Fate of Tetrabromobisphenol A (TBBPA) and Formation of Ester- and Ether-Linked Bound Residues in an Oxic Sandy Soil

Identifying bound compounds in non-extractable residues of pesticides in soil by 4-pool kinetic analysis

This study explores the feasibility of identifying bound compounds in non-extractable residues (NERs) of pesticides in soil by 4-pool kinetic analysis. The 4-pools refer to parent compound, metabolites, NERs, and CO2 in 14C-labeled pesticide soil degradation studies. We discovered the following two characteristic 4-pool kinetic behaviors of formation of NERs: (1) if parent compound is bound as NERs, the metabolites (m(t) in % applied radioactivity (AR)) kinetically drive the evolution of CO2 only; and (2) if a metabolite (x) in a sequential degradation pathway is bound as NERs, m(t) is split into m1(t) and m2(t) at the metabolite (x) that is bound as NERs, which kinetically drive the formation of NERs and evolution of CO2 respectively. We developed two (i.e., Parent➔NER and metabolite➔NER) 4-pool models to capture the kinetic behaviors respectively. By fitting the models to a set of 4-pool data, we not only determine whether NERs form from parent compound or metabolites but also identify the bound metabolite (x) by resolving the metabolites into M1(t) and M2(t) (i.e., the variables used to simulate m1(t) and m2(t)) and then matching m1(t) (i.e., the sum of the bound metabolite (x) and its metabolite precursors) with M1(t). By applying the models to 14C-labeled parent compound-dosed studies and then sequentially to metabolite-dosed studies for 7 pesticides with ≥70 % AR NERs, we identified the bound compounds, which have the moieties known to be responsible for NERs, are bound as NERs instantaneously when dosed into soil, and account for pH dependency of NER formation.

S-Fe/Co@GC reduction-oxidation sequential reaction system for the high-efficiency mineralization of tetrabromobisphenol a in water

The lipophilic, bioaccumulative, persistent nature of Tetrabromobisphenol A (TBBPA) contributes to its widespread detection in various environmental media, posing significant negative implications for the living environment and human health. In this study, a reduction system and a reduction-oxidation sequential reaction system were developed using a magnetic core-shell bimetallic amendment (S-Fe/Co@GC) to investigate the degradation and mineralization properties of TBBPA. Additionally, the degradation mechanism and degradation pathway of TBBPA in various systems were analyzed. In the sole S-Fe/Co@GC reduction system, sulfurized nano-zero-valent iron (S-Fe) and Co0 exhibited remarkable reductive capabilities towards TBBPA. The reaction of S-Fe/Co@GC gradually facilitated the debromination of TBBPA, ultimately leading to its conversion into bisphenol A. The reaction process demonstrated the synergistic effect among S-Fe, Co0, and graphite carbon, leading to a remarkable enhancement in the reduction performance of the material. Consequently, TBBPA removal efficiency reached 97.5% within a time frame of 10 h. In the reduction-oxidation sequential reaction system, the debromination of TBBPA during the reduction stage enhanced the subsequent oxidation stage's total organic carbon (TOC) removal rate. During the oxidation stage (0.03 mmol of PMS added at 30 min), TBBPA underwent attack by sulfate radical (SO4·-), hydroxyl radical (·OH), superoxide radical (O2·-), and singlet oxygen (1O2), leading to cleavage and opening of its structure. This process resulted in the conversion of TBBPA into short-chain fatty acids, ultimately mineralizing it into CO2 and H2O. Thus, this degradation pathway mitigated potential environmental risk associated with intermediates. The final TOC removal rate significantly increased to 72.7% when the dose of composite material was set at 1.0 g/L, surpassing that achieved by the conventional advanced oxidation system. Hence, the S-Fe/Co@GC reduction-oxidation sequential reaction system provides a new strategy for treating high-concentration TBBPA-contaminated water.

Phototransformation of tetrabromobisphenol A bis (allyl ether) in an aqueous solution: Role of environmentally persistent free radicals

Tetrabromobisphenol A bis (allyl ether) (TBBPA-BAE) represents an extensively used brominated flame retardant (BFRs) in the production of many fields and their phototransformation in natural water is still unclear. The environmentally persistent free radicals (EPFRs) with preserved activities could exist in the environment for a long time and involve in the phototransformation of many organic pollutants. Here, the photodegradation of TBBPA-BAE with the degradation rate constant (k = 0.060 h-1) under simulate sunlight and the promoting effect of EPFRs on TBBPA-BAE photodegradation (k = 0.135 h-1) were investigated. According to the detected photogenerated electrons (e-) and singlet oxygen (1O2) rather than hydroxyl radicals (•OH) by the electron paramagnetic resonance (EPR), the effect mechanism may not be related to the typical •OH induced by EPFRs. The possible transformation pathways of the ether cleavage, hydrolysis and hydroxylation of propenyl bond and the debromination were proposed by the primary byproducts identified by UPLC-Q-Exactive Orbitrap MS. EPFRs caused a further debromination and ether cleavage and probably be due to EPFRs directly providing electrons to TBBPA-BAE which promoted the photodegradation of TBBPA-BAE, and their reaction mechanism needed further attention. Overall, this study provided useful information to understand the role of EPFRs on phototransformation of TBBPA-BAE in water.

Mechanism of tartaric acid mediated dissipation and biotransformation of tetrabromobisphenol A and its derivatives in soil

Biotransformation is a major dissipation process of tetrabromobisphenol A and its derivatives (TBBPAs) in soil. The biotransformation and ultimate environmental fate of TBBPAs have been widely studied, yet the effect of root exudates (especially low-molecular weight organic acids (LMWOAs)) on the fate of TBBPAs is poorly documented. Herein, the biotransformation behavior and mechanism of TBBPAs in bacteriome driven by LMWOAs were comprehensively investigated. Tartaric acid (TTA) was found to be the main component of LMWOAs in root exudates of Helianthus annus in the presence of TBBPAs, and was identified to play a key role in driving shaping bacteriome. TTA promoted shift of the dominant genus in soil bacteriome from Saccharibacteria_genera_incertae_sedis to Gemmatimonas, with a noteworthy increase of 24.90-34.65% in relative abundance of Gemmatimonas. A total of 28 conversion products were successfully identified, and β-scission was the principal biotransformation pathway for TBBPAs. TTA facilitated the emergence of novel conversion products, including 2,4-dibromophenol, 3,5-dibromo-4-hydroxyacetophenone, para-hydroxyacetophenone, and tribromobisphenol A. These products were formed via oxidative skeletal cleavage and debromination pathways. Additionally, bisphenol A was observed during the conversion of derivatives. This study provides a comprehensive understanding about biotransformation of TBBPAs driven by TTA in soil bacteriome, offering new insights into LMWOAs-driven biotransformation mechanisms.

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.

Adsorption behaviors and bioavailability of tetrabromobisphenol A in the presence of polystyrene microplastic in soil: Effect of microplastics aging

Microplastics, a kind of emerging pollutant, have become a global environmental research hotspot in recent years due to its wide distribution in soil and its impact on soil ecosystems. However, little information is available on the interactions between microplastics and organic contaminants in soil, especially after microplastic aging. The impact of polystyrene (PS) microplastic aging on the sorption of tetrabromobisphenol A (TBBPA) in soil and the desorption characteristics of TBBPA-loaded microplastics in different environments were studied. The results showed a significant increase of 76.3% in adsorption capacity of TBBPA onto PS microplastics after aging for 96 h. Based on the results of characterization analysis and density functional theory (DFT) calculation, the mechanisms of TBBPA adsorption changed mainly from hydrophobic and π-π interactions on pristine PS microplastics to hydrogen bond and π-π interactions on aged PS microplastics. The presence of PS microplastics increased the TBBPA sorption capacity onto soil-PS microplastics system and significantly altered the distribution of TBBPA on soil particles and PS microplastics. The high TBBPA desorption over 50% from aged PS microplastics in simulated earthworm gut environment suggested that TBBPA contamination combined with PS microplastics might pose a higher risk to macroinvertebrates in soil. Overall, these findings contribute to the understanding of impact of PS microplastic aging in soil on the environmental behaviors of TBBPA, and provide valuable reference for evaluating the potential risk posed by the co-existence of microplastics with organic contaminants in soil ecosystems.

Identification and Prioritization of Environmental Organic Pollutants: From an Analytical and Toxicological Perspective

Exposure to environmental organic pollutants has triggered significant ecological impacts and adverse health outcomes, which have been received substantial and increasing attention. The contribution of unidentified chemical components is considered as the most significant knowledge gap in understanding the combined effects of pollutant mixtures. To address this issue, remarkable analytical breakthroughs have recently been made. In this review, the basic principles on recognition of environmental organic pollutants are overviewed. Complementary analytical methodologies (i.e., quantitative structure-activity relationship prediction, mass spectrometric nontarget screening, and effect-directed analysis) and experimental platforms are briefly described. The stages of technique development and/or essential parts of the analytical workflow for each of the methodologies are then reviewed. Finally, plausible technique paths and applications of the future nontarget screening methods, interdisciplinary techniques for achieving toxicant identification, and burgeoning strategies on risk assessment of chemical cocktails are discussed.

Degradation of Sulfamethoxazole by Manganese(IV) Oxide in the Presence of Humic Acid: Role of Stabilized Semiquinone Radicals

In this work, we demonstrate for the first time the abatement of sulfamethoxazole (SMX) induced by stabilized ortho-semiquinone radicals (o-SQ•-) in the MnO2-mediated system in the presence of humic acid. To evaluate the performance of different MnO2/mediator systems, 16 mediators are examined for their effects on MnO2 reactions with SMX. The key role of the bidentate Mn(II)-o-SQ• complex and MnO2 surface in stabilizing SQ•- is revealed. To illustrate the formation of the Mn(II)-o-SQ• complex, electron spin resonance, cyclic voltammetry, and mass spectra were used. To demonstrate the presence of o-SQ• on the MnO2 surface, EDTA was used to quench Mn(II)-o-SQ•. The high stability of o-SQ•- on the MnO2 surface is attributed to the higher potential of o-SQ•- (0.9643 V) than the MnO2 surface (0.8598 V) at pH 7.0. The SMX removal rate constant by different stabilized o-SQ• at pH 7.0 ranges from 0.0098 to 0.2252 min-1. The favorable model is the rate constant ln (kobs, 7.0) = 6.002EHOMO(o-Qred) + 33.744(ELUMO(o-Q) - EHOMO(o-Qred)) - 32.800, whose parameters represent the generation and reactivity of o-SQ•, respectively. Moreover, aniline and cystine are competitive substrates for SMX in coupling o-SQ•-. Due to the abundance of humic constituents in aquatic environments, this finding sheds light on the low-oxidant-demand, low-carbon, and highly selective removal of sulfonamide antibiotics.

Two halogenated flame retardants and cadmium in the soil-rice system: sorption, root uptake, and translocation

The migration and transformation of Tetrabromobisphenol A (TBBPA), DechloranePlus (DP), and cadmium in soil-rice system was investigated, and the influence on the quality of two varieties of rice was studied. The degradation half-lives of TBBPA, BBPAs, syn-DP, and anti-DP were 23.18 ~ 26.36 days, 30.14 ~ 36.10 days, 72.96-81.55 days, and 169.06-198.04 days in the soil. TBBPA was gradually degraded to tri-BBPA, di-BBPA, mono-BBPA, and bisphenol A by the debromination. TBBPA and its bromide metabolites could be bioaccumulated in different tissues of rice; mono-BBPA and bisphenol A was easy to accumulate in the stems, and bisphenol A was easy to bioaccumulate in the grain. Comparing with single and compound pollution, there was no significant difference in bioaccumulation factors of two rice species. The grain of NO7 had stronger bioaccumulation ability to mono-BBPA and BPA than NO1, and there is no significant difference in TBBPA. Residual level of DP in the rice: roots > stems > grain; there was no significant difference in bioaccumulation of two varieties of rice. Cadmium was easily bioaccumulated in the roots of rice and translocated to the rice stems and grains. NO7 rice had stronger bioaccumulation and transport capacity than NO1. The effects of the three pollutants on the quality of two varieties of rice varied significantly; cadmium had the greatest effect on the iodine blue value (BV) and amylase activity of the grain. This study proved that selecting rice varieties with low bioaccumulation to polluters can effectively reduce the risk of the food chain harming human health.

Response of microbial community in the soil of halophyte after contamination with tetrabromobisphenol A

Coastal wetlands are subjected to increasing tetrabromobisphenol A (TBBPA) pollution, whereas knowledge of TBBPA degradation in marine environments is lacking. The changes of bacterial communities in TBBPA-polluted soil covered with halophytes were investigated. TBBPA could be degraded in the halophyte-covered saline-alkali soil in a microcosm experiment. Higher TBBPA removal occurred in the soil of Kandelia obovata compared with soils covered with Suaeda australis and Phragmites australis within 56 days of cultivation. The rhizosphere soils of S. australis, P. australis, and K. obovata mainly involved the classes of Bacteroidia, Gammaproteobacteria, Alphaproteobacteria, and Anaerolineae. Additionally, manganese oxidation, aerobic anoxygenic phototrophy, and fermentation functions were higher in the rhizosphere soil of K. obovata after TBBPA addition. This study supports that using suitable local halophytic plants is a promising approach for degrading TBBPA-contaminated coastal soil.

Dry-to-wet fluctuation of moisture contents enhanced the mineralization of chloramphenicol antibiotic

Due to livestock wastewater irrigation, soil is becoming one of the major sinks of antibiotics in the environment. Recently, it is getting recognized that a variety of minerals under low moisture conditions can induce strong catalytic hydrolysis to antibiotics. However, the relative importance and implication of soil water content (WC) for natural attenuation of soil residual antibiotics has not been well recognized. In order to explore the optimal moisture levels and the key soil properties dominating for the high catalytic hydrolysis activities of soils, this study collected 16 representative soil samples across China, and assessed their performances to degrade chloramphenicol (CAP) under different moisture levels. The results showed that the soils with low organic matter contents (< 20 g/kg) and high amounts of crystalline Fe/Al were particularly effective in catalyzing CAP hydrolysis when exposed to low WC (< 6%, wt/wt), leading to CAP hydrolysis half-lives of <40 d Higher WC greatly suppressed the catalytic activity of the soil. By utilizing this process, it is possible to integrate abiotic and biotic degradation to enhance the mineralization of CAP, attributing to that the hydrolytic products are more available for soil microorganisms. As expected, the soils experienced periodic dry-to-wet moisture conditions (i.e., the WC shifting from 1 to 5% to 20-35%, wt/wt) exhibited higher degradation and mineralization of ¹⁴C-CAP, in comparison with the constant wet treatment. Meanwhile, the bacterial community composition and the specific genera showed that the dry-to-wet fluctuation of soil WC relieved the antimicrobial stress to bacterial community. Our study verifies the critical role of soil WC in mediating the natural attenuation of antibiotics, and guides to remove antibiotics from both wastewater and soil.

Sorption in soils and bioaccumulation potential of 2,2'-DiBBPA

2,2'-Dibromobisphenol A (2,2'-DiBBPA) is frequently detected in the environment. However, the mobility of 2,2'-DiBBPA in the soil environment is poorly understood. The present study examined the effects of soil components such as the NaClO-resistant fraction, dithionite-citrate-bicarbonate -demineralized fraction, humin fraction, black carbon, DOC-removed fraction, exogenous dissolved organic carbon and heavy metal cations on the adsorption of 2,2'-DiBBPA on several types of agricultural soils. The adsorption isotherms on soils and soil components were well fitted to the linear isotherm equation. 2,2'-DiBBPA sorption onto soils was dominated by soil organic matter content (SOM) and affected by exogenous dissolved organic carbon. Linear regression relationships between adsorption capacity (K_d) and soil characteristics were evaluated to predict partitioning of 2,2'-DiBBPA. Black carbon played a predominant role in the adsorption of 2,2'-DiBBPA. Heavy metal ions significantly inhibited the adsorptive behavior of 2,2'-DiBBPA under alkaline conditions. Semiempirical linear relationships were observed between biota-sediment accumulation factors (1.18-2.47)/logarithm of bioconcentration factors (BCFs, 2.49-2.52) of 2,2'-DiBBPA in lugworms and K_d. These results allow for the prediction of the bioaccumulation of 2,2'-DiBBPA in other soils. Furthermore, values of log BCF > 1.0 indicate the preferential bioaccumulation of 2,2'-DiBBPA in biota. These data are of significance for understanding the migration of 2,2'-DiBBPA in agricultural soils and bioaccumulation in organisms.

Activation persulfate for efficient tetrabromobisphenol A degradation via carbon-based materials: Synergistic mechanism of doped N and Fe

In this study, a novel carbon-based material (Fe-N-PGWBC) utilizing the garden waste, melamine and FeSO₄ as the precursor was successfully synthesized, efficiently activating peroxydisulfate (PDS) to degrade tetrabromobisphenol A (TBBPA). Under typical conditions (Fe-N-PGWBC dose of 100 mg·L^-1, PDS of 0.2 mM and TBBPA of 10 mg·L^-1), Fe-N-PGWBC/PDS system could achieve over 99% TBBPA removal (including adsorption and degradation) within 60 min, and the corresponding rate constant k_s was 0.0724 min^-1, which was almost 40.2 times higher than that of the pristine biochar. The extraction experiments implied that the excellent adsorption performance of Fe-N-PGWBC did not hinder the degradation of TBBPA. Abundant active sites (rich oxygen-containing functional groups, Fe-O and Fe₃C) of Fe-N-PGWBC could effectively promote PDS decomposition to produce reactive oxygen species. The probe-based kinetic modelling methods verified that approximately 87.6% TBBPA was degraded by SO₄^·-, 12.2% TBBPA was degraded by ¹O₂, and 0.2% TBBPA was degraded by ^·OH. Furthermore, based on the calculation of density functional theory and identification of products, TBBPA was mainly involved in three transformation pathways including hydroxylation, debromination and β-scission process. The study proposed a facile resource approach of garden waste and provided deeper understanding for the TBBPA degradation mechanisms in heterogeneous system.

Effect of Cu2+ on the Laccase-Inducted Formation of Non-Extractable Residues of Tetrabromobisphenol A in Humic Acids

We used ¹⁴ C-radiolabelling to study the non-extractable residues (NERs) formation of tetrabromobisphenol A (TBBPA) in a humic acid (HA) suspension under catalysis of laccase in the presence of copper. When entering the suspension after TBBPA adsorbing to HA supramolecular associates, Cu²⁺ at low concentrations (even without toxicity to laccase) significantly reduced the amount and first-order kinetic constant of the NER formation, while Cu²⁺ had no significant effect on the formation after it was complexed with HA. The inhibition effect of Cu²⁺ on the NER formation is explained to be attributed to the prevention of laccase-induced oxidation of TBBPA in the voids of HA associates by complexation of Cu²⁺ with periphery molecules of the associates. The results provide insights into varying effects of heavy metals on the environmental fate of organic contaminants and suggest that co-existing heavy metals could increase their environmental risk by reducing their NER formation.

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.

Rapid debromination of tetrabromobisphenol A by Cu/Fe bimetallic nanoparticles in water, its mechanisms, and genotoxicity after treatments

Tetrabromobisphenol A (TBBPA), a widely used brominated flame retardants, has been detected in various environmental matrices and is known to cause various adverse effects on human bodies. This study examined the feasibility and effectiveness of remediating TBBPA using Cu/Fe bimetallic nanoparticles (Cu/Fe BNPs) at various environmental and operational conditions. In general, TBBPA removal rate and debromination efficiency increased with higher Cu doping, higher Cu/Fe BNPs loading, higher temperature, and lower pH. At optimal conditions, TBBPA was completed removed at a rate constant > 0.2 min^-1 where over 90% TBBPA was transformed to BPA within 30 min. The activation energy was found to be 35.6 kJ/mol, indicating that TBBPA was predominantly removed via surface-controlled reactions. Under pH 3-7 and ≥ 25 °C, debromination was the dominant removal mechanism compared to adsorption. The complete debromination pathway and the time-evolution of intermediates byproducts at different pHs were also presented. Cu/Fe BNPs can be reused for more than 6 times with performance constancy. Genotoxic tests showed that the treated solution did not find a significant hazardous potential. The byproducts can be further degraded by additional H₂O₂ through Fenton reaction. These results demonstrated the efficacy of Cu/Fe BNPs for treating TBBPA and its potential for degrading other halogenated organic compounds.

The fate of erythromycin in soils and its effect on soil microbial community structure

Erythromycin is one of the most commonly used macrolide antibiotics. However, little is known currently about the environmental behavior and fate of erythromycin in soils. Here erythromycin was ¹⁴C-labeled to investigate its degradation, mineralization and bound residues (BRs) in three typical agricultural soils. Results indicated the fate of ¹⁴C-erythromycin in soils varied greatly with soils types. Erythromycin was rapidly mineralized in black soil (BS) and fluvo-aquic soil (FS), whereas it rapidly formed large amounts of BRs in red soil (RS) with slow mineralization. At 120 d, about 90% of the introduced ¹⁴C-erythromycin was mineralized as ¹⁴CO₂ in BS and FS, but only 30% in RS. There was still a certain proportion of BRs in all soils, especially in RS, up to 50%. Erythromycin residues (ERs) may be underestimated if its residues are only assessed by extractable residues. We recommend to include a practical silylation procedure to quantify Type I BRs in regular erythromycin residue monitoring, which can be used as signal of the need to initiate further laboratory BRs experiments. The degradation of erythromycin was mainly attributed to soil microorganisms, which promote erythromycin mineralization and lead to the re-release of BRs. Microbial analysis showed that erythromycin persisted longer in soils with lower microbial diversity and richness. Erythromycin at 2.5 mg kg^-1 showed no significant impact on soil microbial diversity in all treatments, but caused changes in soil community composition. This study provides a reference for scientific evaluation and pollution remediation of erythromycin in soils.

Review of the environmental occurrence, analytical techniques, degradation and toxicity of TBBPA and its derivatives

BFRs (brominated flame retardants) are a class of compounds that are added to or applied to polymeric materials to avoid or reduce the spread of fire. Tetrabromobisphenol A (TBBPA) is one of the known BFR used many in industries today. Due to its wide application as an additive flame retardant in commodities, TBBPA has become a common indoor contaminant. Recent researches have raised concerns about the possible hazardous effect of exposure to TBBPA and its derivatives in humans and wildlife. This review gives a thorough assessment of the literature on TBBPA and its derivatives, as well as environmental levels and human exposure. Several analytical techniques/methods have been developed for sensitive and accurate analysis of TBBPA and its derivatives in different compartments. These chemicals have been detected in practically every environmental compartment globally, making them a ubiquitous pollutant. TBBPA may be subject to adsorption, biological degradation or photolysis, photolysis after being released into the environment. Treatment of TBBPA-containing waste, as well as manufacturing and usage regulations, can limit the release of these chemicals to the environment and the health hazards associated with its exposure. Several methods have been successfully employed for the treatment of TBBPA including but not limited to adsorption, ozonation, oxidation and anaerobic degradation. Previous studies have shown that TBBPA and its derivative cause a lot of toxic effects. Diet and dust ingestion and have been identified as the main routes of TBBPA exposure in the general population, according to human exposure studies. Toddlers are more vulnerable than adults to be exposed to indoor dust through inadvertent ingestion. Furthermore, TBBP-A exposure can occur during pregnancy and through breast milk. This review will go a long way in closing up the knowledge gap on the silent and over ignored deadly effects of TBBPA and its derivatives and their attendant consequences.

Polystyrene Nanoplastics Inhibit the Transformation of Tetrabromobisphenol A by the Bacterium Rhodococcus jostii

Microplastics (MPs) and nanoplastics (NPs) in the environment pose significant risks to organisms of different trophic levels. While the toxicity of MPs and NPs have been extensively investigated, it remains unknown whether these particles affect microbial transformation of organic pollutants. Here, we show that 20 and 100 nm polystyrene NPs (PS-NPs) can inhibit the transformation of tetrabromobisphenol A (TBBPA) by Gram-positive bacterium Rhodococcus jostii in a concentration-dependent manner. We found that smaller PS-NPs were more inhibitory than larger ones and that both PS-NPs affected biotransformation in several ways. PS-NPs adsorbed TBBPA on their surface and reduced the bioavailable concentration of TBBPA for transformation by R. jostii. Furthermore, PS-NPs induced oxidative stress, increased membrane permeability, and downregulated O-methyltransferase enzymes that transform TBBPA into their methylated derivatives. Our results demonstrate that PS-NPs can impact microbial transformation of organic pollutants, and these effects should be accounted for in future environmental risk assessments.

Reducing environmental risks of chlorpyrifos application in typical soils by adding appropriate exogenous organic matter: Evidence from a simulated paddy field experiment

Chlorpyrifos (CPF), as an organophosphate insecticide extensively used in the modern agricultural system, has been gradually banned in many countries due to its reported health risks to organisms, including humans. This study used simulated paddy field experiments and carbon-14 tracing to explore the possibility of reducing environmental risks of chlorpyrifos application through appropriate agronomic practice. Results showed ¹⁴C-CPF concentration in rice plants planted in the red soil (RS) was significantly higher than that in black soil (BS) and fluvo-aquic soil (FS). The application of biochar and chicken manure in RS reduced ¹⁴C-CPF accumulation in rice plants, and the content of ¹⁴C-CPF in rice grains decreased by 25% and 50%, respectively. Adding biochar to all three soils reduced the migration of ¹⁴C-CPF, especially in FS with the highest risk of ¹⁴C-CPF migration. The addition of chicken manure in FS reduced the migration of ¹⁴C-CPF and the total residual amount of ¹⁴C-CPF in the soil. In addition, chicken manure treatment increased the formation of ¹⁴C-bound residues (BRs) in soils and changed the distribution ¹⁴C-BRs in humus. The results indicated that the degree of environmental risks associated with the CPF application varies with soil types and could be reduced by introducing suitable exogenous organic matter into different soils, which is of great significance for guiding the scientific application of chlorpyrifos in agronomic practices.

Effects of polycyclic aromatic hydrocarbon structure on PAH mineralization and toxicity to soil microorganisms after oxidative bioremediation by laccase

While bioremediation using soil microorganisms is considered an energy-efficient and eco-friendly approach to treat polycyclic aromatic hydrocarbon (PAH)-contaminated soils, a variety of polar PAH metabolites, particularly oxygenated ones, could increase the toxicity of the soil after biodegradation. In this study, a typical bio-oxidative transformation of PAH into quinones was investigated in soil amended with laccase using three PAHs with different structures (anthracene, benzo[a]anthracene, and benzo[a]pyrene) to assess the toxicity after oxidative bioremediation. The results show that during a 2-month incubation period the oxidation process promoted the formation of non-extractable residues (NERs) of PAHs, and different effects on mineralization were observed among the three PAHs. Oxidation enhanced the mineralization of the high-molecular-weight (HMW) PAHs (benzo[a]anthracene and benzo[a]pyrene) but inhibited the mineralization of the low-molecular-weight (LMW) PAH (anthracene). The inhibition of anthracene suggests increased toxicity after oxidative bioremediation, which coincided with a decrease in soil nitrification activity, bacterial diversity and PAH-ring hydroxylating dioxygenase gene copies. The analysis of PAH metabolites in soil extract indicated that oxidation by laccase was competitive with the natural transformation processes of PAHs and revealed that intermediates other than quinone metabolites increased the toxicity of soil during subsequent degradation. The different metabolic profiles of the three PAHs indicated that the toxicity of soil after PAH oxidation by laccase was strongly affected by the PAH structure. Despite the potential increase in toxicity, the results suggest that oxidative bioremediation is still an eco-friendly method for the treatment of HMW PAHs since the intermediates from HMW PAHs are more easily detoxified via NER formation than LMW PAHs.

Degradation of Adsorbed Bisphenol A by Soluble Mn(III)

Bisphenol A (BPA), a high production volume chemical and potential endocrine disruptor, is found to be associated with sediments and soils due to its hydrophobicity (log K_OW of 3.42). We used superfine powdered activated carbon (SPAC) with a particle size of 1.38 ± 0.03 μm as a BPA sorbent and assessed degradation of BPA by oxidized manganese (Mn) species. SPAC strongly sorbed BPA, and desorption required organic solvents. No degradation of adsorbed BPA (278.7 ± 0.6 mg BPA g^-1 SPAC) was observed with synthetic, solid α-MnO₂ with a particle size of 15.41 ± 1.35 μm; however, 89% mass reduction occurred following the addition of 0.5 mM soluble Mn(III). Small-angle neutron scattering data suggested that both adsorption and degradation of BPA occurred in SPAC pores. The findings demonstrate that Mn(III) mediates oxidative transformation of dissolved and adsorbed BPA, the latter observation challenging the paradigm that contaminant desorption and diffusion out of pore structures are required steps for degradation. Soluble Mn(III) is abundant near oxic-anoxic interfaces, and the observation that adsorbed BPA is susceptible to degradation has implications for predicting, and possibly managing, the fate and longevity of BPA in environmental systems.

Reducing the Environmental Risk of Chlorpyrifos Application through Appropriate Agricultural Management: Evidence from Carbon-14 Tracking

Chlorpyrifos (CPF) is one of the most critical insecticides in the world. However, many countries are gradually banning its use due to its reported hazardous impacts on humans. This study explored the possibility of reducing the environmental risk of CPF through appropriate agricultural management practices. Results showed that the environmental risk of CPF is lower under drainage conditions because there is more mineralization and less bound residues (BRs) than under submerged conditions. Bioaugmentation significantly enhanced the CPF mineralization and inhibited the formation of CPF-BRs. Biochar adsorbed CPF and thus reduced its bioavailability, but it could not completely eliminate the toxicity of CPF. In addition, bioaugmentation did not significantly affect the native microbial community of CPF-contaminated soil, suggesting its safety in reducing the environmental risk of CPF. The study indicated that the environmental risk of CPF could be reduced by appropriate agricultural management such as water management, bioaugmentation, soil biochar amendment, and selecting suitable soil types.

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.

Long-Term Field Study on Fate, Transformation, and Vertical Transport of Tetrabromobisphenol A in Soil-Plant Systems

Soil contamination with tetrabromobisphenol A (TBBPA) has been an environmental concern for many years, but in situ studies of the fate and potential risk of TBBPA are lacking. In this study, we investigated the dissipation, metabolism, strong alkali-hydrolytic (SAH-TBBPA), and vertical movement of TBBPA in the field with and without rice-wheat rotation and reed growth for 1225 days. After 342 days of incubation, 21.3% of the TBBPA remained in the surface soil accompanied by obvious leaching to deeper soil layers in the first 92 days. By day 1225, TBBPA was nearly absent from the surface soil layer. A very low amount of SAH-TBBPA (2.31-3.43 mg/kg) was detected during the first 342 days of incubation. In the surface soil, five metabolites were identified that represented four interconnected pathways: oxidative skeletal cleavage, O-methylation, type II ipso-substitution, and reductive debromination. Both rice-wheat rotation and monocultural reed growth accelerated TBBPA removal in the field by stimulating the anaerobic debromination and aerobic O-methylation, especially the oxidative skeletal cleavage of TBBPA in the rhizosphere soil. Though far from comprehensive, our study investigated the natural attenuation and metabolism of TBBPA in situ and the influence by crops to estimate the environmental risk of TBBPA in a field scale.

Fate characterization of bound residues of 14C-Pyraoxystrobin in soils

Formation of bound residues (BR) has generally been considered as a detoxification process for organic contaminants. BR is an indispensable component for risk assessment of pesticides. In this study, BR of ¹⁴C-pyraoxystrobin in three soils cultivated for 100 days were characterized in light fraction (LF), loosely combined humus (LCH), stably combined humus (SCH), humic acid (HA), fulvic acid (FA), and humin. Isotope labeling technique was used to detect the distribution of BR of ¹⁴C-pyraoxystrobin in the six fractions of soil organic matter (SOM). The results showed that the amount of total BR was positively correlated with the SOM content (p < 0.05). The BR of ¹⁴C-pyraoxystrobin in cambisol soil was largest at 31.26 ± 0.04% of the induced radioactivity. During the whole incubation period, the BR of pyraoxystrobin in LCH of the three soils were consistently higher than that in SCH, and the amount of BR in FA was consistently greater than that in HA. The BR of ¹⁴C-pyraoxystrobin bound with humin increased over time. In addition, a degradation product 3-(4-chlorophenyl)-1-methyl-1H-pyrazol-5-ol (M1) from the hydrolysis of pyraoxystrobin was detected in cambisol soil, indicating the bonding of M1 with the HA separated from LCH (HA_LCH) via ester or ether linkages. The results provide new insights into the fate of BR of pyraoxystrobin in soils and may help to develop an understanding for the risk assessment of pyraoxystrobin and other strobilurin fungicides.

Coupling-oxidation process promoted ring-opening degradation of 2-mecapto-5-methyl-1,3,4-thiadizaole in wastewater

As an important raw material and intermediate of widely used antibiotics cefazolin and cefazedone, 2-mecapto-5-methyl-1,3,4-thiadizaole (MMTD) in antibiotic wastewater is hardly decyclized during wastewater treatment, posing great risk to the environment. This work proposed a green "coupling-oxidation" process to enhance ring-opening of MMTD during antibiotic wastewater treatment. In particular, the significant role of humic substances (HS) as pre-coupling reagent was emphasized. Real HS and different model HS, especially quinones, not only efficiently pre-coupled MMTD (>95%) but also promoted the MMTD removal by MnO₂ (from 72.4% to 92.4%). Mass spectrometric analysis indicated that MMTD pre-coupled to HS would be oxidized with ring opening to environmental-friendly sulfonated HS, while direct oxidation of MMTD produced MMTD dimers or sulfonated MMTD that would not undergo ring opening. Theoretical calculations indicated that pre-coupling to HS enabled the ring-opening oxidation by increasing the nucleophilicity and decreasing ring-opening barrier of thiadiazole. Based on the density function theory (DFT), the global nucleophilicity index (Nu) followed the trend of HS-MMTD > MMTD dimer > sulfonated MMTD, while the ring-opening barrier followed the trend of HS-MMTD (274 kJ/mol) < first ring of MMTD dimers (286 kJ/mol) < MMTD (338 kJ/mol). Theoretical calculations further confirmed that the cross-coupled HS-MMTD intermediate was more likely to be decyclized than intermediates from direct oxidation. Moreover, nitrogen, acetaldehyde group, sulfate and CO₂ were the products of thiadiazole ring degradation. Pre-coupling of MMTD with HS provides a new idea and strategy in developing a green and sustainable scheme for wastewater treatment.

Synthesis and Toxicity of Halogenated Bisphenol Monosubstituted-Ethers: Establishing a Library for Potential Environmental Transformation Products of Emerging Contaminant

As an important branch of halogenated bisphenol compounds, the halogenated bisphenol monosubstituted-ether compounds have received a lot of attention in environmental health science because of their toxicity and variability. In this study, a synthetic method for bisphenol monosubstituted-ether byproduct libraries was developed. By using the versatile and efficient method, tetrachlorobisphenol A, tetrabromobisphenol A, and tetrabromobisphenol S monosubstituted alkyl-ether compounds were accessed in 39-82 % yield. Subsequently, the cytotoxicity of 27 compounds were screened using three different cell lines (HepG2, mouse primary astrocytes and Chang liver cells). Compound 2,6-dibromo-4-[3,5-dibromo-4-(2-hydroxyethoxy)benzene-1-sulfonyl]phenol was more toxic than other compounds in various cells, and the sensitivity of this compound to the normal hepatocytes and cancer cells was inconsistent. The compounds 2,6-dichloro-4-(2-{3,5-dichloro-4-[(prop-2-en-1-yl)oxy]phenyl}propan-2-yl)phenol and 2,6-dibromo-4-(2-{3,5-dibromo-4-[(prop-2-en-1-yl)oxy]phenyl}propan-2-yl)phenol were the most toxic to HepG2 cells, and most of the other compounds inhibited cell proliferation. Moreover, typical compounds were also reproductive and developmental toxic to zebrafish embryos at different concentrations. The synthetic byproduct libraries could be used as pure standard compounds and applied in research on environmental behavior and the transformation of halogenated flame retardants.

Fate of bisphenol S (BPS) and characterization of non-extractable residues in soil: Insights into persistence of BPS

The environmental fate and persistence of bisphenol S (BPS), a substitute for bisphenol A (BPA), are unclear. This study used ¹⁴C-labeled BPS to examine the fate, biodegradation, and residue properties of BPS incubated in an oxic soil for 28 days. BPS dissipated quickly, with a half-life of 2.8 days. Most of the BPS was mineralized (53.6 ± 0.2% of initial amount by day 28) or transformed into non-extractable residues (NERs) (45.1 ± 0.3%), with generation of minor extractable residues (3.7 ± 0.2%) containing two metabolites. NERs were formed mainly via physico-chemical entrapment (51.1 ± 2.4% of the total NERs, consisting almost exclusively of BPS) and ester-linkages (31.5 ± 3.0% of the total NERs, consisting of both BPS and polar metabolites). When mixed with fresh soil, BPS-derived NERs became unstable and bioavailable. Subsequent mineralization was determined for 19.5 ± 1.1% of the total NERs and 35.5 ± 2.6% of the physico-chemically entrapped BPS. A fate model was used to describe the kinetics of NER formation, which indicated that microbial activity in soil could have strongly reduced the kinetic rate of the release of physico-chemically entrapped NERs into free form and therefore increased the stability of this type of NERs in soil. Our results provide unique insights into the fate of BPS in soil and suggest that while BPS is biodegradable, it includes the formation of large amounts of reversibly physico-chemically entrapped and covalently bound ester-linked NERs. The instability of these NERs should be considered in assessments on environmental persistence and risks of BPS. Our study also points out the environmental importance of NERs of agrochemicals.

Fate of lower-brominated diphenyl ethers (LBDEs) in a red soil - Application of 14C-labelling

Lower-brominated diphenyl ethers (LBDEs) occur ubiquitously in soil, however their fate there has not been well evaluated, mainly owing to that the unavailability of commercial radioactively labelled LBDE congeners hampers the investigation on fate of LBDEs in the environment with complex matrixes, such as soil and sediment. Here, we successfully synthesized three congeners of LBDEs, i.e., 4-bromodiphenyl ether (BDE3), 4,4'-dibromodiphenyl ether (BDE15), and 2,2',4,4'-tetrabromodiphenyl ether (BDE47), with ¹⁴C-labelling on one aromatic ring, starting from commercially available ¹⁴C-labelled phenol in two steps with high yields and high radiochemical purities. Using the ¹⁴C-labelled congeners, we studied the fate of LBDEs in a red soil under oxic conditions, where LBDEs have been frequently detected in high levels. The major fate of the LBDE congeners in the soil was formation of NERs, followed by mineralization to CO₂, while no transformation product was detected in the soil after incubation for 105 days. The mineralization strongly decreased with increasing number of the bromine atom on the congener molecule, amounting to 10.4 ± 0.3%, 2.45 ± 0.04%, and 0.51 ± 0.05% for BDE3, BDE15, and BDE47, respectively, at the end of incubation, while mineralization rate constant was independent of the molecular structure, suggesting that solubility of LBDEs is the limit factor for their persistence in soil. The mineralization was positively linearly correlated with the formation of NERs (22.5 ± 1.9%, 11.0 ± 3.6%, and 6.7 ± 2.7% for BDE3, BDE15, and BDE47, respectively), which was mainly located in humin fraction and formed also in sterilized soil, suggesting a binding of transformation intermediates to soil humic substances and a physico-chemical entrapment of LBDEs in soil. The results provide new insights into fate of LBDE congeners in soil, and suggest a need to elucidate nature of the NERs of LBDEs, especially the stability of NERs in the environment.

Fate of 4-bromodiphenyl ether (BDE3) in soil and the effects of co-existed copper

The quantitative fate of polybrominated diphenyl ethers (PBDEs) in soil is unknown. Furthermore, the effects of co-contamination by toxic copper on the behavior of PBDEs have not been investigated. Using a ¹⁴C-tracer, we studied mineralization, metabolism, and formation of non-extractable residues (NERs) of one PBDE congener, i.e., the 4-bromodiphenyl ether (BDE3) in oxic soil for 50 days, without and with amendment of Cu (400 mg kg^-1 soil dw). BDE3 rapidly dissipated with a half-life of 5.5 days and large amounts of CO₂ (38.8 ± 0.3% of initial applied amount at the end of incubation) and NERs (42.5 ± 0.4%) were rapidly produced. One hydroxylated metabolite (4'-HO-BDE3) was formed (8.1 ± 0.6%) at the beginning of the incubation, but then decreased to 2.2 ± 0.4%. Only BDE3 occurred in physico-chemically entrapped NERs, amounting to 9.2 ± 0.7%, while only 4'-HO-BDE3 in ester-linked NERs (10.9 ± 0.7%). The addition of Cu strongly reduced the kinetics constants of the transformations (including dissipation, mineralization, and NER-formation), the predicted maximal amounts of mineralization, as well as covalent binding of 4'-HO-BDE3 to soil. The results provide first quantitative insights into the fate of low-brominated congeners of PBDEs in soil and indicate that co-contamination by Cu may increase the environmental risks of biodegradable PBDEs in soil by increasing their persistence.

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.

Bioaccumulation, physiological distribution, and biotransformation of tetrabromobisphenol a (TBBPA) in the geophagous earthworm Metaphire guillelmi - hint for detoxification strategy

The mechanisms underlying the bioaccumulation and detoxification of tetrabromobisphenol A (TBBPA) by terrestrial invertebrates are poorly understood. We used uniformly ring-¹⁴C-labelled TBBPA to investigate the bioaccumulation kinetics, metabolites distribution, and subsequent detoxification strategy of TBBPA in the geophagous earthworm Metaphire guillelmi in soil. The modeling of bioaccumulation kinetics showed a higher biota-soil-accumulation-factor of total ¹⁴C than that of the parent compound TBBPA, indicating that most of the ingested TBBPA was transformed into metabolites or sequestered as bound residues in the earthworms. Bound-residue formation in the digestive tract may hinder the accumulation of TBBPA in other parts of the body. Nonetheless, via the circulatory system, TBBPA was transferred to other tissues, especially the clitellum region, where sensitive organs are located. In the clitellum region, TBBPA was quickly transformed to less toxic dimethyl TBBPA ether and rapidly depurated through feces. We conclude that the detoxification of TBBPA in M. guillelmi occurred via bound-residue formation in the digestive tract as well as the generation and depuration of O-methylation metabolites. Our results provided direct evidence of TBBPA detoxification in earthworms. Further researches are needed to confirm whether O-methylation coupled with depuration is a common detoxification strategy for phenolic xenobiotics in other soil organisms needs to be determined.

The bioaccumulation, elimination, and trophic transfer of BDE-47 in the aquatic food chain of Chlorella pyrenoidosa-Daphnia magna

As a persistent organic pollutant, 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) has been widely detected in aquatic environments. However, studies on the fate and transfer of BDE-47 in the aquatic food chain remain scarce. In this study, we investigated the bioaccumulation and elimination of BDE-47 in Chlorella pyrenoidosa, as well as the trophic transfer and biomagnification of BDE-47 in the "C. pyrenoidosa-Daphnia magna" food chain, using C-14 radioactive tracer technology. After 96 h of BDE-47 exposure, the algae accumulated 88.98% ± 0.59% of the initial radioactivity from the medium, and 36.09% ± 9.22% of the accumulated residues in the algae occurred in the form of bound residues. During 96 h of elimination, only 13% ± 0.50% of accumulated radioactivity in the algae was released into the medium. After 24 h of exposure, D. magna accumulated 35.99% ± 2.55% of the initial radioactivity via water filtration from the medium, and 31.35% ± 1.92% of the accumulated radioactivity in D. magna occurred as bound residues. However, D. magna accumulated 66.89% ± 2.37% of the accumulated radioactivity in the algae via food uptake from the contaminated algae, with a high portion of radioactivity observed as bound residues (83.40% ± 0.97% of accumulated radioactivity in D. magna). This indicated a reduction in the environmental risk of BDE-47. There was obvious biomagnification in the food chain between C. pyrenoidosa and D. magna (biomagnification factors, BMFs>1), resulting in environmental hazard transfer in the aquatic food chain. However, no metabolite was found during the exposure experiment, and further studies should be carried out to investigate the intrinsic mechanisms of the trophic transfer of BDE-47, especially in multilevel food chains. Therefore, this study elucidated the effect of dietary uptake on the bioaccumulation of BDE-47 in D. magna and provided new insight for future analysis regarding the bioaccumulation and biomagnification of organic pollutants in the food chain.

Molecular insights into the formation and remobilization potential of nonextractable anthropogenic organohalogens in heterogeneous environmental matrices

Anthropogenic organohalogens (AOHs) are toxic and persistent pollutants that occur ubiquitously in the environment. An unneglectable portion of them can convert into nonextractable residues (NER) in the natural solid substances. NER-AOHs are not detectable by conventional solvent-extraction, and will get remobilized through changes of surrounding environment. Consequently, the formation and fate of NER-AOHs should be investigated comprehensively. In this study, solvent extraction, sequential chemical degradation and thermochemolysis were applied on different sample matrices (sediments, soils and groundwater sludge, collected from industrial areas) to release extractable and nonextractable AOHs. Covalent linkages were observed most favorable for the hydrophilic-group-containing monocyclic aromatic AOHs (HiMcAr-AOHs) (e.g. halogenated phenols, benzoic acids and anilines) incorporating into the natural organic matter (NOM) as NER. Physical entrapment mainly contributed to the NER formation of hydrophobic monocyclic aromatic AOHs (HoMcAr-AOHs) and polycyclic aromatic AOHs (PcAr-AOHs). The hypothesized remobilization potential of these NER-AOHs follow the order HiMcAr-AOHs > HoMcAr-AOHs/ aliphatic AOHs > PcAr-AOHs. In addition, the NOM macromolecular structures of the studied samples were analyzed. Based on the derived results, a conceptual model of the formation mechanisms of NER-AOHs is proposed. This model provides basic molecular insights that are of high value for risk assessment and remediation of AOHs.

Purification, molecular characterization and metabolic mechanism of an aerobic tetrabromobisphenol A dehalogenase, a key enzyme of halorespiration in Ochrobactrum sp. T

Due to the detoxification of tetrabromobisphenol A (TBBPA) varies from different bacterial strains and depends on their specific enzymatic machinery, it is necessary to understand them for potential in situ bioremediation application. The special ability of our previously isolated Ochrobactrum sp. T to simultaneously debrominate and aerobic mineralize TBBPA urgent us to continuously study its degradation molecular mechanism. Herein, the purification and characterization of the dehalogenase which can debrominate TBBPA was investigated based on its corresponding encoding gene tbbpaA. Results showed that an enzyme with molecular mass of 117 kDa, K_m of 26.6 μM and V_max of 0.133 μM min^-1 mg^-1 was purified and designated as bromophenol dehalogenase. It was the only detected dehalogenase which exhibited TBBPA degradation ability (78%). Moreover, its activity was significantly enhanced by adding NADPH or methyl viologen to the reaction solution. The high similarity of substrate spectrum between the dehalogenase from the recombinant strain and the wild strain further indicated that it was the main dehalogenase responsible for the debromination in wild strain. Based on three identified metabolites, a metabolic pathway of TBBPA by purified enzyme under oxic condition was proposed. This study provides an excellent dehalogenase candidate for mechanistic study of aerobic dehalogenation of brominated aromatic compound.

Polymerization of micropollutants in natural aquatic environments: A review

Micropollutants with high ecotoxicological risks are frequently detected in aquatic environments, which has aroused great concern in recent years. Humification is one of the most important natural detoxification processes of aquatic micropollutants, and the core reactions of this process are polymerization and coupling. During humification, micropollutants are incorporated into the macrostructures of humic substances and precipitated from aqueous systems into sediments. However, the similarities and differences among the polymerization/coupling pathways of micropollutants in different oxidative systems have not been systematically summarized in a review. This article reviews the current knowledge on the weak oxidation-induced spontaneous polymerization/coupling transformation of micropollutants. First, four typical weak oxidative conditions for the initiation of micropollutant polymerization reactions in aquatic environments are compared: enzymatic catalysis, biomimetic catalysis, metal oxide oxidation, and photo-initiated oxidation. Second, three major subsequent spontaneous transformation pathways of micropollutants are elucidated: radical polymerization, nucleophilic addition/substitution and cyclization. Different solution conditions are also summarized. Furthermore, the importance of toxicity evolution during the weak oxidation-induced coupling/polymerization of micropollutants is particularly emphasized. This review provides a new perspective for the transformation mechanism and pathways of micropollutants from aquatic systems into sediments and the atmosphere and offers theoretical support for developing micropollutant control technologies.

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

Tetrabromobisphenol A (TBBPA) forms large amount of non-extractable residues (NER) in soil. However, the stability of TBBPA-NER with TBBPA degrader in soil had not been determined. In this study, a ¹⁴C-tracer was used to follow the release and alteration of TBBPA-derived NER during 214 days of incubation in oxic soil and in the presence or absence of the TBBPA-degrading bacterium Ochrobatrum sp. strain T. In the absence of strain T, 1.89% of the TBBPA and its metabolites were slowly released from the NER, with TBBPA as the predominant component, accompanied by 2.47% mineralization by day 91 of the incubation. The addition of active cells strongly stimulated the release and mineralization of NER (10.93% and 4.64%, respectively), reduced the amount of the ester-linked fraction, and transformed NER from humin-bound to HA-bound forms. Cells added to the soil in sterilized form had much smaller effects on the stability and internal alterations of NER. Among the ester-linked compounds, 47.4% consisted of TBBPA; two metabolites were so detected. These results provide new information on the stability and internal transformation of TBBPA-NER in soil during its long-term incubation and underlines the importance of microbial TBBPA degraders in determining the composition of NER in soil.

Tetrabromobisphenol A (TBBPA) inhibits denitrification via regulating carbon metabolism to decrease electron donation and bacterial population

The potential risks of brominated flame retardants (BFRs) like tetrabromobisphenol A (TBBPA) have attracted much attention. However, the influence of TBBPA on functional microbes remains poorly understood, especially with regards to denitrification, which is closely related with the carbon and nitrogen cycles, eutrophication and greenhouse gas emission. Herein, we found that 1.0 mg/L of TBBPA significantly decreased the total nitrogen removal efficiency by 81.7%, but increased the accumulation of NO₂^--N (by 81.5%) and N₂O (by 172-fold). This was found to be underlie by the significant decrease in both the denitrifying capability of denitrifiers and total bacterial population. Further investigation revealed that TBBPA inhibited the pathways of glucolysis and pentose phosphate, and promoted glyoxylate bypass via regulating genes expressions of key enzymes (such as glucose-6-phosphate isomerase, pyruvate dehydrogenase, isocitrate lyase, etc.), then decreased the generation of NADH serving as electron donor for denitrification, and inhibited the denitrifying capability of denitrifiers. Moreover, insufficient NADH stimulated the accumulation of denitrifying intermediates (NO₂^--N and N₂O), which induced the increase of reactive nitrogen species (RNS), whose accumulation decreased proliferation and increased apoptosis of denitrifying bacteria. Finally, the decrease in the denitrifying capability of denitrifier and bacterial population resulted in negative denitrifying performance.

Effects of hydrodynamic disturbances on biodegradation of tetrabromobisphenol A in water-sediment systems

Tetrabromobisphenol A (TBBPA) is an emerging contaminant and exists widely in river and lake systems due to its widespread use. In natural water-sediment systems, hydrodynamic disturbances always exist. However, few studies have investigated the mechanism of TBBPA biodegradation under the influence of water disturbances. In this paper, using a specialized type of racetrack-style flumes, the TBBPA biodegradation in water-sediment systems was studied under the influence of three typical hydrodynamic disturbances. The results of 5-week experiments showed that strong hydrodynamic disturbances greatly accelerate the TBBPA biodegradation rate of the water-sediment systems. The half-lives (T_1/2) under static condition (SC) were approximately 40.2 days, and the T_1/2 was reduced to 16.0 days under strong hydrodynamic condition (SHC). Furthermore, the physicochemical properties and corresponding bacterial communities under these conditions were investigated to help explain the TBBPA biodegradation mechanism. The results showed that strong currents could promote dissolved oxygen (DO) levels, increase nutrient concentrations, and reduce the bacterial diversity in the sediment. Meanwhile, due to the increase in DO and nutrient concentrations, the aerobic bacterial genera conducting TBBPA biodegradation showed rapid growth with strong water disturbances, while the growth of anaerobic bacterial genera was inhibited. Citrobacter, which was the most dominant degrading bacterial genus (0.6%-14.9% in water and 3.5%-17.4% in sediment), was closely related to water disturbances and may be linked to enhanced TBBPA biodegradation. Other minor degrading bacterial genera, such as Bacillus, Sphingomonas, Anaeromyxobacter, Geobacter, Clostridium, and Flavobacterium, were also found in these water-sediment systems. The findings from this study showed the importance of considering hydrodynamic disturbance in understanding TBBPA biodegradation in aquatic environments.

Formation, classification and identification of non-extractable residues of 14C-labelled ionic compounds in soil

The influence of an ionic functional group on the fate of chemicals in the environment, especially the formation of non-extractable residues (NER), has not been systematically investigated. Using 4-n-dodecylphenol[phenylring-¹⁴C(U)], 4-n-dodecylbenzenesulfonicacid[phenylring-¹⁴C(U)] sodiumsalt (¹⁴C-DS^-) and 4-n-dodecylbenzyltrimethylammoniumchloride[phenylring-¹⁴C(U)] (¹⁴C-DA⁺) all with a high structural similarity, the formation, classification and identification of NER of negatively (¹⁴C-DS^-), positively (¹⁴C-DA⁺) and uncharged (¹⁴C-DP) chemicals were investigated in a sterilized and non-sterilized soil. After 84 days of incubation in non-sterile soil, 40.6%, 21.7% and 33.5% of the applied radioactivity (AR) of ¹⁴C-DP, ¹⁴C-DS^- and ¹⁴C-DA⁺, respectively, were converted to NER. In contrast, in sterile soil NER formation was markedly lower. The NER were further investigated with respect to sequestered, covalently bound and biogenic residues (i.e. NER types I, II, and III). Silylation of ¹⁴C-DP, ¹⁴C-DS^- and ¹⁴C-DA⁺ derived NER released 3.0-23.2% AR, indicating that these were sequestered, whereas the residual NER (12.9-33.1% AR) was covalently bound to the soil. Analysis of extracts derived by silylation showed that ¹⁴C-DP, but neither ¹⁴C-DS^- nor ¹⁴C-DA⁺, were released by silylation, suggesting that DP might be part of the sequestered NER. Acid hydrolysis of the NER containing soil and subsequent analysis of soil extracts for ¹⁴C-aminoacids indicated that 2.5-23.8% AR were biogenic residues. Most DP and DS^- derived NER were biogenically or covalently bound, whereas DA⁺ predominantly forms sequestered NER in soil. From these results we propose that chemicals forming high amounts of NER should be investigated regarding types I-III NER because sequestered parent compounds should be considered in persistence assessments.

Relative effects of wind-induced disturbances and vegetation on tetrabromobisphenol A cycling in shallow lakes: Direct and indirect effects

The environmental concerns regarding the possible threats of tetrabromobisphenol A (TBBPA) to aquatic environments are increasing. However, information about TBBPA cycling in the water-vegetation-sediment systems of shallow lakes is limited. In a shallow lake, wind-induced disturbance is considered as the key factor of affecting the cycling of contaminants. To address this issue, the TBBPA distribution and elimination processes were simulated for three typical wind speeds by using an annular flume. Four forms of TBBPA were studied in these systems, including water, suspended solids (SS), vegetation and sediment. The results showed that the mass distributions of TBBPA in water, SS and vegetation increased remarkably while enhancing the wind-induced disturbances, which resulted from the release of TBBPA from the sediment through resuspension and adsorption-desorption processes. However, most of the TBBPA (up to 94%) still accumulated in the sediment. Wind-induced disturbances and vegetation both increased the TBBPA elimination rate in the water-vegetation-sediment systems. The half-life (T_1/2) of TBBPA in the fast wind condition was 16.1 ± 0.2 days, which was shorter than that in the static condition (29.8 ± 0.9 days). Compared to the systems without vegetation, the presence of vegetation shortened the T_1/2 by 7.3 days in the static condition. Furthermore, a structural equation model (SEM) was used to assess the direct and indirect effects of environmental factors on the TBBPA amounts in each form. The main effects of wind speed and vegetation in the TBBPA cycling of each form (except for the TBBPA on vegetation) were indirect by affecting the dissolved oxygen (DO), velocity and suspended solids concentration (SSC). Overall, the findings provide useful information about the fate of TBBPA and other related organic contaminants in shallow lake systems.

Effects of veterinary antibiotics on the fate and persistence of 17β-estradiol in swine manure

The fate and persistence of natural estrogens from livestock manure and the interactions of these compounds with veterinary antibiotics (VAs) have not been well studied. We therefore employed ¹⁴C-labeling to explore the mineralization, degradation, and residual distribution of 17β-estradiol (E2) in swine manure in the absence and presence of six categories of VAs at concentrations of 10 and 100 mg/kg. After 16 days of incubation, 94% of the E2 dissipated, of which 28% was mineralized to ¹⁴CO₂, 18% was transformed into organic-extractable E1 (9%) and other unknown metabolites (9%), and 48% into non-extractable residues (NER). VAs inhibited, enhanced or had no effect on E2 mineralization or its degradation to E1 and other metabolites. Principal component analysis showed that the overall effect of VAs was not necessarily related to their physicochemical properties or concentrations. However, high doses of macrolides inhibited E2 mineralization in manure and increased the retention of E2 and its metabolites in both free and NER forms. Our study demonstrates that considerable amounts of E2 and NER are retained in manure, despite nearly complete mineralization. Thus, VAs administered to livestock may increase the persistence of natural estrogens in manure and, accordingly, the environmental risks posed by these compounds.

Aerobic cometabolism of tetrabromobisphenol A by marine bacterial consortia

The coastal environments worldwide are subjected to increasing TBBPA contamination, but current knowledge on aerobic biodegradability of this compound by marine microbes is lacking. The aerobic removal of TBBPA using marine consortia under eight different cometabolic conditions was investigated here. Results showed that the composition and diversity of the TBBPA-degrading consortia had diverged after 120-day incubation. Pseudoalteromonas, Alteromonas, Glaciecola, Thalassomonas, and Limnobacter were the dominant genera in enrichment cultures. Furthermore, a combination of beef extract- and peptone-enriched marine consortia exhibited higher TBBPA removal efficiency (approximately 60%) than the other substrate amendments. Additionally, Alteromonas macleodii strain GCW was isolated from a culture of TBBPA-degrading consortium. This strain exhibited about 90% of degradation efficiency toward TBBPA (10 mg L^-1) after 10 days of incubation under aerobic cometabolic conditions. The intermediates in the degradation of TBBPA by A. macleodii strain GCW were analyzed and the degradation pathways were proposed, involving β-scission, debromination, and nitration routes.

Species-dependent effects of earthworms on the fates and bioavailability of tetrabromobisphenol A and cadmium coexisted in soils

The activity of e-waste recycling often causes the combined pollution of tetrabromobisphenol A (TBBPA) and cadmium (Cd) in soils. In this study, the effects of their co-existence on each other's fate, further reflecting the bioavailability, were analyzed in the presence of two ecologically different earthworm species, endogeic Metaphire guillelmi and epigeic Eisenia fetida. Mineralization of ¹⁴C-TBBPA combined with 10 mg Cd kg^-1 was suppressed by the presence of M. guillelmi, whereas a facilitating effect was produced by the combination of 1 mg Cd kg^-1 in the soil-E. fetida system after a 14-day exposure. The uptake of ¹⁴C-TBBPA by M. guillelmi (17% of initial amount) and by E. fetida (10%) dominantly contributed to significant (P < 0.05) decrease of extractable (more bioavailable) ¹⁴C residues in soils both with and without Cd spiked, while the mineralization of ¹⁴C-TBBPA in the soils was negligible (<0.4%). Meanwhile the amendments of the two earthworm species exerted different impact on ¹⁴C distribution in bound residues. In general, co-exposure to Cd did not significantly (P > 0.05) influence the accumulation and metabolism of TBBPA in the earthworms. Both earthworms accumulated only ~7% of Cd in soil, however, the bioavailable Cd determined by the diffusive gradients in thin films technique declined by ~46% in the presence of M. guillelmi, and a much smaller decrease was determined in the presence of E. fetida. Amendment of TBBPA at environmental levels did not alter the accumulation and subcellular distribution of Cd in both earthworms unless that at high doses. The results highlighted the importance of considering the difference of the earthworm species and the interaction of pollutants in soil-risk assessments of such combined contamination. CAPSULE: M. guillelmi displayed greater effect on the fate of TBBPA and Cd co-existed in soils than E. fetida, while the accumulation, metabolism, or distribution of the two pollutants in earthworms did not significantly alter due to interactions between the two pollutants.