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Extracellular DNA (eDNA) is widely present in soil, with potential ecological impacts. Metal cations are naturally present on the surface of soil clay minerals, although the adsorption mechanism of eDNA on clay minerals saturated with metal cations is still not fully understood. The research investigated the adsorption of eDNA, using salmon sperm DNA as a representative, on metal cation (Na+, Ca2+, and Fe3+)-saturated montmorillonites (Mt). Metal cation-saturated Mt have higher adsorption capacities for DNA. Compared with Mt (3500 mg⋅kg−1), the amounts of DNA adsorption on metal cation-saturated Mt (pH = 7.0) were increased by 0.74–5.38 times, and followed the descending order of Fe-Mt > Na-Mt > Ca-Mt > Mt. A temperature of 25 °C was found to be more suitable than 15 and 35 °C for DNA adsorption, while an increasing pH value (3.0–9.0) reduced DNA adsorption on Mt and metal cation-saturated Mt. Microscopic and spectroscopic analyses, together with a model computation technique, confirmed that metal cations saturated on the surface of Mt work like a "cation bridge" linking oxygen atoms in the phosphate groups of DNA and the negatively charged moieties of Mt, which were predominantly bound through electrostatic forces, thus, facilitating DNA adsorption at pH > 5. The results of this investigation provide valuable insight into eDNA adsorption on soil clay minerals and the transport and fate of eDNA in the natural soil environment. Image 1 • Metal cation saturation enhances surface properties of montmorillonites. • Metal cation-saturated montmorillonites have higher adsorption capacity for DNA. • DNA molecules cannot intercalate into the montmorillonite layers. • Metal cations as "bridges" link with the oxygen atoms of DNA phosphate groups. [ABSTRACT FROM AUTHOR]

Multiple antibiotics that are used in veterinary medicine coexist in soils, but their interaction and the effects on adsorption and desorption in soils have not been extensively studied. In this study, using batch experiments, we evaluated the adsorption and desorption of sulfadiazine (SDZ), tetracycline (TC), and norfloxacin (NFX) using four different soil aggregate size fractions and discovered that: (1) TC had the highest adsorption (76–98 %) and the lowest desorption in each tested system, whereas SDZ showed opposite adsorption and desorption ability, (2) the highest adsorption and the lowest desorption of all three tested antibiotics were observed with soil macroaggregates (250–2000 µm) in all the cases; in contrast, opposite adsorption and desorption ability were observed for soil clay (<53 µm), and (3) adsorption of each antibiotic was in the following order: single system (71–89 %) > binary system (56–84 %) > ternary system (50–78 %); however, desorption were in the reverse order. The Freundlich equation fitting and Brunauer–Emmett–Teller (BET) analysis further demonstrated that the adsorption competition between the tested antibiotics depended mainly on the specific surface area of each soil aggregate size fractions and its chemical properties. In conclusion, soil macroaggregates play a key role in the retention of antibiotics in soils, and the coexistence of multiple antibiotics greatly increases leaching risk. [Display omitted] • Soil macroaggregates (250–2000 µm) showed the highest adsorption rate and the lowest desorption rate for the tested antibiotics. • The adsorption rates of the antibiotics were in the following order: tetracycline > norfloxacin > sulfadiazine. • The adsorption capacity of each antibiotic was in the following order: single system > binary system > ternary system. This is mainly attributed to the number of available adsorption sites. • Brunauer–Emmett–Teller (BET) analysis showed that the specific surface area of each soil component affects the adsorption of antibiotics. [ABSTRACT FROM AUTHOR]

A clayey soil is an electrically charged porous medium whose behavior is sensitive to the variations in the composition and concentration of pore water. Pronounced physicochemical interaction can occur between the solid particle and the pore water so that the clayey soil shows strong chemomechanical coupling effects and complex mechanical behaviors. If the degree of saturation varies the pore-water composition and concentration can also vary, resulting in intensive physicochemical effects in the soil. In this paper, a conceptual constitutive model for unsaturated soils is proposed to explain the influence of pore-fluid chemistry on the chemomechanical behavior of unsaturated clayey soils. A new intergranular stress which can effectively account for the physicochemical effects including osmosis, capillarity, and adsorption is introduced as the stress-state variable. The formulation of the proposed model can lead to a remarkable unification of the experimental results obtained under complex chemomechanical loading conditions. The proposed model is validated by comparing the theoretical calculations with the experimental results. It is shown that the proposed model is capable of addressing the effect of water content, concentration and species variation on the mechanical behavior of the clayey soil. [ABSTRACT FROM AUTHOR]

The paper presents the results of laboratory studies of the 200 MPa pressure effect on specific surface area of clay. The original high-pressure investigation stand was used for the pressure tests. Determination of the specific surface area was performed by the methylene blue adsorption method. The results of the specific surface area test were compared for non-pressurized clays and for clays pressured in a high-pressure chamber. It was found that the specific surface area of pressurized soil clearly increased. This shows that some microstructural changes take place in the soil skeleton of clays. [ABSTRACT FROM AUTHOR]

• Ability of agricultural clay soil to adsorb Cd, Cu and Cr from water was modelled. • Simulations using PHREEQC geochemical modelling coupled to parameter estimation. • Maximum adsorption efficiencies of Cd, Cu and Cr onto the soil observed at pH 6. • Adsorption of the elements by the soil will be effective in all seasons of the year. • Exudates released by plants will reduce the adsorption of the elements by the soil. Although minerals such as gold and platinum are important for improving life, their processing comes with social and environmental problems. During the processing of these minerals, toxic elements such as cadmium, copper and chromium are released along with wastewater into the environment including soils and surface water leading to plausible migration to groundwater. The removal of these elements from aqueous solutions is of utmost importance however, where no remediation is implemented, the ability of the soil to retain the elements and prevent migration is crucial. Moreover, there is a need for reliable and accurate computational modelling programs that requires minimum set of experiments for calibration in order to determine the success of the sorption of elements by natural and man-made adsorbents since laboratory and field experiments can be expensive, time consuming and often require repetition. In this study, the ability of an agricultural clay soil to adsorb and retain cadmium (Cd), copper (Cu) and chromium (Cr) was investigated by simulating different conditions using PHREEQC (which stands for, pH, re dox, eq uilibrium written in the C language) geochemical modelling code coupled to parameter estimation (PEST). The role of pH (2–9) on the adsorption of Cd, Cu and Cr onto generalised weak, strong and super strong sites of the agricultural soil was determined and used to calibrate the model. The soil was found to be effective in preventing the mobility of Cd, Cu and Cr to groundwater however, the presence of competing ions and plant exudates increased their mobility. PHREEQC geochemical modelling code coupled with PEST was found to be a quick and a reliable tool to determine the performance of natural and man-made adsorbents in different conditions. Thus, PHREEQC coupled to PEST is a suitable decision making tool for environmental sustainability. [Display omitted] [ABSTRACT FROM AUTHOR]

Understanding the adsorption behavior of radiocesium (RCs) in natural soils is crucial for remediation and evaluation of radioactive contaminated sites. In this study, we investigated the adsorption behavior of Cs(I) onto natural soils collected in Beijing by batch adsorption experiments and sequential extraction. A multi-site adsorption model was built to quantitatively analyze the adsorption capacities of soil clay minerals and predict of Cs(I) adsorption ratio of different adsorption sites. Linear programming calculations show that illite/smectite (I/S) mixture and illite(I) are the mainly clay mineral composition. Batch adsorption experiment results show that soils adsorption of Cesium ions is an exothermic process, and the order of influence of competitive cations on the competitive adsorption strength of Cs(I) is:K+>Mg2+≈Ca2+>Na+. HA (Humic Acid)has little effect on soil adsorption. SEM-EDS analysis shows that Cs+ is mainly distributed on the surface (PS) of soil particles. Based on the above results, the adsorption of Cs(I) onto clay minerals in soils is well predicts in both linear programming calculations and a multi-site adsorption model. The multi-site adsorption model can quantitatively describe and predict the adsorption behavior of Cs(I) on different clay sites in the soils. Frayed edge sites (FES) in the soil can effectively fix trace RCs. The higher concentration of cesium ions is mainly adsorbed on the PS and TIIS. Sequential extraction experiment further proved the adsorption form of cesium in soil under trace and high concentration conditions. [Display omitted] • Linear programming was used to quantify the adsorption of Cs(I) onto soils. • Illite and illite/smectite dominate the adsorption of Cs(I) onto natural soils. • A multi-site adsorption model was built to analyze the adsorption capacities. • Cs(I) adsorption ratio of adsorption sites were calculated and proved. [ABSTRACT FROM AUTHOR]

Precise prediction of uranium adsorption at water-mineral interface is of great significance for the safe disposal of radionuclides in geologic environments. Surface complexation modeling (SCM) as a very useful tool has been extensively investigated for simulating adsorption behavior of metals/metalloids at water-mineral interface. Numerous studies concerning the fitting of uranium adsorption on various adsorbents using SCM are well documented, but the systematic and comprehensive review of uranium adsorption using various SCM is not available. In this review, we briefly summarized the rationale of SCM, including constant-capacitance-model (CCM), diffuse-layer-model (DLM), triple-layer-model (TLM); The recent progress in the application of SCM on the fitting of uranium adsorption towards metal (hydr)oxides, clay minerals and soil/sediments was reviewed in details. This review hopefully provides the beneficial guidelines for predicting the transport and fate of uranium in geologic environments beyond laboratory timescales. [Display omitted] • The rationale of various surface complexation modeling (SCM) was briefly summarized. • Application of SCM on uranium sorption on various adsorbents was detailed reviewed. • Understanding the sorption mechanism of uranium at water-mineral interface. • Beneficial guidelines for the actual treatment of radionuclides in environment. [ABSTRACT FROM AUTHOR]

Phenazines, a large group of nitrogen-containing heterocycles with promising bioactivities, can be widely used as medicines and pesticides. But phenazines also generate toxicity risks due to their non-selective DNA binding. The environmental fate of phenazines in soils is the key to assess their risks; however, hitherto, there have been very few related studies. Therefore in the present study, the degradation, adsorption and leaching behaviors of a typical natural phenazine—phenazine-1-carboxamide (PCN) in agricultural soils from three representative places in China with different physicochemical properties were, for the first time, systematically studied in laboratory simulation experiments. Our results indicated that the degradation of PCN in all the tested soils followed the first order kinetics, with half-lives ranging from 14.4 to 57.8 d under different conditions. Soil anaerobic microorganisms, organic matter content and pH conditions are important factors that regulating PCN degradation. The adsorption data of PCN were found to be well fitted using the Freundlich model, with the r2 values above 0.978. Freundlich adsorption coefficient K f of PCN ranged from 5.75 to 12.8 [(mg/kg)/(mg/L)1/n] in soils. The retention factor R f values ranged from 0.0833 to 0.354, which means that the mobility of PCN in the three types of soil is between immobile to moderately mobile. Our results demonstrate that PCN is easily degraded, has high adsorption affinity and low mobility in high organic matter content and clay soils, thus resulting in lower risks of contamination to groundwater systems. In contrast, it degraded slowly, has low adsorption affinity and moderately mobile in soils with low organic matter and clay content, therefore it has higher polluting potential to groundwater systems. Overall, these findings provide useful insights into the future evaluation of environmental as well as health risks of PCN. Image 1 • This is the first report of the environmental behaviors of phenazine in soils. • Anaerobic microorganisms were more important than the aerobic for degradation of PCN. • PCN easily degraded, has high adsorption and low mobility in high OMC and clay soils. • PCN in high OMC and clay soils has lower contamination risks to groundwater systems. PCN degraded slowly, has low adsorption affinity and moderate mobility in low OMC and clay content soils, therefore has higher polluting potential to groundwater systems. [ABSTRACT FROM AUTHOR]