Insight into the mechanism of nano-TiO2-doped biochar in mitigating cadmium mobility in soil-pak choi system.

Soil cadmium (Cd) pollution poses severe threats to food security and human health. Previous studies have reported that both nanoparticles (NPs) and biochar have potential for soil Cd remediation. In this study, a composite material (BN) was synthesized using low-dose TiO2 NPs and silkworm excrement-based biochar, and the mechanism of its effect on the Cd-contaminated soil-pak choi system was investigated. The application of 0.5 % BN to the soil effectively reduced 24.8 % of diethylenetriaminepentaacetic acid (DTPA) Cd in the soil and promoted the conversion of Cd from leaching and HOAc-extractive to reducible forms. BN could improve the adsorption capacity of soil for Cd by promoting the formation of humic acid (HA) and increasing the cation exchange capacity (CEC), as well as activating the oxygen-containing functional groups such as CO and CO. BN also increased soil urease and catalase activities and improved the synergistic network among soil bacterial communities to promote soil microbial carbon (C) and nitrogen (N) cycling, thus enhancing Cd passivation. Moreover, BN increased soil biological activity-associated metabolites like T-2 Triol and altered lipid metabolism-related fatty acids, especially hexadecanoic acid and dodecanoic acid, crucial for bacterial Cd tolerance. In addition, BN inhibited Cd uptake and root-to-shoot translocation in pak choi, which ultimately decreased Cd accumulation in shoots by 51.0 %. BN significantly increased the phosphorus (P) uptake in shoots by 59.4 % by improving the soil microbial P cycling. This may serve as a beneficial strategy for pak choi to counteract Cd toxicity. These findings provide new insights into nanomaterial-doped biochar for remediation of heavy metal contamination in soil-plant systems.

Effect of Foliar Spraying of Gibberellins and Brassinolide on Cadmium Accumulation in Rice.

Cadmium (Cd) is one of the heavy metals that contaminate rice cultivation, and reducing Cd contamination in rice through agronomic measures is a hot research topic. In this study, foliar sprays of gibberellins (GA) and brassinolide (BR) were applied to rice under Cd stress in hydroponic and pot experiments. After foliar spraying of GR and BR, the biomass of rice plants grown in either hydroponics or soil culture was significantly higher or even exceeded that in the absence of Cd stress. In addition, photosynthetic parameters (maximum fluorescence values), root length and root surface area, and CAT, SOD and POD activities were significantly improved. The MDA content decreased in the shoots, suggesting that the application of GR and BA may have enhanced photosynthesis and antioxidant function to alleviate Cd stress. Furthermore, the BR and GA treatments decreased the Cd content of rice roots, shoots and grains as well as the Cd transfer coefficient. Cd chemical morphology analysis of rice roots and shoots showed that the proportion of soluble Cd (Ethanol-Cd and Water-Cd) decreased, whereas the proportion of NaCl-Cd increased. Analysis of the subcellular distribution of Cd in rice roots and above ground showed that the proportion of Cd in the cell wall increased after foliar spraying of GA and BR. The results indicate that after foliar application of GA and BR, more of the Cd in rice was transformed into immobile forms and was fixed in the cell wall, thus reducing the amount in the seeds. In summary, foliar sprays of GA and BR can reduce the toxic effects of Cd on rice plants and reduce the Cd content in rice grains, with GA being more effective.

Fertilization can modify the enantioselective persistence of penthiopyrad in relation to the co-influence on soil ecological health.

Penthiopyrad is a widely used chiral fungicide for controlling rust and Rhizoctonia diseases. Development of optically pure monomers is an important strategy to realize amount reduction and increment effects of penthiopyrad, wherein, fertilizers as the co-exiting nutrient supplement may alter the enantioselective residues of penthiopyrad in soil. In our study, influences of urea, phosphate, potash, NPK compound, organic granular, vermicompost and soya bean cake fertilizers on enantioselective persistence of penthiopyrad were fully evaluated. This study demonstrated that R-(-)-penthiopyrad dissipated faster than S-(+)-penthiopyrad during 120 days. High pH, available nitrogen, invertase activities and reduced available phosphorus, dehydrogenase, urease, catalase activities were situated to benefit removing the concentrations of penthiopyrad and weakening enantioselectivity in soil. With respect to the impact of different fertilizers on soil ecological indicators, vermicompost contributed to enhanced pH. Urea and compound fertilizer played an absolute advantage in promoting available nitrogen. All fertilizers didn't go against available phosphorus. Dehydrogenase responded negatively to phosphate, potash and organic fertilizers. Urea increased invertase, besides, it and compound fertilizer both diminished urease activity. The catalase activity was not activated by organic fertilizer. Based on all the findings, soil application of urea and phosphate fertilizers was recommended and considered as a better option to exhibit high efficiency for the dissipation of penthiopyrad. The combined environmental safety estimation can effectively guide the treatment of fertilization soils in line with the nutrition requirements and pollution regulation from penthiopyrad.

Assessment of the eco-toxicological effects in zoxamide polluted soil amended with fertilizers-An indoor evaluation.

Zoxamide is a benzamide fungicide applied to control diseases caused by oomycete fungi. Fertilizers are important agricultural supplies to adjust soil properties and increase nutrition. To investigate the impact of zoxamide and seven fertilizers urea, phosphate fertilizer, potash fertilizer, compound fertilizer, organic fertilizer, vermicompost and soya bean cakes on the soil environment, the enantioselective dissipation characteristics of zoxamide, soil enzyme activities, pH and N, P nutrition changes were comprehensively analyzed in our present study. The enantioseparation method was successfully validated to quantify the zoxamide enantiomers in soil by HPLC using Chiral NQ (2)-RH column. Our results demonstrated that the R-(-)- and S-(+)-zoxamide half dissipated in the range of 10.88-17.81 and 8.05-14.41 days, respectively. S-(+)-zoxamide disappeared faster in soil. The vermicompost accelerated the dissipation rate of S-(+)-zoxamide, while urea, phosphate, organic and vermicompost fertilizer increased the dissipation selectivity. Zoxamide and fertilizers other than urea caused soil acidification during 80 days. Zoxamide was beneficial to soil catalase, instead inhibited soil urease, dehydrogenase activities and available phosphorus content. No significant effects on sucrase activity and available nitrogen content were found by zoxamide. Vermicompost and soya bean cakes had lasting and outstanding performance in efficiently improving soil enzyme activity and N, P nutrition. The comprehensive understanding of the ecological impact induced by chiral pesticide enantiomers and fertilizers on soil is vital to ensure the sustainable development and safety of agricultural production.

Concentration of precious metals from waste printed circuit boards using supergravity separation.

Printed circuit boards (PCBs) comprise valuable metals, precious metals, and hazardous materials. Thus, they are considered both attractive secondary sources of metals and environmental pollutants. This study is based on the selective separation of Pb-Sn, Sn-Cu, and Cu-Zn alloys, where supergravity separation was used to concentrate precious metals (i.e., Ag, Au, and Pd) from PCBs in Cu-Zn alloy and final residue. The temperature and gravity coefficient were found to have great influence on the concentration of precious metals in said alloy and residue. At the optimized temperature of 1300 °C, gravity coefficient of 1000, and separation time of 5 min, the Ag, Au, and Pd contents in the Cu-Zn alloy increased by 1.65, 2.05, and 1.54 times, respectively, compared to their concentrations in the original PCBs, while those in the final residue increased by 0.63, 1.02, and 2.62 times, respectively. By combining an appropriate hydrometallurgical process with the present supergravity separation and concentration of precious metals, this clean and efficient process provides a new pathway to recycle valuable metals and prevent environmental pollution by PCBs.

Recovery of Cu and Zn from waste printed circuit boards using super-gravity separation.

With technological innovation and intense marketing, more and more electric and electronic equipment wastes (e-wastes) are being generated. Printed circuit boards (PCBs) are fundamental components of electronic wastes, which consist of both valuable metals and hazardous materials. An efficient method to recycle metals is an important measure to eliminate or avoid heavy metal hazard and realize resource recovery. In this research, super-gravity separation achieved by high temperature centrifugation was used to recover copper and zinc from waste PCBs. At an optimized temperature of 1300 °C and a gravity coefficient of 1000, the total recovery values of Cu, Zn, Pb, and Sn were 93.23%, 80.86%, 94.54%, and 97.67%, respectively, in the whole separation process. By combining appropriate hydrometallurgy and super-gravity separation of metals or alloys, this clean and efficient process provides a novel way to recycle valuable metals and effectively prevent environmental pollution from PCBs. A large-scale experimental apparatus was designed for handling large volume of WPCBs.