Effects of sulfonylurea herbicides chlorsulfuron and sulfosulfuron on enzymatic activities and microbial communities in two agricultural soils

Enhanced mobilization of soil heavy metals by the enantioselective herbicide R-napropamide compared to its S-isomer: Analyses of abiotic and biotic drivers

Chiral herbicides applied to agricultural soils are typically mildly to moderately contaminated with heavy metals (HMs), necessitating a thorough investigation into their effects on soil HMs availability. This study evaluated the effect of the chiral herbicide napropamide (NAP) on HMs bioavailability in different soil types, including weakly alkaline clay in Northeast China, neutral sandy loam in Zhejiang, and weakly acidic clay loam in Sichuan, China. The results demonstrate significant differences in the availability of HMs (Cd, Pb, Zn, and Ni) in the soil following enantiomer treatments, with variation ranges of 4.57-45.67 %, 5.03-96.21 %, 2.92-52.30 %, and 10.57-29.79 %, respectively. Overall, R-NAP enhanced the bioavailability of HMs more effectively than S-NAP, specifically by significantly activating available iron 3.33-191.97 % and markedly affecting soil pH and cation exchange capacity. Additionally, R-NAP influenced biotic processes by enriching dominant microbial communities, such as Chitinophaga, Niabella, and Promicromonospora, and by constructing more stable microbial networks. Notably, bioavailable Fe plays a dual regulatory role, affecting both the abiotic and biotic processes affected by soil NAP. In summary, although R-NAP is commonly used in agriculture, it poses a greater risk of HMs contamination in crops, highlighting the need for careful application and management. This study provides a fundamental theoretical basis for the judicious use of chiral herbicides in agricultural soils with mild-to-moderate HMs contamination.

Comparative analysis of bacterial populations in sulfonylurea-sensitive and -resistant weeds: insights into community composition and catabolic gene dynamics

This study aimed to compare the impact of iodosulfuron-methyl-sodium and an iodosulfuron-based herbicidal ionic liquid (HIL) on the microbiomes constituting the epiphytes and endophytes of cornflower (Centaurea cyanus L.). The experiment involved biotypes of cornflower susceptible and resistant to acetolactate synthase inhibition, examining potential bacterial involvement in sulfonylurea herbicide detoxification. We focused on microbial communities present on the surface and in the plant tissues of roots and shoots. The research included the synthesis and physicochemical analysis of a novel HIL, evaluation of shifts in bacterial community composition, analysis of the presence of catabolic genes associated with sulfonylurea herbicide degradation and determination of their abundance in all experimental variants. Overall, for the susceptible biotype, the biodiversity of the root microbiome was higher compared to shoot microbiome; however, both decreased notably after herbicide or HIL applications. The herbicide-resistant biotype showed lower degree of biodiversity changes, but shifts in community composition occurred, particularly in case of HIL treatment.

Ecotoxicological impact of butisanstar and clopyralid herbicides on soil microbial respiration and the enzymatic activities

The application of herbicides in soil has been noted for its detrimental effect on the soil microbial community, crucial for various biochemical processes. This study provides a comprehensive assessment of the impact of butisanstar and clopyralid herbicides, both individually and in combination at different dosage (recommended field dose (RFD), ½, 2 and 5-times RFD). The assessment focuses on soil basal respiration (SBR), cumulative microbial respiration (CMR), and the activities dehydrogenase (DH), catalase (CAT), urease, acid and alkaline phosphatases (Ac-P and Alk-P) enzymes, along with their variations on days 10, 30, 60, and 90 post-herbicide application. Results indicate that, although herbicides, even at lower doses of RFD, demonstrate inhibitory effects on DH, CAT, and microbial respiration, they paradoxically lead to a significant enhancement in urease and phosphatase activities, even at higher doses. The inhibitory/enhancing intensity varies based on herbicide type, incubation period, and dosage. Co-application of herbicides manifests synergistic effects compared to individual applications. The most notable inhibitory effects on DH, CAT, and SBR are observed on the 30th day, coinciding with the highest activities of urease and phosphatases on the same day. The persistent inability to restore respiration and enzyme activities to initial soil (control) levels emphasizes the lasting adverse and inhibitory effects of herbicides, especially clopyralid, over the long term. It becomes apparent that soil microorganisms require an extended duration to decompose and acclimate to the presence of herbicides. Consequently, these agrochemical compounds pose a potential risk to crucial biochemical processes, such as nutrient cycling, ultimately impacting crop production.

Investigating the impact of soil properties, application rates and environmental conditions on pyroxasulfone dissipation and its ecotoxicological effects on soil health in aridisols of Punjab

This study is to understand the fate and ecological consequences of pyroxasulfone in aridisols of Punjab, a detailed dissipation study in soil, its influence on soil enzymes, microbial count and succeeding crops was evaluated. Half-lives (DT50) increased with an increase in the application rate of pyroxasulfone. Dissipation of pyroxasulfone decreased with increase in organic matter content of soil and was slower in clay loam soil (DT50 12.50 to 24.89) followed by sandy loam (DT50 8.91 to 17.78) and loamy sand soil (DT50 6.45 to 14.89). Faster dissipation was observed under submerged conditions (DT50 2.9 to 20.99 days) than under field capacity conditions (DT50 6.45 to 24.89 days). Dissipation increased with increase in temperature with DT50 varying from 6.46 to 24.88, 4.87 to 22.89 and 2.97 to 20.99 days at 25 ± 2, 35 ± 2 and 45 ± 2 °C, respectively. Dissipation was slower under sterile conditions and about 23.87- to 33.74-fold increase in DT50 was observed under sterile conditions as compared to non-sterile conditions. The application of pyroxasulfone showed short-lived transitory effect on dehydrogenase, alkaline phosphatase and soil microbial activity while herbicide has non-significant effect on soil urease activity. PCA suggested that dehydrogenase and bacteria were most sensitive among enzymatic and microbial activities. In efficacy study, pyroxasulfone effectively controlled Phalaris minor germination, with higher efficacy in loamy sand soil (GR50 2.46 µg mL-1) as compared to clay loam soil (GR50 5.19 µg mL-1).

Gut microbiota and transcriptome response of earthworms (Metaphire guillelmi) to polymyxin B exposure

Polymyxin B (PMB) has received widespread attention for its use as a last-line therapy against multidrug-resistant bacterial infection. However, the consequences of unintended PMB exposure on organisms in the surrounding environment remain inconclusive. Therefore, this study investigated the effects of soil PMB residue on the gut microbiota and transcriptome of earthworms (Metaphire guillelmi). The results indicated that the tested doses of PMB (0.01-100 mg/kg soil) did not significantly affect the richness and Shannon's diversity index of the earthworm gut microbiota, but PMB altered its community structure and taxonomic composition. Moreover, PMB significantly affected Lysobacter, Aeromonas, and Sphingomonas in the soil microbiota, whereas Pseudomonas was significantly impacted the earthworm gut microbiota. Furthermore, active bacteria responded more significantly to PMB than the total microbial community. Bacterial genera such as Acinetobacter and Bacillus were highly correlated with differential expression of some genes, including up-regulated genes associated with folate biosynthesis, sulphur metabolism, and the IL-17 signalling pathway, and downregulated genes involved in vitamin digestion and absorption, salivary secretion, other types of O-glycan biosynthesis, and the NOD-like receptor signalling pathway. These results suggest that adaptation to PMB stress by earthworms involves changes in energy metabolism, their immune and digestive systems, as well as glycan biosynthesis. The study findings help elucidate the relationship between earthworms and their microbiota, while providing a reference for understanding the environmental risks of PMB.

Effect of toxicological interaction of chlorpyrifos, cypermethrin, and arsenic on soil dehydrogenase activity in the terrestrial environment

Soil is the most widespread area for the co-occurrence of two or more numbers of contaminants. Therefore, toxicity assessments based on contaminants mixture are urgently required to assess their combined impacts on soil enzymes. In the present study, the median effect plot and the combination index isobologram were studied to evaluate the dose-response curve for individual and interactive impacts of chlorpyrifos (Chl), cypermethrin (Cyp), and arsenic (As) on soil dehydrogenase, a potential marker of soil health. Along with these methods, a two-way ANOVA was also tested and the results showed significant changes with respect to different treatments. The results also showed that the Dm value increases in the order of As<Cyp<Chl. Another side, the m values for Cyp and As were negative, while positive for Chl. The day-dependent variation analysis revealed maximum inhibition in dehydrogenase activity on days 20 and 30 after treatment. The results also revealed that binary mixtures Chl + Cyp- and Chl + As- induced synergistic and antagonistic impacts over dehydrogenase enzyme at 0.1 fa level on different treatment days, whereas, applied binary and ternary combinations exhibited antagonistic effects at >0.25 fa level. However, Chl + Cyp unveiled a synergistic impact over soil dehydrogenase on day 30^th. The overall impact of applied chemicals on dehydrogenase activity was contributed by bioavailability and the nature of toxicological interactions between them. This study would be one of the exclusive studies for the agricultural sector to predict the potential risk associated with the co-existence of these or similar contaminants in the terrestrial environment.

Citric acid modified ultrasmall copper peroxide nanozyme for in situ remediation of environmental sulfonylurea herbicide contamination

Herbicide residues in the environment threaten high-quality agriculture and human health. Consequently, in situ remediation of herbicide contamination is vital. We synthesized a novel self-catalyzed nanozyme, ultrasmall (2-3 nm) copper peroxide nanodots modified by citric acid (CP@CA) for this purpose, which can break down into H₂O₂ and Cu²⁺ in water or soil. Ubiquitous glutathione reduces Cu²⁺ into Cu⁺, which promotes the decomposition of H₂O₂ into •OH through a Fenton-like reaction under mild acid conditions created by the presence of citric acid. The generated •OH efficiently degrade nicosulfuron in water and soil, and the maximum degradation efficiency could be achieved at 97.58% in water at 56 min. The possible degradation mechanisms of nicosulfuron were proposed through the 25 intermediates detected. The overall ecotoxicity of the nicosulfuron system was significantly reduced after CP@CA treatment. Furthermore, CP@CA had little impact on active components of soil bacterial community. Moreover, CP@CA nanozyme could effectively remove seven other sulfonylurea herbicides from the water. In this paper, a high-efficiency method for herbicide degradation was proposed, which provides a new reference for the in situ remediation of herbicide pollution.

Presence and distribution of triazine herbicides and their effects on microbial communities in the Laizhou Bay, Northern China

This study investigated the distribution of triazine herbicides in the Laizhou Bay, China and found that the total concentrations of triazine herbicides in the seawater and sediments were 111.15-234.85 ng/L and 0.902-4.661 μg/kg, respectively. Triazine herbicides especially ametryn, atrazine, and simazine were negatively correlated with prokaryote diversity in the seawater. While ametryn, desethylatrazine and desisopropylatrazine had positively significant effects on eukaryotes Dinophyceae, Bacillariophyta, and Cercozoa in the sediments. Moreover, the degree of fragmentation of eukaryotic networks increased dramatically with the increasing numbers of removed nodes, but prokaryotic networks did not change with the decrease of nodes. In addition, the stability analysis and neutral community models revealed that eukaryotes were more sensitive to triazine herbicides than prokaryotes. These results suggest that triazine herbicides might affect the structure and interactions of microbial communities. Therefore, more attentions should be paid to the ecological risk of triazine herbicides in marine ecosystems.

Effects of long-term exposure to the herbicide nicosulfuron on the bacterial community structure in a factory field

This study aims to investigate the effects of long-term nicosulfuron residue on an herbicide factory ecosystem. High-throughput sequencing was used to investigate the environmental microbial community structure and interactions. The results showed that the main contributor to the differences in the microbial community structure was the sample type, followed by oxygen content, pH and nicosulfuron residue concentration. Regardless of the presence or absence of nicosulfuron, soil, sludge, and sewage were dominated by groups of Bacteroidetes, Actinobacteria, and Proteobacteria. Long-term exposure to nicosulfuron increased alpha diversity of bacteria and archaea but significantly decreased the abundance of Bacteroidetes and Acidobateria compared to soils without nicosulfuron residue. A total of 81 possible nicosulfuron-degrading bacterial genera, e.g., Rhodococcus, Chryseobacterium, Thermomonas, Stenotrophomonas, and Bacillus, were isolated from the nicosulfuron factory environmental samples through culturomics. The co-occurrence network analysis indicated that the keystone taxa were Rhodococcus, Stenotrophomonas, Nitrospira, Terrimonas, and Nitrosomonadaceae_MND1. The strong ecological relationship between microorganisms with the same network module was related to anaerobic respiration, the carbon and nitrogen cycle, and the degradation of environmental contaminants. Synthetic community (SynCom), which provides an effective top-down approach for the critical degradation strains obtained, enhanced the degradation efficiency of nicosulfuron. The results indicated that Rhodococcus sp. was the key genus in the environment of long-term nicosulfuron exposure.

Biodegradation and Subsequent Toxicity Reduction of Co-contaminants Tribenuron Methyl and Metsulfuron Methyl by a Bacterial Consortium B2R

AllyMax is a widely used herbicide formulation in wheat-rice cropping areas of the world. The residues of its active ingredients, tribenuron methyl (TBM) and metsulfuron methyl (MET), persist in soil and water as co-contaminants, and cause serious threats to nontarget organisms. This study was performed to assess the potential of a bacterial consortium for the degradation and detoxification of TBM and MET individually and as co-contaminants. A bacterial consortium (B2R), comprising Bacillus cereus SU-1, Bacillus velezensis OS-2, and Rhodococcus rhodochrous AQ1, capable of degrading TBM and MET in liquid cultures was developed. Biodegradation of TBM and MET was optimized using the Taguchi design of experiment. Optimum degradation of both TBM and MET was obtained at pH 7 and 37 °C. Regarding media composition, optimum degradation of TBM and MET was obtained in minimal salt medium (MSM) supplemented with glucose, and MSM without glucose, respectively. The consortium simultaneously degraded TBM and MET (94.8 and 80.4%, respectively) in cultures containing the formulation AllyMax, where TBM and MET existed as co-contaminants at 2.5 mg/L each. Mass spectrometry analysis confirmed that during biodegradation, TBM and MET were metabolized into simpler compounds. Onion (Allium cepa) root inhibition and Comet assays revealed that the bacterial consortium B2R detoxified TBM and MET separately and as co-contaminants. The consortium B2R can potentially be used for the remediation of soil and water co-contaminated with TBM and MET.

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.

Switchable hydrophilic solvent-based dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography for the determination of four types of sulfonylurea herbicides in soils

In this study, switchable hydrophilic solvent-based dispersive liquid-liquid microextraction coupled with high-performance liquid chromatography was developed for the determination of four sulfonylurea herbicides in soils. For the first time, the sample pretreatment was achieved due to the similar acid-base status of sulfonylurea herbicides and switchable hydrophilic solvent. In the extraction step, sulfonylurea herbicides were extracted as anions and transferred to an alkaline solution with switchable hydrophilic solvent anions. In the concentration step, two types of anions were transformed to their molecular state after the aqueous solution was acidified. In addition, the dispersion and microextraction processes were completed efficiently with the simultaneous formation of analytes and extractants. The factors affecting the extraction performance were optimized. Under the optimized conditions, good linearity was observed for each herbicide with correlation coefficients ranging from 0.9952 to 0.9978. The limits of detection were in the range of 0.1-0.2 μg/g. Moreover, the relative recoveries of the sulfonylurea herbicides at spiking levels of 0.5, 1, and 1.5 μg/g in soil samples were between 75 and 111% (relative standard deviations: 0.4-11.4%). Therefore, the proposed method in this study could be successfully applied to the analysis of four types of sulfonylurea herbicides in soil samples.

Changes in soil microbial community and activity caused by application of dimethachlor and linuron

Soil microorganisms and their activities are essential for maintaining soil health and fertility. Microorganisms can be negatively affected by application of herbicides. Although effects of herbicides on microorganisms are widely studied, there is a lack of information for chloroacetamide herbicide dimethachlor. Thus, dimethachlor and well known linuron were applied to silty-loam luvisol and their effects on microorganisms were evaluated during112 days long laboratory assay. Dimethachlor and linuron were applied in doses 1.0 kg ha-1 and 0.8 kg ha-1 corresponding to 3.33 mg kg-1 and 2.66 mg kg-1 respectively. Also 100-fold doses were used for magnification of impacts. Linuron in 100-fold dose caused minor increase of respiration, temporal increase of soil microbial biomass, decrease of soil dehydrogenase activity, and altered microbial community. Dimethachlor in 100-fold dose significantly increased respiration; microbial biomass and decreased soil enzymatic activities. Microbial composition changed significantly, Proteobacteria abundance, particularly Pseudomonas and Achromobacter genera increased from 7 to 28th day. In-silico prediction of microbial gene expression by PICRUSt2 software revealed increased expression of genes related to xenobiotic degradation pathways. Evaluated characteristics of microbial community and activity were not affected by herbicides in recommended doses and the responsible use of both herbicides will not harm soil microbial community.