvium soils. Land use impacts heavy metal activities. The labile Cd and Pb in paddy soils were higher than those in non-paddy soils, although total metals in the soils were comparable. It could be ascribed to the long-term equilibrium of metals between the solution and solid phases of the paddy soils. The results provide a theoretical basis for preliminary prediction of heavy metal activity and provide a technical support for heavy metal activity management and pollution control based on soil parent materials.

Assessing the efficacy over time of the addition of industrial by-products to remediate contaminated soils at a pilot-plant scale

The effect of the addition of industrial by-products (gypsum and calcite) on the leaching of As and metals (Cu, Zn, Ni, Pb and Cd) in a soil contaminated by pyritic minerals was monitored over a period of 6 months at a two-pit pilot plant. The contaminated soil was placed in one pit (non-remediated soil), whereas a mixture of the contaminated soil (80% w/w) with gypsum (10% w/w) and calcite (10% w/w) was placed in the other pit (remediated soil). Soil samples and leachates of the two pits were collected at different times. Moreover, the leaching pattern of major and trace elements in the soil samples was assessed at laboratory level through the application of the pH_stat leaching test. Addition of the by-products led to an increase in initial soil pH from around 2.0 to 7.5, and it also provoked that the concentration of trace elements in soil extracts obtained from the pH_stat leaching test decreased to values lower than quantification limits of inductively coupled plasma optical emission spectrometry and lower than the hazardous waste threshold for soil management. The trace element concentration in the pilot-plant leachates decreased over time in the non-remediated soil, probably due to the formation of more insoluble secondary minerals containing sulphur, but especially decreased in pit of the remediated soil, in agreement with laboratory data. The pH in the remediated soil remained constant over the 6-month period, and the X-ray diffraction analyses confirmed that the phases did not vary over time, thus indicating the efficacy of the addition of the by-products. This finding suggests that soil remediation may be a feasible option for the re-use of non-hazardous industrial by-products.

The effectiveness of various treatments in changing the nutrient status and bioavailability of risk elements in multi-element contaminated soil

Potential changes in the mobility and bioavailability of risk and essential macro- and micro-elements achieved by adding various ameliorative materials were evaluated in a model pot experiment. Spring wheat (Triticum aestivum L.) was cultivated under controlled condition for 60 days in two soils, uncontaminated Chernozem and multi-element contaminated Fluvisol containing 4900 ± 200 mg/kg Zn, 35.4 ± 3.6 mg/kg Cd, and 3035 ± 26 mg/kg Pb. The treatments were all contained the same amount of sulfur and were as follows: (i) digestate from the anaerobic fermentation of biowaste, (ii) fly ash from wood chip combustion, and (iii) ammonium sulfate. Macro- and micro-nutrients Ca, Mg, K, Fe, Mn, Cu, P, and S, and risk elements Cd, Cr, Pb, and Zn were assayed in soil extracts with 0.11 mol/l solution of CH3COOH and in roots, shoots, and grain of wheat after 30 and 60 days of cultivation. Both digestate and fly ash increased levels of macro- and micro-nutrients as well as risk elements (especially Cd and Zn; the mobility of Pb decreased after 30 days of cultivation). The changes in element mobility in ammonium sulfate-treated soils appear to be due to both changes in soil pH level and inter-element interactions. Ammonium sulfate tended to be the most effective measure for increasing nutrient uptake by plants in Chernozem but with opposite pattern in Fluvisol. Changes in plant yield and element uptake in treated plants may have been associated with the higher proline content of wheat shoots cultivated in both soils compared to control. None of the treatments decreased uptake of risk elements by wheat plants in the extremely contaminated Fluvisol, and their accumulation in wheat grains significantly exceeded maximum permissible levels; these treatments cannot be used to enable cereal and other crop production in such soils. However, the combination of increased plant growth alongside unchanged element content in plant biomass in pots treated with digestate and fly ash suggests that these treatments have a beneficial impact on yield and may be effective treatments in crops grown for phytoremediation.

Leachability of major and minor elements from soils and sediments of an abandoned coal mining area in Southern Brazil

Leachability of major and trace elements from sediment and soil samples of an abandoned coal mining area in southern Brazil was assessed by titration and pH-stat tests according to the SR002.1 and CEN/TS 14429 protocols. Major (Al, Fe, Ca, Mg, and Mn) and trace (Cu, Zn, As, Ni, Pb, Cd, and Hg) elements were quantified in aqueous extracts. Acid and base neutralizing capacity values and pH changes after the addition of certain acid/base amounts were estimated. In general, a decrease in the major metal leaching at pH < 4.0 and an increase at pH > 8.0 was observed. The response to the acid and base additions confirmed that strong acids can cause an effect on Ca- and Mg-bearing silicate phases and Mn oxides, and strong bases can only affect Ca silicates. At pH < 5.0, higher extractability was found for Cu, Zn, Ni, Pb, and Cd. Considering that the samples showed sharp pH changes after acid additions and released major and trace metal into the solution at greater rates, high metal contamination risks can be assumed for the studied area.

The influence of soil organic carbon on interactions between microbial parameters and metal concentrations at a long-term contaminated site

The effects of lead, zinc, cadmium, arsenic and copper deposits on soil microbial parameters were investigated at a site exposed to contamination for over 200 years. Soil samples were collected in triplicates at 121 sites differing in contamination and soil organic carbon (SOC). Microbial biomass, respiration, dehydrogenase activity and metabolic quotient were determined and correlated with total and extractable metal concentrations in soil. The goal was to analyze complex interactions between toxic metals and microbial parameters by assessing the effect of soil organic carbon in the relationships. The effect of SOC was significant in all interactions and changed the correlations between microbial parameters and metal fractions from negative to positive. In some cases, the effect of SOC was combined with that of clay and soil pH. In the final analysis, dehydrogenase activity was negatively correlated to total metal concentrations and acetic acid extractable metals, respiration and metabolic quotient were to ammonium nitrate extractable metals. Dehydrogenase activity was the most sensitive microbial parameter correlating most frequently with contamination. Total and extractable zinc was most often correlated with microbial parameters. The large data set enabled robust explanation of discrepancies in organic matter functioning occurring frequently in analyzing of contaminated soil processes.

Differences in the mobility of Cd, Cu, Pb and Zn during composting of two types of household bio-waste collected in four seasons

The objective of this study was to evaluate the mobility of Cd, Cu, Pb and Zn during 3 different compost aeration rates of household bio-waste, originating in urban settlement (U-bio-waste) and family house buildings (F-bio-waste). The first two weeks, when the thermophilic composting phase became, the highest decline of exchangeable content was recorded. After 12 weeks of composting, lower exchangeable content was found in the case of U-bio-waste composts than F-bio-waste composts, despite higher loss of fresh mass. The order of fractions in both final composts was as follows: residual>oxidizable>reducible>exchangeable. The exchangeable portion of total content in final composts decreased in this order: Zn (17%), Cd (11%), Pb (4%) and Cu (3%). Regarding the low exchangeable content of heavy metals and high-quality organic matter, these types of composts could be used not only as fertilizer, but for remediation of metals contaminated land.

Distribution and speciation of metals (Cu, Zn, Cd, and Pb) in agricultural and non-agricultural soils near a stream upriver from the Pearl River, China

The distribution and chemical speciation of typical metals (Cu, Zn, Cd and Pb) in agricultural and non-agricultural soils were investigated in the area of Nanpan River, upstream of the Pearl River. The investigated four metals showed higher concentrations in agricultural soils than in non-agricultural soils, and the site located in factory district contained metals much higher than the other sampling sites. These observations suggested that human activities, such as water irrigation, fertilizer and pesticide applications might have a major impact on the distribution of metals. Metal speciation analysis presented that Cu, Zn and Cd were dominated by the residual fraction, while Pb was dominated by the reducible fraction. Because of the low mobility of the metals in the investigated area, no remarkable difference could be observed between upstream and downstream separated by the factory site.

Application of Using Sphingomonas-Paucimobilis of Sodium Alginate Fossilization Bacillus Subtilis Pellet to Heavy Metal of Mine Wastewater

This study use purely bacteria on suitable condition, eliminate other bacteria come in life-form bacteria. Through the orthogonal experiment obtains the optimum condition of sodium alginate fossilization bacillus subtilus pellet to chrome adsorption, and discusses the influence of single factor to the sodium alginate fossilization bacillus subtilus pellet to chrome adsorption, including the time, the temperature,pH, the initial adsorbent density, the speed of the shaker, the absorbent which the different periods of growth bacterium does, coexistent ion, desorption. From the research, we know the maximum adsorption rate to chrome is about 80%. Dynamics research indicated that in the several methods of the Sphingomonas-paucimobilis of chrome , the methods of embedded micro-organisms embodies much advantages ,as operating easily, effecting clearly, less pollution, costing low, etc.

Effectiveness of amendments on the spread and phytotoxicity of contaminants in metal-arsenic polluted soil

A metal-arsenic polluted soil from sulphide-mine waste was treated, in all possible combinations, with two different amounts of marble sludge (98% CaCO3), compost (41% organic carbon), and Byferrox (70% Fe). Lixiviate and pore water from each treated and untreated soil were analysed, and lettuce-seed bioassays were performed. None of the treatments decreased the electrical conductivity of lixiviates or the concentrations of all pollutants found in both solutions. Marble sludge and compost increased the pH values and decreased the zinc, cadmium, copper, and lead concentrations in both solutions while increasing the arsenic concentrations in the lixiviates. Byferrox did not alter the physicochemical parameters or the concentrations of zinc, cadmium, copper, or lead in either solution but significantly decreased the arsenic concentrations in pore water. Compared with the Byferrox treatment, the mixture of marble sludge and Byferrox decreased redox potential values, increasing the arsenic concentrations in both solutions and the electrical conductivity of the pore water. All lixiviates were highly phytotoxic and seeds did not germinate. Pore-water phytotoxicity was related to electrical conductivity values and heavy-metal concentrations. The combination of marble sludge and compost was most effective at diminishing toxicity in lettuce. The soils treated with Byferrox, alone or mixed with marble sludge or compost, were the most phytotoxic.

Remediation technologies for heavy metal contaminated groundwater

The contamination of groundwater by heavy metal, originating either from natural soil sources or from anthropogenic sources is a matter of utmost concern to the public health. Remediation of contaminated groundwater is of highest priority since billions of people all over the world use it for drinking purpose. In this paper, thirty five approaches for groundwater treatment have been reviewed and classified under three large categories viz chemical, biochemical/biological/biosorption and physico-chemical treatment processes. Comparison tables have been provided at the end of each process for a better understanding of each category. Selection of a suitable technology for contamination remediation at a particular site is one of the most challenging job due to extremely complex soil chemistry and aquifer characteristics and no thumb-rule can be suggested regarding this issue. In the past decade, iron based technologies, microbial remediation, biological sulphate reduction and various adsorbents played versatile and efficient remediation roles. Keeping the sustainability issues and environmental ethics in mind, the technologies encompassing natural chemistry, bioremediation and biosorption are recommended to be adopted in appropriate cases. In many places, two or more techniques can work synergistically for better results. Processes such as chelate extraction and chemical soil washings are advisable only for recovery of valuable metals in highly contaminated industrial sites depending on economical feasibility.

Application, chemistry, and environmental implications of contaminant-immobilization amendments on agricultural soil and water quality

Contaminants such as nitrogen (N), phosphorus (P), dissolved organic carbon (DOC), arsenic (As), heavy metals, and infectious pathogens are often associated with agricultural systems. Various soil and water remediation techniques including the use of chemical amendments have been employed to reduce the risks associated with these contaminants. This paper reviews the use of chemical amendments for immobilizing principal agricultural contaminants, the chemistry of contaminant immobilization, and the environmental consequences associated with the use of these chemical products. The commonly used chemical amendments were grouped into aluminum-, calcium-, and iron-containing products. Other products of interest include phosphorus-containing compounds and silicate clays. Mechanisms of contaminant immobilization could include one or a combination of the following: surface precipitation, adsorption to mineral surfaces (ion exchange and formation of stable complexes), precipitation as salts, and co-precipitation. The reaction pH, redox potential, clay minerals, and organic matter are potential factors that could control contaminant-immobilization processes. Reviews of potential environmental implications revealed that undesirable substances such as trace elements, fluoride, sulfate, total dissolved solids, as well as radioactive materials associated with some industrial wastes used as amendment could be leached to ground water or lost through runoff to receiving water bodies. The acidity or alkalinity associated with some of the industrial-waste amendments could also constitute a substantial environmental hazard. Chemical amendments could introduce elements capable of inducing or affecting the activities of certain lithotrophic microbes that could influence vital geochemical processes such as mineral dissolution and formation, weathering, and organic matter mineralization.

Toxic trace element assessment for soils/sediments deposited during Hurricanes Katrina and Rita from southern Louisiana, USA: a sequential extraction analysis

Analysis of soil/sediment samples collected in the southern Louisiana, USA, region three weeks after Hurricanes Katrina and Rita passed was performed using sequential extraction procedures to determine the origin, mode of occurrence, biological availability, mobilization, and transport of trace elements in the environment. Five fractions: exchangeable, bound to carbonates, bound to iron (Fe)-manganese (Mn) oxides, bound to organic matter, and residual, were subsequently extracted. The toxic trace elements Pb, As, V, Cr, Cu, and Cd were analyzed in each fraction, together with Fe in 51 soil/sediment samples. Results indicated that Pb and As were at relatively high concentrations in many of the soil/sediment samples. Because the forms in which Pb and As are present tend to be highly mobile under naturally occurring environmental conditions, these two compounds pose an increased health concern.Vanadium and Cr were mostly associated with the crystal line nonmobile residual fraction. A large portion of the Cu was associated with organic matter and residual fraction. Cadmium concentrations were low in all soil/sediment samples analyzed and most of this element tended to be associated with the mobile fractions. An average of 21% of the Fe was found in the Fe-Mn oxide fraction, indicating that a substantial part of the Fe was in an oxidized form. The significance of the overall finding of the present study indicated that the high concentrations and high availabilities of the potentially toxic trace elements As and Pb may impact the environment and human health in southern Louisiana and, in particular, the New Orleans area.

Bioavailability assessment and accumulation by five garden flower species grown in artificially cadmium-contaminated soils

Many studies have been conducted on phytoextraction; however, non-native hyperaccumulator species are not suitable for the natural environment of Taiwan in many cases. Drawing upon previous results, the growth and heavy metal accumulation in artificially cadmium-contaminated soils were compared for five local garden flower species. The treatments included a control (CK), 9.73 +/- 0.05 mg kg(-1) (Cd-10), and 17.6 +/- 0.8 mg kg(-1) (Cd-20). All plants were harvested at 35 days after transplanting and analyzed for Cd content. Cd accumulation in the shoot of French marigold (Tagetes patula L.) and Impatiens (Impatiens walleriana Hook. f.) grown in Cd-20 treatment were 66.3 +/- 6.5 and 100 +/- 11 mg kg(-1), which equated to a removal of 0.80 +/- 0.11 and 0.60 +/- 0.37 mg Cd plant(-1), respectively. The maximum Cd accumulation of Impatiens reached the threshold value (100 mg kg(-1)) characteristic of a Cd hyperaccumulator and its bioconcentration factor (BCF) and translocation factor (TF) were greater than one. Impatiens therefore has the potential to hyperaccumulate Cd from Cd-contaminated soils. With the exception of Garden verbena, significant relationships were found between Cd concentrations in soil extracted by 0.05 M EDTA, 0.005 M DTPA, and 0.01 M CaCl2 and the concentration of Cd in the shoots of the tested garden flowers.

pH(stat) vs. single extraction tests to evaluate heavy metals and arsenic leachability in environmental samples

Here we compared the pH(stat) test, which examines the leachability of major elements (Ca, Mg, Al, Fe, and Mn), dissolved organic carbon, and trace elements (Cd, Zn, Cu, Pb, and As) in a wide pH range, with single extraction tests based on the use of mild extractants (calcium chloride, acetic acid or EDTA). For this purpose, we examined samples from a variety of environmental conditions (sludges, mineral soils, organic soils, and soils with particulate and/or soluble contamination). Extraction yields obtained with CaCl(2) (0.01 mol L(-1)) and CH(3)COOH (0.43 mol L(-1)) correlated well with those from the pH(stat) at the same pH (r=0.98 and 0.95, respectively), while the use of EDTA (0.05 mol L(-1)) led to systematically higher extraction yields than those quantified with the pH(stat) at the same pH. However, the pH(stat) test had three distinct advantages: (1) it revealed the relationship between the solubility of the main soil phases and pH; (2) it showed the variation in pollutant leachability due to changes in pH; and (3) it better predicted the maximum contaminant availability. Thus we propose that the pH(stat) is the best laboratory tests to evaluate the contaminant leachability over a wide range of sample types (soil, sludge, and sediment).

Use of the modified BCR three-step sequential extraction procedure for the study of trace element dynamics in contaminated soils

The modified BCR three-step sequential extraction procedure was used to examine the temporal dynamics of trace elements in soils contaminated by an accidental spill from an opencast mine in south-west Spain. Soils were mainly contaminated with pyritic sludge and acidic wastewater, whereas some soils were affected only by acidic wastewater. The distributions obtained for both some major (Ca, Fe and Mn) and trace elements (As, Cd, Cu, Pb and Zn) in the sludge and soil samples taken at different times after the accident, 1-3 months and 21 months, were compared. Sequential extractions were useful in identifying different sources of contamination, and in obtaining additional information on the solubility of secondary minerals formed by pyrite oxidation. Thus, the effectiveness of the BCR procedure has proved to be a useful tool for predicting short- and long-term mobility of trace elements, even in complex environmental scenarios.

Stabilization of As, Cr, Cu, Pb and Zn in soil using amendments--a review

The spread of contaminants in soil can be hindered by the soil stabilization technique. Contaminant immobilizing amendments decrease trace element leaching and their bioavailability by inducing various sorption processes: adsorption to mineral surfaces, formation of stable complexes with organic ligands, surface precipitation and ion exchange. Precipitation as salts and co-precipitation can also contribute to reducing contaminant mobility. The technique can be used in in situ and ex situ applications to reclaim and re-vegetate industrially devastated areas and mine-spoils, improve soil quality and reduce contaminant mobility by stabilizing agents and a beneficial use of industrial by-products. This study is an overview of data published during the last five years on the immobilization of one metalloid, As, and four heavy metals, Cr, Cu, Pb and Zn, in soils. The most extensively studied amendments for As immobilization are Fe containing materials. The immobilization of As occurs through adsorption on Fe oxides by replacing the surface hydroxyl groups with the As ions, as well as by the formation of amorphous Fe(III) arsenates and/or insoluble secondary oxidation minerals. Cr stabilization mainly deals with Cr reduction from its toxic and mobile hexavalent form Cr(VI) to stable in natural environments Cr(III). The reduction is accelerated in soil by the presence of organic matter and divalent iron. Clays, carbonates, phosphates and Fe oxides were the common amendments tested for Cu immobilization. The suggested mechanisms of Cu retention were precipitation of Cu carbonates and oxy-hydroxides, ion exchange and formation of ternary cation-anion complexes on the surface of Fe and Al oxy-hydroxides. Most of the studies on Pb stabilization were performed using various phosphorus-containing amendments, which reduce the Pb mobility by ionic exchange and precipitation of pyromorphite-type minerals. Zn can be successfully immobilized in soil by phosphorus amendments and clays.

Prediction of radionuclide aging in soils from the Chernobyl and Mediterranean areas

The aging of soil-pollutant interaction, which may lead to an increase in pollutant fixation, is the main driving force in the natural attenuation of contaminated soils. Here a test was evaluated to predict the aging of radiostrontium and radiocesium in soils from the Chernobyl and Mediterranean areas. After contamination, soils were maintained at various temperatures for up to 12 mo, with or without drying-wetting (DW) cycles. Changes in the quantity of radionuclide reversibly sorbed over time were monitored using an extraction test (1 mol L(-1) NH(4)Cl; 10 mL g(-1); 16 h). The fixed fraction could not be predicted from soil properties controlling the sorption step. Aging was not as relevant for Sr as for Cs. The time elapsed since contamination was the main factor responsible for the slight (up to 1.3-fold) decreases in Sr extraction yields. The additional effect of DW cycles was negligible. Instead, all factors accelerated Cs aging due to the enhancement of Cs trapping by clay interlayer collapse, with up to 20-fold increases in Cs fixation. The DW cycles also caused secondary effects on the Cs-specific sorption pool, which were beneficial or detrimental depending on the soil type. Extraction yields from laboratory aged samples agreed with those from field samples taken a few years after the Chernobyl accident. These results confirm the prediction capacity of the laboratory test and its usefulness in risk assessment exercises and in the design of intervention actions, particularly because neither fixation nor aging were related to the soil properties, such as clay content.

Estimating the extractability of potentially toxic metals in urban soils: a comparison of several extracting solutions

Metals released by the extraction with aqua regia, EDTA, dilute HCl and sequential extraction (SE) by the BCR protocol were studied in urban soils of Sevilla, Torino, and Glasgow. By multivariate analysis, the amounts of Cu, Pb and Zn liberated by any method were statistically associated with one another, whereas other metals were not. The mean amounts of all metals extracted by HCl and by SE were well correlated, but SE was clearly underestimated by HCl. Individual data for Cu, Pb and Zn by both methods were correlated only if each city was considered separately. Other metals gave poorer relationships. Similar conclusions were reached comparing EDTA and HCl, with much lower values for EDTA. Dilute HCl extraction cannot thus be recommended for general use as alternative to BCR SE in urban soils.

The distribution and fixation of trace elements by the Vertisols of Malaga, southern Spain

The response of Vertisols to contamination by heavy metals (As, Cd, Pb, Hg) and micronutrients (Co, Cu, Cr, Ni, V, Zn) in toxic concentrations was studied in a series of experiments undertaken with soil samples from the province of Malaga, in Southern Spain. The soil samples were placed in methacrylate columns, passing through a contaminant solution of selected elements in order to study their distribution and fixation the soil. Systematic sampling and sequential extraction analysis show that the Vertisols behave as a buffer to all elements, except cadmium.

Water quality of the Guadiamar River after the Aznalcóllar spill (SW Spain)

In April 1998, a spill of 6 hm3 of pyritic mud and acidic water was released into the Guadiamar River due to the rupture of the Aznalcóllar tailings dam. Before the spill, the river was already strongly affected by acid mine drainage (AMD). In this study, the water quality of the Guadiamar River is analysed from a periodic sampling started after the spill. Previous data of the water quality have also been obtained. A recovery of the water quality is observed from 2002 on. The distribution of arsenic is opposed to that of the rest of metals, with the lowest concentrations to the north, due to the adsorption and/or coprecipitation on ferric oxyhydroxides. In the southern area, when pH values are close to 8, arsenic desorption occurs. There is a seasonal pattern of the trace metal content evolution, different in the northern and southern zones of the river. In the northern area the highest polluting levels occur in summer, due to a lower dilution of the mining leachates. In the southern area, the highest metal levels occur during the winter, since during the summer metals remain held by surface sorption processes in the hyporheic zone of the river.