Release of tetrabromobisphenol A (TBBPA)-derived non-extractable residues in oxic soil and the effects of the TBBPA-degrading bacterium Ochrobactrum sp. strain T

Maize (Zea mays L.) Plants Alter the Fate and Accumulate Nonextractable Residues of Sulfamethoxazole in Farmland Soil

The fate of sulfonamide antibiotics in farmlands is crucial for food and ecological safety, yet it remains unclear. We used [phenyl-U-14C]-labeled sulfamethoxazole (14C-SMX) to quantitatively investigate the fate of SMX in a soil-maize system for 60 days, based on a six-pool fate model. Formation of nonextractable residues (NERs) was the predominant fate for SMX in unplanted soil, accompanied by minor mineralization. Notably, maize plants significantly increased SMX dissipation (kinetic constant kd = 0.30 day-1 vs 0.17 day-1), while substantially reducing the NER formation (92% vs 58% of initially applied SMX) and accumulating SMX (40%, mostly bound to roots). Significant NERs (maximal 29-42%) were formed via physicochemical entrapment (determined using silylation), which could partially be released and taken up by maize plants. The NERs consisted of a considerable amount of SMX formed via entrapment (1-8%) and alkali-hydrolyzable covalent bonds (2-12%, possibly amide linkage). Six and 10 transformation products were quantified in soil extracts and NERs, respectively, including products of hydroxyl substitution, deamination, and N-acylation, among which N-lactylated SMX was found for the first time. Our findings reveal the composition and instability of SMX-derived NERs in the soil-plant system and underscore the need to study the long-term impacts of reversible NERs.

Insights into the influence of polystyrene microplastics on the bio-degradation behavior of tetrabromobisphenol A in soil

Soil contamination by emerging pollutants tetrabromobisphenol A (TBBPA) and microplastics has become a global environmental issue in recent years. However, little is known about the effect of microplastics on degradation of TBBPA in soil, especially aged microplastics. In this study, the effect of aged polystyrene (PS) microplastics on the degradation of TBBPA in soil and the mechanisms were investigated. The results suggested that the aged microplastics exhibited a stronger inhibitory effect on the degradation of TBBPA in soil than the pristine microplastics, and the degradation efficiency of TBBPA decreased by 21.57% at the aged microplastic content of 1%. This might be related to the higher TBBPA adsorption capacity of aged microplastics compared to pristine microplastics. Aged microplastics strongly altered TBBPA-contaminated soil properties, reduced oxidoreductase activity and affected microbial community composition. The decrease in soil oxidoreductase activity and relative abundance of functional microorganisms (e.g., Bacillus, Pseudarthrobacter and Sphingomonas) caused by aged microplastics interfered with metabolic pathways of TBBPA. This study indicated the importance the risk assessment and soil remediation for TBBPA-contaminated soil with aged microplastics.

Composition, Release, and Transformation of Earthworm Tissue-Bound Residues of Tetrabromobisphenol A in Soil

Earthworms accumulate organic pollutants to form earthworm tissue-bound residues (EBRs); however, the composition and fate of EBRs in soil remain largely unknown. Here, we investigated the fate of tetrabromobisphenol A (TBBPA)-derived EBRs in soil for 250 days using a 14C-radioactive isotope tracer and the geophagous earthworm Metaphire guillelmi. The EBRs of TBBPA in soil were rapidly transformed into nonextractable residues (NERs), mainly in the form of sequestered and ester-linked residues. After 250 days of incubation, 4.9% of the initially applied EBRs were mineralized and 69.3% were released to extractable residues containing TBBPA and its transformation products (TPs, generated mainly via debromination, O-methylation, and skeletal cleavage). Soil microbial activity and autolytic enzymes of earthworms jointly contributed to the release process. In their full-life period, the earthworms overall retained 24.1% TBBPA and its TPs in soil and thus prolonged the persistence of these pollutants. Our study explored, for the first time, the composition and fate of organic pollutant-derived EBRs in soil and indicated that the decomposition of earthworms may release pollutants and cause potential environmental risks of concern, which should be included in both environmental risk assessment and soil remediation using earthworms.

Fate of bisphenol A (BPA) in a flooded soil-rice system

In this study, 14C-tracers were used to investigate the fate of BPA in flooded soil with or without rice plants during a complete growing period. In flooded soil, the dissipation of BPA (half-life 14.8 d) was accompanied by its mineralization (8.4% of the initially applied radioactivity) and the formation of non-extractable residues (NERs) in amounts (79.5%) similar to that formed under oxic conditions. The growth of rice significantly accelerated the dissipation of BPA in flooded soil, resulting in a reduction in both the half-life (5.6 d) and the amount of NERs (35.8%). Two non-polar metabolites were detected both in unplanted and in rice-planted soil. At rice harvest, 57.1% of the radioactivity had accumulated in rice plants, mainly as NERs (54.2%) rather than as extractable radioactivity (2.7%), and mainly in roots (34.5 ± 1.4%), stems (9.4 ± 1.1%), and leaves (8.8 ± 0.6%), with trace amounts in seeds (3.6 ± 0.3%) and seed shells (0.7 ± 0.05%). Our study thus demonstrates that the oxic-anoxic interface stimulates the dissipation of BPA in flooded soil. The link between the releasing of NERs in flooded soil and the uptake of BPA metabolites by rice should be considered in environmental risk assessments of agroecosystems.

Nonenantioselective environmental behavior of a chiral antiviral pesticide dufulin in aerobic soils

Dufulin is a promising chiral antiviral agent, but little is known about its fate in soils. In this study, the fate of dufulin enantiomers in aerobic soils was investigated using radioisotope tracing techniques. The result of the four-compartment model showed no significant differences in dissipation, generation of bound residues (BR) and mineralization between S-dufulin and R-dufulin during incubation. Dufulin dissipated most quickly in cinnamon soils, followed by fluvo-aquic and black soils and the half-lives of dufulin in these soils obtained by the modified model were 4.92-5.23, 32.39-33.32 and 60.80-61.34 d, respectively. After 120 d incubation, the percentage of radioactivity of BR increased to 18.2-38.4 % in the three soils. Dufulin formed most bound residues in the black soil, least in the cinnamon soil, and BRs rapidly formed in the cinnamon soil during the early culture period. In these three soils, the cumulative mineralization of ¹⁴CO₂ ranged from 25.0 to 26.7 %, 42.1 to 43.4 % and 33.8 to 34.4 %, respectively, which indicated that the environmental fate of dufulin was primarily influenced by soil characteristics. The study of microbial community structure revealed that the phyla Ascomycota, Proteobacteria and genus Mortierella might be related to the degradation of dufulin. These findings provide a reference for assessing the environmental impact and ecological safety of dufulin application.

Fate characteristics of the chiral pesticide dufulin in flooded anaerobic soils and its interaction with soil microorganisms

Dufulin (DFL), a plant antiviral agent synthesized in China, has been widely used to control viral diseases in rice, tobacco, tomato, and other crops. However, its fate in flooded anaerobic soils, which is essential for environmental risk assessment, remains unknown. Using the ¹⁴C tracer technique, the fate of ¹⁴C-labeled DFL isomers in flooded anaerobic soils was systematically investigated in this study. Over the 100-day incubation, a small part of ¹⁴C-DFL enantiomer was mineralized to ¹⁴CO₂ (< 10.44 %) or entered the surface water phase (< 6.69 %), with most of the ¹⁴C (> 80.40 %) remaining in the subsoil. The residues in all tested soils were gradually converted from extractable residues (ERs) to nonextractable residues (NERs). At the end of incubation, the fraction of ¹⁴C-NERs reached 5.38-23.77 %. The half-life (t_1/2) of the DFL parent in soil is relatively long under submerged anaerobic conditions, especially in Fluvo-aquic soil, up to 277.26-315.07 days, which exceeds the risk threshold recommended by the Stockholm Convention (< 180 days). Soil type and microbial activity influenced the fate of DFL in flooded soils and microbial analysis showed that 2.0 mg kg^-1 DFL had no obvious impact on soil bacterial richness and function. Pseudomonas spp. was estimated to be a potentially efficient degrading genus for DFL. No enantioselective behaviors were detected in this study. This research provides a theoretical basis for evaluating the environmental impact and ecological safety of DFL application.

Environmental fate and metabolism of the systemic triazolinthione fungicide prothioconazole in different aerobic soils

As a best-selling triazolinthione fungicide, prothioconazole (PTZ) has been widely used worldwide and has aroused concern about its environmental effect. This study used phenyl-UL-¹⁴C-labeled PTZ and an improved fate model to investigate the fate and metabolism of this fungicide in aerobic soil. During 120 d of incubation, PTZ rapidly transformed into metabolites and bound residues, with a half-life (DT₅₀) of less than 1 d. After 120 d, approximately 45-55% of PTZ formed bound residues, and the extractable metabolite residues were gradually degraded over time. Approximately 19%, 44% and 27% of phenyl-UL-¹⁴C-PTZ was mineralized in red soil, fluvo-aquic soil and cinnamon soil, respectively, but only approximately 3% was mineralized in black soil. Five metabolites were identified and confirmed, and a possible metabolic pathway for phenyl-UL-¹⁴C-PTZ in soil was proposed. Based on the correlation analysis between soil properties and model rate constants, soil properties exerted important effects on PTZ transformation. These results will provide basic data for environmental risk assessments and removal of the PTZ pollutant and suggest that the soil type should be considered in the selection and application of pesticides.

Insights into the Fate of the Novel Pesticide Vanisulfane from Animal Manure in Plant-Soil Systems: Assisted by Carbon-14 Labeling

Pesticide use can result in plant residues, which can be ingested by livestock consuming plant-derived feed and appear in manure. When this manure is applied as a fertilizer, pesticides can contaminate plant-soil systems. Few studies have focused on pesticide infiltration from applying pesticide-contaminated manure to land. In this study, the fate of pesticide vanisulfane from chicken manure was studied in radish-soil and cabbage-soil systems assisted by carbon-14 labeling. Vanisulfane and its metabolites mostly appeared as bound residues (BRs) after introduction, and BR release was found at 35 d. Notably, manure contaminated with vanisulfane and its metabolites exhibited higher plant accumulation and phytotoxicity than manure contaminated with only the parent. Four metabolites were identified, and germination toxicity assays illustrated that a metabolite with an aldehyde structure induced phytotoxicity. This study provides valuable information on pesticide contamination from manure and emphasizes the importance of considering pesticide metabolites when assessing environmental risks.

Biodegradation characteristics and mechanism of quinoline by Ochrobactrum sp. strain C2

A quinoline-degrading strain, C2, which could completely degrade 250 mg/L of quinoline within 24 h, was isolated from coking wastewater. Strain C2 was identified as Ochrobactrum sp. on the basis of 16S rDNA sequence analysis According to 16S rDNA gene sequence analysis, Strain C2 was identified as Ochrobactrum sp. Strain C2 could utilize quinoline as the sole carbon sources and nitrogen sources to grow and degrade quinoline well under acidic conditions. The optimum inoculum concentration, temperature and shaking speed for quinoline degradation were 10%, 30 °C and 150 r/min, respectively. The degradation of quinoline at low concentration by the strain followed the first-order kinetic model. The growth process of strain C2 was more consistent with the Haldane model than the Monod model, and the kinetic parameters were: Vmax = 0.08 h^-1, Ks = 131.5 mg/L, Ki = 183.1 mg/L. Compared with suspended strains, strain C2 immobilized by sodium alginate had better degradation efficiency of quinoline and COD. The metabolic pathway of quinoline by Strain C2 was tentatively proposed, quinoline was firstly converted into 2(1H) quinolone, then the benzene ring was opened with the action of catechol 1,2-dioxygenase and subsequently transformed into benzaldehyde, 2-pentanone, hydroxyphenyl propionic acid and others.

Fate of chlorpyrifos bound residues in paddy soils: Release, transformation, and phytoavailability

Chlorpyrifos (CPF) is a widely used organophosphorus insecticide that tends to form bound residues (BRs) in soils. However, the stability and biological activity of CPF-BRs remain to be explored. Facilitated by carbon-14 tracing, this study obtained CPF-BRs initially formed in two typical paddy soils (14C-CPF-BRin), and further investigated their release, transformation and phytoavailability using duckweed (Lemna minor) as a model aquatic organism. Most 14C-CPF-BRin in soils were composed of the parent CPF and its metabolite 3,5,6-trichloro-2-pyridinol (2-OH-TCP), which was mainly formed through reversible entrapment by soil fulvic acids and humin (>80%). At 36 d, 66.67-80.90% of the 14C-CPF-BRin was released, of which only 2-OH-TCP could be released into the water and absorbed by the duckweed, with bioconcentration factors ranging from 247.99 to 324.68 L kg-1. The subsequent metabolism of released 14C-CPF-BRin in duckweed included phase I metabolism from 2-OH-TCP to 4-OH-TCP and phase II metabolism of conjugation of TCP with plant endogenous amino acids. The study suggested that CPF bound residues have high bioavailability in paddy field environments. Given that many pesticides and non-pesticide chemicals share structures analogous to CPF, the findings have important implications for better understanding the environmental and human health risks of man-made chemicals.

Formation and nature of non-extractable residues of emerging organic contaminants in humic acids catalyzed by laccase

Formation of non-extractable residues (NERs) is the major fate of most environmental organic contaminants in soil, however, there is no direct evidence yet to support the assumed physical entrapment of NERs (i.e., type I NERs) inside soil humic substances. Here, we used ¹⁴C-radiotracer and silylation techniques to analyze NERs of six emerging and traditional organic contaminants formed in a suspension of humic acids (HA) under catalysis of the oxidative enzyme laccase. Laccase induced formation of both type I and covalently bound NERs (i.e., type II NERs) of bisphenol A, bisphenol F, and tetrabromobisphenol A to a large extent, and of bisphenol S (BPS) and sulfamethoxazole (SMX) to a less extent, while no induction for phenanthrene. The type I NERs were formed supposedly owing to laccase-induced alteration of primary (active groups) and secondary (conformation) structure of humic supramolecules, contributing surprisingly to large extents (23.5%-65.7%) to the total NERs, particularly for BPS and SMX, which both were otherwise not transformed by laccase catalysis. Electron-withdrawing sulfonyl group and bromine substitution significantly decreased amount and kinetics of NER formation, respectively. This study provides the first direct evidence for the formation of type I NERs in humic substances and implies a "Trojan horse" effect of such NERs in the environment.

Fate of the neonicotinoid insecticide cycloxaprid in different soils under oxic conditions

Neonicotinoids are the most widely used pesticides worldwide due to their high toxicity to invertebrates. However, these compounds also increase the probability of environmental contamination. Cycloxaprid (CYC) is a promising neonicotinoid due to its insecticidal effectiveness and low cross resistance, but little is known about its fate in soils. Using radioisotope tracing techniques, the fate of ¹⁴C-labeled CYC enantiomers and racemic mixtures in aerobic soil was investigated in this research. After 100 d of incubation, the extractable residue (ER) of CYC decreased from 89.6% to 36.4% in red clay soil, from 46.1% to 10.1% in yellow loam soil, and from 93.2% to 12.2% in coastal saline soil. The radioactivity was substantially lower in methanol than in the other two solvents, but the distribution of CYC ER in various solvents across the three soils dramatically differed. The fraction of radioactive CYC that diffused into bound residue (BR) in the three soils increased over time to 56.8-83.0%. The variability in BR was influenced by soil properties such as organic matter concentration, pH, and residual microbial activity. Among the soils, yellow loam soil had the greatest tendency (53.0-83.0%) to form BR, while red clay soil showed the lowest capacity (7.5-61.2%). Cumulative mineralization (MI) to ¹⁴CO₂ accounted for 0.12-0.23%, 6.69-7.31% and 14.82-20.06% in acidic soil, neutral soil and alkaline soil, respectively, which suggests that the environmental fate of chiral pesticides may be influenced by soil pH. No stereoselective behavior was detected in this study. These findings provide a framework to assess the environmental impact and ecological safety of CYC application.

Removal kinetics and mechanisms of tetrabromobisphenol A (TBBPA) by HA-n-FeS colloids in the absence and presence of oxygen

The colloid of ferrous sulfide modified by humic acid (HA-n-FeS) shows good reduction and immobilization efficiency for variable-valence heavy metals in wastewater. The removal efficiency of HA-n-FeS for halogenated organic pollutants, however, remains unclear, especially in the absence and presence of oxygen. This study addressed this issue by exploring the effect and mechanism of dissolved oxygen on the degradation of tetrabromobisphenol A (TBBPA) by the HA-n-FeS colloid in water. The results showed that the removal efficiency of different concentrations of TBBPA (5,10, and 20 μm) by the HA-n-FeS colloid was 33.16%, 20.48%, and 22.37% in the absence of oxygen, respectively. When TBBPA reacted with the HA-n-FeS colloid, the concentration of Fe(II) and S(-II) remained stable. The adsorption of HA-n-FeS was the main mechanism of removing TBBPA in the absence of oxygen. In the presence of oxygen, the removal efficiency of TBBPA by the HA-n-FeS colloid was 82.37%, 56.80%, and 43.78% (for the above-mentioned TBBPA concentrations), respectively. In addition, the removal capacity of TBBPA by HA-n-FeS was 39.63, 52.21, and 89.75 mg/g, respectively. The concentration of Fe(II) and S(-II) decreased rapidly in time. Among them, the HA-n-FeS colloid removed part of the TBBPA through chemical adsorption. The main way of chemical adsorption was pore adsorption and functional group (olefin CC, phenolic hydroxyl group O-H, alcohol group C-O) combination. Besides, the HA-n-FeS colloid degraded part of the TBBPA into BPA through reduction, in which 17.72% of TBBPA was removed by the reduction of HA-n-FeS colloid. Fe(II) was the main contributor to the reductive degradation of TBBPA. Furthermore, active species (1O2 and •O2-) played a minor role in the removal of TBBPA by the HA-n-FeS colloids with oxygen, where 13% of TBBPA was removed by 1O2 and •O2-. Therefore, in practical applications, the aeration method can be used to significantly improve the removal efficiency of TBBPA by HA-n-FeS colloids in water.

Enhanced mineralization of chlorpyrifos bound residues in soil through inoculation of two synergistic degrading strains

Bioaugmentation methods are frequently employed for pesticide pollution remediation; however, it is not clear whether the introduced bacteria affect the pesticide bound residue (BRs) composition and whether the BRs can be catabolized by the introduced strains. This study aimed at answering these questions by using ¹⁴C-chlorpyrifos (¹⁴C-CPF) and two CPF-degrading strains (Pseudomonas sp. DSP-1 and Cupriavidus sp. P2). The results showed that the BRs can be up to 83.0%, and that the CPF-BRs formed can be further transformed into ¹⁴CO₂ by the strains. Indeed, the microbial inoculation can increase the CPF mineralization by 1.0-22.1 times and can decrease the BRs by up to ~50% of the control (on day 20). Compared with the control without bioaugmentation, microbial inoculation enhanced the release of BRs by 2.2-18.0 times. Adding biochar to the soil can greatly inhibit CPF mineralization and maintain the BR content at a relatively stable level. The CPF residue can affect the composition of the indigenous soil microbial community, but the introduction of bacteria for remediation did not have a significant effect. The results indicate that Pseudomonas sp. DSP-1 and Cupriavidus sp. P2 are useful for remediating both CPF extractable and bound residues.

Fate of 2,4,6-Tribromophenol in Soil Under Different Redox Conditions

Fate of 2,4,6-tribromophenol (TBP) in environmental matrices is obscure. We used ¹⁴C-tracer to investigated mineralization, transformation, and non-extractable residue (NER)-formation of TBP in a soil under continuously oxic, continuously anoxic, and anoxic-oxic alteration conditions. In all cases, TBP rapidly dissipated, mineralized to CO₂, and formed NERs in the soil. Considerable amounts of transformation products (2-12%) were detected during the incubation. Marked mineralization (13-26%) indicated that soil microorganisms used TBP as their energy source. About 62-70% of the initial radioactivity was transformed into NERs, being mainly attributed to binding to humic and fulvic acid fractions. TBP transformation was significantly faster under oxic conditions than under anoxic conditions, and was boosted when the soil redox changed from anoxic to oxic state. The results provide new insights into fate of TBP in soil and suggest the importance to evaluate the stability of NERs for risk assessment of TBP in soil.