Mobility Of Cd Research Articles

Regulation of rhizosphere microenvironment by rice husk ash for reducing the accumulation of cadmium and arsenic in rice

It is important to reduce Cd and As content in brown rice in contaminated paddy soils. We conducted research on the effects of rice husk ash (RHA) on the Cd and As in the rhizosphere microenvironment (soil, porewater, and iron plaque) and measured the Cd, As, and Si content in rice plants. The main elements in RHA were Si (29.64%) and O (69.17%), which had the maximum adsorption capacity for Cd was 42.49 mg/kg and for As was 18.62 mg/kg. Soil pH and available Si content increased, while soil available Cd and As decreased following application of 0.5%–2% RHA. RHA promote the transformation of Cd to insoluble fraction, while As was transformed from a poorly soluble form to a more active one. RHA reduced Cd content and increased Si content in porewater, and reduced As only at the later rice growth stages. RHA increased the amount of iron plaque, thereby decreasing the Cd content in iron plaque, while increased the As content in it. Cd and inorganic As content in brown rice were decreased, to 0.31 mg/kg and 0.18 mg/kg, respectively. The decrease of Cd in brown rice was due to the decrease of Cd mobility in soil, thereby reducing root accumulation, while the decrease of As in brown rice was affected by the transport from roots to stems. Therefore, RHA can be considered as a safe and efficient in-situ remediation amendment for Cd and As co-contaminated paddy soil.

Cadmium fractionation in soils affected by organic matter application: Transfer of cadmium to cacao (Theobroma cacao L.) tissues

Elevated cadmium (Cd) concentrations in cacao (Theobroma cacao L.) beans have concerned chocolate consumers worldwide because of the potential detrimental human health effects. Compost application on the soil surface could modify the labile Cd in soils and yet it could enhance Cd bound to humic and fulvic acids, forming an organo-metallic complex that could reduce the availability of Cd to plants. This study investigated the effect of surface compost applications at two rates, the chemistry and fractionation of Cd at two soil depths, and the relationship of these soil Cd pools with plant uptake. The research was carried out on four Ecuadorian cacao farms. The compost was applied at 6.25 Mg·ha−1 (low) and 12.5 Mg·ha−1 (high) per annum. There was also a control treatment with no compost application. Soil samples were collected at two depths, surface (0–5 cm) and below surface (5–20 cm). Leaf samples and cacao pots were collected from each treatment. Soil Cd was fractionated into five operational pools. Additionally, the Cd-bound to fulvic acids and humic acids in soils were extracted separately. The EDTA-extractable fraction showed the highest concentration of Cd at both depths. Cadmium bound to fulvic acids was higher in compost-applied soils than in the control (p < 0.05) in all farms. Leaf and bean-Cd were negative and significantly correlated with the Cd extracted by EDTA, NaOH, HNO3, and FA-Cd pools. The mobility of Cd in soils cultivated with cacao, based on plant uptake, was strongly associated with the soils’ chemical characteristics, especially pH and SOC. The surface application of organic matter facilitates the redistribution of Cd in soil fractions, mainly in EDTA-, NaOH-, and HNO3-extractable fractions, suggesting a reduction in Cd soil–plant transfer via adsorption or complexation processes. Apparently, the application of high-quality compost, i.e., high FA content, could aid in mitigating Cd contamination in cacao orchards. Experiments on perennial crops merit a longer evaluation time to better assess the changes in plant-Cd.

Redistribution and isotope fractionation of endogenous Cd in soil profiles with geogenic Cd enrichment

The concentration and speciation of endogenous cadmium (Cd) in soil systems derived from parent materials is continuously altered by rock-soil-plant interactions. Previous studies on the distribution of Cd primarily focused on surface soil at regional scale. However, it lacks a novel approach to provide a new perspective on dynamics and redistribution of Cd in soil profile. Therefore, this study tries to establish the linkage between isotope fractionation and environmental processes of Cd in soil profiles with geogenic Cd enrichment based on Cd isotopes. High Cd concentrations were observed in the profile from forest at accumulation zone and the one from farmland at ridge in a rural area, southwest China. Soil erosion and deposition substantially influence the vertical distribution of total Cd in soil from the accumulation zone. Accordingly, distinct Cd isotope compositions were observed in different layers (δ114/110Cd: −0.087 ‰ to −0.066 ‰ vs −0.325 ‰ to −0.056 ‰). Mineral transformation, pedogenesis and biological activities controlled the dynamics and redistribution of Cd. The mobility of Cd increased during weathering processes, with ~40 % to 60 % of Cd residing in exchangeable fraction in the surface layers. Biological activity is a vital factor that drives Cd isotope fractionation in soil, resulting in depletion of heavy Cd isotopes in surface layers of the studied farmland profile. Contrasting fractionation effects were observed in profiles from forest and farmland due to the variance in soil-plant Cd cycling. Our study revealed the processes that control dynamics and redistribution of endogenous Cd in soil profiles, and proved that Cd isotope is a useful tool to investigate the bio-geochemical processes of Cd in soil systems.

Bioavailability, (im)mobilization kinetics, and spatiotemporal patterns of arsenic and cadmium in surficial sediments of a river–estuary–coast system

• High-resolution distributions of DGT-labile As, Cd, Fe, Mn and S are determined. • Fe cycling dominates As mobility, while aerobic OM oxidation controls Cd mobility. • Terrigenous input and redox condition trigger the contrasting seasonal availability of As and Cd. • Cd bioavailability evaluated by DGT clearly increases with salinity gradient. The mobility and bioavailability of toxic arsenic (As) and cadmium (Cd) in sediments are crucial to aquatic ecosystems, while their geochemical transitions and spatiotemporal patterns associated with manganese (Mn), iron (Fe), sulfur (S) and salinity in a river–estuary–coast system are yet largely unexplained. In this study, seasonal field investigation and salinity-dependent indoor experiments were combined using the diffusive gradients in thin films (DGT) technique to measure DGT-labile species from the simultaneous river-estuary-coast interface. The results revealed that As and Fe presented a strong coupling for both DGT species and solid phases, suggesting that As mobility was exclusively regulated under the redox transition of Fe. Unlike other chemicals, the relative enrichment of DGT-labile Cd in surface layers and the close affiliation between sediment Cd fractions and organic carbon indicated that Cd remobilization was largely associated with the aerobic decomposition of organic matter. In addition, the seasonal availability of As and Cd tended to be influenced by terrigenous input and redox condition. The indoor experiment results of an inconspicuous increase in DGT-labile As, and a steady increase in DGT-labile Cd with rising salinity confirm that the bioavailability of Cd evidently increased with salinity gradient, however, the effect of salinity on As remained further debatable. Nevertheless, a model simulation validated that this salinity-dependent Cd mobilization was suboptimal for sustaining a continuous Cd resupply from the sediment to porewater, particularly under limited labile Cd pools. Therefore, with expanding global marine hypoxia and sea level rising, this study highlights that As and Cd redox geochemistry in dynamic estuarine sediments should receive more attention, considering their distinctly contrasting (im)mobilization kinetics.

Weathering of microplastics and their enhancement on the retention of cadmium in coastal soil saturated with seawater

The plastic contamination and its associated ecological impacts in coastal areas have received great concern. The environmental conditions of varying aquatic-terrestrial ecosystems and physicochemical properties of existing plastics may further affect the transport and fate of subsequent entering contaminants in coastal areas. In this study, a coastal soil accumulated with five commonly-used micro-sized plastics (MPs) and saturated with four seawaters collected along the China coastlines from north to south were applied to investigate their effects on the mobility of Cd. The existing MPs in soil greatly enhanced Cd accumulation, with Cd retention increasing to 23.1 – 78.6%, compared to 18.1 – 26.6% in the soil without MPs. The five MPs showed the increasing trend of Cd retention: polystyrene < polyethylene < polypropylene < polyvinyl chloride < polyethylene terephthalate. The highest Cd retention by polyethylene terephthalate was attributed to its rich oxygen-containing groups which could enhance Cd sorption. The aged MPs was characterized by more oxygen-containing functional groups with higher surface charge, which enhanced the electrostatic interaction with Cd. Modeling showed that the depths for the maximum concentrations of Cd downward migration in the MPs soil are only down to 9 cm after 10-year seawater intrusion, while the depths go down to 26 cm in the soil alone. Overall, MPs existing in soil can retain more Cd in the surface soil, which impel our great attention of the combined pollution of existing microplastics and subsequent entering heavy metals in the coastal topsoil.

Wheat straw- and maize straw-derived biochar effects on the soil cadmium fractions and bioaccumulation in the wheat–maize rotation system

Wheat–maize rotation is one of the most popular systems and successful intensification cropping systems in Northern China, while soils in some of this area are contaminated by cadmium (Cd). However, few studies have performed experiments on the reduction of Cd accumulation in the wheat–maize rotation system. In this study, wheat- and maize-derived biochars are applied to the Cd-contaminated soil to reduce the Cd accumulation in the wheat and maize plants. The results showed that soil biochar applications can significantly decrease DTPA-extracted Cd concentrations by 12.7–26.0% and 13.1–20.5% by wheat- and maize-derived biochars, respectively. Sequential extractions showed that biochar applications significantly reduced the Cd mobility and bioavailability in soils and changed the exchangeable and carbonate-bound fractions of Cd to organic material-bound and residual fractions. The biochar applications increased the plant growth, yield, and quality of both wheat and maize, especially a significant increase in high dosages. The biochar applications also improved the antioxidant enzyme activities and reduced the reduction of MDA in both wheat and maize roots. The Cd concentrations in wheat grains were reduced by 38.1–91.5% and 65.9–80%, and maize grain Cd concentrations were reduced by 20.9–54.2% and 30.8–44% by wheat- and maize-derived biochar applications, respectively, and the Cd concentrations in the root, stem, and leaf were also significantly reduced. The wheat-derived biochar was more effective on the Cd reduction in soil bioavailable fractions and Cd accumulation in crop plants.

Influence of DOM and its subfractions on the mobilization of heavy metals in rhizosphere soil solution

Long-term industrial pollution, wastewater irrigation, and fertilizer application are known factors that can contribute to the contamination of heavy metals (HMs) in agricultural soil. In addition, dissolved organic matter (DOM) plays key roles in the migration and fate of HMs in soil. This study investigated the effects of amending exogenous DOM extracted from chicken manure (DOMc), humus soil (DOMs), rice husk (DOMr), and its sub-fractions on the mobilization and bio-uptake of Cd, Zn, and Pb. The results suggested that the exogenous DOM facilitate the dissolution of HMs in rhizosphere soil, and the maximum solubility of Zn, Cd, and Pb were 1264.5, 121.3, and 215.7 μg L−1, respectively. Moreover, the proportion of Zn-DOM and Cd-DOM increased as the DOM concentration increased, and the highest proportions were 97.5% and 86.9%. However, the proportion of Pb-DOM was stable at > 99% in all treatments. In addition, the proportion of hydrophilic acid (Hy) and Pb/Cd in the rhizosphere soil solution were 17.5% and 8.3%, respectively. This finding suggested that the Hy-metals complex has a vital influence on the mobilization of metals, besides its complexation with fulvic acid and humic acid. Furthermore, the elevated DOM addition contributed to an increment of HMs uptake by Sedum alfredii, in the following order, DOMc > DOMs > DOMr. This study can provide valuable insights to enhance the development of phytoremediation technologies and farmland manipulation. Since the risk that exogenous DOM would increase the uptake of HMs by crops, it is also needed to evaluate this case from an agricultural management perspective.

Annual net input fluxes of cadmium in paddy soils in karst and non-karst areas of Guangxi, China

In recent years, the problems of high cadmium content and low Cd mobility in karst areas compared with non-karst areas have attracted extensive attention. Identifying the difference between the net Cd flux in karst and non-karst areas is crucial for sustainable land management. Basically, rock weathering is a natural source of Cd. While Cd accumulation in soil has increased due to both anthropogenic and natural sources, the contributions of anthropogenic input and rock weathering to soil Cd concentration in karst and non-karst areas remain unclear. In this study, the input (e.g., atmospheric deposition, fertilizer and irrigation) and output fluxes (e.g., leaching and early and later rice harvest) of Cd in farmland soils in karst and non-karst areas of Guangxi from 2017 to 2018 were monitored. The results showed no significant difference (P = 0.289) in the contributions of various input pathways between karst area and non-karst area, and atmospheric deposition (64–55 %) played an important role in the input fluxes. Nevertheless, the low soil pH value and high rainfall in non-karst areas increase Cd mobility and plant availability in soil, causing the output flux in non-karst areas (5.30 g/ha/y) to be greater than that in karst areas (3.17 g/ha/y). According to the national standard, the exceedance rate of Cd in rice grains in non-karst area (17 %) was higher than that in karst area (15 %). Therefore, ecological risk assessment in non-karst areas with high Cd bioavailability should be prioritized. Furthermore, the annual increase rate of Cd concentration in topsoil of karst and non-karst areas was −0.27 μg/kg/y and −1.23 μg/kg/y, respectively. However, the soil Cd concentration in karst and some non-karst areas still exceeded the guideline value. Given that the net input flux of Cd was negative, the accumulation of Cd in soil may be determined by rock weathering.

Effect of biochar amendment on metal mobility, phytotoxicity, soil enzymes, and metal-uptakes by wheat (Triticum aestivum) in contaminated soils

The use of low-cost substances such as biochar could be a sustainable approach to reduce the mobility, accumulation, and toxic impact of heavy metals in crop systems. This study investigates the effect of biochar amendment on heavy metal (Cr, Cd, Cu, Pb, Ni, Zn, Mg and Fe) mobility, bioaccumulation factor (BAF), plant (wheat) metal-uptake, plant oxidative stress, and soil enzymatic profile in contaminated industrial soil. Biochar was obtained from slow pyrolysis of Lantana (LBC), and Parthenium (PBC) biomass, and applied at 3% rates in contaminated soils for wheat crop study under a greenhouse experimental setup. Results show in comparison with control setups, low mobility of Cr (14.15–16.35%), Cd (7.17–15.24%), Cu (9.81–12.97%), Pb (7.99–15.23%), Ni (1.52–2.38%), Zn (10.47–14.42%), Mg (48.85–52.89%), and Fe (19.13–19.90%) contents in soils. The heavy metal uptake rates were 63.08% (Cr), 78.07% (Cd), 74.61% (Cu), 78.11% (Pb), 75.73% (Ni), 69.71% (Zn), 28.78% (Mg), and 49.26% (Fe) lower in biochar amendments, compared with the control treatments. Similarly, the biochar amended treatments exhibited low oxidative stress in wheat plants than control setups. In addition, soil enzymes (dehydrogenase, β-glucosidase, alkaline phosphatase, and urease) alleviated in biochar amended soils indicating reduced toxicity of metals in experimental soils. In summary, this study indicates that biochar amendment in contaminated soils not only improves plant growth but also lowers the rates of soil and plant toxicity and metal bioavailability as well.

Humic acid coupled with coal gasification slag for enhancing the remediation of Cd-contaminated soil under alternated light/dark cycle.

In this study, the synthesis of a coal gasification slag-humic acid (SA) hybrid was purposed for the remediation of cadmium (Cd)-contaminated soil. In order to investigate the effect of SA on the Cd-contaminated soil and plant growth, a series of experiments were carried out under different illumination condition. The results showed that the SA has some the photocatalytic activity, and adding 10 wt% of SA to the soil could obviously improve the soil fertility and decrease the mobility of Cd in the soil under alternated light/dark cycle (12L/12D); the content of the residual fraction in the SA-amended soil reached 69.5%, and the Cd decreasing rates for the leaf, stem, and root of Artemisia ordosica were near 100%, 91.3%, and 75.3%, respectively. Characterizations of amendments suggested that the synergistic effect of precipitation and surface complexation played a major role in the remediation of Cd-contaminated soil.

The assessment of the soil-plant-animal transport of the risk elements at the locations affected by brown coal mining.

The North Bohemian Brown Coal Basin (Czech Republic) is suggested as a source of significant pollution in the surrounding environment with various pollutants, including risk elements. A total of 53 sampling points were selected within the North Bohemian region. The selected sampling points represented either the basin areas (affected by the coal mining and related activities) or the mountain areas (an area unaffected by the coal mining but characterized by the geogenic sources of the risk elements). At each of the sampling points, soils and respective dominant indigenous plant samples were collected. A suite of ecological indices, namely, individual pollution index (Ii), Nemerow index (PN), bioaccumulation factor (BAF), translocation factor (TF), and hazard quotient (HQ), were applied to estimate the environmental risk of As, Be, Cd, and Zn levels in soils, potential soil-plant transfer, and soil-plant-animal transport of these stated elements. The results from Ii showed that the maximum values of As, Be, Cd, and Zn in the investigated soils exceeded the preventive values, where the Ii value was up to 58 for As in the mountain areas, indicating severe pollution. At the same time, mild pollution was recorded in the case of Cd. For Be in the researched soils, its Ii assessment result was a wide range, varying between a clean environment and severe pollution. Whereas As and Be uptake by plants was limited and these elements were retained in the plant's roots, relatively high mobility and soil to plant shoots transport ability of Cd were recorded and documented by the TF values. The HQs calculated for selected herbivorous mammals in the area showed that the potential health risk of As and Be was limited to only plant roots in the hotspots with extreme As and Be contents. In comparison, substantial health risk of Cd was observed in the aboveground biomass of plants. Therefore, the potential remediation of the coal mining areas should be focused on (i) identification of the As and Be hotspots and (ii) to reduce the mobility and plant availability of Cd in the whole investigated area.

Humates mitigate Cd uptake in the absence of NaCl salinity, but combined application of humates and NaCl enhances Cd mobility & phyto-accumulation

Cadmium is among the critical pollutants easily taken up from contaminated media by plants, which can be exploited in the phytoremediation of Cd-contaminated resources, but is also an obstacle in producing food with low Cd content. Crucial variables governing Cd biogeochemistry are complex humates (HA) and chlorides, but the underlying interactions are poorly understood. The aim was to determine the impacts of HA (0–60 mg/L) and NaCl (0–30 mM) on Cd biochemistry in contaminated (2.0 μM Cd) rhizosphere solution and Cd accumulation in various tissues of strawberry (Fragaria x ananassa). The results show that salinity (vs. non-saline NaCl0 control) suppressed vegetative and yield parameters, but increased dry matter and Na, Cl and Cd concentration/accumulation in most of the analysed tissues. The HA application in the NaCl0 treatment decreased tissue Cd content; however, at the highest application rates of NaCl and HA, there were increases in the tissue Cd concentration (by 70 %, 100 % and 120 % in crowns, leaves and fruits, respectively) and accumulation (by 110 %, 126 % and 148 % in roots, fruits and leaves, respectively) in comparison to the control (NaCl0HA0). Tissue Cd concentration/accumulation decreased in the order: roots>crowns>leaves>fruits; the same accumulation pattern was noted for Na and Cl, suggesting that Cd-Cl complexes may represent a major form of Cd taken up. Chemical speciation calculations revealed that the proportions of various Cd forms varied multi-fold across the treatments; in the control (without NaCl and HA), Cd2+ dominated (86 %), followed by CdHPO4 (6.5 %), CdSO4 (6.2 %) and CdNO3+. In other treatments the proportion of Cd2+ decreased with a corresponding increase of Cd-Cl (from 0.02 % in control to 57 % in Cd + NaCl30 treatment) and Cd-HA (from 0 % in control to 44 % in Cd + HA60 treatment), which was associated with higher Cd phytoaccumulation. The results represent a theoretical basis for phytoremediation studies and for producing low-Cd food in relatively complex matrices (contaminated soils, reused effluents); in the absence of salinity, amelioration with humates has a great potential to mitigate Cd contamination.

A new insight into Cd reduction by flooding in paddy soil: The different dominant roles of Fe and S on Cd immobilization under fluctuant pe + pH conditions

The unsteady comprehensive system of pe + pH strongly affects the fate of Cd in paddy soils. However, the specific pe + pH threshold determining Cd bioavailability is largely unknown especially considering the roles of Fe and S reduction. The experiment set different water managements to obtain paddy soil samples with unstable pe + pH, and chemical analysis, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) characterization were applied to reveal the dynamic process and mechanism about how Fe and S controlled Cd mobilization. The results showed that low pe + pH was favorable to soil Cd immobilization. Compared with high and medium pe + pH, the exchangeable Cd content decreased by 67.57 % and 64.71 % at low pe + pH, respectively. The XPS results showed that the contents of Fe(II) and S(−II) increased to 65.1 % and 75.2 % at low pe + pH condition, which was higher than that in other treatments. In the process of flooding for reducing Cd mobility, first it was attributed to the formation of amorphous iron oxides that can provide amount of adsorption sites for Cd. After then, S2− began to play a dominant role to combine with Cd2+ to form CdS with continuous decreased pe + pH. Therefore, Fe and S played the different dominant roles on Cd immobilization in paddy soil, and soil pe + pH value could work as a threshold.

Effects of Red Mud on Cadmium Uptake and Accumulation by Rice and Chemical Changes in Rhizospheres by Rhizobox Method

Red mud (RM), a byproduct of aluminum production, is used as amendments to increase the pH and reduce the available Cd in soil, but the effects of RM treatments on rice and rhizosphere chemistry changes at different radial-oxygen-loss (ROL) rates and developmental stages remain unclear. To address this concern, a rhizobox trial was conducted to investigate the effect of 0%, 0.5%, and 1.0% RM, on Cd accumulation by rice cultivars differing in ROL rate (‘Zheyou12’ (ZY12), ‘Qianyou1’ (QY1), and ‘Chunjiangnuo2’ (CJN2)) at two growth stages (tillering and bolting). The results showed that mobility factors of Cd in the soil were decreased significantly at both stages. The Cd mobility factor (MF) of CJN2 was decreased by 33.01% under 1% RM treatment at bolting stage. The pH value was increased by 0.39–0.53 units at two stages. RM contains large amounts of metals, which can increase soil iron (Fe) and manganese (Mn) concentrations, reduce redox potential, and transform the available Cd into Fe/Mn oxide-bound Cd. In addition, the Fe plaque further increased to inhibit the transformation of Cd. These changes reduced the available Cd in the soil and further decreased Cd absorption by rice. With the increase in RM concentration, the shoot and root biomass increased, and Cd accumulation in the plant significantly decreased. Compared with that under 0% RM treatment, the shoot Cd concentrations of ZY12, QY1, and CJN2 under 1% RM treatment at the bolting stage decreased by 27.59%, 36.00%, and 46.03%, respectively. The relative Cd accumulation ability of the three rice cultivars was CJN2 &lt; QY1 &lt; ZY12. The ROL promotes Fe plaque formation on the root surface. The Fe plaque is an obstacle or buffer between Cd and rice, which can immobilize Cd in Fe plaque and further reduce Cd absorption by rice. The addition of RM, in combination with a high-ROL rice cultivar, is a potential strategy for the safe production of rice on Cd-contaminated soils.

Rape straw application facilitates Se and Cd mobilization in Cd-contaminated seleniferous soils by enhancing microbial iron reduction

Many naturally seleniferous soils are faced with Cd contamination problem, which severely limits crop cultivation in these areas. Straw returning has been widely applied in agricultural production due to its various benefits to soil physicochemical properties, soil fertility, and crops yield. However, effects of straw application on the fates of Se and Cd in Cd-contaminated seleniferous soils remain largely unclear. Therefore, the effects of straw application on the fates of Se and Cd in Cd-contaminated seleniferous soils were investigated in this study. The results showed that iron reduction driven by Clostridium and Anaeromyxbacter was responsible for the variations in Se and Cd fates in soil. Straw application respectively increased the gene copy numbers of Clostridium and Anaeromyxbacter by 19.5–56.3% and 33.6–39.8%, thus promoting iron reductive dissolution, eventually resulting in a high release amount of Se and Cd from Fe(III) (oxyhydr) oxides. Under reducing conditions, the released Cd was adsorbed by the newly formed metal sulfides or reacted with sulfides to generate CdS precipitates. Straw application decreased the soil exchangeable Se and soil exchangeable Cd concentration during flooding phase. However, straw application significantly increased Se/Cd in soil solution which had the highest bioavailability during flooding. In addition, straw application increased soil exchangeable Se concentration, but it had no significant effects on soil exchangeable Cd concentration after soil drainage. Taken together, straw application increased Se bioavailability and Cd mobility. Therefore, straw application is an effective method for improving Se bioavailability, but it is not suitable for the application to Cd-contaminated paddy soils. In the actual agricultural production, straw could be applied in seleniferous soils to improve Se bioavailability. At the same time, straw application should be cautious to avoid the release of Cd from Cd-contaminated soil.

Regularities of cadmium accumulation by red currant (&lt;i&gt;Ribes rubrum&lt;/i&gt; L.) varieties on soddy-podzolic soils adjacent to megapolis Moscow

The article studies the regularities of cadmium (Cd) accumulation by red currant (Ribes rubrum L.) plant varieties grown on soddy-podzolic soils adjacent to the metropolis of Moscow, containing 0.26-1.02 mg/kg of mobile Cd. The researches were carried out in collection plantations of the Federal Horticultural Research Center for Breeding, Agrotechnology and Nursery (Moscow region), including varieties of different ecological and geographical origin: 9 red (Valentinovka, Viksne, Gazelle, Konstantinovskaya, Nadezhda, Niva, Rachnovskaya, Serpantin, Jonkheer Van Tets), 2 pink (Gollandskaya Rozovaya, Lydia) and 2 white (Belaya Feya, Blanca) currant varieties. The agrochemical properties of soils, the content of mobile Cd in the soil, and its content in the fruits and leaves of plants were determined. The agrochemical properties of soils, the content of mobile Cd in the soil, in the fruits and leaves of plants were determined. The coefficients of Cd assimilation by the fruits and leaves of red currant plants were calculated, the statistical dependences of the Cd accumulation parameters on the agrochemical properties of soddy-podzolic soils at different depths of the root layer were determined. Regression dependences of Cd accumulation in fruits and leaves of red currant on parameters of agrochemical properties of the soil and the content of mobile Cd in the soil were constructed. It has been established that when grown on cultivated soddy-podzolic loamy soil with a mobile Cd content of 0.26-1.02 mg/kg in the root layers of the soil, red currant varieties Belaya Feya, Blanca, Valentinovka, Viksne, Gazelle, Konstantinovskaya, Lydia, Rachnovskaya, Serpantin, Jonkheer Van Tets are more resistant to soil contamination with Cd compared to varieties Gollandskaya Rozovaya, Nadezhda, Niva. At the same time, the content of Cd in the leaves of red currant, depending on the variety, is 2-3 times higher than its content in fruits. The regression models indicated a closer dependence on the parametrs of the agrochemical properties of the soil and the Cd content in it of the values of Cd accumulation in fruits than in leaves. The assimilation of Cd by the fruits of red currant plants when cultivated on cultivated soddy-podzolic soils with a mobile Cd content of 0.26-1.02 mg/kg depended on the varietal barrier properties of plants, the content of mobile Cd in it, and also on the mobility of Cd, which depends, in first of all, from the acidity and availability of the soil with alkaline hydrolysable nitrogen.

Chemical Speciation and Potential Mobility of Heavy Metals in Organic Matter Amended Soil

Organic matter (OM) degradation from amendments used in the remediation of metal-contaminated soils leads to modifications in soil chemical properties immediately after addition, which can also affect the soil metal distribution. Therefore, the speciation and potential mobility of heavy metals e.g., lead (Pb) and cadmium (Cd) were evaluated in three soils amended with OM. Soils, both spiked (with lead nitrate and cadmium nitrate solution) and unspiked, were treated with OM at a rate of 5 tons/ha in a moist condition. The samples were in incubation for 30 days in 30% moist condition. A chemical fractionation procedure was applied to determine the distribution of Pb and Cd in soils. The potential mobility of metals was also determined. Metals transformed from mobile to immobile fractions in both spiked and unspiked soils (not treated with organic matter), but OM increased the mobile fraction of Pb in unspiked soil and decreased it in spiked soil. In contrast, the mobile fraction of Cd decreased in soils (not treated with OM), but the OM increased the mobile fractions in spiked and unspiked soils. The mobile fraction (as a percentage of total) of Cd was higher than the mobile fraction of Pb indicating the greater mobility of Cd compared to Pb. However, the three soils showed a more or less similar pattern in transforming Pb and Cd in soils since their characteristics were almost the same.

Cadmium-resistant Chryseobacterium sp. DEMBc1 strain: characteristics and potential to assist phytoremediation and promote plant growth.

The effectiveness of phytoremediation is closely related to the various interactions between pollutants, soil particles, rhizosphere microorganisms, and plants. Therefore, the object of current study was a cadmium-tolerant bacterium isolated from the rye rhizosphere, with a high degree of genetic similarity to the genus Chryseobacterium. Chryseobacterium sp. DEMBc1 was able to grow with 36 different BiologGN2 carbon sources and show the adaptation to stress factors such as Cd (100 μg ml-1), low temperature (8 °C), and salinity (2% NaCl). Furthermore, it was shown that DEMBc1 had the characteristics of plant growth-promoting microorganisms: it was able to produce ammonia, indole acetic acid, 1-aminocyclopropane-1-carboxylic acid deaminase, and siderophores, as well as solubilize Ca3(PO4)3. After inoculation with DEMBc1, a significant decrease in the concentration of Cd was observed in the roots of Festuca ovina grown in Cd-polluted soil, compared to the non-inoculated Cd-polluted soil. It was also noticed that DEMBc1 produced a large amount of extracellular polymeric substances that were significantly higher than the cellular biomass. These polymers can form a barrier to reduce the translocation of Cd from the growth medium to the plant roots. According to the current study, DEMBc1 has a stabilizing potential and can decrease the mobility of Cd in the F. ovina rhizosphere, bioaccumulate metals in plant tissues, and effectively improve the bioavailability of nutrients, especially Fe, N, and P in a polluted environments.

Pyrolysis of exhausted hydrochar sorbent for cadmium separation and biochar regeneration

Sorption is considered a cost-effective technique for cadmium (Cd) removal from water, while the exhausted Cd-enriched sorbent should be properly disposed of. In this study, pyrolysis of exhausted hydrochar sorbent was conducted at 300–900 °C, and the behavior of Cd and the physicochemical properties and environmental applications of the regenerated biochar were investigated. The vaporization of adsorbed Cd in hydrochar was greatly enhanced by elevating pyrolysis temperature, and almost no Cd was observed in the regenerated biochars obtained at 700–900 °C. In comparison with the raw hydrochar, the regenerated biochars showed higher pH, ash content, and carbon content, while the contents of hydrogen and oxygen decreased. According to the toxicity characteristic leaching procedure result, the toxicity and mobility of Cd in hydrochar were greatly reduced after pyrolysis. Notably, the regenerated biochar showed much higher Cd sorption capacity (26.05–30.24 mg/g) than the raw hydrochar (6.70 mg/g). Surface complexation with oxygen-containing functional groups was the dominant Cd sorption mechanism for hydrochar, and precipitation between Cd2+ and carbonates dominated the Cd removal by the regenerated biochars. These results illuminated that pyrolysis can be an effective technique for the harmless disposal of exhausted hydrochar sorbent and the regeneration of valuable biochar.

Low pe+pH induces inhibition of cadmium sulfide precipitation by methanogenesis in paddy soil

Soil flooding is associated with the formation of cadmium (Cd)-sulfide, which is known to decrease Cd solubility and extractability. However, the threshold for Cd-sulfide precipitation is largely unknown, particularly because carbon can capture electrons for methanogenesis during sulfate reduction in highly reducing soil conditions. Using soil microcosms with different water regimens applied, we analyzed the electrochemical and spectroscopic properties and revealed a key mechanism controlling Cd stabilization that is dependent on pe+pH (a comprehensive indicator of soil redox status). The extent of Cd-sulfide precipitation was limited, with the proportion decreasing from 58.5% to 49.6% under flooding conditions (corresponding to a decrease in pe+pH from 3.28 to 2.82). Our data suggest that the increase in Cd mobilization in highly reducing soil is due to methanogenesis outcompeting sulfate reduction for available electrons. Although glucose supply could reduce the competition between oxidized carbon and sulfur in the soil for seizing electrons, the role of glucose as an electron donor/shuttle became weaker when soil was more anaerobic. The optimal soil reductive environment for maximum Cd-sulfide precipitation was observed when pe+pH was between 4.45 and 6.58. Overall, this study provides a quantitative and mechanistic understanding of how redox status (pe+pH), sulfate reduction, and methanogenesis are coupled with Cd remobilization in over-reductive paddy soil.