Adsorption Capacity Of Soil Research Articles

Processing toxic metal source proxies appropriately for better spatial heterogeneity source apportionment

Soil toxic metals have strong spatial heterogeneity, and their sources vary among regions. Thus, this study integrated the Catreg and geographically weighted regression (GWR) models to quantitatively extract the main source proxies (numerical and categorical variables were analyzed simultaneously) for different toxic metals and analyze the spatial heterogeneity of the distributions of these sources. Pb, Cd and Hg were the predominant toxic metals in soil. Of the samples with Pb, Cd and Hg, 84.12 %, 68.03 % and 41.57 % exceeded the background values, and 5.36 %, 6.42 % and 5.43 % were moderately contaminated according to the geoaccmulation index, respectively. Industrial activities, with relative importance values of 17.82 %, 31.54 % and 26.51 % for Cd, Hg and Pb, respectively, were the predominant source of these metals especially, in their high-content cluster areas (central urban areas). Soil available phosphorus was another important factor (relative importance values of 13.03 %, 13.41 % and 25.55 % for Cd, Hg and Pb, respectively), and agricultural activities (especially the overuse of phosphoric fertilizers) were identified as an anthropogenic source of these toxic metals. Soil parent material had the greatest influence on As and Cr, with relative importance values of 19.88 % and 19.09 %, respectively, especially in their high-content accumulation area (the eastern coastal area), indicating that these toxic metals mainly come from natural sources. Slope had important impacts on toxic metal accumulation (relative importance values of 17.48 %, 21.22 %, 12.40 % and 16.13 % for Cd, Hg, Cr and As, respectively) by influencing industrial distribution and pollutant migration. By changing the soil adsorption capacity, soil organic matter (explaining 13.01 % of Pb) and soil pH (explaining 14.58 % of As and 12.40 % of Cr) strongly influenced toxic metal accumulation. This study highlights the benefits of the integrated Catreg-GWR model for analyzing multiple spatially heterogeneous environmental data types (numerical and categorical variables), providing a potential foundation for local pollution prevention.

The Effects of Biochar on Exchangeable Metal Concentration in Paddy Soils

The presence of metals in soil may impact the environment, as well as agricultural products. Biochar can alter some physical and chemical properties of the soil, reducing the concentrations of exchangeable metals in the soil. The aim of this study was to examine the effects of biochar on the exchangeable metal concentration in two paddy soils that have different organic carbon (OC) contents. A pot experiment was conducted in a greenhouse using two soils with high (3.05%) and low (0.54%) OC content mixed with biochar at rates of 0, 1.5, 3, 6, and 12%, and planted with rice in two consecutive seasons. At the end of each season, 30 soil samples (2 soil types x 5 biochar rates x 3 replicates) were collected to determine the exchangeable concentration of Al, Fe, Mn, Cd, Ni, Pb, and Zn, as well as pH. The metal quality index was calculated using principal component/factor analysis. The results showed that biochar increased the pH value after the first rice crop but did not improve after the second rice season. Biochar reduced the exchangeable concentration of some metals, including Al, Fe, Ni, Cd, Pb, and Zn. Compared to the no-biochar treatment, biochar application increased the soil metal quality index from 4.1 to 12.8% after the first crop and from 9.6 to 188.7% after the second rice crop, depending on soil properties and used biochar rate. This effect could be related to the increased pH in biochar-added soil and biochar's adsorption capacity. In conclusion, biochar has promising prospects for reducing exchangeable metal content in arable soils, thus exhibiting the potential to be used in paddy fields to remediate metal-contaminated soils.

Enhancing adsorption capacity and herbicidal efficacy of 2,4-D through supramolecular self-assembly: Insights from cocrystal engineering to solution chemistry

Highly water-soluble pesticides have garnered significant attention due to their poor durability and severe environmental damage caused by easy leaching. Cocrystallization based on a supramolecular self-assembly mechanism has been demonstrated to be an effective method for tuning the dissolution of pharmaceuticals and agrochemicals. However, as a strategy to tune the properties of solid materials, cocrystal engineering appears to be challenging to apply to many liquid formulations of pesticides. Herein, cocrystal of the 2,4-dichlorophenoxyacetic acid (2,4-D) and phenazine (PHE) were developed to explore whether supramolecular assembly in the solid state could be extended to the solution. In the crystalline state, the cocrystal reduced the solubility and dissolution rate of 2,4-D by 71.51 % and 50.55 %, respectively. Notably, when applied in solution, 2,4-D - PHE cocrystal exhibits greater soil adsorption capacity and lower leaching characteristics than pure 2, 4-D. Specifically, only 75% of the cocrystal was leached when 2,4-D was fully leached. Under simulated rainfall, the biological activity experiments in the greenhouse demonstrated that the control efficacy of cocrystal was almost twice as that of the pure 2,4-D. Additionally, two-dimensional NOE Spectroscopy (2D NOESY) and molecular simulations were employed to reveal the mechanism of supramolecular assembly in crystal lattice and aqueous solution. This work reveals that cocrystal engineering is a promising strategy for bridging solid-state and solution chemistry through supramolecular self-assembly to improve the persistence and decrease the off-target threat of highly water-soluble pesticides.

Modified rice husk hydrochars enhanced surfactant leaching remediation of phenanthrene pyrene contaminated soil

AbstractThe adsorption capacity of soil itself makes it difficult to efficiently remove phenanthrene and pyrene from soil by direct leaching. In this article, hydrochar was introduced into the leaching process after modification, and the enhanced leaching effect of hydrothermal carbon was explored under various influencing factors. The experimental results show that the modified hydrochar competes with the soil for adsorption during the leaching process, promotes the desorption of pollutants and adsorbs some pollutants in the leaching solution, which greatly enhances the leaching effect. The elution of phenanthrene increased from 64.06% to 91.08% and of pyrene from 70.26% to 91.13% under the optimum enhanced drenching conditions. This work provides some new ideas for the removal of PAHs from the natural soil environment.

Sorption and mobility of cadmium in soil impacted by irrigation waters

Soil contamination by Cd has drawn global attention, while how irrigation waters modulate Cd sorption and mobility in soil remains obscure. We address this by investigating how cropped sandy soil irrigated with different waters altered Cd sorption and mobility using a rhizobox experiment followed by a batch experiment. Maize were planted in the rhizoboxes and irrigated by reclaimed water (RW), livestock wastewater (LW) and deionized water (CK), respectively. The bulk soil sampled from each treatment after 60 days of growth was employed to measure the Cd sorption and mobility using the isothermal adsorption and desorption experiments. The results showed that, in a small rhizobox experiment, the adsorption rate of Cd by the bulk soil in the adsorption phase was much faster than the desorption rate in desorption phase. Irrigation with RW and LW both reduced the Cd adsorption capacity of soil, and the reducing degree brought by LW was more obvious. Cd desorption rate was very low but keep increasing in the desorption stage, and pre-RW irrigation had the potential to increase Cd desorption from soil. Although the results were obtained based on the bulk soil sampled from a rhizobox experiment, our study strongly suggests that the altered Cd adsorption and desorption behavior in the soil caused by the RW and LW irrigation may risk the farmland ecosystem and deserve more concern.

Fine Particle Adsorption Capacity of Volcanic Soil from Southern Kyushu, Japan.

"Akahoya" is a volcanic soil classified as a special soil deposited in Kyushu, Japan. Many of its properties are not yet clearly understood. We found that Akahoya had the potential to adsorb bacteria in cattle feces, which prompted us to investigate its material properties and perform experiments to comprehensively evaluate its adsorption performance for various fine particles such as acidic and basic dyes, NOx/SOx gas, and phosphoric acid ions, in addition to bacteria. Akahoya had a very high specific surface area owing to the large number of nanometer-sized pores in its structure; it exhibited a high adsorption capacity for both NO2 and SO2. Regarding the zeta potential of Akahoya, the point of zero charge was approximately pH 7.0. The surface potential had a significant effect on the adsorption of acidic and basic dyes. Akahoya had a very high cation exchange capacity when the sample surface was negatively charged and a high anion exchange capacity when the sample surface was positively charged. Akahoya also exhibited a relatively high adsorption capacity for phosphoric acid because of its high level of Al2O3, and the immersion liquid had a very high Al ion concentration. Finally, filtration tests were performed on Escherichia coli suspension using a column filled with Akahoya or another volcanic soil sample. The results confirmed that the Escherichia coli adhered on the Akahoya sample. The results of the Escherichia coli release test, after the filtration test, suggested that this adhesion to Akahoya could be phosphorus-mediated.

Assessing the Effect of Intensive Agriculture and Sandy Soil Properties on Groundwater Contamination by Nitrate and Potential Improvement Using Olive Pomace Biomass Slag (OPBS)

The relationship between agricultural activities, soil characteristics, and groundwater quality is critical, particularly in rural areas where groundwater directly supplies local people. In this paper, three agricultural sandy soils were sampled and analyzed for physicochemical parameters such as pH, water content, bulk density, electrical conductivity (EC), organic matter (OM), cation exchange capacity (CEC), and soil grain size distribution. Major and trace elements were analyzed by inductively coupled plasma-optical emission spectrometry (ICP/OES) to determine their concentrations in the fine fraction (FF) of the soils. Afterward, the elemental composition of the soils was identified by X-ray powder diffraction (XRD) and quantified by X-ray fluorescence (XRF). The surface soil characteristics were determined by the Brunauer–Emmett–Teller (BET) method, whereas the thermal decomposition of the soils was carried out using thermogravimetric analysis and differential scanning calorimetric (TGA-DSC) measurements. The morphological characteristics were obtained by scanning electron microscopy (SEM). Afterward, column-leaching experiments were conducted to investigate the soil’s retention capacity of nitrate (NO−3). Parallelly, a chemical and physical study of olive pomace biomass slag (OPBS) residue was carried out in order to explore its potential use as a soil additive and improver in the R’mel area. The OPBS was characterized by physicochemical analysis, assessed for heavy metals toxicity, and characterized using (XRD, XRF, SEM, and BET) techniques. The results show that the R’mel soils were slightly acidic to alkaline in nature. The soils had a sandy texture with low clay and silt percentage (<5% of the total fraction), low OM content, and weak CEC. The column experiments demonstrated that the R’mel irrigated soils have a higher tendency to release large amounts of nitrate due to their texture and a higher degree of mineralization which allows water to drain quickly. The OPBS chemical characterization indicates a higher alkaline pH (12.1), higher water content (7.18%), and higher unburned carbon portion (19.97%). The trace elements were present in low concentrations in OPBS. Macronutrients in OPBS showed composition rich in Ca, K, and Mg which represent 10.59, 8.24, and 1.56%, respectively. Those nutrients were quite low in soil samples. Both XRD and XRF characterization have shown a quasi-dominance of SiO2 in soil samples revealing that quartz was the main crystalline phase dominating the R’mel soils. Oppositely, OPBS showed a reduced SiO2 percentage of 26,29% while K, Ca, and P were present in significant amounts. These results were confirmed by XRF analysis of OPBS reporting the presence of dolomite (CaMg, (CO3)2), fairchildite (K2Ca (CO3)2), and free lime (CaO). Finally, the comparison between the surface characteristic of OPBS and soils by BET and SEM indicated that OPBS has a higher surface area and pore volume compared to soils. In this context, this study suggests a potential utilization of OPBS in order to (1) increase soil fertility by the input of organic carbon and macronutrients in soil; (2) increase the water-holding capacity of soil; (3) increase soil CEC; (4) stabilize trace elements; (5) enhance the soil adsorption capacity and porosity.

Red Mud-Amended Soil as Highly Adsorptive Hybrid-Fill Materials for Controlling Heavy Metal Sewage Seepage in Industrial Zone.

With the rapid development of urbanization, the problem of environmental pollution is becoming more and more serious. As a major pollutant, heavy metals have caused serious contamination in soil and groundwater. In order to prevent the diffusion of heavy metals in the soil from industrial sewage, the concept of hybrid-fill layer construction improved by red mud was proposed in this study. This study examines the adsorption capacities of lead and zinc ions and engineering characteristics on red mud-amended soils by direct shear, permeability, adsorption, desorption batch and column tests. Two mixing methods, full particle size displacement mixing and partial particle size displacement mixing, were adopted. The results showed that red mud effectively increased the adsorption capacity of soil to heavy metal ions, and the desorption rate of ions after adsorption was less than 3%, which had good anti-desorption ability. The optimum content of red mud in hybrid-fill material can be determined as 20%. The direct shear test showed that the internal friction angle of hybrid-fill material was 38.9°, and the cohesive force was 30.3 kPa, which met the engineering strength requirements of foundation materials. Based on the test results, red mud can be used as a barrier material to prevent heavy metal contamination in industrial sewage from diffusion, which controls not only heavy metal contamination but also consumes industrial by-products.

Ecological risk assessment based on soil adsorption capacity for heavy metals in Taihu basin, China

Due to the toxicity, bioaccumulation, non-biodegradability and perseverance of heavy metals, their risk assessment is essential for soil quality management. The Hakanson potential ecological risk index (RI), which considers the effects of heavy metal concentration and toxicity, has been widely used in soil ecological risk assessment. However, RI overlooks the influence of soil properties on the mobility and availability of heavy metals in risk assessment. To fill this gap, this study sought to develop an improved ecological risk index (IRI), which incorporates soil adsorption into RI, and applied it to evaluate the ecological risk of heavy metals in the soil of the Taihu basin, China. The soil adsorption models based on the Gradient Boosting Decision Tree (GBDT) was used to predict the soil adsorption capacity of five heavy metals (i.e. cadmium, chromium, copper, lead, zinc). The soil adsorption capacity in 1446 sites in the Taihu basin was predicted by the GBDT models and was assigned as the weight of IRI. The risk assessment results of the five metals in the Taihu basin showed that 40% of the sites were at a moderate risk level and 60% of the sites were at a slight risk level based on the RI. The value of IRI in the basin ranged from 11.1 to 75.5, with a mean value of 28.1. IRI differed from RI in spatial distribution due to the influence of soil adsorption. The comparative analysis between the metal contents in sediments and surrounding soils confirmed the tremendous influence of soil adsorption on ecological risks, indicating that soil adsorption should be taken into consideration in soil risk assessment.

Adsorption of nonylphenol on coastal saline soil: Will microplastics play a great role?

Microplastics widely exist in diverse matrices to become important hosts of pollutants. Little information regarding adsorption of emerging contaminants on coastal saline soils influenced by co-existing microplastics is available. Thus, the adsorption behaviors of nonylphenol (NP) on coastal saline soil influenced by microplastics were discussed. Polyvinyl chloride (PVC, 4.7 mm), polyethylene (4.85 mm), and polypropylene (4.51 mm) with addition dose of 10% were used to discuss the effect of microplastic type on adsorption of NP by coastal saline soil while PVC samples with size of 4.7 mm and 0.11 mm were used to explore the effect of microplastic size on NP adsorption. The NP adsorption capacity of the saline soil containing 10% of PVC (4.7 mm) was twice that of soil without PVC. Smaller-size PVC (0.11 mm) with addition amount of 10% enhanced the NP adsorption capacity of the coastal saline soil by 117% to reach 8.91 μg g−1. The desorption capacity of NP on saline soil decreased from 40% to 30% of total adsorption capacity with co-existing PVC. Adsorption/desorption kinetics of NP on coastal saline soil with PVC microplastics could be well explained by pseudo second order model while Freundlich model could better fit the isotherm data of NP adsorption/desorption to show possible occurrence of the multiple-layer adsorption. This study will provide new information regarding the environmental behaviors of typical emerging contaminants on coastal saline soil containing microplastics.

Adsorption behavior of enrofloxacin in soil and sediment and its response mechanism to environmental factors

ABSTRACT As an important part of lake and reservoir ecosystem, sediment is an important “source” and “sink” of pollutants. Antibiotics, as a kind of important emerging organic pollutants, have attracted global attention. In order to understand the adsorption behavior and mechanism of antibiotics in sediment, enrofloxacin (ENR) was used as the target pollutant to evaluate its adsorption behavior in sediment and soil and the response mechanism of environmental factors by using the intermittent equilibrium method. The results showed that the adsorption equilibrium time of ENR in sediment and soil was 6 h, and the adsorption kinetics was in line with the quasi-second-order kinetics. The two-compartment model Herry-Langmuir can better describe the adsorption of ENR by sediment and soil. There is a lag phenomenon in desorption process.The average lag coefficient HI of sediment and soil was 1.08 × 10−3 and 0.43 × 10−3, respectively, indicating that ENR was difficult to be released. When pH = 5, the adsorption capacity is the highest, indicating that the adsorption mechanism of ENR in the sample is mainly cation exchange; the higher the cationic valence state of the background liquid is, the stronger the competitive adsorption capacity is, which leads to the gradual decrease of ENR adsorption capacity in the sample. Because ENR contains -F group, resulting in complex reaction with Al3+ in the solution, thus reducing the activity of Al3+, reducing the competitive adsorption of Al3+ and ENR, then ENR adsorption capacity increased. The change of ENR adsorption capacity of sediment and soil is Q(Al3+)>Q(Na+)>Q(K+)>Q(Ca2+)>Q(Mg2+)>Q(Fe3+). The adsorption capacity of ENR on sediment was higher than that on soil under all conditions.

Effects of dissolved organic matter on the adsorption of norfloxacin on a sandy soil (fraction) from the Yellow River of Northern China

Dissolved organic matter (DOM), which exists widely in the environment, coming from different sources, may greatly affect the adsorption of antibiotics. However, the adsorption mechanisms of antibiotics in a sandy soil and the effects of DOM from different sources on the adsorption remain poorly understood. This study systematically investigated the adsorption characteristics of norfloxacin (NOR) onto a sandy soil obtained from the banks of Xi'an in Yellow River and in the presence of three DOM including HDOM (commercially available humic acids), LDOM (derived from fallen leaves) and MDOM (derived from cattle manure). Elemental analysis, UV–vis spectroscopy, 3D-EEM, XPS, TOC, SEM, and FTIR were used to analyze the adsorption mechanism. It was found that all the DOM sources we used could reduce the adsorption of NOR on sandy soil and prolong the reaction time to reach adsorption equilibrium. The decreasing adsorption capacities of NOR by the three types of DOM (10 mg/L) followed the order as: HDOM < LDOM < MDOM, which was related to their aromaticity, polarity and hydrophobicity. These adsorption processes of NOR on sandy soil in the presence of DOM were well fitted by Double-chamber first-order kinetics, Linear model and Freundlich models. Besides, the adsorption reaction was endothermic and spontaneous. Adsorption competition of DOM molecules with NOR, or formation of DOM-NOR complexes in solution resulted in a decrease of sandy soil adsorption capacity. Correspondingly, co-adsorption and cumulative adsorption were also considered to be the key processes that determined NOR adsorption towards sandy soil after adding DOM. Moreover, the adsorption of NOR onto sandy soil exhibited strong pH-dependent characteristic and NOR might be more easily leached from sandy soil in the aquifer at an alkaline pH. High-ion strength suppressed the adsorption. These results would help to understand the fate and risk of NOR under the action of different DOM.

The potential of organomineral amendments in increasing the adsorption of lead (Pb) and cadmium (Cd) in a sandy loam soil

Sandy loam soils contain low organic carbon and have low ion adsorption capacity. Under certain conditions, the soils contain heavy metals that are harmful to plants. Soil amendments such as biosilica and humic acid from natural sources are expected to increase the soil adsorption capacity to heavy metals. A simulation experiment consisting of two factors was conducted to explore the effectiveness of humic and biosilica, as soil amendments, in adsorbing heavy metals from soils. The first factor was biosilica dose composing 0 t ha&lt;sup&gt;-1&lt;/sup&gt; (S0), 0.5 t ha&lt;sup&gt;-1 &lt;/sup&gt;(S1), 1 t ha&lt;sup&gt;-1 &lt;/sup&gt;(S2), and 1.5 t ha&lt;sup&gt;-1 &lt;/sup&gt;(S3). The second factor was the humic acid dose composing 0 kg ha&lt;sup&gt;-1&lt;/sup&gt; (H0), 20 kg ha&lt;sup&gt;-1&lt;/sup&gt; (H1), 40 kg ha&lt;sup&gt;-1&lt;/sup&gt; (H2), and 60 kg ha&lt;sup&gt;-1&lt;/sup&gt; (H3). The humic acid and biosilica were applied to soil contaminated with Pb and Cd. The results showed that the combination of 0.5 t biosilica ha&lt;sup&gt;-1&lt;/sup&gt; (S1) and 20 kg humic acid ha&lt;sup&gt;-1&lt;/sup&gt; (H1) significantly increased soil pH, organic C content, cation exchange capacity, and reduced the availability of Pb and Cd at 90 days after treatment. The Pb and Cd contents in plant tissue decreased from roots to grains. Humic acid treatment was more effective in absorbing Pb of 86.89-90.49% and Cd of 71.47-76.33% than other treatments.

Iron-Modified Biochar Strengthens Simazine Adsorption and Decreases Simazine Decomposition in the Soil.

Currently, modified biochar has been successfully used in the remediation of soil polluted with heavy metals. However, the effects of the modified biochar on pesticides (such as simazine) are still unclear. Herein, the environmental fate of simazine, such as decomposition, leaching, and adsorption in unamended soil, in the soil amended with unmodified and modified biochar (biochar + FeCl3, biochar + FeOS, biochar + Fe) were evaluated. In addition, an incubation experiment was also performed to observe the influence of modified biochar on the microbial community and diversity in the soil. The results showed that modified biochar significantly decreased the decomposition of simazine in the soil compared to its counterpart. Modified biochar also reduced the concentration of simazine in the leachate. Compared with the control, soil microbial biomass in the soil amended with unmodified biochar, biochar + FeCl3, biochar + Fe, and biochar + FeOS was decreased by 5.3%, 18.8%, 8.7%, and 18.1%, respectively. Furthermore, modified biochar changed the structure of the microbial community. This shows that modified biochar could increase the soil adsorption capacity for simazine and change the amount and microbial community that regulates the fate of simazine in the soil. This study concludes that iron-modified biochar has positive and negative effects on the soil. Therefore, its advantages and side effects should be considered before applying it to the soil.

Adsorption Characteristics of Three Types of Soils on Biogas Slurry Ammonium Nitrogen

Using farmland to digest biogas slurry is an effective measure to overcome the bottleneck of sewage treatment in livestock and poultry farms. However, there is limited research on the soil adsorption characteristics of biogas slurry ammonium nitrogen (NH4+-N). In addition, the maximum adsorption capacity (Qm) of farm soil is unclear. In this study, three typical farmland tillage layer soils (silty loam, loam, and sandy loam) were used to analyze adsorption characteristics through adsorption kinetics experiments (adsorption for 0.25, 0.5, 1, 2, 4, 6, 12, 18, or 24 h with NH4+-N concentrations of 42.90 mg/L) and thermodynamic experiments (adsorption for 3 days with NH4+-N concentrations of 54.25, 88.66, 105.85, 133.71, 178.80, 273.54, and 542.87 mg/L). The Qm value was fitted by models, and its relationship with soil properties was discussed. The results showed the following: 1) the adsorption of biogas slurry NH4+-N by the three types of soils was a composite kinetic process that comprised two stages of rapid and slow reactions. Rapid adsorption predominantly occurred within 0–1 h, and the adsorption capacity accounted for 35.24%–43.55% of the total adsorption. The ExpAssoc equation produced a good fit for the adsorption kinetic behavior in the three soil types. 2) The equilibrium adsorption could be described by the Langmuir equation, the Freundlich equation, the PlPlatt model, and the Langevin model isotherm, among which the Langevin model had the best fit, with a coefficient of determination R2 close to 1. The theoretical saturated Qm fitting results of NH4+-N were 1038.41–1372.44 mg/kg in silty loam, 840.85–1157.60 mg/kg in loam, and 412.33–481.85 mg/kg in sandy loam. The optimal values were 1108.55, 874.86, and 448.35 mg/kg for silty loam, loam, and sandy loam, respectively. 3) The Qm value was significantly positively correlated with soil organic matter, total nitrogen, available phosphorus, available potassium, cation exchange capacity, and particle content of 0.02–0.002 mm (p &amp;lt; 0.01), but significantly negatively correlated with soil pH (p &amp;lt; 0.05). This study can provide a reference for the safe application of biogas slurry on farmland.

Adsorption Kinetics and Adsorption Thermodynamic Properties of Dibutyl Phthalate (DBP) Building Materials in Black Soil

The adsorption of organic pollutants by soil has an important impact on their migration, transformation and bioavailability. Black soil is rich in organic matter that plays an essential role in adsorption, which indicates that black soil may have a high adsorption capacity for DBP. The significant DBP adsorption capacity of black soil was discovered through research into the adsorption kinetics and thermodynamic properties of DBP in black soil. This finding was consistent with pseudo-second-order kinetics. The adsorption was chemical adsorption, and intramolecular diffusion was a critical control step in the adsorption process. The adsorption equilibrium time was 24 h. Analyzing the effects of temperature, pH, ionic strength and other conditions, it was found that reducing the temperature promoted the adsorption of DBP. When the pH was 7, the adsorption capacity was the greatest. The capacity of DBP to adsorb was boosted by the rise in ionic strength, which also hindered DBP adsorption once it reached a certain threshold.

Effect of Acid–Base Modified Biochar on Chlortetracycline Adsorption by Purple Soil

We used three purple soil (Hechuan, Jialing, and Cangxi) samples from the Jialing River basin as the research objects and added different proportions of an acid–base modified Alternanthera philoxeroides biochar (Cm) to the purple soil to study the effect of Cm on the adsorption of chlortetracycline (CTC) in the purple soil. The results indicated the following: (1) At 30 °C and pH = 6, the soil adsorption capacity increased with an increasing initial concentration of CTC. The maximum adsorption amount of CTC for each tested sample was in the range of 2054.63–3631.21 mg/kg, and the adsorption capacity in different Cm amended soils was ranked in the order of 10% Cm &gt; 5% Cm &gt; 2% Cm &gt; CK. The adsorption capacity of CTC increased with an increase in the proportion of Cm. Furthermore, under the same addition ratio of Cm, Hechuan soil was found to have a better adsorption effect for CTC than Jialing and Cangxi soil. (2) The Langmuir model was the most suitable for fitting the adsorption behavior of CTC on different purple soils, and the fitting coefficients were all greater than 0.9, indicating that the adsorption of CTC on each soil sample occurred via monolayer adsorption. The thermodynamic experiment results showed that an increase in temperature was beneficial to the process of CTC adsorption, which was a spontaneous, endothermic, and entropy-adding process. (3) At pH = 6, the ionic strength ranged from 0.01 to 0.5 mol/L and the adsorption capacity of CTC of the soil samples decreased with an increase in ionic strength. In the range of pH 2–10, the adsorption capacity of CTC in all the soil samples decreased with an increase in pH. The inhibition capacity of CTC in the soil samples under acidic conditions was notably higher than that under alkaline conditions.

Greater impacts of phosphorus fertilization on soil phosphatase activity in tropical forests than in non-tropical natural terrestrial ecosystems: A meta-analysis

In phosphorus (P)-poor tropical forests, soil microorganisms are hypothesized to depend on organic P sources more intensively than in other natural terrestrial ecosystems. I tested this hypothesis by conducting a meta-analysis to compare soil phosphatase activity responses to experimental P fertilization between tropical forests and other natural terrestrial ecosystems. I found that P fertilization significantly reduced soil phosphatase activity in tropical forests, and to a significantly greater extent than in non-tropical natural terrestrial ecosystems including temperate forests, supporting the above hypothesis. I suggest three potential mechanisms for this result. First, inorganic P supply may be lower in tropical forests; however, this mechanism is less likely because inorganic P input into tropical forests soils via biological processes is not necessarily small. Second, the strong P adsorption capacity of tropical soils may substantially reduce inorganic P availability, thereby enhancing microbial organic P dependence. Third, higher P demand due to higher biological productivity in tropical forests may intensify microbial organic P dependence.

Earthworm inoculation and straw return decrease the phosphorus adsorption capacity of soils in the Loess region, China

Loess Plateau is important for maize production in China. Therefore, a good understanding of soil phosphorus (P) behavior in the Loess region is crucial for optimizing fertilization in its agriculture systems. To date, research on factors influencing P adsorption/desorption has mainly focused on fertilization. Widespread application of straw return and increasing soil fauna in agricultural croplands inevitably affect soil P behavior either directly or indirectly in this area. However, less attention has been focused on these effects and their interactions. Here, a field plot experiment was performed based on a completely randomized design to investigate the response of P adsorption–desorption characteristics to the presence/absence of earthworms and straw return. Treatments included: (1) control without earthworms and straw (E0S0); (2) treatment with only earthworms (E1S0); (3) treatment with only straw (E0S1); (4) treatment with both earthworms and straw. The Langmuir model was superior to the Freundlich model in interpreting the P adsorption data and allowed better evaluation of the maximum P adsorption values. The maximal P adsorption, P adsorption affinity constant, and maximum buffer capacity in the earthworm and straw treatments were 2.4–8.3%, 8.3–13.9%, and 2.2–26.3% lower than those in E0S0. The readily desorbable P, standard P requirement, and degree of P saturation increased by 15.6–44.3%, 13.1–23.1%, and 4.4–16.5%, respectively, in earthworm and straw treatments. Additionally, earthworm inoculation and straw return treatments significantly increased total soil P, Olsen P, soil organic carbon, free Fe2O3, and CaCO3 contents and specific surface area of the soil. Redundancy analysis showed that soil organic carbon explained most (14.7%) of the total variation in P adsorption and desorption. These results show that combining earthworm inoculation with straw return can effectively reduce soil P adsorption capacity, increase its P desorption capacity, and thus, increase its available P content. These results provide a scientific basis for improving the utilization efficiency of soil P.

HYDRUS-2D simulations of typical pollutant migration in a soil aquifer system in the Zibo-Weifang funnel area of China

To clarify the removal trends of typical pollutants in recharged water samples during soil aquifer treatment (SAT), especially the recharging performances in the funnel areas of arid regions, the Zibo-Weifang funnel area of China was selected as an example where the effects of dry-wet ratio (DWR, the ratio of the dry period to irrigation period), wet period duration (WPD, duration of one irrigation period), irrigation side length (ISL) and irrigation depth (ID) on the 50-year SAT performance were simulated using HYDRUS-2D. Experimental results revealed that the operational parameters of the DWR, WPD, ISL and ID exhibited significant effects on the bulk removal of chemical oxygen demand (COD), nitrate (NO3−), ammonium (NH4+), total phosphorus (TP) and hexavalent chromium (Cr6+). Eventually, the optimal conditions with a DWR of 3, WPD of 7 d, ISL of 100 m, and ID of 200 cm were selected for the SAT based on the simulations, and irrigation loads as high as of 84.12 m/yr were obtained. During the 50-year irrigation simulation, as much as 256 Mm3/yr of new water would be recharged into the Shandong Plain, which would be accompanied by the effective removal of COD, NH4+, TP and Cr6+. In contrast, the NO3− concentrations within the obtained SAT effluent (50 m depth) were higher than those of the influent, which were closely related to the insufficient carbon sources in the deep soil and poor soil adsorption capacity. Thus, a more stringent threshold value for the nitrate reinjection concentration (e.g., 12 mg/L) was proposed. In addition, the pollutants, NO3−, NH4+, TP and Cr6+ all exhibited a penetration potential and posed potential pollution threats, especially under higher irrigation loads. Therefore, appropriate pretreatment measures should be strongly considered for the practical operation of SAT systems.