Search

To investigate the effects of nano-copper oxide (CuO NPs) on plant growth, physio-biochemical characteristics, and heavy metal content under cadmium stress, a hydroponics experiment was conducted on the effects of single and combined treatments of CuO NPs (0, 10, 20, and 50 mg·L -1 ) and Cd (0, 1, and 5 μmol·L -1 ) on the fresh weight, photosynthetic pigment content, MDA content, antioxidant enzyme activity (CAT, POD, SOD, and GR), and Cu and Cd contents in Brassica chinensis L. The results showed that under the single addition of CuO NPs, the fresh weight and activities of CAT, POD, and GR were inhibited as a whole. Photosynthetic pigment content and SOD activity increased first and then decreased with the increase in CuO NPs concentration, whereas MDA content in leaves and roots, and Cu content in subcells of B. chinensis L. increased with the increasing of CuO NPs. As compared with that in the control, CuO NPs promoted the growth of B. chinensis L., and the fresh weight increased by 8.70%-44.87% at 1 μmol·L -1 Cd. When the content of Cd was up to 5 μmol·L -1 , a low content (10 mg·L -1 ) of CuO NPs promoted the growth of B. chinensis L., whereas a high concentration (50 mg·L -1 ) showed an inhibitory effect. The addition of CuO NPs could increase photosynthetic pigment and MDA contents under different Cd stress, and MDA content in leaves and roots of B. chinensis L. increased by 4.34%-36.27% and 13.43%-131.04%, respectively, than that in the control groups. Under the same concentration of 1 μmol·L -1 Cd, the addition of CuO NPs decreased the activities of CAT and GR, whereas the activity of POD increased. When the content of Cd was up to 5 μmol·L -1 , CuO NPs increased the POD activity and inhibited the activity of SOD and GR. The activities of CAT and CAT in the leaves of B. chinensis L. initially showed an increasing and then decreasing trend. CuO NPs and Cd showed antagonistic effects, the maximum reduction of Cd content in leaves and roots of Brassica chinensis L. under 1 μmol·L -1 Cd treatment was 45.64% and 33.39%, and that under 5 μmol·L -1 Cd treatment was 18.25% and 25.35%, respectively. The content of Cu and Cd in subcellular organs of the plants decreased, but the proportion of soluble components increased. These results indicated that CuO NPs at low concentrations promoted plant growth under Cd stress and further inhibited the absorption of Cd but increased the oxidative damage to B. chinensis L.

A field trial was conducted to identify the key factors affecting intraspecific variation in the cadmium (Cd) content in the grain of winter wheat. Three wheat cultivars with low Cd accumulation and two wheat cultivars with high Cd accumulation were planted. The Cd accumulation and transport and ionomic traits were examined in different organs of the tested wheat cultivars. Additionally, correlation analysis and principal component analysis were used to identify the key plant organs, translocation pathways, and elements that determine the intraspecific variation in the Cd content in wheat grain. The results showed that the bioaccumulation factors of Cd in glume, rachis, internode 1, and node 1, as well as the transport factors of Cd from rachis to grain, from rachis to glume, from internode 1 to rachis, and from node 1 to internode 1, were significantly correlated with Cd bioaccumulation factors in grain. The above-mentioned bioaccumulation factors and transport factors of Cd made a great contribution to the principal components that could discriminate between the wheat cultivars with low and high Cd accumulation and were significantly different among cultivars. Therefore, glume, rachis, internode 1, and node 1 were the key organs affecting the genotype differences in Cd content in wheat grain, and Cd translocation from rachis to grain, from rachis to glume, from internode 1 to rachis, and from node 1 to internode 1 were the key pathways controlling the variety differences in Cd accumulation in wheat grain. The analysis of wheat ionome showed that the bioaccumulation factors of Mg and Mn in the key organs and the transport factors of Mo, Cr, and Pb in the key transport pathways were significantly correlated with the bioaccumulation factor of Cd in wheat grain and contributed greatly to the differentiation between the wheat cultivars with low and high Cd accumulation in the principal component analyses. Thus, in the above-mentioned key organs and transport pathways, Mg, Mn, Mo, Cr, and Pb were the key elements affecting the genotype differences in Cd content in wheat grain.

A pot experiment was conducted to reveal the effects of intercropping a low-cadmium (Cd) accumulating cultivar and a Cd hyperaccumulator on the safe utilization and phytoextraction of Cd-polluted soils. Two cultivars of Brassica chinensis L. (the low-Cd accumulating cultivar Huajun, and the common cultivar Hanlü), were intercropped with four cultivars of Tagetes patula L. (Dwarf Red, Dwarf Yellow, Tall Red, and Tall Yellow). We examined the biomass, photosynthetic characteristics, and Cd accumulation in the plants and available Cd content and dissolved organic carbon (DOC) content in the soils. The results show that under the intercropping treatments, the biomass of B. chinensis decreased significantly and those of T. patula increased significantly, compared with the monoculture treatments. When intercropped with T. patula , the net photosynthetic rate, stomatal conductance, and transpiration rate in the leaves of B. chinensis decreased significantly, compared with the monoculture treatments. When Huajun was intercropped with Dwarf Red, the shoot Cd content of Huajun significantly decreased by 14.5%, and that of Dwarf Red increased significantly by 36.5% compared with the monoculture. Under the other intercropping treatments, the shoot Cd content of B. chinensis increased significantly, or showed no significant change, and that of T. patula showed no significant change. Under the intercropping treatments, the total amount of Cd in the shoot of B. chinensis decreased significantly, and that of T. patula increased significantly, compared with the monoculture. There were no significant differences in the Cd extraction ratios between the intercropping treatments and the monoculture of T. patula. The shoot Cd content of B. chinensis was significantly correlated with soil available Cd content and DOC content ( P <0.01 and P <0.05, respectively). In conclusion, the intercropping treatment of Huajun and Dwarf Red significantly reduced shoot Cd content in B. chinensis and increased that in T. patula , and it did not affect the Cd extraction ratio. This is suitable for the safe utilization and phytoextraction of Cd-polluted soils.

Field experiments were conducted to investigate the effects of Mn-based modified rice husk biochar on soil organic carbon, aggregate structure, mass load, and the content of available Cd in aggregates. The results showed that the concentration of soil organic carbon increased gradually with additional modified biochar, resulting in a 3.2%-32% increase compared with the CK. Modified biochar improved the composition structure and stability of soil aggregates, and increased the amount of large aggregates (5-8 mm and 2-5 mm), while micro-aggregate production was inhibited (≤0.25 mm). Compared with the CK, mean weight diameter (MWD), geometrical mean weight (GMD), and soil aggregate structural body ( R 0.25 ) of the soil aggregates increased by 15.1%-20.3%, 8.1%-22.4%, and 0.43%-7.6%, respectively. Cd was preferentially enriched on small aggregates, and the mass loading of Cd in soil aggregates increased gradually with decreasing particle size. The distribution factor of Cd showed significant enrichment in the 0.5-1 mm and 0.25-0.5 mm grain sizes, whereas it showed a clear loss in particle sizes of 5-8 mm and 2-5 mm. The addition of modified biochar reduced the content of DTPA-Cd in soil aggregates, causing 7.6%-15.1%, 15.6%-24.3%, 3.6%-13.8%, and 11.6%-13.7% reductions in 5-8, 2-5, 0.5-1.0, and 0.25-0.5 mm particle sizes, respectively. In general, modified biochar not only has a favorable optimizing function on the structure of soil aggregates, but also decreases the content of available Cd in different sizes of soil aggregates, increasing its significance in the remediation of Cd-contaminated soil.

We explore the effects of different passivating agents on livestock manure treatment by using chicken manure and straw as raw materials and thermophilic rapid fermentation. We investigate the effects of sepiolite (SE), calcium magnesium phosphate fertilizer (NP), biochar (BI), compounds of sepiolite plus calcium magnesium phosphate fertilizer (S+N), sepiolite plus biochar (S+B), calcium magnesium phosphate fertilizer plus biochar (N+B), and sepiolite plus calcium magnesium phosphate fertilizer and biochar (SNB) on the physical and chemical characteristics, heavy metal fraction and distribution, and organic matter content in chicken manure compost. The results showed that the addition of different passivating agents significantly increased the pH in chicken manure organic fertilizer ( P <0.05). The seed germination rate was increased after applying of passivation agents, being>80%, and the germination inhibition rate decreased accordingly, whereas the values of electric conductivity (EC) and organic carbon were inhibited. The total nitrogen content and carbon/nitrogen ratio (C/N) were lower than of those before composting, and all of the indicators reached the standard of organic fertilizer maturity. However, differences among the groups after composting were that the pH increase in the compounding treatment was comparatively higher, and that the EC decreased significantly under the treatment of the single sepiolite and calcium magnesium phosphate, whereas the total nitrogen content and C/N ratio of organic carbon were not significantly different in each group. Although the total amount of heavy metals in our organic chicken manure fertilizer increased due to a concentration effect, the proportion of exchangeable heavy metals in the fertilizer decreased, and while the ratio of the residual heavy metals increased. The passivation effect on heavy metals under combined treatments of different materials was better than that of a single agent, and the SNB treatment had the best effect on the passivation of Ni, Zn, As, and Pb. After composting treatment, the concentrations of humic substances (HS) and humic acid (HA) increased significantly ( P <0.05), and the highest concentrations increased by 19.8% and 78.9%, respectively. The amount of fulvic acid (FA) decreased by 4.47%-20.11% compared with the initial conditions. Infrared spectroscopy analysis showed that the small molecular substances of polysaccharides increased after composting. In summary, the addition of a passivation agent can promote the heavy metal passivation in chicken manure organic fertilizers to potentially render the compost as harmless.

To enhance the adsorption capacity of sepiolite (Sep) on Cd 2+ in solution, an acid-base Sep (ABsep) was obtained using the method of combined acid-base modification. The structural properties of Sep and ABsep were analyzed by adsorption-desorption isotherms of N 2 , scanning electron microscopy with energy dispersive X-ray spectroscopy (SEM-EDS), transmission electron microscopy (TEM), Fourier-transform infrared spectroscopy (FTIR), and X-ray powder diffraction (XRD). Static adsorption experiments were carried out to evaluate the effects of time, mass ratio of ABsep/Cd 2+ , temperature, adsorbent dose, pH, and co-existing ions on the adsorption of Cd 2+ by ABsep. The results showed that the pore structure of the ABsep was more developed than that of Sep. In comparison to Sep, the specific surface area, average pore diameter, and pore volume of ABsep increased by 66.1%, 15.7%, and 34.8%, respectively, and the exchangeable ion contents also increased. The main components of the ABsep were SiO 2 and Mg(OH) 2 . The adsorption process of Cd 2+ by Sep and ABsep could be well fitted with a pseudo-second-order kinetic equation and Langmuir isotherm, and both were spontaneous endothermic reactions, which were mainly chemical adsorption along with physical adsorption. The best mass ratio of ABsep:Cd 2+ was 3:1, and the maximum saturated adsorption capacity fitted by the Sips model of the ABsep on Cd 2+ at 298 K was 142.43 mg·g -1 , which was 3.55 times that of Sep. As the adsorbent dose increased, the adsorption amounts of Cd 2+ first increased and then decreased, with the optimum dose being 0.3 g·L -1 . The amount of Cd 2+ adsorption by the ABsep increased with the initial pH of the solution, whereby the best pH was 7. We also found that the presence of K + , Na + , Mg 2+ , and Ca 2+ at different concentrations could inhibit the adsorption of Cd 2+ , whereby the inhibition of Mg 2+ was the highest.

One hundred and twenty types of chicken manure organic fertilizer samples were collected from five provinces and two cities in the Huang-Huai-Hai region, to investigate heavy metal content, fractionation, and environmental risk through toxicity characteristic leaching procedures. Results showed that content of heavy metals in chicken manure organic fertilizer varied greatly, in the order of Zn > Cu > Pb > As > Cd. When compared with the standard for organic manure, ratios of Cd, As, and Pb exceeded the standard by 6.7%, 47.05%, and 14.28%, respectively. Moreover, the content of heavy metals varied significantly in different provinces. Cd and Zn in organic manure fertilizers were mainly Fe and Mn oxide-bound fractions, accounting for 37.3% and 43.79%, respectively. However, the proportion of residual fractions of Pb, organically-bound fractions of Cu, and exchangeable forms of As were higher. Contents of TCLP-Zn,-Cu,-Cd,-Pb and-As in organic manure were 41.11, 33.3, 0.07, 1.25, and 0.21 mg·kg -1 , respectively. The number of samples in which Zn and Pb in organic manure exceeded the standard was 6 and 5, respectively, with these mainly obtained from Hebei and Jiangsu provinces. There was a significant correlation between total content of Zn, Cu, Cd, and As in organic manure and content of TCLP ( P <0.05). Based on an annual manure application rate of chicken manure of 15 t·hm -2 , safe application of chicken manure is in the order of Henan > Tianjin > Anhui=Shandong=Jiangsu > Hebei > Beijin.

Two cultivars of pakchoi with different cadmium (Cd) accumulation were grown in nutrient solutions containing low and sufficient zinc (Zn) levels. ZnSO 4 and ZnNa 2 EDTA were applied as foliar fertilizers. The bioaccessibilities of Cd and Zn in pakchoi were assessed by the in vitro digestion method, and the bioaccessible established daily intakes (BEDI) of Cd and Zn from pakchoi were calculated. The effect of foliar zinc application on concentrations, bioaccessibilities, and BEDIs of Cd and Zn in pakchoi was evaluated. Results show that the Cd concentrations in shoots of the tested pakchoi cultivars under sufficient Zn condition were significantly lower than those under low Zn condition, and foliar application of ZnNa 2 EDTA significantly decreased the Cd concentrations of pakchoi. The tested pakchoi cultivars with sufficient Zn had a significantly higher mean shoot Zn concentration than those with low Zn. Foliar Zn treatments significantly increased shoot Zn concentrations of pakchoi, with the highest in the ZnSO 4 treatment. Cd bioaccessibility in the tested pakchoi cultivars with sufficient Zn was significantly lower than that with low Zn. Foliar applied Zn could significantly reduce Cd bioaccessibility in the gastric phase, with a maximal reduction of 35.81% compared to the control. Foliar treatment with ZnSO 4 could significantly decrease Cd bioaccessibility in the small intestinal phase, with a maximal reduction of 59.24% compared to the control. Foliar Zn treatments reduced significantly the Zn bioaccessibility of pakchoi in the gastric and small intestinal phases, with a maximal reduction of 68.90% compared to the control. The reduction of Zn bioaccessibility was higher in the ZnSO 4 treatment than in the ZnNa 2 EDTA treatment. Via the consumption of the Cd-contaminated common cultivar Hanlv, the BEDI values of Cd were higher than that of the provisional tolerable daily intake (PTDI) standard of WHO [0.83 μg·(kg·d) -1 ]. However, via the consumption of the low-Cd accumulating cultivar Huajun or pakchoi with foliar application of ZnSO 4 , the BEDI values of Cd decreased significantly and were below the PTDI value. Via the consumption of pakchoi in the control or low-level ZnNa 2 EDTA treatments, the BEDI values of Zn were below that of the recommended nutrient intake for Zn. However, via the consumption of pakchoi with foliar application of ZnSO 4 or high-level ZnNa 2 EDTA, the BEDI values of Zn were higher than that of the recommended nutrient intake and met the human needs for Zn from vegetables. Under the ZnSO 4 treatment, the BEDI values of Zn from pakchoi were the highest. In conclusion, foliar zinc application could significantly reduce the bioaccessibilities of Cd and Zn in pakchoi and the BEDI values of Cd and increase the BEDI values of Zn. Foliar application with ZnSO 4 was the most suitable treatment to reduce Cd intake and increase Zn intake from pakchoi.

A pot experiment was conducted to investigate the immobilization remediation effects of sepiolite on soils artificially combined contamination by Cd and Pb using a set of various pH and speciation of Cd and Pb in soil, heavy metal concentration in Oryza sativa L., and soil enzyme activity and microbial quantity. Results showed that the addition of sepiolite increased the soil pH, and the exchangeable fraction of heavy metals was converted into Fe-Mn oxide, organic and residual forms, the concentration of exchangeable form of Cd and Pb reduced by 1.4% - 72.9% and 11.8% - 51.4%, respectively, when compared with the control. The contents of heavy metals decreased with increasing sepiolite, with the maximal Cd reduction of 39.8%, 36.4%, 55.2% and 32.4%, respectively, and 22.1%, 54.6%, 43.5% and 17.8% for Pb, respectively, in the stems, leaves, brown rice and husk in contrast to CK. The addition of sepiolite could improve the soil environmental quality, the catalase and urease activities and the amount of bacteria and actinomycete were increased to some extents. Although the fungi number and invertase activity were inhibited compared with the control group, it was not significantly different (P > 0.05). The significant correlation between pH, available heavy metal content, urease and invertase activities and heavy metal concentration in the plants indicated that these parameters could be used to evaluate the effectiveness of stabilization remediation of heavy metal contaminated soil.

Biomass-based materials such as biochar have a good performance in heavy metal adsorption. The adsorption of Cd2+ on biochar converted from cotton straw was studied. Adsorption isotherm, kinetics and effect factors such as temperature, pH and ionic strength were investigated. The adsorption of Cd2+ on biochar can be fitted by the Freundlich isotherm better than the Langmuir isotherm. The maximum adsorption amounts of Cd2+ at different temperatures were 9.738 mg x g(-1) (288.15 K), 10.14 mg x g(-1) (298.15 K), 10.40 mg x g(-1) (308.15 K) and 10.71 mg x g(-1) (318.15 K), respectively. The free energies AG(theta) were from -8.346 kJ x mol(-1) to -10.276 kJ x mol(-1) at different temperatures, indicating that the adsorption of Cd2+ onto biochar is spontaneous and is an endothermic process. The adsorption process can reach equilibrium within 40 minutes and can be fitted by the pseudo second order kinetic model. pH showed a significant effect on the adsorption of Cd2+ on biochar in the range of 2-8. The adsorption amount of Cd2+ on biochar shows a reducing trend with the increasing ionic strength.

The effect of new hybrid material and its compound treatments with phosphate on immobilization of cadmium and lead in contaminated soil was investigated using a pot-culture experiment, and the immobilization mechanism of hybrid material was clarified through analysis of heavy metal fractions, sorption equilibration experiment and X-ray photoelectron spectroscopy (XPS). The single treatments of hybrid material could not significantly promote growth of Brassica chinensis, while the compound treatments of hybrid material and phosphate markedly increased dry biomass of shoots and roots, with maximal increases of 75.53% and 151.22%, respectively. Different hybrid material treatments could significantly reduce Cd and Pb concentrations in shoots, with maximal reductions of 66.79% and 48.62%, respectively, and the compound amendment treatments appeared more efficient than the single amendment treatments in reducing Cd and Pb uptake of B. chinensis. Different hybrid material treatments could significantly decrease concentrations of toxicity characteristic leaching procedure (TCLP) extractable Cd and Pb, and the compound hybrid material treatments appeared more efficient than the single treatments in reducing TCLP extractable Cd and Pb. Through the formation of bidentate ligand between metal ions and surface sulfhydryl by complexing reaction, the hybrid material could absorb and fix mobile fractions of Cd and Pb in soil, and promote transformation of acid extractable Cd and Pb into residual fraction, resulting in significant reduction of heavy metals bioavailability and mobility and then fixing remediation of contaminated soil. In summary, the compound treatment of hybrid material and phosphate is the most effective treatment for immobilization of Cd and Pb in contaminated soils, and the hybrid material inactivates Cd and Pb in soil mainly through special chemical adsorption.

The effects of acid and heating treatment on the structure of sepiolite and its adsorption capacities for Pb2+ and Cd2+ were investigated using X-ray powder diffraction, infrared spectroscopy, surface area analyses and batch sorption experiments in this paper. The results showed that the BET surface area of the sepiolite samples grew with increase concentrations of HCl and prolong treatment time and no obvious structural changes were observed. CaCO3 as the impurity in the natural sepiolite can not be removed completely in the treatment process with 0.5 mol x L(-1) HCl. The surface area of sepiolite treated with 6 mol x L(-1) HCl and continuous stirring 72 h reached the maximum 301.47 m2 x g(-1). A decrease in the BET surface area was observed for the samples treated with acid at higher temperature. The BET surface area of samples treated with different acid species arranged in the order HCl > HNO3 > H2SO4. The calcinations process decreased the BET surface area from 21.44 m2 x g(-1) at 100 degrees C to 0.17 m2 x g(-1) at 900 degrees C. The adsorption results indicated that despite increases in the surface areas upon acid activation, improvements in the adsorption were not observed for heavy metal Pb2+ and Cd2+ ions. Pb2+ ions have higher affinity for specific adsorption onto the sepiolite samples than Cd2+ ions. H2SO4 treatment was found to be more effective for the removal of Pb2+ and Cd2+ ions than HCl and HNO3 treatments. It is apparent that PbSO4 and CdSO4 were formed during the sorption process. The calcinations treatment exhibited no significant effects on the adsorption of Pb2+ ions onto sepiolite, but the adsorption of Cd2+ ions obviously increased above 700 degrees C.