A full evaluation for the enantiomeric impacts of lactofen and its metabolites on aquatic macrophyte Lemna minor

Experiments on Pilot-Scale Constructed Floating Wetlands Efficiency in Removing Agrochemicals

The efficiency of constructed floating wetlands (CFWs) in their ability to remove agrochemicals (nutrients and pesticides) is here investigated in a series of pilot-scale systems. Four experimental CFWs were designed and constructed; three of them were planted with the aquatic plant species Lemna minor, Azolla pinnata and Eichhornia crassipes. The fourth did not contain any plants and was used as the control. The aim of the study was to evaluate the efficiency of CFW containing aquatic macrophytes in the reduction of pesticides and nutrients, under field conditions. The CFWs operated continuously from May 2021 to September 2021, and their removal efficiencies of nitrogen and phosphorus ions, and five commonly used pesticides were examined. The CFW systems were fed daily with agricultural wastewater which was prepared by mixing a fertilizer and predetermined doses of pesticides. The hydraulic residence time was kept at 14 days. Samples were collected on a weekly basis from both the influent and the effluent of each experimental tank, and were subsequently analyzed in the laboratory. HPLC-DAD and Ion Chromatography were implemented for sample analysis following a very simple sample preparation. Reductions for nutrient ranged from no reduction to 100% removal, whereas for pesticides these varied from no reduction to 98.8% removal, indicating that these systems can be used as efficient and low-cost pollution control technologies for agrochemical wastewater treatment. Significant reduction for certain pesticides was also observed in the algae control tank, thus, proving the efficiency of algae in organic pollution reduction, and recognizing the limitations of aquatic plant use in decontamination.

Aquatic ecosystem responds differently to press and pulse nutrient disturbances as revealed by a microcosm experiment

Due to climate change and increasing anthropogenic activities, lakes are disturbed frequently, usually by press (e.g., diffused pollution, rising temperatures) or pulse (e.g., storms, rainfall, pollution events) disturbances. Both press and pulse disturbances can affect abiotic and biotic environments, changing the structure of ecosystems and affecting ecosystem services. To confront with the effects of climate change and increasing anthropogenic activities, understanding the different effects of press and pulse disturbances on lake ecosystems is essential. This study assessed the effect of press and pulse disturbances of phosphorus on a microcosmic aquatic ecosystem by measuring the total phosphorus (TP), algae density, and physiological indicators of submerged macrophytes. We found that the microcosmic aquatic ecosystem responded differently to press and pulse disturbances. Our results suggested that it had a lower resistance to pulse phosphorus disturbances than to press phosphorus disturbances. There were significantly higher nutrient concentrations and algal densities in the pulse treatment than in the press treatment. Positive feedback was found between the biomass of submerged macrophytes and the water quality. There was a higher submerged macrophytes biomass at low TP concentration and algal density. In the context of climate change, press and pulse disturbances could have severe impacts on lake ecosystems. Our findings will provide some insight for further research and lake management.

Enantioselective aquatic toxicity and degradation in soil of the chiral fungicide oxathiapiprolin

Oxathiapiprolin is an efficient and chiral fungicide for peronosporomycetes. The enantioselective environmental behavior and ecotoxicity of oxathiapiprolin are still unclear. The enantioselectivity of oxathiapiprolin enantiomers was explored, including their acute toxicity toward aquatic plants (Auxenochlorella pyrenoidosa and Soirodela polyrhiza) along with their influence on photosynthetic pigment production, the acute toxicity and morphological differences for the embryos, larvae and adult stages of zebrafish (Danio rerio), and the degradation in four typical soils (aerobic, anaerobic and sterilized conditions). The enantioselective toxicity of oxathiapiprolin showed that the toxicity of R-oxathiapiprolin was 1.8-2.1 times higher than that of S-oxathiapiprolin toward the two aquatic plants. In particular, the content of photosynthetic pigments decreased significantly stronger after exposure to R-oxathiapiprolin compared with S-oxathiapiprolin. The LC₅₀ values of R-oxathiapiprolin in zebrafish in the different life stages were 1.6-2.1 times higher than those of S-oxathiapiprolin. The zebrafish embryos were most sensitive to the oxathiapiprolin enantiomers. After exposure to R-oxathiapiprolin, zebrafish embryos showed noticeable hatching delays, inhibition or deformation. R-oxathiapiprolin degraded preferentially in all four soils, with an enantiomeric fraction (EF) ranging from 0.28 to 0.42 under aerobic conditions. Enantioselective degradation was not found under anaerobic and sterilized conditions. The enantioselectivity of new chiral pesticides should be fully considered in risk assessments to provide a basis for the development and preparation of pure optical enantiomers.

Herbicidal activity and differential metabolism of lactofen in rat and loach on an enantiomeric level

Enantioselectivity of chiral compounds is receiving growing concern. Lactofen, a chiral herbicide widely used in field crops and vegetables to control broadleaf weeds, is still sold as racemate. In this work, the herbicidal activity and metabolism behavior of lactofen were investigated on an enantiomeric level. Two common broadleaf weeds (Eclipta prostrata L. and Portulaca oleracea L.) were used to evaluate the herbicidal activity of rac-/R- and S-lactofen, and their metabolism behavior in loach and rat liver microsomes was explored. Higher herbicidal activity of S-lactofen was observed, with the 20d-EC₅₀ values being 1.9-3.4 times lower than R-lactofen. Both loach and rat liver microsomes had ability to metabolize rac-lactofen, with half-lives of 1.93 and 1.28 h, respectively. Enantioselective metabolism behaviors were observed in loach and rat liver microsomes and the direction of enantioselectivity were different. R-lactofen was preferentially metabolized in loach liver microsome, while S-lactofen was preferentially metabolized in rat liver microsome. No interconversion of R- and S-lactofen was found. Besides, the main metabolic pathways of R- and S-lactofen were found to be significantly different. R-lactofen was metabolized to R-desethyl lactofen in both loach and rat liver microsomes without further metabolism. However, S-lactofen was metabolized to both S-desethyl lactofen and acifluorfene in rat liver microsome, which was mainly metabolized to acifluorfene in loach liver microsome. This study indicated enantioselectivity and metabolites should be taken into consideration when overall evaluating the environmental behavior of lactofen.

Metabolomic and transcriptomic investigation of the mechanism involved in enantioselective toxicity of imazamox in Lemna minor

Imazamox (IM) is a chiral pesticide that has been widely used in agriculture. Currently, few studies have investigated the toxicity mechanisms of imazamox to aquatic macrophyte from the enantiomer level. In this study, the enantioselective effects of IM on the toxicity and physiological and biochemical system of aquatic macrophyte Lemna minor were systematically investigated. Metabolomic and transcriptomic for Lemna minor were used to identify potential mechanisms of toxicity. 7 d EC₅₀s for racemic-, R-, and S-IM were 0.036, 0.035, and 0.203 mg/L, respectively, showing enantioselective toxicity. In addition, IM caused Lemna minor lipid peroxidation and antioxidant damage, and inhibited the activities of the target enzymes. Metabolomic and transcriptomic data indicated that R-IM interferenced differentially expressed genes and metabolites of Lemna minor which were enriched in carbon fixation during photosynthesis, glutathione metabolic pathway, pentose phosphate pathway, zeatin biosynthesis, and porphyrin and chlorophyll metabolism. S-IM affected phenylalanine metabolism, phenylpropanoid biosynthesis, zeatin biosynthesis and secondary metabolite biosynthesis. Racemic-IM influenced carbon fixation during operation, glutathione metabolic pathway, zeatin biosynthesis and pentose phosphate pathway. The results provide new insights into the enantioselective toxicity mechanisms of IM to Lemna minor, and lay the foundation for conducting environmental risk assessments.

Chemical speciation of ciprofloxacin in aqueous solution regulates its phytotoxicity and uptake by rice (Oryza sativa L.)

Ciprofloxacin (CIP), a widely used fluoroquinolone antibiotic, is frequently detected in aqueous environments, and could be assimilated by vegetable plants to possess potential threats to human and animal health through food chains. However, plant uptake of CIP in different chemical speciation has still far from clear now. Thus, the toxicity and uptake of CIP by rice plants were investigated under different solution pH, owing to its contribution to different chemical speciation of CIP. Results display that high pH-driven changes of CIP from cation (CIP⁺) to anion (CIP^-) decreased its adsorption and uptake by excised roots and intact plants, respectively. However, CIP concentrations in roots, stems and leaves all exhibited no significant differences with increasing solution pH. Moreover, six intermediates of CIP were detected and two possible transformation pathways were proposed in rice plants, including firstly oxidation and following consecutive cleavage of piperazine ring. After accumulated in plant tissues, CIP significantly inhibited the plant growth, decreased the photosynthetic pigments contents and enhanced the antioxidant enzyme activities in a concentration-dependent manner. Besides, high pH exacerbated the growth inhibition and changed the oxidative damage responses of rice plants to CIP. These findings indicate that the uptake and toxicity of CIP in rice plants were influenced by solution pH-driven changes of its chemical speciation.

A novel esterase LanE from Edaphocola flava HME-24 and the enantioselective degradation mechanism of herbicide lactofen

Lactofen is a chiral herbicide and widely used against broadleaf weeds in agriculture. As a pesticide, it is directly released to the environment, and easily caused contamination in soil and aquatic ecosystem. The enantioselective degradation of lactofen in the environment has been reported, but the molecular biological mechanism of this phenomenon is still unclear. In this study, strain Edaphocola flava HME-24 could degrade 96.7% of 50 mg L^-1 lactofen within 72 h. Lactofen was initially hydrolyzed to desethyl lactofen and subsequently acifluorfen by strain HME-24. A novel gene lanE, involved in lactofen transformation, was obtained from Edaphocola flava HME-24. Gene lanE encoded a protein of 471 amino acids that contained the conserved GXSXG esterase motif and clustered into esterase subfamily V. LanE shared the highest identity with esterase EstD (Q9WYH1) from Thermotoga maritima MSB8 (29.14%). This esterase was also able to transform p-nitrophenyl esters (C4-C8), and the activity decreased when the carbon chain length increased. LanE showed enantioselectivity during the degradation of lactofen, diclofop-methyl, and quizalofop-ethyl, with a higher degradation efficiency of (S)-enantiomers than (R)-enantiomers. The three-dimensional structure of LanE was simulated, and molecular docking revealed that when the (S)-enantiomers of lactofen occupied the active sites, the distance between the ligand molecule and the coordination atom was shorter than that when the (R)-enantiomers occupied the active sites, which facilitated the formation of the transition state complex. The results in this study enhanced our understanding of the preferential catabolism of the (S)-enantiomers of lactofen on the molecular level and could illustrate the reported enantioselective degradation of lactofen in the environment.

Seaweed Essential Oils as a New Source of Bioactive Compounds for Cyanobacteria Growth Control: Innovative Ecological Biocontrol Approach

The application of natural compounds extracted from seaweeds is a promising eco-friendly alternative solution for harmful algae control in aquatic ecosystems. In the present study, the anti-cyanobacterial activity of three Moroccan marine macroalgae essential oils (EOs) was tested and evaluated on unicellular Microcystis aeruginosa cyanobacterium. Additionally, the possible anti-cyanobacterial response mechanisms were investigated by analyzing the antioxidant enzyme activities of M. aeruginosa cells. The results of EOs GC-MS analyses revealed a complex chemical composition, allowing the identification of 91 constituents. Palmitic acid, palmitoleic acid, and eicosapentaenoic acid were the most predominant compounds in Cystoseira tamariscifolia, Sargassum muticum, and Ulva lactuca EOs, respectively. The highest anti-cyanobacterial activity was recorded for Cystoseira tamariscifolia EO (ZI = 46.33 mm, MIC = 7.81 μg mL-1, and MBC = 15.62 μg mL-1). The growth, chlorophyll-a and protein content of the tested cyanobacteria were significantly reduced by C. tamariscifolia EO at both used concentrations (inhibition rate >67% during the 6 days test period in liquid media). Furthermore, oxidative stress caused by C. tamariscifolia EO on cyanobacterium cells showed an increase of the activities of superoxide dismutase (SOD) and catalase (CAT), and malondialdehyde (MDA) concentration was significantly elevated after 2 days of exposure. Overall, these experimental findings can open a promising new natural pathway based on the use of seaweed essential oils to the fight against potent toxic harmful cyanobacterial blooms (HCBs).

Developmental toxicity and angiogenic defects of etoxazole exposed zebrafish (Danio rerio) larvae

Etoxazole, a chitin synthesis inhibitor, is widely used to control insects and mites by causing developmental defects. Despite the many advantages of pesticides, the inhibitory effects of most pesticides including etoxazole are based on biochemical reaction and their widespread application is considered as a major risk to human health and the environment because of bioaccumulation and non-target toxic effects. Though used in agricultural area, the pesticide residues run off through rivers or ocean, where diverse aquatic organisms live. Since there are no studies evaluating the risks of etoxazole exposure in embryogenesis of aquatic organisms, we investigated the adverse effects of etoxazole on development and angiogenesis in zebrafish embryos, which are considered to be an effective model for detecting ecotoxicological effects of widely used compounds, especially affecting aquatic organisms. Etoxazole induced yolk sac and heart edema, as well as loss of viability, abnormal heart rate, and developmental deficiency. Through a mechanistic approach, we also showed that etoxazole caused reactive oxygen species accumulation, inhibited the expression of cell cycle activating genes, and induced apoptosis. In addition, we investigated effects of etoxazole on cardiovascular development by demonstrating the loss of vascular structure in response to etoxazole exposure in fli1:eGFP transgenic zebrafish model. Collectively, this first assessment demonstrating the effects of etoxazole on embryogenesis and cardiovascular development provides clear evidence for the toxicity of etoxazole and contributes important data towards formulating safety guidelines on the potential hazards of etoxazole for aquatic environment.

In vitro assessment of corticosteroid effects of eight chiral herbicides

Information regarding the enantioselective endocrine disruption of chiral herbicides is scarce. This study assessed the disrupting effects of eight typical chiral herbicides on corticosteroids (including glucocorticoids and mineralocorticoids). Enantioselectivity of eight chiral herbicides were evaluated for their agonistic/antagonistic effects on glucocorticoid receptor (GR) and mineralocorticoid receptor (MR) with CHOK1 cell line using reporter gene assay. Their influence on the production of corticosteroids were further investigated in H295R cell line using enzyme-linked immunosorbent assay (ELISA). None of the racemates or enantiomers of eight chiral herbicides exhibited GR or MR agonistic activity at non-cytotoxic concentrations. However, rac-propisochlor and S-imazamox antagonized cortisol-induced transactivation of GR by 21.79% and 38.73% at the concentration of 1.0 × 10^-7 M and 1.0 × 10^-6 M, respectively, and R-napropamide remarkably attenuated aldosterone-induced MR transactivation by 68.78% at 1.0 × 10^-6 M. The secretion of cortisol was significantly restrained after treated with 1.0 × 10^-6 M rac-propisochlor and rac-/R-napropamide at the concentration of 1.0 × 10^-6 M by 26.49%, 30.10% and 35.27%, respectively, while this glucocorticoid was remarkably induced by 1.0 × 10^-5 M rac-diclofop-methyl and its two enantiomers at the concentration of 1.0 × 10^-5 M by 75.60%, 100.1% and 68.78%, respectively. Exposure to rac-propisochlor (1.0 × 10^-6 M), S-diclofop-methyl (1.0 × 10^-5 M) or rac-/S-/R- acetochlor (1.0 × 10^-6 M) and rac-/S-/R-lactofen (1.0 × 10^-6 M) inhibited the secretion of aldosterone by approximately 40%. Our findings suggested that chiral herbicides disrupted corticosteroid homeostasis in an enantioselective way. Therefore, more comprehensive screening is required to better understand the ecological and health risks of chiral pesticides.

Duckweed biomarkers for identifying toxic water contaminants?

Surface or ground waters can be contaminated with numerous toxic substances. The duckweeds Lemna minor and Lemna gibba are widely used for assaying waterborne toxicity to higher plants in terms of growth inhibition and photosynthetic pigment reduction. These tests cannot, however, in themselves determine the nature of the agents responsible for toxicity. Morphological, developmental, physiological, biochemical, and genetic responses of duckweeds to exposure to toxic water contaminants constitute biomarkers of toxic effect. In principle, the very detection of these biomarkers should enable the contaminants having elicited them (and being responsible for the toxicity) to be identified. However, in practice, this is severely compromised by insufficient specificity of biomarkers for their corresponding toxicants and by the lack of documentation of biomarker/toxin relationships. The present contribution illustrates the difficulties of using known water contaminant-related duckweed biomarkers to identify toxins, and discusses possibilities for achieving this goal.

Enantiomeric impacts of two amide chiral herbicides on Echinochloa crus-galli physiology and gene transcription

Echinochloa crus-galli is one of the most noxious weeds in the world and causes yield losses in a variety of different field crops. Napropamide and acetochlor are herbicides commonly employed to control this weed. Both compounds are chiral, with enantiomers displaying different activities. However, it is unclear how the enantiomers of these two chiral herbicides act on different tissues of E. crus-galli. The objective of this paper is to investigate the action mechanism of napropamide and acetochlor in the roots and shoots of E. crus-galli. R‑enantiomers were found to be more active than either the racemates or S-enantiomers on the weed. The content of chlorophyll was not significantly affected by treatment with either enantiomer. The impacts on the activity for the oxidative stress enzymes, except catalase (CAT), showed that both napropamide and acetochlor enantiomers could induce oxidative stress. Furthermore, R‑enantiomers caused greater oxidative damage. Enhanced glutathione-S-transferase (GST) activity and expression of GST genes suggested both EcGSTF1 and EcGSTZ1 were present in the roots and shoots, and this will be helpful for detoxification. The changes in both the roots and shoots revealed the two herbicides displayed tissue selectivity in E. crus-galli. These results enable a better understanding on the mechanism of action for napropamide and acetochlor enantiomers on different tissues, including the shoots and roots in E. crus-galli.

Enantiomeric environmental behavior, oxidative stress and toxin release of harmful cyanobacteria Microcystis aeruginosa in response to napropamide and acetochlor

Harmful algal blooms have emerged as a worldwide issue. After concentrations of herbicides entering water, herbicides in water may pose ecological effects on them. The present study investigates the toxicity and environmental behavior of the herbicides, napropamide and acetochlor as enantiomers and as racemates on Microcystis aeruginosa which is the main specie known to produce hepatotoxins. S-napropamide/acetochlor are degraded faster than their corresponding isomer R-napropamide/acetochlor, with the latter more prone to accumulate in algal cells. Moreover, all the enantiomers did not undergo measurable racemization in the medium and algal cells. S-napropamide/acetochlor exhibited much higher toxicity than R-napropamide/acetochlor, with the S-enantiomer inducing a much greater production of antioxidant defense enzymes (superoxide dismutase (SOD) and malondialdehyde (MDA)) and microcystins (MC). SOD and MC increased after treatment with the herbicides and these increases were dependent on the exposure time, whereas MDA showed no apparent change. The information provided in this work will be useful for understanding the toxicity mechanism and environmental behaviors of different amide herbicides (napropamide and acetochlor) in aquatic environments at the enantiomeric level. Additionally, analysis of chiral herbicides in aquatic system needs more attention to aide in the environmental assessment of chiral herbicides.

Enantioselective bioaccumulation and metabolism of lactofen in zebrafish Danio rerio and combined effects with its metabolites

Pesticide residue in agricultural land might led to contamination of fresh waters, creating potential risks to organisms. The environmental behavior of herbicide lactofen may be enantioselective and the metabolites may have high toxic effects in individual or in combination. In this work, the enantioselective bioaccumulation, metabolism and toxic effects of lactofen and three metabolites (desethyl lactofen, acifluorfene, and amino acifluorfene) in zebrafish were investigated. The antioxidase activity (superoxide dismutase, catalase, glutathione peroxidase, and glutathione S-transferase), lipid peroxidation content were measured after exposure, and genetic toxicity was evaluated by a micronucleus test. The integrated biomarker response (IBR) method was used to determine the effects of the lactofen and its metabolites as well as their combinations. The metabolites were found to have higher toxic effects, and enantioselective toxic effects of lactofen and desethyl lactofen were observed, with the S-enantiomer more toxic. Based on IBR values, synergistic effects existed in combination of lactofen and desethyl lactofen, while antagonistic effects of lactofen with acifluorfene or amino acifluorfene were observed. Zebrafish were exposed to 0.5 mg L^-1 lactofen and the bioaccumulation were measured during a 15 d period followed by a 7 d elimination. The half-lives of the metabolites varied between 0.66 and 5.21 d, with bioconcentration factors (BCFs) in the range of 39-120. The metabolic pathways of R- and S-lactofen were found to be significantly different. The results supported our hypothesis. Therefore, the assessment of enantiomers and metabolites in individual or in combination should be taken into consideration in evaluating chiral pesticide risks.

Stereoselective bioactivity, acute toxicity and dissipation in typical paddy soils of the chiral fungicide propiconazole

Propiconazole is a widely used systemic agricultural triazole fungicide with two chiral centers. In the present study, systemic assessments of propiconazole stereoisomers are reported for the first time, including absolute configuration, stereoselective bioactivity toward pathogens (Ustilaginoidea virens, Magnaporthe oryzae, Fusarium moniliforme, Thanatephorus cucumeris, and Rhizoctonia solani), and stereoselective acute toxicity toward aquatic organisms (Scenedesmus obliquus, and Daphnia magna). Moreover, the stereoselective dissipation of propiconazole in three types of paddy soil under laboratory-controlled conditions (aerobic, anaerobic and sterile) was investigated. The degree of bioactivity and acute toxicity of the propiconazole stereoisomers differed depending on the type of target pathogens and non-target organisms. There were 2.43-23.47 and 1.48-2.13 fold differences between the best and worst stereoisomer in bioactivity and toxicity, respectively. Under aerobic conditions, (2S,4S)-propiconazole and (2S,4R)-propiconazole were preferentially degraded in the three types of soils. However, no significant stereoselectivity was observed under anaerobic and sterile conditions. Propiconazole was configurationally stable throughout the study. In comprehensive consideration of bioactivity, toxicity and environmental behavior, using stereoisomer mixture rather than pure stereoisomer may help to control more species of disease in practical application, and the stereoselectivity should be taken into consideration in risk assessment.

Novel chemiluminescent immunochromatographic assay using a dual-readout signal probe for multiplexed detection of pesticide residues

A novel immunochromatographic assay utilizing luminol-reduced Au nanoparticles as a colorimetric/chemiluminescent dual-readout signal probe was developed for multiplexed detection of pesticide residues.

Degradation and Transport of the Chiral Herbicide S-Metolachlor at the Catchment Scale: Combining Observation Scales and Analytical Approaches

Evaluating pesticide degradation and transport in the soil-surface water continuum remains challenging at the catchment scale. Here we investigated the dissipation of the chiral herbicide S-metolachlor (SM) in soil in relation to its transport in runoff. Analyses of SM, transformation products (TPs, i.e., MESA and MOXA), and enantiomers were combined to determine SM degradation at plot and catchment scales. Assisted by modeling, we found that the main dissipation pathways of SM at the plot scale were degradation (71%), volatilization (5%), leaching (8%) and runoff (3%), while 13% of SM persisted in topsoil. This highlights the relevance of degradation processes. TPs could trace the different discharge contributions: MOXA prevailed in runoff water, whereas MESA was associated with slower flowpaths. At the catchment outlet, 11% of SM applied was exported in dissolved or particulate phases or as TPs (in SM mass equivalent). A single event 1 week after application exported 96% of SM, which underlined the potential importance of severe rainfall on seasonal SM export. Enantioselective degradation enriched SM in the R-enantiomer over longer periods and may be associated with slower flowpaths. Altogether, combining observation scales and analytical approaches enabled to quantify SM degradation and to identify how degradation controls SM export at the catchment scale.

Absorption, Distribution, Metabolism, and in Vitro Digestion of Beta-Cypermethrin in Laying Hens

Beta-cypermethrin (beta-CP), an important pyrethroid insecticide, and its main acid metabolites are frequently detected in human samples. Because beta-CP may pose some risk to human health, we studied dynamics and residues of beta-CP and its metabolites in hen egg, droppings, blood, and 15 other tissues after continuous exposure. A digestive model was then used to study beta-CP's digestive fate. Beta-CP and its metabolites significantly accumulated in tissues with high lipid contents and were readily transferred to eggs. Beta-CP was mainly metabolized into acid metabolites that accumulated in egg and edible tissues of laying hens, suggesting that humans may be exposed to beta-CP acid metabolites through food.

Enantioselective accumulation, metabolism and phytoremediation of lactofen by aquatic macrophyte Lemna minor

Pesticides are frequently detected in water bodies due to the agricultural application, which may pose impacts on aquatic organisms. The enantioselective bioaccumulation and metabolism of the herbicide lactofen in aquatic floating macrophyte Lemna minor (L. minor) were studied and the potential L. minor phytoremediation was investigated. Ultra-high performance liquid chromatography - tandem mass spectrometry (UHPLC-MS-MS) analysis for lactofen and its two known metabolites in L. minor was performed. The initial concentrations of racemic lactofen, R-lactofen and S-lactofen were all 30μgL^-1 in the growth solution. The distribution of lactofen and its metabolites in growth solution and L. minor was determined throughout a 5-d laboratory trial. It was observed that S-lactofen was preferentially taken up and metabolized in L. minor. After rac-lactofen exposure, the accumulation amount of S-lactofen was approximately 3-fold more than that of R-lactofen in L. minor and the metabolism rate of S-lactofen (T_1/2=0.92 d) was significantly faster than R-lactofen (T_1/2=1.55 d). L. minor could only slightly accelerate the metabolism and removal of lactofen in the growth solution. As for the metabolites, desethyl lactofen was found to be the major metabolite in L. minor and the growth solution, whereas the metabolite acifluorfene was undetectable. No interconversion of the two enantiomers was observed after individual enantiomer exposure, indicating they were configurationally stable. The findings of this work represented that the accumulation and metabolism of lactofen in L. minor were enantioselective, and L. minor had limited capacity for the removal of lactofen and its metabolite in water.

Biochemical characterization of an enantioselective esterase from Brevundimonas sp. LY-2

BACKGROUND

Lactofen, a member of the diphenylether herbicides, has high activity and is commonly used to control broadleaf weeds. As a post-emergent herbicide, it is directly released to the environment, and easily caused the pollution. This herbicide is degraded in soil mainly by microbial activity, but the functional enzyme involved in the biodegradation of lactofen is still not clear now.

RESULTS

A novel esterase gene lacH, involved in the degradation of lactofen, was cloned from the strain Brevundimonas sp. LY-2. The gene contained an open reading frame of 921 bp, and a putative signal peptide at the N-terminal was identified with the most likely cleavage site between Ala 28 and Ala 29. The encoded protein, LacH, could catalyze the hydrolysis of lactofen to form acifluorfen. Phylogenetic analysis showed that LacH belong to family V of bacterial lipolytic enzymes. Biochemical characterization analysis showed that LacH was a neutral esterase with an optimal pH of 7.0 and an optimal temperature of 40 °C toward lactofen. Besides, the activity of LacH was strongly inhibited by Hg²⁺ and Zn²⁺. LacH preferred short chain p-nitrophenyl esters (C₂-C₆), exhibited maximum activity toward p-nitrophenyl acetate. Furthermore, the enantioselectivity of LacH during lactofen hydrolysis was also studied, and the results show that R-(-)-lactofen was degraded faster than S-(+)-lactofen, indicating the occurrence of enantioselectivity in the enzymatic reaction.

CONCLUSIONS

Our studies characterized a novel esterase involved in the biodegradation of diphenylether herbicide lactofen. The esterase showed enantioselectivity during lactofen degradation, which revealed the occurrence of enzyme-mediated enantioselective degradation of chiral herbicides.

Insecticide pyrethroids in liver of striped dolphin from the Mediterranean Sea

Pyrethroid pesticides were analysed in liver of striped dolphin (Stenella coeruleoalba) from the Alboran Sea (south of Spain, Mediterranean Sea). The occurrence and bioaccumulation of pyrethroid insecticides in marine mammal tissues from the northern hemisphere had never been determined before. Pyrethroids were detected in 87% of the specimens with a mean total concentration of 300 ng g^-1 lw ± 932 (range 2.7-5200 ng g^-1 lw). Permethrin and tetramethrin were the main contributors to the pyrethroid profiles, with enantiospecific accumulation for the first and isomer specific accumulation for the latter. Bioaccumulation of pyrethroids was unlike that of persistent organic pollutants (POPs), as pyrethroid concentrations were not correlated to the maturity stage of the specimens. Concentrations slightly increased from calves to juveniles, whereas juveniles presented similar concentrations to adults. Metabolization of pyrethroids after achieving sexual maturity might account for this pattern.