Cd Availability Research Articles

Formation of ferrihydrite induced by low pe+pH in paddy soil reduces Cd uptake by rice: Evidence from Cd isotope fractionation

Ferrihydrite (Fh) is an important iron mineral in paddy soil and is prone to phase transition during dynamic redox condition, which affects Cd distribution and induces Cd isotope fractionation across soil to rice. Here, we conducted rice culture experiments with or not Fh application under different irrigation regimes to study the relationship between Fe species and Cd availability, as well as the isotope ratio of Cd in different Cd pools in paddy soil-rice system. Fh addition under continuous flooding (FL) with the decrease of pe + pH from 9.36 to 3.44 promoted the formation of amorphous Fe oxides as increased by 120.1% and facilitated Cd immobilization along with the increase of Fe/Mn oxides bound Cd by 25.3%, compared with continuous drying (DY) treatment. The isotopically heavy Cd were preferentially enriched from soil to extractable Cd (Δ114/110Cdextractable Cd-soil = 0.39–0.62‰) and from soil to grain (Δ114/110Cdgrain-soil = 0.40–0.66‰) particularly at low pe + pH and with Fh addition, while light Cd were enriched in Fe/Mn oxides (Δ114/110CdFe/Mn oxides bound Cd-extractable Cd = −0.65 ∼ −0.14‰). Besides, the expression of transporters involved in Cd transport in rice like OsNRAMP1, OsNRAMP1, OsHMA3, OsHMA2 and OsLCT1 were suppressed under low pe + pH condition. These findings indicated that low pe + pH facilitated Cd stabilization by the existence of more amorphous iron oxides, which induced the enrichment of heavy Cd isotope in liquid phase and light in Fe/Mn (oxy)hydroxides, respectively.

Biochar amendment of a metal contaminated soil partially immobilized Zn, Pb, and Cd and reduced ryegrass uptake

Soil heavy metals (HM) contamination threatens soil and water quality, which significantly affects humans and animals. This study focuses on the competitive immobilization of zinc (Zn), lead (Pb), and cadmium (Cd) in soils from a contaminated site using ryegrass (Lolium perenne) in a potting experiment amended with biochars. Increased rates of switchgrass- (SGB) and poultry litter-derived biochars (PLB) were applied before ryegrass cultivation. Soil HM phytoavailability and HM concentrations in plant shoots were determined. Multivariate regression models were used to evaluate the influence of several soil chemical attributes on the HM phytoavailability. The increased rates of both biochars reduced the Zn, Pb, and Cd availability (p < 0.001). Langmuir models showed that the maximum HM immobilization (IMAX) was 169.2 ± 29.5 mg kg–1 for Zn with SGB, and 20 ± 7.4 (Pb) and 1.08 mg kg–1 (Cd) with PLB. The extended Langmuir model (EL) showed competitive HM immobilization since there was a decrease in the IMAX of Zn (∼90 ± 28 mg kg–1 from SGB) and Cd (∼0.70 ± 0.21 mg kg–1). Negative values of Pb and Cd immobilization at low rates of SGB indicated an increase in those HM availabilities and preferential immobilization for Zn. The reduced Zn and Pb uptake in ryegrass shoots ranged from 70% to 98% and were optimum at rates of 0.50% ± 0.00%–0.60% ± 0.06% for both biochars, and 1.6% ± 0.4% of SGB for Cd. The stepwise multiple linear regression (SMLR) and partial least squares (PLS) revealed that pH and organic matter (OM) were the most responsible factors for reducing Zn bioavailability while OM was more impactful in decreasing Pb and Cd levels. This suggests that the preferential immobilization for Zn relies on its higher sensitivity to the pH increase. Also, the ubiquitous positive relationship among the metals studied shows that competitive immobilization is ceased at high rates of biochars application. Path analysis (PA) showed that pH and OM were the common contributors from both biochars to simultaneously affect Zn, Pb, and Cd availability regardless of the contrasting physicochemical properties of the two bioproducts. This work proved the potential of applying low rates of two contrasting feedstock-derived biochars to remediate the contaminants and safely grow ryegrass.

Binding of Cd(II) to birnessite and fulvic acid organo-mineral composites and controls on Cd(II) availability

Manganese oxide minerals (MnOs) are major controls on cadmium (Cd) mobility and fate in the environment. However, MnOs are commonly coated with natural organic matter (OM), and the role of this coating in the retention and availability of harmful metals remains unclear. Herein, organo-mineral composites were synthesized using birnessite (BS) and fulvic acid (FA), during coprecipitation with BS and adsorption to preformed BS with two organic carbon (OC) loadings. The performance and underlying mechanism of Cd(II) adsorption by resulting BS-FA composites were explored. Consequently, FA interactions with BS at environmentally representative (5 wt% OC) increase Cd(II) adsorption capacity by 15.05–37.39% (qm = 156.5–186.9 mg g−1), attributing to the enhanced dispersion of BS particles by coexisting FA led to significant increases in specific surface area (219.1–254.8 m2 g−1). Nevertheless, Cd(II) adsorption was notably inhibited at a high OC level (15 wt%). This might have derived from the supplementation of FA decreased pore diffusion rate and generated Mn(II/III) competition for vacancy sites. The dominant Cd(II) adsorption mechanism was precipitation with minerals (Cd(OH)2), and complexation with Mn–O groups and acid oxygen-containing functional groups of FA. In organic ligand extractions, the exchange Cd content decreased by 5.63–7.93% with low OC coating (5 wt%), but increased to 33.13–38.97% at a high OC level (15 wt%). These findings help better understand the environmental behavior of Cd under the interactions of OM and Mn minerals, and provide a theoretical basis for organo-mineral composite remediation of Cd-contaminated water and soil.

Effects of zero-valent iron added in the flooding or drainage process on cadmium immobilization in an acid paddy soil

Zero-valent iron (ZVI) is a promising material for the remediation of Cd-contaminated paddy soils. However, the effects of ZVI added during flooding or drainage processes on cadmium (Cd) retention remain unclear. Herein, Cd-contaminated paddy soil was incubated for 40 days of flooding and then for 15 days of drainage, and the underlying mechanisms of Cd immobilization coupled with Fe/S/N redox processes were investigated. The addition of ZVI to the flooding process was more conducive to Cd immobilization. Less potential available Cd was detected by adding ZVI before flooding, which may be due to the increase in paddy soil pH and newly formed secondary Fe minerals. Moreover, the reductive dissolution of Fe minerals promoted the release of soil colloids, thereby increasing significantly the surface sites and causing Cd immobilization. Additionally, the addition of ZVI before flooding played a vital role in Cd retention after soil drainage. In contrast, the addition of ZVI in the drainage phase was not conducive to Cd retention, which might be due to the rapid decrease in soil pH that inhibited Cd adsorption and further immobilization on soil surfaces. The findings of this study demonstrated that Cd availability in paddy soil was largely reduced by adding ZVI during the flooding period and provide a novel insight into the mechanisms of ZVI remediation in Cd-contaminated paddy soils.

Influences of biochar with selenite on bacterial community in soil and Cd in peanut

Cadmium (Cd) pollution in crops seriously affects the ecosystem and human health. Effective measures should be employed to reduce the absorption and accumulation of cadmium in crops. Currently, there are many pieces of research on the application of biochar (BC) and selenium (Se) alone to the remediation of soil Cd pollution; however, few investigations have been devoted to the application of BC and Se together to the remediation of soil Cd pollution. The peanut was taken as the target crop to explore the effects of exogenous selenium and biochar on the remediation of soil Cd pollution. The response of the soil bacterial community to two levels of Cd concentration and its relationship with soil properties and Cd availability are methodically investigated. This study sets two cadmium pollution concentrations of low Cd (5 mg/ kg) and high Cd (20 mg/kg), as well as six treatments: blank, BC, soil Se, soil Se-BC, leaf Se, and leaf Se-BC. The achieved results revealed that both Se and BC could noticeably enhance the yield of peanut seeds and reduce the Cd content in peanut seeds. Among them, Se-BC treatment on soil exhibits the most influence, which reduces the Cd content by 47.86%. Se and BC also affect the physical and chemical properties of soil and remarkably magnify the content of soil available phosphorus, organic matter, soil pH, and soil conductivity. For instance, then effect is detected in the case of applying selenium biochar to soil, leading to an increase of about 64.38%, 72.62%, 2.64%, and 61.15%, respectively, and reducing the content of soil available cadmium by 21.02%. Redundancy analysis confirms that these properties enhance the abundance of dominant bacteria Actinobacteria, Proteobacteria, and Chloroflexi. The correlation analysis also indicates that Saccharimonadales, Bacillus, Arthrobacter, and other bacteria with the function of reducing the bioavailability of cadmium in soil reveal a considerable positive correlation with the variations of physical and chemical properties. In general, exogenous Se and BC incorporate to drop the content of available Cd in the soil through direct passivation, passivation caused by soil environmental change, and passivation caused by altering the soil microbial community structure; as a result, the migration and enrichment of Cd in peanut seeds are blocked and reduced. Moreover, the mixed application of BC and soil Se exhibits the best effect.

In-situ Remediation Effect of Cadmium-polluted Agriculture Land Using Different Amendments Under Rice-wheat Rotation

Exploring the effects of one-time amendment treatments on cadmium (Cd)-contaminated farmland soils is beneficial for providing a theoretical basis to effectively prevent Cd pollution in farmland soils and ensure the safe production of crops. Five amendments, including straw biochar, fly ash, sepiolite, white marble powder, and shale (particle size <0.2 mm, application rate 2.25 kg·m-2), were applied to the Cd-contaminated farmland soils. The soil nutrients, pH, soil available Cd, and Cd chemical forms in the soils and grain Cd concentration in the planted crops were determined to investigate the effects and persistence of one-time applications of the five amendments. The results showed that:① the application of the five amendments had little effect on soil nutrient content, but all of them could increase soil pH. Amendment treatments improved the transfer of Cd from the acid extraction fraction to residue fraction and further reduced the Cd availability in the soil. The decreasing amplitudes of straw biochar and white marble powder soil conditioner were 20.42%-22.53%, which was higher than those in the other treatments. ② The grain Cd concentrations in rice and wheat were significantly decreased under the amendment treatments with the decreasing amplitudes of 19.88%-48.77% and 5.06%-24.00%, respectively. The Cd concentrations in rice grains under the treatments of straw biochar, fly ash, and white marble powder soil conditioner were 0.195, 0.196, and 0.223 mg·kg-1, respectively, which were lower than those under the other treatments and were close to or approached the National Standard of Food Safety(GB 2762-2017)(0.2 mg·kg-1). ③ The immobilization effects on Cd in farmland soils were decreasing with time under one-time application of the amendments. The available Cd concentrations in the soil and Cd concentrations in crop grains were still lower than those in the control after three rounds of rice-wheat rotation. The straw biochar and white marble powder soil conditioner had a good and long-term effect on reducing Cd availability in soils and Cd concentrations in crop grain, making them ideal materials for safe production in Cd-contaminated soils.

Microbial driving mechanism of soil conditioner on reducing cadmium uptake by rice and improving soil environment

Soil conditioners can reduce the transfer of heavy metal ions from the soil to crops and play a crucial role in safe food production. However, it remains unclear how soil conditioners reduce cadmium (Cd) accumulation in rice (Oryza sativa L.). In this study, five soil conditioners (U-, N-, T-, L-, and C-type) commonly used in China were selected, and the effects of soil conditioners on bacterial and fungal community diversity, soil enzyme activity, soil pH, and organic matter content were investigated through field experiments in two sites. The Cd content of rice was significantly reduced by 32.4–55.1 % in site I and 16.0–33.3 % in site II under the five soil conditioner treatments. The decrease in Cd content was related to the increase in soil pH, organic matter content, and Cd fixation-related flora caused by soil conditioner application. U-, N- and C-type conditioners increased soil pH, inducing an increase in the relative abundances of microbial populations related to Cd sorption and sequestration (Firmicutes, Nitrospirota, Actinobacteriota, and Methylomirabilota). U-, T-, and L-type conditioners increased soil organic matter, causing an increase in the relative abundance of microbial flora associated with macromolecule degradation, including bacteria (Acidobacteriota and Chloroflexi) and fungi (Ascomycota and Basidiomycota). Conditioner application reduced the availability of soil Cd; indirectly promoted the increased abundance of beneficial soil bacteria; and increased the activities of invertase, urease, dehydrogenase, catalase, and acid protease. In conclusion, soil conditioner reduces the effective soil Cd by adjusting soil pH and organic matter content, increasing Cd-passivating flora and Cd-tolerant flora. Soil conditioner also increases the abundance of other beneficial flora, enhances soil enzyme activity, promotes the microecological balance of soil under Cd stress, and finally reduces Cd accumulation in rice.

Understanding the cadmium passivation and nitrogen mineralization of aminated lignin in soil

Aminated lignin (AL) was prepared and first applied to remediation of cadmium (Cd) pollution in soil. Meanwhile, the nitrogen mineralization characteristics of AL in soil and its effect on soil physicochemical properties were elucidated by soil incubation experiment. The results showed that the Cd availability was dramatically lowered in soil by adding the AL. The DTPA-extractable Cd content of AL treatments was considerably reduced by 40.7–71.4 %. The soil pH (5.77–7.01) and absolute value of zeta potential (30.7–34.7 mV) enhanced simultaneously as the AL additions increased. The content of soil organic matter (SOM) (99.0–264.0 %) and total nitrogen (95.9–301.3 %) were gradually enhanced due to high C (63.31 %) and N (9.69 %) content in AL. Moreover, AL significantly elevated the content of mineral nitrogen (77.2–142.4 %) and available nitrogen (95.5–301.7 %). The first-order kinetic equation of soil nitrogen mineralization revealed that AL greatly enhanced nitrogen mineralization potential (84.7–143.9 %) and reduced environmental pollution by lowering the loss of soil inorganic nitrogen. AL could effectively reduce the availability of Cd through direct (self-adsorption) and indirect effects (improvement of soil pH, SOM and reduction of soil zeta potential), thereby achieving passivation of Cd in soil. In short, this work will develop a novel approach and technical support for soil heavy metal remediation, which is of great significance for improving the sustainable development of agricultural production.

Effects of a novel Cd passivation approach on soil Cd availability, plant uptake, and microbial activity in weakly alkaline soils

Heavy metal pollution, including that caused by cadmium (Cd), is a matter of increasing concern. Although in situ passivation remediation has been widely used to treat heavy metal-polluted soils, most studies have focused on acidic soils, while studies on alkaline soil conditions are scarce. In this study, the effects of biochar (BC), phosphate rock powder (PRP), and humic acid (HA) on Cd2+ adsorption were examined alone and in combination to choose an appropriate Cd passivation approach for weakly alkaline soils. Additionally, the combined impact of passivation on Cd availability, plant Cd absorption, plant physiology indexes, and soil microbial community was elucidated. BC had a higher Cd adsorption capacity and removal rate than those of PRP and HA. Moreover, HA and PRP enhanced the adsorption capacity of BC. A combination of biochar and humic acid (BHA), and biochar and phosphate rock powder (BPRP) significantly affected soil Cd passivation. BHA and BPRP decreased the plant Cd content and soil Cd-DTPA (diethylenetriaminepentaacetic acid) by 31.36 %, 20.80 %, 38.19 %, and 41.26 %, respectively; however, they increased the fresh weight by 65.64–71.48 % respectively, and dry weight by 62.41–71.35 %, respectively. Notably, only BPRP increased the node and root tip number in wheat. Total protein (TP) content increased in BHA and BPRP, with BHA showing lower TP than BPRP. BHA and BPRP showed a reduction in glutathione (GSH), malondialdehyde (MDA), H2O2, and peroxidase (POD); BHA showed a significantly lower GSH than BPRP. Additionally, BHA and BPRP increased soil sucrase, alkaline phosphatase, and urease activities, with BPRP showing considerably higher enzyme activity than BHA. Both BHA and BPRP increased the number of soil bacteria, altered the community composition, and critical metabolic pathways. The results demonstrated that BPRP could be used as a highly effective, novel passivation technique for the remediation of Cd-contaminated soil.

Use of Three Different Nanoparticles to Reduce Cd Availability in Soils: Effects on Germination and Early Growth of Sinapis alba L.

Globally, cadmium (Cd) is one of the metals that causes the most significant problems of contamination in agricultural soils and toxicity in living organisms. In this study, the ability of three different nanoparticles (dose 3% w/w) (hydroxyapatite (HANPs), maghemite (MNPs), or zero-valent iron (FeNPs)) to decrease the availability of Cd in artificially contaminated agricultural soil was investigated. The effect of Cd and nanoparticles on germination and early growth of Sinapis alba L. was also assessed by tolerance/toxicity bioassays. The available Cd contents in the contaminated soil decreased after treatment with the nanoparticles (available Cd decreased with HANPs: >96.9%, MNPs: >91.9%, FeNPs: >94%), indicating that these nanoparticles are highly efficient for the fixation of available Cd. The toxicity/tolerance bioassays showed different behavior for each nanoparticle. The HANPs negatively affected germination (G(%): 20% worsening compared to control soil), early root growth (Gindex: -27.7% compared to control soil), and aerial parts (Apindex: -12%) of S. alba, but showed positive effects compared to Cd-contaminated soils (Gindex: +8-11%; Apindex: +26-47%). MNP treatment in Cd-contaminated soils had a positive effect on germination (G(%): 6-10% improvement) and early growth of roots (Gindex: +16%) and aerial parts (Apindex: +16-19%). The FeNPs had a positive influence on germination (G(%): +10%) and growth of aerial parts (Apindex: +12-16%) but not on early growth of roots (Gindex: 0%). These nanoparticles can be used to reduce highly available Cd contents in contaminated soils, but MNPs and FeNPs showed the most favorable effects on the early growth and germination of S. alba.

Effects of sulfur supply on cadmium transfer and concentration in rice at different growth stages exposed to sulfur-deficient but highly cadmium-contaminated soil

BackgroundSulfur (S) has been widely used to alleviate cadmium (Cd) toxicity and control Cd accumulation in rice under waterlogging conditions. However, the results are contradictory, and the reasons remain unclear. This could be because most studies rarely simultaneously monitor the processes of S-induced soil Cd bioavailability and Cd accumulation in rice throughout its growth period. A pot experiment was conducted to investigate the influence of two sulfur levels (0, and 30 mg S kg−1) on Cd concentration and translocation in rice at three growth stages (booting, filling and maturity) under waterlogging conditions. Paddy soil deficient in S but contaminated with Cd (10.16 mg Cd kg−1) was used for the pot experiment.ResultsS application increased concentrations of Cd in grain at the filling stage partially because S induced the promotion of Cd transfer from roots to stems, leaves, and grains, and S induced the accumulation and fixation of Cd in iron plaques at the filling stage. However, the application of S significantly reduced Cd concentrations in brown rice at the maturity stage, which could be attributed to three aspects, as described below. First, S supply reduced the availability of Cd in soil and iron plaque on the root surface by reducing dissolved Cd in soil pore water and transferring Cd from iron plaque on the root surface to roots. Second, S supply inhibited the transfer of Cd in other tissues to brown rice based on Cd transfer factors from roots, stems, leaves, and husks to brown rice, which were obviously lower with S supply than without S supply at the maturity stage. Third, S induced the dilution of Cd in brown rice because the application of S significantly increased brown rice biomass by 215%.ConclusionsA S-induced decline in Cd accumulation in brown rice was related to S-regulated Cd transfer among rice plants, S-induced promotion of rice growth and a decrease in Cd bioavailability in S-deficient but Cd-contaminated paddy soil under waterlogging conditions. This study provides valuable information for growing rice in low-S and Cd-contaminated paddy soil and reducing the risk of Cd in rice to humans.Graphical abstract

Effects of biochars derived from four crop straws on a Cd-polluted cinnamon soil.

Crop straw biochar is an efficient and low-cost alternative amendment for heavy metal immobilization in acidic soil. However, reports on the effect of these biochars on the amendment of actual Cd-polluted calcareous soil are limited. Therefore, four biochars, derived from peanut, rice, maize, and wheat straws, were applied to determine the changes in the chemical properties of alkaline cinnamon soil and effects on Cd immobilization. The results showed that the cation exchange capacity and the contents of organic C, Mehlich-3K, and Mehlich-3 P in the biochar-amended soil increased by 4.87-22.02%, 68.78-218.83%, 1.9-10.3 times, and 19.18-74.40%, respectively, indicating the potential high performance of biochar in improving soil fertility and productivity. The Community Bureau of Reference sequential extraction results showed that decrease in acid-extractable Cd resulted in a reduced availability of Cd. Thus, crop straw biochar could be a promising alternative for soil Cd decontamination and fertilization.

Improvement of Tomato Fruit Quality and Soil Nutrients through Foliar Spraying Fulvic Acid under Stress of Copper and Cadmium

Fulvic acid (FA), the essence and most active component in humus, is widely used as a fertilizer synergistic agent and for soil improvement. As a synergist, FA can not only highly chelate microelements, but also play a key role as a growth promoter. Due to the small molecular weight and high solubility, FA is usually used by foliar spraying in vegetable production, yet the effect on fruit quality and nutrient absorption is still unclear. Here, ‘Jinpengdashuai’ tomatoes were used to investigate the effects of spraying FA on tomato fruit quality and soil Cu and Cd availability under stress of Cu and Cd by pot experiments. The results showed that the 1000 mg·L−1 FA could significantly improve the biomass of tomato plants to some extents under different stresses of Cu and Cd. After spraying FA, the Cu and Cd content in different organs and the whole accumulation decreased; meanwhile, the transport efficiency of Cu and Cd was also reduced to some degree. The drops of FA significantly changed the chemical form of Cu and Cd in 0~10 cm soil, from the easily absorbed water soluble (or ion) form into the insoluble form, hard to absorb. The Cu content in the residual state increased by 93.8% and 172.5%, respectively, under single and compound stress, and the Cd content in the residual state increased by 16.7% and 58.6%. Foliar spraying FA could promote the absorption and transport of essential nutrients such as nitrogen, phosphorus, potassium, calcium, magnesium and zinc, and maintain the nutrient balance, which alleviates the inhibition of normal metabolism by Cu and Cd stress, to a certain extent. More distinctly, Vc, total sugar and lycopene increased by 11.4~45.9%, 19.2~48.5% and 30.9~84.5%, respectively, indicating that foliar spraying FA could improve the appearance and flavor quality of tomato fruits under stress of Cu and Cd.

Low Cd-accumulating rice grain production through inoculation of germinating rice seeds with a plant growth-promoting endophytic bacterium

This study investigated the effects of the plant growth-promoting endophytic bacterium Cupriavidus taiwanensis KKU2500–3 on the growth of KDML105 rice plants and cadmium (Cd) accumulation in grains. The rice plants were cultivated in soils with 20 and 50 ppm Cd under greenhouse conditions for two consecutive years. At both levels, Cd reduced rice growth and development. Under Cd stress, KKU2500–3 colonized the root surface and interior of rice plants at the early growth stage, and this colonization remained until the late stage. The colonized bacteria increased the pigment contents but reduced the root-to-aboveground translocation of Cd. In soil with 20 ppm Cd, the phytochelatin content of the bacteria-inoculated rice was lower (32.3–89.3%) than that of uninoculated rice. In soil with 50 ppm Cd, the bacteria-inoculated rice exhibited higher glutathione reductase (5–63%) and proline (5–115%) levels, a higher reduced glutathione (GSH)/0.5 oxidized glutathione (GSSG) ratio (4–212%) and decreased lipid peroxidation (1–19%) compared with uninoculated rice. The root-to-grain translocation factor of inoculated rice in soil with 50 ppm Cd was significantly lower than that of inoculated rice in soil with 20 ppm Cd, and this finding was consistent with the 38.6% and 75.1% reductions in Cd accumulation observed in grains from soils with 20 and 50 ppm Cd, respectively. The Cd content of KDML105 grains grown in soil with 50 ppm Cd was 0.36 ppm, which is below the Codex standard for polished rice (0.4 ppm). The levels of available P, Zn, and SO42- also affect Cd availability in soil, and colonized KKU2500–3 showed varying responses to different Cd levels. Thus, bacterial inoculation, the Cd level and soil properties play important roles in Cd accumulation in KDML105 rice grains. The role of C. taiwanensis KKU2500–3 on the production of low-Cd-accumulating rice in paddy fields contaminated with a range of Cd levels should be further investigated.

Effect of selenium and soil pH on cadmium phytoextraction by Urochloa decumbens grown in Oxisol

It has been speculated that selenium (Se) supply can affect cadmium (Cd) ‘availability’ and increase the Cd tolerance of plants used for phytoextraction, in a pH-dependent process. Thus, we evaluated the interaction Cd-Se and the effects of soil pH in this interaction on plant availability of Cd and phytoextraction efficiency of Urochloa decumbens cv. Basilisk grown in Oxisol. Two soil concentrations of Cd (0.93 and 3.6 mg kg-1) and Se (<0.2 and 1 mg kg-1) and two soil pH (0.01 mol L-1 CaCl2) conditions (4.1 and 5.7) were considered. At both pH, Se supply increased the exchangeable fraction of Cd and decreased the residual Cd fraction. At pH 4.1, the growth of U. decumbens was impaired by Se addition, regardless of Cd exposure. The lower root growth and tillering of U. decumbens exposed to Cd disappeared at pH 5.7 due to uptake of low Se concentrations. Thus, the toxic or beneficial effects of Se on growth of U. decumbens used for Cd phytoextraction depend on the amount of Se assimilated. The Cd phytoextraction efficiency of U. decumbens was not improved by Se supply, regardless of soil pH. Therefore, we cannot recommend the application of Se to increase Cd phytoextraction by this grass.

Stabilization Characteristics of Exogenous Cd in Different Types of Soil

To clarify the characteristics of stabilization and availability of exogenous cadmium (Cd) in different types of soils, six main agricultural soils in Sichuan province, including acidic purple soil, neutral purple soil, calcareous purple soil, gray fluvo-aquic soil, typical yellow soil, and rinsed yellow soil, were used in this study. A soil culture experiment was conducted to explore the differences in stabilization time, chemical form, and effective Cd content between the six types of soils. Additionally, the effects of exogenous Cd on the growth and Cd accumulation of cabbage growing in different soils was discussed. The results showed the following: 1 with exogenous Cd treatment, the available Cd content of the six soils decreased sharply within 15 d after Cd addition and then tended to be flat. After 30 d, there was no significant difference. The available Cd contents of rinsed yellow soil and acidic purple soil were significantly higher than that of the other four soils, and the content of calcareous purple soil was significantly lower (1.01 mg·kg-1). 2 After stabilization, exchangeable Cd was the main Cd form in the six soils, up to 42.51%-56.07%. The relative proportions of other Cd forms differed greatly between different soils. The proportion of iron and manganese oxides in the rinsed yellow soil and typical yellow soil was higher, whereas organic complex Cd, residual Cd, and carbonate-bound Cd were higher in the gray fluvo-aquic soil, neutral purple soil, and calcareous purple soil, respectively. 3 The characteristics of availability and bioavailability of Cd among different soils were significantly different with different exogenous Cd doses. With the lowest Cd dose (0.5 mg·kg-1), compared with that in the control, there was no significant decrease in Cd content in the edible parts of the cabbage, but Cd accumulation in the edible parts differed. The Cd contents of edible parts of the cabbage growing in typical yellow soil and rinsed yellow soil were significantly higher than that of the other soils. With the highest Cd dose (2.0 mg·kg-1), the growths of cabbage growing in all six soils were significantly inhibited. The available Cd contents of rinsed yellow soil and acidic purple soil were significantly higher than that of the other four soils, which is consistent with the Cd content in the edible parts of the cabbage. The available Cd contents and the Cd content in the edible parts of the cabbage in calcareous purple soil were the lowest, and acidic soils, especially in rinsed yellow soil, had the highest.

Performance and mechanisms for Cd(II) and As(III) simultaneous adsorption by goethite-loaded montmorillonite in aqueous solution and soil

A series of goethite-modified montmorillonite (GMt) materials was synthesized for the amelioration of cationic cadmium (Cd) and anionic arsenic (As) complex contaminants in soil and water bodies. The results showed that goethite (Gt) was successfully loaded onto the surface of montmorillonite (Mt), which possessed more functional groups (such as Fe–O, and Fe–OH) and a larger specific surface area. GMt-0.5 (Mt loaded with Gt at a ratio of 0.5:1) showed the highest adsorption capacity for Cd(II) and As(III) with the maximum of 50.61 mg/g and 57.58 mg/g, respectively. The removal rate of Cd(II) was highly pH dependent, while the removal rate of As(III) showed little dependence on pH. The goethite on montmorillonite might contribute to the formation of surface complexes with As(III) and oxidation of As(III) to As(V). In the binary system, both, synergistic and competitive adsorption existed simultaneously. Importantly, in the binary system, the removal of As(III) was more favorable because of the electrostatic interaction, formation of a ternary complex, and co-precipitation. In addition, the amendment of GMt-0.5 significantly reduced the availability of Cd and As in the soil. This study suggests that GMt-0.5 is a promising candidate for the simultaneous immobilization of metal (loid)s in both, aqueous solution and mine soil.

Improving bagasse degradability and enzymatic activity of a Cd-polluted soil by inoculation with Phanerochaete chrysosporium

Phanerochaete chrysosporium was used to investigate the degradation of bagasse and the activities of cellulase and β-glucosidase in a Cadium (Cd) contaminated soil. The soil was treated with sugarcane bagasse (5%) and the experiment was performed as a repeated measures design with three factors, a Cd treatment (0, 20 and 40mg Cd kg−1), addition of fungi (inoculation with P chrysosporium and uninoculated) and experimental duration (sampling at days 1, 20, 50 and 90) with three replicates. At the end of the experiment, the concentration of Lignocellulosic compounds, carbon fractions, Cd availability, biological properties and β-glucosidase and cellulase activity were measured. A higher Cd bioavailability (40mg Cd kg−1 compared to 20mg Cd kg−1 with a control) resulted in lower enzyme activity, lower carbon fractions (cold and hot water extractable and peroxidizable carbon), lower soil biological properties (soil respiration and soil microbial carbon) and lower degradation of bagasse (higher amount of cellulose, hemicellulose and lignin). Fungal inoculation and incubation time resulted in these properties being modified to some extent. Lignocellulosic compounds decreased during the incubation and in fungus-inoculated treatments, indicating bagasse degradation. The activity of enzymes was higher in fungus-inoculated treatments (7.12μg PNG g−1 soil−1 h−1 for β-glucosidase and 0.17μmol min−1 for cellulase) than in uninoculated treatments (6.39μg PNG g−1 soil−1 h−1 for β-glucosidase and 0.13μmol min−1 for cellulase). P chrysosporium effectively degraded sugarcane bagasse, even in Cd polluted soil. However, a decrease in Cd availability occurred from day 1 to day 90, but the activity of the different enzymes did not increase as much as might have been expected. For each Cd level, the concentration of lignocellulosic compounds probably had more of an effect on enzyme activity than the bioavailability of Cd.

Effects of microplastics on cadmium accumulation by rice and arbuscular mycorrhizal fungal communities in cadmium-contaminated soil.

Both microplastics (MPs) and cadmium (Cd) are common contaminants in soil-rice systems, but their combined effects remain unknown. Thereby, we explored the effects of three MPs, i.e., polyethylene terephthalate (PET), polylactic acid (PLA), and polyester (PES), on Cd accumulation in rice and the community diversity and structure of arbuscular mycorrhizal fungi (AMF) in soil spiked with or without Cd. Results showed that 2% PLA decreased shoot biomass (-28%), but PET had a weaker inhibitive effect. Overall, Cd alone did not significantly change shoot and root biomass and increased root biomass in combination with 0.2% PES. MPs generally increased soil Cd availability but decreased Cd accumulation in rice tissues. Both MPs and Cd improved the bioavailability and uptake of Fe and Mn in rice roots. MPs altered the diversity and community composition of AMF, depending on their type and dose and co-existing Cd. Overall, 2% PLA caused the most distinct changes in soil properties, plant growth and Cd accumulation, and AMF communities, but showed no synergistic interactions with Cd. In conclusion, MPs can mediate rice performance and Cd accumulation via altering soil properties, nutrient uptake, and root mycorrhizal communities, and biodegradable PLA MPs thought environment-friendly can exhibit higher phytotoxicity than conventional MPs.

Soil pH restricts the ability of biochar to passivate cadmium: A meta-analysis

Soil acidification is the main cause for aggravation of soil cadmium (Cd) pollution. Biochar treatment can increase the soil pH and decrease the Cd availability in soils. However, there is limited information in literature on the comprehensive assessment of the response of Cd fractions to biochar. Therefore, in the present meta-analysis study, we evaluate the response of Cd fractions to biochar application in soils with different pH and to further examine the effect of physicochemical properties of biochar on Cd. Results from the overall analysis indicated that biochar treatment increased the soil pH by 7.0%, thereby decreasing the amount of available Cd (37.3%). In acidic soil, biochar significantly reduced the acid-soluble fraction (Acid-Cd) of Cd by 36.8%, while Oxidizable fraction of Cd (Oxid-Cd, 20.9%) and Residual fraction of Cd (Resid-Cd, 22.2%) were significantly increased. In neutral soils, only Acid-Cd was significantly reduced (33.0%) in the presence of biochar. In alkaline soils, biochar caused significant reduction in Acid-Cd of 12.4% and an increase in Oxid-Cd and Resid-Cd of 26.6% and 47.8%, respectively. Further, our findings showed that biochar with cation exchange capacity >100 cmol+/kg effectively decreased Acid-Cd (32.4%), while biochar with the percentage of hydrogen <2% was more contributory in increasing Resid-Cd (64.3%). These results demonstrate the importance of soil pH in regulating the biological effectiveness of Cd in soil and the complexation between the functional groups of biochar and Cd, and provide key information for the remediation of Cd pollution in soils with different pH by biochar.