Stereoselective uptake and distribution of the chiral neonicotinoid insecticide, Paichongding, in Chinese pak choi (Brassica campestris ssp. chinenesis)

Effects of reduced graphene oxide nanomaterials on transformation of 14C-triclosan in soils

Increasing use and release of graphene nanomaterials and pharmaceutical and personal care products (PPCPs) in soil environment have polluted the environment and posed high ecological risks. However, little is understood about the interactive effects and mechanism of graphene on the behaviors of PPCPs in soil. In the present study, the effects of reduced graphene oxide nanomaterials (RGO) on the fate of triclosan in two typical soils (S1: silty loam; S2: silty clay loam) were investigated with 14C-triclosan, high-resolution mass spectrometry, scanning electron microscopy (SEM), X-ray photoelectron spectroscopy (XPS), density functional theory (DFT) calculations, and microbial community structure analysis. The results showed that RGO prolonged the half-life of triclosan by 23.6-51.3 %, but delayed the formation of transformed products such as methyl triclosan and dechlorinated dimer of triclosan in the two typical soils. Mineralization of triclosan to 14CO2 was inhibited by 48.2-79.3 % in 500 mg kg-1 RGO in comparison with that in the control, whereas the bound residue was 54.2-56.4 % greater than the control. RGO also reduced the relative abundances of triclosan-degrading bacteria (Pseudomonas and Sphingomonas) in soils. Compared to silty loam, RGO more effectively inhibited triclosan degradation in silty clay loam. Furthermore, the DFT calculations suggested a strong association of the adsorption of triclosan on RGO with the van der Waals forces and π-π interactions. These results revealed that RGO inhibited the transformation of 14C-triclosan in soil through strong adsorption and triclosan-degrading bacteria inhibition in soils. Therefore, the presence of RGO may potentially enhance persistence of triclosan in soil. Overall, our study provides valuable insights into the risk assessment of triclosan in the presence of GNs in soil environment.

Insights into the Enantiomeric Uptake, Translocation, and Distribution of Triazole Chiral Pesticide Mefentrifluconazole in Wheat (Triticum aestivum L.)

The uptake, translocation, and accumulation of mefentrifluconazole (MFZ), an innovative chiral triazole fungicide, in plants at the enantiomeric level are still unclear. Herein, we investigated the patterns and mechanisms of enantiomeric uptake, bioaccumulation, and translocation through several experiments. Rac-MFZ shows the strongest uptake and bioaccumulation capacity in wheat compared with its enantiomers, while S-(+)-MFZ has the highest translocation potential. Molecular docking provided evidence of the stronger translocation ability of S-(+)-MFZ than R-(-)-MFZ. Split-root experiments showed that MFZ and its enantiomers could undergo long-distance transport within the wheat. Active transport or facilitated and simple diffusion may be involved in the wheat uptake of MFZ. The limited acropetal translocation capability of MFZ may be attributed to the dominant uptake pathway of apoplastic. The concentrations of Rac-MFZ in different subcellular fractions varied greatly. In summary, this study provides novel insights for further understanding the behaviors of MFZ and its enantiomers in plants.

Unveiling the Contamination Patterns of Neonicotinoid Insecticides: Detection, Distribution, and Risk Assessment in Panax notoginseng across Plant Parts

This study analyzed neonicotinoid insecticides (NEOs) and metabolite (m-NEOs) residues in 136 Panax notoginseng samples via ultra-performance liquid chromatography-tandem mass spectrometry. Imidacloprid was the most detected NEO (88.24% of samples), ranging from 1.50 to 2850 μg/kg. To the best of our knowledge, some novel NEOs were detected in P. notoginseng for the first time. NEO clustering patterns varied among plant parts, with higher contamination in leaves and flowers. Fourteen NEO/m-NEOs, including cycloxaprid and acetamiprid, showed site-specific behavior, indicating the possibility of using multiple NEOs simultaneously during planting, resulting in formation of distinct metabolites in different plant parts. Transfer rates in decoction and infusion ranged from 10.06 to 32.33%, reducing residues postprocessing. Dietary risk assessment showed low hazard quotients (HQa: 7.05 × 10-7 to 2.09 × 10-2; HQc: 3.74 × 10-7 to 2.38 × 10-3), but risk-ranking scores indicated potential hazards with imidacloprid and acetamiprid in flowers and leaves. The findings are expected to promote safety assessment and distribution research of NEOs in plants.

Design, Synthesis, and Insecticidal Activity of Pyridino[1,2-a]pyrimidines Containing Indole Moeites at the 1-Position

Research on mesoionic structures in pesticide design has gained significant attention in recent years. However, the 1-position of pyridino[1,2-a]pyrimidine is usually designed with 2-chlorothiazole, 2-chloropyridine, or cyano moieties commonly found in neonicotinoid insecticides. In order to enrich the available pharmacophore library, here, we disclose a series of new pyridino[1,2-a]pyrimidine mesoionics bearing indole-containing substituents at the 1-position. Most of these target compounds are confirmed to have good insecticidal activity against aphids through bioevaluation. In addition, a three-dimensional structure-activity relationship model is established to allow access to optimal compound F45 with an LC50 value of 2.97 mg/L. This value is comparable to the property achieved by the positive control triflumezopyrim (LC50 = 2.94 mg/L). Proteomics and molecular docking analysis suggest that compound F45 has the potential to modulate the functioning of the aphid nervous system through its interaction with neuronal nicotinic acetylcholine receptors. This study expands the existing pharmacophore library for the future development of new mesoionic insecticides based on 1-position modifications of the pyridino[1,2-a]pyrimidine scaffold.

Computer-aided toxicity prediction and potential risk assessment of two novel neonicotinoids, paichongding and cycloxaprid, to hydrobionts

Paichongding (IPP) and cycloxaprid (CYC) have been effectively used as the alternative products of imidacloprid (IMI) against IMI-resistant insects and exhibit a great market potential. However, risk assessment of IPP and CYC for non-target organisms, especially ecological risk assessment for non-target aquatic organisms, is still lacking. Here, we predicted the toxicity and potential risks of IPP, CYC, and their transformation products (TPs) to hydrobionts. The results indicated that IPP and CYC could generate 428 and 113 TPs, respectively, via aerobic microbial transformation. Nearly half of the IPP TPs and nearly 41 % of the CYC TPs exhibited high or moderate toxicity to Daphnia or fish. Moreover, we found that IPP, CYC, and 80 TPs of them posed potential risks to aquatic ecosystems. Almost all harmful TPs contained a 6-chloropyridine ring structure, suggesting that this structure may be associated with the strong toxicity of these TPs to aquatic organisms, and these TPs (IPP-TP2 or CYC-TP2, IPP-TP197 or CYC-TP71, IPP-TP198 or CYC-TP72, and IPP-TP212 or CYC-TP80) may appear in aquatic environments as final products. The risks posed by these TPs to aquatic ecosystems require more attention. This study provides insights into the toxicity and ecological risks of IPP and CYC.

Reduced graphene oxide accelerates the dissipation of 14C-Triclosan in paddy soil via adsorption interactions

Reduced graphene oxide (RGO) is one of common carbon nanomaterials, which is widely used in various fields. Triclosan is an antimicrobial agent added in pharmaceuticals and personal care products. Extensive release of RGO and triclosan has posed potential risks to humans and the environment. The impact of RGO on the fate of triclosan in paddy soil is poorly known. ¹⁴C-Triclosan was employed in the present study to determine its distribution, degradation and mineralization in paddy soil mixed with RGO. Compared with the control, RGO (500 mg kg^-1) significantly inhibited the mineralization of ¹⁴C-triclosan, and reduced its extractability by 6.5%. The bound residues of triclosan in RGO-contaminated soil (100 and 500 mg kg^-1) were 2.9-13.3% greater than that of the control at 112 d. RGO also accelerated the dissipation of triclosan, and its degradation products in both treatments and controls were tentatively identified via ¹⁴C-labeling method and LC-Q-TOF-MS analysis. The concentrations of the major metabolites (methyl-triclosan and dechlorinated dimer) were inversely related with the concentrations of RGO. RGO at 50 mg kg^-1 or lower had a negligible effect on the degradation of triclosan in paddy soil. Triclosan was strongly adsorbed onto RGO-contaminated soil, which may play a vital role in the fate of triclosan in RGO-contaminated paddy soil. Interestingly, RGO had little effect on triclosan-degrading bacteria via soil microbial community analysis. This study helps understand the effects of RGO on the transformation of triclosan in paddy soil, which is of significance to evaluate the environmental risk of triclosan in RGO-contaminated soil.

Distinct uptake and accumulation profiles of triclosan in youdonger (Brassica campestris subsp. Chinensis var. communis) under two planting systems: Evidence from 14C tracing techniques

Triclosan is a widely used biocide against microorganisms and is ubiquitously distributed in the environment. Triclosan can be accumulated into plants from soil and hydroponic media. However, little information is currently available on the comparative fate of triclosan in plants under soil and hydroponics cultivation conditions and factors governing uptake. Therefore, this study was designed to comparatively elucidate the uptake mechanism of ¹⁴C-triclosan in youdonger (Brassica campestris subsp. Chinensis var. communis) grown under different soils and hydroponics and clarify dominant uptake factors. Results showed that 77.2% of ¹⁴C were accumulated in youdonger grown in a hydroponic system, while only 1.24%-2.33% were accumulated in the two soil-planting systems. In addition, the bioconcentration factor (BCF) of ¹⁴C-triclosan in soil-plant systems was approximately 400-fold smaller than that in the hydroponics. In the soil-planting system, a strong linear correlation was found between concentrations of triclosan in soil pore water and youdonger plant (R² > 0.85, p < 0.01) at different incubation times. Therefore, triclosan in pore water might be a good indicator to estimate its accumulation in plants and is significantly affected by soil pH, clay, and organic matter contents. The estimated average dietary intakes of triclosan for youdonger grown in hydroponic and soil-planting systems were estimated to be 1.31 ng day^-1 kg^-1 and 0.05-0.12 ng day^-1 kg^-1, respectively, much lower than the acceptable dietary intakes of triclosan (83 μg day^-1 kg^-1), indicating no significant human health risks from youdonger consumption. This study provided insights into uptake routes of triclosan into youdonger plants from both soil and hydroponic systems, bioavailability of triclosan in different soils, and further assessment of human exposure to triclosan from youdonger.

Biochar decreased enantioselective uptake of chiral pesticide metalaxyl by lettuce and shifted bacterial community in agricultural soil

A 35-day microcosmic experiment was conducted with lettuce (Lactuca sativa L.) and two metalaxyl (MET) enantiomers (R-MET and S-MET) to understand the roles of biochar in the enantioselective fate of chiral pesticides in soil-plant ecosystems. Wood waste-derived biochar (WBC) amendment effectively decreased the shoot concentrations of R-MET/S-MET and their metabolites R-MET/S-MET acid by 57.7-86.3% and 13.3-32.5%, respectively. The reduced uptake was mainly attributed to the decreased bioavailability of R-MET and S-MET. A lower fraction of R-MET was accumulated by the lettuce in the WBC-amended soils relative to the control, suggesting a decrease in the enantioselective uptake of the chiral pesticide MET in the presence of biochar. Regardless of the WBC amendment, no enantiomerization of MET or MET acid occurred. The application of WBC stimulated soil bacterial diversity, shifted the bacterial community, and enhanced the abundance of pesticide degrading bacteria (e.g., Luteimonas, Methylophilus, and Hydrogenophaga), which were responsible for the enantioselective degradation of MET in the soil. This work expands our understanding of the enantioselective fate of chiral pesticides in the biochar-amended soil ecosystems. These findings can be used to develop biochar-based technologies to remediate soils contaminated with these chiral pesticides to ensure food safety.

Uptake, subcellular distribution and metabolism of 14C-caffeine in leafy vegetables from water

Irrigation with treated wastewater could lead to the accumulation of caffeine in agricultural fresh. Caffeine is one of the most frequently detected compounds in treated wastewater; however, little is known about its subcellular distribution and metabolism in vegetables. This study reported the uptake, subcellular distribution, and metabolism of ¹⁴C-caffeine in Chinese flowering cabbage and water spinach. The results showed that 98% of caffeine lost from solution after 768 h of cultivation. Caffeine was taken up by vegetables and most ¹⁴C-activity was accumulated in the bottom leaves. At the subcellular level, ¹⁴C-activity was mainly distributed in the organelles in root and stem cells, while in the leafy cells it was dominant in the solution. The metabolism of caffeine was investigated using LC-QTOF-MS. Caffeine underwent demethylation forming xanthine and theobromine, and mineralization to release CO₂. Approximately 40.2% of the initially applied caffeine was accumulated in Chinese flowering cabbage as the parent compound (28.3%) and metabolites (11.9%), and 50.9% of the added caffeine was mineralized to CO₂ after 768 h of exposure. The knowledge obtained herein is key to evaluating potential risks of caffeine present in treated wastewater, and the quality and safety of agricultural fresh produced by irrigation with treated wastewater.

Enantioselective fate of dinotefuran from tomato cultivation to home canning for refining dietary exposure

Understanding the enantioselective fate of chiral neonicotinoid dinotefuran is of vital importance for accurate dietary exposure assessment and food safety regulation. The study investigated the enantioselectivity in respect to dissipation, metabolism, and removal, of dinotefuran from tomato cultivation to tomato paste processing. The chiral analytical method of dinotefuran, UF and DN was developed in tomato using ultrahigh performance supercritical fluid chromatography/tandem mass spectrometry. Under greenhouse cultivation R-dinotefuran preferentially degraded (T_1/2, 9.1-12.6 days), resulting in relative enrichment of S-dinotefuran (T_1/2, 10.3-13.3 days) by foliage and root uptake pathways. (-)-UF generated at a faster rate and was more persistent than its antipode in tomato by foliage treatment. Furthermore, changes in the enantiomeric removal and enantioselectivity orientation of dinotefuran and metabolites were evaluated during home canning of tomato paste, including washing, peeling, homogenization, simmering, and sterilization. Peeling played the key role in reducing S-dinotefuran by 67.3% and R-dinotefuran by 69.9% with processing factor of 0.313 and 0.287, respectively. Simmering was the most effective way to remove UF enantiomers (Pf, 0.336-0.421) by elevated temperature. This study sheds light on the chiral profiles of the fate of dinotefuran from cultivation to processing, providing scientific importance to protect human health from hazardous effects.

Uptake, translocation and accumulation of 14C-triclosan in soil-peanut plant system

Triclosan is an antimicrobial agent that is ubiquitously present in water, biosolids and soil. Current agricultural practices, such as irrigation with treated wastewater and soil amendment with biosolids, often cause further triclosan contamination in agricultural fields. However, the fate and crop uptake of triclosan in agrofood systems and related human exposure are still not fully understood. In the present study, ¹⁴C-triclosan was used to trace the fate and distribution of triclosan in a soil-peanut plant system. ¹⁴C-triclosan in the system maintained an excellent mass balance ranging from 92.5% to 102.7%. ¹⁴C-triclosan uptake from soil to peanut plants at the harvest stage (120 d) was only 1.02 ± 0.17% of the applied ¹⁴C. The bioconcentration factors in different tissues followed the order of roots > stems > leaves > fruits. The concentration of ¹⁴C-triclosan in peanut fruits was 0.76-0.84 μg g^-1. ¹⁴C-triclosan was more easily accumulated in peanut kernels (69.2 ± 6.30%) than peanut hulls (27.5 ± 5.77%) and skin (3.28 ± 0.53%). The estimated daily intake (EDI) values suggested that peanut consumption represented a minimal risk to human health. The results of this study help to develop a better understanding of the fate of triclosan in the soil-peanut plant system and assess its environmental and human health risks.

The role of stereochemistry of antibiotic agents in the development of antibiotic resistance in the environment

Antibiotic resistance (ABR) is now recognised as a serious global health and economic threat that is most efficiently managed via a 'one health' approach incorporating environmental risk assessment. Although the environmental dimension of ABR has been largely overlooked, recent studies have underlined the importance of non-clinical settings in the emergence and spread of resistant strains. Despite this, several research gaps remain in regard to the development of a robust and fit-for-purpose environmental risk assessment for ABR drivers such as antibiotics (ABs). Here we explore the role the environment plays in the dissemination of ABR within the context of stereochemistry and its particular form, enantiomerism. Taking chloramphenicol as a proof of principle, we argue that stereoisomerism of ABs impacts on biological properties and the mechanisms of resistance and we discuss more broadly the importance of stereochemistry (enantiomerism in particular) with respect to antimicrobial potency and range of action.

Eukaryal composition and diversity in anaerobic soils influenced by the novel chiral insecticide Paichongding

Paichongding (IPP) is a neonicotinoid chiral insecticide with independent intellectual property in China. IPP application can increase crop yield, and also lead to insecticide residue and pollution in soils, which will affect microbial population and community composition in soils. In this study, four different types of soils were employed to inquire into the impact of IPP on eukaryal community and species-group through pyrosequencing of 18S rRNA gene amplicons. Fungal population differed in different soils at different days after IPP treatment (DAT). Eukaryal community species in CK (control check) groups were more rich than that with Paichongding sprayed at 5 DAT, while eukaryal species in CK soils at 60 DAT was relatively slight. Shannon's H' analysis indicated fungal species in CK soils were also higher at 5 DAT and relative lower at 60 DAT, except in soil C. There are also differences in the phyla and genus levels of the eukaryotic communities in the soil. After IPP application, the relative abundance of Nectriaceae increased 3-4 times in soil C. In soil F, Phaeosphaeriaceae increased to 57.3% at 5 DAT. The genus of Guehomyces, Aspergillus and Alternaria increased from 3.1 to 9.7, 1.1 to 4.6, 1.5 to 6.7% in soil H, respectively.

Enantioselective reductive transformation of climbazole: A concept towards quantitative biodegradation assessment in anaerobic biological treatment processes

An efficient chiral method-based using liquid chromatography-high resolution-mass spectrometry analytical method has been validated for the determination of climbazole (CBZ) enantiomers in wastewater and sludge with quantification limits below the 1 ng/L and 2 ng/g range, respectively. On the basis of this newly developed analytical method, the stereochemistry of CBZ was investigated over time in sludge biotic and sterile batch experiments under anoxic dark and light conditions and during wastewater biological treatment by subsurface flow constructed wetlands. CBZ stereoselective degradation was exclusively observed under biotic conditions, confirming the specificity of enantiomeric fraction variations to biodegradation processes. Abiotic CBZ enantiomerization was insignificant at circumneutral pH and CBZ was always biotransformed into CBZ-alcohol due to the specific and enantioselective reduction of the ketone function of CBZ into a secondary alcohol function. This transformation was almost quantitative and biodegradation gave good first order kinetic fit for both enantiomers. The possibility to apply the Rayleigh equation to enantioselective CBZ biodegradation processes was investigated. The results of enantiomeric enrichment allowed for a quantitative assessment of in situ biodegradation processes due to a good fit (R² > 0.96) of the anoxic/anaerobic CBZ biodegradation to the Rayleigh dependency in all the biotic microcosms and was also applied in subsurface flow constructed wetlands. This work extended the concept of applying the Rayleigh equation towards quantitative biodegradation assessment of organic contaminants to enantioselective processes operating under anoxic/anaerobic conditions.

Bioaccumulation and bound-residue formation of 14C-decabromodiphenyl ether in an earthworm-soil system

Decabromodiphenyl ether (DecaBDE) is one of the most frequently detected flame retardants in terrestrial environments. However, the fate of DecaBDE and its transport in an earthworm-soil system with and without a DecaBDE-degrading strain have rarely been evaluated. In this study, ¹⁴C-DecaBDE was self-synthesized, and a DBDE-degrading strain, Rhodococcus erythropolis, was used in an earthworm-soil system. DecaBDE showed limited degradation and mineralization after 35days of all treatments. The bound-residue (BR) formation in soil was <2.5% in the system containing earthworms, which was significantly higher (p<0.05) than that observed in the absence of earthworms (<0.45%). DecaBDE could be adsorbed by the earthworms with a BSAF of ≤0.31. The distribution of ¹⁴C-DecaBDE concentrations in the earthworm roughly followed the pattern of crop gizzard>digestive system>head>tail>body wall, suggesting that DecaBDE was mainly uptaken through ingestion. Up to 31% of the ¹⁴C-DecaBDE in the earthworms was not extractable, revealing that the total concentration of accumulated ¹⁴C-DecaBDE was underestimated. The results also showed that the presence of DecaBDE-degrading bacteria did not significantly affect the fate of DecaBDE and its accumulation in earthworms. The study indicates that the conventional assessment of the bioaccumulation and ecological effects of DecaBDE, which is based only on extractable concentrations, may underestimate the risks.

Uptake and subcellular distribution of triclosan in typical hydrophytes under hydroponic conditions

The increasing discharge of pharmaceuticals and personal care products (PPCPs) into the environment has generated serious public concern. The recent awareness of the environmental impact of this emerging class of pollutants and their potential adverse effects on human health have been documented in many reports. However, information regarding uptake and intracellular distribution of PPCPs in hydrophytes under hydroponic conditions, and potential human exposure is very limited. A laboratory experiment was conducted using ¹⁴C-labeled triclosan (TCS) to investigate uptake and distribution of TCS in six aquatic plants (water spinach, purple perilla, cress, penny grass, cane shoot, and rice), and the subcellular distribution of ¹⁴C-TCS was determined in these plants. The results showed that the uptake and removal rate of TCS from nutrient solution by hydrophytes followed the order of cress (96%) > water spinach (94%) > penny grass (87%) > cane shoot (84%) > purple perilla (78%) > rice (63%) at the end of incubation period (192 h). The range of ¹⁴C-TCS content in the roots was 94.3%-99.0% of the added ¹⁴C-TCS, and the concentrations in roots were 2-3 orders of magnitude greater than those in shoots. Furthermore, the subcellular fraction-concentration factor (3.6 × 10²-2.6 × 10³ mL g^-1), concentration (0.58-4.47 μg g^-1), and percentage (30%-61%) of ¹⁴C-TCS in organelles were found predominantly greater than those in cell walls and/or cytoplasm. These results indicate that for these plants, the roots are the primary storage for TCS, and within plant cells organelles are the major domains for TCS accumulation. These findings provide a better understanding of translocation and accumulation of TCS in aquatic plants at the cellular level, which is valuable for environmental and human health assessments of TCS.

Isolation of the Novel Chiral Insecticide Paichongding (IPP) Degrading Strains and Biodegradation Pathways of RR/SS-IPP and SR/RS-IPP in an Aqueous System

Chiral insecticide paichongding (IPP) is a member of cis-nitromethylene neonicotinoid insecticides used in China. IPP was the promising replacement for imidacloprid as a result of its higher activity against imidacloprid-resistant insects. Two pairs of enantiomers, RR/SS-IPP and SR/RS-IPP, were separated by preparative high-performance liquid chromatography and employed in an aqueous system to investigate their biodegradation process. In this study, the strains G1-13/G1-14 and G2-19 with effective IPP degrading capability were isolated from agricultural soils. G1-14 was mutated from G1-13 by ultraviolet light exposure. Sequence alignment of 16S rRNA proved that these three strains belonged to the genus of Sphingobacterium. The degradation rate of RR/SS-IPP by Sphingobacterium sp. G1-13 and G1-14 reached 13 and 30% within 6 and 4 days, respectively. The degradation rate of SR/RS-IPP by Sphingobacterium sp. G2-19 could reach 35% within 5 days. Degradation intermediates (I1-I6) of enantiomers were detected, and two possible biodegradation pathways were proposed on the basis of the identification of metabolites.

Stereoselective Degradation and Transformation Products of a Novel Chiral Insecticide, Paichongding, in Flooded Paddy Soil

Paichongding is a chiral neonicotinoid insecticide currently marketed as racemate against sucking and biting insects. Under anaerobic condition, all paichongding stereoisomers underwent appreciable degradation in soil during 100 days of incubation, with estimated t_1/2 values between 0.18 and 3.15 days. Diastereoselectivity in paichongding degradation was observed, with enantiomers (5S,7R)- and (5R,7S)-paichongding being more preferentially degraded in soils than enantiomers (5R,7R)- and (5S,7S)-paichongding. The half-lives of (5R,7R)- and (5S,7S)-paichongding were 3.05 and 3.15 days, respectively, as compared to 0.18 day for (5R,7S)- and (5S,7R)-paichongding. A total of nine intermediates were identified, of which depropylated paichongding was the predominant metabolite and appeared to be stable and recalcitrant to further degradation. Paichongding is degraded via denitration, depropylation, nitrosylation, demethylation, hydroxylation, and enol-keto tautomerism, producing chiral and biologically active products. These findings could have implications for environmental risk and food safety evaluations.

Effects of the novel cis-nitromethylene neonicotinoid insecticide Paichongding on enzyme activities and microorganisms in yellow loam and Huangshi soils

Soil enzyme activity and microbial population play important roles in maintaining soil fertility and ensure crop yield. Paichongding (IPP) is a novel cis-nitromethylene neonicotinoid insecticide, which was recently developed in China. In this study, in order to better understand IPP ecological toxicity, the impact of IPP on soil enzyme activity and microbial population in soils was investigated. The results showed that, urease activity was inhibited by IPP before 75 days incubation, after that this inhibiting effect gradually weakened. IPP had different stimulating effects on the activities of dehydrogenase, protease, and catalase. They were consistently stimulated from the initial time in soils. The results of microbial population indicated that the number of bacteria increased after IPP application compared with the control, fungal number increased before 45 days incubation and then decreased. While actinomycete number decreased during degradation period. DT50 (half-life value), k (degradation rate constant) of IPP in S1 (yellow loam soil), and S2 (Huangshi soil) were found 90 days and 173 days, 0.0077 day(-1), and 0.0040 day(-1), respectively.

Impact of the novel neonicotinoid insecticide Paichongding on bacterial communities in yellow loam and Huangshi soils

Insecticides are widely sprayed in modern agriculture for ensuring the crop yield, which could also lead to contamination and insecticide residue in soils. Paichongding (IPP) is a novel neonicotinoid insecticide and was developed recently in China. Soil bacterial community, diversity, and community composition vary widely depending on environmental factors. As for now, little is known about bacterial species thriving, bacterial community diversity, and structure in IPP-spraying soils. In present study, IPP degradation in yellow loam and Huangshi soils was investigated, and bacterial communities and diversity were examined in soil without IPP spray and with IPP spray through pyrosequencing of 16S ribosomal RNA (rRNA) gene amplicons. The degradation ratio of IPP at 60 days after treatment (DAT) reached 51.22 and 34.01 % in yellow loam and Huangshi soil, respectively. A higher richness of operational taxonomic units (OTUs) was found in yellow loam soil (867 OTUs) and Huangshi soil (762 OTUs) without IPP spray while OUTs were relatively low in IPP-spraying soils. The community composition also differed both in phyla and genus level between these two environmental conditions. Proteobacteria, Firmicutes, Planctomycetes, Chloroflexi, Armatimonadetes, and Chlorobi were stimulated to increase after IPP application, while IPP inhibited the phyla of Bacteroidetes, Actinobacteria, and Acidobacteria.

Enantioselective sorption of the chiral fungicide metalaxyl on soil from non-racemic aqueous solutions: Environmental implications

Mechanisms governing the enantioselectivity of the processes that determine the behavior of chiral pollutants in the environment need to be better understood. Understanding these mechanisms should help improve predictions of the hazards and risks chiral compounds can pose to people and the environment. We report the results of batch sorption experiments indicating that the sorption of the chiral fungicide metalaxyl on soil from non-racemic initial solutions was enantioselective. While from a racemic initial solution the two enantiomers of metalaxyl were sorbed on the soil to the same extent, increasing the fraction of R-enantiomer in the initial solution led to enhanced sorption of this enantiomer and to reduced sorption of the S-enantiomer. Considering the shape of the sorption isotherms (S-type) and the sorption behavior of model sorbents, we attributed this effect to molecular interactions between metalaxyl enantiomer species at the sorbed state, where R-R metalaxyl interactions appeared to be more favorable than R-S metalaxyl interactions. We discuss important environmental implications of the proposed mechanism, such as those related to the fact that the biological degradation of metalaxyl is known to be an enantioselective process that can yield non-racemic residues in soils shortly after application of the fungicide as a racemic mixture.

Stereoselective fate kinetics of chiral neonicotinoid insecticide paichongding in aerobic soils

Man-made chemicals such as pesticides, when released into the soil environment, are transformed into extractable residue (ER), bound residue (BR), or mineralized. These processes all play a pivotal role in the risk assessment for the use of man-made chemicals. In this study, BR, ER, and mineralization of a novel chiral pesticide, paichongding (IPP), 1-((6-chloropyridin-3-yl)methyl)-7-methyl-8-nitro-5-propoxy-1,2,3,5,6,7-hexahydro-imidazo[1,2-a]pyridine, were investigated in different soils under aerobic conditions. Significant specificity was observed for diastereoisomers of IPP in the formation of BR or mineralization in neutral and alkaline soils. In contrast, no significant difference was found between enantiomers. The overall mineralization was less than 8% of the applied radioactivity and was related to soil pH. Our findings suggest that the environmental fate of chiral pesticides may be influenced by many factors such as soil properties (e.g. pH). More comprehensive and individualized risk assessments should be carried out for individual stereoisomers of a chiral product.

Degradation of chloroacetanilide herbicides and bacterial community composition in lab-scale wetlands

Degradation of chloroacetanilide herbicides rac-metolachlor, acetochlor, and alachlor, as well as associated bacterial populations, were evaluated in vertical upflow wetland columns using a combination of hydrochemical and herbicide analyses, and DNA-based approaches. Mass dissipation of chloroacetanilides, continuously supplied at 1.8-1.9 μM for 112 days, mainly occurred in the rhizosphere zone under nitrate and sulphate-reducing conditions, and averaged 61±14%, 52±12% and 29±19% for acetochlor, alachlor and rac-metolachlor, respectively. Metolachlor enantiomer fractions of 0.494±0.009 in the oxic zone and 0.480±0.005 in the rhizosphere zone indicated preferential biodegradation of the S-enantiomer. Chloroacetanilide ethane sulfonic acid and oxanilic acid degradates were detected at low concentrations only (0.5 nM), suggesting extensive degradation and the operation of yet unknown pathways for chloroacetanilide degradation. Hydrochemical parameters and oxygen concentration were major drivers of bacterial composition, whereas exposure to chloroacetanilides had no detectable impact. Taken together, the results underline the importance of anaerobic degradation of chloroacetanilides in wetlands, and highlight the potential of complementary chemical and biological approaches to characterise processes involved in the environmental dissipation of chloroacetanilides.

Microbial Degradation Mechanism and Pathway of the Novel Insecticide Paichongding by a Newly Isolated Sphingobacterium sp. P1-3 from Soil

Using 1-((6-chloropydidin-3-yl)methyl)-7-methyl-8-nitro-5propoxy-1,2,3,5,6,7-hexahydroimidazo[1,2-α-]-pyridine (IPP) as the sole carbon source, we isolated a strain with a higher activity of IPP-degrading bacterium Sphingobacterium sp. P1-3 from soil. At 30 °C, pH 7.0 ,and 10 mg L(-1) IPP content, the degradation rate of IPP by Sphingobacterium sp. P1-3 could reach 57.75 and 62.47% in 20 and 30 days, respectively. The value of DT50 of IPP was 27 d at the level of 30 mg L(-1) IPP, while DT50 in the blank test was 151 d. During the IPP biodegradation process, five intermediates (M1-M5) were monitored and identified. On the basis of the identified metabolites and their biodegradation courses, a possible biodegradation pathway was proposed. IPP biodegradation mainly occurred on the tetrahydropyridine ring. IPP was transformed to five different metabolites by strain P1-3 through the oxidation and elimination of methyl, propyl, and nitro groups. Moreover, a new pathway involving M2 (1-((6-chloropydidin-3-yl)methyl)-7-methyl-8-hydroxy-5-propoxy-1,2,3,5,6,7-hexahydroimidazo [1,2-α-]-pyridine), M3 (1-((6-chloropydidin-3-yl)methyl)-7-methyl-5-carbonyl-1,2,3,5,6,7-hexahydroimidazo[1,2-α-]-pyridine), and M5 (8-amino-1,2,3,5,6,7-hexahydroimidazo[1,2-α-]-pyridine) was first monitored and identified.