Phytoextraction and biodegradation of atrazine by Myriophyllum spicatum and evaluation of bacterial communities involved in atrazine degradation in lake sediment

Iron-doped bismuth oxybromides as visible-light-responsive Fenton catalysts for the degradation of atrazine in aqueous phases

Pesticides and its degradation products, being well-known residues in soil, have recently been detected in many water bodies as pollutants of emerging concerns, and thus there is a contemporary demand to develop viable and cost-effective techniques for the removal of related organic pollutants in aqueous phases. Herein, a visible-light-responsive Fenton system was constructed with iron-doped bismuth oxybromides (Fe-BiOBr) as the catalysts. Taking the advantage of sustainable Fe(III)/Fe(II) conversion and optimized H2O2 utilization, the optimal Fe-BiOBr-2 catalyst showed an excellent atrazine removal efficiency of 97.61% in 120 min, which is superior than the traditional homogeneous Fenton and the majority of heterogeneous processes documented in the literature. In this photo-Fenton system, hydroxyl (·OH) and superoxide (·O2-) radicals were dominant active species contributed to the oxidative degradation of atrazine. Due to the production of various active radicals, five degradation pathways were proposed based on the identification of intermediates and degradation products. Overall, this work not only demonstrates a fundamental insight into creating highly efficient and atom economic photo-Fenton systems, but also provides a complementary strategy for the treatment of organic pollutants in water.

Degradation of atrazine by electro-peroxone enhanced by Fe and N co-doped carbon nanotubes with simultaneous catalysis of H2O2 and O3

Fe and N co-doped carbon nanotubes (Fe-N-CNT) was synthesized and attempted as efficient heterogeneous catalysts for simultaneous catalysis of H2O2 and O3 to improve electro-peroxone (Fe-N-CNT/EP) process efficiency for atrazine (ATZ) degradation. The removal and mineralization of ATZ was significantly enhanced, obtaining the degradation rate constant (k) by Fe-N-CNT/EP (0.23 min-1) about two times that of EP (0.12 min-1) owing to the formation of Fe0 and Fe-N coordination in Fe-N-CNT catalyst for co-catalysis of H2O2 and O3. The important factors such as applied current and ozone concentration were investigated, demonstrating that the optimized performance could be achieved at current of 30 mA and ozone concentration of 55 mg L-1. The oxidation capacity of Fe-N-CNT/EP maintained stably under wide pH range of 3∼7, obtaining the degradation rate constant 1.23-1.92 times that of EP and overcoming the defect of EP at acidic and neutral conditions. Capture experiments and electron paramagnetic resonance (EPR) experiments verified that .OH, generated by accelerating decomposition of H2O2/O3 and peroxone reaction, was the dominant active specie in Fe-N-CNT/EP. Besides, Fe-N-CNT showed high catalytic activity and good stability during six cycles. This work provides an efficient activator for enhanced EP process, exhibiting a promising prospect for water and wastewater purification.

Changes of atrazine dissipation and microbial community under coexistence of graphene oxide in river water

The coexistence of herbicide atrazine (ATZ) and the nanomaterial graphene oxide (GO) in natural water bodies will be an inevitable scenario due to their widespread application and consequent release into aquatic ecosystems. But the dissipation of ATZ with GO and the response of the microbial community to their combination are still not clear. Here, we investigated the dissipation dynamics and transformation of ATZ with and without GO in river water after 21-d incubation. In the presence of GO, ATZ residue significantly decreased by 11%-43%; the transformation of ATZ markedly increased by 11%-17% when ATZ concentrations were not above 1.0 mg∙L-1. The direct adsorption of ATZ on GO, mainly via π-π interactions, proton transfer and hydrogen bonding, contributed 54%-68% of the total increased ATZ dissipation by GO. ATZ and ATZ+GO exerted effects of similar magnitude on microbial OTU numbers with an increase of bacterial diversity. The coexisting GO increased the relative abundance of ATZ-degradation bacteria and Chitinophagales, thus improving ATZ transformation. This work indicated that the coexistence of GO at environmentally relevant concentrations can effectively reduce ATZ residues and promote the transformation of ATZ to degradation products in river water; nevertheless, the potential risk of GO acting as an ATZ carrier should be given more prominence.

Microbiology and Biochemistry of Pesticides Biodegradation

Pesticides are chemicals used in agriculture, forestry, and, to some extent, public health. As effective as they can be, due to the limited biodegradability and toxicity of some of them, they can also have negative environmental and health impacts. Pesticide biodegradation is important because it can help mitigate the negative effects of pesticides. Many types of microorganisms, including bacteria, fungi, and algae, can degrade pesticides; microorganisms are able to bioremediate pesticides using diverse metabolic pathways where enzymatic degradation plays a crucial role in achieving chemical transformation of the pesticides. The growing concern about the environmental and health impacts of pesticides is pushing the industry of these products to develop more sustainable alternatives, such as high biodegradable chemicals. The degradative properties of microorganisms could be fully exploited using the advances in genetic engineering and biotechnology, paving the way for more effective bioremediation strategies, new technologies, and novel applications. The purpose of the current review is to discuss the microorganisms that have demonstrated their capacity to degrade pesticides and those categorized by the World Health Organization as important for the impact they may have on human health. A comprehensive list of microorganisms is presented, and some metabolic pathways and enzymes for pesticide degradation and the genetics behind this process are discussed. Due to the high number of microorganisms known to be capable of degrading pesticides and the low number of metabolic pathways that are fully described for this purpose, more research must be conducted in this field, and more enzymes and genes are yet to be discovered with the possibility of finding more efficient metabolic pathways for pesticide biodegradation.

Investigation of the Persistence, Toxicological Effects, and Ecological Issues of S-Triazine Herbicides and Their Biodegradation Using Emerging Technologies: A Review

S-triazines are a group of herbicides that are extensively applied to control broadleaf weeds and grasses in agricultural production. They are mainly taken up through plant roots and are transformed by xylem tissues throughout the plant system. They are highly persistent and have a long half-life in the environment. Due to imprudent use, their toxic residues have enormously increased in the last few years and are frequently detected in food commodities, which causes chronic diseases in humans and mammals. However, for the safety of the environment and the diversity of living organisms, the removal of s-triazine herbicides has received widespread attention. In this review, the degradation of s-triazine herbicides and their intermediates by indigenous microbial species, genes, enzymes, plants, and nanoparticles are systematically investigated. The hydrolytic degradation of substituents on the s-triazine ring is catalyzed by enzymes from the amidohydrolase superfamily and yields cyanuric acid as an intermediate. Cyanuric acid is further metabolized into ammonia and carbon dioxide. Microbial-free cells efficiently degrade s-triazine herbicides in laboratory as well as field trials. Additionally, the combinatorial approach of nanomaterials with indigenous microbes has vast potential and considered sustainable for removing toxic residues in the agroecosystem. Due to their smaller size and unique properties, they are equally distributed in sediments, soil, water bodies, and even small crevices. Finally, this paper highlights the implementation of bioinformatics and molecular tools, which provide a myriad of new methods to monitor the biodegradation of s-triazine herbicides and help to identify the diverse number of microbial communities that actively participate in the biodegradation process.

Characterization and novel pathway of atrazine catabolism by Agrobacterium rhizogenes AT13 and its potential for environmental bioremediation

Agrobacterium rhizogenes AT13, a novel bacterial strain that was isolated from contaminated soil, could utilize atrazine as the sole nitrogen, thereby degrading it. Optimization of the degradation reaction using a Box-Behnken design resulted in 99.94% atrazine degradation at pH 8.57, with an inoculum size of 3.10 × 10⁹ CFU/mL and a concentration of 50 mg/L atrazine. Ultra-high performance liquid chromatography-electrospray ionization-high resolution mass spectrometry (UPLC-ESI-HRMS), liquid chromatography tandem mass spectrometry (LC-MS/MS) and high performance liquid chromatography (HPLC) analyses identified and quantified six reported metabolites and a novel metabolite (2-hydroxypropazine) from atrazine degradation by AT13. On the basis of these metabolites, we propose an atrazine degradation pathway that includes dichlorination, hydroxylation, deamination, dealkylation and methylation reactions. The toxicity of the degradation products was evaluated by Toxicity Estimation Software Tool (T.E.S.T). Bioaugmentation of atrazine-polluted soils/water with strain AT13 significantly improved the atrazine removal rate. Thus, AT13 has potential applications in bioremediation.

Degradation of atrazine in river sediment by dielectric barrier discharge plasma (DBDP) combined with a persulfate (PS) oxidation system: response surface methodology, degradation mechanisms, and pathways

Single degradation systems based on dielectric barrier discharge plasma (DBDP) or persulfate (PS) oxidation cannot achieve the desired goals (high degradation efficiency, high mineralization rate, and low product toxicity) of degrading atrazine (ATZ) in river sediment. In this study, DBDP was combined with a PS oxidation system (DBDP/PS synergistic system) to degrade ATZ in river sediment. A Box-Behnken design (BBD) including five factors (discharge voltage, air flow, initial concentration, oxidizer dose, and activator dose) and three levels (- 1, 0, and 1) was established to test a mathematical model by response surface methodology (RSM). The results confirmed that the degradation efficiency of ATZ in river sediment was 96.5% in the DBDP/PS synergistic system after 10 min of degradation. The experimental total organic carbon (TOC) removal efficiency results indicated that 85.3% of ATZ is mineralized into CO₂, H₂O, and NH₄⁺, which effectively reduces the possible biological toxicity of the intermediate products. Active species (sulfate (SO₄•^-), hydroxy (•OH), and superoxide (•O₂^-) radicals) were found to exert positive effects in the DBDP/PS synergistic system and illustrated the degradation mechanism of ATZ. The ATZ degradation pathway, composed of 7 main intermediates, was clarified by Fourier transform infrared spectroscopy (FTIR) and gas chromatography-mass spectrometry (GC-MS). This study indicates that the DBDP/PS synergistic system is a highly efficient, environmentally friendly, novel method for the remediation of river sediment containing ATZ pollution.

Enhanced phytoremediation of atrazine-contaminated soil by vetiver (Chrysopogon zizanioides L.) and associated bacteria

The intensive and long-term use of atrazine (ATZ) has led to the contamination of agricultural soils and non-target organisms, posing a series of threats to human health through the transmission of the food chain. In this study, a 60-day greenhouse pot experiment was carried out to explore the phytoremediation by Chrysopogon zizanioides L. (vetiver). The uptake, accumulation, distribution, and removal of ATZ were investigated, and the degradation mechanisms were elucidated. The results showed that the growth of vetiver was inhibited in the first 10 days of the incubation; subsequently, the plant recovered rapidly with time going. Vetiver grass was capable of taking up ATZ from the soil, with root concentration factor ranging from 2.36 to 15.55, and translocating to the shoots, with shoot concentration factor ranging from 7.51 to 17.52. The dissipation of ATZ in the rhizosphere soil (97.51%) was significantly higher than that in the vetiver-unplanted soil (85.14%) at day 60. Metabolites were identified as hydroxyatrazine (HA), deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA) in the samples of the shoots and roots of vetiver as well as the soils treated with ATZ. HA, DEA, DIA, and DDA were reported first time as metabolites of ATZ in shoots and roots of vetiver grown in soil. The presence of vetiver changed the formation and distribution of the dealkylated products in the rhizosphere soil, which remarkably enhanced the occurrence of DEA, DIA, and DDA. Arthrobacter, Bradyrhizobium, Nocardioides, and Rhodococcus were the major atrazine-degrading bacterial genera, which might be responsible for ATZ degradation in the rhizosphere soil. Our findings suggested that vetiver grass can significantly promote ATZ degradation in the soil, and it could be a strategy for remediation of the atrazine-contaminated agricultural soil.

Real-Time Monitoring of the Atrazine Degradation by Liquid Chromatography and High-Resolution Mass Spectrometry: Effect of Fenton Process and Ultrasound Treatment

High resolution mass spectrometry (HRMS) was coupled with ultra-high-performance liquid chromatography (uHPLC) to monitor atrazine (ATZ) degradation process of Fenton/ultrasound (US) treatment in real time. Samples were automatically taken through a peristaltic pump, and then analysed by HPLC-HRMS. The injection in the mass spectrometer was performed every 4 min for 2 h. ATZ and its degradation metabolites were sampled and identified. Online Fenton experiments in different equivalents of Fenton reagents, online US experiments with/without Fe²⁺ and offline Fenton experiments were conducted. Higher equivalents of Fenton reagents promoted the degradation rate of ATZ and the generation of the late-products such as Ammeline (AM). Besides, adding Fe²⁺ accelerated ATZ degradation in US treatment. In offline Fenton, the degradation rate of ATZ was higher than that of online Fenton, suggesting the offline samples were still reacting in the vial. The online analysis precisely controls the effect of reagents over time through automatic sampling and rapid detection, which greatly improves the measurement accuracy. The experimental set up proposed here both prevents the degradation of potentially unstable metabolites and provides a good way to track each metabolite.

Toxicological effects, environmental behaviors and remediation technologies of herbicide atrazine in soil and sediment: A comprehensive review

Atrazine has become one of the most popular applied triazine herbicides in the world due to its high herbicidal efficiency and low price. With its large-dosage and long-term use on a global scale, atrazine can cause widespread and persistent contamination of soil and sediment. This review systematically evaluates the toxicological effects, environmental risks, environmental behaviors (adsorption, transport and transformation, and bioaccumulation) of atrazine, and the remediation technologies of atrazine-contaminated soil and sediment. For the adsorption behavior of atrazine on soil and sediment, the organic matter content plays an extremely important role in the adsorption process. Various models and equations such as the multi-media fugacity model and solute transport model are used to analyze the migration and transformation process of atrazine in soil and sediment. It is worth noting that certain transformation products of atrazine in the environment even have stronger toxicity and mobility than its parent. Among various remediation technologies, the combination of microbial remediation and phytoremediation for atrazine-contaminated soil and sediment has wide application prospects. Although other remediation technologies such as advanced oxidation processes (AOPs) can also efficiently remove atrazine from soil, some potential problems still need to be further clarified. Finally, some related challenges and prospects are proposed.

Degradation of Residual Herbicide Atrazine in Agri-Food and Washing Water

Atrazine, an herbicide used to control grassy and broadleaf weed, has become an essential part of agricultural crop protection tools. It is widely sprayed on corn, sorghum and sugar cane, with the attendant problems of its residues in agri-food and washing water. If ingested into humans, this residual atrazine can cause reproductive harm, developmental toxicity and carcinogenicity. It is therefore important to find clean and economical degradation processes for atrazine. In recent years, many physical, chemical and biological methods have been proposed to remove atrazine from the aquatic environment. This review introduces the research works of atrazine degradation in aqueous solutions by method classification. These methods are then compared by their advantages, disadvantages, and different degradation pathways of atrazine. Moreover, the existing toxicological experimental data for atrazine and its metabolites are summarized. Finally, the review concludes with directions for future research and major challenges to be addressed.

Removal of atrazine from submerged soil using vetiver grass (Chrysopogon zizanioides L.)

The long-term widespread application of atrazine poses significant threats to the eco-environment and human health. To investigate the potential of vetiver (Chrysopogon zizanioides L.) for phytoremediation of the environmental media contaminated by atrazine, an indoor incubation experiment was conducted in submerged soil over 30 days. Results showed that the chlorophyll level of the vetiver was not significantly affected by exposure to atrazine. Vetiver could take up and accumulate atrazine from submerged soil and peaked around the 20th day with a concentration of 1.0 mg kg^-1 in leaf. The metabolites Hydroxyatrazine (HA), deethylatrazine (DEA), Deisopropylatrazine (DIA), and didealkylatrazine (DDA) were detected in the leaf on the 30th day, indicating vetiver could degrade atrazine inside the leaf tissue. The atrazine removal rate in the vetiver planted and unplanted jars were 69.72 and 60.29%, respectively, indicating that 9.43% higher atrazine removal was achieved in the presence of vetiver (p < 0.05). The atrazine dissipation in the submerged soil followed first-order kinetics, the degradation constant was 0.066, and the half-life of atrazine dissipation was shortened by 6.86 days in the presence of vetiver. The present study suggests that vetiver can take up atrazine from submerged soil and accumulate in the leaf, which could then degrade in the leaf.Novelty statement: Although the fate of atrazine in agricultural soils has been extensively investigated through various experiments, little is known about the effect of vetiver grass on atrazine dissipation from submerged soil. With the identification of soil-leaf transportation and four metabolites in vetiver leaf and soils, significantly accelerated atrazine dissipation from the submerged soil was achieved in the presence of vetiver. Particularly, the formation of less toxic dealkylated products in the leaf indicated vetiver is a promising grass for atrazine removal from submerged soil.

Land use and roles of soil bacterial community in the dissipation of atrazine

Atrazine (ATZ) is one of the most widely used herbicides in the world even though it is classified as a carcinogenic endocrine disruptor. This study focused on how land use (grazing versus cultivation in parallel soils, the latter under no-till with a seven-year history of ATZ application) and bacterial community diversity affected ATZ dissipation. Proteobacteria, Bacteroidetes, Firmicutes, Actinobacteria, Acidobacteria, Verrucomicrobia, Planctomycetes, and Gemmatimonadetes were the dominant phyla in both soils. The mineralization of ATZ was much higher in soils under cultivation up to the onset of moderate diversity depletion (dilution =10^-3), corresponding to 44-52% of the amount applied (< 5% in the grazed soil). This was attributed to the higher diversity and complexity of the soils´ bacterial communities which consist of microbial groups that were more adapted as a result of previous exposure to ATZ. In these cases, ATZ dissipation was attributed mainly to mineralization (DT₅₀ = 4-11 d). However, formation of non-extractable ATZ residues was exceptionally important in the other cases (DT₅₀ = 17-44 d). The cultivated soils also presented a higher number of bacterial genera correlated with ATZ dissipation, in which Acidothermus, Aquicela, Arenimonas, Candidatus_Koribacter, Hirschia, MND1, Nitrospira, Occallatibacter, OM27_clade, and Ralstonia are suggested as potential ATZ-degraders. Finally, ATZ dissipation was mostly associated with an abundance of microbial functions related to energy supply and N-metabolism, suggesting co-metabolism is its first biodegradation step.

Impacts of earthworm casts on atrazine catabolism and bacterial community structure in laterite soil

Atrazine accumulation in agricultural soil is prone to cause serious environmental problems and pose risks to human health. Vermicomposting is an eco-friendly approach to accelerating atrazine biodegradation, but the roles of earthworm cast in the accelerated atrazine removal remains unclear. This work aimed to investigate the roles of earthworm cast in promoting atrazine degradation performance by comprehensively exploring the change in atrazine metabolites and bacterial communities. Our results showed that earthworm cast amendment significantly increased soil pH, organic matters, humic acid, fulvic acid and humin, and achieved a significantly higher atrazine removal efficiency. Earthworm cast addition also remarkably changed soil microbial communities by enriching potential soil atrazine degraders (Pseudomonadaceae, Streptomycetaceae, and Thermomonosporaceae) and introducing cast microbial degraders (Saccharimonadaceae). Particularly, earthworm casts increased the production of metabolites deethylatrazine and deisopropylatrazine, but not hydroxyatrazine. Some bacterial taxa (Gaiellaceaea and Micromonosporaceae) and humus (humic acid, fulvic acid and humin) were strongly correlated with atrazine metabolism into deisopropylatrazine and deethylatrazine, whereas hydroxyatrazine production was benefited by higher pH. Our findings verified the accelerated atrazine degradation with earthworm cast supplement, providing new insights into the influential factors on atrazine bioremediation in vermicomposting.

Occurrence and spatial-temporal distribution of atrazine and its metabolites in the aquatic environment of the Volturno River estuary, southern Italy

The present study assesses the spatial distribution and temporal trends of the water dissolved phase (WDP), suspended particulate matter (SPM) and sediment partitioning of atrazine (ATR) and its metabolites in the Volturno River estuary. The load contribution of ATR and its metabolites in this river to the Central Mediterranean Sea was estimated. Samples were collected in 10 sampling sites during the four seasons. The total concentrations of ATR and DPs detected ranged from 18.1 to 105.5 ng L^-1 in WDP, from 4.5 to 63.2 ng L^-1 in SPM, and from 4.6 to 18.6 ng g^-1 in sediment samples, indicating high levels of these pollutants. Structural equation model and the ratio study indicated that the relationship between sediment and WDP pollutants occurred through the SPM. The pollutants load at the Volturno River in its mouth was evaluated in about 30.4 kg year^-1, showing that this river is an important source of these analytes through discharge into Central Mediterranean Sea. Principal component analysis indicated that ATR and its metabolites pollution moves from Volturno River mouth southward and increased in the rainy season. The desethylatrazine-to-atrazine ratio was higher than 0.5 for all samples analyzed, indicating an historical discharge and a long residence time of ATR in sediment about two decades after its ban, and classifying ATR as a nonpoint source contaminant. This study makes up the first record of ATR and its metabolites in superficial water of Southern Italy and provides helpful data as starting point for future studies.

Atrazine uptake, translocation, bioaccumulation and biodegradation in cattail (Typha latifolia) as a function of exposure time

The extensive use and environmental persistence of atrazine has resulted in its ubiquitous occurrence in water resources. Some reports have described atrazine bioaccumulation and biodegradation pathways in terrestrial plants, but few have done so in aquatic macrophytes. Thus, in this study, we aimed to analyze morphological changes, uptake, translocation and bioaccumulation patterns in tissues of the aquatic macrophyte Typha latifolia (cattail) after long-term atrazine exposure and to determine the presence of atrazine biodegradation metabolites, desethylatrazine (DEA) and desisopropylatrazine (DIA), in tissues. Plants were hydroponically exposed to 20 μg/L atrazine (18 exposed and 18 non-exposed) for 7, 14, 21, 28, 35 and 42 days. Plants were separated into root, rhizome, stem, and lower, middle and upper leaf sections. Atrazine was analyzed by LC-MS/MS and DIA and DEA by LC-DAD. Plants showed reductions in weight (after 21 days) and transpiration (after 28 days), both symptoms of chronic phytotoxicity. The distribution of atrazine within tissues, expressed as concentration levels (μg/kg dry weight), was as follows: middle leaf (406.10 ± 71.77) = upper leaf (339.15 ± 47.60) = lower leaf (262.43 ± 7.66) = sprout (274.53 ± 58.1) > stem (38.63 ± 7.55) = root (36.00 ± 3.49) = rhizome (26.15 ± 3.96). In submerged tissues, DEA and DIA were detected at similar concentrations. In leaves, DIA was the main metabolite identified. Results indicated that atrazine was taken up from roots to shoots and induced phytotoxicity effects that reduced the translocation to shoots. Typha likely is able to biodegrade atrazine via different metabolic pathways.

Degradation of Diuron by a Bacterial Mixture and Shifts in the Bacterial Community During Bioremediation of Contaminated Soil

Diuron, a phenylurea herbicide, has been extensively applied in controlling a wide range of weeds in several crops. In the current study, a mixed culture of three bacterial strains, i.e., Bacillus subtilis DU1, Acinetobacter baumannii DU, and Pseudomonas sp. DUK, isolated from sugarcane soil, completely degraded diuron and 3,4-DCA in liquid media at 20 mg L^-1 within 48 h. During diuron degradation, a few metabolites (DCPMU, DCPU, and 3,4-DCA) were produced. Further determination of ring-cleavage pathways demonstrated that Acinetobacter baumannii DU and Pseudomonas fluorescens DUK degraded diuron and 3,4-DCA via ortho-cleavage. In contrast, Bacillus subtilis DU transformed these compounds via meta-cleavage pathways. Moreover, diuron caused a significant shift in the bacterial community in soil without diuron history. The augmentation of mountain soil with the isolated bacteria resulted in nearly three times higher degradation rate of diuron than the degradation by indigenous microorganisms. This study provides important information on in situ diuron bioremediation from contaminated sites by bioaugmentation with a mixed bacterial culture.

Anaerobic Degradation of Propanil in Soil and Sediment Using Mixed Bacterial Culture

The widespread use of the herbicide, propanil, causes severe environmental problems. In this study, the effects of propanil on the bacterial community in a sediment slurry were determined. Moreover, the degradation of the herbicide by pure and mixed cultures was first conducted under anaerobic conditions. The results showed that propanil caused significant changes in the bacterial community under anaerobic conditions. Four bacterial strains, i.e., Geobacter sp. Pr-1, Paracoccus denitrificans Pr-2, Pseudomonas sp. Pr-3, and Rhodococcus sp. Pr-4, isolated from the an enrichment sediment slurry were the first pure cultures that degraded propanil and 3,4-dichloroaniline (3,4-DCA) under anaerobic conditions. Some individual isolates showed the slow degradation of propanil and 3,4-DCA, but the mixture of the four strains increased the degradation rates of both compounds. The mixed culture of these isolates transformed more than 90% of propanil within 10 days in liquid media with the amendment of dextrose, glucose, or acetate. The determination of degradation pathway showed that propanil was transformed to 3,4-DCA and some other products before degrading completely. This study provides valuable information on the effects of propanil on the bacterial community and the synergistic degradation of propanil under anaerobic conditions.

Transcriptomic profiling of atrazine phytotoxicity and comparative study of atrazine uptake, movement, and metabolism in Potamogeton crispus and Myriophyllum spicatum

The accumulation of atrazine in sediments raises wide concern due to its potential negative effects on aquatic environments. Here we collected sediments and different submerged macrophytes to simulate natural shallow lakes and to measure atrazine levels and submerged macrophyte biomass. We determined gene expressions in submerged macrophytes treated with or without atrazine. We also examined atrazine concentrations and its metabolite structures in submerged macrophytes. When the initial concentration of atrazine in sediments ranged from 0.1 to 2.0 mg kg^-1 dry weight (DW), atrazine levels in the pore water of the sediments ranged from 0.003 to 0.05 mg L^-1 in 90 days. Atrazine did not show obvious long-term effects on the biomass of Potamogeton crispus and Myriophyllum spicatum (P > 0.05). On day 90, gene expressions related to cell wall in P. crispus were changed by atrazine phytotoxicity. Moreover, the decrease in the number genes controlling light-harvesting chlorophyll a/b-binding proteins verified the toxic effects of atrazine on the photosynthesis of M. spicatum. Compared with unexposed plants on day 90, ribosome pathway was significantly enriched with differentially expressed genes after submerged macrophytes were exposed to 2.0 mg kg^-1 DW atrazine (P < 0.05). In addition, shoots and roots of P. crispus and M. spicatum could absorb the equal amount of atrazine (P > 0.05). Once absorbed by submerged macrophytes, atrazine was degraded into 1-hydroxyisopropylatrazine, hydroxyatrazine, deethylatrazine, didealkylatrazine, cyanuric acid, and biuret, and some of its metabolites could conjugate with organic acids, cysteinyl β-alanine, and glucose. This study establishes a foundation for aquatic ecological risk assessments and the phytoremediation of atrazine in sediments.

Aquaculture-derived distribution, partitioning, migration, and transformation of atrazine and its metabolites in seawater, sediment, and organisms from a typical semi-closed mariculture bay

Atrazine (ATR) is one of the most commonly used herbicides that could directly impair the growth and health of organisms in mariculture areas and adversely affect human health through the food chain. This study investigated the contaminant occurrence, migration, and transformation of ATR and three of its chlorinated metabolites, namely deethylatrazine (DEA), deisopropylatrazine (DIA), and didealkylatrazine (DDA), in surface seawater, sediment, and aquatic organisms from the Xiangshan Harbor. ATR was detected in all samples, while DIA and DDA were only respectively detected in aquatic and seawater samples. The distribution of ATR and its metabolites presented different patterns depending on the geographic location and showed a higher level in the aquaculture area than that in the non-aquaculture area. The bioaccumulation of ATR in aquaculture organisms showed that benthic organisms, such as Ditrema, and Sinonovacula constricta (Sin), had increased levels. The ecological risks indicated that ATR posed medium or high risks to algae in the water phase of the study area. The microcosm experiment showed that the main fate of ATR in the simulated microenvironment was sedimentation, which followed the first-order kinetic equation. The ATR in the sediment could be enriched 3-5 times in Sin, and its major metabolites were DEA and DIA.

FeS2 assisted degradation of atrazine by bentonite-supported nZVI coupling with hydrogen peroxide process in water: Performance and mechanism

In this study, bentonite-supported nZVI (B-nZVI) was used as a catalyst to activate H₂O₂ for atrazine (ATZ) degradation in the presence of FeS₂. Results indicated that ATZ degradation by B-nZVI/H₂O₂ process was significantly enhanced when FeS₂ was introduced, and nearly 98% of ATZ was degraded by B-nZVI/FeS₂/H₂O₂ process within 60 min under the optimum conditions. ATZ degradation of B-nZVI/FeS₂/H₂O₂ process was much higher than the sum of B-nZVI and FeS₂/H₂O₂ processes. The presence of HCO₃^-, PO₄^3- and F^- exhibited significant negative effects on the ATZ degradation, whereas both Cu²⁺ and Ni²⁺ exhibited positive effects on that. Both citric acid (CA) and ethylenediaminetetraacetic acid (EDTA) with lower concentration enhanced ATZ degradation rate, but significant suppression effects on that with higher concentration. The degradation of ATZ and 2,4-Dichlorophenol (2,4-DCP) could be simultaneously achieved in B-nZVI/FeS₂/H₂O₂ process under certain conditions. High soluble Fe²⁺ induced an excellent decomposition of H₂O₂ by B-nZVI and FeS₂. OH was dominant radical, and contributed to nearly 86% of the overall ATZ removal. A total of five intermediate products of ATZ were identified, and ATZ degradation was achieved via de-alkylation and hydroxylation processes. An enhanced reaction mechanism for ATZ degradation by B-nZVI/FeS₂/H₂O₂ process was proposed, and B-nZVI/FeS₂/H₂O₂ process exhibited an excellect catalytic performance within four successive runs.

Rapid uptake of atrazine from aqueous phase by thermally activated MCM-41

This study was designed to prepare an adsorbent without any complex modification process for the removal of atrazine (AZN) from aqueous phase. Thus, Mobil composition of matter No. 41 (MCM-41) was synthesized and modified by physical activation at high temperature (650 °C). The synthesized adsorbent was tested by XRD, SEM, EDX, FT-IR and BET to confirm the successful synthesis as well as effectiveness for the adsorption of AZN. The average particle size of prepared material was found to be about 500 nm, while the BET calculations showed that adsorbent was porous with a specific surface area of 25.9 m²/g. Later, it was used in batch removal studies of AZN for which, it showed a high adsorption capacity of 89.99 (mg/g). The pH of 6, temperature of 313 K was found to be the optimized conditions for the maximum removal of AZN. Of the four kinetic models studied, the pseudo-first-order yielded a superior fit in comparison with the other three models. The results indicated that the five linearized adsorption equilibrium isotherm models (Langmuir, Freundlich, Dubinin-Radushkevich, Temkin and Harkins-Jura models) closely correlate the AZN adsorption removal process with Pearson correlation coefficient (R²) values of 0.9955, 0.8551, 0.8736, 0.8913 and 0.7253, respectively. The energy functions obtained by thermodynamic analysis suggested that the AZN sorption follows a non-spontaneous and endothermic path.

Impact of Bacillus on Phthalides Accumulation in Angelica sinensis (Oliv.) by Stoichiometry and Microbial Diversity Analysis

Plant-microorganism interaction in the rhizosphere is thought to play an important role in the formation of soil fertility, transformation and absorption of nutrients, growth and development of medicinal plants, and accumulation of medicinal ingredients. Yet, the role that they play in the phthalides accumulation of Angelica sinensis (Oliv.) Diels remains unclear. In the present study, we report a correlative analysis between rhizosphere microorganisms and phthalides accumulation in A. sinensis from Gansu, China where was the major production areas. Meanwhile, Bacillus was explored the potential functions in the plant growth and phthalide accumulation. Results revealed that the common bacterial species detected in six samples comprised 1150 OTUs which were involved in 368 genera, and predominant taxa include Actinobacteria, Acidobacteria, and Proteobacteria. The average contents of the six phthalides were 4.0329 mg/g. The correlation analysis indicated that 20 high abundance strains showed positive or negative correlations with phthalides accumulation. Flavobacterium, Nitrospira, Gaiella, Bradyrhizobium, Mycobacterium, Bacillus, RB41, Blastococcus, Nocardioides, and Solirubrobacter may be the key strains that affect phthalides accumulation on the genus level. By the plant-bacterial co-culture and fermentation, Bacillus which were isolated from rhizosphere soils can promote the plant growth, biomass accumulation and increased the contents of the butylidenephthalide (36∼415%) while the ligustilide (12∼67%) was decreased. Altogether, there is an interaction between rhizosphere microorganisms and phthalides accumulation in A. sinensis, Bacillus could promote butylidenephthalide accumulation while inhibiting ligustilide accumulation.

Advanced biodegradation process of atrazine in the peroxidase-mediated sequencing batch reactor (SBR) and moving-bed SBR (MSBR): mineralization and detoxification

The advanced biodegradation process of atrazine was stimulated with hydrogen peroxide (H₂O₂) in a sequencing batch reactor (SBR) under different operational conditions due to in situ generation of H₂O₂-peroxidase. The complete biodegradation and mineralization of 50 mg/L atrazine was achieved in the SBR with a biomass concentration of 328 mg/L stimulated with 10 mM of H₂O₂. The presence of H₂O₂ in the SBR induced the generation of H₂O₂-peroxidase resulted in acceleration of atrazine biodegradation. Adding moving media to the SBR system and converting it to the MSBR considerably improved the rate of atrazine biodegradation and mineralization under H₂O₂ mediation. The highest specific utilization rate of atrazine in the SBR operated at the biomass concentration of 55 mg/L was 19.4 mg/g_biomass.h, while it was 33.5 mg/g_biomass.h in the MSBR operated at the biomass concentration of 37 mg/L. The low ATZ removal along with no peroxidase activity in the bioreactor in absence of H₂O₂ clearly ideated that the biodegradation and mineralization of ATZ was considerably mediated by H₂O₂-peroxidase enzyme. The toxicity of atrazine solution decreased markedly when treated in the MSBR under optimum conditions. Accordingly, the MSBR stimulated with H₂O₂ is an efficient and thus promising process for biodegradation of recalcitrant compounds.

Changes in rhizobacterial community mediating atrazine dissipation by arbuscular mycorrhiza

Although it was well known that arbuscular mycorrhizal fungus (AMF) inoculation significantly increased atrazine dissipation in the soil, the effect of AMF on bacterial community, especially potential atrazine-degrading bacteria mediating atrazine dissipation has been overlooked. In the present study, there were four different treatments: Funnelliformis mosseae inoculation with or without atrazine; and non-AMF inoculation with or without atrazine. F. mosseae significantly increased atrazine dissipation rate from 28.7% to 53.3%. Then 16S rRNA gene sequencing results indicated that bacteria community differed significantly by F. mosseae inoculation and atrazine addition. The Shannon index decreased significantly with AMF and atrazine at phylum and family level, and significant inhibition of atrazine on evenness was also observed. LEFSe analysis revealed that Terrimonas and Arthrobacter were significantly associated with F. mosseae, as well as unidentified_Nitrospiraceae associated with atrazine addition. There are several bacterial taxa associated with both F. mosseae inoculation and atrazine addition. Totally, twelve atrazine-degrading bacterial genera (>0.10%) were identified. When atrazine was added, the abundance of Arthrobacter, Burkholderia, Mycobacterium and Streptomyces increased in F. mosseae inoculation treatment, but Nocardioides, Pseudomonas, Bradyrhizobium, Rhizobium, Rhodobacter, Methylobacterium, Bosea and Shinella decreased. In the presence of atrazine, activities of dehydrogenase, urease, acid and alkaline phosphatase in F. mosseae inoculation treatment were significantly higher than those in non-inoculation. However, there was no significant relationship between bacterial community and any soil enzyme activity in four treatments. Our findings reveal the potential relationship between soil bacterial community and AMF inoculation during atrazine dissipation.

Fate of atrazine and its relationship with environmental factors in distinctly different lake sediments associated with hydrophytes

Atrazine contamination is of great concern due to its widespread occurrence in shallow lakes. Here, the distribution and degradation of atrazine in acidic and alkaline lake systems were investigated. Meanwhile, the bacterial communities in different sediments and the effects of environmental factors on atrazine-degrading bacteria were evaluated. In the lake systems without plants, atrazine levels in sediment interstitial water reached peak concentrations on the 4th d. More than 90% of atrazine was then degraded in all sediment interstitial water by day 30. Meanwhile, the degradation rate of atrazine in alkaline sediments was faster than that in acidic sediments. Values of hydroxylated metabolites in the acidic lake sediments tended to be greater. Moreover, the amounts of Proteobacteria, Actinobacteria, Firmicute, Nitrospinae, Aminicenantes, Ignavibacteriae and Saccharibacteria in acidic Tangxunhu Lake sediments were significantly different from alkaline Honghu Lake sediments, while the amounts of Cyanobacteria and Saccharibacteria in sediments treated with atrazine were significantly greater than those in sediments without atrazine (P < 0.05). Notably, pH was the most relevant environmental factor in the quantitative variation of atrazine-degrading bacteria, including in Clostridium-sensu-stricto, Pseudomonas, Comamonas and Rhodobacter. The Mantel test results indicated that the degradation of atrazine in different sediments was mainly affected by the sediment physicochemical properties rather than by the addition of atrazine and the cultivation of hydrophytes.

Cumulative impact of long-term intensive mariculture on total and active bacterial communities in the core sediments of the Ailian Bay, North China

The exponential growth of off-shore mariculture worldwide over the last 20 years has had significant impact on coastal sediment biogeochemistry. However, there are no long-term records of the cumulative impacts of mariculture on the benthic bacterial community. Here, total (DNA) and active (RNA) bacterial community compositions were characterized using MiSeq sequencing of 16S rRNA gene in four core sediments of the Ailian Bay, one of the typical intensive mariculture areas in China with more than fifty-year history of kelp and scallop cultivation. The γ-Proteobacteria, δ-Proteobacteria, Acidobacteria and Acitinobacteria were more abundant in the total bacterial communities, while β-Proteobacteria, Anaerolineae, Clostridia, Spirochaetes and Cyanobacteria were enriched in the active bacterial communities. Significant differences were observed between total and active benthic bacterial communities. The influences of different mariculture modes on the total bacterial communities were more significant than those on the active bacterial communities. Only limited groups of the total bacterial communities were significant influenced by the cumulative effects of the long-term mariculture. The bacterial genera with the function in the sulfide cycling and organic consumption were enriched in the total bacterial population of the integrated multi-trophic aquaculture (IMTA) areas. The variations of both total and active bacterial communities were significantly influenced by grain sizes, total organic carbon and nutrients. Both total and active bacterial communities exhibited a slightly stronger response to environmental factors than to spatial (distance) factors. The effects of mutualism might dominate the total and active bacterial networks in the Ailian Bay. The present study demonstrated that the cumulative influences of the long-term and intensive IMTA mariculture on total benthic bacterial communities in the sub-surface sediments of the Ailian Bay were stronger than those on the active benthic bacterial communities, which provided some insights into the potential ecological roles of specific taxa in the sediments of the IMTA ecosystems.

Substratum-associated microbiota

This survey of 2018 literature on substratum-associated microbiota presents brief highlights on research findings from primarily freshwaters, but includes those from a variety of aquatic ecosystems. Coverage of topics associated with benthic algae and cyanobacteria, though not comprehensive, includes new methods, taxa new to science, nutrient dynamics, trophic interactions, herbicides and other pollutants, metal contaminants, nuisance, bloom-forming and harmful algae, bioassessment, and bioremediation. Coverage of bacteria, also not comprehensive, focused on methylation of mercury, metal contamination, toxins, and other environmental pollutants, including oil, as well as the use of benthic bacteria as bioindicators, in bioassessment tools and in biomonitoring. Additionally, we cover trends in recent and emerging topics on substratum-associated microbiota of relevance to the Water Environment Federation. PRACTITIONER POINTS: This review of literature from 2018 on substratum-associated microbiota presents highlights of findings on algae, cyanobacteria, and bacteria from primarily freshwaters. Topics covered that focus on algae and cyanobacteria include findings on new methods, taxa new to science, nutrient dynamics, trophic interactions, herbicides and other pollutants, metal contaminants, nuisance, bloomforming and harmful algae, bioassessment, and bioremediation. Topics covered that focus on bacteria include findings on methylation of mercury, metal contamination, toxins and other environmental pollutants, including oil, as well as the us e of benthic bacteria as bioindicators, in bioassessment tools and in biomonitoring. A brief presentation of new, noteworthy and emerging topics on substratum-associated microbiota, build on those from 2017, to highlight those of particular relevance to the Water Environment Federation.

Growth and Physiological Responses in Myriophyllum spicatum L. Exposed to Linear Alkylbenzene Sulfonate

The exogenous organic pollutant linear alkylbenzene sulfonate (LAS) is frequently detected in water. Myriophyllum spicatum L., a submerged aquatic plant, is a popular choice for phytoremediation. The present study investigated the growth and physiological responses of M. spicatum to different concentrations of LAS (0, 0.1, 0.5, 1, 10, 50, 100, and 500 mg/L) after 14 and 28 d of treatment. After 14 d, higher LAS doses (50-100 mg/L) significantly reduced the growth of M. spicatum compared with controls. Plants died at 500 mg/L LAS. Chlorophyll a and total chlorophyll contents were markedly increased at higher doses of LAS (10-100 mg/L). Significantly enhanced peroxidase (POD) activity was found at 50 mg/L of LAS, and decreased superoxide dismutase (SOD) activity at 100 mg/L of LAS; other indices showed no significant changes under LAS stress. After 28 d, no significant effect was observed on the growth of plants exposed to LAS doses of 0.1 to 100 mg/L, whereas plants died at 500 mg/L LAS. Compared with controls. SOD activity increased significantly at 0.1 mg/L LAS and maintained the same level as controls at higher concentrations. At all LAS exposures, POD activity was higher than that of controls. Other indices for M. spicatum were not remarkably changed at 28 d. Our results indicate that the oxidative damage to M. spicatum caused by LAS stress after 28 d is clearly less than such damage at 14 d. Environ Toxicol Chem 2019;38:2073-2081. © 2019 SETAC.

Development of a novel bio-organic fertilizer for the removal of atrazine in soil

The accumulation of atrazine in farmland is prone to cause phytotoxicity to kinds of sensitive crops, such as soybean. In addition, some kinds of agricultural solid wastes have long been considered as the important non-point pollution source. The aim of this experiment was to investigate the feasibility of removing atrazine from soil and alleviating the stress of atrazine on the growth of soybean by application a novel bio-organic fertilizer developed by agricultural solid wastes, such as cow manure organic fertilizer, biochar and poly-(γ-glutamic acid), as well as an atrazine-degrading strain Arthrobacter sp. DNS10. Sixteen potential bio-organic fertilizer formulations were designed by D-optimal mixture design of Design Expert software and atrazine-removal ability was selected to single out the optimal formulation. As a result, the optimal formulation of bio-organic fertilizer (named as DNBF10) was produced by the cow manure organic fertilizer 76.20%, biochar 4.46%, poly-(γ-glutamic acid) 8.63% (m/m) and the number of Arthrobacter sp. DNS10 with 0.91 × 10⁸ CFU/g. The atrazine removal percentage of DNBF10 for the atrazine in soil with the initial atrazine concentration 15.26 ± 0.49 mg/kg was 95.05% after 10 days' application with DNBF10 at the adding dosage of 5 mg/kg (relative to the dry weight of the soil). Furthermore, pot experiment results suggest that the growth of soybean seedlings in the soil (initial atrazine was 8.14 ± 0.16 mg/kg) that adding both of DNBF10 (25%) and chemical fertilizer (75%) were better than those of the treatment only adding chemical fertilizer (100%) under the same nutrient addition level. All the results indicate that the application of DNBF10 was a new alternative to reuse the typical agricultural solid wastes, as well as to reduce the harm caused by residual atrazine to soybean.