RESUMEN
Co-contamination of Cd and As in strongly acidic paddy soil has posed great challenges for remediation practice due to their distinct properties. Liming is a necessary but inadequate measure for normal growth of paddy rice and for Cd and As remediation in strongly acidic paddy soils rich in iron minerals. A greenhouse rice pot cultivation experiment was conducted to explore the efficiency and mechanisms of how foliar supply of different sulfur forms (K2S, K2SO4) could further mediate the uptake, translocation and grain accumulation of Cd and As by paddy rice on basis of liming. Results showed that compared to liming alone (CK), co-application of liming and foliar supply of K2S (L + FK2S) significantly reduced contents of Cd and As in brown rice by 44.4 % and 24.7 %, respectively. Contrastingly, co-application of liming and foliar supply of K2SO4 (L + FK2SO4) decreased Cd content of brown rice by 55.5 %, but had no effect on As content. Foliar supply of K2S and K2SO4 dramatically facilitated Cd upward transfer from roots to shoots by enhancing root Cd transfer from cell wall into trophoplast. On the other hand, both sulfur forms remarkably elevated sulfur contents in leaves and significantly inhibited Cd translocation from leaves to grain by enhancing vacuolar sequestration of Cd in leaves. Compared to CK and L + FK2SO4 treatment, it was by enhancing glutathione synthesis, cell wall deposition in roots and vacuolar sequestration of As in leaves that L + FK2S showed greater inhibiting effects on transfer of As from roots, stems and leaves to grain. Foliar supply of either sulfate or sulfide could efficiently decrease grain Cd of paddy rice, but only foliar supply of sulfide is effective in reducing grain As.
Asunto(s)
Oryza , Contaminantes del Suelo , Cadmio/análisis , Suelo , Azufre , Sulfuros/farmacología , Contaminantes del Suelo/análisisRESUMEN
Ca-Fe-Si material (CIS), a novel composite material rich in calcium, iron, manganese and silicon showed marvelous immobilization properties for heavy metal(loid)s in soils. To elucidate the acid stability of Cd fixed by CIS (CIS-Cd) and the underlying immobilization mechanisms, the acid dissolution characteristics of CIS-Cd were investigated by using acid titration method and X-ray diffraction (XRD) technique. The results showed that CIS-Cd had distinctive acid buffering capacity in different pH ranges. Based on the titration curve between dissolution rate of CIS-Cd and pH, CIS-Cd can be divided into non acid-stable Cd (9.4%), moderately acid-stable Cd (22.5%) and acid-stable Cd (68.1%). XRD analysis of CIS-Cd at different pH intervals and the correlation curves of dissolution rates of Cd and concomitant elements indicated that non acid-stable Cd was mainly bound by carbonate, silicate and sulfate (CdCO3, Cd2SiO4 and CdSO4) or co-precipitated with the corresponding calcium salts. Moderately acid-stable Cd was mainly bound by magnesium-aluminum-silicon containing minerals or electrically bound by manganese iron minerals. Acid-stable Cd remaining undissolved at pH < 2.42 included CdFe2O4 and ferromanganese minerals strongly bound Cd. It was by multilateral fixation mechanisms that Ca-Fe-Si material possessed marvelous immobilization capability for Cd and strong resilience to environmental acidification as well. The findings implicated that proper combination of calcium-iron-silicon containing minerals could develop novel promising amendments with high efficiency in heavy metal(loid)s immobilization and strong resilience to environmental change.
Asunto(s)
Metales Pesados , Contaminantes del Suelo , Cadmio/química , Contaminantes del Suelo/análisis , Manganeso , Silicio , Calcio , Solubilidad , Suelo/química , Metales Pesados/análisis , Hierro/química , MineralesRESUMEN
Liming is a safe and effective remediation practice for Cd contaminated acid paddy soil. The fate of Cd can also be strongly influenced by redox chemistry of sulfur. But it is unclear if, to what extent and how the combination of liming and sulfur mediation could further control Cd uptake by paddy rice. A rice cultivation pot experiment was conducted to evaluate the impact of different sulfur forms (S0 and SO42- in K2SO4) on the solubility, uptake and accumulation of Cd in the soil-paddy rice system and how liming and reducing organic carbon mediate the process. Results showed that under neutral soil circumstances achieved by liming, co-application of K2SO4 and glucose significantly reduced brown rice Cd by 33%, compared to liming alone. They made it more readily for Cd2+ to be precipitated into CdS/CdS2 or co-precipitate with newly formed FeS/FeS2/iron oxides. The higher pH balancing capability of K2SO4 as well as liming kept the newly formed sulfide or iron containing minerals negatively charged to be more prone to adsorb Cd2+, that kept the porewater Cd2+ the lowest among all the treatments. Individual K2SO4 showed significant promoting effect on soil Cd solubility due to SO42- chelation effect. Furthermore, K2SO4 had much weaker inhibiting effect on Cd translocation from root to grain, it showed no significant attenuating effect on brown rice Cd. S0 containing treatments displayed weaker or no attenuating effect on brown rice Cd due to its strong soil acidification effect. On the basis of liming, organic carbon induced sulfur (K2SO4) mediation showed great application potential for safe production on large areas of acid paddy soil contaminated by Cd.
Asunto(s)
Oryza , Contaminantes del Suelo , Cadmio/análisis , Carbono , Óxidos , Suelo , Contaminantes del Suelo/análisis , Solubilidad , AzufreRESUMEN
A novel FeSiCa rich material (IS), chicken manure (CM) and its biochar were investigated for their efficiency in simultaneous remediation of Cd and As uptake by the vegetable Brassica chinensis L. Wet chemistry analysis and X-ray powder diffraction, scanning electron microscopy/energy dispersive X-ray spectroscopy as well as Fourier transform infrared spectroscopy were used to reveal the mechanisms responsible for Cd and As fixation in the amended soils. The IS treatment performed best in reducing Cd uptake, while the combination of IS and CM was the optimal one for As fixation. The precipitation/co-precipitation (in cadmium silicate/phosphate/phosphate hydroxide, cadmium iron and manganese oxides under alkaline conditions, and calcium/magnesium/ferric arsenates) and specific chemisorption (by amorphous iron/manganese oxides) were proved to be more efficient in simultaneously lowering As and Cd phytoavailability than was organic complexation. These findings demonstrate that FeSiCa and FeSiCaC amendments are highly efficient and promising in-situ remediation systems for safe crop production on soils contaminated with Cd and As.
Asunto(s)
Arsénico/metabolismo , Cadmio/metabolismo , Restauración y Remediación Ambiental/métodos , Contaminantes del Suelo/metabolismo , Arsénico/análisis , Brassica/química , Cadmio/análisis , Carbón Orgánico , Hierro , Compuestos de Manganeso , Estiércol , Óxidos , Fosfatos/química , Suelo/química , Contaminantes del Suelo/análisis , VerdurasRESUMEN
Contamination of rice (Oryza sativa) by Cd is of great concern. Steel slag could be used to amend Cd-contaminated soils and make them safe for cereal production. This work was conducted to study the effects of steel slag on Cd uptake and growth of rice plants in acidic and Cd-contaminated paddy soils and to determine the possible mechanisms behind these effects. Pot (rhizobag) experiments were conducted using rice plants grown on two acidic and Cd-contaminated paddy soils with or without steel slag amendment. Steel slag amendment significantly increased grain yield by 36-45% and root catalase activity, and decreased Cd concentrations in brown rice by 66-77% compared with the control, in both soils. Steel slag amendment also markedly decreased extractable soil Cd, Cd concentrations in pore-water and Cd translocation from roots to above-ground parts. It also significantly increased soil pH, extractable Si and Ca in soils and Ca concentrations in roots. Significant positive correlations were found between extractable soil Cd and Cd concentrations in rice tissues, but it was negatively correlated with soil pH and extractable Si. Calcium in root tissues significantly and negatively correlated with Cd translocation factors from roots to straw. Overall, steel slag amendment not only significantly promoted rice growth but decreased Cd accumulation in brown rice. These benefits appear to be related to improvements in soil conditions (e.g. increasing pH, extractable Si and Ca), a reduction in extractable soil Cd, and suppression of Cd translocation from roots to above-ground parts.
Asunto(s)
Cadmio/análisis , Restauración y Remediación Ambiental/métodos , Oryza/química , Contaminantes del Suelo/análisis , Acero/química , Ácidos , Cadmio/química , Grano Comestible/química , Contaminación Ambiental , Oryza/crecimiento & desarrollo , Raíces de Plantas/química , Suelo/química , Contaminantes del Suelo/químicaRESUMEN
Cadmium uptake in rice is believed to be mediated by the Fe transport system. Phyto-available Cd can be changed by Fe fertilization of substrates. This work investigated whether and how Fe fertilization affects mitigation of Cd accumulation in paddy rice. A 90-d soil column experiment was conducted to study the change of Cd and Fe availability in soil after Fe fertilization (ionic and chelated Fe). A low-Cd accumulating cultivar (TY116) and a high-Cd accumulating cultivar (JY841) were grown in two Cd-polluted paddy soils amended with chelated Fe fertilizers. Additionally, both cultivars were grown in hydroponics to compare Fe-related gene expression in EDDHAFe-deficient and EDDHAFe-sufficient roots. The column experiment showed that EDTANa2Fe(II) and EDDHAFe(III) fertilization had a better mitigation effect on soil Cd availability compared to FeSO4·7H2O. Moreover, the field experiment demonstrated that these two chelated fertilizations could reduce Cd concentrations in brown rice by up to 80%. Iron concentrations in the brown rice were elevated by Fe chelates. Compared to EDDHAFe(III), EDTANa2Fe(II) fertilization had a stronger mitigation effect by generating more EDTANa2Cd(II) in the soil solution to decrease phyto-available Cd in the soil. While EDDHAFe(III) fertilization could increase soil pH and decrease soil Eh which contributed to decreasing phyto-available Cd in a contaminated soil. In the hydroponic experiment, Fe sufficiency significantly reduced Cd concentrations in above-ground organs. In some cases, the expression of OsIRT1, OsNRAMP1 and OsNRAMP5 was inhibited under Fe sufficiency relative to Fe deficiency conditions. These results suggest that mitigation of rice Cd by Fe chelate fertilization results from a decrease in available Cd in substrates and the inhibition of the expression of several Fe-related genes in the IRT and NRAMP families.
Asunto(s)
Cadmio/análisis , Restauración y Remediación Ambiental/métodos , Fertilizantes , Hierro/química , Contaminantes del Suelo/análisis , Monitoreo del Ambiente , Contaminación Ambiental , Hidroponía , Hierro/análisis , Oryza/metabolismo , Raíces de Plantas/metabolismo , SueloRESUMEN
Economic and highly effective methods of in situ remediation of Cd and As polluted farmland in mining areas are urgently needed. Pot experiments with Brassica chinensis L. were carried out to determine the effects of three soil amendments [a novel iron-silicon material (ISM), a synthetic zeolite (SZ) and an alkaline clay (AC)] on vegetable uptake of As and Cd. SEM-EDS and XRD analyses were used to investigate the remediation mechanisms involved. Amendment with ISM significantly reduced the concentrations of As and Cd in edible parts of B. chinensis (by 84-94 % and 38-87 %, respectively), to levels that met food safety regulations and was much lower than those achieved by SZ and AC. ISM also significantly increased fresh biomass by 169-1412 % and 436-731 % in two consecutive growing seasons, while SZ and AC did not significantly affect vegetable growth. Correlation analysis suggested that it was the mitigating effects of ISM on soil acidity and on As and Cd toxicity, rather than nutrient amelioration, that contributed to the improvement in plant growth. SEM-EDS analysis showed that ISM contained far more Ca, Fe and Mn than did SZ or AC, and XRD analysis showed that in the ISM these elements were primarily in the form of silicates, oxides and phosphates that had high capacities for chemisorption of metal(loid)s. After incubation with solutions containing 800 mg L-1 AsO42- or Cd2+, ISM bound distinctly higher levels of As (6.18 % in relative mass percent by EDS analysis) and Cd (7.21 % in relative mass percent by EDS analysis) compared to SZ and AC. XRD analysis also showed that ISM facilitated the precipitation of Cd2+ as silicates, phosphates and hydroxides, and that arsenate combined with Fe, Al, Ca and Mg to form insoluble arsenate compounds. These precipitation mechanisms were much more active in ISM than in SZ or AC. Due to the greater pH elevation caused by the abundant calcium silicate, chemisorption and precipitation mechanisms in ISM treatments could be further enhanced. That heavy metal(loid)s fixation mechanisms of ISM ensure the remediation more irreversible and more resilient to environmental changes. With appropriate application rate and proper nutrients supplement, the readily available and economic ISM is a very promising amendment for safe crop production on multi-metal(loids) polluted soils.
Asunto(s)
Arsénico/farmacocinética , Brassica/metabolismo , Cadmio/farmacocinética , Contaminantes del Suelo/farmacocinética , Verduras/metabolismo , Zeolitas , Agricultura , Silicatos de Aluminio , Arsénico/análisis , Biomasa , Brassica/efectos de los fármacos , Cadmio/análisis , China , Arcilla , Restauración y Remediación Ambiental/métodos , Concentración de Iones de Hidrógeno , Hierro , Minería , Silicio , Suelo/químicaRESUMEN
Paddy soils and rice (Oryza sativa L.) contaminated by mixed heavy metals have given rise to great concern. Field experiments were conducted over two cultivation seasons to study the effects of steel slag (SS), fly ash (FA), limestone (LS), bioorganic fertilizer (BF), and the combination of SS and BF (SSBF) on rice grain yield, Cd, Pb, and Zn and nutrient accumulation in brown rice, bioavailability of Cd, Pb, and Zn in soil as well as soil properties (pH and catalase), at two acidic paddy fields contaminated with mixed heavy metals (Cd, Pb, and Zn). Compared to the controls, SS, LS, and SSBF at both low and high additions significantly elevated soil pH over both cultivation seasons. The high treatments of SS and SSBF markedly increased grain yields, the accumulation of P and Ca in brown rice and soil catalase activities in the first cultivation season. The most striking result was from SS application (4.0 t ha-1) that consistently and significantly reduced the soil bioavailability of Cd, Pb, and Zn by 38.5-91.2 % and the concentrations of Cd and Pb in brown rice by 20.9-50.9 % in the two soils over both cultivation seasons. LS addition (4.0 t ha-1) also markedly reduced the bioavailable Cd, Pb, and Zn in soil and the Cd concentrations in brown rice. BF remobilized soil Cd and Pb leading to more accumulation of these metals in brown rice. The results showed that steel slag was most effective in the remediation of acidic paddy soils contaminated with mixed heavy metals.
Asunto(s)
Cadmio/metabolismo , Grano Comestible/crecimiento & desarrollo , Plomo/metabolismo , Oryza/crecimiento & desarrollo , Contaminantes del Suelo/metabolismo , Zinc/metabolismo , Cadmio/análisis , Ceniza del Carbón , Grano Comestible/metabolismo , Concentración de Iones de Hidrógeno , Plomo/análisis , Oryza/metabolismo , Estaciones del Año , Suelo/química , Contaminantes del Suelo/análisis , Zinc/análisisRESUMEN
Zinc (Zn) and cadmium (Cd) are two closely related chemical elements with very different biological roles in photosynthesis. Zinc plays unique biochemical functions in photosynthesis. Previous studies suggested that in some Zn/Cd hyperaccumulators, many steps in photosynthesis may be Cd tolerant or even Cd stimulated. Using RNA-seq data, we found not only that Cd and Zn both up-regulated the CA1 gene, which encodes a ß class carbonic anhydrase (CA) in chloroplasts, but that a large number of other Zn up-regulated genes in the photosynthetic pathway were also significantly up-regulated by Cd in leaves of the Zn/Cd hyperaccumulator Sedum alfredii. These genes also include chloroplast genes involved in transcription and translation (rps18 and rps14), electron transport and ATP synthesis (atpF and ccsA), Photosystem II (PSBI, PSBM, PSBK, PSBZ/YCF9, PSBO-1, PSBQ, LHCB1.1, LHCB1.4, LHCB2.1, LHCB4.3 and LHCB6) and Photosystem I (PSAE-1, PSAF, PSAH2, LHCA1 and LHCA4). Cadmium and Zn also up-regulated the VAR1 gene, which encodes the ATP-dependent zinc metalloprotease FTSH 5 (a member of the FtsH family), and the DAG gene, which influences chloroplast differentiation and plastid development, and the CP29 gene, which supports RNA processing in chloroplasts and has a potential role in signal-dependent co-regulation of chloroplast genes. Further morphological parameters (dry biomass, cross-sectional thickness, chloroplast size, chlorophyll content) and chlorophyll fluorescence parameters confirmed that leaf photosynthesis of S. alfredii responded to Cd much as it did to Zn, which will contribute to our understanding of the positive effects of Zn and Cd on growth of this plant.