Microbial community composition and glyphosate degraders of two soils under the influence of temperature, total organic carbon and pH

Effects of biochar and compost on microbial community assembly and metabolic processes in glyphosate, imidacloprid and pyraclostrobin polluted soil under freezethaw cycles

Biochar and organic compost are widely used in agricultural soil remediation as soil immobilization agents. However, the effects of biochar and compost on microbial community assembly processes in polluted soil under freezingthawing need to be further clarified. Therefore, a freezethaw cycle experiment was conducted with glyphosate (herbicide), imidacloprid (insecticide) and pyraclostrobin (fungicide) polluted to understand the effect of biochar and compost on microbial community assembly and metabolic behavior. We found that biochar and compost could significantly promote the degradation of glyphosate, imidacloprid and pyraclostrobin in freezethaw soil decrease the half-life of the three pesticides. The addition of immobilization agents improved soil bacterial and fungal communities and promoted the transformation from homogeneous dispersal to homogeneous selection. For soil metabolism, the combined addition of biochar and compost alleviated the pollution of glyphosate, imidacloprid and imidacloprid to soil through up-regulation of metabolites (DEMs) in amino acid metabolism pathway and down-regulation of DEMs in fatty acid metabolism pathway. The structural equation modeling (SEM) results showed that soil pH and DOC were the main driving factors affecting microbial community assembly and metabolites. In summary, the combined addition of biochar and compost reduced the adverse effects of pesticides residues.

Nitro-PAHs: Occurrences, ecological consequences, and remediation strategies for environmental restoration

Nitrated polycyclic aromatic hydrocarbons (nitro-PAHs) are persistent pollutants that have been introduced into the environment as a result of human activities. They are produced when PAHs undergo oxidation and are highly resistant to degradation, resulting in prolonged exposure and significant health risks for wildlife and humans. Nitro-PAHs' potential to induce cancer and mutations has raised concerns about their harmful effects. Furthermore, their ability to accumulate in the food chain seriously threatens the ecosystem and human health. Moreover, nitro-PAHs can disrupt the normal functioning of the endocrine system, leading to reproductive and developmental problems in humans and other organisms. Reducing nitro-PAHs in the environment through source management, physical removal, and chemical treatment is essential to mitigate the associated environmental and human health risks. Recent studies have focused on improving nitro-PAHs' phytoremediation by incorporating microorganisms and biostimulants. Microbes can break down nitro-PAHs into less harmful substances, while biostimulants can enhance plant growth and metabolic activity. By combining these elements, the effectiveness of phytoremediation for nitro-PAHs can be increased. This study aimed to investigate the impact of introducing microbial and biostimulant agents on the phytoremediation process for nitro-PAHs and identify potential solutions for addressing the environmental risks associated with these pollutants.

Perfluoroalkyl acid precursors in agricultural soil-plant systems: Occurrence, uptake, and biotransformation

Perfluoroalkyl acid (PFAA) precursors have been used in various consumer and industrial products due to their hydrophobic and oleophobic properties. In recent years, PFAA precursors in agricultural soil-plant systems have received increasing attention as they are susceptible to biotransformation into metabolites with high biotoxicity risks to human health. In this review, we systematically assessed the occurrence of PFAA precursors in agricultural soils, taking into account their sources and biodegradation pathways. In addition, we summarized the findings of the relevant literature on the uptake and biotransformation of PFAA precursors by agricultural plants. The applications of biosolids/composts and pesticides are the main sources of PFAA precursors in agricultural soils. The physicochemical properties of PFAA precursors, soil organic carbon (SOC) contents, and plant species are the key factors influencing plant root uptakes of PFAA precursors from soils. This review revealed, through toxicity assessment, the potential of PFAA precursors to generate metabolites with higher toxicity than the parent precursors. The results of this paper provide a reference for future research on PFAA precursors and their metabolites in soil-plant systems.

Co-exposure of microplastics and sulfamethoxazole propagated antibiotic resistance genes in sediments by regulating the microbial carbon metabolism

The concerns on the carriers of microplastics (MPs) on co-existing pollutants in aquatic environments are sharply rising in recent years. However, little is known about their interactions on the colonization of microbiota, especially for the spread of pathogens and antibiotic resistance genes (ARGs). Therefore, this study aimed to investigate the influences on the propagation of ARGs in sediments by the co-exposure of different MPs and sulfamethoxazole (SMX). The results showed that the presence of MPs significantly enhanced the contents of total organic carbon, while having no effects on the removal of SMX in sediments. Exposure to SMX and MPs obviously activated the microbial carbon utilization capacities based on the BIOLOG method. The propagation of ARGs in sediments was activated by SMX, which was further promoted by the presence of polylactic acid (PLA) MPs, but significantly lowered by the co-exposed polyethylene (PE) MPs. This apparent difference may be attributed to the distinct influence on the antibiotic efflux pumps of two MPs. Moreover, the propagation of ARGs may be also dominated by microbial carbon metabolism in sediments, especially through regulating the carbon sources of carboxylic acids, carbohydrates, and amino acids. This study provides new insights into the carrier effects of MPs in sediments.

Combined pollution and soil microbial effect of pesticides and microplastics in greenhouse soil of suburban Tianjin, Northern China

Current-used pesticides (CUPs) and plastic films are essential materials used in greenhouse cultivation, which can lead to the residual accumulation of CUPs and microplastics (MPs) over time. The impact of CUPs and MPs on soil quality and food safety cannot be overlooked. However, the combined pollution resulting from CUPs and MPs in greenhouse soil remains poorly understood. In this study, we conducted a survey at 30 greenhouse sites in the Wuqing District of Tianjin, China, to investigate the pollution levels and characteristics of CUPs and MPs using QuEChERS combined with LC-MS/MS, and density extraction, 30% H2O2 digestion and micro-fourier transform infrared spectroscopy, respectively. Additionally, we aimed to evaluate the interactions among these two pollutants, soil physicochemical properties, and the bacterial community in the soil. CUPs were frequently detected in the examined soil samples; however, they posed no significant ecological risks due to their low levels. Furthermore, MPs, which predominantly comprised fragmented and fibrous polyethylene (PE) and polypropylene (PP) particles smaller than 1.0 mm, could potentially degrade into nanoplastics, which might subsequently enter the food chain and pose a serious threat to human health. We observed no substantial correlations between CUPs and MPs, except for a negative correlation between dimethomorph and film MPs. The soil pH and total organic carbon (TOC) exhibited interactions with both types of pollutants, whereas soil clay content (CC) only correlated with CUPs, and soil available nitrogen (AN) only correlated with MPs. The variability of soil bacterial communities among the 30 sampling sites was minimal, with the dominant genus being Bacillus. Soil pH, TOC, and CC collectively exerted a strong influence on the microbial community across all samples; however, the effects of CUPs and MPs on the soil microbial structure were marginal. These results contribute to a comprehensive understanding of the environmental stress and ecological risks associated with the combined pollution of CUPs and MPs.

How Benthic Sediment Microbial Communities Respond to Glyphosate and Its Metabolite: a Microcosm Experiment

Glyphosate is the most commonly used agricultural herbicide in the world. In aquatic ecosystems, glyphosate often adsorbs to benthic substrates or is metabolized and degraded by microorganisms. The effects of glyphosate on microbial communities vary widely as microorganisms respond differently to exposure. To help understand the impacts of glyphosate on the sediment microbiome, we conducted a microcosm experiment examining the responses of benthic sediment microbial communities to herbicide treatments. Sediments from a prairie pothole wetland were collected, and 16S rRNA gene sequencing was used to analyze community composition 2-h and 14-days after a single treatment of low (0.07 ppm), medium (0.7 ppm), or high (7 ppm) glyphosate, aminomethylphosphonic acid (glyphosate metabolite), or a glyphosate-based commercial formula. We found no significant differences in microbial community composition across treatments, concentration levels, or day of sampling. These findings suggest that microbial species in the Prairie Pothole Region of North America may be tolerant to glyphosate exposure.

Response characteristics of denitrifying bacteria and denitrifying functional genes to woody peat during pig manure composting

This study aimed to explore the impacts of adding different proportions of woody peat (WP) (0%(CK), 5%(T1), and 15%(T2)) on denitrification during composting. The results demonstrated that compared with CK, T1 and T2 increased the total Kjeldahl nitrogen content (8% and 14%, respectively) and reduced the nitrate nitrogen (7% and 23%) content after composting. After composting, the abundances of nirK and nirS decreased by 4-9% and 33-35% under T1 and T2, respectively. Adding 15% WP reduced the abundances of key denitrifying bacteria such as Pseudomonas, Pusillimonas, Achromobacter, and Rhizobiales by 5-90%. The main factors that affected denitrification genes were the carbon content, nitrogen form (nitrite nitrogen and ammonium nitrogen), and denitrifying bacteria community. In summary, adding 15% WP has the best ability to reduce nitrogen loss by decreasing the abundances of denitrifying bacteria and denitrifying functional genes, thereby improving the agricultural value of composting products.

Development of chitosan-magnetic sawdust hydrochar for Pb and Zn immobilization process on various soil conditions

A series of 60-day soil immobilized incubations were performed to explore the impacts of various factors (incubation time, chitosan modified magnetic sawdust hydrochar (CMSH) dosages, initial pH values, moisture contents, and humic acid (HA)) on CMSH immobilization of Pb and Zn. DTPA and BCR extraction techniques were undertaken to study the distribution of form transformations of Pb and Zn. CMSH showed significant immobilization ability for both DTPA-Pb and DTPA-Zn, and the highest removal rates were shown to be 57.40% and 90.00% for Pb and Zn respectively. After 60 days of incubation, the residual Pb was enhanced by 34-61% and residual Zn increased by 25-41%, which indicated that CMSH was effective in immobilizing Pb and Zn. Meanwhile, the immobilization efficiency improved with increasing incubation time, CMSH dosage, HA dosage, and initial solution pH. In particular, 5% HA application increased the soil TOC and accelerated the metal stabilization processes, with the residual forms of Pb and Zn eventually reaching a maximum of 73% and 71%, respectively. In addition, the alkaline initial solution promoted the ion exchange, surface complexation reaction, and cationic-π interaction, resulting in a better immobilization of Pb and Zn by CMSH. Finally, according to the orthogonal analysis of BCR results, HA dosage was the major factor affecting Pb and Zn immobilization by CMSH compared to soil pH and moisture content in this study.

Effects of Free or Immobilized Bacterium Stenotrophomonas acidaminiphila Y4B on Glyphosate Degradation Performance and Indigenous Microbial Community Structure

The overuse of glyphosate has resulted in serious environmental contamination. Thus, effective techniques to remove glyphosate from the environment are required. Herein, we isolated a novel strain Stenotrophomonas acidaminiphila Y4B, which completely degraded glyphosate and its major metabolite aminomethylphosphonic acid (AMPA). Y4B degraded glyphosate over a broad concentration range (50-800 mg L^-1), with a degradation efficiency of over 98% within 72 h (50 mg L^-1). Y4B degraded glyphosate via the AMPA pathway by cleaving the C-N bond, followed by degradation of AMPA and subsequent metabolism. Y4B demonstrated strong competitiveness and substantially accelerated the degradation of glyphosate in different soils, degrading 71.93 and 89.81% of glyphosate (400 mg kg^-1) within 5 days in sterile and nonsterile soils, respectively. The immobilized cells of Y4B were more efficient than their free cells and they displayed excellent biodegradation efficiency in a sediment-water system. Taken together, Y4B is an ideal degrader for the bioremediation of glyphosate-contaminated sites.

Double-edged effects of elevating temperature on the aging of exogenous arsenic in flooded paddy soils

Temperature variation can have a significant impact on arsenic (As) bioavailability in paddy soils. However, details regarding the transformation of exogenous As during the aging process in paddy soils at various temperatures remain unclear. This work investigated the effects of temperature on the As extractability and As species transformation of three paddy soils spiked with exogenous arsenate at 60 mg kg^-1 under flooded aging and explored the related chemical and microbial mechanisms. The results showed that 0.05 M NH₄H₂PO₄-extractable As decreased over time during flooded aging for 192 days, and it decreased by approximately one-third at 35 °C compared with 15 °C and 25 °C at the same aging time, indicating that higher temperatures facilitated the decrease in As extractability. As(V) reduction mainly occurred at 35 °C because the abundance and As(V)-reducing capacity of the predominant indigenous bacteria, the Bacillus sp strains, and the abundance of the arrA gene were significantly higher than those at 15 °C and 25 °C. The reduction of As(V) to As(III) and aging occurred simultaneously. The kinetic models were established, and the rate constants of the reduction and aging processes were obtained. Soil properties significantly affected the aging and reduction processes of extractable As(V). Our study indicated that elevating temperature had dual effects on the environmental risk of As in the flooded aging process. The previous definition of "aging" based on cationic metals needs to be updated according to the transformation characteristics of As species in flooded conditions. Our results addressed the necessity of impeding the reduction of As(V) in paddy soils under global warming.

Dissipation Residue Behaviors and Dietary Risk Assessment of Boscalid and Pyraclostrobin in Watermelon by HPLC-MS/MS

Fungicides containing active ingredients of boscalid and pyraclostrobin have been widely applied in watermelon disease control. To provide data for avoiding health hazards caused by fungicides, we investigated its terminal residues and evaluated the dietary risk. In this work, watermelon samples were collected from field sites in six provinces and analyzed with high-performance liquid chromatography-tandem mass spectrometry (HPLC-MS/MS). The average recoveries of boscalid and pyraclostrobin in the watermelon matrix were 97–108% and 93–103%, respectively, with the relative standard deviations (RSDs) ≤ 9.1%. The limits of quantifications (LOQs) were 0.01 and 0.005 mg/kg for boscalid and pyraclostrobin. Twenty-one days after applying the test pesticide with 270 g a.i./ha, the terminal residues of boscalid and pyraclostrobin were all below 0.05 mg/kg and below the maximum residue limits (MRLs) recommended by European Food Safety Authority (EFSA). According to the national estimated daily intake (NEDI), the risk quotients (RQs) of boscalid and pyraclostrobin were 48.4% and 62.6%, respectively. That indicated the pesticide evaluated in watermelon exhibited a low dietary risk to consumers. All data provide a reference for the MRL establishment of boscalid in watermelon for China.