Cadmium (Cd) and polystyrene microplastics (PS) co-contamination always occurs in environment; however, the trophic transfer of Cd and PS is still poorly understood. A hydroponic experiment was ...conducted to investigate the behavior of Cd in lettuce, together with the root or foliar exposure of different sized PS. Accumulation and chemical form distributions of Cd in leaves were distinguished into young and mature leaves. Subsequently, a 14-day snail feeding experiment was performed. Data showed that Cd accumulation in roots, rather than in leaves, are significantly affected by PS coexistence. However, mature leaves had a higher Cd content than young leaves under the root exposure of PS, while a reverse effect was observed in the foliar exposure. There existed a positive correlation between the food-chain transfer associated Cd (CdFi+Fii+Fiii) in mature leaves and Cd content in snail soft tissue (r = 0.705, p < 0.001), but not in young leaves. Though no bio-amplification of Cd in food chain was observed, an increase of Cd transfer factor (TF) from lettuce to snail was noted in the root exposure of 5 μm PS and the foliar exposure of 0.2 μm PS. Moreover, we observed a highest increase rate of 36.8 % in TF values from lettuce to snail viscera, and a chronic inflammatory response in snail stomach tissue. Therefore, more attentions should be paid to study the ecological risks of heavy metals and microplastics co-contamination in environment.
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•Presence of PS significantly affected Cd content in roots, but not in leaves.•CdFi+Fii+Fiii content in mature leaf was the main source of Cd in snail soft tissue.•Coexistence of PS increased TF values of Cd along the food chain.•Cd distribution in organism was closely linked to the exposure pathway and size of PS.
Soil erosion of sloped farmland in the Three Gorges Reservoir area (TGRA) has led to the serious loss of nutrients, soil quality degradation and the downstream water quality being threatened. Thus, a ...series of ecological agricultural engineering measures was established in 2011, as a field experiment using citrus (navel orange) plants to reduce soil erosion, which was monitored from 2011 to 2018. These ecological agricultural engineering measures included three treatments: 1) citrus intercropped with white clover (WC), 2) citrus orchard land mulched with straw (SM) and 3) citrus intercropped with hemerocallis (Hemerocallis flava) contour hedgerows (CH). The conventional citrus orchard management was regarded as control (CK). The results show, that compared with CK, nutrient loss from the experiments were reduced by the following amounts: for nitrogen - WC (35.5%), SM (44.0%) and CH (52.0%); for phosphorus - WC (40.0%), SM (51.7%) and CH (58.3%). Therefore, the ecological agricultural engineering measures effectively mitigate the nutrient loss loads of the navel orange citrus gardens. The citrus intercropped with the hemerocallis hedgerows is the most effective measure for the control of nutrient loss. After 8 years of experiment, the soil quality represented by average soil quality index (SQI) in these three treatments, are significantly higher than that of the CK (and the beginning of the experiment). This is because the application of these measures prevented the loss of: soil organic matter, bulk density and total phosphorus. It is predicted that the soil qualities of these three treatments will remain in the range of soil grade II and I for the next 5 years but the soil quality of CK will decrease to soil quality grade II and III. These results show that ecological agricultural engineering measures are a long-term promising and feasible method to reduce soil erosion and enhance soil quality.
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•Long-term benefits of applying ecological agricultural measures were examined.•Soil nutrient losses and properties changes in sloping farmland were explored.•The SQI was used to measure the impact of soil indexes changes on soil quality.•The future changes in soil quality of different ecological measures were predicted.
A two‐dimensional cellular automaton (CA) model of microstructure evolution is developed to visually and quantitatively simulate and predict the dynamic recrystallization (DRX) behavior of a typical ...Ni‐based superalloy during hot power spinning. The high‐temperature plane strain compression test and hot power spinning experiment are carried out to verify the developed CA model, and results show that the flow stress can be well predicted and the simulated average grain sizes are in good accordance with the experimental ones. The evolution of DRX and dislocation density as well as influence of processing parameters on DRX during hot power spinning are simulated and discussed. It is found that the DRX nucleation starts at grain boundaries when a large thinning ratio of wall thickness is reached. With the increasing of thinning ratio, the growth of crystal nuclei and secondary nucleation occurs. Furthermore, the average grain size and DRX fraction are greatly influenced by the forming temperature and thinning ratio, while the average grain sizes decrease slightly with the increasing of roller feed rate.
A two‐dimensional cellular automaton model of microstructure evolution is developed to study the dynamic recrystallization (DRX) behavior of Haynes 230 alloy during hot power spinning. The predicted results conform well with that of high‐temperature plane strain compression test and hot power spinning experiment. The DRX mechanism of Haynes 230 alloy and influence of processing parameters on its DRX are obtained.
Rainfed agriculture is important to meet the increasing demands of food production. However, there is a lack of knowledges for the rainfed wheat systems in abundant rainfall areas, where the erratic ...rainfall may constrain the wheat yield and increases N losses from wheat fields with excessive fertilizer inputs. In the present study, a 6 consecutive years field experiments were conducted to investigate the wheat yield and N losses responses to different N fertilizer rates in the Taihu Lake region. Despite the fluctuations in the wheat yield, a 10–30% reduction of the district average N input sustained the current-level of wheat yield for the 6 consecutive years. The N rate of 168 kg ha−1 might be the threshold N application rate, because if it was exceeded, it was no longer the predominant factor determining the wheat yield, but significantly increased the N losses fluxes. The seasonal total N losses fluxes were 69.2 kg N ha−1, which accounted for 28.8% of district averaged N input. Runoff was the predominant pathway of N loss from the wheat field, followed by ammonia volatilization and leaching. Nitrate was the predominant form in the runoff and leakage water. Seasonal cumulative nitrate losses via runoff and ammonia volatilization averaged 25.2 and 20.1 kg ha−1 per wheat season, respectively, corresponding to 10.5% and 8.38% of the regional N application rates. However, the seasonal nitrate loss via leakage was the lowest, less than 8.98 kg ha−1. Reducing the fertilizer N rates significantly decreased the N losses via runoff and ammonia volatilization, but not by leaching. Our findings indicated that reducing N fertilizer was impressive for the sustainable development of agriculture in Eastern China and 168 kg N ha−1 was recommended for the rainfed wheat.
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•Reducing N inputs (168–216 kg ha−1) sustained current-level of wheat yields for 6 years in rice-wheat rotation.•N loss (kg ha−1) was affected by, in order, N runoff (30.7) > ammonia volatilization (20.1) > nitrate leaching (11.0).•Precipitations, solar radiations and sunshine durations were the critical factors determining wheat yields.
The efficiency of biological nitrate reduction depends on the community composition of microorganisms, the electron donor pool, and the electron mediators participating in the biological reduction ...process. This study aims at creating an in situ system comprising of denitrifiers, electron donors, and electron mediators to reduce nitrate in surface waters. The ubiquitous periphytic biofilm in waters was employed to promote in situ nitrate reduction in the presence of titanium dioxide (TiO2) nanoparticles (NPs). The nitrate removal rate in the periphytic biofilm and TiO2 NPs system was significantly higher than the control (only periphytic biofilm or TiO2 NPs). TiO2 NPs optimized the community composition of periphytic biofilm for nitrate reduction by increasing the relative abundance of four dominant denitrifying bacteria. Periphytic biofilm showed a substantial increase in extracellular polymeric substance, especially the humic acid and protein content, due to the presence of TiO2 NPs. The synergistic action of humic acid, protein, denitrifying bacteria of the periphytic biofilm, and TiO2 NPs contributed to 80% of the nitrate reduction. The protein and humic acid, acting as electron mediators, facilitated the transfer of exogenous electrons from photoexcited TiO2 NPs to periphytic biofilm containing denitrifiers, which enhanced nitrate reduction in surface waters.
The reuse of arsenic (As)-contaminated paddy fields is a global challenge because long-term flooding would result in As release due to the reductive dissolution of iron minerals. Biochar amendment is ...a common and effective remediation technique for As-contaminated paddy soil. However, the literature is still lacking in systematic research on the function of biochar in controlling the complexation of released dissolved organic matter (DOM) and iron oxides and its synergistic impact on the availability of As in flooded paddy soil. In the present study, bamboo biochar was prepared at different pyrolysis temperatures (300, 450 and 600 °C), as BB300, BB450 and BB600. Four paddy soil treatments including BB300, BB450, BB600 applications (1% ratio, m/m, respectively) and control (CK, no biochar application) were set and incubated for 60 d in flooding condition. The results showed that As availability represented by adsorbed As species (A-As) was mitigated by BB450 amendment compared with CK. The amendment of BB450 in paddy soil facilitated the complexation of HCl extractable Fe(III)/(II) and DOM and formation of amorphous iron oxides (e.g. complexed Fe species). Moreover, the abundance of Geobacteraceae and Xanthomonadaceae, as common electroactive bacteria, was promoted in the BB450 treated paddy soil in comparison to CK, which assisted to form amorphous iron oxides. The formed amorphous iron oxides then facilitated the formation of ternary complex (As–Fe-DOM) with highly stability, which could be considered as a mechanism for As immobilization after biochar was applied to the flooding paddy soil. Thus, the synergistic effect between amorphous iron oxides and electroactive stains could make main contribution to the passivation of released As in paddy soil under long-term flooding condition. This study provided a new insight for As immobilization via regulating iron-organic ligand complexation amendment with biochar in flooding paddy soil.
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•Bamboo biochar (BB) was prepared under different pyrolysis temperatures.•BB at 450 °C altered electroactive bacteria activity (e.g. Geobacteraceae, Xanthomonadaceae).•Presence of BB changed the bacterial community composition and α diversity.•Co-deposition of Fe, As in the presence of DOM contributed to As passivation in paddy soil.
Ni-based superalloy cylindrical parts widely used in the fields of aviation and aerospace have high requirements for the microstructure and mechanical properties. Hot flow spinning is an effective ...forming technology for manufacturing cylindrical parts with thin walls. The high-temperature plane strain compression test was put forward as the physical simulation test of hot backward flow spinning (HBFS) of cylindrical parts, and a new method for controlling the microstructure and mechanical properties of spun parts precisely based on hot processing map was proposed as the basis of selecting the reasonable processing parameters of HBSF. The results show that the relationships between the large true strains and stresses of Haynes 230 alloy during HBFS can be obtained effectively by the high-temperature plane strain compression test; the reasonable processing parameters which are beneficial for dynamic recrystallization and hot plastic deformation can be selected directly on the basis of the hot processing map. The influence of the processing parameters of HBSF on the microstructure of Haynes 230 cylindrical spun workpiece was also investigated, the results show that the influence of thinning ratio and forming temperature on the microstructure of the spun workpiece is remarkable, while the average grain size of spun workpiece decreases slightly with the increasing of feed rate. The yield strength and tensile strength of the Haynes 230 cylindrical spun part at the temperature of 800°C are both increased obviously compared with the original cylindrical blank, and the elongation is also slightly increased, which is particularly helpful in the high-temperature service of the Ni-based superalloys.
Although complexation between dissolved organic matter (DOM) and ubiquitous Fe is known to have a major influence on electron transferring ability in redoximorphic soil, it was unclear whether and ...how this complexation affected nitrate reduction and N2O productivity. The nitrate reduction of paddy soil in the presence of crop residues returning under flooding conditions was explored in this study. The rate of nitrate reduction in control soil was 0.0677 d−1, while it improved 1.99 times in treatment soil with Chinese milk vetch (CMV) straw returning. During a 28-day incubation period, N2O productivity decreased 0.08–0.91 ppb in CMV soil and 0.43–0.50 ppb in rice straw soil compared with control. The presence of crop residue increased DOC content and Fe (III) reduction rate, which aided in the formation of Fe (II)-DOC complexation. Meanwhile, the addition of CMV increased the content of DOC by 5.14–78.77 mg/kg and HCl extractable Fe (II) by 35.12–1221.03 mg/kg. Crop residues returning to soil increased the relative abundance of iron reductive and electroactive genera, as well as denitrifying genera with more copies of denitrification genes (Archangiaceae, Gemmatimonadaceae, and Burkholderiaceae). The synergistic effect of Fe-DOC complexation, electroactive genera, and denitrifying genera contributed to up-regulated expression of napA and narG (5.84 × 106 and 3.39 × 107 copies increased in the CMV soil compared to the control) numbers and equally accelerated reduction of nitrate to nitrite, while further nitrite reduction was primarily attributed to the abiotic reaction by Fe (II). From a bio-electrochemical point of view, this work provided new insight into the nitrate reduction of paddy soil impacted by Fe-DOC complexation.
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•Decomposition of Chinese milk vetch facilitated formation of Fe-DOC complexation.•Fe-DOC complexation improved the relative abundance of denitrifiers in paddy soil.•Fe-DOC facilitated the expression of napA and narG gene numbers.•The synergistic effect between Fe-DOC and denitrifiers promoted nitrate reduction.
The soil-water interface is replete with photic biofilm and iron minerals; however, the potential of how iron minerals promote biotic nitrate removal is still unknown. This study investigates the ...physiological and ecological responses of photic biofilm to hematite (Fe2O3), in order to explore a practically feasible approach for in-situ nitrate removal. The nitrate removal by photic biofilm was significantly higher in the presence of Fe2O3 (92.5%) compared to the control (82.8%). Results show that the presence of Fe2O3 changed the microbial community composition of the photic biofilm, facilitates the thriving of Magnetospirillum and Pseudomonas, and promotes the growth of photic biofilm represented by the extracellular polymeric substance (EPS) and the content of chlorophyll. The presence of Fe2O3 also induces oxidative stress (•O2−) in the photic biofilm, which was demonstrated by electron spin resonance spectrometry. However, the photic biofilm could improve the EPS productivity to prevent the entrance of Fe2O3 to cells in the biofilm matrix and mitigate oxidative stress. The Fe2O3 then promoted the relative abundance of Magnetospirillum and Pseudomonas and the activity of nitrate reductase, which accelerates nitrate reduction by the photic biofilm. This study provides an insight into the interaction between iron minerals and photic biofilm and demonstrates the possibility of combining biotic and abiotic methods to improve the in-situ nitrate removal rate.
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•The interaction between hematite and photic biofilm promoted nitrate removal.•The majority of Fe2O3 was distributed in the EPS matrix in particle form.•Hematite resulted in enhanced growth of biofilm with higher EPS productivity.•Hematite promoted the growth of denitrified biofilm to accelerate nitrate removal.
Purpose
The role of microplastics (MPs), as vectors for coexisting contaminants, in affecting the adsorption and desorption behavior of cadmium (Cd) by regulating soil properties such as dissolved ...organic matter (DOM) is still under debate.
Methods
A 2-month incubation of soil contaminated with different sizes and concentrations of non-biodegradable polyethylene (PE) and three types of biodegradable MPs were conducted. Subsequently, three-dimensional excitation-emission matrix (3D-EEM) with fluorescence region integration (FRI) analysis of DOM and a batch experiment of Cd behavior on MP-contaminated soils were further conducted.
Results and discussion
Soil properties such as pH, ammonium nitrogen, and urease activity were significantly affected by MP properties. 3D-EEM analysis indicated that the microbial by-product substances and the humic acid–like substances were the major components of DOM in MP-contaminated soil, accounting for approximately 50%. Overall, Cd adsorption was decreased by higher MP concentration and larger size, and PE-contaminated soils had similar or higher adsorption capacities than soil with biodegradable MPs. MPs can decrease in Cd adsorption and increase in Cd desorption when compared to the control. Both the Langmuir and Freundlich models fitted well with Cd adsorption and desorption isotherms. Correlation analysis confirmed that the characteristics of DOM, such as the humification index values and major components, rather than other soil properties, contributed more to the adsorption behaviors of Cd on MP-contaminated soils.
Conclusion
Addition of MPs could mitigate soil Cd adsorption capacity, mainly due to the changes of soil DOM characteristics, which will enhance the mobility and risks of Cd to agricultural soil.
