Acute toxicity of the fungicide azoxystrobin on the diatom Phaeodactylum tricornutum

Effects of acute exposure to azoxystrobin on embryos and juveniles of the freshwater snail Lymnaea stagnalis

Azoxystrobin (AZ) is a systemic fungicide applied to soil to control a wide range of plant pathogenic fungi. AZ residues have been detected in surface waters due to excessive release, posing a risk to aquatic organisms. This study evaluated the toxic effects of short-term AZ exposure on embryos and juveniles of Lymnaea stagnalis. First, the 96-h LC50 values of AZ were estimated as 7.98 (6.50-9.85) mg/L for embryos and 2.90 (2.30-3.86) mg/L for juveniles, indicating that juveniles are more sensitive to acute AZ toxicity. Additional experiments were conducted to assess the sublethal effects of AZ on embryos and juveniles. The highest sublethal exposure concentrations were set at approximately 20 % of the respective estimated LC50 values for embryos and juveniles, while the lower concentrations were determined by successive ten-fold dilutions to include environmentally relevant AZ levels. Accordingly, embryos were exposed to 0, 15, 150, and 1500 μg/L, whereas juveniles were exposed to 0, 5, 50, and 500 μg/L over a 96-h period. In embryos, AZ exposure led to developmental delays, reduced growth, decreased hatching success and mortality at 1500 μg/L. Likewise, juvenile snails displayed marked biochemical and molecular alterations across all tested concentrations. AZ-induced ROS generation and elevated MDA levels were observed, alongside increased activities of SOD, CAT, GPx, and GR. Additionally, mRNA transcripts of HSP40, HSP70, SOD, CAT, GPx, and GR were upregulated in juveniles, even at the lowest exposure concentration. In conclusion, AZ contamination poses a significant ecological risk to the early life stages of freshwater gastropods.

Biodegradation of the Fungicide Picoxystrobin by Hyphomicrobium sp. H-9 and Detoxification Mechanism as Indicated by the Microalgae Tetradesmus obliquus

Picoxystrobin is widely used in agriculture, causing residual contamination of habitats and ecotoxicity. In this study, a picoxystrobin-degrading strain H-9 was isolated and identified as Hyphomicrobium sp. It can rapidly degrade four strobilurin fungicides (picoxystrobin, trifloxystrobin, azoxystrobin, and kresoxim-methyl) to produce the corresponding SF acids and methanol via the hydrolysis of ester bonds. Picoxystrobin can significantly inhibit the growth of algal cells and the synthesis of chlorophyll in Tetradesmus obliquus. The detoxification capacity of strain H-9 was evident as it mitigated picoxystrobin-induced growth inhibition and oxidative stress in T. obliquus. Strain H-9 modulated the expression of genes involved in photosynthesis, the Calvin cycle, the tricarboxylic acid cycle, glycolysis, oxidative stress, and chlorophyll synthesis, thereby alleviating picoxystrobin toxicity to T. obliquus. This study enhances our understanding of the detoxification mechanism of microorganisms on microalgae exposed to SF stress and provides a novel insight into the microbial remediation of SFs-contaminated environments.

Acute toxicity of salicylic acid and its derivatives on the diatom Phaeodactylum tricornutum: Physico-Biochemical and transcriptomic insights

Salicylate pollutants (SAs) poses a serious threat to marine ecosystems as emerging contaminants. However, the toxic effects of SAs on marine phytoplankton, as well as the potential mechanisms and their ecological risks linked with them, are remain largely unknown. In this study, we aimed to evaluate the toxic effects of salicylic acid (SA) and its 5-substituted derivatives (5-sSA) on the marine diatom Phaeodactylum tricornutum, as well as the potential molecular mechanism involved in the toxicity. Physiological assays conducted on P. tricornutum revealed significant changes in photosynthetic pigments, chlorophyll fluorescence parameters, and antioxidant enzyme activities. The results showed that exposure of P. tricornutum to SAs caused a significant decline in chlorophyll contents and damage to the photosystem II (PSII) core resulting in the decline of photosynthesis. Although the activities of superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT) were enhanced, oxidative damage occurred. Transcriptome analysis showed that a large number of differentially expresses genes (DEGs) were significantly enriched in metabolic pathways such as porphyrin metabolism, terpenoid backbone biosynthesis, and carbon fixation in photosynthetic organisms after SA and 5-BrSA treatments. In addition, key genes in transcriptomic metabolic pathways were further analyzed and validated using weighted correlation network analysis (WGCNA) and real-time fluorescence quantitative PCR (qPCR). Considering the above results, SAs mainly inhibit the processes of photosynthesis by repressing the expression of genes involved in secondary metabolite synthesis and photosynthetic carbon sequestration pathways, thus exerting toxic effects on algal cells. The results of the study will provide key data for understanding the ecological risk and toxicity mechanisms of SA pollutants.

Benzophenone-4 inhibition in marine diatoms: Physiological and molecular perspectives

Benzophenone-4 (BP-4), a widely utilized organic ultraviolet (UV) filter, is recognized as a pseudo-persistent contaminant in aquatic environments. To elucidate the effects and mechanisms of BP-4 on marine diatoms, an investigation was conducted on the growth rate, photosynthetic pigment content, photosynthetic parameters, antioxidant enzyme activity, malondialdehyde (MDA) levels, cellular structure, and transcriptome profile of the model species, Phaeodactylum tricornutum. The results showed a pronounced inhibition of algal growth upon exposure to BP-4, with a 144 h-EC50 value of 201 mg·L-1. In addition, BP-4 exposure resulted in a significant reduction in biomass, disruption of cell membrane integrity, and increased MDA accumulation, with levels escalating 3.57-fold at 125 mg·L-1 of BP-4. In the BP-4-treated samples, 1556 differentially expressed genes (DEGs) were identified, of which 985 were upregulated and 571 were downregulated. Gene ontology and KEGG pathway enrichment analysis revealed that the carbon fixation and carbon metabolism processes in P. tricornatum were disrupted in response to BP-4 exposure, along with excessive reactive oxygen species (ROS) production. The upregulation of genes associated with photosynthetic pigment (chlorophyll and carotenoids) synthesis, phospholipid synthesis, ribosome biogenesis, and translation-related pathways may be regarded as a component of P. tricornatum's tolerance mechanism towards BP-4. These results provide preliminary insights into the toxicity and tolerance mechanisms of BP-4 on P. tricornatum. They will contribute to a better understanding of the ecotoxicological impacts of BP-4 on the marine ecosystem and provide valuable information for elimination of BP-4 in aquatic environment by bioremediation.

Variation in phytotoxicity of rice seedlings caused by differential accumulation of azoxystrobin and pyraclostrobin in leaves

The effectiveness of pyraclostrobin (Pyr) and azoxystrobin (Azo) with highly targeting the rice blast is noteworthy, but they have varied toxic levels towards non-target aquatic organisms. Nevertheless, the toxic selectivity and mechanism of non-target plants, specifically rice, remain uncertain. In this study, we investigated the potential phytotoxic effects of Pyr and Azo on rice seedlings, including plant morphology, plant growth, physiological and biochemical changes. The findings revealed that both Pyr and Azo caused toxic effects on rice, resulting in symptoms of chlorosis and inhibited growth. The toxicity of Azo was found to be more severe when applied at the recommended field dose. Disruption of oxidative stress could significantly impact the demonstrated levels of REC, leading to a decrease in photosynthetic pigments and potentially culminating in cell death. Furthermore, the toxic effect of Azo had a greater impact on rice leaves compared to Pyr at treatments of 400, 800, 1600, and 4000 mg/L. However, the in vitro cytotoxicity of Azo on rice leaves was lower than that of Pyr. Therefore, it can be inferred that the mechanism of phytotoxicity of Azo is directly linked to the increased accumulation of the compound on the leaf tips and edges. Additionally, the positive effects observed on plant morphology and growth parameters suggest that the mixed application of plant growth regulators (sodium nitrophenolate aqueous solution of 14 mg/L and diethyl aminoethyl hexanoat of 50 mg/L) can be a promising approach to mitigate the rice phytotoxicity of Azo at 400 and 800 mg/L.

Insights into the growth and biochemical defense responses associated with fenitrothion toxicity and uptake by freshwater cyanobacteria

The extensive use of fenitrothion (FNT) in agricultural practices induces its persistence in soil and waterways. Therefore, it is essential to implement effective management practices such as using cyanobacteria for FNT removal and accumulation, particularly under accidental contamination. To this end, we evaluated the responses of two freshwater cyanobacteria taxa, Nostoc muscorum and Anabaena laxa to mild (7.5 mg L-1) and high (15 mg L-1) levels of FNT over a period of 7 d. Compared to N. muscorum, A. laxa was more tolerant to FNT, exhibiting higher FNT uptake and removal efficiencies at mild (16.3%) and high (17.5%) levels. FNT induced a dose-dependent decrease in cell growth, Chl a, phosphoenolpyruvate carboxylase and ribulose-1,5-bisphosphate carboxylase/oxygenase activities, which were more pronounced in N. muscorum. Moreover, FNT significantly increased oxidative damage markers i.e., increased lipid peroxidation (MDA), protein oxidation, H2O2 levels and NADPH oxidase enzyme activity, to more extent in N. muscorum. Compared to N. muscorum, A. laxa had high antioxidant capacity (FRAP), glutathione and increased activities of glutathione-S-transferase, glutathione reductase, glutathione peroxidase and superoxide dismutase, suggesting a robust antioxidant defense mechanism to mitigate FNT toxicity. However, N. muscorum devoted the induction of ascorbate content and the activity of catalase, peroxidase, monodehydroascorbate reductase, ascorbate peroxidase, and dehydroascorbate reductase enzymes. Although A. laxa had greater intracellular FNT, it experienced less FNT-induced oxidative stress, likely due to over production of antioxidants. Consequently, A. laxa is considered as a promising candidate for FNT phycoremediation. Our findings provide fundamental information on species-specific toxicity of FNT among cyanobacteria and the environmental risk of FNT toxicity in aquatic environments.

Efficient and practical in-jar silicone rubber based passive sampling for simultaneous monitoring of emerging fungicides in water and soils

The occurrence and ecological impacts of emerging fungicides in the environment has gained increasing attention. This study applied an in-jar passive sampling device based on silicone rubber (SR) film to measuring the freely dissolved concentration (Cfree) of 6 current-use fungicides as a critical index of bioavailability in water and soils. The kinetics parameters including SR-water, soil-water, and organic carbon-water partition coefficients and sampling rates of the target fungicides were first attained and characterized well with their physicochemical properties. The in situ and ex situ field deployment in Hefei City provided the assessment of contaminated levels for these fungicides in rivers and soils. The Cfree of triadimefon and azoxystrobin was estimated at 0.54 ± 0.07-17.4 ± 2.5 ng L-1 in Nanfei River and Chao Lake, while triadimefon was only found in Dongpu Reservoir water with Cfree below 0.66 ± 0.04 ng L-1. The results exhibited that the equilibrium duration of 7 d was suitable for water application but a longer interval of 14 d was recommended for soil sampling. This work demonstrated the advantages of the proposed strategy in terms of fast monitoring within 2 weeks and high sensitivity down to detection limits in 0.5-5 ng L-1. The in-jar passive sampling device can be extrapolated to the evaluation for a wide coverage of organic pollutants in water and soils.

Toxic mechanisms of imazalil, azoxystrobin and their mixture to hook snout carp (Opsariichthys bidens)

While combinations of pesticides better represent actual conditions within aquatic ecosystems, the specific toxic effects of these combinations have not been determined yet. The objective of this research was to assess the combined impact of imazalil and azoxystrobin on the hook snout carp (Opsariichthys bidens) and delve into the underlying causes. Our findings indicated that the 4-day LC50 value for imazalil (1.85 mg L-1) was greater than that for azoxystrobin (0.90 mg L-1). When imazalil and azoxystrobin were combined, they presented a heightened effect on the species. Enzyme activities like SOD, CAT, GST, and CarE, along with androgen and estrogen levels, displayed marked differences in most single and combined treatments in comparison to the baseline group. Moreover, four genes (mn-sod, cu-sod, il-1, and esr) related to oxidative stress, immunity, and the endocrine system exhibited more pronounced expression changes when exposed to combined pesticides rather than individual ones. Our tests revealed that the combined use of imazalil and azoxystrobin had more detrimental effect on aquatic vertebrates than when evaluated individually. This finding suggested that future ecological hazard analyses based only on individual tests might not sufficiently safeguard our aquatic ecosystems.

Phthalocyanine blue leaching and exposure effects on Microcystis aeruginosa (cyanobacteria) of photoaged microplastics

Light-stabilizing additives may contribute to the overall pollution load of microplastics (MPs) and potentially enter the food chain, severely threatening aquatic life and human health. This study investigated the variation between polystyrene (PS) MPs and phthalocyanine blue (CuPC)-containing MPs before and after photoaging, as well as their effects on Microcystis aeruginosa. The presence of PS-MPs increased cell mortality, antioxidant enzyme activity, and the variation in extracellular components, while the presence of CuPC exacerbated these variations. CuPC-containing MPs caused different increasing trends in superoxide dismutase and malondialdehyde activities due to electron transfer across the membrane. Transcriptomic analysis revealed that the MPs and CuPC affected various cellular processes, with the greatest impact being on cell membranes. Compared with MPs, CuPC negatively affected ribosome and polysaccharide formation. These findings provide insights into the molecular mechanisms underlying the cellular response to MPs and their associated light-stabilizer pollution and imply the necessity for mitigating the pollution of both MPs and light-stabilizers.

Oxidative stress and DNA alteration on the earthworm Eisenia fetida exposed to four commercial pesticides

Modern agriculture is mainly based on the use of pesticides to protect crops but their efficiency is very low, in fact, most of them reach water or soil ecosystems causing pollution and health hazards to non-target organisms. Fungicide triazoles and strobilurins based are the most widely used and require a specific effort to investigate toxicological effects on non-target species. This study evaluates the toxic effects of four commercial fungicides Prosaro® (tebuconazole and prothioconazole), Amistar®Xtra (azoxystrobin and cyproconazole), Mirador® (azoxystrobin) and Icarus® (Tebuconazole) on Eisenia fetida using several biomarkers: lipid peroxidation (LPO), catalase activity (CAT), glutathione S-transferase (GST), total glutathione (GSHt), DNA fragmentation (comet assay) and lysozyme activity tested for the first time in E. fetida. The exposure to Mirador® and AmistarXtra® caused an imbalance of ROS species, leading to the inhibition of the immune system. AmistarXtra® and Prosaro®, composed of two active ingredients, induced significant DNA alteration, indicating genotoxic effects. This study broadened our knowledge of the effects of pesticide product formulations on earthworms and showed the need for improvement in the evaluation of toxicological risk deriving from the changing of physicochemical and toxicological properties that occur when a commercial formulation contains more than one active ingredient and several unknown co-formulants.

Border cell population size and oxidative stress in the root apex of Triticum aestivum seedlings exposed to fungicides

Fungicides reduce the risk of mycopathologies and reduce the content of mycotoxins in commercial grain. The effect of fungicides on the structural and functional status of the root system of grain crops has not been studied enough. In this regard, we studied the phytocytotoxic effects tebuconazole (TEB) and epoxiconazole (EPO) and azoxystrobin (AZO) in the roots of Triticum aestivum seedlings in hydroponic culture. In the presence of EPO and AZO (but not TEB) inhibition of the root growth was accompanied by a dose-dependent increase in the content of malondialdehyde, carbonylated proteins, and proline in roots. TEB was characterized by a dose-dependent decrease in the total amount of border cells (BCs) and the protein content in root extracellular trap (RET). For EPO and AZO, the dose curves of changes in the total number of BCs were bell-shaped. AZO did not affect the protein content in RET. The protein content in RET significantly decreased by 3 times for an EPO concentration of 1 µg/mL. The obtained results reveal that the BC-RET system is one of the functional targets of fungicides in the root system of wheat seedlings. Studied fungicides induce oxidative stress and structural and functional alterations in the BC-RET system that can affect their toxicity to the root system of crops.

Environmental levels of azoxystrobin disturb male zebrafish behavior: Possible roles of oxidative stress, cholinergic system, and dopaminergic system

A widely applied pesticide of azoxystrobin, is increasingly detected in the water environment. Concern has been raised against its potential detriment to aquatic ecosystems. It has been shown that exposure to azoxystrobin interfere with the locomotor behavior of zebrafish larvae. This study aims to investigate whether exposure to environmental levels of azoxystrobin (2 μg/L, 20 μg/L, and 200 μg/L) changes the behavior of male adult zebrafish. Herein, we evaluated behavioral response (locomotor, anxiety-like, and exploratory behaviors), histopathology, biochemical indicators, and gene expression in male adult zebrafish upon azoxystrobin exposure. The study showed that exposure to azoxystrobin for 42 days remarkably increased the locomotor ability of male zebrafish, resulted in anxiety-like behavior, and inhibited exploratory behavior. After treatment with 200 μg/L azoxystrobin, vasodilatation, and congestion were observed in male zebrafish brains. Exposure to 200 μg/L azoxystrobin notably elevated ROS level, MDA concentration, CAT activity, and AChE activity, while inhibiting SOD activity, GPx activity, ACh concentration, and DA concentration in male zebrafish brains. Moreover, the expression levels of genes related to the antioxidant, cholinergic, and dopaminergic systems were significantly changed. This suggests that azoxystrobin may interfere with the homeostasis of neurotransmitters by causing oxidative stress in male zebrafish brains, thus affecting the behavioral response of male zebrafish.

Preparation of Azoxystrobin-Zinc Metal-Organic Framework/Biomass Charcoal Composite Materials and Application in the Prevention and Control of Gray Mold in Tomato

In order to reduce the use of fungicide and ensure food safety, it is necessary to develop fungicide with low toxicity and high efficiency to reduce residues. Azoxystrobin (AZOX), which is derived from mushrooms, is an excellent choice. However, conventional AZOX release is difficult to regulate. In this paper, a pH-responsive fungicide delivery system for the preparation of AZOX by impregnation method was reported. The Zinc metal-organic framework/Biomass charcoal (ZIF-8/BC) support was first prepared, and subsequently, the AZOX-ZIF-8/BC nano fungicide was prepared by adsorption of AZOX onto ZIF-8/BC by dipping. Gray mold, caused by Botrytis cinerea, is one of the most important crop diseases worldwide. AZOX-ZIF-8/BC could respond to oxalic acid produced by Botrytis cinerea to release loaded AZOX. When pH = 4.8, it was 48.42% faster than when pH = 8.2. The loading of AZOX on ZIF-8/BC was 19.83%. In vitro and pot experiments showed that AZOX-ZIF-8/BC had significant fungicidal activity, and 300 mg/L concentration of AZOX-ZIF-8-BC could be considered as a safe and effective control of Botrytis cinerea. The above results indicated that the prepared AZOX-ZIF-8/BC not only exhibited good drug efficacy but also demonstrated pH-responsive fungicide release.

A photocatalytic-microbial coupling system for simultaneous removal of harmful algae and enhanced denitrification: Construction, performance and mechanism of action

Recently, harmful algal blooms (HABs) have become occurred with increasingly frequency worldwide. High nitrate content is one of the primary causes of eutrophication. Research has shown that photocatalytic materials enhance the effectiveness of microbial denitrification while removing other contaminants, despite some shortcomings. Based on this, we loaded TiO2/C3N4 heterojunctions onto weaveable, flexible carbon fibers and established a novel photocatalytically enhanced microbial denitrification system for the simultaneous removal of harmful algae and Microcystin-LR. We found that 99.35% of Microcystis aeruginosa and 95.34% of MC-LR were simultaneously and effectively removed. Compared to existing denitrification systems, the nitrate removal capacity improved by 72.33%. The denitrifying enzyme activity and electron transport system activity of microorganisms were enhanced by 3.54-3.86 times. Furthermore, the microbial community structure was optimized by the regulation of photogenerated electrons, and the relative abundance of main denitrifying bacteria increased from 50.72% to 66.45%, including Proteobacteria and Bacteroidetes. More importantly, we found that the increased secretion of extracellular polymeric substances by microorganisms may be responsible for the persistence of the reinforcing effect caused by photogenerated electrons in darkness. The higher removal of Microcystis aeruginosa and Microcystin-LR (MC-LR) achieved by the proposed system would reduce the frequency of HAB outbreaks and prevent the associated secondary pollution.

The kisspeptin-GnIH signaling pathway in the role of zebrafish courtship and aggressive behavior induced by azoxystrobin

Azoxystrobin, a strobilurin widely used to control rice diseases, has raised concerns about possible adverse effects on aquatic ecosystems. At present, very little is known about the effects of azoxystrobin on courtship and aggressive behavior and the potential underlying mechanisms. In the present study, after exposing adult male and female zebrafish to worst-case scenario concentrations of azoxystrobin (0, 2 μg/L, 20 μg/L, and 200 μg/L) for 42 d, we observed a decrease in courtship behavior and an increase in aggressive behavior in both male and female zebrafish. In addition, to elucidate the molecular mechanism of the behavioral effects of azoxystrobin, we quantified the changes in the concentrations of kisspeptin, 5-HT, GnIH, and their corresponding receptor mRNA expression in the brain. The results showed that 200 μg/L azoxystrobin decreased the concentrations of kisspeptin and increased the concentration of GnIH in both male and female zebrafish brain. In addition, azoxystrobin also significantly reduced 5-HT concentration in female zebrafish brain. Further investigation revealed that altered courtship and aggressive behavior were associated with the expression levels of genes (kiss1, kiss2, gnrh3, gnrhr3, 5ht1a, and 5ht2a) involved in kisspeptin-GnIH signaling pathway. In conclusion, our study suggested that azoxystrobin may impair courtship and aggressive behavior in zebrafish by interfering with the kisspeptin-GnIH signaling pathway, which may have more profound effects on natural zebrafish populations.

The inhibitory effects of simulated light sources on the activity of algae cannot be ignored in photocatalytic inhibition

Harmful algal blooms (HABs) destroy the balance of the aquatic ecosystem, causing huge economic losses and even further endangers human health. In addition to traditional methods of algae removal, photocatalytic inhibition of algae is drawing more and more interests with rich application scenarios and considerable potential. Simulated visible light sources are used to excite photocatalytic materials and optimize their performance. However, most of the light irradiation intensities used in the study exceeded 50 mW/cm². And the effects of intense light irradiation conditions on algal growth have rarely been addressed in previous studies. So we focused on the effect of different intensity of light irradiation on the growth of algae. We explored the relationship between light irradiation intensity and algal inactivation rate, and investigated the changes in ROS levels in algal cells under different light irradiation and the resulting response of the antioxidant system. We have found that several major antioxidant enzyme activities, such as SOD and CAT, were significantly higher and lipid peroxidation products (MDA) were accumulating. Intense light irradiation had the most direct effect on the photosynthetic system of algal cells, with the photosynthetic rate and relative electron transfer rate decaying to almost 0 within 30 min, indicating that algal photosynthesis was inhibited in a fairly short period of time. We further observed the physiological and morphological changes of algal cells during this process using TEM and found that the progressive dissolution of the cell membrane system and the damage of organelles associated with photosynthesis play a major role in promoting cell death. We thus conclude that light irradiation has a significant effect on the physiological activity of algal cells and is a non-negligible factor in the study of photocatalytic removal of harmful algae. It will provide theoretical guidance for the future study of photocatalysis on algae inhibition.

1-Tetradecanol, Diethyl Phthalate and Tween 80 Assist in the Formation of Thermo-Responsive Azoxystrobin Nanoparticles

The occurrence of crop fungal diseases is closely related to warm environmental conditions. In order to control the release of fungicides in response to warm conditions, and enhance the efficacy, a series of thermo-responsive fungicide-loaded nanoparticles were developed. The fungicide azoxystrobin, solvent DEP, emulsifier Tween 80 and thermo-responsive component TDA were combined to create thermal-response oil phases, conditions for emulsification were then optimized. LDLS, zeta potential, FTIR, DSC, TGA, XRD, SEM and antifungal efficacy assays were carried out to investigate the characteristics and forming mechanism. The results indicated that the formula with 5 g azoxystrobin, 10 mL DEP, 6 mL Tween 80 and 2.5 g TDA constructed the proposed oil phase with the ability to transform from solid at 20 °C to softerned at 31.5 °C. Both DEP and TDA played key roles in interfering with the crystallization of azoxystrobin. The optimal T3t-c12 nanoparticles had a mean particle size of 162.1 nm, thermo-responsive morphological transformation between 20 °C and 30 °C, AZO crystal reforming after drying, the ability to attach to fungal spores and satisfied antifungal efficacy against P. nicotiana PNgz07 and A. niger A1513 at 30 °C. This report provides referable technical support for the construction of smart-release nanoparticles of other agrochemicals.

Toxic effect of nickel on microalgae Phaeodactylum tricornutum (Bacillariophyceae)

Nickel acts as an essential trace nutrient or toxicant for organisms, depending on its concentration. The increased concentrations of nickel, due to anthropogenic activity, in the aquatic environment are potential threats to aquatic organisms. However, the knowledge on toxic mechanisms of nickel to microalgae remains incompletely understood. In the present study, we investigated the toxic effects of nickel in the cosmopolitan diatom Phaeodactylum tricornutum via evaluation of physiological and transcriptome responses. The results showed that the median effective concentration-72 h (EC₅₀-72 h) and EC₅₀-96 h of nickel was 2.48 ± 0.33 and 1.85 ± 0.17 mg/L, respectively. The P. tricornutum cell abundance and photosynthesis significantly decreased by 1 mg/L of nickel. Results from photosynthetic parameters including efficiency of the oxygen evolving complex (OEC) of photosystem II (PSII) (Fv/F₀), maximum photosynthetic efficiency of PS II (Fv/Fm), electron transport rate (ETR), actual photosynthetic efficiency of PS II (Y(II)), non-photochemical quenching (NPQ), and photochemical quenching (qP) indicated that OEC of PS II might be impaired by nickel. The transcriptome data also reveal that OEC apparatus coding gene PS II oxygen-evolving enhancer protein 2 (PsbP) was regulated by nickel. Moreover, induced reactive oxygen species (ROS) production and chlorophyll a content were also detected under nickel stress. Transcriptome analysis revealed that nickel affected a variety of differentially expressed genes (DEGs) that involved in redox homeostasis, nitrogen metabolisms, fatty acids, and DNA metabolism. However, thiol-disulfide redox system might play important roles in nickel-induced oxidative stress resistance. This study improved the understanding of the toxic effect of nickel on the diatom P. tricornutum.

Azoxystrobin increases the infection of spring viraemia of carp virus in fish

Azoxystrobin (AZ) has entered aquatic ecosystems and produced serious damages to fish associated with potentially increasing the susceptibility to pathogens. This study characterized the defense abilities of fish by exposed to AZ on challenging with the infection of spring viraemia of carp virus (SVCV). The results showed that SVCV replication increased significantly in EPC cells and zebrafish that were exposed to up to 50 μg/L of AZ at 3, 5, 7, and 14 d. Intracellular biochemical assays indicated that AZ at 5 and 50 μg/L inhibited the activation of Nrf2-ARE pathway including a decrease in Nrf2 expression, Nrf2 phosphorylation, HO-1 content, and three antioxidant activities. While no significant difference in ERK1/2 and JNK MAPKs in zebrafish was observed, P38 phosphorylation was significantly decreased at 7 and 14 d, and the changes in MAPKs were more evident in EPC cells previously exposed to AZ at 7 d. These results revealed that AZ initially induced low phosphorylation of MAPKs, triggering the attenuation of Nrf2 phosphorylation to weaken Nrf2 translocation into the nucleus in a longer exposure period (more than 5 d). The data in the cells and fish also showed that antioxidant activities were decreased to some extent at 5-7 d for the cells and 7-14 d for the fish. Furthermore, interferon-related factors were decreased in AZ-exposed zebrafish, explaining the reason that fish can't resist the virus infection. Overall, the present study provided a new adverse threat of AZ by amplifying the viral outbreak to endanger ecological safety in aquatic environment.

Behavioral and developmental toxicity assessment of the strobilurin fungicide fenamidone in zebrafish embryos/larvae (Danio rerio)

Strobilurin fungicides are among the most widely used in the world and have characteristics that include high water solubility and toxicity to aquatic organisms. While several studies report on mechanisms of toxicity of strobilurins in fish, there are no data on the sub-lethal toxicity of fish to the fungicide fenamidone. To address this gap, survival and hatch rate, deformities, mitochondrial bioenergetics, expression of oxidative stress and apoptotic genes, and behavior (locomotor activity and anxiolytic-related behaviors) were assessed in zebrafish embryos and larvae following exposure to fenamidone. Fenamidone negatively affected development of zebrafish embryos, causing a delay of hatching time at concentrations of 2.5 and 5 μM. Fenamidone caused morphological deformities in zebrafish, including pericardial edema, yolk sac edema, tail deformities, and spinal curvature. Exposure to 1.5 μM fenamidone reduced surface area of swim bladder in larvae at 6 dpf. Fenamidone significantly reduced oxygen consumption rates of embryos; 5 μM fenamidone decreased basal respiration (~85%), oligomycin induced ATP-linked respiration (~70%), FCCP-induced maximal respiration (~75%) and non-mitochondrial respiration (~90%) compared to controls. Sod2 mRNA levels were decreased by fenamidone in larval fish. Locomotor activity was significantly decreased in zebrafish larvae following exposure to 2 μM fenamidone but there was no evidence for anxiolytic nor anxiety-related behaviors (exposures of 100 nM up to 1.5 µM). This study addresses a data gap for potential risks associated with fenamidone exposure in developing fish.

Algicidal mechanism of Raoultella ornithinolytica against Microcystis aeruginosa: Antioxidant response, photosynthetic system damage and microcystin degradation

Water eutrophication caused by harmful algal blooms (HABs) occurs worldwide. It causes huge economic losses and has serious and potentially life-threatening effects on human health. In this study, the bacterium Raoultella sp. S1 with high algicidal efficiency against the harmful algae Microcystis aeruginosa was isolated from eutrophic water. The results showed that Raoultella sp. S1 initially flocculated the algae, causing the cells to sediment within 180 min and then secreted soluble algicidal substances that killed the algal cells completely within 72 h. The algicidal activity was stable across the temperature range -85.0 to 85.0 °C and across the pH range 3.00-11.00. Scanning electron microscopy (SEM) revealed the crumpling and fragmentation of cells algal cells during the flocculation and lysis stages. The antioxidant system was activated under conditions of oxidative stress, causing the increased antioxidant enzymes activities. Meanwhile, the oxidative stress response triggered by the algicidal substances markedly increased the malondialdehyde (MDA) and glutathione (GSH) content. We investigated the content of Chl-a and the relative expression levels of genes related to photosynthesis, verifying that the algicidal compounds attack the photosynthetic system by degrading the photosynthetic pigment and inhibiting the expression of key genes. Also, the results of photosynthetic efficiency and relative electric transport rate confirmed that the photosynthetic system in algal cells was severely damaged within 24 h. The algicidal effect of Raoultella sp. S1 against Microcystis aeruginosa was evaluated by analyzing the physiological response and photosynthetic system impairment of the algal cells. The concentration of microcystin-LR (MC-LR) slightly increased during the process of algal cells ruptured, and then decreased below its initial level due to the biodegradation of Raoultella sp. S1. To further investigate the algicidal mechanism of Raoultella sp. S1, the main components in the cell-free supernatant was analyzed by UHPLC-TOF-MS. Several low-molecular-weight organic acids might be responsible for the algicidal activity of Raoultella sp. S1. It is concluded that Raoultella sp. S1 has the potential to control Microcystis aeruginosa blooms.

Occurrence and risk assessment of herbicides and fungicides in atmospheric particulate matter in Hanoi, Vietnam

Vietnam is a Southeast Asian developing country with rapidly increasing air pollution, especially in large cities. Over 350,000 chemicals and chemical mixtures are produced and used in Vietnam; however, the country has only implemented air quality standards for 44 substances, which are primarily focused on inorganic and volatile organic compounds. Although numerous pesticides are frequently applied across large cities in Vietnam, information on their concentrations in atmospheric particulate matter (APM) is limited. Therefore, to investigate their occurrence and health effects, 187 pesticides in APM were screened using the liquid chromatography-mass spectrometry-quadrupole time of flight- Sequential Window Acquisition of All Theoretical Fragment Ion Spectra method (LC-QTOF-MS-SWATH). A total of 22 pesticides (16 fungicides and 6 herbicides) were quantified in the dry and rainy seasons. Among them, 19 substances were quantified in APM for the first time in Vietnam. Their median total concentrations in the dry season were higher than those in the rainy season, and the concentrations in the daytime were one-third of the night-time concentrations in both seasons. Their total levels ranged from 0.82 to 21.1 ng m^-3 (median, 3.63 ng m^-3), the detection frequencies of 9 pesticides were higher than 70%, and 7-14 pesticides were detected per sample (median, 10). Some of the detected pesticides were likely sourced from their prevalent use in amenity turf protection (e.g., in parks and public roads) and weed control (e.g., in gardens, floriculture, and agriculture). The total daily intake (DI_air) values for adults, children, and infants were 8.17E-06, 2.06E-05, and 2.45E-05 mg kg^-1 d^-1, respectively, and the highest Hazard Quotients (HQs) were 4.81E-04, 1.22E-03, and 1.44E-03, respectively. All HQs and HIs of the pesticides were < 1 for all population groups (adults, children, and infants), indicating negligible exposure risks.

Behavior of acetamiprid, azoxystrobin, pyraclostrobin, and lambda-cyhalothrin in/on pomegranate tissues

Pomegranate crop is affected by several insect pests and requires usage of a large number of pesticides, but the information on their behavior in pomegranate tissues is limited. A study was conducted to assess the behavior of acetamiprid, azoxystrobin, pyraclostrobin, and lambda-cyhalothrin in pomegranate fruits and leaves. The QuEChERS analytical method and LC-MS/MS and GC-MS were used for quantification of the analytes. The LOD (limit of detection) of acetamiprid, azoxystrobin, and pyraclostrobin was 0.0015 mg kg^-1 and lambda-cyhalothrin was 0.003 mg kg^-1. The respective LOQ (limit of quantification) was 0.005 and 0.01 mg kg^-1. The dissipation of the analytes best fitted into first-order rate kinetics and the half-lives of the chemicals in pomegranate fruits were 9.2-13 days and in the leaves were 13.5-17 days. In the pomegranate aril, the residue levels of acetamiprid, lambda-cyhalothrin, and pyraclostrobin were always < LOQ of these chemicals. Azoxystrobin was detected in pomegranate aril, and its residue was highest at 0.04 mg kg^-1 on the 10th day and reached < LOQ by the 25th day. The pre-harvest interval (PHI) required for acetamiprid, azoxystrobin, pyraclostrobin, and lambda-cyhalothrin at standard-dose treatment was 50, 58, 44, and 40 days, respectively. From double-dose treatment, the PHIs were 70, 75, 58, and 54 days, respectively. The pesticides used in this study were more persistent in the pomegranate leaves compared to the fruits. The outcome of this study can be incorporated into production of pomegranate fruits safe for consumption and to meet the domestic and export quality control requirements.

Azoxystrobin amine: A novel azoxystrobin degradation product from Bacillus licheniformis strain TAB7

Azoxystrobin (AZ) is a broad-spectrum synthetic fungicide widely used in agriculture globally. However, there are concerns about its fate and effects in the environment. It is reportedly transformed into azoxystrobin acid as a major metabolite by environmental microorganisms. Bacillus licheniformis strain TAB7 is used as a compost deodorant in commercial compost and has been found to degrade some phenolic and agrochemicals compounds. In this article, we report its ability to degrade azoxystrobin by novel degradation pathway. Biotransformation analysis followed by identification by electrospray ionization-mass spectrometry (MS), high-resolution MS, and nuclear magnetic resonance spectroscopy identified methyl (E)-3-amino-2-(2-((6-(2-cyanophenoxy)pyrimidin-4-yl)oxy)phenyl)acrylate, or (E)-azoxystrobin amine in short, and (Z) isomers of AZ and azoxystrobin amine as the metabolites of (E)-AZ by TAB7. Bioassay testing using Magnaporthe oryzae showed that although 40 μg/mL of (E)-AZ inhibited 59.5 ± 3.5% of the electron transfer activity between mitochondrial Complexes I and III in M. oryzae, the same concentration of (E)-azoxystrobin amine inhibited only 36.7 ± 15.1% of the activity, and a concentration of 80 μg/mL was needed for an inhibition rate of 56.8 ± 7.4%, suggesting that (E)-azoxystrobin amine is less toxic than the parent compound. To our knowledge, this is the first study identifying azoxystrobin amine as a less-toxic metabolite from bacterial AZ degradation and reporting on the enzymatic isomerization of (E)-AZ to (Z)-AZ, to some extent, by TAB7. Although the fate of AZ in the soil microcosm supplemented with TAB7 will be needed, our findings broaden our knowledge of possible AZ biotransformation products.

Detoxification Esterase StrH Initiates Strobilurin Fungicide Degradation in Hyphomicrobium sp. Strain DY-1

Strobilurin fungicides are widely used in agricultural production due to their broad-spectrum and fungal mitochondrial inhibitory activities. However, their massive application has restrained the growth of eukaryotic algae and increased collateral damage in freshwater systems, notably harmful cyanobacterial blooms (HCBs). In this study, a strobilurin fungicide-degrading strain, Hyphomicrobium sp. strain DY-1, was isolated and characterized successfully. Moreover, a novel esterase gene, strH, responsible for the de-esterification of strobilurin fungicides, was cloned, and the enzymatic properties of StrH were studied. For trifloxystrobin, StrH displayed maximum activity at 50°C and pH 7.0. The catalytic efficiencies (k _cat/K_m ) of StrH for different strobilurin fungicides were 196.32 ± 2.30 μM^-1 · s^-1 (trifloxystrobin), 4.64 ± 0.05 μM^-1 · s^-1 (picoxystrobin), 2.94 ± 0.02 μM^-1 · s^-1 (pyraclostrobin), and (2.41 ± 0.19)×10^-2μM^-1 · s^-1 (azoxystrobin). StrH catalyzed the de-esterification of a variety of strobilurin fungicides, generating the corresponding parent acid to achieve the detoxification of strobilurin fungicides and relieve strobilurin fungicide growth inhibition of Chlorella This research will provide insight into the microbial remediation of strobilurin fungicide-contaminated environments.IMPORTANCE Strobilurin fungicides have been widely acknowledged as an essential group of pesticides worldwide. So far, their residues and toxic effects on aquatic organisms have been reported in different parts of the world. Microbial degradation can eliminate xenobiotics from the environment. Therefore, the degradation of strobilurin fungicides by microorganisms has also been reported. However, little is known about the involvement of enzymes or genes in strobilurin fungicide degradation. In this study, a novel esterase gene responsible for the detoxification of strobilurin fungicides, strH, was cloned in the newly isolated strain Hyphomicrobium sp. DY-1. This degradation process detoxifies the strobilurin fungicides and relieves their growth inhibition of Chlorella.

Increasing temperature elevates the variation and spatial differentiation of pesticide tolerance in a plant pathogen

Climate change and pesticide resistance are two of the most imminent challenges human society is facing today. Knowledge of how the evolution of pesticide resistance may be affected by climate change such as increasing air temperature on the planet is important for agricultural production and ecological sustainability in the future but is lack in scientific literatures reported from empirical research. Here, we used the azoxystrobin-Phytophthora infestans interaction in agricultural systems to investigate the contributions of environmental temperature to the evolution of pesticide resistance and infer the impacts of global warming on pesticide efficacy and future agricultural production and ecological sustainability. We achieved this by comparing azoxystrobin sensitivity of 180 P. infestans isolates sampled from nine geographic locations in China under five temperature schemes ranging from 13 to 25°C. We found that local air temperature contributed greatly to the difference of azoxystrobin tolerance among geographic populations of the pathogen. Both among-population and within-population variations in azoxystrobin tolerance increased as experimental temperatures increased. We also found that isolates with higher azoxystrobin tolerance adapted to a broader thermal niche. These results suggest that global warming may enhance the risk of developing pesticide resistance in plant pathogens and highlight the increased challenges of administering pesticides for effective management of plant diseases to support agricultural production and ecological sustainability under future thermal conditions.

A comprehensive review of strobilurin fungicide toxicity in aquatic species: Emphasis on mode of action from the zebrafish model

Strobilurins are popular fungicides used in agriculture on a global scale. Due to their widespread use as agrochemicals, they can enter aquatic environments at concentrations that can elicit adverse effects in organisms. This review synthesizes the current state of knowledge regarding the toxic effects of strobilurin fungicides on aquatic species, including algal species, Daphnia magna, and fish species, to determine risk to aquatic organisms and ecosystems. Data show that the toxicities of strobilurins vary widely across aquatic species. Strobilurins bind cytochrome bc1 in mitochondrial complex III in fungi, and as such, research in aquatic species has focused on mitochondria-related endpoints following exposures to strobilurins. In fish, studies into the activities of mitochondrial complexes and the expression of genes involved in the electron transfer chain have been conducted, converging on the theme that mitochondrial complexes and their enzymes are impaired by strobilurins. In general, the order of toxicity of strobilurins for fish species are pyraoxystrobin > pyraclostrobin ≈ trifloxystrobin > picoxystrobin > kresoxim-methyl > fluoxastrobin > azoxystrobin. In addition to mitochondrial toxicity, studies also report genotoxicity, immunotoxicity, cardiotoxicity, neurotoxicity, and endocrine disruption, and each of these events can potentially impact whole organism-level processes such as development, reproduction, and behavior. Screening data from the US Environmental Protection Agency ToxCast database supports the hypothesis that these fungicides may act as endocrine disruptors, and high throughput data suggest estrogen receptor alpha and thyroid hormone receptor beta can be activated by some strobilurins. It is recommended that studies investigate the potential for endocrine disruption by strobilurins more thoroughly in aquatic species. Based on molecular, physiological, and developmental outcomes, a proposed adverse outcome pathway is presented with complex III inhibition in the electron transfer chain as a molecular initiating event. This review comprehensively addresses sub-lethal toxicity mechanisms of strobilurin fungicides, important as the detection of strobilurins in aquatic environments suggests exposure risks in wildlife.

Pollutant toxicology with respect to microalgae and cyanobacteria

Microalgae and cyanobacteria are fundamental components of aquatic ecosystems. Pollution in aquatic environment is a worldwide problem. Toxicological research on microalgae and cyanobacteria can help to establish a solid foundation for aquatic ecotoxicological assessments. Algae and cyanobacteria occupy a large proportion of the biomass in aquatic environments; thus, their toxicological responses have been investigated extensively. However, the depth of toxic mechanisms and breadth of toxicological investigations need to be improved. While existing pollutants are being discharged into the environment daily, new ones are also being produced continuously. As a result, the phenomenon of water pollution has become unprecedentedly complex. In this review, we summarize the latest findings on five kinds of aquatic pollutants, namely, metals, nanomaterials, pesticides, pharmaceutical and personal care products (PPCPs), and persistent organic pollutants (POPs). Further, we present information on emerging pollutants such as graphene, microplastics, and ionic liquids. Efforts in studying the toxicological effects of pollutants on microalgae and cyanobacteria must be increased in order to better predict the potential risks posed by these materials to aquatic ecosystems as well as human health.

Ecotoxicology of strobilurin fungicides

Strobilurin fungicides (SFs), a class of new fungicides, use strobilurin A as a lead compound. However, with excessive production and usage, the SF residues in soil and aquatic ecosystems may lead to environmental pollution. The mechanism of action (MOA) of SFs is respiratory inhibition of fungal mitochondria. Specifically, azoxystrobin (AZO), pyraclostrobin (PYR), trifloxystrobin (TRI), fluoxastrobin (FLUO), picoxystrobin (PICO), and kresoxim-methyl (KRE) are considered the most widely used SFs. The toxicities of those six fungicides in the environment are still unclear. The present review summarized the toxicities of the six SFs to terrestrial and aquatic biota, including mice, amphibians, aquatic organisms (fish, daphnia, algae, etc.), apoidea, soil animals (earthworms and Folsomia fimetaria), and soil microorganisms. We also review the residue, fate, and transportation of SFs. The results indicate that SFs are highly toxic to aquatic and soil organisms and pose potential risks to ecosystems. Current toxicology studies are more focused on acute or chronic toxicity, but the underlying mechanisms are still unclear and require further analysis. In addition, a simple and scientific analysis method is needed to compare the toxicity differences of different SFs to the same test organisms or differences in the same SFs to different test organisms.

Metabolomic modulations in a freshwater microbial community exposed to the fungicide azoxystrobin

An effective broad-spectrum fungicide, azoxystrobin (AZ), has been widely detected in aquatic ecosystems, potentially affecting the growth of aquatic microorganisms. In the present study, the eukaryotic alga Monoraphidium sp. and the cyanobacterium Pseudanabaena sp. were exposed to AZ for 7 days. Our results showed that 0.2-0.5 mg/L concentrations of AZ slightly inhibited the growth of Monoraphidium sp. but stimulated Pseudanabaena sp. growth. Meanwhile, AZ treatment effectively increased the secretion of total organic carbon (TOC) in the culture media of the two species, and this phenomenon was also found in a freshwater microcosm experiment (containing the natural microbial community). We attempted to assess the effect of AZ on the function of aquatic microbial communities through metabolomic analysis and further explore the potential risks of this compound. The metabonomic profiles of the microcosm indicated that the most varied metabolites after AZ treatment were related to the citrate cycle (TCA), fatty acid biosynthesis and purine metabolism. We thereby inferred that the microbial community increased extracellular secretions by adjusting metabolic pathways, which might be a stress response to reduce AZ toxicity. Our results provide an important theoretical basis for further study of fungicide stress responses in aquatic microcosm microbial communities, as well as a good start for further explorations of AZ detoxification mechanisms, which will be valuable for the evaluation of AZ environmental risk.

Photosynthetic toxicity of non-steroidal anti-inflammatory drugs (NSAIDs) on green algae Scenedesmus obliquus

The widespread use of pharmaceuticals and personal care products (PPCPs) has raised serious concerns regarding their potential ecotoxicological effects. We examined the photosynthetic toxicity of four non-steroidal anti-inflammatory drugs (NSAIDs), i.e. ibuprofen (rac-IBU and S-(+)-IBU), aspirin (ASA) and ketoprofen (KEP) on the green alga Scenedesmus obliquus. Our results showed that NSAIDs exerted inhibitory effects on algal growth; the IC_50-24h of S-(+)-IBU, rac-IBU, ASA, and KEP was 123.29, 107.91, 103.05, and 4.03 mg/L, respectively. KEP was the most toxic, ASA was slightly more toxic than rac-IBU, and S-(+)-IBU was the least toxic. NSAIDs adversely affected the cellular ultrastructure, as evident from plasmolysis, chloroplast deformation and disintegration. NSAID treatments decreased the chlorophyll and carotenoid content, and chlorophyll fluorescence parameters such as minimum fluorescence yield (F₀), maximum fluorescence yield (F_m), maximum photochemical quantum yield (F_v/F_m), PSII (photosystem II) effective quantum yield [Y(II)], photosynthetic electron transfer rate (ETR), and the photochemical quenching (qP), were also adversely affected. Algal photosynthetic and respiratory rates decreased following NSAID treatments, and the expression of genes involved in photosynthetic electron transport (psaA, psaB, psbB, psbD, and rbcL) was down-regulated. Furthermore, the functioning of the photosynthetic electron transport chain from PSI (photosystem I) to PSII, carbon assimilation, and photorespiration were affected. Our results suggest that NSAIDs can exert considerable toxic effects on the photosynthetic system of S. obliquus. These results provide a basis for evaluating the environmental safety of NSAIDs.

Differential responses of two cyanobacterial species to R-metalaxyl toxicity: Growth, photosynthesis and antioxidant analyses

Metalaxyl is a broad-spectrum chiral fungicide that used for the protection of plants, however extensive use of metalaxyl resulted in serious environmental problems. Thus, a study on the detoxification mechanism in algae/cyanobacteria and their ability for phycoremediation is highly recommended. Here, we investigated the physiological and biochemical responses of two cyanobacterial species; Anabaena laxa and Nostoc muscorum to R-metalaxyl toxicity as well as their ability as phycoremediators. Two different levels of R-metalaxyl, at mild (10 mg/L) and high dose (25 mg/L), were applied for one-week. We found that A. laxa absorbed and accumulated more intracellular R-metalaxyl compared to N. muscorum. R-metalaxyl, which triggered a dose-based reduction in cell growth, photosynthetic pigment content, and photosynthetic key enzymes' activities i.e., phosphoenolpyruvate carboxylase (PEPC) and ribulose‒1,5‒bisphosphate carboxylase/oxygenase (RuBisCo). These decreases were significantly less pronounced in A. laxa. On the other hand, R-metalaxyl significantly induced oxidative damage markers, e.g., H₂O₂ levels, lipid peroxidation (MDA), protein oxidation and NADPH oxidase activity. However, these increases were also lower in A. laxa compared to N. muscorum. To alleviate R-metalaxyl toxicity, A. laxa induced the polyphenols, flavonoids, tocopherols and glutathione (GSH) levels as well as peroxidase (POX), glutathione peroxidase (GPX), glutathione reductase (GR) and glutathione-s-transferase (GST) enzyme activities. On the contrary, the significant induction of antioxidants in N. muscorum was restricted to ascorbate, catalase (CAT) and ascorbate peroxidase (APX), dehydroascorbate reductase (DHAR) enzyme activities. Although A. laxa accumulated more R-metalaxyl, it experienced less stress due to subsequent induction of antioxidants. Therefore, A. laxa may be a promising R-metalaxyl phycoremediator. Our results provided basic data for understanding the ecotoxicology of R-metalaxyl contamination in aquatic habitats and the toxicity indices among cyanobacteria.

Temperature-Mediated Plasticity Regulates the Adaptation of Phytophthora infestans to Azoxystrobin Fungicide

Fungicide is one of the main approaches used in agriculture to manage plant diseases for food production, but their effectiveness can be reduced due to the evolution of plant pathogens. Understanding the genetics and evolutionary processes responsible for the development of fungicide resistance is a key to food production and social sustainability. In this study, we used a common garden experiment to examine the source of genetic variation, natural selection, and temperature contributing to the development of azoxystrobin resistance in Phytophthora infestans and infer sustainable ways of plant disease management in future. We found that plasticity contributed to ~40% of phenotypic variation in azoxystrobin sensitivity while heritability accounted for 16%. Further analysis indicated that overall population differentiation in azoxystrobin sensitivity (QST) was significantly greater than the overall population differentiation in simple sequence repeat (SSR) marker (FST), and the P. infestans isolates demonstrated higher level of azoxystrobin sensitivity at the higher experimental temperature. These results suggest that changes in target gene expression, enzymatic activity, or metabolic rate of P. infestans play a more important role in the adaptation of the pathogen to azoxystrobin resistance than that of mutations in target genes. The development of azoxystrobin resistance in P. infestans is likely driven by diversifying selection for local adaptation, and elevated temperature associated with global warming in the future may increase the effectiveness of using azoxystrobin to manage P. infestans. The sustainable approaches for increasing disease control effectiveness and minimizing the erosion of the fungicide efficacy are proposed.

Ecotoxicological Effects of Fungicides Azoxystrobin and Pyraclostrobin on Freshwater Aquatic Bacterial Communities

Extensive use of the fungicides azoxystrobin (AZ) and pyraclostrobin (PYR) can have negative effects on aquatic environments, but comprehensive studies on their effect on aquatic microbial communities are still lacking. We found that AZ and PYR could both inhibit the growth of Chlorella vulgaris, but PYR also inhibited Microcystis aeruginosa more strongly than did AZ. High-throughput sequencing analysis showed that AZ promoted the growth of Cyanobacteria in microcosms, and both PYR and AZ disturbed the ecological balance in the aquatic bacterial community and created distinct ecological risks. Our study suggests that the ecological risk of fungicides is complex, and fungicide use should be better managed to reduce potential risks to the environment.

Proteomic analysis of the hepatotoxicity of Microcystis aeruginosa in adult zebrafish (Danio rerio) and its potential mechanisms

Microcystis aeruginosa is one of the main species of cyanobacteria that causes water blooms. M. aeruginosa can release into the water several types of microcystins (MCs), which are harmful to aquatic organisms and even humans. However, few studies have investigated the hepatotoxicity of M. aeruginosa itself in zebrafish in environments that simulate natural aquatic systems. The objective of this study was to evaluate the hepatotoxicity of M. aeruginosa in adult zebrafish (Danio rerio) after short-term (96 h) exposure and to elucidate the potential underlying mechanisms. Distinct histological changes in the liver, such as enlargement of the peripheral nuclei and sinusoids and the appearance of fibroblasts, were observed in zebrafish grown in M. aeruginosa culture. In addition, antioxidant enzyme activity was activated and protein phosphatase (PP) activity was significantly decreased with increasing microalgal density. A proteomic analysis revealed alterations in a number of protein pathways, including ribosome translation, immune response, energy metabolism and oxidative phosphorylation pathways. Western blot and real-time PCR analyses confirmed the results of the proteomic analysis. All results indicated that M. aeruginosa could disrupt hepatic functions in adult zebrafish, thus highlighting the necessity of ecotoxicity assessments for M. aeruginosa at environmentally relevant densities.

Effects of imazethapyr spraying on plant growth and leaf surface microbial communities in Arabidopsis thaliana

Imazethapyr (IM) is an acetolactate synthase (ALS)-inhibiting herbicide that has been widely used in recent years. However, IM spraying can lead to the accumulation of herbicide residues in leaves. Here, we determined the effects of IM spraying on the plant growth and leaf surface microbial communities of Arabidopsis thaliana after 7 and 14 days of exposure. The results suggested that IM spraying inhibited plant growth. Fresh weight decreased to 48% and 26% of the control value after 7 and 14 days, respectively, of 0.035 kg/ha IM exposure. In addition, anthocyanin content increased 9.2-fold and 37.2-fold relative to the control content after 7 and 14 days of treatment, respectively. Furthermore, IM spraying destroyed the cell structures of the leaves, as evidenced by increases in the number of starch granules and the stomatal closure rate. Reductions in photosynthetic efficiency and antioxidant enzyme activity were observed after IM spraying, especially after 14 days of exposure. The diversity and evenness of the leaf microbiota were not affected by IM treatment, but the composition of community structure at the genus level was altered by IM spraying. Imazethapyr application increased the abundance of Pseudomonas, a genus that includes species pathogenic to plants and humans, indicating that IM potentially increased the abundance of pathogenic bacteria on leaves. Our findings increase our understanding of the relationships between herbicide application and the microbial community structures on plant leaves, and they provide a new perspective for studying the ecological safety of herbicide usage.

The fungicide azoxystrobin perturbs the gut microbiota community and enriches antibiotic resistance genes in Enchytraeus crypticus

The use of pesticides to ensure global food security is the most important pest control strategy in modern agriculture but causes extensive soil pollution. This pollution involves potential risks to human health and ecosystems. In addition to soil animal growth, the adverse impact of pesticides on the gut microbiomes of nontarget soil fauna remains largely unknown. Here, the effect of the fungicide azoxystrobin (AZ) on soil and the gut microbiota of soil animals (Enchytraeus crypticus) was studied. The tested concentrations of AZ altered the bacterial community in the soil and E. crypticus gut and were slightly toxic with respect to E. crypticus adult mortality and reproduction. The most abundant bacterial phylum, Proteobacteria, significantly increased in response to the 2 and 5 mg/kg AZ treatments, which implied a disordered unhealthy gut bacterial community. Furthermore, bacterial community analysis between the soil and gut showed that the main effect of AZ on the gut microbiota was directly through AZ, not soil microbiota. In addition, AZ exposure significantly enhanced the number and total abundance of antibiotic resistance genes (ARGs) in the E. crypticus gut; these genes may enter the soil food web to affect higher trophic levels and cause a more serious ecological risk. Our study reported the effect of pesticides on the gut of soil animals and on the enrichment of ARGs as global emerging contaminants, revealing unknown potential impacts of fungicides on ecosystem services and sustainable food production.

The fungicide azoxystrobin promotes freshwater cyanobacterial dominance through altering competition

BACKGROUND

Sharp increases in food production worldwide are attributable to agricultural intensification aided by heavy use of agrochemicals. This massive use of pesticides and fertilizers in combination with global climate change has led to collateral damage in freshwater systems, notably an increase in the frequency of harmful cyanobacterial blooms (HCBs). The precise mechanisms and magnitude of effects that pesticides exert on HCBs formation and proliferation have received little research attention and are poorly constrained.

RESULTS

We found that azoxystrobin (AZ), a common strobilurin fungicide, can favor cyanobacterial growth through growth inhibition of eukaryotic competitors (Chlorophyta) and possibly by inhibiting cyanobacterial parasites (fungi) as well as pathogenic bacteria and viruses. Meta-transcriptomic analyses identified AZ-responsive genes and biochemical pathways in eukaryotic plankton and bacteria, potentially explaining the microbial effects of AZ.

CONCLUSIONS

Our study provides novel mechanistic insights into the intertwined effects of a fungicide and eutrophication on microbial planktonic communities and cyanobacterial blooms in a eutrophic freshwater ecosystem. This knowledge may prove useful in mitigating cyanobacteria blooms resulting from agricultural intensification.

Leaching behavior of fluorescent additives from microplastics and the toxicity of leachate to Chlorella vulgaris

Chemical additives leaching from microplastics and their effects on physiology of microalgae are of environmental significance. So far, these issues remain unclear. Here, the leaching behavior of fluorescent additives from polyurethane sponge microplastics in simulated (acidic, saline, and basic water) and natural waters (river, lake, wetland, and sea water) was investigated. Release amount of additives increased with increasing solution pH and leaching time. The maximum release amount was reached at the leaching time of 12-24 h and the 3,3'-diaminobenzidine-like substances were identified in the leachate. The leached concentrations of fluorescent additives in simulated and natural waters followed the order of basic water > saline water > seawater > West Lake > River > Wetland. Effects of leachate and microplastics on growth and photosynthesis of Chlorella vulgaris were further evaluated. The maximum quantum efficiency of photosystem II (F_v/F_m) decreased with increasing leachate concentrations. Only high content (1.6 g L^-1) of microplastics exerted significant inhibitory influence on cell photosynthesis when microalgae were exposed to microplastics alone. Retention of algal cells inside the porous sponge microplastics did not change their photosynthetic efficiency. These findings indicate that leaching process of additives from microplastics depends mainly on water environments and the leached chemicals may pose ecological risks to aquatic organisms.

Evaluation of the taxonomic and functional variation of freshwater plankton communities induced by trace amounts of the antibiotic ciprofloxacin

Ciprofloxacin (CIP), one of the most frequently detected antibiotics in water systems, has become an aquatic contaminant because of improper disposal and excretion by humans and animals. It is still unknown how trace amounts of CIP affect the aquatic microbial community diversity and function. We therefore investigated the effects of CIP on the structure and function of freshwater microbial communities via 16S/18S rRNA gene sequencing and metatranscriptomic analyses. CIP treatment (7 μg/L) did not significantly alter the physical and chemical condition of the water body as well as the composition of the main species in the community, but slightly increased the relative abundance of cyanobacteria and decreased the relative abundance of eukaryotes. Metatranscriptomic results showed that bacteria enhanced their phosphorus transport and photosynthesis after CIP exposure. The replication, transcription, translation and cell proliferation were all suppressed in eukaryotes, while the bacteria were not affected in any of these aspects. This interesting phenomenon was the exact opposite to both the antibacterial property of CIP and its safety for eukaryotes. We hypothesize that reciprocal and antagonistic interactions in the microcosm both contribute to this result: cyanobacteria may enhance their tolerance to CIP through benefiting from cross-feeding and some secreted substances that withstand bacterial CIP stress would also affect eukaryotic growth. The present study thus indicates that a detailed assessment of the aquatic ecotoxicity of CIP is essential, as the effects of CIP are much more complicated in microbial communities than in monocultures. CIP will continue to be an environmental contaminant due to its wide usage and production and more attention should be given to the negative effects of antibiotics as well as other bioactive pollutants on aquatic environments.