Adsorption Capacity Of Soil Research Articles

Unraveling the competitive transport of metformin and erythromycin in saturated sandy soil: Experimental investigation, modeling insights and implications on SDGs

The presence of metformin (MTN) and erythromycin (ETM) in groundwater is a growing global concern due to their persistence and toxicity. This study addresses a critical gap in understanding the fate and transport of these pharmaceutical and personal care products in saturated sandy soil columns at environmentally relevant concentrations, an underexplored area. The results show that MTN, due to its high mobility, appeared earlier in the soil column with a recovery rate exceeding 90 % and an adsorption coefficient (Kd) of 1.063 Lkg−1. In contrast, ETM, with a higher Kd value of 5.426 Lkg−1, exhibited delayed breakthrough and recovery of less than 15 %, indicating stronger adsorption potential. Desorption studies indicated a greater risk of MTN leaching into groundwater, while ETM remained strongly adsorbed to soil particles. Despite the limited organic matter content in sandy soil, a significant amount of ETM was adsorbed, suggesting sands' high adsorption capacity and potential for natural remediation. This research fills a knowledge gap regarding the adsorption capacity of sandy soils at environmentally relevant concentrations, providing essential insights for environmental risk assessments and groundwater contamination mitigation strategies, directly supporting Sustainable Development Goals 3 (Health and Well-being), 6 (Clean Water and Sanitation), and 14 (Life Below Water).

Photoaged tire wear particles hinder the transport of Pb(II) in urban soils under acid rain: Experimental and numerical investigations

Rapid urbanization brought lots of serious environmental contamination, including the accumulation of heavy metals, acid rain, and the emission of tire wear particles (TWPs), with detrimental effects for terrestrial ecosystems. Nevertheless, how naturally aged TWPs affect the mobilization of heavy metals in soils under acid rain is still unclear. Here, we investigate the adsorption and transport mechanisms of Pb(II) co-existing with acid rainwater in soil-TWP mixtures via batch experiments, column experiments and modeling. Results showed that photoaged TWP significantly prolonged the Pb(II) adsorption equilibrium time (1 to 16 h) and enhanced the Pb(II) adsorption capacity of soils. Soil column profiles confirmed that TWP effectively boosted the initial accumulation of lead in the topsoil and thus impeded the downward transport of lead. The retardation factor (R) estimated by the linear two-site sorption model (TSM) fitting the Pb(II) breakthrough curves gradually increased from 1.098 to 16.38 in soils with TWP (0–10 %). Comparative results of linear or nonlinear TSM suggested nonlinear sorption replacing linear sorption as the main Pb(II) sorption mechanism under 1 % and 10 % TWP. This research provides significant insights into the implications of TWP on the Pb(II) retention behaviors and highlights the severer potential remobilization risks of Pb(II) in urban soils under different acid rain environments.

Phosphorus Adsorption as Affected by Concretionary Nodules of Oxic Rhodustalf in Southern Guinea Savannah Agroecological Zone of Nigeria

Hard, rounded masses of mineral matter, known as concretionary nodules, can be found in soil or sedimentary rock. These nodules are typically made up of minerals like iron oxides, hydroxides, and carbonates that have been deposited in groundwater. Their sizes can range from small pebbles to large boulders, and they often differ in composition or hardness compared to the surrounding rock or soil. Nodules act as a highly effective storage space for extra P, leading to a significant increase in overall P requirements. Phosphorus, although an essential element for all living organisms, including plants and animals, is scarce. Despite its importance, only a small fraction of the total phosphorus available can be readily absorbed by plants. Given the worldwide demand for phosphorus in food production, it is crucial to devise techniques for extracting it from different sources. However, there has been limited research on the understanding of phosphorus availability and adsorption mechanisms in these areas. Therefore, the study focused on exploring the impact of concretionary nodules on phosphorus sorption and the characteristics of low-activity clay soil in the Guinea savannah of Nigeria. Soil samples collected from the study area were used to investigate the soil’s ability to absorb phosphorus at depths ranging from 0 to 30-60-90-120-150 cm in different soil and concretion locations. Various soil and concretion types demonstrated distinct capacities for phosphorus adsorption, as indicated by the adsorption isotherm. The maximum monolayer adsorption capacities (Qmax values) were 161.0, 154.5, 149.6, 141.7, 139.8, and 139.3 mg/g for OBC, OBS, OC, OIS, OS, and OIC, respectively. At equilibrium with a 50-ppm solution, the pseudo-second-order rate constants for P sorption were 1.180 x 10<sup>–4</sup>, 9.740 x 10<sup>–5</sup>, 1.120 x 10<sup>–4</sup>, 1.140 x 10<sup>–4</sup>, 1.000 x 10<sup>–4</sup>, and 8.010 x 10<sup>–5</sup> g mg<sup>–1</sup> min<sup>–1</sup> for OIS, OIC, OBS, OBC, OS, and OC, in that order. In the 300-ppm equilibrium solution, the OIS, OIC, OBS, OBC, OS, and OC pseudo-second-order rate constants were 1.250 x 10<sup>–4</sup>, 1.130 x 10<sup>–4</sup>, 9.550 x 10<sup>–5</sup>, 1.040 x 10<sup>–4</sup>, 2.750 x 10<sup>–4</sup>, and 1.420 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. At the 500-ppm equilibrium, the pseudo-second-order rate constants for OIS, OIC, OBS, OBC, OS, and OC were 1.240 x 10<sup>–4</sup>, 1.090 x 10<sup>–4</sup>, 1.020 x 10<sup>–5</sup>, 1.100 x 10<sup>–4</sup>, 2.730 x 10<sup>–4</sup>, and 1.180 x 10<sup>–4</sup> g mg<sup>–1</sup> min<sup>–1</sup>, respectively. Consequently, the soil adsorption capacity increased with higher pseudo-second-order rate constants.

Adsorption behavior and mechanism of different types of (aged) microplastics for napropamide in soils

The role of microplastics (MPs) as pollutant carriers and their influence on the fate of organic pollutants has received considerable attention. However, the impacts of MPs on the adsorption of amide herbicides in soil, have not been investigated. In this study, non-biodegradable (polyethylene, PEM) and biodegradable (polybutylene adipate terephthalate, PBATM) MPs were aged by exposure to one month of ultraviolet irradiation. The impacts of MPs on the adsorption of napropamide (Nap) in two agricultural soils (black soil [BS] and fluvo-aquic soil [CS]) were investigated through batch experiments. The findings suggested that the adsorption of Nap onto PEM was mainly governed by physical processes, while, chemical mechanisms, should not be overlooked on PBATM. With the addition of 0.2% MPs, the maximum adsorption capacity (Qm) and adsorption distribution coefficient (KF) of soil containing PEM (soil-PEM) were higher than that of soil-PBATM, however, the Qm and KF values of soil-PBATM for Nap were higher when the addition of MPs was 2%. After UV aging, the increased specific surface area of MPs led to an increased adhesion of soil particles. These were attributed to the different surface properties and concentrations of different (aged) MPs, resulting in differences in the inhibition effect by soil particles. The adhesion of soil particles was confirmed by X-ray photoelectron spectroscopy. Additionally, regardless of the addition of MPs, the Qm values of BS for Nap were higher than those for CS. In summary, MPs can alter the adsorption of Nap in soil, influencing both its mobility within the soil ecosystem and the environmental risk.

Effect of Polystyrene Microplastics on Pb(II) Adsorption onto a Loessial Soil (Sierozem) and Its Mechanism.

Microplastics (MPs) have received significant attention recently. However, their influence on soil heavy metal adsorption remains unclear. The effect of polystyrene (PS) MPs on the adsorption of Pb(II) onto a loessial soil (sierozem) was studied by batch experiments in single soil (S), soil with 1 mm PS (S-PS1), and soil with 100 μm PS (S-PS100) systems. The mechanisms of Pb(II) adsorption reduction were investigated. The adsorption of Pb(II) reached equilibrium within 12 h, and the pseudo-second-order model fitted the adsorption processes best. The Langmuir adsorption model provided a better fit to the isotherms, compared to the Freundlich one. The presence of PS decreased the level of adsorption of Pb(II). Larger PS particle size, dose, and fulvic acid (FA) concentration inhibited Pb(II) adsorption onto the soil. The solution pH value showed a positive correlation with the adsorption amount. The adsorption amounts (q e) of Pb(II) in binary metal systems (Cu-Pb and Cd-Pb) were lower than those in single Pb systems, indicating the competitive adsorption among the ions. The adsorption amount presented a trend of S > S-PS100 > S-PS1. The primary mechanism on which PS reduced the adsorption of Pb(II) was the "dilution effect" of MPs. Conclusively, the presence of MPs might elevate the availability of heavy metals by reducing the soil's adsorption capacity for them and then amplifying the risk of heavy metal contamination and migration.

Removal of Cefuroxime from Soils Amended with Pine Bark, Mussel Shell and Oak Ash

The global increase in antibiotics consumption has caused hazardous concentrations of these antimicrobials to be present in soils, mainly due to the spreading of sewage sludge (or manure or slurry) and wastewater, and they could enter the food chain, posing serious risks to the environment and human health. One of these substances of concern is cefuroxime (CFX). To face antibiotics-related environmental pollution, adsorption is one of the most widely used techniques, with cost-effective and environmentally friendly byproducts being of clear interest to retain pollutants and increase the adsorption capacity of soils. In light of this, in this work, three low-cost bioadsorbents (pine bark, oak ash, and mussel shell) were added to different soil samples (at doses of 12 and 48 t/ha) to study their effects on the adsorption of CFX. Specifically, batch experiments were carried out for mixtures of soils and bioadsorbents, adding a range of different antibiotic concentrations at a fixed ionic strength. The results showed that the addition of pine bark (with pH = 3.99) increased the adsorption to 100% in most cases, while oak ash (pH = 11.31) and mussel shell (pH = 9.39) caused a clearly lower increase in adsorption (which, in some cases, even decreased). The Freundlich and linear models showed rather good adjustment to the experimental data when the bioadsorbents were added at both doses, while the Langmuir model showed error values which were too high in many cases. Regarding desorption, it was lower than 6% for the soils without bioadsorbents, and there was no desorption when the soils received bioadsorbent amendments. These results show that the addition of appropriate low-cost bioadsorbents to soils can be effective for adsorbing CFX, helping in the prevention of environmental pollution due to this emerging contaminant, which is a result of clear relevance to environmental and human health.

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Soil Properties Related to Phosphorus Sorption and Prediction of Maximum Phosphorus Adsorption Capacity of Soils from Southern Brazil

Phosphate removal by acid-activated and chitosan-composite clayey soils

Phosphate is a vital nutrient for aquatic organism growth, but excessive levels can lead to eutrophication, with detrimental effects on receiving water bodies. Adsorption using clay soils can address phosphate release and has gained attention owing to its cost-efficiency and environmental friendliness. To overcome the limited phosphate adsorption capacity of clay soils due to surface charges, the combined effects of acid activation and composite formation with chitosan were investigated. Kaolin and bentonite were selected for acid activation, while chitosan varieties with low, medium, and high molecular weights were chosen for composite formation. Batch tests were individually conducted on acid-activated clay soils and composites of acid-activated clay soils with chitosan over 24 h, varying the initial phosphate concentrations. For acid activation, clay soils were treated with 6N hydrochloric acid, whereas composite formation was achieved via combination with each chitosan variant. Acid-activated kaolin and bentonite individually exhibited phosphate removal efficiencies ranging 99.8–79.8% and 97.1–47.2%, respectively. Among their respective composites, acid-activated kaolin with medium-molecular-weight chitosan and acid-activated bentonite with low-molecular-weight chitosan had the highest phosphate removal efficiencies. Therefore, in contrast to kaolin, acid activation or composite formation of acid-activated bentonite with chitosan can improve its phosphate removal efficiency.

The interaction between nutrients and heavy metals in lakes and rivers entering lakes

This study investigated the conditions and modes of interaction between nutrients and heavy metals within river and lake environments under multivariate conditions. Nitrogen and phosphorus nutrients were categorized into dissolved phosphorus, inorganic phosphorus, dissolved nitrogen, ammonium nitrogen, and nitrate nitrogen based on their chemical composition. Their correlations with heavy metal elements were scrutinized utilizing Bayesian models. The results revealed the following: (1) A robust interrelationship was observed between sediment metals and soluble metals within lake sediments and water bodies. (2) In lake environments, the competition between metals was relatively weak, and the influence of environmental factors was variable, without discernible patterns. This phenomenon may be attributed to the low concentration of soluble metals in the overlying water in the absence of external inputs. (3) Competition between metals in river sediment was weaker than that in lakes. This may be attributed to the flow dynamics and velocity of rivers, coupled with their strong self-purification ability. (4) Dissolved phosphorus (DP) exhibited greater control over the direction of metal adsorption and desorption compared to inorganic phosphorus (IP). (5) Similarly, dissolved total nitrogen (DTN) exhibited greater control over the direction of metal adsorption and desorption in river sediments compared to total nitrogen (TN). (6) Nitrate (NO3–-N) and ammonium (NH4+-N) simultaneously controlled the adsorption and desorption directions of metals such as Cr, Mn, Ni, Zn, and Pb in river sediment, with the direction of metal action dependent on soil adsorption capacity. These findings provide valuable insights into the complex interactions shaping nutrient-metal dynamics in aquatic systems, offering potential avenues for enhanced environmental management and remediation strategies.

Respective evolution of soil and biochar on competitive adsorption mechanisms for Cd(II), Ni(II), and Cu(II) after 2-year natural ageing

To reveal the respective evolution of soil and biochar on competitive heavy metal adsorption mechanisms after natural ageing, three soils and two biochars were tested in this study. The soil-biochar interlayer samples were buried in the field for 0.5, 1, and 2 years, for which competitive adsorption characteristics and mechanisms of soils and biochars in four systems (Cd, Cd+Ni, Cd+Cu, and Cd+Ni+Cu) were investigated. Results showed that physicochemical properties, adsorption capacity and mechanisms of soils and biochars all changed the most in the first 0.5 years. The properties and adsorption capacity of biochars gradually weakened with the ageing time, meanwhile, those of soils gradually enhanced. After co-ageing with acidic soil for 0.5 years, the Cd(II) adsorption capacity of modified biochar decreased by 86.59% in the ternary system; meanwhile, that of acidic soil increased by 65.52%. The contributions of mineral mechanisms decreased significantly, while non-mineral mechanisms were slightly affected by ageing. This study highlighted that when using biochar to remediate heavy metal-contaminated soils, biochar should be applied at least half a year in advance before planting crops so that biochar can fully contact and react with the soil.

Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

The effects of Cu-phenanthrene co-contamination on adsorption-desorption behaviors of phenanthrene in soils

Polycyclic aromatic hydrocarbons (PAHs) are persistent organic pollutants in the environment, which are teratogenic, carcinogenic, and mutagenic. Co-contamination of PAHs and heavy metal commonly exists in soil. In this study, 20 types of soils with different properties in China were collected and comprehensively characterized. Phenanthrene (Phe) and Cu (II) were selected as representatives of PAHs and heavy metals, respectively. The adsorption-desorption behaviors of Phe under Phe contamination and Cu (II)-Phe co-contamination in 20 types of soils were studied. The adsorption-desorption behaviors of Phe in 20 types of soils varied greatly, and adsorption of Phe in the soils followed both linear partitioning and nonlinear surface adsorption. Soil organic matter (SOM) plays an important role in the adsorption-desorption behavior of Phe. When the concentrations of Phe were >50 μg/L, soft carbon (SC) fraction of SOM not black carbon (BC) contributed more to the adsorption of Phe. Soil dissolved organic matter (DOM), especially fulvic acid and humic acid fractions, contributes to the adsorption of Phe. Under the effect of Cu (II) (60 mg/L in solution), the adsorption capacity of soil for Phe increased, which possibly resulted from lowered pH, the existence of the cation-π bonding and the "bonding bridge" effect. The systematic investigation of adsorption-desorption behaviors of Phe in soils under heavy metal-PAHs co-contamination will provide a scientific basis for the calculation of soil environmental capacity in the future.

Irrversible cesium adsorption capacity of granite-origin soil

Irrversible cesium adsorption capacity of granite-origin soil

Migration of nanocolloid-carrying antibiotics in paddy red soil during the organic fertilization process

Soil nanocolloids are highly mobile and can act as carriers for the transport of antibiotics to a wider and deeper range of soils; however, the inherent behavior and mechanism of nanocolloid-carrying antibiotics in soil remain unclear. In this study, we conducted a comprehensive investigation of the migration of antibiotics in paddy red soil during the organic fertilization process using four common soil nanocolloids: kaolin (KL), montmorillonite (MT), hematite (HT), and humic acid (HA). The results showed that nanocolloid carriers promoted the intra-medium (from soil surface to the bottom) and inter-medium transfer (from organic fertilizers to soil) of antibiotics. The migration mechanisms of antibiotics carried by the nanocolloids differed: the phenolic hydroxyl and carboxyl groups of HA esterified with the carboxyl groups of quinolones and phenolic hydroxyl groups of tetracyclines, respectively, while the oxygen atoms of HT formed stabilizing complexes with the soil, which could further adsorb antibiotics using their functional group-rich complexes. Smaller antibiotic compounds were adsorbed in the metal oxide interlayer of MT via cation exchange, whereas KL adsorbed antibiotics on its metal oxide surface layer in the same way but were susceptible to desorption. Additionally, nanocolloids changed the adsorption capacity of soil for antibiotics and influenced the enrichment of dominant/functional bacteria (e.g., Burkholderiaceae) and thus varied the vertical distribution of antibiotics in soil. These findings enhance our understanding of the migration behavior and mechanism of nanocolloid-carrying antibiotics in red paddy soil and provide a theoretical foundation for preventing and controlling antibiotic pollution in arable systems.

A novel eco-friendly strategy for removing phenanthrene from groundwater: Synergism of nanobubbles and rhamnolipid

Nanobubbles (NBs), given their unique properties, could theoretically be paired with rhamnolipids (RL) to tackle polycyclic aromatic hydrocarbon contamination in groundwater. This approach may overcome the limitations of traditional surfactants, such as high toxicity and low efficiency. In this study, the remediation efficiency of RL, with or without NBs, was assessed through soil column experiments (soil contaminated with phenanthrene). Through the analysis of the two-site non-equilibrium diffusion model, there was a synergistic effect between NBs and RL. The introduction of NBs led to a reduction of up to 24.3 % in the total removal time of phenanthrene. The direct reason for this was that with NBs, the retardation factor of RL was reduced by 1.9 % to 15.4 %, which accelerated the solute replacement of RL. The reasons for this synergy were multifaceted. Detailed analysis reveals that NBs improve RL's colloidal stability, increase its absolute zeta potential, and reduce its soil adsorption capacity by 13.3 %–19.9 %. Furthermore, NBs and their interaction with RL substantially diminish the surface tension, contact angle, and dynamic viscosity of the leaching solution. These changes in surface thermodynamic and rheological properties significantly enhance the migration efficiency of the eluent. The research outcomes facilitate a thorough comprehension of NBs' attributes and their relevant applications, and propose an eco-friendly method to improve the efficiency of surfactant remediation.

The effect of water molecules on paraquat salts: from physicochemical properties to environmental impact in the Brazilian Cerrado.

Introduction: The green revolution model that is followed in the Brazilian Cerrado is dependent on mechanization, chemical fertilization for soil dressing and correction, and the use of herbicides. Paraquat is a methyl viologen herbicide marketed as bipyridylium dichloride salts and used (in low doses) to combat weeds in their post-emergence stage. It is a non-selective pesticide that causes the peroxidation of the lipids that make up the cell membrane, and when it comes into contact with foliage, it results in the death of the plant. Methods: The effect of water molecules co-crystallized in Paraquat salt structures was analyzed in anhydrous, dihydrate, and trihydrate forms to understand those physicochemical properties in its redox activity. The frontier molecular orbitals were also carried out using DFT to obtain the chemical reactivity of the bipyridylium cation. Finally, the supramolecular arrangements were evaluated to analyze the physicochemical stability and acquire insights on superoxide anions. Results and discussion: The electronic structure indicated that the BP cation presents an acidic character due to its low ELUMO value, while the salt has a more basic character due to its high EHOMO value. For this reason, the BP ion is more susceptible to reduction during the weeds' photosynthesis process. During the process of plant photosynthesis, PQ is reduced to form a stable radical cation. In the supramolecular arrangement, the presence of water molecules increases the number of strong H-bonds, while the weak/moderate H-bonds are stabilized. PQ's toxic effects are observed in wildlife, domesticated animals, human populations, and ecosystems. The influence of PQ on the terrestrial environment is limited because of the soil adsorption capacity associated with good agricultural practices. The current use of good agricultural practices in the Cerrado seems not to prevent the environmental impacts of herbicides like PQ because it aims for the expansion and profitability of large-scale farming based on input-intensive practices instead of sustainable agriculture processes.

The effect of slow adsorption of phosphate on its transport during the infiltration process in saturated agricultural soils

ABSTRACT Assessment of phosphorus (P)-infiltrating croplands is essential for the preservation of the water environment. It has been pointed out that a huge discrepancy lies in the different evaluation methods of P adsorption, such as batch experiments and column experiments, which makes it difficult to demonstrate P mobility under flow conditions. The objective of this study was to evaluate the applicability of the convective-dispersion equation using the parameters of the Langmuir-type isotherm obtained from batch experiments with different reaction times: the adsorption capacity of soil (q max) = 0.112 (g kg−1) for a Gray lowland soil with 24 h reaction time, q max = 0.484 (g kg−1) for an Andosol (volcanic ash soil) with 24 h reaction time, and q max = 1.17 (g kg−1) for an Andosol with 32 d reaction time, for describing P mobility in typical Japanese agricultural soils under fast flow conditions. The breakthrough curves of P infiltrating the soil columns demonstrate nonequilibrium P adsorption by the soil. The chemical nonequilibrium model, with a kinetic adsorption rate of α = 0.40 (Gray lowland soil) and 0.098 (Andosol), succeeded in describing the observations in the column experiments. Compared with Gray lowland soil, which is relatively rich in iron oxide, P mobility was largely affected by kinetic sorption in Andosol, which is relatively rich in allophane. It is suggested that the P adsorption capacity of soils should be evaluated reflecting the soil composition in order to simulate the P mobility under flow conditions. In particular, the slow adsorption (long-lasting adsorption) of P by the soil should be considered in the estimation of the P transport.

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.