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.

Analyzing microbial communities and their biodegradation of multiple pharmaceuticals in membrane bioreactors.

Pharmaceuticals are of concern to our planet and health as they can accumulate in the environment. The impact of these biologically active compounds on ecosystems is hard to predict, and information on their biodegradation is necessary to establish sound risk assessment. Microbial communities are promising candidates for the biodegradation of pharmaceuticals such as ibuprofen, but little is known yet about their degradation capacity of multiple micropollutants at higher concentrations (100 mg/L). In this work, microbial communities were cultivated in lab-scale membrane bioreactors (MBRs) exposed to increasing concentrations of a mixture of six micropollutants (ibuprofen, diclofenac, enalapril, caffeine, atenolol, paracetamol). Key players of biodegradation were identified using a combinatorial approach of 16S rRNA sequencing and analytics. Microbial community structure changed with increasing pharmaceutical intake (from 1 to 100 mg/L) and reached a steady-state during incubation for 7 weeks on 100 mg/L. HPLC analysis revealed a fluctuating but significant degradation (30-100%) of five pollutants (caffeine, paracetamol, ibuprofen, atenolol, enalapril) by an established and stable microbial community mainly composed of Achromobacter, Cupriavidus, Pseudomonas and Leucobacter. By using the microbial community from MBR1 as inoculum for further batch culture experiments on single micropollutants (400 mg/L substrate, respectively), different active microbial consortia were obtained for each single micropollutant. Microbial genera potentially responsible for degradation of the respective micropollutant were identified, i.e. Pseudomonas sp. and Sphingobacterium sp. for ibuprofen, caffeine and paracetamol, Sphingomonas sp. for atenolol and Klebsiella sp. for enalapril. Our study demonstrates the feasibility of cultivating stable microbial communities capable of degrading simultaneously a mixture of highly concentrated pharmaceuticals in lab-scale MBRs and the identification of microbial genera potentially responsible for the degradation of specific pollutants. KEY POINTS: • Multiple pharmaceuticals were removed by stable microbial communities. • Microbial key players of five main pharmaceuticals were identified.

Formation, characterization, and mineralization of bound residues of tetrabromobisphenol A (TBBPA) in silty clay soil under oxic conditions.

The nature and stability of bound residues (BRs) derived from the widely used brominated flame retardant tetrabromobisphenol A (TBBPA) in fine-textured soil is unknown. We incubated 14C-labeled TBBPA in silty clay rice paddy soil for 93days under oxic conditions. TBBPA dissipated with a first-order kinetic constant kd of 0.0474±0.0017day-1 (t1/2 14.6±0.3days) and mineralized with a km of 0.0011±0.00002day-1. At the end of the incubation, four metabolites, including two methylation products (TBBPA monomethyl and dimethyl ether), accounted for 7.9±0.1% of the initial TBBPA. The BRs continuously increased in amount to a maximum of 80.1±3.6%. About 86.3±0.9% of the BRs localized in the humin fraction and 55.9±1.5% was hydrolyzable with strong alkali (SAH-BRs), which represents reversible BRs. Together with results previously reported for coarse-textured soil, these results indicate that the absolute amounts of both BRs and SAH-BRs of TBBPA as well as the relative contribution of SAH-BRs to total BRs in fine-textured soil are markedly higher than in coarse-textured soil. When BRs-containing soil was incubated with fresh soil for 231days, 9.2±0.3% was mineralized (km 0.00047±0.00002day-1) and SAH-BRs decreased to 34.1±1.1%, accompanied by transformation into other BR forms. These indicate that BRs are bioavailable in the soil. Amendment with rice root exudates did not effectively affect the mineralization, release, and distribution of BRs, suggesting that bioavailability of BRs but not microbial activity limits the degradation of BRs in the silty clay soil. This study provides first insights into the nature and stability of TBBPA-derived BRs in fine-textured soil under oxic conditions and indicates the significant role of reversible BRs in the environmental risk of TBBPA.

Degradation of sulfonamide antibiotics by Microbacterium sp. strain BR1 - elucidating the downstream pathway.

Microbacterium sp. strain BR1 is among the first bacterial isolates which were proven to degrade sulfonamide antibiotics. The degradation is initiated by an ipso-substitution, initiating the decay of the molecule into sulfur dioxide, the substrate specific heterocyclic moiety as a stable metabolite and benzoquinone imine. The latter appears to be instantaneously reduced to p-aminophenol, as that in turn was detected as the first stable intermediate. This study investigated the downstream pathway of sulfonamide antibiotics by testing the strain's ability to degrade suspected intermediates of this pathway. While p-aminophenol was degraded, degradation products could not be identified. Benzoquinone was shown to be degraded to hydroquinone and hydroquinone in turn was shown to be degraded to 1,2,4-trihydroxybenzene. The latter is assumed to be the potential substrate for aromatic ring cleavage. However, no products from the degradation of 1,2,4-trihydroxybenzene could be identified. There are no signs of accumulation of intermediates causing oxidative stress, which makes Microbacterium sp. strain BR1 an interesting candidate for industrial waste water treatment.

Enhanced transformation of tetrabromobisphenol a by nitrifiers in nitrifying activated sludge.

The fate of the most commonly used brominated flame retardant, tetrabromobisphenol A (TBBPA), in wastewater treatment plants is obscure. Using a (14)C-tracer, we studied TBBPA transformation in nitrifying activated sludge (NAS). During the 31-day incubation, TBBPA transformation (half-life 10.3 days) was accompanied by mineralization (17% of initial TBBPA). Twelve metabolites, including those with single benzene ring, O-methyl TBBPA ether, and nitro compounds, were identified. When allylthiourea was added to the sludge to completely inhibit nitrification, TBBPA transformation was significantly reduced (half-life 28.9 days), formation of the polar and single-ring metabolites stopped, but O-methylation was not significantly affected. Abiotic experiments confirmed the generation of mono- and dinitro-brominated forms of bisphenol A in NAS by the abiotic nitration of TBBPA by nitrite, a product of ammonia-oxidizing microorganisms (AOMs). Three biotic (type II ipso-substitution, oxidative skeletal cleavage, and O-methylation) and one abiotic (nitro-debromination) pathways were proposed for TBBPA transformation in NAS. Apart from O-methylation, AOMs were involved in three other pathways. Our results are the first to provide information about the complex metabolism of TBBPA in NAS, and they are consistent with a determining role for nitrifiers in TBBPA degradation by initiating its cleavage into single-ring metabolites that are substrates for the growth of heterotrophic bacteria.

Degradation and metabolism of tetrabromobisphenol A (TBBPA) in submerged soil and soil-plant systems.

Contamination by tetrabromobisphenol A (TBBPA), the most widely used brominated flame retardant, is a matter of environmental concern. Here, we investigated the fate and metabolites of (14)C-TBBPA in a submerged soil with an anoxic-oxic interface and planted or not with rice (Oryza sativa) and reed (Phragmites australis) seedlings. In unplanted soil, TBBPA dissipation (half-life 20.8 days) was accompanied by mineralization (11.5% of initial TBBPA) and the substantial formation (60.8%) of bound residues. Twelve metabolites (10 in unplanted soil and 7 in planted soil) were formed via four interconnected pathways: oxidative skeletal cleavage, O-methylation, type II ipso-substitution, and reductive debromination. The presence of the seedlings strongly reduced (14)C-TBBPA mineralization and bound-residue formation and stimulated debromination and O-methylation. Considerable radioactivity accumulated in rice (21.3%) and reed (33.1%) seedlings, mainly on or in the roots. While TBBPA dissipation was hardly affected by the rice seedlings, it was strongly enhanced by the reed seedlings, greatly reducing the half-life (11.4 days) and increasing monomethyl TBBPA formation (11.3%). The impact of the interconnected aerobic and anaerobic transformation of TBBPA and wetland plants on the profile and dynamics of the metabolites should be considered in phytoremediation strategies and environmental risk assessments of TBBPA in submerged soils.

Fate and metabolism of tetrabromobisphenol A in soil slurries without and with the amendment with the alkylphenol degrading bacterium Sphingomonas sp. strain TTNP3.

Transformation of ring-(14)C-labelled tetrabromobisphenol-A (TBBPA) was studied in an oxic soil slurry with and without amendment with Sphingomonas sp. strain TTNP3, a bacterium degrading bisphenol-A. TBBPA degradation was accompanied by mineralization and formation of metabolites and bound-residues. The biotransformation was stimulated in the slurry bio-augmented with strain TTNP3, via a mechanism of metabolic compensation, although this strain did not grow on TBBPA. In the absence and presence of strain TTNP3, six and nine metabolites, respectively, were identified. The initial O-methylation metabolite (TBBPA-monomethyl ether) and hydroxytribromobisphenol-A were detected only when strain TTNP3 was present. Four primary metabolic pathways of TBBPA in the slurries are proposed: oxidative skeletal rearrangements, O-methylation, ipso-substitution, and reductive debromination. Our study provides for the first time the information about the complex metabolism of TBBPA in oxic soil and suggests that type II ipso-substitution could play a significant role in the fate of alkylphenol derivatives in the environment.