Mercapto-palygorskite efficiently immobilizes cadmium in alkaline soil and reduces its accumulation in wheat plants: A field study

Cadmium (Cd) contamination in wheat fields has become a major environmental issue in many regions of the world. Mercapto-palygorskite (MPAL) is a high-performance amendment that can effectively immobilize Cd in alkaline wheat soil. However, MAPL as an in-situ Cd immobilization strategy for alkaline wheat soil remains to be evaluated on a field-scale and the underlying mechanisms requires further evaluation. Here, MPAL were used as soil amendment to evaluate their immobilization efficiency on Cd-contaminated alkaline soil in the field experiments. The field experiments showed that MPAL application significantly reduced wheat grain Cd concentration from 0.183 mg/kg to 0.056 mg/kg, with Cd concentration in wheat grain treated with MPAL all falling below the limit value of 0.1 mg/kg as defined in China's food safety standard (GB 2762-2022). The maximal immobilization efficiency of MPAL on soil Cd figured out by diethylenetriaminepentaacetic acid (DTPA) extraction was 61.5%. The mechanisms involved in Cd immobilization by MPAL were mainly related to the enhanced sorption of Cd onto Fe oxides, and the removal of amorphous or free Fe oxides from soil had a substantial impact on Cd immobilization efficiency by MPAL. Furthermore, the antagonistic effect between Mn and Cd uptake may also contribute to the reduction of wheat Cd accumulation after MPAL application. The current research can provide theoretical and technical support for the large-scale application of MPAL in Cd-contaminated wheat fields.

Effects of Fe oxides and their redox cycling on Cd activity in paddy soils: A review

Cadmium (Cd) contamination of soils is a global problem, particularly in paddy soils. Fe oxides, as a key fraction of paddy soils, can significantly affect the environmental behavior of Cd, which is controlled by complicated environmental factors. Therefore, it is necessary to systematically collect and generalize relevant knowledge, which can provide more insight into the migration mechanism of Cd and a theoretical basis for future remediation of Cd contaminated paddy soils. This paper summarized that (1) Fe oxides influence Cd activity through adsorption, complexation, and coprecipitation during transformation; (2) compared with the flooded period, the activity of Cd during the drainage period is stronger in paddy soils, and the affinity of different Fe components for Cd was distinct; (3) Fe plaque reduced Cd activity but was associated with plant Fe²⁺ nutritional status; (4) the physicochemical properties of paddy soils have the greatest impact on the interaction between Fe oxides and Cd, especially with pH and water fluctuations.

Silicon facilitated the physical barrier and adsorption of cadmium of iron plaque by changing the biochemical composition to reduce cadmium absorption of rice roots

Silicon effectively inhibits cadmium (Cd) uptake in rice, iron plaque on root surface was the primary link and first interface of Cd entering into rice root. To elucidate the mechanism of iron plaque under silicon treatment on root Cd uptake, the morphological characteristics of iron plaque, mechanisms of Cd adsorption of iron plaque and effect of iron plaque on Cd uptake by rice roots of Yuzhenxiang (YZX) and Xiangwanxian (XWX) rice varieties were studied by employing energy spectrum analysis technique, non-invasive micro-test technique, and isothermal-kinetic adsorption method. Scanning electron microscopy-X-ray energy dispersive (SEM-EDX) analysis showed that denser crystal structure of iron plaque was observed at Si treatment, silicon promoted the thickening of iron plaque and strengthened the isolation of iron plaque to Cd, which reduced the Cd content of white roots of YZX and XWX varieties by 30.2% and 20.9% respectively. However, the blocking effect of iron plaque on Cd was weakened under silicon treatment with iron plaque removed, Cd content in iron plaque of YZX and XWX cultivars was significantly decreased by 36.3% and 18.4%, Cd concentrations in white root and shoot was significantly increased, and the influxes of Cd²⁺ at elongation and maturation zone of root were increased in multiples. The results of adsorption test showed that the adsorption process of iron plaque was mainly a monolayer adsorption completed by boundary diffusion. The X-ray photoelectron spectroscopy (XPS) results demonstrated that silicon changed the biochemical composition of iron plaque and increased the density of the carbon-oxygen bound groups on iron plaque, which is the most likely reasons for the higher affinity of Cd adsorption ability of iron plaque observed in the silicon treated iron plaque. This study suggested the silicon-facilitated iron plaque have played critical effects in controlling the Cd accumulation in rice roots by changing the morphology and chemical composition of iron plaque.

Phosphorus fractions and iron oxides responsible for the variations in the Cd retention capacity in tropical soil aggregates under different cropping patterns

The environmental behavior of Cd in soil has been widely studied because of its close relationship with food security and soil environmental pollution. In this study, the roles of P fractions and Fe oxides in the retention of Cd in typical tropical soil from five cropping patterns were investigated. Although there was no evident relationship between the Cd adsorption capacity and soil aggregate particle sizes, strong spatial associations of P, Fe, and Cd at the soil aggregates were observed via energy dispersive spectroscopy analysis. Among five cropping patterns, citrus plantations exhibited highest ratios (calculated by pixel area) of P overlapped with Cd (8.61%) and Fe overlapped with Cd (9.53%) in the microaggregates. Furthermore, the random forest model revealed that humic P and labile organic P greatly contributed to the sorptivity of Cd²⁺ by < 0.053 mm (13.3%) and 0.25-0.053 mm (13.4%) soil aggregates, respectively. Compared with the P fractions in different-sized soil aggregates, the contribution of Fe oxides to the sorption of Cd²⁺ by soil aggregates was more significant. Amorphous ferric oxide had the most significant contribution to the sorptivity of Cd²⁺ by < 0.053 mm (26.0%), 0.25-0.053 mm (23.0%), 2.0-0.25 mm (25.1%), and > 2.0 mm (33.9%) soil aggregates.

Source, Distribution, and Risk Estimation of Hazardous Elements in Farmland Soils in a Typical Alluvial-Lacustrine Transition Basin, Hunan Province

Increased concentrations of heavy metals in soil due to anthropogenic activities pose a considerable threat to human health and require constant attention. This study investigates the spatial distribution of heavy metals (Cd, Pb, Zn, Sb) and metalloids (As) in a typical alluvial-lacustrine transition basin and calculates the bioavailable forms of elements posing a direct threat. Qualitative and quantitative methods were used to identify the sources of contaminants, after which an ecological risk assessment was conducted. Total (T) As, Pb, and Zn decreased with the depth, whereas Cd and Sb increased in surface (0-20 cm) soil. Bioavailable (Bio) Cd and Pb in the topsoil were regulated by pH and organic matter, whereas Bio-Zn was regulated by soil pH. Within deeper soil layers, the combined effects of pH, organic matter, and clay contents regulated the bio-elements. The results of multiple methods and local investigation showed that TSb (65.3%) was mainly derived from mining activities, TCd (53.2%) and TZn (53.7%) were derived from direct pollution by industrial production and agricultural fertilizers, respectively, and TA (55.6%) was mainly derived from the soil parent material. TPb was related to vehicle exhaust emissions and atmospheric deposition from industrial activities. Although the potential ecological risk in the study area remains relatively low, there is a need for continuous monitoring of the potential ecological risks of Cd and Sb. This study can act as a reference for the prevention and mitigation of heavy metal contamination of alluvial-lacustrine transition basins.

Silicon fertilizers, humic acid and their impact on physicochemical properties, availability and distribution of heavy metals in soil and soil aggregates

It has been confirmed that silicon (Si) fertilizer and humic acid (HA) could effectively decrease the heavy metals in soil. Nonetheless, the impact of these additives on soil aggregate characteristics was ignored. Therefore, the effects of Si fertilizer, HA, and their combinations on the physicochemical characteristics, availability of heavy metals (Cu, Cd, Pb, Zn), and fraction changes in soils and soil aggregates were investigated in this research. The results showed that Si fertilizer and HA significantly modified soil properties such as soil pH, electrical conductivity total organic carbon, water-soluble organic carbon, and nitrate‑nitrogen. HA and Si-HA (SHA) supplementation significantly decreased the availability of Cu, Cd, Pd, and Zn. Besides, there was no significant difference in physicochemical properties between soil and soil aggregates. The availability of Cu, Cd, Pd, and Zn in soil aggregates could be significantly inhibited by the addition of HA and SHA, and the content in microaggregates was greater than that in macroaggregates. After the addition of the three additives, the main fractions of heavy metals in different particle sizes were changed and eventually transformed to the residue state. These results indicated that Si fertilizer, HA, and SHA were influential in physicochemical properties and metal availability in soil aggregates. Therefore, it is of great scientific significance to study the impact of heavy metal pollution on the ecological environment in different aggregates, which will provide reference data for future sustainable management of heavy-metal polluted soils.

Accumulation and relationship of metals in different soil aggregate fractions along soil profiles

Different aggregates vary in their ability to retain or adsorb metals in soil. Five soil profiles were sampled from different soil horizons and grouped, and the concentrations of Al, Mg, Ca, Fe, Mn, Cd, Cu and Pb were determined in six sizes of aggregates (> 2, 2-1, 1-0.6, 0.6-0.25, 0.25-0.053, < 0.053 mm). Significantly high (p < 0.05) structural stability indexes (SSI) and aggregate stability indexes (ASI) were recorded in the topsoil horizon, which may be attributed to the high soil organic matter (SOM) content in aggregates from topsoil. In addition, ASI and SSI were positively correlated (r = 0.569, p < 0.05) with each other, which indicated that the stability of soil aggregates could contribute to the structural stability of bulk soil. Moreover, accumulation factors (AF), principal component analysis (PCA) and Pearson's correlation coefficients were used for metal element assessment. The results indicated that SOM was not a key factor affecting the accumulation of Ca, Mg, Al, Fe, Mn, Pb, Cd and Cu in soil aggregates. In general, AF values for metal elements in microaggregates (< 0.25 mm) were high, which showed that metals preferred to accumulate in fine soil aggregates. The PCA and Pearson's correlation coefficients indicated that soil parent materials primarily controlled the distribution of Al, Ca, Fe, Mg and Mn, while materials derived from technogenic sources have important impacts on the distribution of Cd, Cu and Pb in soil aggregates along the soil profile.

The Adsorption and Aging Process of Cadmium and Chromium in Soil Micro-aggregates

The particle size and components of soil aggregates have played important roles in the migration and transformation of heavy metals. The present study focused on the adsorption behavior and aging characteristics of cadmium (Cd) and chromium (Cr) in various granular aggregates and soil components, which were studied by analyzing the adsorption isotherm, adsorption kinetics, and heavy metal speciation distribution. The results showed that, compared with other aggregates, clay aggregates (0-0.002 mm) had the strongest adsorption effect on Cd and Cr and that there was no significant positive correlation between the adsorption amount and the particle size of aggregates for Cd and Cr. In general, the influence of three components on Cd was organic matter > amorphous iron > free iron oxide, and the influence on Cr was free iron oxide > amorphous iron > organic matter. The adsorption isotherm showed that the correlation coefficient of the Langmuir model (R² ) was higher than that of the Freundlich model (R² ), indicating that the adsorption of Cd and Cr by soil aggregates can be well described by the Langmuir model with monolayer adsorption behavior. Kinetic adsorption studies showed that quasi-first-order kinetics and quasi-second-order kinetics were more consistent with the actual adsorption amounts of Cd and Cr in soil aggregates, respectively. At the same time, the forms of Cd and Cr gradually transformed from unstable to stable after entering the soil. After 60 days, Cd was mainly oxidized, and residual, and Cr was mainly reduced and residual. These results provide a theoretical basis for assessing the environmental risks of Cd and Cr and providing prevention and treatment methods. Environ Toxicol Chem 2022;41:975-990. © 2022 SETAC.

Exposure to potentially toxic elements through the soil-tobacco-human pathway: causative factors and probabilistic model

High concentrations of potentially toxic elements (PTEs) in tobacco leaves are possible from the soil contamination and would have adverse health risks on residents. A large-scale survey of 306 tobacco fields in southern China was conducted to investigate the accumulation of PTEs in tobacco leaves through the soil-tobacco-human pathway and the associated health risks for local smokers and passive smokers. Significant enrichment of As, Cd, Hg, and Pb was observed in the investigated tobacco fields, with industrial emissions and applied fertilizers as the major potential sources. Dynamic interactions between factors in the soil acidic labile pool showed site-specific effects on the uptake of PTEs by tobacco plants. It was 99.6% and 91.8% probable that exposure of local adult men smokers to Cd and As exceeded the permitted safety limits, respectively. The population of men smokers had a 20-fold higher Cd exposure risk than did passive smokers. A probability-based transfer model was developed to demonstrate that interactions between soil factors could affect the Cd exposure risk of men smokers of locally harvested tobacco. Optimizing the pH (>6.0) and organic matter content (>40 g kg-1) of tobacco-growing soils, and setting a safe tobacco consumption rate of 2.80 g dry weight per day would help protect 90.4% of men smokers from excessive risks of exposure to Cd.

Assessment of Contamination Management Caused by Copper and Zinc Cations Leaching and Their Impact on the Hydraulic Properties of a Sandy and a Loamy Clay Soil

Soil hydraulic properties are crucial to agriculture and water management and depend on soil structure. The impact of Cu and Zn cations on the hydraulic properties of sandy and loamy clay soil samples of Central Greece, was investigated in the present study. Metal solutions with increased concentrations were used to contaminate the soil samples and the effect on hydraulic properties was evaluated, demonstrating the innovation of the current study. The soil samples were packed separately into transparent columns and the initial values of hydraulic conductivity, cumulative infiltration, infiltration rate and sorptivity were estimated. In order to evaluate soil adsorption, metal concentrations were measured at the water leachate. After the contamination of the soil samples, the hydraulic properties under investigation were determined again, using distilled water as the incoming fluid; the differences at the hydraulic parameters were observed. After doubling metal concentrations into the incoming solution of loamy clay soil, metal adsorption and the values of the hydraulic parameters increased significantly. Loamy clay soil showed interaction between the clay particles and the positive charge in the incoming fluid, which led to a possible increase in aggregation. Furthermore, aggregation may led to pore generation. Contamination of sandy soil exhibited no impact on aggregation and soil structure. In order to evaluate the differences on the hydraulic properties and soil structure, the experimental points were approximated with two infiltration models.

The adsorption characteristics of Cu(II) and Zn(II) on the sediments at the mouth of a typical urban polluted river in Dianchi Lake: taking Xinhe as an example

This study is to determine the spatial distribution characteristics of Cu and Zn adsorption on the sediments of the estuary of Dianchi Lake, as well as the composite adsorption law of Cu and Zn on combinations of sediment organic matter, metal oxides, and organic-inorganic composites. The relationship between the adsorption contribution of each component of the substance. A static adsorption experiment was applied to the sediments in the estuary of Dianchi Lake. The relationship between adsorption capacity and sediment composition was analyzed through correlation analysis and redundant analysis. The results show that along the direction of the river flow and the vertical depth, the adsorption capacity presents a relatively obvious spatial distribution law; the change trend of sediment component content is not the same as the change trend of Cu and Zn adsorption capacity. The change trend of the sediment component content is not the same as the change trend of the adsorption amount of Cu and Zn, and the compound effect between the components affects the adsorption amount. The adsorption of Cu by the four groups of sediments after different treatments is more in line with the Freundlich isotherm adsorption model; When adsorbing Zn, the untreated and removed organic matter and iron-aluminum oxide group are in good agreement with the Freundlich model, while the organic matter-removed group and the iron-aluminum oxide removal group are more consistent with the Langmuir isotherm adsorption model; The adsorption contribution rate of organic-inorganic composites in sediments is not a simple addition of organic matter and iron-aluminum oxides, but a more complex quantitative relationship.

Effects of soil particle size on the adsorption, distribution, and migration behaviors of heavy metal(loid)s in soil: a review

In recent years, toxic pollution from heavy metal(loid)s in soil has become a severe environmental problem worldwide. The migration and transformation of heavy metal(loid)s in soil have become hot topics in the field of environmental research. Soil particle size plays an important role in influencing the environmental behavior of heavy metal(loid)s in soil. This review collates and synthesizes the research on the adsorption, distribution, and migration of heavy metal(loid)s in soil particles. There is no unified method for soil particle separation, since the purposes of different studies are different. Regardless of adsorption or distribution characteristics, fine soil particles generally exhibit a higher capacity to combine heavy metal(loid)s; however, certain studies have also observed a contrary phenomenon, according to which heavy metal(loid)s were more enriched in coarser particles. The adsorption and distribution of heavy metal(loid)s in soil particles were essentially determined by the physicochemical properties of the soil particles. Land use obviously affected the distribution of heavy metal(loid)s in the soil particles. Organic matter had an important influence on the distribution and availability of heavy metal(loid)s in agricultural and forest soils, while for urban soils and sediments, clay minerals or metal (hydr)oxides may play the dominant role. Preferential surface migration of fine particles during erosion processes did not always lead to the enrichment of heavy metal(loid)s in the lost soil. Further research should be conducted to explore the relationships among the soil aggregates, organic matter, heavy metal(loid)s, and soil microorganisms; the association between the distribution and availability of heavy metal(loid)s and the properties of soil particles; and the migration patterns of heavy metal(loid)s in soil particles at different scales.

Effect of multiple factors on the adsorption of Cd in an alluvial soil from Xiba, China

The effects of organic matter, free Fe oxides and Mn oxides in an alluvial soil on adsorption of Cd were studied through selective chemical extraction and adsorption experiments. Compared to untreated soil, after H₂O₂ treatment for removal of organic matter and NH₂OH·HCl treatment for removal Mn oxides, the distribution coefficient (K_d) decreased by a maximum of 25.2% and 64.1%, respectively. After dithionite-citrate-bicarbonate treatment for removal of free Fe oxides, K_d increased by 1670.2%. After increasing the solution pH from 2 to 3, K_d increased by 2842.1%, whereas after increasing the solution pH from 3 to 7, the adsorption tended stabilize. As the ionic strength increased from 0.001 M to 0.1 M NaNO₃, K_d gradually decreased, whereas at the same ionic strength, K_d decreased as the initial concentration of Cd increased. The effects of different background electrolytes on Cd adsorption was as follows: Ca²⁺ > Mg²⁺ > K⁺ > Na⁺ for cations and Cl^- ≈ SO₄^2- > NO₃^- for anions. The adsorption capacity of Cd increased as the increased of temperature, and it's a spontaneous endothermic process. The pseudo second-order rate model described the process of Cd adsorption well.

Binding characteristics of cadmium and zinc onto soil organic matter in different water managements and rhizosphere environments

Soil organic matter (SOM) could immobilize most of metals, but it could promote the migration of a small part of metals in special environments. Heavy rainfall and drought makes wetlands affected by the alternation of drought and flood, altering the mobility of metals. Few studies have been conducted on the changes of binding characteristics of metals onto SOM which derived from different water conditions and rhizospheric environments. The objective of this paper was to explore the sequential differences of spectral variations of fluorescent groups and UV-Vis groups of metals onto SOM which derived from different water managements and rhizospheric environments. The method adopted was mainly two-dimensional correlation analysis (2DCOS). The results showed that flooding samples contained more aromatic substances compared to draining samples, which could promote metal binding. The binding characteristics were shown in the following: (1) Cd²⁺ and Zn²⁺ could react with aromatic substances, react with functional groups in SOM, and promote the formation of new groups such as carboxyl; (2) both Zn²⁺ and Cd²⁺ could bind with functional groups on proteins but relatively reductive environment can weaken the binding ability of Cd²⁺; (3) the protein-like or fulvic-like groups gave the fastest responses and then came the amide and carboxyl groups in nearly all flooding samples; (4) in flooding samples, Cd²⁺ was most easily to bind with fulvic-like groups, while Zn²⁺ was most easily to bind with protein-like groups. This work is conducive to the long-term management of heavy metal pollutants in wetlands.

Loss characteristics of Cd in soil aggregates under simulated rainfall conditions

Soil particles exert a significant influence on the migration of heavy metals in soil and water environments. In this study, a simulated rainfall experiment was conducted to investigate the loss characteristics of cadmium (Cd) from a red soil surface. Two rainfall intensities (50 and 100 mm h^-1) were considered and the distribution of Cd in different fractions (>1, 1-0.25, 0.25-0.05 and <0.05 mm) of aggregates lost from the soil was examined. The result showed that in the artificially polluted soil, the Cd content in different aggregates decreased with particle size, with the lowest Cd content in the <0.05 mm fraction aggregates. In the rainfall experiment, the runoff rate generally increased with the rainfall duration, while the sediment yield rate first increased and then remained stable. The loss rates of various fractions of aggregates in the sediment generally followed the order of (<0.05) mm > 1-0.25 mm > 0.25-0.05 mm > (>1) mm. The proportions of the <0.05 mm-fraction aggregates were the highest in the loss sediment throughout the entire rainfall process. The lost Cd was transported mainly in the sediment-bound form, while only a very small portion of Cd was lost in the water phase of runoff. High rainfall intensity led to greater Cd loss in runoff. In the lost sediment, the concentration of Cd was higher in the macroaggregates. The phenomenon of Cd enrichment in the fine particles was not observed. Although the concentration of Cd in the <0.05 mm fraction was the lowest, the contribution of this fraction to the total Cd content in the sediments was the highest.

Soil properties and agronomic factors affecting cadmium concentrations in cacao beans: A nationwide survey in Ecuador

Recent cadmium (Cd) regulation in chocolate threatens the sustainability of cacao production in Southwest America. Cadmium contamination in cacao beans has not been assessed at a country level. A nationwide survey was conducted in Ecuador to identify the spatial distribution of Cd in cacao beans, as well as soil and agronomic factors involved. Paired soil and plant samples (pods and leaves) were collected at 560 locations. Information on agronomic practices was obtained through a prepared questionnaire for farmers. Total soil Cd averaged 0.44 mg kg^-1 which is typical for young and non-polluted soils. Mean Cd concentration in peeled beans was 0.90 mg kg^-1 and 45% of samples exceeded the 0.60 mg kg^-1 threshold. Bean Cd hotspots were identified in some areas in seven provinces. Multivariate regression analysis showed that bean Cd concentrations increased with increasing total soil Cd and with decreasing soil pH, oxalate-extractable manganese (Mn_ox) and organic carbon (OC) (R² = 0.65), suggesting that Cd solubility in soil mainly affects Cd uptake. Bean Cd concentration decreased a factor of 1.4 as the age of the orchard increased from 4 to 40 years. Bean Cd concentration was inconsistently affected by genotype (CCN-51 vs. Nacional), pruning or application of fertilizers. It is concluded that the relatively larger bean Cd concentrations in Ecuador are related to the high Cd uptake capacity of the plants combined with their cultivation on young soils, instead of Cd depleted weathered soils. Mitigation strategies should consider the application of amendments to modify such soil properties to lower soil Cd availability. There is scope for genetic mitigation strategy to reduce bean Cd, but this needs to be properly investigated.

Distribution characteristics of heavy metal(loid)s in aggregates of different size fractions along contaminated paddy soil profile

Soil aggregates exert a significant influence on the retention and availability of heavy metal(loid)s in soil. In this study, the concentration distribution and chemical forms of heavy metals (Cu, Zn, Cd, Pb, and Hg) and a metalloid (As) in different aggregate-sized fractions (2-0.25, 0.25-0.05, 0.05-0.002, and < 0.002 mm) along the profile (0-1, 1-5, 5-15, and 15-25 cm) of a contaminated paddy field were investigated. The results showed that the values of pH, free Fe oxides (Fe_d), bulk density, and catalase activity gradually increased, whereas the soil organic matter (SOM), cation exchange capacity (CEC), electrical conductivity (EC), microbial biomass carbon (MBC), and urease activity decreased with depth. Long-term heavy metal pollution might impact the catalase activity but showed no obvious influence on the urease activity. Additionally, there was a notable difference in physicochemical properties among the soil aggregates of various particle sizes. The 2-0.25-mm fraction aggregates contained more organic matter, whereas the highest values of CEC and Fe_d were observed in the < 0.002-mm fraction. The concentrations of all six heavy metals/metalloid decreased with depth. In different layers, Cu and Cd showed the highest concentrations in the 2-0.25 mm-fraction, followed by the < 0.002-mm fraction, whereas the highest concentrations of Zn, Pb, and As appeared in the < 0.002-mm fraction. No obvious distribution regularity was observed for Hg among the aggregates. All of the metal(loid)s had lower activity in the deeper soil layers, except for Hg. Furthermore, Cu and Cd displayed more stable forms in the < 0.002-mm fraction aggregates.

Effect of land use pattern change from paddy soil to vegetable soil on the adsorption-desorption of cadmium by soil aggregates

The influence of land use change from paddy soil to vegetable soil on the adsorption-desorption behavior of Cd in soil aggregates and the variation in soil properties were investigated. The vegetable soil was characterized by lower pH, organic matter content, cation exchange capacity (CEC), free iron oxides, manganese oxides, and catalase activity and higher urease activity compared with the paddy soil. In the isothermal adsorption and desorption experiments, the adsorption characteristics of Cd of the two soils could be well described by Langmuir and Freundlich equations. The adsorption capacity of vegetable soil decreased 22.72 %, and the desorption rate increased 35 % with respect to paddy soil. Therefore, conversion from paddy to vegetable field can reduce the adsorption ability to Cd of the soil to a certain extent. Both the two soils reached the maximum adsorption capacity and the minimum desorption rate in the <0.002-mm faction. The adsorption capacity of Cd in paddy and vegetable soils exhibited great reliance on the content of CEC. Desorption rate was negatively correlated with the four indicators: organic matter, CEC, free iron oxides, and manganese oxides, and specific adsorption was primarily controlled by soil organic matter and manganese oxides.

Comparison of the removal and adsorption mechanisms of cadmium and lead from aqueous solution by activated carbons prepared from Typha angustifolia and Salix matsudana

H₃PO₄ activated Typha angustifolia and Salix matsudana carbons provide good adsorption/desorption characteristics for Cd and Pb.