Geochemical Fractionation Research Articles

Geochemical Fractions of Heavy Metals in Bottom Sediments of the Pobeda Hydrothermal Cluster in the Mid-Atlantic Ridge (17°07′–17°08′ N)

In this study, to better understand the influence of hydrothermal processes on ore metal accumulation in bottom sediments, we examined distribution of Fe, Mn, Cu, Zn, As, and Pb in core of metalliferous sediments from the Pobeda hydrothermal cluster, and in core of non-mineralized (background) carbonate sediments (located 69 km northwards). Mechanisms of Fe, Mn, Cu, and Zn accumulation in sediments (12 samples) were evaluated based on sequential extraction of geochemical fractions, including a conditional mobile (F-1, exchangeable complex; F-2, authigenic Fe-Mn oxyhydroxides and associated metals; F-3, metals bound to organic matter/sulfides), and residual (F-4), fixed in crystalline lattices ones. The element contents were determined by the XRF and AAS methods, total carbon (TC) and total organic carbon (TOC) were determined using a Shimadzu TOC-L-CPN. Mineral composition and maps of element distribution in sediment components were obtained using the XRD and SEM-micro-X-ray spectrometry methods, respectively. In metalliferous sediments, according to our data, the major Fe mineral phase was goethite FeOOH (37–44% on a carbonate-free basis, cfb). In the metalliferous core, average contents (cfb), of Fe and Mn were 32.1% and 0.29%, whereas those of Cu, Zn, Pb, and As, were 0.74%, 0.27%, 0.03%, and 0.02%, respectively. Metalliferous sediments are enriched in Fe, Cu, Zn, Pb, and As, relatively to background ones. The exception was Mn, for which no increased accumulation in metalliferous core was recorded. Essential mass of Fe (up to 70% of total content) was represented by the residual fraction composed of crystallized goethite, aluminosilicates, the minerals derived from bedrock destruction processes mineral debris. Among geochemically mobile fractions, to 80% Fe of the (F-1 + F-2 + F-3) sum was determined in the form of F-2, authigenic oxyhydroxides. The same fraction was a predominant host for Mn in both metalliferous and background sediments (to 85%). With these Fe and Mn fractions, a major portion of Cu, Zn, and Pb was associated, while a less their amount was found in sulfide/organic fraction. In the metalliferous sediment core, maximal concentrations of metals and their geochemically mobile fractions were recorded in the deeper core sediment layers, an observation that might be attributed to influence of hydrothermal diffused fluids. Our data suggested that ore metals are mostly accumulated in sediment cores in their contact zone with the underlying serpentinized peridotites.

Effects of sheep bone biochar on soil quality, maize growth, and fractionation and phytoavailability of Cd and Zn in a mining-contaminated soil

Biochar prepared from various feedstock materials has been utilized in recent years as a potential stabilizing agent for heavy metals in smelter-contaminated soils. However, the effectiveness of animal bone-derived biochar and its potential for the stabilization of contaminants remains unclear. In the present study, sheep bone-derived biochar (SB) was prepared at low (500 °C; SBL) and high temperatures (800 °C; SBH) and amended a smelter-contaminated soil at 2, 5, and 10% (w/w). The effects of SB on soil properties, bioavailable Zn and Cd and their geochemical fractions, bacterial community composition and activity, and the response of plant attributes (pigments and antioxidant activity) were assessed. Results showed that the SBH added at 10% (SBH10) increased soil organic carbon, total nitrogen, and phosphorus, and also increased the oxidizable and residual Zn and Cd fractions at the expense of the bioavailable fractions. The SBH10 lowered the Zn and Cd contents in maize roots (by 57 and 60%) and shoot (by 42 and 61%), respectively, compared to unamended control. Additionally, SBH10 enhanced urease (98%) and phosphates (107%) activities, but reduced dehydrogenase (58%) and β-glucosidase (30%) activities. Regarding the effect of the pyrolysis temperature, SBH enhanced the activity of Acidobacteria, Bacteroidetes, Firmicutes, Nitrospirae, Verrucomicrobia, Chlorobi, and Microgenomates, but reduced Actinobacteria and Parcubacteria in comparison to SBL. However, only the SBL10 reduced the Proteobacteria community (by 9%). In conclusion, SB immobilized Zn and Cd in smelter-affected soils, enhanced the bacterial abundance and microbial function (urease, phosphates), and improved plant growth. However, validation of the results, obtained from the pot experiment, under field conditions is suggested.

Trace metal fractions, sources, and risk assessment in sediments from Umurbey Stream (Çanakkale-Turkey).

Trace metal contamination has become a worldwide problem for aquatic systems, as sediments act as a sink for trace metals. This study was conducted to assess geochemical fractions, sources and potential risks of trace metals (Cd, Cr, Cu, Ni, Pb, and Zn) in sediments of Umurbey stream (Çanakkale-Turkey). Sediment samples were taken from seven different locations of Umurbey stream. Aqua regia wet digestion procedure was applied to determine total contents of trace metals and BCR sequential extraction procedure was applied to determine geochemical fractions of trace metals. Trace metal total values were ordered as Zn > Pb > Cr > Cu > Ni > Cd. Just because of topography, geology, and agricultural practices, S4, S5, S6, and S7 sampling points had greater total trace metal concentrations than the other locations. Potential mobility of trace metals in sediment samples was ordered as Cd (62.1%) > Zn (60.8%) > Pb (54.8%) > Cu (46.1%) > Cr (43.0%) > Ni (29.7%). Cd, Zn, Pb, and partially Cu were encountered mostly in mobile phases. Multivariate analyses revealed that pollution in sediment samples was originated from not only anthropogenic but also natural factors. Except for Zn, trace metal concentrations were found to be at tolerable levels of biota. When the contamination factor and risk assessment code results were assessed together, it was observed that Cd, Zn, and partially Pb were weakly adsorbed onto sediments, thus might pose risks on environment in the long run.

Invasive Weed Asystasia gangetica as a Potential Biomonitor and a Phytoremediator of Potentially Toxic Metals: A Case Study in Peninsular Malaysia.

The invasive weed Asystasia gangetica was investigated for its potential as a biomonitor and as a phytoremediator of potentially toxic metals (PTMs) (Cd, Cu, Ni, Pb, and Zn) in Peninsular Malaysia owing to its ecological resistance towards unfavourable environments. The biomonitoring potential of PTMs was determined based on the correlation analysis of the metals in the different parts of the plant (leaves, stems, and roots) and its habitat topsoils. In the roots, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 2.18, 9.22 to 139, 0.63 to 5.47, 2.43 to 10.5, and 50.7 to 300, respectively. In the leaves, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.16, 7.94 to 20.2, 0.03 to 6.13, 2.10 to 21.8, and 18.8 to 160, respectively. In the stems, the concentrations (mg/kg dry weight) of Cd, Cu, Ni, Pb, and Zn ranged from 0.03 to 1.25, 5.57 to 11.8, 0.23 to 3.69, 0.01 to 7.79, and 26.4 to 246, respectively. On the other hand, the phytoremediation potential of the five metals was estimated based on the bioconcentration factor (BCF) and the translocation factor (TF) values. Correlation analysis revealed that the roots and stems could be used as biomonitors of Cu, the stems as biomonitors of Ni, the roots and leaves as biomonitors of Pb, and all three parts of the plant as biomonitors of Zn. According to the BCF values, in the topsoil, the “easily, freely, leachable, or exchangeable” geochemical fractions of the five metals could be more easily transferred to the roots, leaves, and stems when compared with total concentrations. Based on the TF values of Cd, Ni, and Pb, the metal transfer to the stems (or leaves) from the roots was efficient (>1.0) at most sampling sites. The results of BCF and TF showed that A. gangetica was a good phytoextractor for Cd and Ni, and a good phytostabilizer for Cu, Pb, and Zn. Therefore, A. gangetica is a good candidate as a biomonitor and a phytoremediator of Ni, Pb, and Zn for sustainable contaminant remediation subject to suitable field management strategies.

Geochemical fractionation and spectroscopic fingerprinting for evaluation of the environmental transformation of potentially toxic metal(oid)s in surface-subsurface soils.

The contamination of soil by toxic metal(oid)s has emerged as a major concern worldwide, particularly in developing countries. A metals behavior in the soil environment is influenced by organic matter, mineral phases, and oxidation states in which a particular metal exists. However, the spectroscopic evidence of metal(oid)s interactions in soil with organic matter and mineral phases can induce an extensive understanding. The surface and sub-surface soils (0-50cm) from four sites of upper Indus basin, Pakistan, were collected and analyzed by using FTIR (Fourier-transform infrared spectroscopy), XRD (X-ray diffraction) and XPS (X-ray photoelectron spectroscopy) in addition to ICP-MS (inductively coupled plasma mass spectrometry) and geochemical fractionation. Geochemical fractionation of metal(oid)s indicated that As, Cu, Ni, Pb, and Zn were mostly found in the potentially bioavailable fractions. However, an increase in the residual fraction was observed from top to bottom. The absorption bands of FTIR spectra were divided into three spectral regions 700-400, 1700-800, and 3700-2800cm-1. The soil was found rich in organic matter and capable of retaining metals as abundant peaks were observed in the mid-infrared region. The mineralogical analysis of soil samples testified silicon oxides and zeolite as major mineral phases. The XPS spectra showed broad peaks of As(III), As2O3, As4S4, PbO2, and PbCo3. The study concludes that the source identification of metal(oid)s in the upper Indus is crucial to find out the particular source of contamination in the soil.

Soils from abandoned shooting range facilities as contamination source of potentially toxic elements: distribution among soil geochemical fractions

Civilian and military shooting range facilities cause environmental issues in several countries due to the accumulation of Potentially Toxic Elements; as a result of weathering of ammunitions accumulated into the soils. The contents and distribution of Cu, Ni, Pb and Zn were analyzed in 12 soils in an abandoned clay target shooting range at two different depths (0-15 and 15-30cm). Single extractions (CaCl2 and DTPA) and Tessier sequential extraction were conducted to assess the PTE mobility and the PTE distribution in the different soil geochemical fractions at both depths. High total contents of Pb were found at both soil depths, while Cu, Ni and Zn showed lower significance levels. Copper, Ni and Zn are mainly associated with the residual fraction (> 95% of total content in all cases). However, Pb was highly associated with exchangeable fractions (21-52%), showing a high mobility at both depths. With moderate-high contents of organic matter (6-12%), the studied soils have acidic values and low levels of Al, Fe and Mn oxides that favors the migration of Pb through the soil profile and potential transformation to more mobile forms (Pb0 to Pb2+ and Pb4+). Although Pb reduced downward mobility in soils, due to the specific conditions of these facilities and the lead source (weathering of ammunition), risk assessment studies on clay-target shooting and firing range facilities should study the potential migration of Pb through the soil profile.

Thallium geochemical fractionation and migration in Tl-As rich soils: The key controls

Thallium (Tl) pollution caused by mining and processing of Tl-enriched ores has become an increasing concern. This study explored the geochemical fractionation and vertical transfer of Tl in a soil profile (200 cm) from a representative Tl-As mineralized area, Southwest China. The results showed that the soils were heavily enriched by Tl and As, with concentration ranging from 3.91–17.3 and 1830–8840 mg/kg (6.79 and 2973 mg/kg in average), respectively. Approximately 50% of Tl occurred in geochemically mobile fractions in the topsoil, wherein the reducible fraction was the most enriched fraction. Further characterization using LA-ICP-MS and TEM revealed that enriched Tl and As in soils were mainly inherited from the weathering of mine tailing piles upstream. XPS characterization indicated that Fe oxides herein may play a critical role in the oxidation of Tl(I) to Tl(III) which provoked further adsorption of Tl onto Fe oxides, thereby facilitating Tl enrichment in the reducible fraction. The findings highlight that the pivotal role of Fe oxides from mineralized area in the co-mobility and migration of Tl and As in the depth profile.

Variability factors of heavy metals in soils and transfer to pasture plants of Mayabeque in Cuba.

Studies to assess variability factors of heavy metals in soils are essential to understand their behavior in the environment and for the assessment of contaminated areas. In this context, this research aimed to study the factors that influence the variability of heavy metal levels and their bioavailability in pasture areas in the Alturas de Nazareno region, Mayabeque, Cuba, as well as the transfer to plants. Forty-five points were distributed in a natural pasture and at two depths (0-20 and 20-40 cm) as a function of relief and soil type. Pseudo-total heavy metal contents were determined according to method 3051A of USEPA, geochemical fractionation according to the Community Bureau of Reference method, and plant digestion according to method 3052 of USEPA. Soil samples were separated into two groups, according to cluster analysis. The type of soil associated with the pH and Ca attributes were the factors that most influenced the variability of the total and bioavailable levels of metals in natural pasture soils in the region of Alturas de Nazareno. Group 1 showed the lowest heavy metal contents and the highest pH and calcium values, which were predominantly associated with carbonate soils. Group 2 had the highest contents of heavy metals and Fe, corresponding mainly to the soil Ferralítico Rojo. The concentration of metals in plants was directly related to their bioavailable content in the soil, where G2 represents the group with the highest risk of transferring metals to the food chain.

Geochemical fractionation, source identification and risk assessments for trace metals in agricultural soils adjacent to a city center (Çanakkale, NW Turkey)

Agricultural lands around city centers are exposed to trace metal pollution through urbanization especially and industrialization-related human activities. This study investigates potential sources of trace metals (Cd, Cr, Cu, Ni and Pb) in agricultural lands surrounding Canakkale city center (NW Turkey) and estimates their environmental impacts with the sequential extraction procedure. Soil samples were taken from agricultural fields adjacent to the city center that represent all types of land use. The aqua regia wet digestion method was used to determine trace metal contents and the sequential extraction procedure was used to determine geochemical fractions of trace metals. Multivariate analysis was applied for source identification of trace metals. Contamination factors and risk assessment codes were used to assess current pollution. Trace metal contents were in the order: Ni > Cr > Pb > Cu > Cd. Recorded values were greater than the values specified for agricultural land. Trace metal mobility based on totals for the first three fractions was in the order: Cd (62%) > Pb (57%) > Cu (40%) > Ni (32%) > Cr (15%) and these findings indicate that Cd and Pb exist mostly in mobile phases. These mobile phases were mostly attributed to anthropogenic sources. These findings comply with the outcomes of statistical analysis. It was concluded that the soils were contaminated with Pb and Cd. While Pb poses moderate risks for the environment, Cd poses high risks. Considering the present findings, it was observed that primarily Cd and partially Pb reached soils near urban areas, exhibited accumulation and may be easily incorporated into water and plants through the mobile phases. Therefore, it is concluded that the relevant metals, especially Cd, should be controlled and monitored.

Synergetic loss of heavy metal and phosphorus: Evidence from geochemical fraction and estuary sedimentation

The synergetic loss mechanism of heavy metals (HMs) and phosphorus (P), as well as the relationships between their different geochemical fractions remain unclear. This study employs field research, source identification and sedimentary geochemistry in Yellow River basin to investigate the internal mechanisms of the different geochemical fractions, terrestrial source signatures, and synergetic loss fluxes. The average contents of As, Cd, Cr, Cu, Pb, Zn and P in the basin were 8.29 mg/kg, 0.15 mg/kg, 47.52 mg/kg, 11.78 mg/kg, 10.65 mg/kg, 46.56 mg/kg and 578.78 mg/kg, respectively. Based on Pearson’s correlation and redundancy analyses, the impact factors on the transport of HMs and P, and the internal relationships between different geochemical fractions were analyzed. According to the constant rate of supply (CRS) model, the terrestrial losses of As, Cd, Cr and Cu showed significant positive relationships with the TP flux, with r2 value of 0.981, 0.991, 0.996 and for 0.984, respectively. It has been proven that the extensive fine particles in the Yellow River basin carry a large amount of diffuse pollutants, thus ultimately increasing the estuarine pollutant load. This research provides new insights from the level of microscopic fractions to macroscopic fluxes to investigate the impacts of anthropogenic activity on regional environmental changes.

Cadmium and lead distribution in pyrite ores

The pyrite ores are strategic industrial resources which generally serve as raw material for producing sulfuric acid. However, during the mining and industrial processing activities, associated toxic elements of cadmium (Cd) and lead (Pb) could be released into the surroundings, posing a significant threat to local environment and human health. In this study, the Institute for Reference Materials and Measurement (IRMM) sequential extraction scheme was used to investigate the geochemical fractionation of Cd and Pb in pyrite ores from a mining area located in Yunfu, western Guangdong, China. The results showed that most of Cd and Pb (>90%) were predominantly found in the geochemically mobile fractions, indicating that Cd and Pb were readily bioaccessible thus easily assimilated and accumulated by organisms. FESEM-EDS results showed that the studied pyrite ores were mainly composed of O, S, and Fe, while the XRD characterizations suggested that FeS2 and SiO2 were the major minerals. The high-resolution transmission electron microscope and element mapping characterization further confirmed that FeS2 was the main mineral of pyrite ores which contained relatively enriched toxic heavy metals (e.g., Pb and Cd). The findings highlight that an extremely large amount of geochemically mobile heavy metals can be released into the environmental media during the mining and utilization processes of pyrite ores based on IRMM sequential extraction protocol. Therefore, proper countermeasures against environmental risks of utilizing pyrite ores should be taken to mitigate the impacts on local ecosystem and human health.

Composição de elementos maiores de rochas fonte, solos e sedimentos derivados de rochas graníticas em clima subtropical úmido: contribuição aos estudos de proveniência sedimentar

O estudo dos processos sedimentares e da modificação da composição detrítica entre rocha, solo e sedimento é fundamental para compreender o fracionamento composicional nos primeiros estágios do ciclo sedimentar. Estudos em ambientes atuais são necessários para desvendar a inter-relação complexa entre os processos que geram todo o espectro composicional dos sedimentos detríticos. Neste trabalho, a influência dos processos sedimentares na composição dos sedimentos foi avaliada utilizando-se amostras de rochas fonte, solos e sedimentos detríticos em uma bacia hidrográfica na qual rochas graníticas estão expostas em clima subtropical úmido. As amostras foram separadas em oito intervalos granulométricos de seixo a lama. A composição geoquímica dessas amostras foi analisada por Inductively Coupled Emission Optical Spectroscopy — ICP-EOS. A relação entre a composição química e o tamanho de grão foi analisada por métodos estatísticos utilizando-se diagramas, gráficos de dispersão, análise dos componentes principais e avaliação da estrutura de covariância via análise biplot. Os resultados demonstram o controle do tamanho de grão na composição dos solos e sedimentos e têm implicação no entendimento da influência do intemperismo e do transporte no fracionamento geoquímico. A análise da relação entre a composição de rocha, solo e sedimento em ambientes atuais contribui para a construção e tem potencial para a construção de modelos quantitativos que permitam determinar o efeito dos processos sedimentares na composição das rochas siliciclásticas.

Post depositional changes of sedimentary organic matter influence chromium speciation in continental slope sediments - A case study.

Influences of post depositional changes of sedimentary organic matter (SOM) on chromium (Cr) speciation in continental slope sediments from the east and west coast of India are presented in this study. Average concentrations of total sedimentary Cr (CrT) in the slope areas of both the coasts were not elevated and ranged from 56.8 to 163mg·kg-1 (avg. 97.3±28.3mg·kg-1). The geology of adjacent land masses influenced sedimentary Cr concentration in the slope areas. Geochemical fractionation study showed that a major fraction (51.6-159mg·kg-1; avg. 89.6±24.3mg·kg-1) of the total sedimentary Cr was present in residual part of the sediments. Prime hosting phase for non-residual sedimentary Cr was oxidizable binding phase (SOM) (1.4-23.9mg·kg-1; avg. 6.7±6.3mg·kg-1) followed by reducing binding phase (Fe/Mn-oxyhydroxide phase) (0.1-1.7mg·kg-1; avg. 0.7±0.3mg·kg-1). Concentration of Cr (VI) in the slope sediments, varied from 0.2 to 8.3mg·kg-1 (avg. 1.2±1.0mg·kg-1), was also predominantly associated with the SOM. The δ13Corg values of the SOM (ranged from -19.4 to -21.4‰; avg. -20.3±0.5‰) suggests that they were derived from marine sources. Based on molar C/N ratio (ranged from 6.3-12.9; avg. 9.0±2.0), the SOM were classified as labile organic matter. Increasing molar C/N ratio in the studied sediments was used as a proxy to reflect post depositional changes of the SOM. Association of normalized Cr (VI) (with respect to CrT) increased with increasing SOM concentration by 0.008mg·kg-1. One unit increase of sedimentary molar C/N ratio was found to increase normalized Cr (VI) (w.r.t. CrT) by 0.003mg·kg-1 in the sediments. This study suggests that post-depositional changes of SOM may increase Cr binding capacity and control its speciation and mobility in marine sediment system.

Copper dynamics in a tropical estuarine system during dry season

This is the first study to comprehend copper (Cu)-dynamics in a monsoon fed Indian estuarine system (the Mandovi estuary from the central west coast of India). Distribution and speciation of Cu in estuarine sediment, pore water, suspended particulate matter (SPM) and water column was used to understand geochemical cycling of Cu in the estuary. Geochemical fractionation study reveals that sedimentary organic carbon (Corg) was the major hosting phase for non-residual Cu in the sediments. Experimental analysis and chemical speciation modelling suggests that leaching of sedimentary Cu2+, CuCO3 and a fraction of Cu-Corg complexes increased Cu-concentrations in the pore water towards the downstream of the estuary. Dissolved Cu concentration in overlying water column was observed to increase with increasing Cu concentrations in the pore water. This study suggests that chemical speciation of sedimentary Cu play key role in controlling its distribution and dynamics in the tropical estuarine system during dry period.

Remediation of Lead-contaminated Farmland Soil: Efficacy of Low-cost Natural Amendments in [Im]mobilization of Lead

The control of Pb mobility is a success key in remediation of contaminated soil. This research aimed to explore the effective low-cost amendments in mobilizing or immobilizing lead in contaminated soil, assess environmental risk, and evaluate important amendment properties. Lead-contaminated soil was incubated with 13 materials included chars, bioslurry, limes, rice husk, gypsum, citric acid, natural organic acids and the efficiency of lead immobilization (E) was studied. Soil incubated with 10% amendments was sequentially extracted to determine Pb geochemical fractions and its risk. Selected amendment properties were evaluated through a correlation study with E. The results showed that 6 amendments immobilized lead in the order of chars > gypsum > bioslurry > rice husk. Chicken manure and chicken bone biochars, effectively decreasing lead solubility, were the best immobilising amendments, redistributed lead into the residual fraction and remediated the soil from moderate to low environmental risk. The order of mobilizing amendments was: citric acid > baby orange juice > limes > tamarind > lemon juice > tomato. The citric acid was the most effective mobilizing amendment which increased soluble lead and shifted the soil into high environmental risk status. The three most important amendment properties in influencing soil-Pb mobility were pH, P, and Ca content.

Sorption dynamics, geochemical fraction and driving factors in phosphorus transport at large basin scale

The transport and deposition of phosphorus (P) in large-scale basin are closely associated with the spatial distribution characteristics and nutritional status of river sediments. Samples of surface water (SW), suspended sediment (SS), bed sediment (BS), and sediment cores from the Yellow River (YR) were collected. The different fractions including total phosphorus (TP), organic P (OP), inorganic P (IP), HCl–P and NaOH–P were determined by standard measurement and testing method. The results showed that upper, middle, and downstream sedimentary texture exhibit spatial heterogeneity. Pearson correlation analysis and redundancy analysis revealed that medium grain size (Mz) is the most negative factor that influence P and fractions, indicating the importance of silt content. Additionally, TP and HCl–P content were positively and significantly correlated, and the calculated correlation coefficient was 0.96 (p < 0.05). Fe oxides had the greatest positive effect on the absorption of NaOH–P in sediments, followed by Al and Mn oxides. From the sediment cores perspective, the rose figure and logistic regression curve showed that significant growth trend, which indicates that vertical pollution status becomes more severe with increasing silt content. Overall, due to the strong adsorption ability of finer particle as silt that driving the P distribution, this study suggests a greater focus on the effects of fine sediment particles transport for the diffuse pollution control towards the whole basin.

Geochemical fractionation of radiocesium in coral atoll soil

This study investigates the fractionation of 137Cs across the geological phases of coral soils using a sequential extraction scheme. For three of the four soil samples analyzed, the largest fraction of radiocesium (70–80%) was associated with the final fraction or “acid-soluble” phase of soil, which would typically include clays and other refractory minerals that are difficult to destroy. This is common behavior for radiocesium due to its strong affinity for clays, but surprising here because these primarily calcium carbonate soils contain very minimal amounts of such minerals.

Occurrence, geochemical fraction, ecological and health risk assessment of cadmium, copper and nickel in soils contaminated with municipal solid wastes

Unscientific municipal solid waste (MSW) dumping provokes heavy metal (HM) associated ecological and human health hazards through heightened bioavailability and bioaccumulation. In this study, we focused on three important HMs Cadmium (Cd), Copper (Cu) and Nickel (Ni) and their geochemical fractions, to enable clutter free data management, analysis and interpretation. Stratified random soil sampling was carried out from twenty different locations around a Ramsar site (Deepor Beel) in Guwahati, India. The spatial concentration profiles of Cd, Cu and Ni were determined by data elicited from geochemical fractionation and the Geographic Information System (GIS). Ecological and health risks indices were used to evaluate the severity of soil pollution and assess the level of health risks. All the three HMs thus evaluated, conformed to the potential bioavailable category. Cd (54.59%) was associated mostly with the carbonate bound fraction (F3), while 25.53% of Cu and 40.60% Ni were associated with the exchangeable fraction (F2). Significant contamination levels and higher ecological risks posed by these metals were in the order Cd > Ni > Cu. Children were found to be more vulnerable towards Cd associated health risks whereas, Ni posed threats to both adults and children. Cu posed no risk to human health. Geochemical fractionation and different indices played a critical role in the integrated assessment of soil pollution, ecological and health risk assessment, and provided an empirical basis for the sustainable future planning and comprehensive adaptive management practices for MSW.

Fir bark modified by Phanerodontia chrysosporium: A low-cost amendment for cd-contaminated water and agricultural soil

In this study, a modified fir barks (MFB) was prepared by mixing fir barks (FB) and white-rot fungi (Phanerodontia chrysosporium) under aerobic fermentation. The potential of MFB for Cd2+ adsorption was investigated by batch experiments combined with kinetic, isotherm, and thermodynamics analyses. The results revealed that the modification greatly increased the porous structures on the surfaces of fir barks and the surface area of MFB was much higher than that of FB. As a result, the adsorption capacity of Cd2+ on MFB (17.4 mg g−1) was more than two times higher than that on FB (7.2 mg g−1), and the adsorption of Cd2+ on MFB was controlled by physisorption and chemisorption. The immobilization of Cd by MFB in a contaminated agricultural soil was also investigated. The effect of MFB on the bioavailability of Cd was investigated using a leaching test (the European standard EN 12457–2) combined with a typical sequential extraction procedure (the community bureau of reference, BCR). The experimental results showed that the Cd leachability was reduced by 71% when the added MFB dosage was 30 mg g−1. Besides, the MFB amendment could transform Cd from unstable geochemical fractions into more stable fractions. In total, the MFB, as a chemical-free and eco-friendly material, could be potentially employed for in-situ remediation of Cd-contaminated agricultural soils.

Pristine and iron-engineered animal- and plant-derived biochars enhanced bacterial abundance and immobilized arsenic and lead in a contaminated soil

In this study, typical animal- and plant-derived biochars derived from pig carcass (PB) and green waste (GWB), and their iron-engineered products (Fe-PB and Fe-GWB) were added at the dose of 3% (w/w) to an acidic (pH = 5.8) soil, and incubated to test their efficacy in improving soil quality and immobilizing arsenic (As = 141.3 mg kg−1) and lead (Pb = 736.2 mg kg−1). Soil properties, microbial activities, and the geochemical fractions and potential availabilities of As and Pb were determined in the non-treated (control) and biochar-treated soil. Modification of PB (pH = 10.6) and GWB (pH = 9.3) with Fe caused a decrease in their pH to 4.4 and 3.4, respectively. The application of PB and GWB significantly increased soil pH, while Fe-PB and Fe-GWB decreased soil pH, as compared to the control. Application of Fe-GWB and Fe-PB decreased the NH4H2PO4-extractable As by 32.8 and 35.9%, which was more effective than addition of GWB and PB. However, PB and GWB were more effective than Fe-PB and Fe-GWB in Pb immobilization. Compared to the control, the DTPA-extractable Pb decreased by 20.6 and 21.7%, respectively, following PB and GWB application. Both biochars, particularly PB significantly increased the 16S rRNA bacterial gene copy numbers, indicating that biochar amendments enhanced the bacterial abundance, implying an alleviation of As and Pb bio-toxicity to soil bacteria. The results demonstrated that pristine pig carcass and green waste biochars were more effective in immobilizing Pb, while their Fe-engineered biochars were more effective in As immobilization in co-contaminated soils.