Impact of sludge treatments on the extractability and fate of acetyl sulfamethoxazole residues in amended soils

Environmental sulfonamides pollution and microbial adaptation: Genome, transcriptome, and toxicology reveal Bacillus sp. HC-1 biotransformation and antibiotic resistance mechanisms

Sulfonamides (SAs) residue in the environment presents significant challenges to both environmental safety and medical security. Currently, the reaction and transformation mechanisms of microorganisms in the presence of SAs remain unclear. This study employed multiomics to investigate the gene response and enzymatic transformation mechanisms of Bacillus sp. HC-1 under SAs exposure conditions. Strain HC-1 demonstrated the ability to transform sulfaquinoxaline (SQX), sulfamethoxazole (SMX), and sulfamethazine (SMZ) into their respective N4-acetylated products. Within 12 hours, the transformation rates of SQX, SMX, and SMZ reached 51.7 %, 44.7 %, and 42.70 % respectively. Transcriptome analysis revealed that differentially expressed genes (DEGs) related to cellular transport, membrane channel activity, and various metabolic pathways were significantly enriched in strain HC-1 exposed to SQX. Through genomic analysis, we identified three types of arylamine N-acetyltransferases (NATs), which were named BaNATA, BaNATB, and BaNATC. Their highest homologies with reported NATs were 35.29 %, 40.82 %, and 35.32 %, respectively. Resistance and toxicological assessments indicated that NATs functioned as resistance genes against SAs, and the toxicity of transformation products to microorganisms and plant seeds was diminished. This study offers a valuable reference for a more in-depth understanding of microbial reactions, potential resistance, and transformation mechanisms in antibiotic-contaminated environments.

Reversible transformations of sulfamethoxazole and its submoieties by manganese-oxidizing bacteria and biogenic manganese oxides in the presence of humic substances

Manganese-oxidizing bacteria (MnOB) and biogenic manganese oxides (BioMnOx) play key roles in the breakdown of organic matter (including pollutants) in water and soil environments. The degradation of some organic compounds (such as sulfonamides selected in this study) by BioMnOx in the presence of active MnOB is poorly understood. Thus far, it has been shown that the transformation of sulfonamides by either BioMnOx or MnOB (but thus far not studied in a binary system) can be modulated using naturally occurring redox mediators, such as humic substances, leading to the formation of coupling products of unknown stability. The co-occurrence of sulfonamides, MnOB, BioMnOx, and humic constituents is pertinent to many natural and engineered settings. This study used syringaldehyde, which is a model humic constituent, to investigate the nature of modulation in a binary system of BioMnOx and MnOB for the first time. The MnOB strain Pseudomonas putida MnB6 was cultivated and used in batch degradation tests. Initial tests with eight sulfonamides showed comparably poor degradation. In the next step of this study, sulfamethoxazole (SMX) and two SMX submoieties (sulfanilamide (SNM) and 3-amino-5-methylisoxazole (ISX)) were examined. After 48-60 hours in active cultures with BioMnOx, the degradation of all the three substances was negligible. However, syringaldehyde increased the degradation efficiency by 26% for SMX, 58% for SNM, and 27% for ISX. The active culture and BioMnOx synergistically improved degradation, highlighting the importance of BioMnOx regeneration. Removal was partially reversible (10-30%) owing to the retransformation of the reaction products into parent compounds, which was induced by syringaldehyde depletion. Unstable reaction products were conjugates of SMX, SNM, and ISX with syringaldehyde or its oxidation product DMBQ (2,6-dimethoxy-1,4-benzoquinone). This deconjugation likely contributes to process reversibility, potentially negatively impacting the environment and the safety of water and wastewater treatment systems.

Occurrence, dissipation kinetics and environmental risk assessment of antibiotics and their metabolites in agricultural soils

Antibiotics are among the emerging contaminants of greatest concern to the scientific community. However, the occurrence and behaviour of their metabolites in soils have been scarcely studied. To address this research gap, this study investigates the occurrence, sorption, dissipation kinetics, and environmental risk of highly important antibiotics (sulfamethazine, sulfadiazine, sulfamethoxazole, trimethoprim) and their main metabolites in Mediterranean agricultural soils. Batch experiments were conducted under natural conditions for 120 days. Five different dissipation kinetics models were applied to elucidate antibiotics degradation. The sorption isotherms were evaluated by three different models. Most of the antibiotics and metabolites tested showed a good fit with the Linear Isotherm model (R2 >0.96) and biphasic dissipation kinetic models (R2 >0.90). The dissipation and the endpoints values (DT50 and DT90) depended on the soil type properties. A Lixisol soil demonstrated reduced degradation of the investigated compounds. Trimethoprim showed the highest persistence, followed by sulfamethazine, sulfamethoxazole, and sulfadiazine. Parent compounds exhibited lower degradation rates than their metabolites. Remaining antibiotic concentrations were found to be below the predicted no-effect concentration in soil, suggesting that they may not pose a risk to terrestrial biota. This study provides valuable insights into the behaviour of these antibiotics and their metabolites in soil.

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.

Emerging organic contaminants in the soil-plant-receptor continuum: transport, fate, health risks, and removal mechanisms

There is a lack of comprehensive reviews tracking emerging organic contaminants (EOCs) within the soil-plant continuum using the source-pathway-receptor-impact-mitigation (SPRIM) framework. Therefore, this review examines existing literature to gain insights into the occurrence, behaviour, fate, health hazards, and strategies for mitigating EOCs within the soil-plant system. EOCs identified in the soil-plant system encompass endocrine-disrupting chemicals, surfactants, pharmaceuticals, personal care products, plasticizers, gasoline additives, flame retardants, and per- and poly-fluoroalkyl substances (PFAS). Sources of EOCs in the soil-plant system include the land application of biosolids, wastewater, and solid wastes rich in EOCs. However, less-studied sources encompass plastics and atmospheric deposition. EOCs are transported from their sources to the soil-plant system and other receptors through human activities, wind-driven processes, and hydrological pathways. The behaviour, persistence, and fate of EOCs within the soil-plant system are discussed, including sorption, degradation, phase partitioning, (bio)transformation, biouptake, translocation, and bioaccumulation in plants. Factors governing the behaviour, persistence, and fate of EOCs in the soil-plant system include pH, redox potential, texture, temperature, and soil organic matter content. The review also discusses the environmental receptors of EOCs, including their exchange with other environmental compartments (aquatic and atmospheric), and interactions with soil organisms. The ecological health risks, human exposure via inhalation of particulate matter and consumption of contaminated food, and hazards associated with various EOCs in the soil-plant system are discussed. Various mitigation measures including removal technologies of EOCs in the soil are discussed. Finally, future research directions are presented.

Isolation and characterization of a marine bacterium Vibrio diabolicus strain L2-2 capable of biotransforming sulfonamides

Sulfonamides (SAs) have attracted much attention because of their high detection rates in natural water. In this study, a marine bacterium Vibrio diabolicus strain L2-2 was isolated which could metabolize 9 SAs to a different extent. Compared with SAs and their analogs, SAs with N-oxides of heterocyclic structure were easier to be transformed to their N⁴-acetylated metabolites or their isoxazole ring rearrangement isomers by strain L2-2. And, gene vdnatA and vdnatG were likely to be the key genes in SAs acetylation process, which might code Arylamine N-acetyltransferase. The biotransformation rates of sulfathiazole(STZ), sulfamonomethoxine(SMT), sulfadiazine(SDZ), sulfamethoxazole(SMX) and sulfisoxazole(SIX) could reach 29.39 ± 5.63, 24.97 ± 4.45, 79.41 ± 4.05, 64.64 ± 1.71, 32.82 ± 4.46% in 6 days, respectively. Besides, the overall optimal conditions for SAs biotransformation were less than 100 mg/L for total SAs in neutral or weakly alkaline medium with the salinity of 10-20‰ and additional nutrients like glucose, sucrose or glycerine. Furthermore, toxicity was demonstrated to be significantly reduced after biotransformation. Together, this study introduced a strategy to use V. diabolicus strain L2-2 to realize simultaneous removal and detoxification of multiple SAs in freshwater and seawater, and revealed SAs removal pathways and relevant molecular mechanism.

Detection, occurrence, and fate of emerging contaminants in agricultural environments (2019)

A review of 82 papers published in 2018 is presented. The topics ranged from detailed descriptions of analytical methods, to fate and occurrence studies, to ecological effects and sampling techniques for a wide variety of emerging contaminants likely to occur in agricultural environments. New methods and studies on veterinary pharmaceuticals, microplastics, and engineered nanomaterials in agricultural environments continue to expand our knowledge base on the occurrence and potential impacts of these compounds. This review is divided into the following sections: Introduction, Analytical Methods, Fate and Occurrence, Pharmaceutical Metabolites, Anthelmintics, Microplastics, and Engineered Nanomaterials. PRACTITIONER POINTS: New research describes innovative new techniques for emerging contaminant detection in agricultural settings. Newer classes of contaminants include human and veterinary pharmaceuticals. Research in microplastics and nanomaterials shows that these also occur in agricultural environments and will likely be topics of future work.

Fate of 14C-acetyl sulfamethoxazole during the activated sludge process

Compared to antibiotic parent molecule, human metabolites are generally more polar and sometimes not less toxic in wastewater. However, most researches focus on the fate of parent molecule. Therefore, behaviors of human metabolites are little known. Moreover, though much has been done on the fate of antibiotics during activated sludge process, there are still some limitations and gaps. In the present study, [Ring-¹⁴C] acetyl sulfamethoxazole (¹⁴C-Ac-SMX) was used to investigate the fate of human metabolite of SMX during activated sludge process at environmentally relevant concentration. At the end of 216 h, 3.1% of the spiked activity in the initial aqueous phase was mineralized, 50% was adsorbed onto the solid phase, and 36.5% still remained in the aqueous phase, indicating that adsorption, not biodegradation, was the main dissipation pathway. In the existence of microbial activities, accumulation into the solid phase was much higher, which was less bioavailable by chemical sequential extraction. The multimedia kinetic model simultaneously depicted the fate of Ac-SMX in the gas, aqueous, and solid phases, and demonstrated that microbially accelerated accumulation onto the solid phase was attributed to lower desorption rate from the solid phase to the aqueous phase, where adsorption rate was not the key factor. Therefore, Ac-SMX cannot be efficiently mineralized and remain in the aqueous or the solid phases. The accumulation in the solid phase is less bioavailable and is hard to be desorbed in the existence of microbial activities, and should not be easily degraded, and may lead to the development of antibiotic-resistant bacteria and genes after discharge into the environment.

Environmental availability of sulfamethoxazole and its acetylated metabolite added to soils via sludge compost or bovine manure

The fate of antibiotics and their metabolites in soils after application of organic waste depends on their environmental availability, which depends on the quality and biodegradability of the added exogenous organic matter (EOM). This study aimed at better understanding the fate of sulfamethoxazole (SMX) and N-acetyl-sulfamethoxazole (AcSMX) metabolite added to soils via sludge compost or cow manure application, during a 28-day incubation. Experimental results obtained for mineralized, extractable, and non-extractable fractions as well as EOM mineralization were used to couple SMX and AcSMX dynamics to the EOM evolution using the COP-Soil model. According to various mechanisms of extraction, CaCl₂, EDTA and cyclodextrin solutions extracted contrasted available fractions (31-96% on day 0), resulting in different sets of parameter values in the model. CaCl₂ extraction was the best method to assess the sulfonamide availability, leading to low relative root mean squared errors and best simulations of SMX and AcSMX dynamics. The decrease of SMX and AcSMX availability over time went with the formation of non-extractable residues, mostly of physicochemical origin. Using the COP-Soil model, the co-metabolism was assumed to be responsible for the formation of biogenic non-extractable residues and the low mineralization of SMX and AcSMX.

Hierarchical magnetic petal-like Fe3O4-ZnO@g-C3N4 for removal of sulfamethoxazole, suppression of photocorrosion, by-products identification and toxicity assessment

Herein, a petal-like photocatalyst, Fe₃O₄-ZnO@g-C₃N₄ (FZG) with different g-C₃N₄ to ZnO ratios was synthesized with hierarchical structure. The FZG1 photocatalyst, having the weight ratio of 1:1 for the initial urea and Fe₃O₄-ZnO (Fe-ZnO), presented the highest sulfamethoxazole (SMX) degradation rate of 0.0351 (min^-1), which was 2.6 times higher than that of pristine ZnO. Besides the facile separation, the performance of photocatalyst was improved due to the function of iron oxide as an electron acceptor that reduced the electron/hole recombination rate. The coating of g-C₃N₄ on the Fe-ZnO surface not only acted as a protective layer for ZnO against photocorrosion, but it also enhanced the photocatalytic activity of the catalyst for SMX degradation through the heterojunction mechanism. By using the FZG1 photocatalyst, 95% SMX removal was obtained after 90 min reaction, while 47% COD and 30% TOC removal were achieved after 60 min treatment under a low energy-consuming UV lamp (10 W). Moreover, a substantial reduction in the solution toxicity was shown after the treatment, as compared with the SMX solution before treatment. The LC-HR-MS/MS analysis results showed that the concentration of most detected by-products produced after 90 min reaction by FZG1 was considerably lower than those obtained using other synthesized photocatalysts. By performing radical scavenging experiments, OH^° radical was found to be the major reactive species. The FZG1 photocatalyst also displayed excellent reusability in five cycles and the leaching of zinc and iron ions was reduced by 54% and ∼100%, respectively, after coating Fe-ZnO with g-C₃N₄.