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.

     

Early detection of the effects of compaction in forested soils: evidence from selective extraction techniques

Purpose

Soil compaction resulting from mechanisation of forest operations reduces air permeability and hydraulic conductivity of soil and can result in the development of hydromorphic and/or anoxic conditions. These hydromorphic conditions can affect physico-chemical properties of the soils. However, early detection of these effects on mineralogical portion of soils is methodologically difficult.

Materials and methods

To analyse the effects of soil compaction on iron minerals in loamy Luvisol, three compacted and three non-compacted soil profiles up to the depth of 50 cm were collected from an artificially deforested and compacted soils after 2 years of treatment. Soil was compacted with the help of 25 Mg wheeler’s load to increase the dry bulk density of soil from 1.21?±?0.05 to 1.45?±?0.1 g cm^?3. Soil samples were analysed by X-ray diffraction (XRD) and were treated by citrate bicarbonate (CB) and dithionite citrate bicarbonate (DCB) under controlled conditions. Major and minor elements (Fe, Al, Mg, Si and Mn) were analysed by ICP-AES in the CB and DCB extracts.

Results and discussion

It was found that X-ray diffraction is not an enough sensitive method to detect the quick mineralogical changes due to soil compaction. Results obtained from CB-DCB extractions showed that soil compaction resulted in larger CB and smaller DCB extractable elements as compared to non-compacted soil. Labile Fe was found 30 % of total Fe oxides in compacted soil against 10–14 % in non-compacted soils. Compaction thus resulted in Fe transfer from non-labile to labile oxides (s.l.). Results showed that soil compaction leads to the reduction of Fe³⁺ to Fe²⁺. The effects of hydromorphic conditions due to soil compaction were observed up to the depth of 35 cm in forest soil profile. Furthermore, a close association of Al with Fe oxides was observed in the soil samples, while Mn and Si were mainly released from other sources, Mg showing an intermediate behaviour.

Conclusions

Hydromorphic conditions owing to soil compaction affect the mobility and crystallisation process of iron mineral. CB-DCB selective extraction technique, in contrast to XRD technique, can be effectively used to examine the possible effects of soil compaction on iron minerals.

     

Influence of redox processes on clay mineral transformation in Retisols in the Carpathian Foothills in Poland. Is a ferrolysis process present?

Purpose

Ferrolysis is a soil-forming process, which involves destruction of clay minerals due to cyclic reduction and oxidation in acidic and periodically wet soils. The main objectives of this study were as follows: (1) to determine the influence of redox processes on clay mineral transformation in Retisols (Albeluvisols) in the Carpathian Foothills in Poland and (2) to verify the occurrence of ferrolysis in Retisols showing various degrees of bleaching.

Materials and methods

Twelve representative soil profiles were selected for analysis. All were formed entirely from loess except for two profiles, in which the lowermost horizons (2C) had developed from weathered flysch rocks residuum. Soil mineral analysis was done using x-ray diffraction (XRD), Fourier-transform infrared (FTIR) spectroscopy, and Mössbauer spectroscopy (MS).

Results and discussion

The obtained results indicate that the qualitative and quantitative mineral compositions of the clay fraction in the E and Eg horizons obtained from Retisols in the Carpathian Foothills exhibiting marked differences in bleaching (strong, moderate, weak, and lack of bleaching) caused by periodic stagnation of water above a slowly permeable fragipan and cyclic redox processes are the same. The E and Eg horizons are characterized by the presence of 2:1 clay minerals with likely organic interlayer fillings, dioctahedral mica, kaolinite, and chlorite.

Conclusions

The results indicate that (1) redox processes occurring in the soils do not affect clay mineral transformation in Retisols of the Carpathian Foothills in Poland and (2) ferrolysis is not the main soil-forming process operating in these soils. This is most likely because iron-bearing minerals are not abundant in the Retisols and/or undergo eluviation to the lower part of the soil profiles. The lower content of the clay fraction in the E and Eg horizons versus that in the lower soil horizons of the Retisols is related to clay illuviation (lessivage), and not to clay decomposition due to ferrolysis.

     

Laser-based spectroscopic methods to evaluate the humification degree of soil organic matter in whole soils: a review

Purpose

The objective of this review is to survey critically the results obtained by the application of laser-induced fluorescence spectroscopy (LIFS) and laser-induced breakdown spectroscopy (LIBS) to the evaluation of the humification degree (HD) of soil organic matter (SOM) directly in untreated, intact whole soils.

Materials and methods

A large number of soils of various origin and nature, either native or under various cultivations, land use, and management, at various depths, have been studied to evaluate the HD of their SOM directly in intact whole samples. The LIFS spectra were obtained by either a bench or a portable argon laser apparatus that emits UV-VIS light of high power, whereas the LIBS spectra were obtained using a Q-switched Nd:YAG laser at 1064 nm.

Results and discussion

The close correlations found by comparing H_LIF values of whole soil samples with values of earlier proposed humification indexes confirmed the applicability of LIFS to assess the HD of SOM in whole soils. The high correlation found between HD_LIBS values and H_LIF values showed the promising potential of LIBS for the evaluation HD of SOM.

Conclusions

The LIFS technique shows to be a valuable alternative to evaluate the HD of SOM by probing directly the whole solid soil sample, thus avoiding the use of any previous chemical and/or physical treatments or separation procedures of SOM from the mineral soil matrix. The emerging application of LIBS to evaluate the HD of SOM in whole soils appears promising and appealing due to its sensitivity, selectivity, accuracy, and precision.

     

Transformation of beech forest litter as a factor that triggers arsenic solubility in soils developed on historical mine dumps

Purpose

Soils that develop on the dumps in historical arsenic mining sites contain high concentrations of As thus constituting a serious environmental risk. This study was aimed to examine the changes in arsenic solubility in mine soils as induced by organic matter introduced with forest litter.

Materials and methods

Four large samples of initially developed soils were collected from the dumps remaining in former mining sites and were incubated for 90 days at various moistures: 80% of maximum water holding capacity and 100% (flooded conditions), with and without addition of beech forest litter (BL), 50 g/kg. Soils contained up to 5.0% As. Soil pore water was collected periodically with MacroRhizon suction samplers and examined on As, Mn, and Fe concentrations, pH, Eh, and dissolved organic carbon (DOC). The properties of dissolved organic matter were characterized by UV-VIS spectroscopic parameters A4/A6 and SUVA₂₅₄.

Results and discussion

Application of BL resulted in an intensive release of As from soils, particularly at 100% moisture. As concentrations in soil pore water increased strongly during the first 2 or 4 weeks of incubation and then started to decrease in all cases, except for one flooded soil. As was released particularly intensively from carbonate-containing soils. The mechanisms of As mobilization, including reductive dissolution of Mn and Fe oxides and the competition with DOC for sorption sites on the oxides, were discussed as related to soil properties. Pore water concentrations of DOC were increasing at the beginning of incubation and started to decrease after two or four weeks. Spectroscopic parameters of dissolved organic matter in ZS soils indicated increasing aromaticity and progress of humification.

Conclusions

Forest litter introduced to mine dump soils causes a mobilization of As into soil pore water. This effect, particularly strong in carbonate-rich soils, is apparently related to high concentrations of DOC and usually declines with time, which may be explained by the progress in humification. The relationships between DOC properties and As speciation in soil pore water should be dissected for better interpretation of experimental results.

     

Relationship between particle density and soil bulk chemical composition

Purpose

An analytical database containing XRF chemical analyses and real density measurements of unconsolidated sediments of the Padania Plain (Northern Italy) has been used to understand the relationship that exists between the soil particle density (ρ_s) and their bulk chemical composition.

Materials and methods

Using a linear regression, we built an equation able to link the particle density with the soil elemental composition.

Results and discussion

Positive correlations were found between ρ_s and SiO₂, MgO, CaO and Na₂O and negative correlations with K₂O, TiO₂, Al₂O₃, Fe₂O₃ and LOI, reflecting the presence in the soils of quartz and feldspars/mineral clays respectively.

Conclusions

Our equation is very useful because it helps to know the density properties of a soil when it is not possible to measure ρ_s with a pycnometer. On the other hand, by knowing the ρ_s, it is possible to have a quite precise knowledge about the chemistry of the studied soils.

     

Impacts of continuous excessive fertilization on soil potential nitrification activity and nitrifying microbial community dynamics in greenhouse system

Purpose

Sampling and analysis of greenhouse soils were conducted in Shouguang, China, to study continuous excessive fertilization effect on nitrifying microbial community dynamics in greenhouse environment.

Materials and methods

Potential nitrification activity (PNA), abundance, and structure of nitrifying microbial communities as well as the correlations with soil properties were investigated.

Results and discussion

Short-term excessive fertilization increased soil nutrient contents and the diversity of nitrifying microbial communities under greenhouse cultivation. However, the abundance and diversity of nitrifying communities decreased greatly due to the increase of soil acidity and salinity after 14 years of high fertilization in greenhouse. There was a significant positive correlation between soil PNA and the abundance of ammonia-oxidizing bacteria (AOB) but not that of ammonia-oxidizing archaea (AOA) in topsoil (0–20 cm) when pH ≥7. Soil PNA and AOB were strongly influenced by soil pH. The groups of Nitrososphaeraceae, Nitrosomonadaceae, and Nitrospiraceae were predominant in the AOA, AOB, and nitrite-oxidizing bacteria (NOB) communities, respectively. Nitrifying community structure was significantly correlated with soil electrical salinity (EC), organic carbon (OC), and nitrate nitrogen (NO₃ ^?–N) content by redundancy analysis (RDA).

Conclusions

Nitrification was predominated by AOB in greenhouse topsoil with high fertilizer loads. Soil salinity, OC, NO₃ ^?–N content, and pH affected by continuous excessive fertilization were the major edaphic factors in shaping nitrifying community structure in greenhouse soils.

     

Evaluation of palygorskite for remediation of Cd-polluted soil with different water conditions

Purpose

The study aimed at comparing the effects of different water managements on soil Cd immobilization using palygorskite, which was significant for the selection of reasonable water condition.

Materials and methods

Field experiment was taken to discuss the in situ remediation effects of palygorskite on Cd-polluted paddy soils, under different water managements, using a series of variables, including pH and extractable Cd in soils, plant Cd, enzyme activity, and microorganism number in soils.

Results and discussion

In control group, the pH in continuous flooding was the highest under three water conditions, and compared to conventional irrigation, continuous flooding reduced brown rice Cd by 37.9%, and brown rice Cd in wetting irrigation increased by 31.0%. In palygorskite treated soils, at concentrations of 5, 10, and 15 g kg^?1, brown rice Cd reduced by 16.7, 44.4, and 55.6%; 13.8, 34.5, and 44.8%; and 13.1, 36.8, and 47.3% under continuous flooding, conventional irrigation, and wetting irrigation (p < 0.05), respectively. The enzyme activity and microbial number increased after applying palygorskite to paddy soils.

Conclusions

Continuous flooding was a good candidate as water management for soil Cd stabilization using palygorskite. Rise in soil enzyme activity and microbial number proved that ecological function regained after palygorskite application.

     

The solid-solution distribution of copper added to soils: influencing factors and models

Purpose

A series of empirical and mechanistic geochemical models were developed to describe the solid-solution partitioning of copper (Cu) in typical fresh spiked Chinese soils.

Materials and methods

The influence of soil properties on Cu partitioning was assessed in a wide range of soils using multiple regression analysis. Geochemical models (WHAM VI and Visual MINTEQ) and simulation analyses in combination with experimental data (i.e., the bulk of soil properties and Cu contents) were performed in order to provide additional insight into the mechanisms controlling the Cu partitioning. Calculation of soluble Cu contents based on the two models was then simplified and optimized by adjusting input variables, and the calibrated outputs were used to produce reasonable predictions of soluble metal concentrations.

Results and discussion

The results of the multiple regression analyses presented in this paper show strong correlations between soluble Cu concentrations and soil Cu concentrations and properties, with adjusted coefficients of determination (R_adj²) ranging between 0.84 and 0.91. Soil organic carbon (OC) content was an insignificant factor in most cases, but the active fraction of dissolved organic matter was important in improving model estimates. The best fit of root mean square error (RMSE) varied between 0.42 and 0.77 for the WHAM VI model and between 0.28 and 0.57 for the Visual MINTEQ model across all pH categories.

Conclusions

The models presented in this paper are suitable for investigating and simulating Cu solid-solution partitioning in a wide range of Chinese soils.

     

Fractionation of copper and uranium in organic and conventional vineyard soils and adjacent stream sediments studied by sequential extraction

Purpose

Particularly in organic viticulture, copper compounds are intentionally released into the environment as fungicide, whereas uranium originates from conventional phosphate fertilization. Both activities contribute to the metal contamination in wine-growing areas. This pilot study aimed to better understand how soil properties influence the presence and environmental fate of copper and uranium with respect to viticultural management.

Materials and methods

We characterized metal binding forms, i.e., their association with different soil constituents, in organically and conventionally cultivated vineyard soils and adjacent upstream and downstream sediments. The available metal fraction and the fractions associated with manganese oxides, organic matter, iron oxides, and total contents were extracted sequentially.

Results and discussion

Total soil copper ranged from 200 to 1600 mg kg^?1 with higher contents in topsoil than subsoil. The majority of copper (42–82%) was bound to soil organic matter. In all fractions, copper contents were up to 2-fold higher in organic than in conventional vineyards, whereas the sediment concentrations were independent of the adjacent viticultural management. A net increase of copper in downstream sediments was found only when water-extractable organic carbon (WEOC) in an adjacent vineyard was elevated. With 11 ± 1 mg kg^?1, total uranium was 25% higher in conventional than in organic vineyard soils. Its affinity to iron or WEOC potentially rendered uranium mobile leading to a substantial discharge to downstream sediments.

Conclusions

Translocation of copper and uranium from vineyards into adjacent stream sediments may rather be attributed to WEOC and iron contents than the viticultural management. Follow-up studies should scrutinize the processes driving metal availability and transport as well as their interaction at the aquatic–terrestrial interface.

     

Characterization of kaolinite in the hardsetting clay fraction using atomic force microscopy,X-ray diffraction,and the Rietveld method

Purpose

Brazilian soils that present extremely hard sub-superficial horizons when dry and friable when humid are similar to the Australian and South African hardsetting horizons whose hardness can be mainly related to low crystallinity. Studies involving refinement by the Rietveld method with X-ray diffraction (RM-XRD), atomic force microscopy (AFM), scanning electron microscopy (SEM), and their relation have not been carried out in hardsetting horizon soils. Thus, the objective of this study is to obtain information about the kaolinite in the hardsetting horizon of a Yellow Argisol clay fraction, taking into consideration the results of isomorphic substitution, crystallite average size, and microstrains, relating them to particle image analysis regarding their morphology and size.

Materials and methods

Soil samples were collected in the hardsetting horizon of a Yellow Argisol in the Coastal Tablelands region, which covers the whole Brazilian Northeast coast and part of the Southeast region. The sample was powdered, sieved, and submitted to dispersion and physical fractioning process by sedimentation. The clay fraction was analyzed by RM-XRD, AFM, and SEM techniques.

Results and discussion

The RM-XRD provided improvement of indices with isomorphic substitutions in the goethite [Fe_0.70Al_0.30O(OH)], kaolinite [Al_1.44Fe_0.56Si₂O₅(OH)₄], and halloysite [Al_1.42Fe_0.58Si₂O₅(OH)₄]; 29 nm crystallite average size; 5 × 10^?3 microstrain; and 49.5% kaolinite. AFM analyses indicated particle average size from 80 to 250 nm and average height from 60 to 80 nm. By relating this data, it was possible to estimate that the particles under analysis are kaolinite composed of 3 to 9 crystallites and stacking of 88 to 112 layers.

Conclusions

The process, analyses, and comparisons such as crystallographic and morphologic information about the kaolinite mineral particles contribute to the comprehension of the hardsetting horizon soil nature as well as other soils that present minerals with a high degree of isomorphic substitution.

     

Urban soil resources of medium-sized cities in Poland: a comparative case study of Toruń and Zielona Góra

Purpose

Despite the many studies of urban soils, a comparative analysis for cities of a similar size has not yet been conducted. Thus, the aim of this review paper was to compare the soil distribution patterns in the area of two medium-sized Polish cities (Toruń and Zielona Góra). The authors attempted to answer the question of how natural and technogenic factors contributed to the transformation of urban soils and what the similarities and differences are between these two studied cities.

Materials and methods

First, both the natural and the human-related (including historical) factors influencing the soil formation in the studied cities were analysed. Then, a comparison of the degree of transformation of the urban soil environment was presented. The data obtained by the authors during nearly two decades of research (over 200 soil profiles) were used.

Results and discussion

Intensive development of the built-up areas in Toruń brought heavy and long-term transformations of soils, which demonstrate the typical properties of Urbic Technosols, Ekranic Technosols and other technogenic soils. Zielona Góra showed a similar state of soil transformation over a considerably smaller area. Currently, the differences in the soil properties in many built up areas have been blurred, despite the habitat and historical base. The similarities of the soil properties concerned, in particular, a high content of skeletal remains (from a few to over 30%), elevated pH (in KCl) values (even above 8.0) and the artificial soil horizons formation. Both cities struggle with similar problems regarding the changes in the land use within the areas covered by these soils.

Conclusions

It was found that, despite the significant habitat and historical differences between the two studied cities, most of the urban soils, especially Urbic Technosols, Ekranic Technosols and Regosols (Relocatic and Technic), are characterised by similar morphology and properties. The most important differences are the time and scale of the area transformation, which influence the extent of Technosols and Anthrosols within the city borders. The most distinct differences concern the natural and slightly transformed soils, which are the results of various soil-forming factors.

     

Phosphate adsorption on uncoated and humic acid-coated iron oxides

Purpose

The phosphate adsorption on natural adsorbents is of particular importance in regulating the transport and bioavailability of phosphates in environmental system. In soils, oxides are often associated with organic matter and form mineral-organic complexes. The aim of the present paper was to investigate the mechanisms of phosphate adsorption on these complexes.

Materials and methods

Phosphate adsorption on uncoated and humic acid (HA)-coated iron oxide complexes was investigated at different ionic strengths and pH by isotherm experiments and attenuated total reflectance Fourier transform infrared (ATR-FTIR) spectroscopy.

Results and discussion

Results showed that HA-coated iron oxide complexes caused a decrease in the specific surface area (SSA) and the isoelectric point (IEP) of oxides. Phosphate adsorption on iron oxides was insensitive to changes of ionic strength, while it increased on the complexes with increasing ionic strength. The presence of HA decreased the maximum adsorption and the affinity of phosphate on the complexes. The zeta potential of phosphate-bound iron oxides linearly reduced with the increment of phosphate surface coverage, while the zeta potential of complexes with adsorbed phosphate kept at the same level. ATR-FTIR analysis suggested the formation of phosphate-metal complexation. The presence of HA promotes the formation of the monodentate phosphate complexes at pH 4.5 and significantly influenced phosphate species at pH 8.5.

Conclusions

The amount of phosphate adsorbed was reduced, and the phosphate speciation was also influenced when phosphate was adsorbed on HA-coated iron oxide complexes compared with phosphate adsorption on pure goethite and hematite.

     

Arsenic modulates the composition of anode-respiring bacterial community during dry-wet cycles in paddy soils

Purpose

Bacteria able to extracelluar respiration, which could be enriched in the anode of microbial fuel cells (MFCs), play important roles in dissimilatory iron reduction and arsenic (As) desorption in paddy soils. However, the response of the bacteria to As pollution is unknown.

Materials and methods

Using soil MFCs to investigate the effects of As on anode respiring bacteria (ARB) communities in paddy soils exposed to As stress. The soil MFC performances were evaluated by electrochemical methods. The bacterial community compositions on anodes were studied using Illumina sequencing.

Results and discussion

In wet 1 phase, polarization curves of MFCs showed cathode potentials were enhanced at low As exposure but inhibited at high As exposure. In the meantime, anode potentials increased with As levels. The dry-wet alternation reduced As levels in porewater and their impacts on electrodes microorganisms. Arsenic addition significantly influenced the anode microbial communities. After dry-wet cycles, Deltaproteobacteria dominated in the anode with high As.

Conclusions

The dynamic changes of the communities on cathodes and anodes of soil MFCs in paddy soils with different As addition might be explained by their different mechanisms for As detoxification. These results provide new insights into the microbial evolution in As-contaminated paddy soils.

     

Exclosure on CT-measured soil macropore characteristics in the Inner Mongolia grassland of northern China

Purpose

Grassland exclosure is a widely-used option to prevent from grazing in degraded grasslands for restoration. However, the influence of exclosure on soil macropore of grassland remain scarce. The objective of this study was to quantify the pore architecture of grassland soils under exclosure.

Materials and methods

Two treatments, 9E (grassland enclosed for 9 years) and 5E (grassland enclosed for 5 years), were designed, with grazing as a control in the experiment. Nine soil columns (0–50 cm deep) were taken at the three sites with three replicates. At each site, three soil columns were from the grassland, and cores were scanned with a Philips Brilliance ICT Medical Scanner. Numbers of macropores, macroporosity, network density, length density, and node density within the 50-cm soil profile were interpreted from X-ray computed tomography to analyze soil pore architecture.

Results and discussion

The results indicated that exclosure significantly influenced CT-measured soil macroporosity in the Inner Mongolia grassland of northern China. Soils under enclosed grassland had greater macroporosity, length density, total volume, and node density than that of under freely grazed grassland. Macroporosity increased as the enclosure age increased. For soils under enclosed grassland, macropores were concentrated at 0–300-mm soil layers, and macropores were mainly present at 0–100-mm soil depth under freely grazed grassland. The large number of macropores found in soil under enclosed grassland can be attributed to greater root development.

Conclusions

Exclosure increases soil macroporosity and improve soil structure.

     

Sustainability of in situ remediation of Cu- and Cd-contaminated soils with one-time application of amendments in Guixi,China

Purpose

In situ immobilization of heavy metal-contaminated soils with the repeated incorporation of amendments can effectively reduce the bioavailability of soil heavy metals. However, the long-term application of amendments would lead to the destruction of soil structure and accumulation of soil toxic elements, ultimately affecting food security and quality. Thus, the sustainability of the amendments in a heavy metal-contaminated soil was evaluated from 2010 to 2012.

Materials and methods

Batch field experiments were conducted in the soils, which were amended with apatite (22.3 t ha^?1), lime (4.45 t ha^?1), and charcoal (66.8 t ha^?1), respectively. The amendments were applied only one time in 2009, and ryegrass was sown each year. Ryegrass and setaria glauca (a kind of weed) were harvested each year. Concentrations of copper (Cu) and cadmium (Cd) were determined by batch experiments. Five fractions of Cu and Cd were evaluated by a sequential extraction procedure.

Results and discussion

Ryegrass grew well in the amended soils in the first year, but it failed to grow in all the soils in the third year. However, setaria glauca could grow with higher biomass in all the amended soils. The treatment of apatite combined with plants was more effective than lime and charcoal treatments in removing Cu and Cd from the contaminated soils by taking biomass into account. Apatite had the best sustainable effect on alleviating soil acidification. The Cu and Cd concentrations of CaCl₂-extractable and exchangeable fractions decreased with the application of amendments. Moreover, apatite and lime could effectively maintain the bioavailability of Cu and Cd low.

Conclusions

Apatite had a better sustainable effect on the remediation of heavy metal-contaminated soils than lime and charcoal. Although all the amendment treated soils did not reduce soil total concentrations of Cu and Cd, they could effectively reduce the environmental risk of the contaminated soils. The findings could be effectively used for in situ remediation of heavy metal-contaminated soils.

     

Biosynthesis of schwertmannite by <Emphasis Type="Italic">Acidithiobacillus ferrooxidans</Emphasis> and its application in arsenic immobilization in the contaminated soil

Purpose

Soil contamination with arsenic (As) is an increasingly worldwide concern. Immobilization is a potentially reliable, cost-effective technique for the reclamation of As-contaminated soils. The aim of this study is to develop new soil amendments with high As immobilization efficiency, cost-effective, environmental-friendly, and without soil acidification for As-contaminated soil remediation.

Materials and methods

Biosynthesis of schwertmannite by Acidithiobacillus ferrooxidans has been conducted, and two types of biogenetic schwertmannites SCH and A-SCH were prepared and characterized by X-ray diffraction (XRD), transmission electron microscopy (TEM), Fourier transform infrared spectroscopy (FTIR), etc. The A-SCH was formed through pretreating SCH by acidic and alkaline activation. The potential of SCH and A-SCH in As immobilization in contaminated soil was evaluated. The effect of ferrous sulfate and A-SCH on soil pH and immobilization of NaHCO₃-extractable As were also investigated for comparison.

Results and discussion

The chemical formula of SCH and A-SCH can be expressed as Fe₈O₈(OH)_4.89(SO₄)_1.55 and Fe₈O₈(OH)_5.19(SO₄)_1.41, respectively. Compared to SCH, A-SCH exhibits much higher specific surface area of 74.99 m² g^?1 and contains more hydroxyl groups and inner-sphere sulfate complexes. Immobilization efficiency of water-soluble As above 99.5 % can be achieved with A-SCH dosage of 5 % and SCH dosage of 10 %, respectively. The immobilization percentages of NaHCO₃-extractable As increased from 31.5 to 90.4 % and from 40.2 to 93.8 % with increasing dosage from 0.5 to 10 wt % for SCH and A-SCH, respectively. In general, both SCH and A-SCH immobilize As in contaminated soil effectively, and the immobilization performance of A-SCH was better than that of SCH, especially at lower dosage.

Conclusions

Biogenetic schwertmannite could be used as a potential effective soil amendment for As immobilization in contaminated soil. Our findings in this study also have important implications for in situ immobilization of As in contaminated soils, especially the soils related to acidic iron and sulfate-rich environments.

     

Effect of nanoparticles on crops and soil microbial communities

Purpose

Nanoparticles (NPs) have received increased attention in recent past due to their unique distinct properties. Metal-based NPs are widely used in chemical and allied sector. Most of the research is directed to study the efficiency of NPs in medicine and agriculture. The aim of this review is to explore the possible threats posed by toxicity of various NPs on plants and microbial diversity.

Materials and methods

First, major sources of NPs to the environment were analyzed. The effects of metal-based NPs on the microbiota and plants are presented in this review. The results obtained by the authors during last 12 years of research are used.

Results and discussion

The exposure of soil to nanoparticles causes a decrease in soil microbial biomass and enzymatic activity, which impacts microbial community composition including yeasts, bacteria, fungi, and biological diversity. The effects of NPs on plants result in various types of abnormalities. Nanoparticles can also pose risks to human health.

Conclusions

Increased applications of NPs pose a threat to beneficial microbial communities as well as crops and soils. Thus, it is important to explore whether NPs could compromise crop yield, soil properties, soil organisms, and functional activities of soil.

     

Characteristics of permafrost-affected soil in a cliff in the central part of the Polish Baltic coastal zone

Purpose

The study aimed to characterise a fossil permafrost-affected (Stagnic Fluvisol Relictiturbic) soil, occurring in a cliff in the central part of the Polish Baltic coastal zone near Orzechowo (54° 35.664′ N, 16° 54.123′ E).

Materials and methods

The soil was sampled at 22 points and analysed using standard procedures in soil science. After standard preparation, disturbed and undisturbed soil samples were made subject to laboratory analyses concerning their physical and chemical properties. Radiocarbon dates and pollen analysis results were also obtained for the selected soil samples.

Results and discussion

The permafrost-affected soil lies beneath a fossil Dystric Histic Stagnosol, which is covered by about 8 m of aeolian deposits. The radiocarbon age of the Dystric Histic Stagnosol was 3061 ± 60 cal. years BP, and that of the Stagnic Fluvisol Relictiturbic 10,161 ± 110 cal. years BP. However, the results of pollen analysis suggest rejuvenation of the obtained dates. The Stagnic Fluvisol Relictiturbic developed in the marginal part of a body of water, from fluvioglacial and aeolian sands deposited on grey glacial till. The mineral substrates of the soil are moderately and poorly sorted sands and silt loam in the bottom part of the profile. This fine-textured material has been moved to the upper parts of the profile due to the impact of the water freezing and thawing cycles in the permafrost active layer. The observed microstructures on quartz grain (0.5–1.0 mm) surfaces, including conchoidal fractures, breakage blocks and v-shaped pits, are typical for periglacial soils. The fossil Stagnic Fluvisol Relictiturbic is poor in total iron. The observed vertical distribution of free iron oxides suggests their displacement in the permafrost active layer. Soil organic matter was found to be moderately or strongly humified, which is not typical for permafrost-affected soils and can suggest its allochthonous, probably alluvial, character.

Conclusions

The studied Stagnic Fluvisol Relictiturbic developed at the close of the Pleistocene in the marginal part of a body of water. It constitutes a sequence of horizons of varied thickness and abundance in organic matter. The influence of a periglacial environment is reflected in morphology of the soil (cryoturbations) and some chemical properties and partially in microstructures observed on quartz grain surfaces.

     

Characterizing urban soils in New York City: profile properties and bacterial communities

Purpose

The influence of human activities on the development and functioning of urban soils and their profile characteristics is still inadequately understood. Microbial communities can change due to anthropogenic disturbances and it is unclear how they exist along urban soil profiles. This study investigates the dynamic soil properties (DSPs) and the bacterial communities along the profiles of urban soils in New York City (NYC) with varying degree of human disturbances.

Materials and methods

Eleven pedons were investigated across NYC as well as one control soil in a nearby non-urban area. Six soils are formed in naturally deposited materials (ND) and five in human-altered and human-transported materials (HAHT). For each soil, the profile was described and each horizon was sampled to assess DSPs and the bacterial community composition and diversity.

Results and discussion

The development and the DSPs of NYC soils are influenced by the incorporation of HAHT materials and atmospheric deposits. The most abundant bacterial taxa observed in the NYC soils are also present in most natural and urban soils worldwide. The bacterial diversity was lower in some soils formed in ND materials, in which the contribution of low-abundance taxa was more restricted. Some differences in bacterial community composition separated the soils formed in ND materials and in dredged sediments from the soils formed in high artifact fill and serpentinite till. Changes in bacterial community composition between soil horizons were more noticeable in urban soils formed in ND materials than in those formed in HAHT materials which display less differentiated profiles and in the non-urban highly weathered soil.

Conclusions

The bacterial diversity is not linked to the degree of disturbance of the urban soils but the variations in community composition between pedons and along soil profiles could be the result of changes in soil development and properties related to human activities and should be consistently characterized in urban soils.