A novel phytoremediation technology for polluted cadmium soil: Salix integra treated with spermidine and activated carbon.

A variety of plants have been used as phytoremediation materials to remove Cd from polluted soil. However, the disadvantages of using plants for decontamination include low biomass, low uptake, and inefficiency. We conducted experiments to determine the effects of spermidine and activated carbon treatments of Salix integra on Cd removal. The results showed that exogenous spermidine and activated carbon increased plant growth and root development compared with the CK. The increased dry mass (39.65-92.95%) with the combined spermidine and activated carbon treatments was higher than that with either single treatment (14.79-62.80%). The root length, surface area, root volume, and root diameter with the combined spermidine and activated carbon treatments (53.51-189.35%, 113.08-207.62%, 111.71-499.27%, and 32.51-106.62%, respectively) were higher than those of the lone application treatments (19.35-132.23%, 52.33-111.57%, 35.08-297.07%, and 24.22-81.38%, respectively). In addition, spermidine and activated carbon application reduced the toxicity of Cd to S. integra by improving the antioxidant capacity, thereby increasing the accumulation of Cd. The application of spermidine and activated carbon also changed the distribution of Cd in each part of S. integra. There was increased accumulation of Cd in the shoots and better absorption by the S. integra shoots, thereby improving their Cd remediation efficiency. The combined 0.8 mM spermidine and 0.5 g kg-1 activated carbon were most effective on removing Cd from the soil. The Cd removal efficiency was 78.11-120.86% higher than that of the CK. Our results may provide foundational information for understanding the mechanisms for the sustainable remediation of Cd-contaminated soil using a combination of spermidine and activated carbon.

Consistent inter-annual reduction of rice cadmium in 5-year biannual organic amendment.

Organic fertilizers may contain cadmium (Cd) and the transformation of organic materials in soil also has a role in soil-plant Cd distribution, both of which lead to Cd accumulation in plant edible parts. However, the advisability of applying organic fertilizer to remediate soils that are moderately and slightly contaminated with Cd has not been clarified. In this study, we investigated the impacts of an organic amendment (chicken manure) on the Cd concentration in rice grains (CdR) and the soil chemical properties over a five year period (10 rice seasons) within a slightly contaminated paddy soil in Hunan Province, subtropical China. We found that the CdR was reduced by 28%-56% as a result of the organic amendment. The within-year reduction in CdR was higher in late rice (43%-56%, averaging 51%) than in early rice (28%-45%, averaging 38%); however, the inter-annual reduction in CdR was fairly stable (40%-49%), which suggests that chicken manure amendment has a long-term and persistent remediation potential. The concentrations of DTPA-extractable Cd and exchangeable plus water-soluble Cd fractions in soil were reduced, whereas soil pH and the concentrations of soil organic C and its labile fractions increased. These results indicate a lower apparent phytoavailability of Cd in soil following organic amendment. A two-variable empirical model using DTPA-Cd extracted from the soil at the full heading stage of rice and a climatic factor (total precipitation during the rice growing season) showed great potential in effectively predicting CdR. Our study suggests that Cd phytoavailability in soil (indexed by DTPA-extractable and exchangeable Cd) and climatic factors (such as temperature and precipitation) may control inter-annual reductions in CdR following organic amendment in slightly contaminated paddy soils.

Inter-annual reduction in rice Cd and its eco-environmental controls in 6-year biannual mineral amendment in subtropical double-rice cropping ecosystems.

The alkaline mineral amendment is a practical means of alleviating Cd concentration in rice grain (CdR) in the short-term; however, the long-term remediation effect of mineral amendment on the CdR and the eco-environmental controls remains unknown. Here a mineral (Si-Ca-Mg) amendment, calcined primarily from molybdenum tailings and dolomite, was applied biannually over 6 years (12 seasons) to acidic and moderately Cd-contaminated double-rice cropping ecosystems. This study investigated the inter-annual variation of Cd in the rice-soil ecosystem and the eco-environmental controls in subtropical rice ecosystems. CdR was reduced by 50%-86% following mineral amendment. The within-year reduction in CdR was similar between early rice (50%-86%, mean of 68%) and late rice (68%-85%, mean of 74%), leading to CdR in all early rice and in 83% of late rice samples below the upper limit (0.2 mg kg-1) of the China National Food Safety Standards. In contrast, the inter-annual reduction in CdR was moderately variable, showing a greater CdR reduction in the later 3 years (73%-86%) than in the former 3 years (54%-79%). Three years continuous mineral amendment was required to guarantee the safety rice production. The concentrations of DTPA-extractable and exchangeable Cd fractions in soil were reduced, while the concentration of oxides-bound Cd was increased. In addition, the soil pH, concentrations of Olsen-P and exchangeable Ca and Mg were elevated. These imply a lower apparent phytoavailability of Cd in the soil following mineral amendment. An empirical model of the 3-variable using soil DTPA-Cd, soil Olsen-P, and a climatic factor (precipitation) effectively predicted temporal changes in CdR. Our study demonstrates that Cd phytoavailability in soil (indexed by DTPA-extractable Cd) and climatic factors (e.g., temperature and precipitation) may directly/indirectly control the inter-annual reduction in CdR following mineral amendment in slightly and moderately Cd-contaminated paddy ecosystems.

[Reduction of Soil Cadmium Activity and Rice Cadmium Content by 4-year-consecutive Application of Organic Fertilizer].

Because commercial organic fertilizers may contain cadmium (Cd) and may cause the dual effect of "inhibition" and "activation" on Cd availability in paddy soil with organic fertilizer input, the reduction of rice Cd following organic fertilizer application is still uncertain. Herewith, typical purple mud paddy fields were selected in the eastern Hunan Province. The effect of commercial organic fertilizer input on Cd reduction of double-rice paddy ecosystem was monitored for four consecutive years. The relationships between brown rice Cd content, soil available Cd, and soil factors (pH, soil labile organic carbon fractions, and iron oxide) at different growth stages in double-rice paddy fields were investigated. Results showed that the input of organic fertilizer reduced the Cd content in brown rice by 28%-56%. Meanwhile, the decrease of Cd content in brown rice of late rice (43%-56%) was higher than that of early rice (28%-45%), and the inter-annual fluctuation of the decrease was relatively small. On the one hand, soil available Cd content decreased by 6%-7% during several growth stages of double-rice (from tillering peak stage to full heading stage) with organic fertilizer input. Additionally, the content of soil exchangeable Cd was decreased by 11%, whereas the content of organic bound Cd was increased by 14%. This directly reflects the decrease of soil Cd availability. On the other hand, the soil pH value was steadily increased by 0.1-0.3 units following organic fertilizer input, which promoted the development of soil from acidity to slight acidity. Besides, the content of soil active organic carbon (light fraction organic carbon, coarse particulate organic carbon, and fine particulate organic carbon) was increased significantly (53%, 77%, and 107%, respectively). This indirectly reflects the decrease in soil Cd availability. This study implies that the decrease of soil Cd availability may be the primary driving force for the reduction of rice Cd content with consecutive organic fertilizer input in purple mud paddy fields.

Characterization and Application of PVDF and Its Copolymer Films Prepared by Spin-Coating and Langmuir-Blodgett Method.

Poly(vinylidene fluoride) (PVDF) and its copolymers are key polymers, displaying properties such as flexibility and electroactive responses, including piezoelectricity, pyroelectricity, and ferroelectricity. In the past several years, they have been applied in numerous applications, such as memory, transducers, actuators, and energy harvesting and have shown thriving prospects in the ongoing research and commercialization process. The crystalline polymorphs of PVDF can present nonpolar α, ε phase and polar ß, γ, and δ phases with different processing methods. The copolymers, such as poly(vinylidene fluoride-trifluoroethylene) (P(VDF-TrFE)), can crystallize directly into a phase analogous to the ß phase of PVDF. Since the ß phase shows the highest dipole moment among polar phases, many reproducible and efficient methods producing ß-phase PVDF and its copolymer have been proposed. In this review, PVDF and its copolymer films prepared by spin-coating and Langmuir-Blodgett (LB) method are introduced, and relevant characterization techniques are highlighted. Finally, the development of memory, artificial synapses, and medical applications based on PVDF and its copolymers is elaborated.