Dissipation and phytotoxicity of imazethapyr and imazamox in soils amended with β-cyclodextrin-chitosan biocomposite

Insights on persistent herbicides in cropland soils in northern China: Occurrence, ecological risks, and phytotoxicity to subsequent crops

Herbicides are essential inputs in agriculture, but their long-term persistence creates underappreciated risks in intensive cropping systems. While previous studies focused on single-herbicide persistence, the cumulative ecological and agronomic impacts of multi-herbicide residues remain poorly understood, particularly in phytotoxicity to subsequent crops. This study investigated the occurrence, ecological risk, and phytotoxicity of six persistent herbicides in cropland soils in northern China. Herbicide contamination was widespread, with at least one herbicide detected in 90.9 % of soil samples. The most frequently detected herbicides were atrazine (54.6 %), deethylatrazine (41.1 %), fomesafen (47.3 %), and nicosulfuron (54.3 %), with mean concentrations of 9, 7, 41, and 99 μg/kg dw, respectively. Clomazone and imazethapyr were detected in 5.5 % and 0.8 % of samples, with mean concentrations of 8 and 4 μg/kg dw, respectively. Risk quotient (RQ) values indicated that clomazone (0.004), fomesafen (0.001), and imazethapyr (0.00006) pose low ecological risk (RQ<0.01), whereas nicosulfuron (26.95) and atrazine (2.54) present high ecological risk (RQ≥1). Phytotoxicity risks to subsequent crops, including tobacco, were identified for atrazine (28.6 % of soils), nicosulfuron (26.4 % of soils), and fomesafen (14 % of soils). Most subsequent crops, like soybean and wheat, were unaffected by atrazine residues in over 99 % of the soils. These findings provide key data for agricultural management.

A simple approach to fabricate chitosan-delivered avermectin controlled release microparticles for improved efficacy and reduced residues

The presence of a synergistic effect between carrier and insecticide in controlled release formulations is highly desirable to improve efficacy to target pests and reduce insecticide use. Herein, controlled release microparticles of avermectin (AVM) were fabricated using natural chitosan (CTS) as a carrier by a pH adjustment method. The resulted AVM@CTS microparticles displayed high encapsulation efficiency (73.3 %), outstanding photostability, obvious pH/temperature sensitivity, and good deposition behavior on Chinese cabbage leaves. Instrument detections in combination with molecular dynamics simulations showed that AVM interacted with CTS mainly through physical adsorption, adhesion, and weak H-bonds. In vitro release data of the controlled release formulation obeyed the first-order kinetic equation. Toxicity tests exhibited a significantly synergistic effect between CTS and AVM, resulting in better quick-acting and long-term efficacy against Plutella xylostella larvae than that of the AVM acetone solution. The 72 h LC50 of the formulation for a 21-day efficacy was 12.73 mg/L, much lower than the value (31.53 mg/L) of the AVM solution. Moreover, the AVM@CTS microparticles exhibited shorter half-life (19.6 days) than the unformulated AVM (23.0 days) under natural conditions in soil. This work contributes to the development of controlled release system with carrier-insecticide synergistic effect for sustainable pest control.

Construction of Sub-Nano Channels of Amino Pillar[6]arene Inspired Biomimetic Porous Roots for Specific Remove of Imazamox

The root ducts play an important role in the plant's transport of nutrients from the soil. Based on the selective transport characteristics of plant roots, amino pillar[6]arene bionic porous root sub-nano channel membrane were constructed to remove Imazamox. Imazamox (IM) is an effective imidazolinone herbicide frequently utilized in soybean fields to control a wide range of annual grasses and broad-leaved weeds. However, it is important to note that while IM is effective in controlling the growth of weeds, its residues can affect the plants that are later planted. Developing a material that can efficiently and selectively remove IM from the environment poses a significant challenge in the realm of agricultural residue removal. A layer-upon-layer covalent assembly was formed through the reaction of amino pillar[6]arene with terephthalaldehyde using an aldehyde-amine Schiff-base reaction. The cavity of amino pillar[6]arenal is used to realize the host-guest interaction of IM. This enabled the development of a membrane with high selectivity for the extraction and removal of IM. The removal rate is 4.66-21.91 times higher than that of other pesticide chemicals. The successful development of the highly selective porous root bionic membrane provides a broad prospect for its application and development in agricultural production.

Insights into adsorption performance and mechanism of chitosan-bentonite biocomposites for removal of imazethapyr and imazamox

In the present study, chitosan-bentonite biocomposites were synthesised by ultrasonication, characterized using spectral techniques and assessed for their effectiveness in removing imazethapyr and imazamox from aqueous solution. The response surface methodology based box behnken design was utilized to generate optimum conditions viz. pH (1 to 9), adsorbent dose (0.01 to 1.0 g), contact time (0.5 to 48 h) and temperature (15 to 55 °C) for adsorption of herbicides on biocomposites. Based on model predictions, 60.4 to 91.5 % of imazethapyr and 31.7 to 46.4 % of imazamox was efficiently removed under optimal conditions. Adsorption data exhibited a strong fit to pseudo-second-order kinetic (R2 > 0.987) and Freundlich isotherm (R2 > 0.979). The adsorption capacity ranged from 3.88 to 112 μg1-ng-1mLn and order of adsorption was: low molecular weight chitosan-bentonite> medium molecular weight chitosan-bentonite> high molecular weight chitosan-bentonite> bentonite. Thermodynamic experiments suggested a spontaneous, exothermic process, reducing the system randomness during adsorption. Desorption experiments revealed successful desorption ranging from 91.5 to 97.0 % using 0.1 M NaOH. The adsorption mechanism was dominated by synergistic electrostatic interactions and hydrogen bonding. These results collectively indicated the potential environmental remediation application of chitosan-bentonite biocomposites to adsorb imazethapyr and imazamox from wastewaters.

Exploration of the biodegradation pathway and enhanced removal of imazethapyr from soil by immobilized Bacillus marcorestinctum YN1

Excessive or inappropriate applications of imazethapyr cause severe ecological deteriorations and health risks in human. A novel bacterial strain, i.e., Bacillus marcorestinctum YN1, was isolated to efficiently degrade imazethapyr, with the degradation pathways and intermediates predicted. Protein mass spectrometry analysis identified enzymes in strain YN1 potentially involved in imazethapyr biodegradation, including methylenetetrahydrofolate dehydrogenase, carbon-nitrogen family hydrolase, heme degrading monooxygenase, and cytochrome P450. The strain YN1 was further immobilized with biochar (BC600) prepared from mushroom waste (i.e., spent mushroom substrate) by pyrolysis at 600 °C to evaluate its degrading characteristics of imazethapyr. Scanning electron microscope observation showed that strain YN1 was adsorbed in the rich pore structure of BC600 and the adsorption efficiency reached the maximum level of 88.02% in 6 h. Both energy dispersive X-ray and Fourier transform infrared spectroscopy analyses showed that BC600 contained many elements and functional groups. The results of liquid chromatography showed that biochar-immobilized strain YN1 (IBC-YN1) improved the degradation rate of imazethapyr from 79.2% to 87.4%. The degradation rate of imazethapyr by IBC-YN1 could still reach 81.0% in the third recycle, while the bacterial survival rate was 67.73% after 180 d storage at 4 °C. The treatment of IBC-YN1 significantly shortened the half-life of imazethapyr in non-sterilized soil from 35.51 to 11.36 d, and the vegetative growth of imazethapyr sensitive crop plant (i.e., Cucumis sativus L.) was significantly increased in soil remediated, showing that the inhibition rate of root length and fresh weight were decreased by 12.45% and 38.49% respectively. This study exhanced our understanding of microbial catabolism of imazethapyr, and provided a potential in situ remediation strategy for improving the soil environment polluted by imazethapyr.

Artificially constructing mixed bacteria system for bioaugmentation of nitrogen removal from saline wastewater at low temperature

To alleviate the inhibition effects of multi-stresses, a multi-bacterial bioaugmentation based on stimulating cell-to-cell interactions was applied to improve the stress potential of salt-tolerant aerobic granular sludge (AGS). Results showed that the consortium formed by a combination of salt-tolerant ammonia-nitrogen utilizing bacteria, salt-tolerant nitrite-nitrogen utilizing bacteria and salt-tolerant nitrate-nitrogen utilizing bacteria with a whole biomass ratio of 1:2:1 achieved maximum nitrogen consumption rate (μNH₄⁺-N, μNO₂^--N and μNO₃^--N of 1.03, 0.57 and 11.62 mgN/L·h, respectively) at 35 gNaCl/L salinity and 15 °C. The flocculent consortium was aggregated by Aspergillus tubingensis mycelium pellet, which was made into a compound bacterial agent (CBA), and the comprehensive nitrogen consumption capability of CBA was further improved to 2.47-4.36-fold of single functional bacteria. 5% CBA (m/m) was introduced into the seafood processing wastewater in batches, in winter (12-16 °C), the removal efficiencies of NH₄⁺-N and total nitrogen increased from 66.89% to 52.77% of native AGS system to 79.02% and 69.97% of nascent bioaugmentation system, respectively. The analysis of key enzyme activities demonstrated that the ammonia monooxygenase and nitrate reductase activities of the bioaugmentation system were increased to 2.73-folds and 1.94-folds those of the native system. Moreover, due to an increase of 6.18 mg/gVSS and 0.11 in the secreted exopolysaccharide and tightly-bound/total extracellular polymeric substances, respectively, bioaugmentation boosted the cell bioflocculation ability by 13.53%, which enhanced the robustness. This work provided a detailed and feasible technical proposal for enhancing the biological treatment performance of saline wastewater in cold regions.

Adaptive regulation of activated sludge's core functional flora based on granular internal spatial microenvironment

A great deal of efforts has been put into studying the influence of the external macroenvironment for activated sludge to survive on microbial community succession, while granular internal spatial microenvironment should be given equal attention, because it is more directly involved in the information exchange and material transfer among microorganisms. This study systematically investigated the effects of granular microenvironment on spatial colonization and composition of sludge's core functional flora, and the corresponding difference of biological treatment performance. High content of extracellular-proteins (67.53 mg/gVSS) or extracellular-polysaccharide (65.02 mg/gVSS) stimulated the microbial flocculation and aggregation of 0.5-1.5 mm granules (GS) or 1.5-3.0 mm granules (GM), respectively, which was resulted from excellent cell hydrophobicity (59.26%) or viscosity (3.47 mPa s), therefore, constituted relatively dense porous frame. More hollow space existed in 3.0-5.0 mm granules (GL), which formed loose skeleton with 0.213 mL/g of total pore volume and 17.21 nm of average pore size. Combining scanning electron microscope images and fluorescent in-situ hybridization based microbiological analysis, aerobic nitrifiers were observed to wrap or surround anaerobic bacteria, or facultative/anaerobic bacteria were self-encapsulated, which created granule's unique microenvironment with alternating aerobic and anaerobic zones. GS has the most rich organic matter degrading bacteria and anaerobic heterotrophic denitrifiers, while GM and GL presented the greatest relative abundance of facultative and aerobic denitrifiers, respectively. The activity of dehydrogenase and nitrogen invertase of GM showed be 1.32-3.09 times higher than those of GS and GL, contributing to its higher carbon and nitrogen removal. These findings highlight the importance of granular microenvironment to adaptive regulation of activated sludge's core functional flora and corresponding pollutant removal performance.

Effect of Herbicide Clopyralid and Imazamox on Dehydrogenase Enzyme in Soil of Regenerated Pedunculate Oak Forests

Clopyralid and imazamox are successfully used for weed control during the first years of regeneration of pedunculate oak forests. Hence, the question that arises is how these herbicides affect microorganisms, especially the activity of dehydrogenase enzyme, when they reach the soil. Two study sites were selected in regenerated pedunculate oak forests, and the two herbicides were applied in two doses that are used for weed control (clopyralid, 100 g a.i. ha−1 and 120 g a.i. ha−1; imazamox, 40 g a.i. ha−1 and 48 g a.i. ha−1). The effect of the herbicides was evaluated 7, 14, 21, 30, and 60 days after application. A significant reduction in dehydrogenase activity was found on days 7 and 14 at both sites. However, after 14 days there was a recovery of dehydrogenase activity for all treatments such that the values obtained on day 21 did not differ from the control values. The effect of clopyralid and imazamox on dehydrogenase activity was not dose-dependent. Dehydrogenase activity also depended on soil properties, soil sampling time and climatic conditions during the investigation years. The results show that clopyralid and imazamox can reduce soil dehydrogenase activity, but this effect is transient. This can be attributed to the ability of microorganisms to overcome the stress caused by the herbicide by developing the capability to utilize herbicides as a nutrient source and proliferating in such an environment.

Study on degradation characteristics of imazamox by Streptomycetaceae

The residues of imazamox (IMX) will cause phytotoxicity to subsequent crops after long-term use, and will also pollute the soil and its surrounding environment. This study isolates and identifies two strains of Streptomycetaceae JX02 and JX06 that can effectively degrade IMX. Use response surface method Box-Behnken design to optimize physicochemical parameters. The optimal degradation conditions of strains JX02 and JX06 are obtained and verified: IMX concentration is 150 mg L^-1, the initial dosage is 9.9%, 9.1% (OD600 = 0.1), the temperature is 26.4 and 27.5 °C, and pH value is 7.0 and 7.7, respectively. The degradation rates of 150 mg L^-1 IMX detected by HPLC within 4 d were 99 and 94%, respectively. After adding strains JX02 and JX06, the half-life of IMX in the soil is shortened to 11 d and 13 d, indicating that Streptomycetaceae had a positive effect on the remediation of soil. It is expected to provide scientific information for the rational use, environmental safety evaluation of IMX, and provide a basis for future research and development of microbial agents.

Enhancing robustness of activated sludge with Aspergillus tubingensis as a protective backbone structure under high-salinity stress

High salt seriously destroys the stable interactions among key functional species of activated sludge, which in turn limits the performance of high-salinity wastewater biological treatment. In this study, pelletized Aspergillus tubingensis (AT) was used as a protective backbone structure for activated sludge under high-salinity stress, and a superior salt-tolerant AT-based aerobic granular sludge (AT-AGS) was developed. Results showed that the COD and NH₄⁺-N removal efficiencies of salt-domesticated AT-AGS were 11.83% and 7.18% higher than those of salt-domesticated flocculent activated sludge (FAS) at 50 gNaCl/L salinity. Compared to the salt-domesticated FAS, salt-domesticated AT-AGS showed stronger biomass retention capacity (with a MLVSS concentration of 7.92 g/L) and higher metabolic activity (with a dehydrogenase activity of 48.06 mgTF/gVSS·h). AT modified the extracellular polymeric substances pattern of microbes, and the total extracellular polysaccharide content of AT-AGS (80.7 mg/gVSS) was nearly twice than that of FAS (46.3 mg/gVSS) after salt-domestication, which demonstrated that extracellular polysaccharide played a key role in keeping the system stable. The high-throughput sequencing analysis illustrated that AT contributed to maintain the microbial richness and diversity of AT-AGS in high-salt environment, and Marinobacterium (with a relative abundance of 32.04%) became the most predominant genus in salt-tolerant AT-AGS. This study provided a novel insight into enhancing the robustness of activated sludge under high-salinity stress.

Chemical and physical Chitosan modification for designing enzymatic industrial biocatalysts: How to choose the best strategy?

Chitosan is one of the most abundant natural polymer worldwide, and due to its inherent characteristics, its use in industrial processes has been extensively explored. Because it is biodegradable, biocompatible, non-toxic, hydrophilic, cheap, and has good physical-chemical stability, it is seen as an excellent alternative for the replacement of synthetic materials in the search for more sustainable production methodologies. Thus being, a possible biotechnological application of Chitosan is as a direct support for enzyme immobilization. However, its applicability is quite specific, and to overcome this issue, alternative pretreatments are required, such as chemical and physical modifications to its structure, enabling its use in a wider array of applications. This review aims to present the topic in detail, by exploring and discussing methods of employment of Chitosan in enzymatic immobilization processes with various enzymes, presenting its advantages and disadvantages, as well as listing possible chemical modifications and combinations with other compounds for formulating an ideal support for this purpose. First, we will present Chitosan emphasizing its characteristics that allow its use as enzyme support. Furthermore, we will discuss possible physicochemical modifications that can be made to Chitosan, mentioning the improvements obtained in each process. These discussions will enable a comprehensive comparison between, and an informed choice of, the best technologies concerning enzyme immobilization and the application conditions of the biocatalyst.