Soil Solids Research Articles

Antibiotic Resistance Genes in Plague Ecosystems: Threatening the Emergence of Resistant Plague

The study aimed to investigate the prevalence of antibiotic resistance genes (ARGs) within the ecosystem of natural plague foci, assessing their potential impact on the efficacy of plague treatments. Employing 16S rRNA gene sequencing and high-throughput quantitative PCR, microbial communities and ARGs were detected, with subsequent analysis of interactions among ARGs, mobile genetic elements (MGEs), environmental factors, and microbial species. Tetracycline resistance genes were found to be dominant, with multidrug and tetracycline resistance ARGs primarily associated with marmots and ecological soil, while pikas predominantly harbored β-lactam resistance ARGs. High detection rates were observed for resistance genes rpsl and sul1, which are relevant to streptomycin and sulfonamides, antibiotics commonly used in plague treatment. The total dissolved solids (TDS) in soil significantly promoted the presence of tetR-02, and Ni was found to inhibit vanHB. The tnpA-03 MGE was identified as a significant contributor to the dissemination of the aadE gene. The high prevalence of ARGs, particularly rpsl and sul1, poses a potential risk to the efficacy of main antibiotic treatments for plague. The study suggests that environmental microbiomes may be the greatest risk factor for the emergence of drug-resistant Yersinia pestis, given the low misuse of antibiotics in animals within natural plague foci. Monitoring the risk of drug-resistant strain emergence and preparing alternative antibiotic or combination therapy strategies based on ARG pollution levels in plague-affected areas is deemed necessary.

Effect of soil pH and mineralogy on the sorption and desorption of phosphite and phosphate in Ultisols of the Southeastern Coastal Plain

AbstractThe development of transgenic crop varieties capable of utilizing phosphite (Phi) as a phosphorus (P) source is a promising strategy to increase P use efficiency while decreasing reliance on phosphate (Pi)‐based fertilizers. However, little information is available on Phi sorption and desorption in soils. We conducted batch experiments to investigate the sorption of Phi and Pi by three Ultisols from the Coastal Plain of the southeastern United States. At the soils' acidic field pH (pH 4.7–6.2), Pi had a higher affinity than Phi for soil solids, where maximum sorbed concentrations of Pi were an average of 44% greater than those of Phi. The sorption of both P species decreased when experiments were repeated adjusting soil pH to 6.5. More Phi than Pi was recovered during desorption experiments, indicating that Phi was more reversibly sorbed and, therefore, may be more plant‐available than Pi. Multiple linear regression between calculated linear distribution coefficients (KD; 10 mg P L−1 input solutions) and soil properties suggested that amorphous Al‐ and Fe‐oxides controlled Pi sorption. Alternatively, amorphous Al‐oxides and gibbsite controlled Phi sorption. Our results show that a lower affinity of Phi than Pi in Ultisols could improve P availability for plant uptake of Phi‐based fertilizers but may increase the risk of soil P buildup over time.

Deciphering the crop-soil-enzyme C:N:P stoichiometry nexus: A 5-year study on manure-induced changes in soil phosphorus transformation and release risk

Carbon:nitrogen:phosphorus (C:N:P) stoichiometry plays a vital role in regulating P transformation in agriculture ecosystems. However, the impact of balanced C:N:P stoichiometry in paddy soil, particularly regarding relative soil P transformation, remains unknown. This study explores the response of C:N:P stoichiometry to manure substitution and its regulatory role in soil P transformation, along with the associated release risk to the environment. Based on a 5-year field study, our findings reveal that replacing 30 % of chemical P fertilizer with pig manure (equal total NPK amounts with chemical P fertilizer treatment, named CFM) increased soil total C without altering soil total P, resulting in an elevated soil C:P ratio, despite the homeostasis of crop stoichiometry. This increase promoted microbial diversity and the accumulation of organic P in the soil. The Proteobacteria and Actinobacteria produced lower C:PEEA metabolism together, and enhanced in vivo turnover of P. Additionally, by integrating high-resolution dialysis (HR-Peeper), diffusive gradients in thin films (DGT), DGT-induced fluxes in the soil (DIFS), and sediment P release risk index (SPRRI) models, we observed that, in addition to organic P, CFM simultaneously increased soil Al-P, thereby weakening the diffusion and resupply capacity of P from soil solids to the solution. Consequently, this decrease in P release risk to the environment was demonstrated. Overall, this study establishes a connection between crop-soil-enzyme C:N:P stoichiometry, soil microorganisms, and soil P biogeochemical processes. The study further evaluates the P release risk to the environment, providing a novel perspective on both the direct and indirect effects of manure substitution on soil P cycling.

Assessing changes in geotechnical properties of soil caused by oil contaminants

Soil pollution seriously threatens the integrity of geotechnical soil properties, considerably altering physical and mechanical characteristics. Therefore, the geotechnical characteristics of contaminated soils should be studied. Samples used in this study were obtained from Peshawar, Khyber Pakhtunkhwa Province, Pakistan. Tests such as Atterberg limits, direct shear strength, sieving analysis, consolidation, and unconfined compression were conducted. The internal friction angle, cohesiveness, and shear strength of the soil decreased when oil pollution was introduced, probably owing to the lubricating effect of oil, which also causes a decrease in the dielectric constant. Surprisingly, in certain cases, bioremediation could reduce soil swelling, relieve pressure from swelling, and prevent soil settlement. Oil contamination resulted in decreased permeability and mechanical strength in the analyzed soil samples. Importantly, the effect of oil contamination on the shear strength parameters is not uniform and depends on the soil type. A thorough study is required because of the long-term consequences of oil contamination, particularly the long-term aging effects on geotechnical soil properties and behavior. Therefore, these results must be compared with those of the most recent tests. Furthermore, future research should consider the complex interplay between the functional groups inherent in soil solids and the injected contaminated oil.

Spatial variation of soil organic matter and metal mobility in wetland soils: Implications for biogeochemical processes in lateritic landscape

The evolution of the lateritic landscape over time changes the path of pedogenesis and soil hydrology. The occurrence of upland wetlands in the savannah flat plateau transforms well-drained lateritic soils into hydric soils enriched in organic matter. We investigated the composition of soil organic matter (SOM) produced in a wetland and their link with the mineral constituents of soil and their contribution to the mobility of Si, Fe, and Al in the soil. Six tranches were opened in a soil catena located from the plateau toward the center of the wetland, representing different hydromorphic features. Soil morphology was described, and chemical, physical and mineralogical analyses were performed to evaluate soil properties. Chemical fractionation of Soil Organic Matter (SOM) was performed and total organic carbon (TOC), dissolved organic carbon (DOC), particulate organic carbon (POC), and water-extractable organic matter (WEOM) were determined in the soil horizons. Metal complexing properties of DOM were determined using an excitation-emission matrix of fluorescence. The occurrence of Fe eluviation in the superficial horizons, Fe2O3 enrichment in the mottled horizons, and ferricrete formation in the center of the wetland were observed. Geochemical transfer assessment and the variation of oxides within the horizons showed that Fe2O3 and SiO2 were more mobile than Al2O3, whose variability in the gley horizon reflected the mobility of Fe2O3 and SiO2. The stability constants of Al and Cu showed an increase with the depth for WEOM and SOM. The pattern of the organic carbon fraction varied according to the level of hydromorphy and soil depth. It was also observed an increase in the C/N ratio with depth, possibly related to the reduced bioavailability of DOC due to its adsorption with soil solids.

Seismic analysis of buildings with basements

This research work analyzes how seismic waves affect buildings with basements that are usually studied independently: In surface structures the inertial forces originated by the movement of their base and in subway structures the deformations due to ground motion are considered. The building located in the city of Quito with twelve elevated floors and five subfloors is studied using nonlinear finite element modeling, considering that the subsoil depends on seismic excitations in a dynamic soil-basement-structure set, for which it is modeled together with its geotechnical components. The superstructure is integrated to the infrastructure and a time-history analysis is included with the most representative earthquakes can affect the building. The present investigation has three basic components: seismic, geotechnical, and structural, which are merged by means of specialized 3D structural engineering programs. In the seismic component, local and regional information about tectonic faults within Ecuador is collected; the building is then located on a seismic risk map and the magnitudes, types, and other parameters of the site where the building is located are determined. Using the results of the Earthquake Risk Assessment Project for the city of Quito (TREQ) and the Pacific Earthquake Engineering Research Center (PEER) database, three relevant seismic events are chosen for the time-history analysis that meet the seismic risk data for the building. For the geotechnical soil component, the geotechnical parameters of the original design of the building foundation, stratigraphy, and characteristics of soil solids, among others, are used. The structural component considers the type of material, geometry, dimensions, joints between elements and others of the original design for both basements and superstructure. The connection of these three components is carried out using Midas Gen and Midas GTS NX. The results of deformations as a function of time are compared with similar standards, studies, and investigations.

Bearing capacity factor for strip foundations on unsaturated clay

ABSTRACT The matric suction in unsaturated soil depends on the type of soil and various flux conditions i.e., infiltration, evaporation and no flow. The shear strength of unsaturated soil changes with change in matric suction leading to varying resistance of soil under various flow conditions. In this study, the bearing capacity of strip foundations resting over unsaturated clay considering variation of matric suction with depth for different surface flux conditions and position of water table, has been obtained using finite element lower bound limit analysis. Modified Mohr-Coulomb yield criteria based on unified effective stress approach has been employed to incorporate the contribution of matric suction stress to the failure condition. A non-dimensional bearing capacity factor was introduced to estimate the bearing capacity of strip foundations and presented as a function of different influencing parameters such as foundation width, water table depth, soil properties, various flow conditions and their flow rate, and surcharge pressure. The influence of variation of unit weight of soil in the unsaturated zone, air entry and pore size distribution parameters, residual degree of saturation of soil, specific gravity of soil solids, and foundation-soil interface roughness on the bearing capacity has also been examined and found to be insignificant.

Empirical model to assess leaching of pesticides in soil under a steady-state flow and tropical conditions

An empirical model of leaching of pesticides was developed to simulate the concentration of fungicides throughout unsaturated soil. The model was based on chemical reactions and the travel time of a conservative tracer to represent the travel time required for water to flow between soil layers. The model’s performance was then tested using experimental data from dimethomorph and pyrimethanil applied to the soil under field and laboratory conditions. The empirical model simulated fungicide concentration on soil solids and in soil solution at different depths over time (mean square error between 2.9 mg2 kg−2 and 61mg2 kg−2) using sorption percentages and degradation rates under laboratory conditions. The sorption process was affected by the organic carbon, clay, and the effective cation exchange capacity of the soil. The degradation rate values of dimethomorph (0.039 d−1–0.009 d−1) and pyrimethanil (0.053 d−1–0.004 d−1) decreased from 0 to 40 cm and then remained constant in deeper soil layers (60–80 cm). Fungicide degradation was a critical input in the model at subsurface layers. The model was determined to be a reliable mathematical tool to estimate the leachability of pesticides in tropical soil under a steady-state flow. It may be extended to other substances and soils for environmental risk assessment projects.Graphical abstract

Energy of dispersing of loamy soils to elementary particles using ultrasound

Elementary soil particles are the first soil-specific level in the soil structure hierarchy, which is also the object of the soil texture analysis. To disperse soil solids to elementary soil particles (ESP), it is necessary to break the strong bonds between particles by physical action. An effective way of physical dispersion is to treat soil suspensions with ultrasound. However, depending on the type of soil, the required energy level varies, as it is determined by the stability of the soil structure. In this work the experiment with increasing energy (from 65 to 1 101 J·mL-1) of ultrasonic dispersion at constant power equal to 32.4 W is described. Soil samples from the upper horizons of three types of loamy soils (Retisol, Phaeozem, Chernozem) were used in the experiment. For this purpose, a horn-type ultrasonic disruptor Digital Sonifier S-250D (Branson Ultrasonics, USA) with a stepped solid horn tip (13 mm) was used. It was found that the value of the total energy of dispersion Et required for complete destruction of soil aggregates to ESP depends on soil type and varies within 200–800 J·mL-1 for loamy soils with an organic matter content of 1.8–4.6 g. 100 g-1 soil. For sample preparation of soils for grain-size analysis with a subsequent determination of soil texture class according to Kachinsky classification, the value Et = 250 J·mL-1 is sufficient, as it allows obtaining the maximum amount of physical clay (<10 µm) at the minimum duration of sample preparation.

Pullout capacity of vertical plate anchors in unsaturated clay considering variable surface flow conditions

Vertical plate anchors are placed in the soil to improve the lateral resistance of various geotechnical structures. Extensive research has been conducted to find out the pullout capacity of vertical anchors in saturated or dry soil. Despite all these attempts, no research is available to study the behavior of anchors in unsaturated soil where the shearing resistance of soil is governed by the matric suction depending on the surface flow conditions and water table positions. Since the soil in field is mostly in unsaturated state; thus, the pullout resistance of vertical plate anchor has been aimed to be evaluated in this study. Finite element limit analysis solutions in terms of a non-dimensional pullout factor have been presented to find the pullout capacity of vertical anchors. The solutions are inclusive of the effect of soil properties, embedment depth, height of anchor plate, depth of water table from the ground surface, flow conditions and flow rate under an immediate breakaway condition. The effect of variation of other factors like the degree of saturation, unit weight of soil, van-Genuchten SWRC parameters, specific gravity of soil solids, and anchor-soil interface conditions has also been evaluated.

Laser induced breakdown spectroscopy for strength assessment in Ca binded soils

In this study, two distinct types of soil having different parent mineral (WS: White Soil and RS: Red Soil) is chosen and efforts are made to identify the presence/influence of Calcium (Ca), on these bulk soil solids following chemical processing. The two doped samples are named as “WS_DOPED” where Ca is doped in White Soil and “RS_DOPED” with Ca doped in Red Soil. Laser Induced Breakdown Spectroscopy (LIBS) is performed on the surface of these soil samples to understand the variation in spatial deposition of Ca with different soil matrices. Also, the influence onto the compressive strength of the soil samples is probed using LIBS. Using LIBS the ratio of ionization to the neutral state of the most predominant element “Silicon (Si)” in these samples are compared to the unconfined compressive strength of the WS_DOPED and RS_DOPED soil samples which is found to be 13.6 kPa and 15.7 kPa respectively wherein the virgin soil samples are non-cohesive in nature. Also, a comparison of LIBS with EDX measurements is carried out wherein LIBS found to be more sensitive towards detecting trace elements.

Localization of C Cycle Enzymes in Arable and Forest Phaeozems within Levels of Soil Microstructure.

Soil microbial and enzyme activities are closely related to the spatial variability of soil environmental conditions at the microscale (μm-mm). The origin and localization of the enzymes are somewhat neglected when the measured activity is used to evaluate specific soil functions. The activity of four hydrolytic enzymes (β-glucosidase, Cellobiohydrolase, Chitinase, Xylanase) and microbial diversity based on community-level physiological profiling were determined in samples of arable and native Phaeozems with increasing physical impact to soil solids. The level of impact on the soil solids had a significant effect on enzyme activity and depended on both the enzyme type and soil land use. The highest proportion of the activity of Xylanase and Cellobiohydrolase of arable Phaeozem was determined at the dispersion energy in the range of 450-650 J·mL-1 and was associated with the primary soil particles' hierarchy level. The highest proportions of β-glucosidase and Chitinase activities were determined for forest Phaeozem after applying energies lower than 150 J·mL-1 and characterizing the level of soil microaggregates. The increased activity of Xylanase and Cellobiohydrolase in primary soil particles of arable soil compared to those in forest soil might be a reflection of the substrates being unavailable to decomposition, leading to enzyme accumulation on the solid surface. For the Phaeozems, the lower the level of soil microstructure organization, the greater the differences observed between soils of different land use type, i.e., microbial communities, associated with lower microstructure levels, were more specific to land use type.

Assessment of nitrogen and phosphorus in the soil of longitudinal direction affected by in-situ oxidation remediation

ABSTRACT The application of in-situ chemical oxidative remediation for contaminated soils has attracted extensive attention, but the effects of remediation processes on soil physical and chemical properties are rarely studied. Herein, a ferrous-activated persulphate oxidation system for remediating dibutyl phthalate (DBP)-polluted soil was simulated in the soil column to explore the effects of in-situ oxidative remediation on soil properties in the longitudinal direction. The DBP content in the soil column was used as an indicator of oxidation strength and the correlation between N, P, soil particle size and oxidation strength was analysed. The experiment results showed that the settling performance of polluted soil after remediation improved and the distribution of the soil particle size at 128 nm disappeared after oxidation, indicating that the suspended solids in the experimental soil were mainly fine clay particles. The oxidation system can promote the conversion of organic nitrogen to inorganic nitrogen and migration characteristics of nitrogen and phosphorus, to aggravate the loss of TN and TP in the soil. The average soil particle size (d 50), TN, NH4-N, available phosphorus (Ava-P), exchangeable phosphorus (Ex-P) and organic phosphorus(Or-P) were significantly correlated with oxidation strength; and stable pH in the soil column (pH = 3), showing that the changes in the longitudinal direction of d 50 (smaller), TN, NH4-N, Ava-P, Ex-P, and Or-P resulted from the weakening of the longitudinal oxidation strength in the direction of the soil column.

Effects of Five–Year Inorganic and Organic Fertilization on Soil Phosphorus Availability and Phosphorus Resupply for Plant P Uptake during Maize Growth

A better understanding of the P dynamic resupply roles of fertilization from soil solids to solution is urgently required to optimize sustainable P fertilizer management practices for efficient supply. A five–year fertilization experiment was used to investigate the effects on soil P fractions and availability, the kinetic P resupply based on a novel simulation technique (Diffusive gradients in thin films (DGT) and DGT–induced fluxes in sediments and soils (DIFS) ) and to identify dominant factors during the maize season under five treatments (no fertilizer (CK), chemical fertilizer (NPK), chemical fertilizer combined with bone meal fertilizer (NPKC), crop straw (NPKS) and bioorganic fertilizer (NPKM)). The results showed that the NPKC and NPKM treatments had higher enhancement effects on Olsen–P and organic P and inorganic Ca2–P, Ca8–P, Al–P and Fe–P at maize growth stages, and they buffered pH decrease to delay the substantial Fe–P and Al–P release until a late stage. Inorganic Ca2–P, Ca8–P, Al–P and Fe–P heavily effected the Olsen–P levels. The NPKS, NPKC and NPKM treatments yielded higher CDGT–P levels and a stronger resupply capacity, reflected by higher R and CE/Csoln and smaller Tc values. The simulation and path model results revealed that the maize plant P uptake was determined by soil P resupply and an inorganic P supply pool. They were positively dominated by soil organic matter (SOM). Our results suggested that organic fertilization, especially NPKC and NPKM treatments, provided greater enhancement effects on the P supply pool and P resupply for higher plant P uptake, identifying them as highly effective P management practices for developing sustainable agriculture.

Case study of ground penetration radar (GPR) to assess lead migration

This paper describes research to characterize subsurface contamination caused by leaching of lead (Pb) from batteries disposed of at the surface, which has spread with groundwater movement. The contaminated soils and aquifer are located in the Matano formation (Sulawesi, Indonesia). Ground Penetrating Radar (GPR) was used to detect and delineate Pb-contaminated soils (i.e., solid-phase Pb). Lead in the solid and aqueous phase have different characteristics and responses when subjected to electromagnetic (EM) waves. Many studies have used GPR to map solid-phase Pb contamination in the subsurface. GPR uses EM as the base medium to receive subsurface images and is useful for the detection of solid-phase Pb contamination but cannot detect aqueous-phase Pb. The first step in the remediation process was to delineate solid-phase Pb contamination in the subsurface using GPR, which required a geotechnical survey to support GPR. Samples of soil and aquifer solids were then taken to quantify lead concentrations using X-ray fluorescence (XRF). We collected 15 lines of GPR measurements and 11 soil samples to quantify Pb. Frequencies of 600 MHz and 900 MHz were used for the GPR antenna. The results identified a clay layer at a depth of between 3 m and 4 m, which appears to have served as barrier to downward migration of Pb-contaminated groundwater. A shadow zone and low reflectance in the GPR subsurface section images were used to identify as the Pb contamination, which has a distinct wavelength ranging between 0.36 m and 0.45 m. We conclude from the results of this study that GPR was an effective tool for the delineation of the vertical and horizontal spread of Pb contamination eastward from the source.

Constant void ratio vs. constant confining pressure tests on partially saturated silty soil

The presence of soil solids, water, and air complicates understanding unsaturated soil dynamics. A thorough understanding of unsaturated soil behavior is essential for the fruitful design of slopes, embankments, and retaining structures. A series of constant void ratio and constant confining pressure triaxial compression tests were carried out under constant water content conditions (pore air pressure drained and pore water pressure undrained) to study the shear strength and deformation characteristics of a partially saturated silty soil. Test specimens were prepared with a water content of 15%, 20% (Optimum water content), and 25%, with the corresponding degree of saturation of 37, 49, and 62.5%. The degree of compaction of all specimens was kept at 83% while the dry density was 1.29 g/cm3, and the void ratio was around 1.045. All the samples were isotropically consolidated under 500kPa by keeping deviatoric stress at 0kPa. The constant void ratio test results showed that the deviatoric stress reached a peak value followed by a sudden decrease within the axial strain of 0-1.5%. In contrast, the deviatoric stress increased continuously until reaching the critical state without depicting any peak for constant confining pressure tests. However, in both cases, the lower the water content at the time of specimen preparation, the higher the shear resistance.

Comprehensive Multi-compartment Sampling for Quantification of Long-Term Accumulation of PAHs in Soils.

Long-term accumulation in the soils of ubiquitous organic pollutants such as many polycyclic aromatic hydrocarbons (PAHs) depends on deposition from the atmosphere, revolatilization, leaching, and degradation processes such as photolysis and biodegradation. Quantifying the phase distribution and fluxes of these compounds across environmental compartments is thus crucial to understand the long-term contaminant fate. The gas-phase exchange between soil and atmosphere follows chemical fugacity gradients that can be approximated by gas-phase concentrations, yet which are difficult to measure directly. Thus, passive sampling, measured sorption isotherms, or empirical relationships to estimate sorption distribution have been combined in this study to determine aqueous (or gas) phase concentrations from measured bulk concentrations in soil solids. All these methods have their strengths and weaknesses but agree within 1 order of magnitude except for ex situ passive samplers employed in soil slurries, which estimated much lower concentrations in soil water and gas likely due to experimental artifacts. In field measurements, PAH concentrations determined in the atmosphere show a pronounced seasonality with some revolatilization during summer and gaseous deposition during winter, but overall dry deposition dominates annual mean fluxes. The characteristic patterns of PAHs in the different phases (gas phase, atmospheric passive samplers, bulk deposition, and soil solids) confirm the expected compound-specific distribution pattern and behavior. Since revolatilization fluxes in summer are only minor and wet and dry deposition is ongoing, our results clearly show that the PAH loads in topsoils will continue to increase.

The removal of manganese ions from industrial wastewater using local Saudi and commercial bentonite clays

Manganese compounds exist naturally in the environment as solids in soils and small particles in water. Human industrial activities and the burning of fossil fuels increase the manganese concentration in the air. Studies have shown that exposure to manganese has extremely dangerous, toxic effects on humans, resulting in ailments such as the “metal fume fever” which produces symptoms such as metallic taste in the mouth, headache, fever and chills, anxieties, chest tightness, and cough. This has led many researchers to try different techniques to eliminate this harmful metal from the environment. Among methods, adsorption is one of the most effective and efficient for the removal of contaminants, such as heavy metals, from wastewater. We focused on local (from Saudi Arabia) and commercial (from India) bentonite clay to verify the importance of natural bentonite clay as an adsorbent for water treatment. While other purification techniques are expensive, bentonite clay is cheap, natural, and accessible. Therefore, we investigated how the concentration of the solution pH, temperature, adsorbent amount, contact time and bentonite procedure (washing and heat treatment) affect the removal process. Our results demonstrated success in the local bentonite clay's adsorptive capacities, and we encourage the generalization of its use in the Saudi kingdom's industries.

Flooding and drainage induced abiotic reactions control metal solubility in soil of a contaminated industrial site

Intense industrialization has led to the increasing leaching risk of metals into groundwater at heavily polluted industrial sites. However, metal dissolution in polluted industrial soils has been neither fully investigated nor quantified before. In this study, the dissolution of Zn, Ni, and Cu in soil from a heavily contaminated industrial site during a flooding-drainage period was investigated by sequential extraction, geochemical modelling, and X-ray absorption near edge structure spectroscopy. The results showed a steady decrease in metal solubility during both reduction and oxidation stages. During reduction, with limited decrease in Eh (>100 mV), formation of carbonate precipitates rather than sulfide precipitates and adsorption on soil solids was responsible for Zn and Ni dissolution, whereas bound to soil organic matter (SOM) and iron oxides dominated Cu dissolution, due to its lower concentration and higher affinity to SOM and iron oxides compared to Zn and Ni. During oxidation, the acidity caused by ferrous oxidation was buffered by calcite dissolution, while metal precipitation ceased and adsorption on soil surface controlled metal solubility. The metal solubility and speciation during the flooding-drainage process were quantitatively predicted by geochemical model. The findings demonstrate that due to high metal concentrations and weak microbial effect in the industrial soil, metal release was largely regulated by abiotic reactions rather than biotic reactions, which is somehow different from that of the wetland or rice field soils.

Simultaneous evaluation of kinetic release of labile arsenic and phosphorus in agricultural soils using cerium oxide-based DGT

The adsorption/desorption of arsenic (As) in agricultural soils is of utmost importance for the evaluation of its kinetic release and potential of entering the food chain by uptake of crops. However, the mobility of As in soils is closely related to the migration behavior of soil phosphorus (P) due to their chemical similarity. Here, the distribution and desorption kinetics of As and P in four different types of farmland soils were simultaneously estimated by cerium oxide-based diffusive gradients in thin films technique (CeO2-DGT) coupled with dynamic model of DGT induced fluxes in soils (DIFS). CeO2-DGT was deployed in the soils over 400 h to investigate the interactions between As and P for their migration behaviors. The accumulated masses of As in the DGT devices showed reverse orders with those of P among the four soils, indicating their competitive adsorption on soil solids. The distribution coefficients (Kdl) for the labile As and P derived from the DIFS model were mutually exclusive. Clay in the soil reduced the pool size of the labile As by increasing the irreversible adsorption of As on soil particles. The adsorption rate constants of As were much smaller than P but their desorption rate constants were comparable. Among the four soils, the soil with the highest soil labile As/P molar ratio measured by DGT showed the largest potential of As phytotoxicity. Both As and P could reach the equilibrium of resupply within 0.7– 18 min under DGT depletion, and significant negative correlation was observed between the desorption rate (kb) of As and clay content in the soils.