In order to study the effect of cadmium ions on the mechanical properties and micro-structure characteristics of the red clay in Guilin, we have conducted triaxial test and the scanning electron microscope tests to analyze the effects of cadmium ion concentration and the number of dry and wet cycles on the mechanical properties and micro-structure changes of the red clay. The results showed the effects of cadmium ions and dry-wet cycles destroy the structure of red clay. The cohesive force of red clay decreases with the increase of cadmium ion concentration, and the internal friction angle first increases and then decreases. With the rise in the number of dry and wet cycles, the cohesive force of cadmium-contaminated red clay first increases and then decreases, and the angle of internal friction rises gradually. Under the action of different cadmium ion concentrations, the stress-strain curve is strain hardening. With the concentration of cadmium ions increases, the strain hardening becomes more apparent; the peak value reached faster. and the axial strain corresponding to the peak value of the line decreases. With the increase in the number of wet and dry cycles, the volume of cadmium-contaminated red clay shrinks and its compactness increases; it gets the peak shear strength faster during the shearing process, and its peak value becomes larger and larger. The main reason for the phenomenon is that cadmium ions destroy the cementation between the particles. The soil particles are mainly in point contact which loosens the structure of the soil; on the other hand, the thickness of the surface diffusion layer of the clay particles increases through chemical action, The exchange of cations increases the porosity of the soil and weakens its strength. The dry-wet cycle shrinks the volume of the red clay, and the soil particles are mainly in surface contact; as the number of dry-wet cycles increases, the soil particles connection is closer, the soil porosity decreases and the strength increases.

The inconsistency of available methods and the lack of harmonization in current microplastics (MPs) analysis in soils demand approaches for extraction and quantification which can be utilized across a wide variety of soil types. To enable robust and accurate assessment of extraction workflows, PET MPs with an inorganic tracer (Indium, 0.2% wt) were spiked into individual soil subgroups and standard soils with varying compositions. Due to the selectivity of the metal tracer, MPs recovery rates could be quickly and quantitatively assessed using ICP-MS. The evaluation of different methods specifically adapted to the soil properties were assessed by isolating MPs from complex soil matrices by systematically investigating specific subgroups (sand, silt, clay, non-lignified and lignified organic matter) before applying the workflow to standard soils. Removal of recalcitrant organic matter is one of the major hurdles in isolating MPs for further size and chemical characterization, requiring novel approaches to remove lignocellulosic structures. Therefore, a new biotechnological method (3-F-Ultra) was developed which mimics natural degradation processes occurring in aerobic (Fenton) and anaerobic fungi (CAZymes). Finally, a Nile Red staining protocol was developed to evaluate the suitability of the workflow for non-metal-doped MPs, which requires a filter with minimal background residues for further chemical identification, e.g. by μFTIR spectroscopy. Image analysis was performed using a Deep Learning tool, allowing for discrimination between the number of residues in bright-field and MPs counted in fluorescence mode to calculate a Filter Clearness Index (FCI). To validate the workflow, three well-characterized standard soils were analyzed applying the final method, with recoveries of 88% for MPs fragments and 74% for MPs fibers with an average FCI of 0.75. Collectively, this workflow improves our current understanding of how to adapt extraction protocols according to the target soil composition, allowing for improved MPs analysis in environmental sampling campaigns.

Source apportionment can be an effective tool in mitigating soil pollution but its efficacy is often limited by a lack of information on the factors that influence the accumulation of pollutants at a site. In response to this limitation and focusing on a suite of heavy metals identified as priorities for pollution control, the study established a comprehensive pollution control framework using factor identification coupled with spatial agglomeration for agricultural soils in an industrialized part of Zhejiang Province, China. In addition to elucidating the key role of industrial and traffic activities on heavy metal accumulation through implementing a receptor model, specific influencing factors were identified using a random forest model. The distance from the soil sample location to the nearest likely industrial source was the most important factor in determining cadmium and copper concentrations, while distance to the nearest road was more important for lead and zinc pollution. Soil parent materials, pH, organic matter, and clay particle size were the key factors influencing accumulation of arsenic, chromium, and nickel. Spatial auto-correlation between levels of soil metal pollution and industrial agglomeration can enable a more targeted approach to pollution control measures. Overall, the approach and results provide a basis for improved accuracy in source apportionment, and thus improved soil pollution control, at the regional scale.

Fungicide application for controlling fungal diseases can increase copper (Cu) accumulation in soil. More urgently, Cu released from fungicides can associate with soil clay and favour the mutual aggregation of Cu and soil clay, thereby potentially intensifying the accumulation of Cu. We investigated the effects of Cu salt and six common Cu-based fungicides on colloidal dynamics of a clay fraction from citrus cultivated soil. Batch experiments were carried out to provide the loading capacity of the clay fraction for Cu. The colloidal dynamic experiments were performed over a pH range from 3 to 8 following a test tube method, while surface charge, the key electrochemical factor of the solid-liquid interface, was quantified by a particle charge detector. It was found that all the studied fungicides, via releasing Cu²⁺, acted to effectively favour clay aggregation. The dissolved organic matter obtained from the dissolution of polymers in fungicides can theoretically stimulate clay dispersion. However, their effects were obscured due to the overwhelming effect of Cu²⁺. Therefore, Cu²⁺ appears as the most active agent in the fungicides that intensifies clay aggregation. These findings imply that the intensive application of fungicides for plant protection purposes can inadvertently reduce clay mobility, favour the co-aggregation of clay and fungicides, and hence potentially exacerbate the contamination of the citrus soil.

Plastic mulching and straw incorporation are common agricultural practices in China. Plastic mulching is suspected to be a significant source of microplastics in terrestrial environments. Straw incorporation has many effects on the storage of soil organic carbon (SOC) and greenhouse gas emissions, but these effects have not been studied in the presence of microplastic pollution. In this study, 365-day soil incubation experiments were conducted to assess the effects of maize straw and polyethylene microplastics on SOC fractions and carbon dioxide (CO₂) and nitrous oxide (N₂O) emissions in two different soils (fluvo-aquic and latosol). Against the background of straw incorporation, microplastics reduced the mineralization and decomposition of SOC, resulting in a microbially available SOC content decrease by 18.9%. In addition, microplastics were carbon-rich, but relatively stable and difficult to be used by microorganisms, thus increasing the mineral-associated SOC content by 52.5%. This indicated that microplastics had adverse effects on microbially available SOC and positive effects on mineral-associated SOC. Microplastics also decreased coarse particulate SOC (>250 μm), and increased non-aggregated silt and clay aggregated SOC (<53 μm). Furthermore, microplastics changed microbial community compositions, thereby reducing the CO₂ and N₂O emissions of straw incorporation by 26.5%–33.9% and 35.4%–39.7%, respectively. These results showed that microplastics partially offset the increase of CO₂ and N₂O emissions induced by straw incorporation. Additionally, the inhibitory effect of microplastics on CO₂ emissions in fluvo-aquic soil was lower than that in latosol soil, whereas the inhibitory effect on N₂O emissions had the opposite trend.

Surfactants, after use, enter the environment through diffuse and point sources such as irrigation with treated and non-treated waste water and urban and industrial wastewater discharges. For the group of non-ionic synthetic surfactant alcohol ethoxylates (AEOs), most of the available information is restricted to the levels and fate in aquatic systems, whereas current knowledge of their behavior in soils is very limited. Here we characterize the behavior of different homologs (C12–C18) and ethoxymers (EO3, EO6, and EO8) of the AEOs through batch experiments and under unsaturated flow conditions during infiltration experiments. Experiments used two different agricultural soils from a region irrigated with reclaimed water (Guadalete River basin, SW Spain). In parallel, water flow and chemical transport were modelled using the HYDRUS-1D software package, calibrated using the infiltration experimental data. Estimates of water flow and reactive transport of all surfactants were in good agreement between infiltration experiments and simulations. The sorption process followed a Freundlich isotherm for most of the target compounds. A systematic comparison between sorption data obtained from batch and infiltration experiments revealed that the sorption coefficient (Kd) was generally lower in infiltration experiments, performed under environmental flow conditions, than in batch experiments in the absence of flow, whereas the exponent (β) did not show significant differences. For the low clay and organic carbon content of the soils used, no clear dependence of Kd on them was observed. Our work thus highlights the need to use reactive transport parameterization inferred under realistic conditions to assess the risk associated with alcohol ethoxylates in subsurface environments.

For many years, the dispersal of modified clay (MC) has been used to control harmful algal blooms (HABs) in coastal waters of China. MC flocculation efficiency can be influenced by many factors in variable and complex natural environments, including high concentrations of dissolved organic matter (DOM) in the water to be treated. Since many HABs occur in nearshore waters where DOM concentrations are high, this is a significant problem that requires urgent attention. This study involved the use of humic acid as a representative form of DOM to study the influence of organic matter on the MC flocculation process. At high concentrations, humic acid was adsorbed onto MC particles, resulting in a decrease in surface potential and an increase in electrostatic repulsion between the clay particles; this decreased the MC settling rate and increased the water clarification time. Flocs were characterized by their relatively small particle size, high particle concentration, and low collision efficiency, which together resulted in slow clarification of the water after MC spraying. Based on the mechanism of the DOM-MC interaction and combined with the Derjaguin-Landau-Verwey-Overbeek theory and theoretical considerations of clay surface modification, the “ionic atmosphere compression” method was used to improve MC flocculation efficiency in high-organic water. This method increased the ionic strength of the clay stock solution by adding salt, thereby compressing the ionic atmosphere of MC particles and lowering the potential barrier, allowing the MC particles in the treated water to flocculate rapidly and form large flocs, followed by further floc growth and rapid settling via differential sedimentation. The settling rate of MCs improved by a factor of two and the removal efficiency of the HAB cells increased by 7–28%. This study provides important baseline information that will extend the application of MC to HAB control in water bodies with high organic loadings.

Soils have the ability to modify contaminant bioavailability and toxicity. Prediction the modifying effect of soil on arsenic phytoaccumulation and phytoavailability using either soil property data or soil chemical extraction data in risk assessment of contaminated soil is highly desirable. In this study, plant bioassays important to ecological receptors, were conducted with 20 soils with a wide range in chemical and physical soil properties to determine the relationships between As measured by soil chemical extraction (soil pore water, Bray-1, sodium phosphate solution, hydroxylamine hydrochloride, and acid ammonium oxalate) or soil physico/chemical properties on arsenic phytotoxicity and phytoaccumulation. Soil pore water As and Bray-1 extracted As were significantly (P < 0.01) correlated with lettuce tissue As and those extractants and sodium phosphate were correlated with ryegrass tissue As. Hydroxylamine and acid ammonium oxalate extractions did not correlate with plant bioassay endpoints. Simple regression results showed that lettuce tissue relative dry matter growth (RDMG) was inversely related to tissue As concentration (r² = 0.85, P < 0.01), with no significant relationship for ryegrass. Soil clay exhibited strong adsorption for As and significantly reduce tissue As for lettuce and ryegrass. In addition to clay content, reactive aluminum oxide (AlOx), reactive Fe oxide (FeOx) and eCEC was inversely related to ryegrass tissue As. Multiple regression equation was strongly predictive (r² = 0.83) for ryegrass tissue As (log transformed) using soil AlOx, organic matter, pH, and eCEC as variables. Soil properties can greatly reduce contaminant phytoavailability, plant exposure and risk, which should be considered when assessing contaminant exposure and site-specific risk in As-contaminated soils.

Southwestern China contains the largest and most well-developed karst region in the world, and the potentially toxic elements (PTEs) content in the soils of the region is remarkably high. To explore the internal and external control factors and sources of soil PTEs enrichment in this area and to provide a basis for the treatment of PTE pollution, 113 soil samples were collected from Hengxian County, a karst region in Guangxi Province, southwestern China. The importance of eighteen influencing factors including parent material, weathering, physicochemical properties, topography and human activities were quantitatively analyzed by (partial) redundancy analysis. The sources of PTEs were identified using the Pb isotope ratio and absolute principal component score/multiple linear regression (APCS-MLR) model. The contents of all soil PTEs were higher than the corresponding background values of Guangxi soils. The contents in Cu, Zn, Cd, Hg and Pb were the highest in the soil from carbonate rock. The factor group of geological background and weathering explained 26.5% for the accumulation and distribution of soil PTEs and the influence of physicochemical properties was less than 2% but increased to 25.6% through interaction with weathering. Fe (47.1%), Al (42.1%), Mn (22%), chemical index of alteration (12.8%) and clay (11.9%) were the key factors affecting the soil PTEs, while the influence of human activities was weak. Pb isotope ratio and APCS-MLR classified 62.8–74% of soil PTEs as derived from natural sources, whereas 18.23% and 18.95% were derived from industrial activities and agricultural practice/traffic emissions, respectively. The Pb isotope ratio showed that the natural sources account for up to 90% of the Pb in the soil from carbonate rock, the highest contribution among the studied soils. The results of the study can provide background information on the soil PTEs contamination in the karst areas of China and other areas worldwide.

Pharmaceutically active compounds (PhACs) have attracted increasing attention due to their large consumption volumes, high bioactivity and potential ecotoxicity. In this study, a total of 150 commonly used drugs were investigated in sediments of Jiaozhou Bay (JZB). Twenty-five target compounds were detected, of which ten were discovered for the first time in marine sediments. The range of total PhAC content was 3.62–21.4 ng/g dry weight. Ketoprofen (2.49 ng/g), oxytetracycline (1.00 ng/g) and roxithromycin (0.97 ng/g) were the preponderant PhACs. PhACs gradually decreased from east to west, and the distribution of PhACs in the sediment was controlled by the source channel, seawater dynamic process and sediment composition. The diatom, organic matter, and clay proportions in the sediments and the nutrients in the overlying water were the most important environmental factors affecting the distribution of PhACs. PhAC pollution in the sediments of the JZB exhibited an increasing trend. Coprostanol could be used as a chemical indicator of the PhAC concentration in JZB sediments. PhACs were mainly derived from direct pollution due to human fecal excretion in the eastern region. Ofloxacin, tetracycline and oxytetracycline were found to pose high or medium risks to aquatic organisms. It is necessary and urgent to improve the treatment technology of drug residues in sewage treatment plants to decrease the pollution of PhAC residues. With the continuous aging of the global population, the use of PhACs will increase rapidly, which may cause more unpredictable threats to the marine ecosystem. Therefore, the monitoring of PhACs in the marine environment needs to be strengthened, and studies on PhAC occurrence and effects must be considered a priority in global environmental research.