To reveal conflict among carbon neutrality, food security, and agricultural economy (C-F-E) and support agricultural sustainability in land-constrained coastal regions of China. Zhejiang Province was selected as an example, a C-F-E nexus analytical framework integrated carbon accounting, coupling coordination degree model, and Geodetector model was established to analyze its spatiotemporal evolution and drivers during 2000-2023. The results indicated that the agricultural economy of all cities and the carbon emission intensity of most cities exhibited a gradual improvement trend from 2000 to 2023. However, spatially, the carbon emission intensity and economic indicators were higher in the northeastern plain region and lower in the southwestern mountainous areas. In contrast, the food security index for each city exhibited a significant declining trend with fluctuations, with a lower rate of decline in the southwestern mountainous areas.The coupling relationship among C-F-E nexus was generally moving towards a coordinated direction, but the levels of coupled and coordinated development exhibited significant spatial heterogeneity. Specifically, the "southwest" region served as ecological barrier, maintained a good balance among C-F-E. Conversely, the "northeast" region developing efficient urban agriculture, led to a fragile balance among C-F-E and faced the pressures of food security risks and high carbon emission intensity. Geodetector model analysis revealed that excessively pursuing "economic back-feeding" was the main factor affecting the coordination relationship among C-F-E. Which indicated a strategic imbalance has occurred in coastal regions of China, where sacrificing a certain degree of food self-sufficiency to achieve higher economic returns and lower agricultural carbon emission intensity.

Excessive ammonia nitrogen has been demonstrated to cause a serious hazard to water environments.Bacteria performing simultaneous nitrification and denitrification(SND)can be effective biological instruments to remove ammonia nitrogen completely from effluents.For the first time,Pseudomonas oleovorans QS-7 with SND function,isolated from the biogas treatment system of a pig farm,was found to efficiently remove ammonia nitrogen.Through the determination of key enzymes and functional genes related to the nitrogen metabolism of strain QS-7,combined with nitrogen balance measurements of the nitrogen metabolic process,it was speculated that the SND pathway of the novel strain is NH4+→NH2OH→NO2-→NO3-→NO2-→NO→N2O→N2.QS-7 exhibited 98.6％ammonia nitrogen removal and a maximum ammonia degradation rate of 9.2 mg/(L·h)at 18 h in 100 mg/L ammonia nitrogen solution.This strain also has a certain capacity to remove nitrate and nitrite nitrogen;the maximum removal efficiencies were 54.22％and 73.93％,respectively,in systems with 100 mg/L of nitrate or nitrite nitrogen as the sole nitrogen source.Nitrogen metabolic balance analysis for QS-7,using ammonia(100 mg/L)as the sole nitrogen source,demonstrated that assimilation(56.1％)is the main mode of nitrogen removal,followed by conversion to N2(43.6％).Meanwhile,NO-2 was not detected,and almost no NOx was produced,which indicates that the nitrogen removal process of QS-7 is environmentally friendly.The optimal environmental conditions for QS-7 were found to be sodium citrate as the carbon source,C/N=10,pH=7.0,150 r/min,and 30℃.The above results indicate that QS-7 may provide a material and conceptual basis for the advancement of SND technology.

This study aims to optimize the use of lacquer residue biomass (LBM). We investigated the ability of LBM to remove Pb2+ heavy metal ions and the typical cationic dye methylene blue (MB) and anionic dye Congo red (CR) by simultaneous adsorption from composite systems, as well as the relevant factors. Scanning electron microscopy (SEM), X-ray diffraction (XRD), and Fourier transform infrared spectroscopy (FTIR) were used to characterize adsorption behavior. The adsorption kinetics of Pb2+-MB/CR composite systems can be effectively characterized by the pseudo-second-order kinetic model (R2> 0.97). In the Pb2+-MB composite system, adsorption was antagonistic with similar adsorption sites. However, in the Pb2+-CR composite system, we found that adsorption was synergistic with different adsorption sites, which led to a higher simultaneous adsorption capacity for a higher initial Pb2+-CR concentration, unlike the Pb2+-MB system. In both composite systems, an appropriate increase in LBM dosage and system temperature within a certain range was conducive to simultaneous adsorption and removal of Pb2+-MB/CR composite systems. The optimal solid–liquid ratio and temperature were 1:75 and 30 °C, respectively. The adsorption and removal rates of Pb2+ and MB were 99.98

In order to understand whether Chlorella has the potential and feasibility to remove and resource nutrient pollutants from eutrophic water with different carbon to nitrogen ratios (C/N). A series of incubation experiments with Chlorella sp. HL-1 (C sp. HL-1) in eutrophic wastewater with C/N different carbon to nitrogen ratios (C/N 1–12) were investigated in the present study, and removal efficiency of nutrient pollutants (nitrogen (N), phosphorus (P), and chemical oxygen demand (COD)) and the quality parameters (biomass, contents of N, P, C, and fat) of C sp. HL-1 were analyzed. The results showed that the introduction of Chlorella could remove over 99

A novel alkalizing strain Enterobacter sp. LYX-2 that could resist 400 mg/L Cd was isolated from Cd-contaminated soil, which immobilized 96.05% Cd2+ from medium. Cd distribution analysis demonstrated that more than half of the Cd2+ was converted into extracellular precipitated Cd through mobilization of the alkali-producing mechanism by the strain LYX-2, achieving the high immobilization efficiency of Cd2+. Biosorption experiments revealed that strain LYX-2 had superior biosorption capacity of 48.28 mg/g for Cd. Pot experiments with Brassica rapa L. were performed with and without strain LYX-2. Compared to control, 15.92% bioavailable Cd was converted to non-bioavailable Cd and Cd content in aboveground vegetables was decreased by 37.10% with addition of strain LYX-2. Available Cd was mainly immobilized through extracellular precipitation, cell-surface biosorption and intracellular accumulation of strain LYX-2, which was investigated through Cd distribution, Scanning Electron Microscope and Energy-Dispersive X-ray Spectroscopy (SEM-EDS), Fourier Transform Infrared Spectroscopy (FT-IR), X-ray Photoelectron Spectroscopy (XPS) and Transmission Electron Microscopy (TEM) analysis. In addition, the application of strain LYX-2 significantly promoted the growth of vegetables about 2.4-fold. Above results indicated that highly Cd-resistant alkalizing strain LYX-2, as a novel microbial passivator, had excellent ability and reuse value to achieve the remediation of Cd-contaminated soil coupled with safe production of vegetables simultaneously.

The rapid development and widespread use of ZnO nanoparticles (nZnO) in various industries have raised concerns about their potential environmental impact. Therefore, understanding the fate and role of nZnO in the natural environment is crucial for mitigating their hazardous effects on the environment and human safety. The purpose of the present study was to provide scientific support for understanding and eliminating the joint risk of nanoparticle and heavy metal pollution in the soil environment by revealing the co-transport characteristics of Cd(II) and ZnO nanoparticles (nZnO) in soil under different ionic strength (IS) and pH. The impacts of different IS and pH on the co-transport of Cd(II) and nZnO in a 20 cm long with an inner diameter of 2.5 cm acrylic column packed with 10 cm high soil samples were investigated in the present study. In the above system, a 500 μg L−1 Cd(II) loaded nZnO suspension pulse with varying IS or pH was introduced into the soil column for leaching over 5 PVs, followed up by 5 PVs background solutions without nZnO. The IS was 1, 10, or 50 mM NaCl, with pH6, or the pH was 6, 7 or 8 with 1 mM NaCl. Meanwhile, Sedimentation experiments for nZnO, adsorption of Cd(II) on soil, and nZnO, DLVO theory calculation for the same background condition were conducted. The presence of nZnO significantly increased the mobility of Cd(II) as a result of its strong adsorption capacity for nZnO-associated Cd(II). However, with the increase of IS, the co-transport of nZnO and Cd(II) was decreased and the retention of nZnO in the soil column due to more nZnO attended to aggregate and sediment during the transport and the decrease in the adsorption capacity of nZnO for Cd(II) by competition of Na+. When pH was 6, 7, and 8, the co-transport of nZnO and Cd(II) increased with higher pH due to the lower electrostatic attraction between nZnO and soil under higher pH. Meanwhile, the DLVO theory was fitted to describe the above co-transport process of nZnO and Cd(II). More attention should be paid to the presence of nZnO on the migration of Cd(II) in the natural soil to control the potential risk of nanoparticles and heavy metals to the environment. The risk of co-transport of nZnO and Cd(II) might be controlled by adjusting IS and pH in the soil solution.

Given the huge carbon footprint of agricultural activities, reduction in agricultural carbon emission (ACE) is important to achieve China's carbon peaking and carbon neutrality goals, but it may affect agricultural food security and economic development. Therefore, it is important for scientific carbon reduction measures to understand the multi-year trends and the influencing factors of ACE, and clarify whether the process of ACE affects food security and economic development. This study analyzed the trends of total ACE and ACE caused by different agricultural carbon sources (ACS) from 2001 to 2020 in Zhejiang Province, then we revealed the main influencing factors of ACE based on the logarithmic mean Divisia index (LMDI) model and dissected the relationship between ACE and food security and economic development. Results show that the total ACE fluctuated from 6.10 Mt in 2001 to 3.93 Mt in 2020, and the process included a decrease in 2001-2003 and 2005-2020 and an increase in 2003-2005. The decrease in ACE, from 2001 to 2014, was mainly due to the decline in rice acreage, which contributed 90.38%; from 2014 to 2020, it was by the reduction in the use of fertilizer, diesel, and pesticide, which contributed 83.9%. As drivers, agricultural economic development effect and total population size effect drove 4.25 and 1.54 Mt of ACE, respectively. As inhibitors, planting structure effect, technology development effect, and population structure effect inhibited 3.12, 2.11, and 2.74 Mt of ACE, respectively. With the reduction of ACE, the agricultural economy continued to grow, but the food security situation was pessimistic, indicating that ACE reduction has achieved synergy with economic development, but not with food security.

A heterotrophic nitrifier and aerobic denitrifier was isolated from chaff bedding of a pig farm and identified as Enterobacter cloacae DK-6. The strain DK-6 showed efficient nitrogen removal abilities under aerobic condition, with the ammonium-N (105.56mg/L), nitrate-N (101.70mg/L) and nitrite-N (86.19mg/L) removal efficiency of 86.98, 94.66 and 100% under aerobic condition, respectively. Further experiments demonstrated that the nitrate-N removal efficiency was improved and strain DK-6 preferred to utilize nitriteN when ammonium-N, nitrate-N and nitrite-N were used as mixed nitrogen sources. Nitrogen balance showed ammonium-N removal was mainly achieved by assimilation in the process of nitrification, while nitrate-N removal was mainly realized through N2 loss and hardly no greenhouse gas (N2O) was generated during denitrification. Efficient nitrate-N removal occurs at sodium succinate as carbon source, carbon/nitrogen ratio of 8-10, dissolved oxygen concentration of 4.3-5.2 mg/L, pH of 6-7, temperature at 25-35 degrees C and initial nitrate-N concentration of 50-200 mg/L. Above results suggested strain DK-6 has significant potential involving in multiple nitrogen pollutants treatment of wastewater under aerobic condition and lower carbon/nitrogen ratio. (c) 2022 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

[目的]揭示稻田经济草坪化种植后的土壤质量变化规律,以期为草坪化种植稻田复垦快速精准改良提供依据.[方法]基于海宁市丁桥镇近133.3 hm2稻田被经济草坪化种植后存在需复垦为稻田的改良需求,选择稻田草坪化种植(0、1、2、3、4年)后的土壤为研究对象,分析土壤的机械组成、容重、pH值、有机质、阳离子交换量、氮、磷、钾总量及其有效态含量等理化与养分指标,并对其进行相关性分析和土壤肥力综合评价,探讨土壤理化性质与养分指标的时空变异特征,明晰经济草坪化种植后稻田关键肥力因子的变化特点.[结果]稻田草坪化种植后,随着种植年限增长,不同深度土壤(0～15 cm、15～30 cm、30～45 cm)的各理化性质与养分含量指标变化趋势具有一致性.随草坪化种植年限增长,土壤砂粒含量减少,粘粒含量增加,容重增大,pH逐渐升高,土壤有机质和阳离子交换量呈现出先快后慢的下降态势;土壤全量和速效氮、磷、钾含量逐渐降低,土壤速效氮、磷、钾含量在草坪化种植初期下降尤其显著.全量及速效养分含量总体以及土壤砂粒含量与草坪化种植年限呈极显著负相关(P<0.01),土壤pH和容重的变化量以及粘粒含量与草坪化种植年限呈极显著正相关(P<0.01),有机质和阳离子交换量的变化量与草坪化种植年限呈显著负相关(P<0.05),草坪化种植4年后,土壤肥力综合等级退化为瘦瘠水平.[结论]稻田经济草坪化种植后导致其土壤肥力显著退化.

In this study, a novel biocontrol bacterium was isolated and identified as Paenibacillus sp. LYX-1 from soils in the peach orchard. Both Cd 2+ resistance and biosorption behavior of strain LYX-1 was explored. Meanwhile, the Cd 2+ resistance and biosorption mechanisms were further identified by Cd-resistant genes, SEM–EDS, FTIR, XPS, and TEM analysis. The results showed that strain LYX-1 could resist 50 mg/L Cd 2+ and had the CzcD gene responsible for Cd 2+ efflux. Under pH 8.0 and at a dose of 1.0 g/L sorbent dose, the removal efficiencies of living and dead cells were as high as 90.39% and 75.67% at 20 mg/L Cd 2+ , respectively. For the adsorption isotherm test, results revealed that both Langmuir ( R 2 = 0.9704) and Freundlich ( R 2 = 0.9915) model could describe the Cd 2+ biosorption well for living strain LYX-1. The maximum equilibrium biosorption capacities of living and dead biomass were 30.6790 and 24.3752 mg/g, respectively. In the adsorption kinetic test, the adsorption process of both living and dead strain LYX-1 all satisfied the pseudo-second kinetic equation. A desorption study showed that strain LYX-1 sorbents could be recycled and regenerated by eluents efficiently. SEM–EDS analysis reflected that Cd 2+ was bound to the cell wall. Besides, the biosorption process was controlled by chemisorption with the participation of the -OH, -NH, -C = O, O = C-O, C-N, S 2− , and phosphate functional groups on the cell surface of strain LYX-1, which were identified by FTIR and XPS. Bioaccumulation also made a contribution to the Cd 2+ removal during the biosorption process of living sorbent. The above results indicated that strain LYX-1 had higher Cd 2+ tolerance and Cd 2+ removal capacity. This strain exhibits promising application to the removal of Cd 2+ in the Cd-contaminated environment.

To achieve a mostly nutrients recovery from wastewater to biomass production, a protein-rich Chlorella sp. HL-1 was isolated from piggery anaerobic digestion effluent (PADE), and then a series of experiments were conducted in PADE to optimize culture conditions. The optimal cultivation conditions were initial inoculation of 0.61 g·L−1, pH 8.5, the salinity of 1.5‰, and the dilution rate of 1:2 (PADE: freshwater was 1:2, v/v, 587.67 mg·L−1 TIN). Based on the above conditions, construct a continuous protein-rich Chlorella sp. HL-1 production system in a six-day production interval in undiluted PADE. In the system, at the end of every cycle, discharge 1/3 volume of the culture broth to separate Chlorella. Meanwhile, add the same volume of PADE to start new cyclic cultivation. After five consecutive production cycles, the system could obtain 10.50 ± 0.34 g·L−1 biomass production, and heavy metals such as Cd and Pb in Chlorella sp. HL-1 were within the standards (EC No 1881/2006). Furthermore, the protein content of Chlorella sp. HL-1 was stable at 51.14 ± 0.86

A novel heterotrophic nitrification and aerobic denitrification (HNAD) bacteria, identified as Bacillus thuringiensis strain WXN-23, was isolated from husk feed filtrate of a pig farm. It was the first report of Bacillus thuringiensis with the capability for HNAD and could adapt to the condition of low Carbon/Nitrogen (C/N) ratio. Nitrogen could be efficiently removed by the strain WXN-23 in simulated wastewater, be it in single or mixed form nitrogen sources. The nitrogen balance revealed that 63.5% of the initial nitrogen (5.32 mg) was lost in the form of N-2. The conditions for maximum total nitrogen (TN) removal efficiency (95.996%) were shaking speed of 126.89 r/min, a carbon C/N ratio of 5.91, the temperature of 32.81. C, and a pH value of 8.17. The nitrification-denitrification metabolic pathway (NH4+-N -> NH2OH -> NO2--N -> NO3--N -> NO2--N.NO -> N2O -> N-2) under aerobic conditions was determined on the basic of characteristic of N removal, N balance analysis, enzyme assay and functional genes amplification results. Strain WXN-23 was effective at wastewater treatment, with TN, NH4+-N, NO3--N and NO2--N removal efficiencies of 82.12%, 86.74%, 90.74% and 100%, respectively.

In order to reveal the mechanism of silicon (Si) fertilizer in improving nitrogen (N) and phosphorus (P) nutrient availability in paddy soil, we designed a series of soil culture experiments by combining application of varying Si fertilizer concentrations with fixed N and P fertilizer concentrations. Following the recommendations of fertilizer manufacturers and local farmers, we applied Si in concentrations of 0, 5.2, 10.4, 15.6, and 20.8 µg/kg. At each concentration of added Si, the availability of soil N and P nutrients, soil microbial activity, numbers of ammonia-oxidizing bacteria and P-decomposing bacteria which means that the organic P is decomposed into inorganic nutrients which can be absorbed and utilized by plants, and urease and phosphatase activity first increased, and then decreased, as Si was added to the soil. These indicators reached their highest levels with a Si application rate of 15.6 µg/kg, showing values respectively 19.78%, 105.09%, 8.34%, 73.12%, 130.36%, 28.12%, and 20.15% higher than those of the controls. Appropriate Si application (10.4 to 15.6 µg/kg) could significantly increase the richness of the soil microbial community involved in cycling of N and P nutrients in the soil. When the Si application rate was 15.6 µg/kg, parameters for characterizing microbial abundance such as sequence numbers, operational taxonomic unit (OTU) number, and correlation indices of microbial community richness such as Chao1 index, the adaptive coherence estimator (ACE) index, Shannon index, and Simpson index all reached maximum values, with amounts increased by 14.46%, 10.01%, 23.80%, 30.54%, 0.18%, and 2.64%, respectively, compared with the control group. There is also a good correlation between N and P mineralization and addition of Si fertilizer. The correlation coefficients between the ratio of available P/total P (AP/TP) and the number of ammonia-oxidizing bacteria, AP/TP and acid phosphatase activity (AcPA), AP/TP and the Shannon index, the ratio of available N/total amount of N (AN/TN) and the number of ammoniated bacteria, and AN/TN and AcPA were 0.9290, 0.9508, 0.9202, 0.9140, and 0.9366, respectively. In summary, these results revealed that enhancement of soil microbial community structure diversity and soil microbial activity by appropriate application of Si is the key ecological mechanism by which application of Si fertilizer improves N and P nutrient availability.

To observe the co-transport of Cd(Ⅱ) with nanoscale As2S3 (nAs2S3) in a soil-packed column under different ionic strength (IS). A soil-packed column experiment with Cd(Ⅱ) and nAs2S3 was conducted. The results show that the transport of Cd(Ⅱ) was facilitated remarkably in the presence of nAs2S3, and nano-associated-Cd(Ⅱ) was the major migration type. However, the co-transport of Cd(Ⅱ) and nAs2S3 was affected by IS. The Cd(Ⅱ) concentration in the effluent to initial Cd(Ⅱ) concentration decreased from 38.75% to 29.95% and 22.28% as IS increased from 1 mM to 10 mM and 50 mM. When IS was 1 mm, 10 mm and 50 mm, the retention of nAs2S3 increased from 74.29% to 78.95% and 85.9% respectively. The agglomeration and sedimentation of nAs2S3 were the main reason for the rise of retention. Due to the increase of retention and reduction in adsorption capacity of nAs2S3 to Cd(Ⅱ), the ratio of migration in the form of nano-associated-Cd(Ⅱ) reduced from 53% (IS 1 mM) to 27.4% (IS 10 mM) and 18.2% (IS 50 mM). During the transport, the IS promoted desorption of Cd(Ⅱ) from nAs2S3 so that more soluble Cd was monitored in the effluent as IS increased. In general, these findings can provide references for controlling the risk caused by the co-transport of nAs2S3 and Cd(Ⅱ) in saline-alkali soil.

为了揭示红壤地区铅锌冶炼厂冶炼渣中的铅淋溶释放后在堆放场地土壤中的垂直迁移特征,以湖南株洲某铅锌冶炼厂冶炼渣堆放场地土壤为研究对象,采用等温吸附及土柱淋溶模拟试验探究了冶炼渣淋溶释放的铅在冶炼渣堆放场地土壤中的吸附与垂直迁移特征.结果表明:堆放场地土壤对冶炼渣淋溶释放的铅有较强的吸附能力,吸附由低能位和高能位共同控制,其中高能位对铅的最大吸附量为7392.771 mg/kg,低能位对铅的最大吸附量为13518.278 mg/kg,说明铅在堆放场地土壤中不易迁移.10 cm厚冶炼渣淋溶模拟释放的铅在堆放场地土壤中缓慢向下迁移,较长时间内(3 a)冶炼渣淋溶释放的铅主要富集在30 cm以内的土层中,30 cm处淋出液中的铅在0.006 mg/L内浮动;可采用多物理场仿真软件COMSOL对铅的垂直淋溶迁移过程进行定量描述和预测,预测结果与淋溶试验实测值基本相符,3 a内淋出液中的铅实测值均匀分布于模拟值曲线两侧,COMSOL预测结果进一步表明冶炼渣淋溶9 a释放的铅仍主要富集在30 cm以内的土层中,但呈现缓慢下移趋势.

This study was conducted to reveal the effects of silicon (Si) application on nutrient utilization efficiency by rice and on soil nutrient availability and soil microorganisms in a hybrid rice double-cropping planting system. A series of field experiments were conducted during 2017 and 2018. The results showed that Si nutrient supply improved grain yield and the utilization rates of nitrogen (N) and phosphorus (P) to an appropriate level for both early and late plantings, reaching a maximum at 23.4 kg/ha Si. The same trends were found for the ratios of available N (AN) to total N (TN) and available P (AP) to total P (TP), the soil microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), microbial biomass phosphorus (MBP), and the ratios of MBN to TN and MBP to TP, at different levels of Si. Statistical analysis further revealed that Si application enhanced rice growth and increased the utilization rate of fertilizer due to an ecological mechanism, i.e., Si supply significantly increased the total amount of soil microorganisms in paddy soil compared to the control. This promoted the mineralization of soil nutrients and improved the availability and reserves of easily mineralized organic nutrients.

为探究有机硅助剂协同对双季稻叶面喷施的在氨基酸微量元素肥增效潜力,选择江西省宜春市双季稻系统为研究对象,以农用有机硅和氨基酸微量元素叶面肥为研究材料,系统地比较早、晚稻施用添加不同体积分数的有机硅助剂的叶面肥后水稻叶片中微量元素锌(Zn)、锰(Mn)的含量、成熟期水稻相关的生长性状以及添加不同体积分数的有机硅助剂对肥液的理化性质的影响.结果表明:当有机硅助剂添加体积分数达到0.05％(胶束临界浓度)时,3次叶面肥喷施后,Zn、Mn在早、晚稻叶片中的含量均达到最大,与对照组相比,均提高了30％以上;同时早、晚稻的株高、稻草生物量、有效分蘖率、千粒质量及产量均达到最大,与对照组相比,其中早、晚稻的产量分别增长了13.76％、7.72％.有机硅助剂的对叶面肥的协同增效机制主要是通过改善肥液的界面性质,提高肥液在叶片的附着面积、附着量和附着时间实现,在试验设计的有机硅助剂添加的体积分数范围内,有机硅助剂添加的体积分数与肥液的表面张力、润湿直径或铺展面积呈显著相关,相关系数分别为-0.982(P<0.01)、0.995(P<0.01)、0.988(P<0.01);随着有机硅助剂添加的体积分数的增大,肥液的干燥时间及其叶片最大持留量呈现出先增后减的趋势,最佳有机硅助剂添加量为体积分数0.05％,此时肥液在水稻叶片上的最大持留量分别较对照组增加了25.90％、88.79％.可见有机硅助剂的合理应用可显著促进水稻叶片对叶面肥中微量元素(Zn、Mn)的吸收利用,提高水稻产量,是叶面肥的有效增效剂.

The study investigated the potential of ensuring safe production of rice from paddy fields affected by heavy cadmium contamination. A paddy soil polluted with heavy cadmium (total Cd content of 2.52 mg·kg-1) surrounding a lead-zinc mining area in Guiyang County of Chenzhou City, Hunan province was selected for analysis. We investigated production using a low cadmium accumulation rice variety (Oryza sativa L. Jia-33) and passivation additives for heavy metal activity (including humic acid and sepiolite). Results showed that:Oryza sativa L. Jia-33 showed good low cadmium accumulation characteristics in rice fields with heavy cadmium pollution. When humic acid and sepiolite were applied (alone or combined), the accumulation of Cd in different organs of the rice declined, and the transport coefficient of Cd for stem to root and polished rice to stem also declined. The rate of decline increased with increased application dosage. The cadmium content in polished rice was lower than the limit established in the National Food Safety Standard (GB 2715-2012), when applying 5.250 t·hm-2 humic acid, 6.750 t·hm-2 sepiolite, or a combination of 1.125 t·hm-2 humic acid and 3.37 5 t·hm-2 sepiolite; Cd content in polished rice was (0.171±0.01), (0.184±0.01), and (0.181±0.01) mg·kg-1, respectively. Single or combined application of humic acid and sepiolite promoted the transformation of soil Cd to residual and Fe Mn oxide bound forms, significantly reducing the content of available Cd and the bioavailability of Cd in soil, and further reducing Cd content in all rice organs. The reduction was more effective with single application of sepiolite or combined application of humic acid and sepiolite. The effects of combined application of humic acid and sepiolite were also more beneficial for soil nutrients, while soil available phosphorus, available potassium, phosphorus, and organic matter content increased with increased application of amendments. Soil nitrogen content did not change. In conclusion, results indicate that joint application of humic acid, sepiolite, and a low Cd accumulation rice variety are best for safe production on heavy cadmium-contaminated soil.

Quantum dots have unique physical and chemical properties and optical properties due to its special structure. In recent years, as a new type of fluorescent probe materials applied in chemical and biological analysis, medical diagnosis and other fields, quantum dots have become the focus of research. At present, some studies have been reported on the detection of heavy metal, veterinary drug and pesticide residues in food by using quantum dots as fluorescent probes. Related research reports showed that the use of quantum dots as a fluorescent probe to analyze the analyte with impact of food safety had advantages of high sensitivity, good selectivity, short response time, and less investment, which indicated the quantum dots as a fluorescent probe had wide application prospects in food safety inspection field. The malachite green had good antibacterial effect and low price, which was often illegally used in aquaculture as insecticides and fungicides. The malachite green had the potential carcinogenic effects, which was clearly listed in Chinese Food Animal Banned Veterinary Drugs and Compounds List in 2002, but in fact, malachite green residue has been detected in aquatic products breeding from time to time due to illegal addition. Malachite green residue detection method has been mainly reported, such as high performance liquid chromatography, surface enhanced Raman scattering spectroscopy, liquid chromatography-mass spectrometry (LC-MS), ultraviolet spectrometry,which were not easy to be applied and popularized at the basic unit, due to lower sensitivity, or longer single sample detection time, or expensive equipment, or complicated operation. Therefore, it was urgent to develop a detection method with high sensitivity, good selectivity, short response time and less input. Quantum dot fluorescent probe method in residue detection had the potential to meet the demand, but the current studies using the method of quantum dots to detect malachite green were rarely reported. In view of this, based on the application prospects of residue detection by quantum dot fluorescent probe method in the field of food safety, the feasibility of detecting malachite green residue with illegal addition in aquaculture was researched in the present study by a water-soluble quantum dot fluorescent probe method, and the purpose was to establish a method to detect trace residues of malachite green in actual water and fish products. In this study, water- soluble CdTe/ZnS quantum dot fluorescent probe was synthesized under mild conditions with 3-mercaptopropionic acid as a stabilizer. The main influence factors of water-soluble CdTe/ZnS quantum dot fluorescent probe to detect malachite green in the detection system were investigated, including buffer system type, buffer pH, buffer concentration, concentration of quantum dots, reaction time, concentration of malachite green, coexisting ions, etc. The best condition was obtained for the water-soluble CdTe/ZnS quantum dot probe method to detect malachite green on the basis of above investigation. Under the optimal detection condition, water-soluble CdTe/ZnS quantum dot fluorescent probe for quantitative detection of trace residues of malachite green was carried out in water and fish products. At the same time, the mechanism of water-soluble CdTe/ZnS quantum dot fluorescent probe method being used for the detection of trace residues of malachite green was studied by using ultraviolet-visible (UV-Vis) absorption spectroscopy and resonance light scattering technique. As a result, a simple, rapid and sensitive approach to quantitative determination of illegally added malachite green residues in aquaculture was developed based on the fluorescence quenching of water-soluble CdTe/ZnS quantum dots by malachite green. Under the optimized conditions, i.e., pH=8.0, 0.065 mol/L Tris-HCl and 1.60×10-4 mol/L CdTe/ZnS in the detection system, the linear range of water-soluble CdTe/ZnS quantum dot fluorescent quenching intensity versus the concentration of malachite green from 0.0193 mg/L to 1.28 mg/L, with a correlation coefficient of r=0.999 and a limit of detection of 0.00543 mg/L. The proposed method had been applied to quantitative determination of malachite green in muscle tissue of fish and water for freshwater and marine aquaculture successfully, with the recovery percentage of 90.4%- 100.3% and relative standard deviations of 0.37%-1.01% for added malachite green. The detection results of aquatic products and aquaculture water were consistent with the results of LC-MS method, while the results of false positive rate and false negative rate test were the same with real samples, which indicated that the water-soluble quantum dot fluorescent probe method of malachite green residue detection was more specific. The fluorescence quenching mechanism was further investigated by using UV-Vis absorption spectra and resonance light scattering. The results indicated that the fluorescence quenching of water-soluble CdTe/ZnS quantum dots by malachite green was due to fluorescence resonance energy transfer system being constructed between CdTe/ZnS quantum dots (donor) and malachite green (acceptor).

Summary Ferrous ion (Fe2+ ) and reduced sulfur ion (S2 -) were main toxic elements in the cold waterlogged paddy soil . How to remove Fe2+ and S2 - effectively was the key to improve the quality of cold waterlogged paddy soil . Steel slag has been confirmed as a good sorption material in waste water treatments for some heavy metals and organic pollutants . These properties suggested that steel slag might have the ability to adsorb and fix Fe2+ and S2 - from cold waterlogged paddy soil , and improve the quality of cold waterlogged paddy soil by reducing Fe2+ and S2- . The characteristics of Fe2+ and S2 - adsorption‐desorption by steel slag were studied in the present study , to reveal whether steel slag was a good sorption material for Fe2+ and S2 - , and to understand whether steel slag had the potentiality in controlling Fe2+ and S2 - and improving the quality of cold waterlogged paddy soil . The sorption of Fe2+ and S2 - by steel slag was studied using batch incubation experiments , while the effects of adsorption time (0 .25 ,0 .5 ,1 ,1 .5 ,2 ,3 or 4 h ,respectively) ,Fe2+ and S2 - concentration (10 ,30 ,50 ,100 , 150 mg/L Fe2+or 10 , 30 , 50 , 80 , 100 mg/L S2 - , respectively) , pH ( the pH range of adsorption system was from 1.00to12.00),temperature(designedas15,25,35or45 ℃ ,respectively)andionicstrength(0.01mol/LNaCl, 0 .02 mol/L NaCl or 0 .005 mol/L MgCl2 , respectively) in adsorption reaction solution on the sorption were investigated . Except for adsorption time experiments , all treatments were shook 3 h and stood for one night for complete adsorption reaction . Then , the adsorption reaction solution was centrifuged at 4 000 r/min for 10 min and filtrated for further determination of Fe2+ and S2 -concentrations . The stability of Fe2+ and S2 -adsorbed by steel slag was further validated by desorption experiments under similar conditions . The results showed that the adsorption kinetics of Fe2+ and S2 - by steel slag followed the Elovich kinetics equation , and the correlation coefficients were 0 .94 and 0 .89 respectively . Freundlich isotherm model could simulate the adsorption processes better than other models , and the correlation coefficients for Freundlich isotherm model were 0 .97 and 0 .94 respectively . Their parameters were all less than 1 , which indicated that the adsorption processes were non‐preferential adsorption . Free energy variation (ΔG) for the Fe2+ sorption was greater than 0 , which indicated that this reaction was non‐spontaneous; but ΔG for the S2 - sorption was less than 0 , which indicated that this reaction was spontaneous . The adsorption process was endothermic because high temperature was beneficial to their adsorption . And the adsorption process had greater pH adaptability range from 1 .50 to 11 .50 . The adsorption of Fe2+ was major in inner sphere complexation , while the adsorption of S2 - was major in outer complexation , which were consistent with the results in thermodynamic experiments . The adsorption rates were all very high , but the desorption rates were low in all experimental conditions , which showed that the adsorption stability of steel slag was superior . On the whole , steel slag had good ability to remove Fe2+ and S2 - , might be a potential adsorbent in controlling Fe2+ and S2 - and improving the quality of cold waterlogged paddy soil .