The impact of a copper smelter on adjacent soil zinc and cadmium fractions and soil organic carbon

Purpose  

We investigated the chemical fractions of Zn, Cd and Cu in soils collected from positions at different distances from a copper smelter and studied the relationships between distribution patterns of Zn, Cd and Cu, fractions and soil organic carbon (SOC), especially “black carbon” (BC), in contaminated soils. The relationships between soil particle size and concentrations of Zn and Cd in contaminated soil were also examined.     

Effect of polar-dissolved organic matter fractions on the mobility of prometryne in soil

Purpose  

Using two fractions of dissolved organic matter (DOM) with different polarity, we carried out the experiments with standard batch equilibration, soil column leaching, and soil thin layer chromatography to investigate the behavior of the herbicide prometryne in soils. The purpose of the study was to: (1) separate DOM into hydrophilic matter and hydrophobic acid forms and characterize their chemical properties; (2) analyze interaction between the DOM fractions and prometryne in soils.     

Adsorption of Pseudomonas putida on soil particle size fractions: effects of solution chemistry and organic matter

Purpose  

Attachment of bacteria on soil particles is ubiquitous and governs the transformation of nutrients and degradation of pollutants in soil and associated environments. The nature on the binding of bacteria by soil particles has remained unclear. The objectives of the present study were to investigate the adsorption of Pseudomonas putida on particle size fractions from an Ultisol as influenced by solution chemistry and organic matter.     

Element fractionation in soil from urban-industrialized areas using sequential extraction

Background Goal and Scope  

The application of solid-liquid extraction is proposed to assess extractable fractions of components in soil. The application of a several step scheme could give a lot of information about mobility of metals associated with specific solid phases, especially after separation of top and bottom layers of studied soil. In this study, it was aimed to take into solution metal fractions of major (Ca, Mg, Mn, Fe) and trace elements (Cr, Co, Cu, Zn, As, Cd, Pb) from soil collected in urban areas. The fractions were defined by using chemical extraction operationally. The extraction behavior of studied elements in a six-step sequential extraction procedure is discussed with respect to the properties of the reagents used.     

Transformations and availability of phosphorus in three contrasting soil types from native and farming systems: A study using fractionation and isotopic labeling techniques

Background, aim, and scope  

Despite the contribution of many sequential P fractionation schemes to the study of P transformations in agricultural soils, the nature of P in each fraction remains qualitative rather than mechanistic. This study used the sequential extraction and isotopic dilution techniques to assess the recovery of a tracer (³²P) in soil P fractions and to elucidate the transformation of soil P in different P pools and its lability.     

Effects of bacteria on metal bioavailability,speciation, and mobility in different metal mine soils: a column study

Purpose  

Successful phytoremediation depends mainly on the bioavailability of heavy metals in the soil. Recently, soil microbes possess several mechanisms that are able to change metal bioavailability in the soil, which provides a new strategy for investigating biogeochemical cycling of metals in contaminated soils. Three metal mines soils with elevated concentrations of Cd, Pb, and Zn from China were applied in this column study to (1) evaluate the effects of metal tolerant bacterial inoculation (Burkholderia cepacia, accession number: AB051408) on metal release, (2) monitor the migration of metals in the rhizospheric horizon (0–20 cm), and (3) investigate metal speciation and sequential fractions in soil.     

Organic mulch and fertilization affect soil carbon pools and forms under intensively managed bamboo (<Emphasis Type="Italic">Phyllostachys praecox</Emphasis>) forests in southeast China

Purpose  

Phyllostachys praecox is one of the bamboo species used for the production of fine edible bamboo shoots and is widely distributed in Southern China. To maintain or increase the productivity of bamboo shoots, P. praecox forests are intensively managed through heavy fertilization and surface mulch of organic residues such as rice husk to increase soil temperature in the winter. Such management techniques can markedly influence soil quality and the dynamics of soil carbon (C). The objectives of this study were to investigate the long-term impact of intensive management practices on carbon pools and forms in the soil of bamboo forests and explore relationships between different soil organic C fractions, as little such information is currently available.     

Effects of Soil Amendment on Potassium Fractions of Southwestern Nigerian Soils

Incubation and pot experiments were done to determine the effect of poultry manure on soil potassium (K) fractions and soybean K concentration. Representative soils from southwestern Nigeria were used. The treatments applied consisted of five rates of manure (0, 2.5, 5.0, 7.5, and 10 t ha^?1). The experiments were arranged in a completely randomized design with three replicates. Soybean (TGx 1448-2E) was grown for three consecutive cycles (7 weeks each), analyzed for K. Order of abundance of soil fractions in the soil was as follows: Total K > non-exchangeable K > mineral K > > 1 N (hydrochloric acid) HCl K > 1 N (nitric acid) HNO₃K > available K > exchangeable K > water-soluble K. Most of the K is in nonavailable forms; and the exchangeable forms are less than non-exchangeable forms. Organic manure increased soil K fractions, but these increases could not be sustained with cycles of soybean growth due to crop uptake.     

Estimating Be-7 association with soil particle size fractions for erosion and deposition modelling

Purpose

Estimates of beryllium-7 (⁷Be) enrichment in soil particle size fractions are important for correction in existing soil redistribution models. Little attention has been given to documenting methods of estimating ⁷Be enrichment and assessing differences in enrichment between soil types in the context of soil redistribution modelling. Here, we detail a method for estimating ⁷Be enrichment and correcting soil redistribution estimates.

Materials and methods

Beryllium from a solution of BeCl₂ was adsorbed to two soils with contrasting texture using a batch procedure. Soil fractions were separated by settling according to Stokes’ Law, and samples of bulk and settled fractions were digested and analysed for Be concentration and for specific surface area.

Results and discussion

Both soils demonstrated increasing enrichment of Be with increasing specific surface area. There was a marked difference in enrichment between the soil types with the coarse soil showing greater enrichment in the finer fractions. Calculated enrichment ratios for the coarse soil more than doubled between subfractions of the <63 μm class. Failure to account for the selective transport of fractions during soil redistribution studies could incur substantial errors in soil erosion estimates.

Conclusions

Stable Be provides a practical means of estimating ⁷Be enrichment in soil and subsequent corrections can be incorporated into the conversion model where it is proposed that corrections should be applied to the inventory deficit at each eroding point. The marked difference in enrichment between soil types in these experiments suggested that characterising enrichment and associated correction factors should be done on a site-specific basis. Implementation of the particle size correction procedures requires additional field and laboratory data to standard application of the established soil erosion conversion model.     

The influence of temperature,pH/molarity and extractant on the removal of arsenic,chromium and zinc from contaminated soil

Purpose  

Normal soil washing leave high residual pollutant content in soil. The remediation could be improved by targeting the extraction to coarser fractions. Further, a low/high extraction pH and higher temperature enhance the pollutant removal, but these measures are costly. In this study, the utility of NaOH, oxalate–citrate (OC) and dithionite–citrate–oxalate (DCO) solutions for extracting of arsenic, chromium and zinc from contaminated soil were assessed and compared. In addition the effects of NaOH concentration and temperature on NaOH extractions, and those of temperature and pH on OC and DCO extractions, were evaluated.     

Carbon and nitrogen pools in different aggregates of a Chinese Mollisol as influenced by long-term fertilization

Purpose  

It is known that soil organic matter (SOM) dynamics are sensitive to fertilizations, but it is different from soil to soil. It is unclear how the long-term applications of organic manure and mineral fertilizers impact the accumulation and distribution of soil organic carbon (SOC) and total nitrogen (TN) especially in soil aggregate fractions of Chinese Mollisols, which have been intensively cultivated for decades under maize monocropping and conventional tillage ways. Thereby, the research of this kind is very important for the sustainable use of agricultural land in China, where land resources are extremely limited for its huge population. The objectives of this study were to identify how the long-term fertilization treatments would affect the aggregate, SOC and TN distribution pattern in the Chinese Mollisol, and how soil aggregation contribute to the storage and stabilization process of SOC and TN.     

The change of heavy metals fractions during hydrochar decomposition in soils amended with different municipal sewage sludge hydrochars

Purpose

This study was to investigate the changes of heavy metals in the soils amended with different municipal sewage sludge hydrochars.

Materials and methods

Sewage sludge hydrochars prepared at either 190 or 260 °C, for 1, 6, 12, 18, or 24 h, respectively, were added to soil samples and then incubated for 60 days. Water-extractable organic carbon (WEOC) and CO₂ evolution were determined during the incubation. The total quantities of heavy metals and their different fractions were analyzed by inductively coupled plasma spectrometry (ICP).

Results and discussion

Hydrochar-amended soils had much higher water-extractable carbon and more CO₂ evolution than control soil, indicating that the added hydrochars contained a significant amount of WEOC and could be decomposed during the incubation. Hydrochar addition immediately and significantly increased the total heavy metals of the soil. Moreover, both oxidizable and residual fractions of all heavy metals were significantly higher in all the hydrochar-added soils than those in control soil. Both oxidable and residual fractions of heavy metals decreased in the hydrochar-amended soils during 60-day incubation. In contrary, both acid soluble and reducible fractions of heavy metals increased in the hydrochar-amended soils during incubation. It is thus obvious that the heavy metals in both oxidable and residual fractions may be released during hydrochar decomposition and then be adsorbed by soil matrix such as carbonates, iron oxides, and clays.

Conclusions

Municipal sewage sludge can be readily carbonized into hydrochar. However, it is watchful of applying the hydrochar into soil since hydrochar addition increases in both total and bioavailable heavy metals in soil. More work is particularly required to investigate the long-term impacts on soil and environment.

     

Effect of the size of variable charge soil particles on cadmium accumulation and adsorption

Purpose

The size of soil particles strongly affects the accumulation and adsorption of heavy metals which partly controls the co-transport of heavy metals by soil colloids. However, the effect of the size of soil particles on the accumulation and adsorption of heavy metals in the colloidal dimension has seldom been studied. In this study, variable charge soils were selected and separated into five size fractions to elucidate the effect of the size of soil particles on Cd accumulation and adsorption.

Materials and methods

Five soil particle size fractions (>10, 10–1, 1–0.45, 0.45–0.2 and <0.2 μm) were obtained from Cd-contaminated soil by natural sedimentation and fractional centrifugation. The concentrations and species of Cd were measured in various sized soil particles. Batch adsorption experiments of Cd on the obtained soil particles were conducted under different pH values and concentrations of NaCl.

Results and discussion

Generally, the concentration of Cd increased with decreasing soil particle sizes, and the Cd proportion of exchangeable and carbonate fraction decreased from 43.84 to 17.75% with decreasing particle size. The soil particles with a size of 10–1 and <0.2 μm possessed a stronger adsorption ability than the other fractions in most cases. Moreover, the Cd adsorption capacities of the soil particles increased with increasing pH values and decreasing concentrations of NaCl, especially for soil particles containing more organic matter (OM) and variable charge minerals.

Conclusions

Smaller soil particles are more capable of accumulating Cd and make Cd more stable. The adsorption capability of Cd is negatively related to the particle size and NaCl concentration and is positively related to the pH. The effects of the size of variable charge soil particles on Cd accumulation and adsorption are attributed to the differences in the physicochemical properties among various soil particle size fractions. This study contributes to the understanding of the co-transport of heavy metals in soil by soil colloids.

     

Organic carbon and nitrogen dynamics in different soil fractions between broad-leaved Korean pine forests and aspen–birch forests in northeastern China

Purpose

Both overharvesting and climate changes have greatly altered forest composition in northeastern China; however, forest-specific effects on soil organic carbon (SOC), N, and compositional features in different soil fractions have not yet been defined.

Materials and methods

By sampling from broad-leaved Korean pine forest (the climax vegetation) and aspen–birch forest (the secondary forest), five soil fractions were separated by a physicochemical soil fractionation method, and Fourier transform infrared spectroscopy, X-ray diffraction analysis, and X-ray photoelectron spectrometry were used for functional groups, mineral diffraction, and elemental composition determination together with SOC and N measurements.

Results and discussion

Aspen–birch forests tended to sequestrate more SOC in the slow fractions (sand and aggregate [SA] and easily oxidized fractions) and more N in the sensitive fractions (particulate and soluble fractions), indicating that in aspen–birch forests, high SOC sequestration (1.26-fold) coincided with the active and rapid N supply. Much higher percentages (13.1–40.5 %) of O–H and N–H stretching, O–H bending, and C=O, COO–, and C–H stretching, and also the much lower quartz grain size and mineral diffraction peaks in SA and acid-insoluble fraction (over 85 % of total soil mass), in aspen–birch forests were possibly associated with the 1.17- to 1.53-fold higher SOC compared to broad-leaved Korean pine forest. However, elemental composition on soil particles might marginally contribute to the SOC and N forest-dependent differences.

Conclusions

Considering the increase of aspen–birch forests and the decrease of broad-leaved Korean pine forests in historical and future scenarios in northeastern China, more SOC has been and also will sequestrate in intact soils and stable soil fractions, with more N in sensitive fractions, and these should be highlighted in evaluating forest C and N dynamics during forest successions in this region.

     

Contribution of bricks to urban soil properties

Purpose

Bricks are regularly found in urban soils where they can strongly impact soil properties. The purpose of this study is to investigate abundance, especially in the fine earth fraction, and properties of bricks in urban soils, focusing on rooting, plant nutrition and contamination.

Materials and methods

Three different urban soils from the city of Berlin have been studied for their brick contents in the coarse and fine earth fractions by hand sorting. Light (LM) and scanning electron microscopy (SEM) was employed to investigate bricks for proofs of rooting. Third, CEC, pH, EC, C_org, nutrient and contaminant storage and availability have been investigated for bricks and the fine earth fractions of the corresponding soil horizons.

Results and discussion

The fine earth fractions of the investigated soils contain 3 to 5 % of bricks, while the coarse fractions contain up to 50 %. The LM and SEM micrographs made the proof that roots enter brick pores or attach to brick surfaces. Therefore, they can use the water and nutrients stored in bricks and bypass pore system discontinuities between bricks and surrounding soil. The CEC of bricks is grain size dependent and reaches a maximum of 6 cmol_c kg^?1 for particles smaller than 0.063 mm. This dependency is the result of the restricted diffusion into the brick pore system due to the short shaking time in the CEC analysis protocol and of the rising surface with decreasing particle size. From the nutrient storage and availability, we conclude that bricks can better supply plants with K, Mg, Ca and S than the investigated sandy bulk soil.

Conclusions

The nutrient availability from bricks is low compared to control soils, except for Ca and S. Because of the water and nutrient storage, low contamination status and the possible rooting of bricks, they can be used for amelioration of poor sandy soils and for constructed Technosols, preferably employed in small grain sizes.     

Effects of temperature on soil organic carbon fractions contents,aggregate stability and structural characteristics of humic substances in a Mollisol

Purpose

Under a global warming scenario, understanding the response of soil organic carbon fractions and aggregate stability to temperature increases is important not only for better understanding and maintaining relevant ecosystem services like soil fertility and crop productivity, but also for understanding key environmental processes intimately related with the maintenance of other regulatory ecosystem services like global climate change mitigation through carbon sequestration. An increase in temperature would accelerate the mineralization of soil organic carbon. However, the properties of organic carbon remained in soil after mineralization is not well known.

Materials and methods

Mollisol was collected at 0–20-cm depth from maize (Zea mays L.) field in Northeast China. A 180-day incubation experiment was conducted at three different temperatures (10, 30, and 50 °C) under constant soil moisture (60 % water holding capacity). Soil samples were assayed for total organic carbon (TOC), water-soluble organic carbon (WSOC), easily oxidizable organic carbon (EOC), humic fractions carbon, aggregate-associated carbon, and water stability of aggregates. Elemental analysis and solid-state ¹³C nuclear magnetic resonance spectroscopy were used to characterize humic acid and humin fractions.

Results and discussion

The contents of soil TOC, EOC, humic fractions carbon, and aggregate-associated carbon decreased with the increase in temperature. The proportion of 2–0.25-mm macroaggregate and the mean weight diameter (MWD) of aggregates also decreased. The C, H, N, S, alkyl C, and O-alkyl C contents of humic acid and humin decreased, whereas the O, aromatic C, and carbonyl C contents increased. The H/C, aliphatic C/aromatic C, and O-alkyl C/aromatic C ratios in humic acid and humin fractions decreased.

Conclusions

The increase in temperature has a negative impact on soil organic carbon content, soil aggregation, and aggregate stability. Moreover, humic acid and humin molecules become less aliphatic and more decomposed with the increase in temperature.

     

Hydrophobicity of electrophoretic fractions of different soil humic acids

Purpose

The fractionation of soil humic acids (HAs) according to their hydrophobicity is a common procedure in the study of this polydispersed complex natural mixture, so that reversed-phase high-performance liquid chromatography (RP-HPLC) is used resulting in humic components of differing hydrophobic/hydrophilic properties. However, a comparative study of the hydrophobicity of fractions isolated from different soil HAs have not been addressed so far.

Materials and methods

The RP-HPLC with online absorbance detection was used for analysis of International Humic Substances Society soil standard HAs, chernozem soil HAs, and their electrophoretic fractions A, B, and C?+?D, obtained by tandem size exclusion chromatography–polyacrylamide gel electrophoresis. The strong relationship between hydrophobicity, electrophoretic mobility (EM), molecular size (MS), specific absorbance at 280 nm and aromaticity of HAs fractions was found.

Results and discussion

Independently of soil HAs genesis fraction A with lowest EM and highest MS is essentially more hydrophobic (60–73 % of the fraction amount remained adsorbed on the RP column) than medium EM and MS fraction B (33–47 % of the fraction amount remained adsorbed on the RP column). The lowest hydrophobicity belongs to fraction C?+?D with highest EM and lowest MS.

Conclusions

The most hydrophilic aromatic fraction C?+?D seems to have been bound with other mostly aliphatic hydrophobic fractions A and B through non covalent (possibly hydrogen) bonds. These data could be relevant to better understanding the overall makeup of soil HAs and their structural organization.     

The influence of compost addition on heavy metal distribution between operationally defined geochemical fractions and on metal accumulation in plant

Purpose

Metal distribution patterns among geochemical fractions are informative for metal phytoavailability. Compost added to polluted soils may adsorb metals on the less phytoavailable fractions. A bioassay experiment was conducted to establish possible correlations between metal concentrations in different soil fractions and metal contents in edible plant parts and to investigate the influence of different compost loads on heavy metal availability to plants.

Materials and methods

Chinese cabbage plants were grown in pots with sandy and clayey soils and soils mixed with different doses of biosolid compost spiked with soluble heavy metal salts (Cd, Cu, and Pb). The metals’ distribution pattern in the soil and mixed samples was determined by sequential extraction procedure (modified BCR protocol). The studied fractions, from most to least bioavailable, were water-extractable (WE), exchangeable-adsorbed (EXC), associated with carbonates and acetic acid-soluble forms (CARB), occluded by reducible (hydro)oxides of Fe and Mn (RO), and associated with organic matter (OM) and a residual fraction (RES). Metal concentrations in soil extracts and in the digested plant tissue were measured by ICP-AES.

Results and discussion

The highest compost doses (72 and 115 Mg ha^?1) enhanced cabbage yield significantly. No excessive phytoaccumulation of metals was observed in plants grown in the clayey soil or its mixtures with compost. The compost dose of 72 Mg ha^?1 was optimal in decreasing Cu accumulation by plants grown in sandy soil, and 28.8 Mg ha^?1 was found to be effective in reducing Cd and Pb uptake. Metals were accumulated in plants primarily from the WE, EXC, and CARB fractions, whereas other fractions decreased phytoaccumulation. Compost addition suppressed heavy metal mobility, but different fractions were active in pollutant sorption, depending on soil type and metal.

Conclusions

Compost addition increased metal proportions in the RO and OM fractions, reducing metal phytoavailability. This is especially important for sandy soils with low adsorption ability and higher vulnerability to metal pollution than clayey soils. A compost dose of 20% v/v (or 28.8 Mg ha^?1) effectively reduced plant accumulation of Cd and Pb. We propose using the first three steps of the modified BCR protocol as a three-step sequential-extraction procedure for the most phytoavailable fractions of heavy metal: WE, EXC, and CARB.     

Using humic products as amendments to restore Zn and Pb polluted soil: a case study using rapid screening phytotest endpoint

Purpose

Heavy metal contamination is a priority issue affecting millions of hectares of soil throughout the world. One of the most promising, environmentally friendly, and cost-effective approaches to restore polluted soils could be applying organic amendments. We investigated the remediation potential of three types of humic products with regard to their effect on the bioavailability of Pb and Zn, content of nutrients, and the ability to mitigate acute phytotoxicity in contaminated soil.

Materials and methods

Spodosol samples were spiked with Pb (550 mg kg^?1) and Zn (880 mg kg^?1). Then, two different commercial humic products (from peat and lignosulfonate) and natural humic acids (from brown oxidized coal) were added in two doses to reach an equal content of carbon: a 10% increment and a 30% increment of the initial total organic carbon in the soil. After 30 days, the content of metals and nutrients (S, K, Na, Ca, Mn, P) was determined by the sequential extraction (i?H₂O, ii?NH₄COOH pH 4.8, iii–CH₃COOH). The effect of humic products on heavy metals bioavailability was evaluated using the calculated partition indexes. Seed germination and root elongation of Sinapis alba were also determined. Chemical and biochemical variables were aggregated by the principal component analysis.

Results and discussion

Humic products reduced the amount of bioavailable fractions of Pb and Zn in soils. The partition index, which quantitatively describes bioavailable fractions of the Zn and Pb in the soil, was 28–49% lower than in the spiked (Pb+Zn) control. The inhibition of root elongation and seed germination of mustard by Zn and Pb was significantly mitigated by humic products; in the soil test, the root length and seed germination were up to 36–87% higher than those of the Pb+Zn control and did not differ from those in the non-amended treatments. This effect may have been associated with the structural differences (H/C and O/C ratio) and content of nutrients (Na and K) in humic products.

Conclusions

Commercial humic products used in poor multi-contaminated soils can maintain plant growth by improving nutrient status due to heavy metals immobilization and can be a promising approach to remediate the soil contaminated with heavy metals at extremely high concentrations.

     

Fractions of Cu, Cd, and enzyme activities in a contaminated soil as affected by applications of micro- and nanohydroxyapatite

Purpose

With the rapid development of nanotechnology, hydroxyapatite-based nanoparticles have been applied in wastewater and soil remediation. However, limited studies have been conducted on the remediation of heavy metal-contaminated soils by microhydroxyapatite (MHA) and nanohydroxyapatite (NHA). Thus, we investigated the effects of MHA and NHA on soil pH values and fractions of copper (Cu) and cadmium (Cd). The changes of soil enzymes with application of MHA and NHA were also evaluated.

Materials and methods

Pots contained 200 g of the soil with MHA and NHA ranging from 1 % to 5 % incubated for 60 days under greenhouse condition, and maintained at 60 % of soil water holding capacity by adding deionized water. Soil pH, catalase, urease, and acid phosphatase were analyzed at incubation times of 7, 14, 30, and 60 days by chemical assays. The fractions of Cu and Cd were analyzed after 60 days by a sequential extraction procedure.

Results and discussion

Application of MHA and NHA significantly increased soil pH values. Especially, we found for the first time that soil pH values with 3 % (pH?>?7.90) and 5 % (pH?>?8.83) application rates of MHA were larger than that of MHA itself (pH?=?7.71). MHA was more effective than NHA in immobilizing Cu and Cd by significantly decreasing exchangeable fractions of Cu and Cd and transforming them from active to inactive fractions. Soil catalase and urease significantly increased, but acid phosphatase apparently decreased with increasing application rates of MHA. However, three enzymes activities changed slightly for NHA treatments.

Conclusions

MHA was more effective than NHA in immobilizing Cu and Cd. MHA had a more positive effect on soil catalase and urease activities than NHA. Furthermore, Pearson’s correlation coefficients showed that soil pH value was a key factor to influence the bioavailability of Cu and Cd and the activity of soil enzymes. The results of this study provided an efficient method for the remediation of heavy metal-contaminated soils.