Evaluation of the toxic response induced by azoxystrobin in the non-target green alga Chlorella pyrenoidosa

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.

Integrated proteome and pangenome analysis revealed the variation of microalga Isochrysis galbana and associated bacterial community to 2,6-Di-tert-butyl-p-cresol (BHT) stress

The phenolic antioxidant 2,6-Di-tert-butyl-p-cresol (BHT) has been detected in various environments and is considered a potential threat to aquatic organisms. Algal-bacterial interactions are crucial for maintaining ecosystem balance and elemental cycling, but their response to BHT remains to be investigated. This study analyzed the physiological and biochemical responses of the microalga Isochrysis galbana and the changes of associated bacterial communities under different concentrations of BHT stress. Results showed that the biomass of I. galbana exhibited a decreasing trend with increasing BHT concentrations up to 40 mg/L. The reduction in chlorophyll, carotenoid, and soluble protein content of microalgal cells was also observed under BHT stress. The production of malondialdehyde and the activities of superoxide dismutase, peroxidase, and catalase were further determined. Scanning electron microscopy analysis revealed that BHT caused surface rupture of the algal cells and loss of intracellular nutrients. Proteomic analysis demonstrated the upregulation of photosynthesis and citric acid cycle pathways as a response to BHT stress. Additionally, BHT significantly increased the relative abundance of specific bacteria in the phycosphere, including Marivita, Halomonas, Marinobacter, and Alteromonas. Further experiments confirmed that these bacteria had the ability to utilize BHT as the sole carbon resource for growth, and genes related to the degradation of phenolic compounds were detected through pangenome analysis.

Impacts of UV light on the effects of either conventional or nano-enabled azoxystrobin on Daphnia magna

Agri-chemicals such as fungicides are applied in natural settings and hence are exposed to the environment's ultraviolet (UV) light. Recently, many fungicides in commerce are being modified as nano-enabled formulations to increase agricultural productivity and reduce potential off-target effects. The present study investigated the impacts of sunlight-grade UV emission on the effects of either conventional or nano-enabled azoxystrobin (Az or nAz, respectively), a commonly applied agricultural fungicide, on Daphnia magna. Daphnids were exposed to increasing concentrations of Az or nAz under either full-spectrum (Vis) or full-spectrum Vis + UV (Vis + UV) lighting regimes to evaluate LC50s. Az LC50 was calculated at 268.8 and 234.2 μg/L in Vis or Vis + UV, respectively, while LC50 for nAz was 485.6 and 431.0 μg/L under Vis or Vis + UV light, respectively. Daphnids were exposed to 10% LC50 of either Az or nAz under Vis or Vis + UV lighting regime for 48 h or 21 d (acute and chronic, respectively). By 48 h, both Az and nAz reduced O2 consumption and increased TBARS. Heart rate was increased in Az-exposed daphnids but not in nAz groups. Neither of the two chemicals impacted thoracic limb activity. In 21 d exposures, Az significantly reduced biomass production and fecundity, but nAz groups were not significantly different from controls. The results of the present study demonstrate that conventional Az is more toxic to D. magna at lethal and sub-lethal levels in acute and chronic exposures, and sunlight strength UV can potentiate both acute and chronic effects of Az and nAz on D. magna.

Unveiling the molecular mechanisms of size-dependent effect of polystyrene micro/nano-plastics on Chlamydomonas reinhardtii through proteomic profiling

Microplastics have become a prevalent environmental pollutant due to widespread release and production. Algae, as primary producers, play a crucial role in maintaining the ecological balance of freshwater environments. Despite reports on the inhibition of microalgae by microplastics, the size-dependent effects on microalgae and associated molecular mechanism remain poorly understood. This study investigates the impacts of three polystyrene micro/nano-plastics (PS-MNPs) with different sizes (100 nm, 350 nm, and 6 μm) and concentrations (25-200 mg/L) on Chlamydomonas reinhardtii (C. reinhardtii) throughout its growth period. Results reveal size- and concentration-dependent growth inhibition and induction of oxidative stress by PS-MNPs, with microalgae exhibiting increased vulnerability to smaller-sized and higher-concentration PS-MNPs. Proteomics analysis elucidates the size-dependent suppression of proteins involved in the photosynthesis process by PS-MNPs. Photosynthetic activity assays demonstrate that smaller PS-MNPs more significantly reduce chlorophyll content and the maximal photochemical efficiency of photosystem II. Finally, electron microscope and Western blot assays collectively confirm the size effect of PS-MNPs on microalgae growth is attributable to suppressed protein expression rather than shading effects. This study contributes to advancing our understanding of the intricate interactions between micro/nano-plastics and algae at the molecular level, emphasizing the efficacy of proteomics in dissecting the mechanistic aspects of microplastics-induced biological effects on environmental indicator organisms.

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.

Biological activity and molecular mechanism of inactivation of Microcystis aeruginosa by ultrasound irradiation

Harmful algal blooms (HABs) significantly impact on water quality and ecological balance. Ultrasound irradiation has proven to be an effective method for algal control. Nevertheless, the molecular mechanisms underlying the inactivation of M. aeruginosa by ultrasound are still unknown. In this study, the physiological activity and molecular mechanism of algal cells exposed to different frequencies of ultrasound were studied. The results indicated a pronounced inhibition of algal cell growth by high-frequency, high-dose ultrasound. Moreover, with increasing ultrasound dosage, there was a higher percentage of algal cell membrane ruptures. SEM and TEM observed obvious disruptions in membrane structure and internal matrix. Hydroxyl radicals generated by high-frequency ultrasound inflicted substantial cell membrane damage, while increased antioxidant enzyme activities fortified cells against oxidative stress. Following 2 min of ultrasound irradiation at 740 kHz, significant differential gene expression occurred in various aspects, including energy metabolism, carbohydrate metabolism, and environmental information processing pathways. Moreover, ultrasound irradiation influenced DNA repair and cellular apoptosis, suggesting that the algal cells underwent biological stress to counteract the damage caused by ultrasound. These findings reveal that ultrasound irradiation inactivates algae by destroying their cell structures and metabolic pathways, thereby achieving the purpose of algal suppression.

Modulation in growth, oxidative stress, photosynthesis, and morphology reveals higher toxicity of alpha-cypermethrin than chlorpyrifos towards a non-target green alga at high doses

Considering the frequent detection of pesticides in the aquatic environment, the ecotoxicological effects of Chlorpyrifos (CHP), an organophosphate, and alpha-cypermethrin (ACM), a pyrethroid, on freshwater microalgae were compared for the first time in this study. High concentrations of both CHP and ACM significantly suppressed the growth of test microalga Graesiella emersonii (p < 0.05). The 96-h EC50 of CHP and ACM were 54.42 mg L-1 and 29.40 mg L-1, respectively. Sub-inhibitory doses of both pesticides increased ROS formation in a concentration-dependent manner, which was accompanied by changes in antioxidant enzymes activities, lipid peroxidation, and variations in photosynthetic pigment concentration. Furthermore, both pesticides influenced photosystem II performance, oxygen-evolving complex efficiency and, intracellular ATP levels. Scanning electron microscopy analysis revealed that high concentrations of both CHP and ACM caused considerable morphological changes in the microalga. In comparison, CHP was more toxic than ACM at low concentrations, whereas ACM was more toxic at high concentrations.

Evidence of strobilurin fungicides and their metabolites in Dongjiang River ecosystem, southern China: Bioaccumulation and ecological risks

Despite the widespread application of strobilurin fungicides (SFs) in agriculture, little is known about their distribution and bioaccumulation in aquatic ecosystems. In this study, the concentrations of 12 SFs and two of their metabolites were determined in abiotic (water and sediment; n = 83) and biotic (plant, algae, zooplankton, and fish; n = 123) samples collected from a subtropical freshwater ecosystem, namely, Dongjiang River wetland, in southern China. Among the 12 SFs measured, azoxystrobin (AZ) was the major fungicide found in surface water (median: 2.20 ng/L) and sediment (0.064 ng/g dry wt.). Azoxystrobin acid (AZ-acid), a metabolite of AZ, was the major analyte in the plant samples and had a median concentration at 0.36 ng/g dry wt. In algae and zooplankton, (Z)-metominostrobin was the predominant fungicide and had median concentrations of 3.52 and 5.55 ng/g dry wt., respectively. In fish muscle, dimoxystrobin (DIMO) was the major SF and had a median concentration of 0.47 ng/g dry wt. The bioconcentration factor (BCF) values of AZ-acid, trifloxystrobin (TFS), and pyraclostrobin (PYR) in algae and zooplankton and AZ-acid, PYR, TFS, TFS-acid, picoxystrobin, and DIMO in fish muscle exceeded 1000 L/kg (algae, zooplankton, and fish concentrations were expressed on a dry weight basis), suggesting that these fungicides can accumulate in biota. A positive association between log BCFs of SFs in fish and logKow of SFs and a negative correlation between log BCFs and the log solubility index were observed. Additionally, the risk quotient (RQ) was calculated to evaluate the potential ecotoxicological risk of SFs to different aquatic organisms (algae, zooplankton, and fish). The PYR and DIMO concentrations at 19 sampling sites had RQ values >0.1, indicating moderate ecotoxicological risks to aquatic organisms. This study is the first to document the widespread occurrence of SFs and their metabolites in aquatic ecosystems and to elucidate the bioaccumulation potential of SFs in aquatic organisms.

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.

Biochemical responses of freshwater microalgae Chlorella sorokiniana to combined exposure of Zn(Ⅱ) and estrone with simultaneous pollutants removal

With the development of livestock industry, contaminants such as divalent zinc ions (Zn (Ⅱ)) and estrone are often simultaneously detected in livestock wastewater. Nevertheless, the combined toxicity of these two pollutants on microalgae is still unclear. Moreover, microalgae have the potential for biosorption and bioaccumulation of heavy metals and organic compounds. Thus, this study investigated the joint effects of Zn (Ⅱ) and estrone on microalgae Chlorella sorokiniana, in terms of growth, photosynthetic activity and biomolecules, as well as pollutants removal by algae. Interestingly, a low Zn (Ⅱ) concentration promoted C. sorokiniana growth and photosynthetic activity, while the high concentration experienced inhibition. As the increase of estrone concentration, chlorophyll a content increased continuously to resist the environmental stress. Concurrently, the secretion of extracellular polysaccharides and proteins by algae increased with exposure to Zn (Ⅱ) and estrone, reducing toxicity of pollutants to microalgae. Reactive oxygen species and superoxide dismutase activity increased as the increase of pollutant concentration after 96 h cultivation, but high pollutant concentrations resulted in damage of cells, as proved by increased MDA content. Additionally, C. sorokiniana displayed remarkable removal efficiency for Zn (Ⅱ) and estrone, reaching up to 86.14% and 84.96% respectively. The study provides insights into the biochemical responses of microalgae to pollutants and highlights the potential of microalgae in pollutants removal.

Elevated pCO2 alleviates the toxic effects of polystyrene nanoparticles on the marine microalga Nannochloropsis oceanica

Concerns about the environmental effects of nanoplastics on marine ecosystems are increasing. Ocean acidification (OA) has also become a global environmental problem. Plastic pollution occurs concomitantly with anthropogenic climate stressors such as OA. However, the combined effects of NP and OA on marine phytoplankton are still not well understood. Therefore, we have investigated the behavior of ammonia (NH2) polystyrene nanoparticles (PS NP) in f/2 medium under 1000 μatm pCO2 and discussed the toxicity of PS NP (100 nm; 0.5 and 1.5 mg/L) on Nannochloropsis oceanica under long and short-term acidification (LA and SA; pCO2 ~ 1000 μatm). We observed PS NP suspended in pCO2 1000 μatm f/2 medium aggregated to a size greater than nanoscale (1339.00 ± 76.10 nm). In addition, we found that PS NP significantly inhibited the growth of N. oceanica at two concentrations, which also produced oxidative stress. Whereas, the growth of algal cells under the coupling of acidification and PS NP was significantly better than that of single PS NP exposure. This indicated that acidification significantly alleviated the toxic effects of PS NP on N. oceanica, and long-term acidification can even promote the growth of N. oceanica under low-density NP. To further understand the mechanism, we analyzed a comparative transcriptome. The results showed that PS NP exposure inhibited the expression of genes involved in the TCA cycle. The acidification was possibly reflected in ribosomes and corresponding processes, which alleviated the negative effects of PS NP on N. oceanica by promoting the synthesis of related enzymes and proteins. This study provided a theoretical basis for assessing the damage of NP to marine phytoplankton under OA. We propose that future studies evaluating the toxicology of NP to marine ecology should consider the changing ocean climate.

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 role of algal EPS in reducing the combined toxicity of BPA and polystyrene nanoparticles to the freshwater algae Scenedesmus obliquus

Both Bisphenol A (BPA) and polystyrene nanoplastics (PSNPs) are routinely found in several consumer products such as packaging materials, flame retardants, and cosmetics. The environment is seriously endangered by nano- and microplastics. In addition to harming aquatic life, nanoplastics (NPs) also bind to other pollutants, facilitating their dispersion in the environment and possibly promoting toxicity induced by these pollutants. The toxic effects of polystyrene nanoplastics (PS-NPs) and BPA were examined in this study, as well as the combined toxic impacts of these substances on the freshwater microalgae Scenedesmus obliquus. In addition, the exopolymeric substances (EPS) secreted by algae will interact with the pollutants modifying their physicochemical behaviour and fate. This work aimed to investigate how algal EPS alters the combined effects of BPA and PSNPs on the microalgae Scenedesmus obliquus. The algae were exposed to binary mixtures of BPA (2.5, 5, and 10 mg/L) and PSNPs (1 mg/L of plain, aminated, and carboxylated PSNPs) with EPS added to the natural freshwater medium. Cell viability, hydroxyl and superoxide radical generation, cell membrane permeability, antioxidant enzyme activity (catalase and superoxide dismutase), and photosynthetic pigment content were among the parameters studied to determine the toxicity. It was observed that for all the binary mixtures, the carboxylated PSNPs were most toxic when compared to the toxicity induced by the other PSNP particles investigated. The maximum damage was observed for the mixture of 10 mg/L of BPA with carboxylated PSNPs with a cell viability of 49%. When compared to the pristine mixtures, the EPS-containing mixtures induced significantly reduced toxic effects. A considerable decrease in reactive oxygen species levels, activity of antioxidant enzymes (SOD and CAT), and cell membrane damage was noted in the EPS-containing mixtures. Reduced concentrations of the reactive oxygen species led to improved photosynthetic pigment content in the cells.

Toxicity effects of microplastics and nanoplastics with cadmium on the alga Microcystis aeruginosa

The extensive spread of microplastics (MPs) and nanoplastics (NPs) in the aquatic environment has attracted widespread attention. The toxicity of cadmium (Cd) combined with microplastics (MPs) and nanoplastics (NPs) toward freshwater algae Microcystis aeruginosa (M. aeruginosa) was investigated to evaluate the environmental behavior of the Cd complexation in fresh water. Cd alone has the highest toxicity to algae. Both MPs and NPs also have a negative effect on the growth of algae as individual components due to their adsorption of nutrients and disruption of the alga's activity in a single MPs/NPs system. Compared with the single system, the toxicity of compound pollution including MPs + Cd and NPs + Cd becomes stronger, which presents a synergistic effect. In the presence of NPs, more extracellular polymeric substances (EPS) appeared, which helped to reduce the toxic effect on the algal cells. Moreover, MPs/NPs + Cd stimulate the production of microcystin-LR (MC-LR) under different treatments. Overall, the aquatic environmental assessment shows potentially elevated risks associated with combined MPs/NPs with Cd, which should be considered.

Acute effects of three surface-modified nanoplastics against Microcystis aeruginosa: Growth, microcystin production, and mechanisms

As plastic pollution continues to increase and plastic waste is shredded to form smaller plastic particles, there is growing concern about the potential impact of nanoplastics (NPs) on freshwater ecosystems. In this work, the effects of three surface-modified NPs, including polystyrene (PS), PS-NH₂, and PS-COOH, on the growth, photosynthetic activity, oxidative damage, and microcystins (MCs) production/release of Microcystis aeruginosa (M. aeruginosa) were investigated. Results indicated that all three NPs significantly inhibited the growth of M. aeruginosa after a 96 h exposure, and the growth inhibition followed the order of PS-NH₂ > PS > PS-COOH (p < 0.05). Meanwhile, all three NPs at the concentration of 100 mg/L significantly increased the content of intra-MCs (115 %, 147 %, and 121 % higher than the control, respectively) and extra-MCs (142 %, 175 %, and 151 % higher than the control, respectively) after a 96 h exposure (p < 0.05). Moreover, our findings also suggested that the potential mechanisms of surface-modified PS NPs on M. aeruginosa growth and MCs production/release were associated with physical constraints, photosynthetic activity obstruct, and oxidative damage. Our findings provided direct evidence for different kinds of surface modifications of PS NPs on freshwater algae and improve the understanding of the potential risk of NPs in aquatic ecosystems.

Toxic responses of freshwater microalgae Chlorella sorokiniana due to exposure of flame retardants

Flame retardants, such as Tetrabromobisphenol A (TBBPA), Tris(1,3-dichloro-2-propyl) phosphate (TDCPP) and tributyl phosphate (TBP), are frequently detected in surface water. However, the effects of FRs exposure on aquatic organisms especially freshwater microalgae are still unclear. In this study, the toxicities of TBBPA, TDCPP and TBP to microalgae Chlorella sorokiniana, in terms of growth inhibition, photosynthetic activity inhibition and oxidative damage, were investigated, and according ecological risks were assessed. The results showed that TBBPA, TDCPP and TBP had inhibitory effects on C. sorokiniana, with 96 h EC₅₀ (concentration for 50% of maximal effect) values of 7.606, 41.794 and 49.996 mg/L, respectively. Fv/Fm decreased as the increase of exposure time under 15 mg/L TBBPA. Under 50 mg/L TDCPP and 80 mg/L TBP exposure, Fv/Fm decreased significantly after 24 h. However, Fv/Fm rose after 96 h, indicating that the damaged photosynthetic activity was reversible. The content of chlorophyll a decreased, as the increase of TBBPA concentration from 3 to 15 mg/L. However, chlorophyll a increased first and then decreased, as the increase of TDCPP and TBP concentrations from 0 to 50 mg/L and 0-80 mg/L, respectively. Results indicated that C. sorokiniana could use the phosphorus of TDCPP and TBP to ensure the production of chlorophyll a. The risen content of reactive oxygen species, malondialdehyde as well as superoxide dismutase activity indicated that exposure to FRs induced oxidative stress. Additionally, the risk quotients showed that tested FRs had ecological risks in natural waters or wastewaters. This study provides insights into the toxicological mechanisms of different FRs toward freshwater microalgae for better understanding of according environmental risks.

Ecotoxicological effects and bioaccumulation in Eichhornia crassipes induced by long-term exposure to triclosan

In this study, the ecotoxicological effects and bioaccumulation of triclosan (TCS) in Eichhornia crassipes (E. crassipes) were investigated with 28 d exposure experiments. The results showed that chlorophyll content was increased after 7 d exposure to 0.05-0.1 mg L^-1 TCS, while it was inhibited significantly by 0.5 mg L^-1 TCS after 21 d exposure. The concentrations of soluble protein in the leaves increased during the initial stage (7 d and 14 d), whereas they decreased during 21 d and 28 d. The concentrations of soluble protein in the roots gradually reduced during the exposure time. The antioxidant enzyme activities in roots decreased continually with the exposure time. However, the antioxidant enzyme (SOD and CAT) activities in leaves decreased after exposure longer than 14 d. Moreover, differentially expressed genes (DEGs) were observed in the root of E. crassipes after a 28 d exposure to 0.5 mg L^-1 TCS, with 11023 DEGs down-regulated and 3947 DEGs up-regulated. 5 SOD down-regulated genes and 3 CAT down-regulated genes were identified from transport and catabolism in cellular processes. After 28 d exposure, the TCS content in roots and leaves stressed by 0.5 mg L^-1 TCS were up to 13.04 μg g^-1 and 1.97 μg g^-1, respectively. SOD in leaves was negatively correlated with TCS content in leaves, CAT in roots was negatively correlated with TCS content in roots. These results provide experimental data to assess the ecological risk of TCS with long exposure in aquatic systems.

Removal mechanisms of erythromycin by microalgae Chlorella pyrenoidosa and toxicity assessment during the treatment process

Microalgae-based biotechnology for antibiotic removal has received increasing attention as an economical and green method. This study investigated the removal mechanism of erythromycin by Chlorella pyrenoidosa and its correlation with the ecotoxic responses of microalgae. The degradation products (DPs) were identified, and their toxicity was predicted. The results indicated that only 4.04 %, 6.28 % and 23.53 % of erythromycin were left after 21-day microalgae treatment in 0.1, 1.0 and 10 mg/L treatments, respectively. Biodegradation contributed 48.62-67.01 %, 16.67-52.32 % and 6.42-24.82 %, while abiotic degradation contributed 8.76-29.61 %, 5.19-41.39 %, and 16.55-51.22 % to erythromycin attenuation in 0.1, 1.0, and 10 mg/L treatments, respectively. The growth and physiological-biochemical parameters of microalgae were slightly affected in low concentration treatment, which may be the main reason that biodegradation was the prominent removal mechanism. By contrast, oxidative damage in high concentration treatment inhibited the cell growth and chlorophyll content of microalgae, which hindered erythromycin biodegradation. In addition, eleven erythromycin degradation products (DPs) were identified during microalgae treatment of 21 days. Seven DPs including DP717, DP715, DP701A, DP701B, DP657, DP643, and DP557, represented higher toxicity to aquatic organisms than erythromycin.

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.

Eco-toxicological effect of a commercial dye Rhodamine B on freshwater microalgae Chlorella vulgaris

In this study, the acute toxicity effects of a fluorescent xanthene dye, Rhodamine B (RhB), widely used in textile, paper, and leather industries was investigated on a freshwater microalgae Chlorella vulgaris. The acute toxicity of RhB on C. vulgaris was determined by examining the growth, cell morphology, pigment production, protein content, and the activities of oxidative stress enzymes. Based on the results of the toxicity study of 24-96 h, the median inhibitory concentration (IC₅₀) values ranged from 69.94 to 31.29 mg L^-1. The growth of C. vulgaris was conspicuously inhibited by RhB exposure, and the cell surfaces appeared to be seriously shrunk in SEM analysis. The growth of C. vulgaris was hindered after exposure to graded concentrations (10-50 mg L^-1) of RhB. A significant reduction in growth rate, pigment synthesis (chlorophyll a, chlorophyll b, and carotenoid), and protein content was recorded in a dose-dependent manner. After 96 h exposure of C. vulgaris to 50 mg L^-1 RhB, chlorophyll a, chlorophyll b, carotenoids, and protein contents were reduced by 71.59, 74.90, 65.84, and 74.20%, respectively. The activities of the antioxidant enzymes peroxidase (POD), and catalase (CAT) also increased markedly in the presence of RhB. A notable effect was observed on oxidative enzymes catalase and peroxidase, indicating that oxidative stress may be the primary factor in the inhibition of growth and pigment synthesis. Consequently, the experimental acute toxicity data were compared to the QSAR prediction made by the ECOSAR programme. Results showed that the experimental acute toxicity values were 67.74-fold lower than the ECOSAR predicted values. The study provides convincing evidence for the metabolic disruption in the ubiquitous microalgae C. vulgaris due to the RhB dye toxicity.

Toxic effects of fludioxonil on the growth, photosynthetic activity, oxidative stress, cell morphology, apoptosis, and metabolism of Chlorella vulgaris

Fludioxonil is widely used in the control of crop diseases because of its broad spectrum and high activity, but its presence is now common in waterways proximate to treated areas. This study examined the toxic effects and mechanisms of fludioxonil on the microalgal taxa Chlorella vulgaris. The results showed that fludioxonil limited the growth of C. vulgaris and the median inhibitory concentration at 96 h was 1.87 mg/L. Concentrations of 0.75 and 3 mg/L fludioxonil reduced the content of photosynthetic pigments in algal cells to different degrees. Fludioxonil induced oxidative damage by altering C. vulgaris antioxidant enzyme activities and increasing reactive oxygen species levels. Fludioxonil at 0.75 mg/L significantly increased the activity of antioxidant enzymes. The highest level of activity was 1.60 times that of the control group. Both fludioxonil treatment groups significantly increased ROS levels, with the highest increase being 1.90 times that of the control group. Transmission electron microscope showed that treatment with 3 mg/L fludioxonil for 96 h disrupted cell integrity and changed cell morphology, and flow cytometer analysis showed that fludioxonil induced apoptosis. Changes in endogenous substances indicated that fludioxonil negatively affects C. vulgaris via altered energy metabolism, biosynthesis of amino acids, and unsaturated fatty acids. This study elucidates the effects of fludioxonil on microalgae and the biological mechanisms of its toxicity, providing insights into the importance of the proper management of this fungicide.

Evaluation of phoxim toxicity on aquatic and zebrafish intestinal microbiota by metagenomics and 16S rRNA gene sequencing analysis

Phoxim is one of the main organophosphorus pesticides used in agricultural production. However, little information is known about how it affects the aquatic microbial community and the intestinal microbiota of fish. Herein, we utilized shotgun metagenomics and 16S rRNA gene sequencing to reveal the aquatic eco-risk of phoxim. Seven days of phoxim exposure significantly changed the composition of aquatic microbial community, obliterated the interactions between microorganisms, and thus reduced the complexity and stability of the microbial community. During long-time exposure (i.e., 14 days), most of the ecological functions were restored due to the redundancy of the microbial community. However, phoxim exposure promoted the dissemination of elfamycin resistance gene. The zebrafish gut microbial community also recovered from a temporary ecological disorder of aquatic microbiota, but phoxim continually affected zebrafish growth and swimming behavior. Overall, our results demonstrated that phoxim exposure significantly changed the structure and function of the microbial community and displayed a negative impact on freshwater ecosystems in a short exposure time.

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.

Distinct Responses of Biofilm Carbon Metabolism to Nanoplastics with Different Surface Modifications

Recently, there is an increasing concern regarding the toxicity of nanoplastics (NPs) on freshwater organisms. However, knowledge about the potential impacts of NPs with different surface modification on freshwater biofilms is still very limited. In this research, biofilms were cultured in lab and exposed to nano polystyrene (PS) beads: non-functionalized PS NPs, PS-COOH NPs, and the carbon source utilization of biofilms were measured by BIOLOG ECO microplates. The results showed that both two types of PS NPs significantly reduced the total carbon metabolic activity of biofilms, compared with the controls, whereas the carbon metabolic rate increased notably, especially for the PS-COOH NPs treatments at day 14. Moreover, results from six categories of carbon sources analysis suggested that PS NPs with different surface chemical properties exhibit distinct effects on the carbon utilization of biofilms, and the divergent changes of the specific carbon source category were observed at day 21 from the two PS NPs treatments. In addition, the metabolic functional diversity of biofilms were not altered by the PS NPs treatments. These findings highlighted that chemical properties of NPs play an important role in the toxic effects on the carbon metabolism activities of the biofilms. This study offers new insights that nanoplastics of different chemical characteristics have the ability to affect the microbial-mediated carbon cycling process in aquatic ecosystems.

Transcriptomics unveiled metabolic perturbations in Desmodesmus quadricauda by sulfacetamide: Key functional genes involved in the tolerance and biodegradation process

Antibiotic contamination in the environment has significant adverse effects on benthic microorganisms, which causes dysfunction of normal ecological processes. However, in-depth molecular mechanisms underlying the potential ecological impacts of these emerging pollutants are poorly understood. In this study, metabolic perturbations in a freshwater microalga, Desmodesmus quadricauda by sulfacetamide (SFM) were investigated using transcriptomics. The results found 28 genes in the tricarboxylic acid cycle and oxidative phosphorolysis pathways were significantly downregulated by 3.97 to 6.07, and 2.47 to 5.99 folds by 0.1 and 1 mg L^-1 SFM, respectively. These results indicated that SFM disrupted the microalgal cellular activities through inhibition of energy metabolism. Whilst, the upregulated genes have been most enriched in porphyrin and chlorophyll metabolism (hemE, hemL, hemY, chlD, chlP, PAO, and CAO), and arachidonic acid metabolism (GGT1_5 and gpx). Expression of these genes was significantly upregulated by up to 3.36 times for tolerance against SFM. Moreover, the genes encoding decarboxylase, oxidoreductases, α-amylase, hydrolases, O-acetyltransferase, and lyase were upregulated by >2 folds, which can induce di/hydroxylation, decarboxylation, bond cleavage and deamination. These findings provide insights into the molecular mechanisms of the ecotoxicological effects of antibiotics on microalgae, and supply useful information for their environmental risk assessment and management.

Evaluation of the acute toxic response induced by triazophos to the non-target green algae Chlorella pyrenoidosa

Residues of triazophos in aquatic ecosystems due to extensive use for controlling pests in agriculture has became worldwide concern, while the toxic response of triazophos on the non-target green algae in aquatic environment is not well studied. Therefore, the acute (96 h) toxic effects of 1 and 10 mg/L triazophos on green algae Chlorella pyrenoidosa were evaluated in present study. The results showed that the growth was notably inhibited when treated with triazophos and the 96 h-EC₅₀ (median inhibition concentration) were 12.79 mg/L. The content of photosynthetic pigments (including chl a, chl b, total-chl and carotinoids) clearly decreased under two treatments after 48 h and 96 h with exception for the values at 48 h exposure in 1 mg/L treatment. In addition, the transcript abundance of photosynthesis-related genes (psbA, psbC and rbcL) showed obvious decrease in above two treatments after exposure 96 h to triazophos. In response to 10 mg/L triazophos treatment, the morphology of thylakoid chloroplast of algal cells were obviously damaged. It was also found that starch granules increased with down-regulation of atpB gene expression in 10 mg/L treatment, which suggests that triazophos may inhibit the energy metabolism of C. pyrenoidosa. Moreover, the algal growth inhibition was along with the increase of intracellular reactive oxygen species (ROS), activity of antioxidant enzymes and malondialdehyde content indicating oxidative damage and lipid peroxidation in the algal cells. Our findings reveal that triazophos has potential toxicity and environmental risks to one of the primary producers green algae.

The combined toxicity of binary mixtures of antibiotics against the cyanobacterium Microcystis is dose-dependent: insight from a theoretical nonlinear combined toxicity assessment method

The entry of antibiotics into aquatic ecosystems has a serious impact. Antibiotics usually exist as mixtures in natural water bodies. Therefore, it is particularly important to evaluate the mixed toxicity of antibiotic mixtures. The study of the combined toxicity of binary mixtures of antibiotics is the basis for exploring the mixed toxicity of multiple antibiotics. In this investigation, Microcystis aeruginosa (M. aeruginosa) was used as the test organism, and a theoretical nonlinear combined toxicity assessment method was adopted to evaluate the effects of binary mixtures of antibiotics consisting of tetracycline (TC), sulfadiazine (SD), and sulfamethoxazole (SMX) on cell growth, enzymatic activity, and gene expression. The median lethal concentrations of TC, SD, and SMX to M. aeruginosa were 0.52 mg L^-1, 1.65 mg L^-1, and 0.71 mg L^-1, respectively. The results from the theoretical nonlinear combined toxicity assessment method showed that SD + TC was synergistic at low concentrations and antagonistic at high concentrations, while the combinations of SMX + SD and SMX + TC were synergistic. The determination of enzymatic activity and gene expression indicated that the antibiotics could inhibit the growth of M. aeruginosa by destroying the cell membrane structure, inhibiting photosynthesis, impeding the cell division process and the electron transfer process, and destroying the molecular structure of proteins and DNA. Different combinations of antibiotics have different degrees of damage to the antioxidant system and cell membrane self-repair function of M. aeruginosa, which are the reasons for the different combined toxicity effects.

Tylosin toxicity in the alga Raphidocelis subcapitata revealed by integrated analyses of transcriptome and metabolome: Photosynthesis and DNA replication-coupled repair

Tylosin (TYN) is widely used in veterinary prophylactic as a macrolide and frequently detected in the surface water. Previous studies showed that exposure to TYN caused suppression of chlorophyll biosynthesis and inhibition of photosynthesis at the physiological level, associated with reduced growth performances in algae, but the molecular mechanisms remain unknown, especially at environmental exposure levels. The present study elucidated the underlying molecular mechanism(s) of TYN toxicity in a model green alga Raphidocelis subcapitata using approaches of transcriptomics and metabolomics. Following a 7-day exposure, algal growth performances were reduced by 26.3% and 58.3% in the 3 (an environmentally realistic level) and 400 μg L^-1 TYN treatment group, respectively. A total of 577 (99) and 5438 (180) differentially expressed genes (differentially accumulated metabolites) were identified in algae treated with 3 and 400 μg L^-1 TYN, respectively. Signaling pathways including photosynthesis - antenna protein, porphyrin and chlorophyll metabolism, carbon fixation in photosynthetic organisms, and DNA replication were altered in the 400 μg L^-1 TYN treatment, while photosynthesis and DNA replication were the shared pathways in both TYN treatments. The metabolomic data further suggest that molecular pathways related to photosynthesis, DNA replication-coupled repair and energy metabolism were impaired. Photosynthesis was identified as the most sensitive target of TYN toxicity in R. subcapitata, in contrast to protein synthesis inhibition caused by TYN in bacteria. This study provides novel mechanistic information of TYN toxicity in R. subcapitata.

Physiological, biochemical and transcription effects of roxithromycin before and after phototransformation in Chlorella pyrenoidosa

Photodegradation is an important transformation pathway for macrolide antibiotics (MCLs) in aquatic environments, but the ecotoxicity of MCLs after phototransformation has not been reported in detail. This study investigated the effects of roxithromycin (ROX) before and after phototransformation on the growth and physio-biochemical characteristics of Chlorella pyrenoidosa, and its toxicity were explored using transcriptomics analysis. The results showed that 2 mg/L ROX before phototransformation (T0 group) inhibited algae growth with inhibition rates of 53.06%, 54.17%, 47.26%, 31.27%, and 28.38% at 3, 7, 10, 14, and 21 d, respectively, and chlorophyll synthesis was also inhibited. The upregulation of antioxidative enzyme activity levels and the malondialdehyde content indicated that ROX caused oxidative damage to C. pyrenoidosa during 21 d of exposure. After phototransformation for 48 h (T48 group), ROX exhibited no significant impact on the growth and physio-biochemical characteristics of the microalgae. Compared with the control group (without ROX and its phototransformation products), 2010 and 2988 differentially expressed genes were identified in the T0 and T48 treatment groups, respectively. ROX significantly downregulated genes related to porphyrin and chlorophyll metabolism, which resulted in the inhibition of chlorophyll synthesis and algae growth. ROX also significantly downregulated genes of DNA replication, suggesting the increased DNA proliferation risks in algae. After phototransformation, ROX upregulated most of the genes associated with the porphyrin and chlorophyll metabolism pathway, which may be the reason that the chlorophyll content in T48 treatment group showed no significant difference from the control group. Almost all light-harvesting chlorophyll a/b (LHCa/b) gene family members were upregulated in both T0 and T48 treatment groups, which may compensate part of the stress of ROX and its phototransformation products.

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.

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.

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.

Ecotoxicity evaluation of azoxystrobin on Eisenia fetida in different soils

Azoxystrobin, a widely used broad-spectrum strobilurin fungicide, may pose a potential threat in agricultural ecosystems. To assess the ecological risk of azoxystrobin in real soil environments, we performed a study on the toxic effects of azoxystrobin on earthworms (Eisenia fetida) in three different natural soils (fluvo-aquic soil, black soil and red clay soil) and an artificial soil. Acute toxicity of azoxystrobin was determined by filter paper test and soil test. Accordingly, exposure concentrations of chronic toxicity were set at 0, 0.1, 1.0 and 2.5 mg kg^-1. For chronic toxicity test, reactive oxygen species, activity of antioxidant enzymes (superoxide dismutase, catalase and peroxidase), detoxifying enzyme (glutathione transferase), level of lipid peroxidation (malondialdehyde) and level of oxygen damage of DNA (8-hydroxydeoxyguanosine) in earthworms were determined on the 7th, 14th, 21st, 28th, 42nd and 56th days after treatment. Both acute and chronic toxic results showed azoxystrobin exhibit higher toxicity in natural soil than in artificial soil, indicating that traditional artificial soil testing method underestimate ecotoxicity of azoxystrobin in a real agricultural environment on the earthworm population. Combining with the analysis of soil physicochemical properties, the present experiment provided scientific guidance for rational application of azoxystrobin in agricultural production systems.

Polystyrene nanoplastics affect growth and microcystin production of Microcystis aeruginosa

Nanoplastics are widely distributed in freshwater environments, but few studies have addressed their effects on freshwater algae, especially on harmful algae. In this study, the effects of polystyrene (PS) nanoplastics on Microcystis aeruginosa (M. aeruginosa) growth, as well as microcystin (MC) production and release, were investigated over the whole growth period. The results show that PS nanoplastics caused a dose-dependent inhibitory effect on M. aeruginosa growth and a dose-dependent increase in the aggregation rate peaking at 60.16% and 46.34%, respectively, when the PS nanoplastic concentration was 100 mg/L. This caused significant growth of M. aeruginosa with a specific growth rate up to 0.41 d^-1 (50 mg/L PS nanoplastics). After a brief period of rapid growth, the tested algal cells steadily grew. In addition, the increase in PS nanoplastics concentration promoted the production and release of MC. When the PS nanoplastic concentration was 100 mg/L, the content of the intracellular (intra-) and extracellular (extra-) MC increased to 199.1 and 166.5 μg/L, respectively, on day 26, which was 31.4% and 31.1% higher, respectively, than the control. Our results provide insights into the action mechanism of nanoplastics on harmful algae and the potential risks to freshwater environments.

Integrative analyses of transcriptomics and metabolomics in Raphidocelis subcapitata treated with clarithromycin

As a macrolide antibiotic, clarithromycin (CLA) has a high detection rate in surface water and sewage treatment plant effluents worldwide, posing a considerably high ecological risk to aquatic ecosystem. However, algal transcriptome and metabolome in response to CLA remains largely unknown. In this study, a model alga Raphidocelis subcapitata (R. subcapitata), was exposed to CLA at the concentrations of 0, 3, 10, and 15 μg L^-1. Transcriptomic analysis was performed for all the treatment groups, whereas metabolomics was merely applied to 0, 3, and 10 μg L^-1 groups because of the limited amount of algal biomass. After 7 d cultivation, the growth of R. subcapitata was significantly hindered at the concentrations above 10 μg L^-1. A total of 115, 1833, 2911 genes were differentially expressed in 3, 10, and 15 μg L^-1 groups, respectively; meanwhile, 134 and 84 differentially accumulated metabolites (DAMs) were found in the 3 and 10 μg L^-1 groups. Specifically, expression levels of DEGs and DAMs related to xenobiotic metabolism, electron transport and energy synthesis were dysregulated, leading to the produced reactive oxygen species (ROS). To confront the CLA-induced injury, the biosynthesis of unsaturated fatty acids and carotenoids of R. subcapitata in 3 μg L^-1 were up-regulated; although the photosynthesis was up-regulated in both 10 μg L^-1 and 15 μg L^-1 groups, the energy synthesis and the ability to resist ROS in these two groups were down-regulated. Overall, this study shed light on the mechanism underlying the inhibitory effects of macrolide antibiotics in algae.

Growth inhibition, toxin production and oxidative stress caused by three microplastics in Microcystis aeruginosa

Microplastics (MPs) have aroused widespread concern due to their extensive distribution in aquatic environments and adverse effects on aquatic organisms. However, the underlying toxicity of different kinds of MPs on freshwater microalgae has not been examined in detail. In this study, we investigated the effects of polyvinyl chloride (PVC), polystyrene (PS) and polyethylene (PE) MPs on the growth of Microcystis aeruginosa, as well as on its toxin production and oxidative stress. We found that all three kinds of MPs had an obvious inhibition effect on the growth of M. aeruginosa. Considering the results of antioxidant-related indicators, the activity of superoxide dismutase (SOD) and catalase (CAT), and cell membrane integrity were greatly affected with exposure to PVC, PS and PE MPs. Moreover, the content of intracellular (intra-) and extracellular (extra-) microcystins (MCs) had a noticeable increase due to the presence of PVC, PS, and PE MPs. Finally, according to the comprehensive stress resistance indicators, the resistance of M. aeruginosa to three MPs followed the order: PE (3.701)> PS (3.607)> PVC (2.901). Our results provide insights into the effects of different kinds of MPs on freshwater algae and provide valuable data for risk assessment of different types of MPs.

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.

Self-Assembled Surfactant-Templated Synthesis of Porous Hollow Silica Nanoparticles: Mechanism of Formation and Feasibility of Post-Synthesis Nanoencapsulation

SiO₂ is bioinert and highly functionalizable, thus making it a very attractive material for nanotechnology applications such as drug delivery and nanoencapsulation of pesticides. Herein, we synthesized porous hollow SiO₂ nanoparticles (PHSNs) by using cetyltrimethylammonium bromide (CTAB) and Pluronic P123 as the structure-directing agents. The porosity and hollowness of the SiO₂ structure allow for the protective and high-density loading of molecules of interest inside the nanoshell. We demonstrate here that loading can be achieved post-synthesis through the pores of the PHSNs. The PHSNs are monodisperse with a mean diameter of 258 nm and a specific surface area of 287 m² g^-1. The mechanism of formation of the PHSNs was investigated using 1-D and 2-D solid-state nuclear magnetic resonance (SS-NMR) and Fourier-transform infrared spectroscopy (FTIR). The data suggest that CTAB and Pluronic P123 interact, forming a hydrophobic spherical hollow cage that serves as a template for the porous hollow structure. After synthesis, the surfactants were removed by calcination at 550 °C and the PHSNs were added to an Fe³⁺ solution followed by addition of the reductant NaBH₄ to the suspension, which led to the formation of Fe(0) NPs both on the PHSNs and inside the hollow shell, as confirmed by transmission electron microscopy imaging. The imaging of the formation of Fe(0) NPs inside the hollow shell provides direct evidence of transport of solute molecules across the shell and their reactions within the PHSNs, making it a versatile nanocarrier and nanoreactor.

Inactivation of harmful Anabaena flos-aquae by ultrasound irradiation: Cell disruption mechanism and enhanced coagulation

Harmful algal blooms pose a potential threat to the safety of drinking water sources. Ultrasound is an effective method for algae removal. However, this method can lead to the release of algal organic matter and the effects and toxic mechanisms of ultrasound on Anabaena are still poorly understood. The destruction mechanism of Anabaena flos-aquae cells under different ultrasonic conditions, the safety of intracellular organic matter (IOM) release to water and the enhanced coagulation efficiency of ultrasound were studied. Results showed that high-frequency ultrasound was effective in breaking down algae cells. After 10 min ultrasonication at 20 kHz, 5 min at 740 kHz and 1 min at 1120 kHz, the algae cells were inactivated and algae growth was halted. Ultrasound radiation can lead to the release of IOM, primarily chlorophyll a and phycocyanin, followed by some tryptophan and humic substances, polysaccharides, and proteins. The sonicated ribosomes were considerably reduced, and the antioxidant system of cells was also damaged to some extent. The coagulation effect of algae cells was substantially improved after ultrasonication. Thus, the safety of algae cell removal could be improved by controlling the changes in physiological structure and IOM release of algae cells by adjusting the ultrasound parameters.

Ecotoxicological evaluation of fungicides used in viticulture in non-target organisms

The effect of fungicides, commonly used in vine cultures, on the health of terrestrial and aquatic ecosystems has been poorly studied. The objective of this study was to evaluate the toxicity of three viticulture fungicides (myclobutanil, cymoxanil, and azoxystrobin) on non-target organisms, the bacteria Rhodopirellula rubra, Escherichia coli, Pseudomonas putida, and Arthrobacter sp., the microalgae Raphidocelis subcapitata, and the macrophyte Lemna minor. Fungicide toxicity was performed in acute cell viability assay for bacteria; 72-h and 7-day growth inhibition tests for R. subcapitata and L. minor, respectively. Contents of photosynthetic pigments and lipid peroxidation in L. minor were evaluated. Arthrobacter sp. and P. putida showed resistance to these fungicides. Even though azoxystrobin affected R. rubra and E. coli cell viability, this effect was due to the solvent used, acetone. Cell viability decrease was obtained for R. rubra exposed to cymoxanil and E. coli exposed to myclobutanil (30 min of exposure at 10 mg/L and 240 min of exposure at 46 mg/L, respectively). R. subcapitata showed about 10-fold higher sensitivity to azoxystrobin (EC_50-72h = 0.25 mg/L) and cymoxanil (EC_50-72h = 0.36 mg/L) than L. minor to azoxystrobin and myclobutanil (EC_50-72h = 1.53 mg/L and EC_50-72h = 1.89 mg/L, respectively). No lipid peroxidation was observed in L. minor after fungicide exposure, while changes of total chlorophyll were induced by azoxystrobin and myclobutanil. Our results showed that non-target aquatic organisms of different trophic levels are affected by fungicides used in viticulture.

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.

Transcriptome analysis of the effect of bisphenol A exposure on the growth, photosynthetic activity and risk of microcystin-LR release by Microcystis aeruginosa

Bisphenol A (BPA), one of the most abundant endocrine-disrupting compounds, is frequently detected in diverse aquatic environments, which imposes a substantial burden on the aquatic ecosystem. However, the correlation between BPA levels and the outbreak of a cyanobacterial bloom remains largely unknown. In this study, the cellular and transcriptomic responses to BPA exposure were investigated. Exposure to a high concentration of BPA (50 μM) significantly inhibited the growth of cyanobacterial cells, with the highest inhibition ratio of 51.3%, photosynthesis, and the release of extracellular microcystin-LR (MC-LR) (p < 0.05). However, exposure to low concentrations of BPA (0.1 and 1 μM) also affected these indicators, but the differences were closely related to the growth phase of the cyanobacterial cells. In addition, an imbalance between the antioxidant system and oxidative stress was observed in cyanobacteria under BPA stress. Folate biosynthesis, ABC transporters and ubiquinone and other terpenoid-quinone biosynthesis were the central metabolic pathways triggered by BPA stress. The up-regulated genes, including queC, VTE3 and PsbO were the controller of cellular growth and photosynthesis. The down-regulated genes, including VET4, MlaE and DnaA were potential biomarkers of oxidative damage. The up- and down-regulated genes, including CA, Ppc and CyoE were the main regulators of energy generation. The findings will provide important insights into the role of endocrine disruptors in the frequent outbreak of cyanobacterial blooms.

Transcriptomic analysis reveals common pathways and biomarkers associated with oxidative damage caused by mitochondrial toxicants in Chironomus dilutus

A variety of chemicals are capable of provoking mitochondrial dysfunction and thereby contribute to metabolic disorder related effects in wildlife and human. For better identifying new mitochondrial toxicants and assessing mitochondria-related risk, an in-depth understanding of toxic mechanisms and biomarkers should be attained. In the current study, a representative mitotoxicant, azoxystrobin, was assessed for lethal and sublethal outcomes in Chironomus dilutus after 96-h exposure and the toxic mechanism was explored. Global transcriptomic profiles by RNA-sequencing revealed that ampk, acc1, atp2a, gsk3b, pi3k, fak, atr, chk1, and map3k5 were the key genes which involved in the toxic action of azoxystrobin and could serve as potential molecular biomarkers. A major network of common toxicity pathways was then developed for mitotoxicants towards aquatic insects. In particular, calcium ion-PI3K/AKT and cAMP-AMPK-lethality pathways were demonstrated, in addition to the well-known mitochondrial electron transfer-oxidative damage-apoptosis pathway. These analyses could help developing adverse outcome pathways that integrate toxicological information at various levels and support more effective risk assessment and management of mitotoxicants.

Toxic effect and mechanism of tris (1,3-dichloro-2-propyl)phosphate (TDCPP) on the marine alga Phaeodactylum tricornutum

Tris (1,3-dichloro-2-propyl)phosphate (TDCPP) is an organophosphate-based plasticizer and flame retardant with a high production volume. The ubiquitous distribution and persistence of TDCPP in aquatic environment have led to concerns over its possible toxic effects on aquatic organism. However, data regarding the toxicity of TDCPP on algae are limited, and the molecular mechanism remains largely unknown. Therefore, we determined the growth characteristics, physiological changes and transcriptome profiles of Phaeodactylum tricornutum in response to 4 mg L^-1 TDCPP for 24 h. TDCPP caused morphological damage and growth inhibition with an EC₅₀ value of 3.71 mg L^-1 at 96 h. A decline in pigments and photosynthetic activity was observed, indicating the occurrence of photosynthesis inhibition. Although the activities of both glutathione peroxidase and glutathione reductase were stimulated, oxidative stress was not relieved in the algal cells, as evidenced by the elevated levels of reactive oxygen species and lipid peroxidation. Transcriptomic analyses revealed 3312 differentially expressed genes (DEGs), and photosynthesis was a key target, as genes related to this process were greatly altered under TDCPP stress. Moreover, some DEGs were also enriched in amino acid metabolism, nitrogen metabolism, nucleotide metabolism and lipid metabolism, implying that TDCPP-induced damage towards algae by various pathways. Additionally, several TFs related to stress signaling were differentially expressed, suggesting roles in the TDCPP stress response. The results will provide critical data to understand the ecological risks and toxic mechanism of OPFRs entering into marine habitat.

Evaluation of the acute toxic effect of azoxystrobin on non-target crayfish (Astacus leptodactylus Eschscholtz, 1823) by using oxidative stress enzymes, ATPases and cholinesterase as biomarkers

Azoxystrobin is a broad-spectrum fungicide used worldwide. Since azoxystrobin spreads to large areas, its toxic effects on non-target organisms have aroused interest. In this study, the acute toxicity (96 h) of azoxystrobin on the crayfish (Astacus leptodactylus) was examined by using various biomarkers. The 96 h-LC₅₀ dose (1656 mg L^-) and its three sub-doses (828, 414, 207 mg L^-1) were applied to crayfish. Superoxide dismutase (SOD) and glutathione peroxidase (GPx) activities were increased significantly compared to the control in hepatopancreas, gill and muscle tissues. The activities of acetylcholinesterase (AChE) and glutathione S-transferase (GST) increased, and glutathione reductase (GR) activity decreased significantly in hepatopancreas. Level of reduced glutathione (GSH) decreased significantly. The content of malondialdehyde (MDA) increased in a dose-dependent manner in all azoxystrobin treatments with the exception of the lowest dose (207 mg L^-1)treatment. ATPases (Na⁺/K⁺ -ATPase, Mg²⁺ -ATPase, Ca²⁺ -ATPase, total ATPase) were significantly inhibited in gill and muscle tissues. The results of the present study indicate that azoxystrobin induces oxidative stress, and has adverse effects on activities of AChE and ATPases in crayfish.

Respiratory Toxicity of Azoxystrobin, Pyraclostrobin and Coumoxystrobin on Chlorella vulgaris

Azoxystrobin (AZ), pyraclostrobin (PYR) and coumoxystrobin (COU) exert negative impacts on Chlorella vulgaris. Thus, in this study, C. vulgaris was used to assess the respiratory toxicity of AZ, PYR and COU by determining the acute toxicity, complex III activity and ATP viability. The 96 h-EC₅₀ values of AZ, PYR and COU for C. vulgaris were 1.85, 2.21 and 1.62 mg/L, respectively. AZ, PYR and COU exerted significant effects on complex III activity and ATP viability after exposure to 0.71, 1.01 and 1.08 mg/L of the fungicides. The binding potentials of AZ, PYR and COU toward ubiquinone were - 10.44, - 9.31 and - 12.98 kcal/mol, respectively, which had adverse effects on amino acids. These results provided new insight into the potential acute respiratory toxicity mechanisms of these strobilurin fungicides in algae.

Fluoxastrobin-induced effects on acute toxicity, development toxicity, oxidative stress, and DNA damage in Danio rerio embryos

Strobilurin fungicides (SFs), the most commonly used fungicides, pose threats for controlling fungal diseases. The fungicides were monitored in aquatic ecosystems and may have negative effects on nontarget organisms. This project was undertaken to monitor the toxic effects of fluoxastrobin (FLUO) on Danio rerio embryos and to evaluate the SF risks in aquatic ecosystems. The 96-hour median lethal concentration (96 h LC₅₀), hatching rates, and morphological abnormalities were used to analyze acute toxicity and teratogenicity of FLUO to Danio rerio embryos at an FLUO dose of 0.549 mg/L (95% confidence limits: 0.423 to 0.698 mg/L); the results showed that FLUO has high toxicity in embryos that is analogous to the toxicity observed in adult Danio rerio. Fluoxastrobin may lead embryos to delayed hatching at concentrations >0.6 mg/L, and it may lead to teratogenicity (i.e., pericardial edema and spinal curvature). Based on the 96 h LC₅₀ results, the following parameters were evaluated in Danio rerio: development-related indicators (body length and heart rates), reactive oxygen species (ROS) levels, lipid peroxidation (LPO) levels, the levels of three antioxidants, 8-hydroxy-2-deoxyguanosine (8-OHdG), and apoptosis. The results elucidated that FLUO inhibition of spinal and heart development may be induced by oxidative stress. In addition, FLUO induced a notable climb in ROS content, LPO, the activated activity of superoxide dismutase (SOD) and catalase (CAT), and it inhibited glutathione peroxidase (GSH-PX) activity. Fluoxastrobin led to DNA damage (i.e., a notable climb of 8-OHdG contents and apoptotic cells). Collectively, FLUO posed threats to Danio rerio embryos at multiple levels, and this investigation could be a reminder for people to be more judicious in SF-use to avoid or relieve SF toxicity to nontarget organisms.