Bioavailability Of Cd In Soil Research Articles

Effects of Biochar and AM Fungi on Growth, Mineral Elements and Cadmium Uptake of Mulberry under Cadmium Stress

In order to explore the synergistic effect of biochar and arbuscular mycorrhizal (AM) fungi on plant growth under cadmium (Cd) stress, a pot experiment was conducted to investigate the effects of biochar application and AM fungal inoculation on mulberry (Morus alba) seedling growth, mineral element absorption, Cd uptake, soil pH and Cd availability under Cd contamination at 2 levels (0 and 4 mg⋅kg−1). The results showed that biochar application could increase the mycorrhizal infection rate of AM fungi. Biochar application and AM fungal inoculation alone or their combination could all increase plant height, biomass, mineral element content and soil pH, while reduce Cd bioavailability in soil and Cd uptake by mulberry seedlings. The effects of biochar application in increasing soil pH and N and K uptake were better compared with AM fungal inoculation. However, AM fungal inoculation presented better effects in promoting mulberry seedling growth, improving P, Ca and Mg absorption by mulberry seedlings, and reducing Cd availability in soil and Cd absorption by mulberry seedlings. The combination of biochar application and AM fungal inoculation obtained the best effect. Under Cd level of 4 mg⋅kg−1, the combination of biochar application and AM fungal inoculation increased plant height and N, P, K, Ca and Mg contents in mulberry leaves by 43.28%, 125.56%, 178.48%, 3.63%, 181.04% and 128.04%, respectively. While, Cd concentration in the roots, stems and leaves of mulberry seedlings decreased by 46.48%, 67.86% and 58.97%, respectively. Moreover, pH increased by 5.33%, while Cd availability in soil decreased by 69.53%. In conclusion, biochar and AM fungi alone or their combination can all reduce Cd stress, and promote plant growth and mineral element absorption. The combination of biochar and AM fungi presents the best effect. Biochar combined with AM fungi can be used as an effective measure for ecological restoration of degraded soil and agricultural production safety.

Cd bioavailability and nitrogen cycling microbes interaction affected by mixed amendments under paddy-pak choi continued planting.

Cadmium (Cd) is the most concerning soil pollutant, and a threat to human health, especially in China. The in-situ immobilization of Cadmium by amendments is one of the most widely adopted methods to remedy soil contamination. The study was designed to evaluate the effect of organo-chemical amendments on soil Cd bioavailability and nitrogen cycling microbes under continuous planting of rice (Oryza sativa) and pak choi (Brassica chinensis L.). The experiment was carried out using four amendments, Lime, Zeolite, Superphosphate, and Biochar, at two different ratios; M1: at the ratio of 47:47:5:1, and M2 at the ratio of 71:23:5:1, respectively. Moreover, both M1 and M2 were enriched at four levels (T1: 0.5%; T2: 1%; T3: 2%; T4: 4%). Results showed that compared with CK (Cd enriched soils), the yield of rice under treatments of M1T1 and M2T1 increased by 8.93% and 8.36%, respectively. While the biomass (fresh weight) of pak choi under M1 and M2 amendments increased by 2.52-2.98 times and 0.76-2.89 times respectively, under enrichment treatments T1, T2, and T3. The total Cd concentrations in rice grains treated with M1T3 and M2T3 decreased by 89.25% and 93.16%, respectively, compared with CK. On the other hand, the total Cd concentrations in pak choi under M1T3 and M2T2 decreased by 92.86% and 90.23%, respectively. The results showed that soil pH was the main factor affecting Cd bioavailability in rice and pak choi. The Variance partitioning analysis (VPA) of rice and pak choi showed that soil pH was the most significant contributing factor. In the rice season, the contribution of soil pH (P) on Cd bioavailability was 10.14% (P=0.102), and in the pak choi season, the contribution of soil pH was 8.38% (P=0.133). Furthermore, the abundance of ammonia oxidation and denitrifying microorganisms had significantly correlation with soil pH and exchange Cd. In rice season, when the enrichment level of amendments increased from 0.5% (T1) to 2% (T3), the gene abundance of AOA, AOB, nirK, nirS and nosZ (І) tended to decrease. While in pak choi season, when the enrichment level increased at the level of 0.5% (T1), 1% (T2), and 2% (T3), the gene abundance of AOB, nirS, and nosZ (І) increased. Additionally, the gene abundance of AOA and nirK showed a reduction in the pak choi season contrasting to rice. And the mixed amendment M2 performed better at reducing Cd uptake than M1, which may have correlation with the ratio of lime and zeolite in them. Finally, we conclude that between these two amendments, when applied at a moderate level M2 type performed better than M1 in reducing Cd uptake, and also showed positive effects on both gene abundance and increase soil pH.

Cadmium Bioavailability and Accumulation in Rice Grain are Controlled by pH and Ca in Paddy Soils with High Geological Background of Transportation and Deposition.

Cadmium (Cd) threatens rice quality and human health, yet this risk remains uncertain in paddy fields with high geological background of transportation and deposition. In this study, we collected 31 pairs of soil and rice grain samples in Doumen and Xinhui Districts in Guangdong province, China and investigated which factors controlled Cd bioavailability in soil and accumulation in rice. Soil samples were mostly acidic and contained a range of organic matter. Total Cd in soil varied from 0.10 to 1.03 mg kg- 1 and was positively correlated with those of calcium (Ca), manganese (Mn) and iron (Fe), suggesting that these elements shared same sources and Cd was most likely originated from parent material. The activity ratio (AR, CaCl2-extractable Cd/soil Cd) and bioconcentration factor (BCF, rice grain Cd/soil Cd) of Cd were negatively correlated with soil pH. The coupling relationship between soil and rice grain Cd could be described by a linear model, which was used to predict soil Cd threshold values to keep rice grain Cd concentration from exceeding the Chinese limit (0.2 mg kg- 1). In summary, Cd pollution was not very severe in the paddy soils of studied area but the risk could not be neglected when soil was acidified, which could increase Cd bioavailability and accumulation in rice grain.

Attapulgite and processed oyster shell powder effectively reduce cadmium accumulation in grains of rice growing in a contaminated acidic paddy field

Heavy-metal contamination is widespread in agricultural soils worldwide, especially paddy soils contaminated by Cd. Amendment-induced immobilization of heavy metals is an attractive and effective technique, provided that cost-effective materials are used. This field experiment compared three alkaline passivators (attapulgite, processed oyster shell powder, and mixed soil conditioner) at a rate of 2.25 t ha−1 for their effectiveness in decreasing Cd bioavailability in soils and accumulation in rice plants in a paddy field contaminated by Cd (0.38 Cd mg kg−1). The utilization of attapulgite and processed oyster shell powder decreased labile fractions but increased stable fractions of Cd in soils through ion exchange, precipitation and complexation. The addition of attapulgite decreased the concentration of bioavailable Cd in both bulk and rhizosphere soils, whereas the amendment of processed oyster shell powder decreased it only in bulk soil. The Cd accumulation in rice plants correlated significantly with acid-soluble and residual Cd fractions in the rhizosphere soil but not in the bulk soil. The addition of attapulgite and processed oyster shell powder decreased Cd accumulation in rice grains from 0.26 mg kg−1 to 0.14 and 0.19 mg kg−1, respectively, meeting the National Food Safety Standard (< 0.20 mg kg−1). However, the mixed soil conditioner did not decrease the Cd accumulation in rice shoots or grains. This study demonstrated that attapulgite and processed oyster shell powder were economic agents in reducing Cd accumulation in rice grains.

The use of bentonite and organic amendments for remediation of Cd contaminated fields: An environmental perspective

AbstractA successful technique for remediation of cadmium (Cd) contaminated soil could not only reduce its availability but also improve soil biological function. However, there are few studies that evaluate the efficiency of remediation of Cd‐contaminated soil within a sustainability framework. Therefore, a field study was conducted to investigate the remediation effectiveness and environmental impact of Cd‐contaminated vegetable soils using bentonite (B), bentonite + mushroom residue (BMR1, BMR2), and bentonite + vermicompost (BVC1, BVC2). Soil Cd bioavailability were inhibited after applying of B, BMR and BVC, and the most significant reduction of CaCl2‐ and HCl‐Cd was obtained at BMR2, being 45.5 and 24.9% decreases, respectively, relative to the control groups. Meanwhile, the concentration of Cd in the edible parts of vegetables was reduced by amendments and lettuce and leafy lettuce met the maximum limit of contaminants in vegetables (0.2 mg kg−1) (GB2762‐2017). Combined treatments had greater effects on soil fertility parameters (e.g., higher values of available N, P and K, soil organic matter, and microbial biomass C and N) as well as microbial community composition which were characterized by significant increases in the Shannon and the Simpson indices, and the quantity and abundance of dominant genera. These findings offer evidence that combined amendments could be more efficiently used for the remediation of Cd‐contaminated soils, with the goal of low Cd availability in soil and uptake in the vegetables, and improving soil quality.

Worldwide cadmium accumulation in soybean grains and feasibility of food production on contaminated calcareous soils.

Elevated toxins in soybeans extensively threaten Asian residents and over one billion vegetarians worldwide. An integrated dataset of toxic trace metal(loid)s especially cadmium (Cd) analysis in soybean grain samples (n=5217) from 12 countries/regions of origin was compiled for risk analysis. Worldwide grain Cd averaged 0.093mgkg-1, but mean values varied 16-fold between regions, with South China (0.32mgkg-1)>Argentina (0.15mgkg-1)=German (0.13mgkg-1)>Japan (0.11mgkg-1)>the United States (0.064mgkg-1)>Central-North China (0.020-0.60mgkg-1)≥Iran (0.042mgkg-1)=Brazil (0.023mgkg-1)=South Korea (0.020mgkg-1). Regression analysis suggested widespread contamination and acidic soil features significantly contributed the elevated food Cd contamination worldwide. Arsenic (As) and lead (Pb) are also of concern because excessive levels were often observed in grains. Given that soil Cd bioavailability is generally low in alkaline pH ranges, the feasibility of producing safe food from contaminated land was investigated by greenhouse experiments with one low-Cd soybean cultivar grown on 20 contaminated calcareous soils. Equilibrium-based approaches i.e., 0.01M CaCl2 and in-situ porewater extractions, and diffusion-based diffusive gradients in thin-films technique were used to determine the plant-available fractions of soil metal(loid)s to explain the bioaccumulation variation. The results suggested that soybean grains bioaccumulated mean 0.76mg Cd kg-1, ranging from 0.16 to 2.1mgkg-1, whereas As and Pb bioaccumulation was low. Cadmium accumulation was closely correlated with plant-available Cd fractions especially the 0.01M CaCl2-extractable Cd, but negatively correlated with soil pH. Even in the alkaline pH range, a slight decrease of soil pH would increase grain Cd significantly. Study region and those arable lands that have similar soil conditions are not recommended for growing soybean unless novel remediation strategies are developed.

Typical sources of Cd to paddy fields in different contaminated areas and their impacts on Cd accumulation in topsoil and rice in Changzhutan, China

Heavy metal pollution of soils has been worsening increasingly in China, which brings significant health risk to human, it is critical to investigate the sources of heavy metals in agricultural soils and explore the effects of heavy metal accumulation in crops. In this paper, the sources of cadmium (Cd) and their effects on Cd accumulation in soil and rice grown on urban farmland in Changzhutan were investigated. Among the main Cd sources (irrigation water, commercial fertilizer, and atmospheric deposition), the input flux of atmospheric deposition accounted for 76.36%–98.25% of total input flux, significantly higher than the input fluxes of irrigation water and commercial fertilizer. Manure fertilizer was also an important source of Cd in livestock breeding areas. The accumulation behaviors of Cd in soils and plants presented significant spatial variation among the study areas. Higher Cd input flux from atmospheric deposition resulted in higher Cd bioavailability in soil and more Cd accumulation in rice, and the newly deposited Cd contributed 7.35–41.23% in rice tissues. The use of manure fertilizer increased the soil pH and amount of available Cd in soil, as well as the accumulation of Cd in rice roots. Based on sequential extraction, acid-extractable Cd accounted for approximately 52.54%–61.88% of total Cd in atmospherically deposited particles in the study area, resulting in a high proportion of acid-extractable Cd in soil. This study provides useful reference data on the sources of Cd and its bioavailability in soil and rice.

Reducing cadmium bioavailability and accumulation in vegetable by an alkalizing bacterial strain

Cadmium (Cd) contamination in agricultural soils is a widespread environmental problem that can affect food safety and human health. Effective remediation methods are needed to reduce Cd bioavailability in soil and Cd accumulation in food crops. In the present study, we isolated a Cd-resistant and alkalizing bacterium strain XT-4 from a Cd-contaminated soil and evaluated its potential application in Cd bioremediation. Based on its morphological, physiological and biochemical characteristics, together with 16S rRNA gene sequence analysis, strain XT-4 was identified as a member of the Bacillus genus. Strain XT-4 showed a strong ability to increase the pH and decrease Cd solubility in the medium. A greenhouse-based pot experiment with a Cd-contaminated soil was conducted to evaluate the effect of strain XT-4 inoculation on the growth and Cd accumulation of the vegetable Pak choi (Brassica rapa ssp. chinensis). Inoculation increased the rhizosphere pH, decreased CaCl2-extractable Cd in the soil and decreased Cd concentration in the edible part of Pak choi by 28–40%. The results suggest that inoculation with alkalizing bacterial strain XT-4 represents an effective solution to increase rhizosphere pH and decrease Cd uptake by vegetable crops in Cd-contaminated acid soils.

Does biochar inhibit the bioavailability and bioaccumulation of As and Cd in co-contaminated soils? A meta-analysis

Biochar, an effective and low-cost amendment for immobilizing heavy metals, has been extensively studied. However, the simultaneous inhibition effects of biochar on the plant uptake for arsenic (As) and cadmium (Cd) in co-contaminated soils are still ambiguous due to their distinct environmental behaviors. A meta-analysis was conducted to quantitatively assess the effects using 1030 individual observations from 52 articles. On average, biochar application significantly decreased the bioavailability of Cd in soils by 50.12%, while slightly increased the bioavailability of As in soils by 2.39%. The more instructive result is that biochar application could also simultaneously reduce the concentration of As and Cd in plants by 25.48% and 38.66%, respectively. The orders of the decreased percentage of As and Cd in various tissues were root < stem< leaf < grain, and root < leaf < stem < grain, respectively. According to the analysis of critical factors, manure biochar, low pyrolysis temperature (at <400 °C), low application rate (<2%), and high SOC (>30 g/kg) were more conducive to reduce the bioaccumulation of As and Cd simultaneously in co-contaminated soils. Pristine and modified biochar could inhibit As and Cd accumulation in crops, but their efficiencies need to be further improved to ensure the safety of crop productions. Overall, the meta-analysis suggests that biochar has the potential to remedy the As and Cd co-contaminated soils.

The dual beneficial effects of vermiremediation: Reducing soil bioavailability of cadmium (Cd) and improving soil fertility by earthworm (Eisenia fetida) modified by seasonality

This study aimed to assess earthworm's capability of reducing the bioavailability of cadmium (Cd) in soil and increasing soil fertility with the modification of seasonal variations of ambient temperatures on the efficacy of vermiremediation. Earthworms were exposed in soil fortified with 0, 5, 10, and 20 mg Cd kg−1, for 7, 14 and 21 days in winter and spring. The bioavailability of Cd in soil, which is represented in the form of diethylenetriaminepentaacetic acid-extractable fraction (DTPA-Cd), were significantly reduced, ranging from 7.9 to 18.3% in winter and 8.8 to 20.8% in spring. Meanwhile, we found earthworm activities could significantly improve the soil fertility as the results of increasing the availability of nitrogen, phosphorous, and potassium in soil, a prominent advantage of vermiremediation in heavy metal-contaminated soil. Although seasonality could increase Cd toxicity in earthworms, higher ambient temperature in spring season also promoted the reduction of Cd bioavailability and the increase of soil fertility, due to significant increase of microbial populations. In conclusion, we reported the dual beneficial effects of vermiremediation in reducing bioavailability of Cd in soil and simultaneously improving soil fertility in which both outcomes were modified by seasonality.

Securing of an Industrial Soil Using Turfgrass Assisted by Biostimulants and Compost Amendment

This work aimed to study the effects of compost (applied at two rates) and two commercial microbial biostimulants on the mobility and bioavailability of potentially toxic elements (PTEs) in an industrial soil phytostabilized by Dactylis glomerata L. or a mixed stand of grasses (Lolium perenne L., Poa pratensis L. and Festuca arundinacea Shreb.). The soil showed very high pseudototal and bioavailable concentrations of cadmium (Cd) and lead (Pb), due to improper lead-acid batteries storage. Compost amendment in combination with the two biostimulants produced the best outcomes in terms of plant growth and nutrient uptake. The same mix of beneficial microbes improved soil biological fertility enhancing soil nitrogen fixing and ammonia oxidizing bacteria, while reduced the pore water and NH4NO3 extractable concentrations of Cd and at lower extent of Pb in soil. Accordingly, the lower mobility and bioavailability of Cd in soil determined a lower uptake and accumulation of Cd in shoots of different grass species. Our results suggest that a green cap with turfgrass assisted by biostimulants and compost amendment in PTE-contaminated industrial sites could be a reliable and effective practice to protect and restore soil biological fertility and to reduce the risk of PTE dispersion in the surrounding environment.

Effects of composited organic mobilizing agents and their application periods on cadmium absorption of Sorghum bicolor L. in a Cd-contaminated soil

Organic mobilizing agents have been advocated for phytoremediation of heavy metals contaminated soils, while the effects of application period of such agents remain unclear. A pot experiment was conducted, with two composited organic agents (oxalic acid or citric acid + dissolved organic fertilizer (OA + DOF and CA + DOF)) and four application periods (seeding, jointing, flag leaf and heading stages) of sorghum (Sorghum bicolor L.), to investigate their impacts on Cd bioavailability in soil. Results indicated that application of the two composited agents increased soil dissolved organic carbon (DOC) and DTPA extractable Cd by 7.31–49.13%, Cd contents in roots and shoots by 21.49–72.10%, bioaccumulation factor (BCF) and translocation factor (TF) of shoots by 4.44–71.99%, while reduced soil pH by 0.25–0.53 units, respectively. Most of these indices increased with the application periods, and largely peaked with their application during the flag leaf to heading stages. Meanwhile, the maximum sorghum biomass (132.84 g pot−1) and Cd bioaccumulation quantity (BCQ, 0.71 mg pot−1) in shoots were obtained for the CA + DOF applied at the heading. The DTPA extractable Cd was closely related to soil pH and DOC. Similar close relationships were observed between the Cd contents in shoots and soil DTPA extractable Cd, pH and DOC. The BCQ of Cd was positively related to the shoots biomass rather than their Cd contents. Therefore, the sorghum combined with the CA + DOF may be advocated as an alternative phytoremediation mode in Cd-contaminated soils, and the mobilizing agent should be primarily applied at the heading stage.

Effects of biochars combined with ferrous sulfate and pig manure on the bioavailability of Cd and potential phytotoxicity for wheat in an alkaline contaminated soil

Reducing the content of Cd in wheat grains is necessary for human health, especially in alkaline farmland in northern China where a large area of soils is heavily polluted with Cd. A field experiment was conducted to investigate the effects of wheat straw biochar (WB) and maize straw biochar (MB) combined solely with ferrous sulfate (FeSO4) or combined with FeSO4 and pig manure (PFWB and PFMB) on Cd bioavailability in soil and the phytotoxicity of Cd in wheat in an alkaline contaminated soil. The results showed that the application of these treatments decreased the concentrations of CaCl2-extractable Cd by 32.8–60.5% and increased the soil organic matter by 36.8–106.7% compared with those of the control treatment. The acid-soluble fraction of Cd was decreased by 3.7–16.8% but the residual fraction was increased by 1.7–13.7%. Furthermore, the addition of WB and MB increased the soil pH by 0.29 and 0.16 units, respectively, while the other treatments decreased the soil pH by 0.16–0.37 units. The concentrations of Cd in different wheat tissues were decreased in amended soils, and these decreases were positively correlated with CaCl2-extractable Cd and the acid-soluble fraction of Cd. The ability to accumulate Cd was in the order of root>straw>grain. In addition, there was a downward trend in the bio-concentration and translocation factors under different amendments. The amendments of PFWB and PFMB had better efficiency in the immobilization of Cd in soil and the inhibition of Cd uptake of wheat than WB and MB. In addition, the treatments of PFWB and PFMB increased the wheat yield by 14.3–16.2%, and thus have a great application prospect based on the cost-benefit analysis.

Reduction of Cd accumulation in Se-biofortified rice by using fermented manure and fly ash.

Large areas of soils in China are contaminated with Cd and are deficient in Se. Therefore, here, we aimed to reduce Cd accumulation while increasing Se content in rice grain, and to elucidate the mechanisms associated. A greenhouse pot experiment was conducted to determine grain concentrations of Se and Cd upon foliar spraying of Se combined with the application of horse manure and/or fly ash to different contaminated soils containing Cd 0.51 (T1), 1.46 (T2), and 4.59mg Cd kg-1 (T3). The amount of Fe, Si, and Cd in root iron plaque, and concentrations of Cd and Si in rice tissues were also determined. Foliar spray of Se increased Se concentration in brown rice from approximately 0.04 to 0.15mgkg-1. Fly ash significantly reduced Cd concentration in brown rice from 0.07 to 0.05, 0.15 to 0.09, and 1.00 to 0.55mgkg-1 at the T1, T2, and T3 treatment levels, respectively, and soil Cd bioavailability (by at least 33.3%), while it increased Si content in rice roots and shoots by at least 34%. The increase of Si concentration in rice tissues inhibited Cd translocation to brown rice by at least 17%. Horse manure increased the formation of root Fe plaque by approximately 2.3-fold, which resulted in the significant reduction of Cd accumulation in brown rice, shoots, and roots by 36-56%. Thus, foliar spray of Se in combination with the application of fly ash and horse manure proved an effective method to produce Cd-low and Se-rich rice.

Effects of Water Management on Soil Properties and Cd Behavior of Typical Paddy Soils

To explore the effects of water management mode on Cd environmental behavior in different parent-material-developed paddy soils, two parent-material-developed paddy soils (yellow clayey soil and granitic sandy soil) under three exogenous Cd levels (0.5, 2.0, and 5.0 mg·kg-1) with different water management modes (long-term flooding, moistening irrigation, and wet-dry rotation) were cultured in this study. The soil redox potential (Eh value), pH value, Cd concentration in soil solution, and Cd fractionation were also determined. The results showed that water management mode had different effects on the pH and Eh values of soils developed from different parent materials. The change rates of soil pH value were as follows:long-term flooding:-2.61% (yellow clayey soil), 2.25% (granitic sandy soil); alternation of dry and wet:-1.96% (yellow clayey soil); 0.52% (granitic sandy soil); wet irrigation:-4.08% (yellow clayey soil) and -0.52% (granitic sandy soil). The Eh value of the soils was negatively correlated with the pH value. The influence pattern of water management model on Cd mass concentration of soil solutions in two parent-material soils was consistent. The Cd mass concentration of soil solutions in granitic sandy soil was higher than that in yellow clayey soil. The mean values of Cd concentration were 1.03 μg·L-1 for yellow clayey soil and 1.07 μg·L-1 for granitic sandy soil. Water management mode had no significant effect on the proportions of organic bound Cd or Fe-Mn bound Cd in two different parent-material-developed soils. The long-term flooding mode promoted the transformation of exogenous Cd to residual Cd, and this promotion in yellow clayey soil was higher than that in granitic sandy soil. In conclusion, during the process of regulating soil Cd bioavailability through water management, the role of soil parent materials needs to be considered.

Reduction mechanism of Cd accumulation in rice grain by Chinese milk vetch residue: Insight into microbial community

Chinese milk vetch is an efficient approach to reduce Cd accumulation in rice, nevertheless, its reduction mechanism is not well understood. In this study, we investigated the rice grain Cd, soil properties and microbial community in a Cd-polluted paddy field amended with milk vetch residue (MV) or without (CK) during rice growth period. We found that milk vetch residue averagely decreased the Cd content in rice grain by 45%. Decrease of Cd in rice mainly attributed to the inhibition of Cd activation by milk vetch residue at heading stage probably by the formation of HA-Cd (Humic Acid) and CdS. Increased pH and organic matter (OM) promoted the reduction of available Cd. In addition, nonmetric multidimensional scaling (NMDS) analysis revealed that microbial community structure was significantly different between MV and CK treatment (r = 0.187, p = 0.002), and the core functions of differentially abundant genera were mainly associated with N-cycling, organic matter degradation and sulfate-reducing. The application of milk vetch residue increased the abundance of sulfate-reducing bacteria (SRB) by 8–112% during the rice growth period, which may involve in promoting the transformation of Cd to a more stably residual Cd (CdS). Canonical correspondence analysis (CCA) and mantel test analysis indicated that available K (p = 0.004) and available N (p = 0.005) were the key environmental factors of shaping the SRB. Altogether, changes in soil properties affected microbial structure and functional characteristics, especially the response of SRB in MV treatment would provide valuable insights into reducing the bioavailability of Cd in soil.

Mitigation of Cd accumulation in rice with water management and calcium-magnesium phosphate fertilizer in field environment.

Pollution of Cd has seriously threatened environmental safety and human health. The field experiment was conducted to investigate the effects of calcium-magnesium phosphate fertilizer and water management on bioavailability of Cd in soils and its accumulation in rice. The results revealed that continuous flooding has enhanced soil pH from 5.10 to 5.72 and reduced soil redox potential (Eh) from 164 to - 60mV. Application of calcium-magnesium phosphate fertilizer has significantly raised soil pH from 5.10 to 6.45 (P < 0.05). The treatment of calcium-magnesium phosphate fertilizer and continuous flooding has reduced available content of Cd in soils by 28.57%. The content of Cd in brown rice was significantly diminished by 51.36% (P < 0.05). The continuous flooding has promoted formation of residual Cd in soil with application of calcium-magnesium phosphate fertilizer. The biomass and grain production of rice was not significantly decreased compared with control.

Simultaneous reduction of arsenic and cadmium bioavailability in agriculture soil and their accumulation in Brassica chinensis L. by using minerals.

In situ immobilization of heavy metal cations in contaminated soil using natural minerals is an attractive remediation technique. However, little research has focused on the remediation of arsenic (As) and cadmium (Cd) co-contaminated. In this work, three different crystal structures and chemical compositions minerals, zeolite; bentonite; and dolomite, were applied to simultaneously reduce the uptake of As and Cd in Brassica chinensis L., and the mechanism on reducing As and Cd bioavailability in soil were also investigated. The results showed that the three minerals decreased the bioavailability of As and Cd and restrained their uptake by Brassica chinensis L. with the order followed bentonite>zeolite>dolomite. Particularly, bentonite decreased the exchangeable As and Cd by 4.05% and 32.5% and the concentrations of As and Cd in shoots of Brassica chinensis L. by 36.2% and 64.6%, as compared with the controls. Moreover, with the addition of minerals increased, the dry biomass of Brassica chinensis L. and the rhizosphere microbial functional diversity increased significantly, and the highest biomass increased by 289% at 4.0% addition of bentonite. Correlation analysis indicated that the uptake of As and Cd was positive with the available Cd and As in soil, and was negative with soil pH and available N. Furthermore, the Scanning Electron Microscopy-Energy Dispersive Spectroscopy and Fourier Transform Infrared Spectroscopy analysis illustrated the interaction between minerals and Cd mainly involved ion-exchange and adsorption, while As was mainly immobilized by calcium and magnesium through forming precipitation. In conclusion, this present study implied that the bentonite can be recommended as the more effective amendment to immobilize metal (loid)s in soil and thereby reduce the exposure risk of metal (loid)s associated with grains consumption.

Immobilization of cadmium in simulated contaminated soils using thermal-activated serpentine

ABSTRACT The thermal-activated serpentine prepared by heating natural serpentine at different temperatures was used to immobilize cadmium (Cd) in simulated contaminated soils. The results showed that the increasing soil pH induced by adding serpentine was primarily responsible for reducing the content of TCLP-Cd (toxicity characteristic leaching procedure-Cd) in soil. Furthermore, adding thermal-activated serpentine could promote the transformation from exchangeable form of Cd in soil to low bioavailable Cd (Fe-Mn oxides, carbonate, and residual form) by surface adsorption and surface precipitation, and then reduced the bioavailability of Cd in soil. Under the same treatment condition, adding S700 (serpentine activated at 700°C) exhibited better performance to immobilization of Cd, and it could reduce exchangeable Cd by 23.76~36.49%, and increase carbonate, Fe-Mn oxide, and residual form of Cd by 6.03~8.03%, 6.05~8.35%, and 11.17~19.58%, respectively. These results indicated that thermal-activated serpentine would be the great potential for immobilization of Cd in soil.

Effect of Metal Oxide Nanoparticles on the Chemical Speciation of Heavy Metals and Micronutrient Bioavailability in Paddy Soil.

The effects of engineered nanoparticles (ENPs) on heavy metal fate and biotoxicity in farmland soil are mostly unknown. A flooding–drying simulation experiment was conducted to study the effects of three typical metal oxide nanoparticles (TiO2-NPs, ZnO-NPs and CuO-NPs) on the chemical speciation of heavy metals and micronutrient bioavailability in paddy soil. The results showed that the addition of ZnO-NPs and CuO-NPs caused significant increases in soil pH, Eh and EC after a 90-d flooding–drying process. ZnO-NPs and CuO-NPs addition caused clearly increase in the Zn and Cu concentrations in the acid-soluble fraction, Fe/Mn oxides-bound fraction and organic-bound fraction, leading to higher bioavailability in the soil. DTPA-extractable Zn and Cu increased to 184.6 mg kg−1 and 145.3 mg kg−1 in the maximum ZnO-NPs and CuO-NPs concentration treatments (500 mg kg−1). TiO2-NPs promoted the transformation of Mn from a Fe/Mn oxides-bound fraction to an acid-soluble fraction. Soil Cd bioavailability obviously decreased in the TiO2-NPs treatment but increased in the ZnO-NPs and CuO-NPs treatments.