Enhanced immobilization of cadmium and lead in contaminated soil using calcium alginate-modified HAP biochar: Improvements in soil health and microbial diversity.

A novel adsorbent, calcium alginate-modified HAP (Hydroxyapatite)-wood ear mushroom sticks biochar (CA-HAPMB), was synthesized to enhance the immobilization of Cd and Pb in soil. Over 150 days, applying CA-HAPMB at concentrations of 0%-3% in contaminated soils from Chenzhou City in Hunan Province (CZ) and Shenyang City in Liaoning Province (SY) resulted in decreased effective concentrations of Cd and Pb. Specifically, in CZ soil, Cd and Pb decreased by 30.9%-69.3% and 31.9%-78.6%, respectively, while in SY soil, they decreased by 27.5%-53.7% and 26.4%-62.3%, respectively. Characterization results, obtained after separating CA-HAPMB from the soil, indicate that complexation, co-precipitation, and ion exchange play crucial roles in the efficient immobilization of Cd and Pb by CA-HAPMB. Additionally, adjusting the amount of CA-HAPMB added allows modulation of soil pH, leading to increased soil organic matter and nutrient content. Following treatment with CA-HAPMB for immobilizing Cd and Pb, soil bacteria abundance and diversity increased, further promoting heavy-metal immobilization.

Identification and Mechanistic Analysis of Toxic Degradation Products in the Advanced Oxidation Pathways of Fluoroquinolone Antibiotics.

The degradation of fluoroquinolones (FQs) via advanced oxidation processes (AOPs) is a promising avenue, yet the complete mineralization of certain FQ molecules remains elusive, raising concerns about the formation of toxic by-products. This study delineates five primary AOP degradation pathways for 16 commercially available FQ molecules, inferred from existing literature. Density functional theory (DFT) was employed to calculate the bond dissociation energies within these pathways to elucidate the correlation between bond strength and molecular architecture. Subsequently, Comparative Molecular Similarity Index Analysis (CoMSIA) models were constructed for various degradation reactions, including piperazine ring cleavage, defluorination, hydroxylation, and piperazine ring hydroxylation. Three-dimensional contour maps generated from these models provide a deeper understanding of the interplay between FQ molecular structure and bond dissociation energy. Furthermore, toxicity predictions for 16 FQ molecules and their advanced oxidation intermediates, conducted using VEGA 1.2.3 software, indicate that degradation products from pathways P2 and P5 pose a heightened health risk relative to their parent compounds. Furthermore, the application of the Multwfn program to compute the Fukui function for FQ molecules discerns the disparity in degradation propensities, highlighting that N atoms with higher f0 values can augment the likelihood of piperazine ring cleavage. HOMO-LUMO distribution diagrams further confirm that methoxy substitution at the 1-position leads to a dilution of HOMOs on the piperazine ring and an increased energy gap for free radical reactions, diminishing the reactivity with hydroxyl radicals. This study elucidates the pivotal role of structural characteristics in FQ antibiotics for their degradation efficiency within AOPs and unveils the underlying mechanisms of bond dissociation energy disparities. The toxicity parameter predictions for FQ molecules and their intermediates offer unique perspectives and theoretical underpinnings for mitigating the use of high-risk FQs and for devising targeted degradation strategies to circumvent the generation of toxic intermediates in AOPs through molecular structure optimization.

Reduction strategies of polycyclic aromatic hydrocarbons in farmland soils: Microbial degradation, plant transport inhibition, and their mechanistic analysis.

This study focuses on the abatement of polycyclic aromatic hydrocarbons (PAHs), a global pollutant, in farmland soils. Seven controlled PAHs in China were used as the target ligands, and four key target receptors degradable PAHs and two key target receptors transport PAHs were used as the target receptors. Firstly, the degradation abilities of the four key target receptors on PAHs were quantified, and the dominant target receptors that could efficiently degrade PAHs were screened out. Then, the co-degradation abilities of PAHs under the coexistence of the dominant target receptors (microbial diversity) were assessed, and 30 external condition-adding schemes to promote the microbial (co-)degradation of PAHs were designed. In addition, the microbial dominant target receptor mutants and the plant key target receptor mutants were obtained, the degradation and transportation of PAHs were improved by 8.06%∼22.27% and 39.86%∼45.43%. Finally, the mechanism analysis of PAHs biodegradation and transportation found that the Van der Waals interactions dominated the enhancement of PAHs' degradation in soil, and the solvation capacity dominated the decrease of PAHs' transportation in plant. This study aims to provide theoretical support for the prevention and control of PAHs residue pollution in farmland soil, as well as the protection of human dietary health.

Molecular design of environment-friendly chlorophenol (CP) derivatives based on 3D-QSAR assisted with a comprehensive evaluation method combining bioaccumulation and degradation.

In this study, a chlorophenol (CP) 3D-QSAR model with a double activity (bioaccumulation and degradation) combination was established. 19 CPs were divided into a training set and test set according to the ratio of 4:1. The cross-validation coefficient (q2) and non-cross-validation coefficient (R2) of the model were 0.803 (> 0.5) and 0.925 (> 0.9), respectively, indicating a good stability and predictive ability of the 3D-QSAR. 2,4,6-trichlorophenol (2,4,6-TCP) was used as a target molecule, and 46 derivatives with low comprehensive effects were designed. Out of the 46 derivatives, 11 derivatives were screened to have the good insecticidal and preservative properties. From the perspective of the toxicity of zebrafish, 4 out of the 11 derivatives were found to have lower aquatic toxicity effects. Through the food chain simulation of cyanobacteria-daphnia-swamp-mandarin fish, it was found that the bioaccumulation effect of the four derivatives was lower than that of 2,4, 6-TCP. Finally, molecular dynamics simulation was conducted using 2-CH2NH2 substituted derivatives, and it was found that the degradation effect by laccase (white rot fungi) was significantly improved in the presence of violuric acid, hydroxybenzotriazole, and syringaldehyde. This study can provide theoretical support for the development of environment-friendly technology for emerging pollutants.

Molecular Design and Mechanism Analysis of Phthalic Acid Ester Substitutes: Improved Biodegradability in Processes of Sewage Treatment and Soil Remediation.

Phthalic acid esters (PAEs) have the characteristics of environmental persistence. Therefore, improving the biodegradability of PAEs is the key to reducing the extent of ecological harm realized. Firstly, the scoring function values of PAEs docking with various degrading enzymes in sewage treatment were calculated. Based on this, a 3D-quantitative structure-activity relationship (3D-QSAR) model for PAE biodegradability was built, and 38 PAE substitutes were created. By predicting the endocrine-disrupting toxicity and functions of PAE substitutes, two types of PAE substitutes that are easily degraded by microorganisms, have low toxicity, and remain functional were successfully screened. Meanwhile, the differences in the mechanism of molecular degradation difference before and after PAE modification were analyzed based on the distribution characteristics of amino acid residues in the molecular docking complex. Finally, the photodegradability and microbial degradability of the PAE substitutes in the soil environment was evaluated. From the 3D-QSAR model design perspective, the modification mechanism of PAE substitutes suitable for sewage treatment and soil environment degradation was analyzed. We aim to improve the biodegradability of PAEs at the source and provide theoretical support for alleviating the environmental hazards of using PAEs.

Multi-Dimensional Elimination of ß-Lactams in the Rural Wetland: Molecule Design and Screening for More Antibacterial and Degradable Substitutes.

Restricted economic conditions and limited sewage treatment facilities in rural areas lead to the discharge of small-scale breeding wastewater containing higher values of residual beta-lactam antibiotics (ß-lactams), which seriously threatens the aquatic environment. In this paper, molecular docking and a comprehensive method were performed to quantify and fit the source modification for the combined biodegradation of ß-lactams. Using penicillin (PNC) as the target molecule, combined with contour maps for substitute modification, a three-dimensional quantitative structure-activity relationship (3D-QSAR) model was constructed for the high-performance combined biodegradation of ß-lactams. The selected candidate with better environmental friendliness, functionality, and high performance was screened. By using the homology modeling algorithms, the mutant penicillin-binding proteins (PBPs) of Escherichia coli were constructed to have antibacterial resistance against ß-lactams. The molecular docking was applied to obtain the target substitute by analyzing the degree of antibacterial resistance of ß-lactam substitute. The combined biodegradation of ß-lactams and substitute in the constructed wetland (CW) by different wetland plant root secretions was studied using molecular dynamics simulations. The result showed a 49.28% higher biodegradation of the substitutes than PNC when the combined wetland plant species of Eichhornia crassipes, Phragmites australis, and Canna indica L. were employed.

Theoretical design and process control of neonicotinoids insecticides suitable for synergistic degradation with the rubisco enzyme from rhizobia and carbon-fixing bacteria in soil.

In this study, we studied and developed the modification schemes of environmentally friendly substitutes of neonicotinoid insecticides (NNIs) along with the regulatory measures that effectively enhanced the synergistic degradation of NNIs by soil rhizobia and carbon-fixing bacteria. Firstly, the binding ability of NNIs to the two key proteins was characterized by molecular docking; secondly, the mean square deviation decision method, which is a comprehensive evaluation method, was used to investigate the binding ability of NNI molecules with the two Rubisco rate-limiting enzymes. The three-dimensional quantitative structure-activity relationship (3D-QSAR) model was established for the synergistic degradation and single effect of rhizobia and carbon-fixing bacteria. Finally, after combining the 3D-QSAR model with a contour map analysis of the synergistic degradation effect of soil rhizobia and carbon-fixing bacteria, 102 NNI derivatives were designed. Flonicamid-36 and other four NNI derivatives passed the functional and environmentally friendly evaluation. Taguchi orthogonal experiment and factorial experiment-assisted molecular dynamics method were used to simulate the effects of 32 regulation schemes on the synergistic degradation of NNIS and its derivatives by rhizobia and carbon fixing bacteria. The synergistic degradation capacity of soil rhizobia and carbon-fixing bacteria was increased to 33.32% after right nitrogen supplementation. This indicated that supplementing the correct amount of nitrogen in the soil environment was beneficial to the microbial degradation of NNIs and their derivatives.