Enantioselective oxidative stress and oxidative damage caused by Rac- and S-metolachlor to Scenedesmus obliquus

What can reactive oxygen species (ROS) tell us about the action mechanism of herbicides and other phytotoxins?

Reactive oxygen species (ROS) are formed in plant cells continuously. When ROS production exceeds the antioxidant capacity of the cells, oxidative stress develops which causes damage of cell components and may even lead to the induction of programmed cell death (PCD). The levels of ROS production increase upon abiotic stress, but also during pathogen attack in response to elicitors, and upon application of toxic compounds such as synthetic herbicides or natural phytotoxins. The commercial value of many synthetic herbicides is based on weed death as result of oxidative stress, and for a number of them, the site and the mechanism of ROS production have been characterized. This review summarizes the current knowledge on ROS production in plants subjected to different groups of synthetic herbicides and natural phytotoxins. We suggest that the use of ROS-specific fluorescent probes and of ROS-specific marker genes can provide important information on the mechanism of action of these toxins. Furthermore, we propose that, apart from oxidative damage, elicitation of ROS-induced PCD is emerging as one of the important processes underlying the action of herbicides and phytotoxins.

Slightly acidic electrolyzed water significantly restrains the accumulation of the microalgae Pseudokirchneriella subcapitata in hydroponic systems

AIMS

This study explored the effects of slightly acidic electrolyzed water (SAEW) on algae to exploit technologies that effectively suppress algal growth in hydroponic systems and improve crop yield.

METHODS AND RESULTS

The effects of SAEW on algal growth and the response mechanisms of algae to SAEW were investigated. Moreover, we studied whether the application of SAEW adversely affected tomato seedling growth. The results showed that SAEW significantly inhibited algal growth and destroyed the integrity of the algal cells. In addition, the intracellular oxidation-reduction system of algae was greatly influenced by SAEW. The H2O2, O2-, malondialdehyde (MDA), and reactive oxygen species (ROS) fluorescence signals were significantly induced by SAEW, and superoxide dismutase (SOD), peroxidase (POD), and glutathione reductase (GR) activities were greatly enhanced by a low SAEW concentration but significantly inhibited by SAEW with a high available chlorine concentration, which may contribute to heavy oxidative stress on algal growth and cell structure break down, eventually causing the death of algae and cell number decrease. We also found that regardless of the concentration of SAEW (from 10 to 40 mg L-1), there was no significant change in the germination index, length, or fresh weight of the hydroponic tomato seedlings.

CONCLUSIONS

Our findings demonstrate that SAEW can be used in hydroponic systems to restrain algae with no negative impact on tomato plants.

Central Chirality and Axial Chirality Recognition of the Enantioselective Antibodies to Herbicide Metolachlor

Enantioselective antibodies have emerged as efficient tools in the field of chiral chemical detection and separation. However, it is complicated to obtain a highly stereoselective antibody due to the unclear recognition mechanism. In this study, the hapten of metolachlor was synthesized and enantio-separated. The absolute configuration of the four haptens obtained was identified by the computed and experimental electronic circular dichroism comparison. Five polyclonal antibodies against the Rac-metolachlor and its enantiomers were generated by immunization. The cross-activity of all the 5 antibodies with 44 structural analogues, including metolachlor enantiomers, was tested. It demonstrated that antibodies have higher specificity to recognize central chirality than axial chirality. Especially, αRR-MET-Ab exhibited excellent specificity and stereoselectivity. Accordingly, 3D-QSAR models were constructed and revealed that paired stereoisomers exhibited opposite interactions with the antibodies. It is the first time that the antibodies against four stereoisomers were prepared and analyzed, which will be conducive to the rational design of the stereoselective antibodies.

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.

Developmental and cardiovascular toxicities of acetochlor and its chiral isomers in zebrafish embryos through oxidative stress

Acetochlor (ACT) is a widely used pesticide, yet the environmental and health safety of its chiral isomers remains inadequately evaluated. In this study, we evaluated the toxicity of ACT and its chiral isomers in a zebrafish model. Our findings demonstrate that ACT and its chiral isomers disrupt early zebrafish embryo development, inducing oxidative stress, abnormal lipid metabolism, and apoptosis. Additionally, ACT and its chiral isomers lead to cardiovascular damage, including reduced heart rate, decreased red blood cell (RBC) flow rate, and vascular damage. We further observed that (+)-S-ACT has a significant impact on the transcription of genes involved in cardiac and vascular development, including tbx5, hand2, nkx2.5, gata4, vegfa, dll4, cdh5, and vegfc. Our study highlights the potential risk posed by different conformations of chiral isomeric pesticides and raises concerns regarding their impact on human health. Overall, our results suggest that the chiral isomers of ACT induce developmental defects and cardiovascular toxicity in zebrafish, with (+)-S-ACT being considerably more toxic to zebrafish than (-)-R-ACT.

Comparative studies of transformation behaviors and mechanisms of halophenols in multiple chemical oxidative systems

Due to wide applications, halophenols (HPs), especially bromophenols, chlorophenols, and fluorophenols, are commonly detected but resistant to biological removal in wastewater treatment plants (WWTPs). This study investigated the overall transformation behaviors of three representative HPs (2,4-dichlorophenol: 24-DCP, 2,4-dibromophenol: 24-DBP, 2,4-difluorophenol: 24-DFP) in six chemical oxidative systems (KMnO₄, K₂FeO₄, NaClO, O₃, UV, and persulfate (PS)). The results revealed fast removal of selected HPs by O₃, PS and K₂FeO₄, while a large discrepancy in their removal efficiencies occurred under UV irradiation, KMnO₄ oxidation and particularly chlorination. Based on the analysis of the identified intermediates and products, coupling among the five routes was the general route, and dimers were the main intermediates for HP oxidation. The effect of the halogen atom on the transformation pathways of HPs was highly reaction type dependent. Among the six chemical treatments, PS could induce HPs to yield relatively low-molecular-weight polymers and obtain the highest coupling degree. Transition state (TS) calculations showed that the H atom linked to the phenoxy group of HPs was the most easily abstracted by hydroxyl radicals to form the coupling precursor, i.e., phenoxy radicals. This high coupling behavior further resulted in the increased toxicity to green algae. Characterization revealed that HP reaction solutions treated with PS had a severely negative effect on algae growth, photosynthetic pigment synthesis, and the antioxidant enzyme system. These findings can shed light on the reaction mechanisms of advanced oxidation technologies and some risk management and control of PS technique may be considered when treating phenolic pollutants.

Enantioselective Oxidative Stress and DNA Damage Induced by Rac- and S-metolachlor on the Earthworm Eisenia fetida

Metolachlor is a widely used chiral herbicide. However, information on its enantioselective toxicity to earthworms, an important soil organism, remains limited. Herein, the effects of Rac- and S-metolachlor on oxidative stress and DNA damage in Eisenia fetida were investigated and compared. Moreover, the degradation of both herbicides in the soil was also determined. The results showed that reactive oxygen species (ROS) in E. fetida were more easily induced by Rac-metolachlor than S-metolachlor at a higher concentration (above 16 µg/g). Similarly, the effects of Rac-metolachlor on superoxide dismutase (SOD) activity and DNA damage in E. fetida were more significant than those of S-metolachlor at the same exposure concentration and time. Rac- and S-metolachlor did not result in severe lipid peroxidation. The toxic effects of both herbicides on E. fetida gradually decreased after 7 days as the exposure was prolonged. At the same concentration, S-metolachlor degrades faster than Rac-metolachlor. These results suggest that Rac-metolachlor has a greater effect on E. fetida than S-metolachlor, providing a significant reference for the rational use of metolachlor.

Growth, ROS accumulation site, and photosynthesis inhibition mechanism of Chlorella vulgaris by triclosan

Although the addition of triclosan (TCS) in consumer products has been strictly restricted, its continuous applications in hospitals and other medical facilities and its numerous residues still pose a potential risk to aquatic organisms and aquatic ecosystems. In this study, we investigated the growth, biochemical alterations, and physiological responses of Chlorella vulgaris exposed to different concentrations of TCS. The potential toxicity mechanisms associated with excessive production of reactive oxygen species (ROS) and disruption of photosynthetic system II (PSII) were also analyzed. The results indicated that the growth, cellular ultrastructure, and physiology of C. vulgaris were severely affected by TCS in a dose-effect dependent manner. TCS inhibited the growth of C. vulgaris, leading to mitochondria enlargement, the disordering of the arrangement of thylakoids, cell wall rupture, organelles loss, and the cytoplasm lysis. TCS induced severe oxidative damage characterized by ROS accumulation, elevated malondialdehyde (MDA), and up-regulation of antioxidant enzyme activities. Moreover, in TCS-induced algal cells, the main sites of ROS accumulation were chloroplasts, mitochondria, and cell membranes, with ROS accumulating most in the mitochondria. In addition, TCS caused damage to the reaction center (RC inactivation), donor side (OEC damage), and accepted side (electron transport from Q_A to Q_B) of PSII in C. vulgaris, leading to inhibition of photosynthetic activity. These results could provide novel insights into the mechanisms of TCS-induced ROS accumulation and photosynthetic inhibition in C. vulgaris, which would contribute to a deep understanding of TCS toxicity on algae.

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.

Toxicological effects of different ionic liquids on growth, photosynthetic pigments, oxidative stress, and ultrastructure of Nostoc punctiforme and the combined toxicity with heavy metals

Ionic liquids (ILs¹) are used widely because of their excellent properties. However, their ecotoxicity for environment has aroused great concern. Here we studied, the toxicity of three ILs with different numbers of methyl substituents and anions as well as the combined effect of heavy metals to edible algae Nostoc punctiforme. The results show that fresh weight and chlorophyll content decreased, indicating that the growth and photosynthesis were adversely affected. Polysaccharides and soluble protein contents decreased, resulting in a reduced nutritional value of Nostoc punctiforme. ILs can produce many reactive oxygen species (ROS), which lead to increased the malondialdehyde (MDA) content. In order to remove excessive ROS, antioxidant enzymes activity is increased, but decreases under high IL concentration, because the structure and function of the enzymes became damaged. ILs cause stress to algae, as the cell ultrastructure is indicating by increased amounts of starch and osmiophilic globules. The combined action of heavy metals with ILs decreases the antioxidant enzymes activity and chlorophyll content, and increases the MDA content. The results show that the order of toxicity is [C₈MIM]Cl >[C₈MIM]Br> [C₈DMIM]Br. The combination of heavy metals and ILs cause an increase of the toxicity to Nostoc punctiforme.

Stereoselective degradation pathway of amide chiral herbicides and its impacts on plant and bacterial communities in integrated vertical flow constructed wetlands

This study demonstrates the stereoselective degradation patterns and biodegradation mechanisms of metolachlor (MET) and napropamide (NAP) in integrated vertical flow constructed wetlands (IVCW). The higher interphase transferability of NAP resulted in higher degradation rates of 90.60 ± 4.09%. The enantiomeric fraction (EF) values of 0.38 ± 0.02 and 0.54 ± 0.03, respectively, recorded for the enantiomers S-MET and R-NAP, with higher herbicidal activities, demonstrated their highly selective biodegradation patterns. The antioxidant enzyme activities and fluorescence parameters of plants showed positive correlations with the degradation efficiency and enantioselectivity of MET and NAP. Adaptive regulations by plants promoted the proliferation of microbial genera like Enterobacter and unclassified_Burkholderiales, which could facilitate plant growth. Moreover, enrichment of the herbicide-degrading functional bacteria Terrimonas (5.10%), Comamonas (4.05%) Pseudoxanthomonas (4.49%) and Mycobacterium (1.42%) demonstrably promoted the preferential degradation of S-MET and R-NAP. Furthermore, the abundance of Ferruginibacter favored the use of R-NAP as carbon source to achieve co-removal of R-NAP and NO₃^--N.

Toxic effects and molecular mechanisms of sulfamethoxazole on Scenedesmus obliquus

The antibiotic sulfamethoxazole (SMX) is a pollutant that is widely distributed in the global water environment.This substance has toxic effects on various aquatic organisms. Previous studies on SMX have focused on its acute toxicity towards algae and the changes induced at biological and cellular levels, rather than its biotoxicity and mechanisms at the molecular level. In this study, we investigated the effects of SMX on Scenedesmus obliquus as the model organism by performing transmission electron microscopy and transcriptome sequencing analyses. Exposure to SMX promoted gene expression, resulting in changes to algal cell ultrastructure. The cell walls became blurred, the chloroplast structure was seriously damaged, and the number and volume of mitochondria per cell increased. These changes were related to the inhibition of cell growth, decrease in chlorophyll content, increase in cell membrane permeability, and increased production of reactive oxygen species, which led to increased amounts of the lipid peroxidation product malondialdehyde, and higher activities of antioxidant enzymes. Our results suggest that SMX affects gene expression by influencing non-coding RNA metabolic processes, leading to changes in nuclear structures. Abnormally expressed long non-coding RNAs extensively regulate downstream gene expression through various mechanisms, such as chromatin recombination, thereby promoting tumor occurrence, invasion, and metastasis. This abnormal expression may be an important mechanism underlying the carcinogenic effects of SMX.

Co-hydrothermal carbonization of sewage sludge and model compounds of food waste: Influence of mutual interaction on nitrogen transformation

This study reports the transformation behavior of nitrogen during the co-hydrothermal carbonization of sewage sludge and model compounds (microcrystalline cellulose, starch, lignin, and xylan) of food waste at 220 °C, with a focus on the reaction routes between starch/xylan and NH₄⁺. Most of the nitrogen in the raw sludge was transformed into organic-N (44.6%) and NH₄⁺ (23.3%) in the aqueous product, and only 20.3% of nitrogen was retained in the hydrochar. The added model compounds could react with organic-N (i.e., amino acids and amines) and NH₄⁺ in aqueous products through Maillard and Mannich reactions, generating heterocyclic-N (especially pyrrole-N) which further polymerizes to form nitrogen-containing polyaromatic hydrochar. This leads to an increase in the retention rate of nitrogen to 36.8-50.9%, especially upon the addition of starch and xylan. During the hydrothermal carbonization of starch/xylan in the NH₄⁺ solution, the polymers are first hydrolyzed into monomers, followed by their further reaction with NH₄⁺ to generate pyrrole-N and pyridine-N in aqueous products (especially xylan), and the pyrrole-N can then polymerize with aromatic clusters to form hydrochar-N. The results show that the model compounds of food waste substantially affect the nitrogen transformation pathways during hydrothermal carbonization, mainly because of the structures of their monomers. These findings can guide the production of sludge-based hydrochar with the targeted regulation of nitrogen content and species.

A Common Feature of Pesticides: Oxidative Stress-The Role of Oxidative Stress in Pesticide-Induced Toxicity

Pesticides are important chemicals or biological agents that deter or kill pests. The use of pesticides has continued to increase as it is still considered the most effective method to reduce pests and increase crop growth. However, pesticides have other consequences, including potential toxicity to humans and wildlife. Pesticides have been associated with increased risk of cardiovascular disease, cancer, and birth defects. Labels on pesticides also suggest limiting exposure to these hazardous chemicals. Based on experimental evidence, various types of pesticides all seem to have a common effect, the induction of oxidative stress in different cell types and animal models. Pesticide-induced oxidative stress is caused by both reactive oxygen species (ROS) and reactive nitrogen species (RNS), which are associated with several diseases including cancer, inflammation, and cardiovascular and neurodegenerative diseases. ROS and RNS can activate at least five independent signaling pathways including mitochondrial-induced apoptosis. Limited in vitro studies also suggest that exogenous antioxidants can reduce or prevent the deleterious effects of pesticides.

Bioaccumulation, metabolism and endocrine-reproductive effects of metolachlor and its S-enantiomer in adult zebrafish (Danio rerio)

The aim of the present study was to evaluate the enantioselective bioaccumulation, metabolism, and toxic effects of metolachlor and S-metolachlor in zebrafish. Five-month-old zebrafish were exposed to metolachlor and S-metolachlor for 28 days, then transferred to clean water and purified for 7 days. In the uptake phase, S-metolachlor was preferentially accumulated at low concentrations, while metolachlor was preferentially accumulated at high concentrations. The two chemicals were metabolized by >70% in zebrafish on the first day and showed same metabolic process. At the accumulation endpoint, S-metolachlor had no significant inhibitory effect on the enzymes activities of superoxide dismutase (SOD), catalase (CAT) and glutathione S-transferase (GST) and developmental indicators of zebrafish. However, 300 μg/L metolachlor significantly inhibited the enzymes activities of SOD, CAT and GST and affected the liver development. The preferential enrichment of metolachlor at the high concentration may be the reason for its higher toxicity to zebrafish. Further research demonstrated that metolachlor significantly altered the expression of hypothalamic-pituitary-gonadal (HPG) axis-related genes, including gnrh2, gnrh3, lhβ, 17βhsd and cyp19a, thereby reducing the levels of testosterone (T) in females and sex hormones (estradiol and testosterone) in males. S-metolachlor increased the levels of estradiol (E2) in females by altering the expression of HPG axis-related genes such as fshβ, cyp17, 17βhsd and cyp19a. The mechanism of metolachlor and S-metolachlor on the endocrine disrupting effects of zebrafish is different, which may be sex-specific. 7 days after transferring the exposed zebrafish to clean water, most of the enzymes activities, sex hormone levels and related gene expression levels returned to normal, which may be related to the rapid metabolism of the two chemicals.

The toxicological mechanism of two typical imidazole ionic liquids in textile industry on Isatis tinctoria

Ionic liquids (ILs¹) which are called "green solvents", are used widely in the textile industry as adjuvants due to their many advantages. However, their persistent residues may cause ecotoxicity. The aim of the study is to explore the toxicity of different anions on imidazole ILs and their toxicological mechanism. For the experiments 1-butyl-3-methylimidazole tetrafloroborate ([C₄mim]BF₄) and 1- butyl -3-methylimidazolium chloride ([C₄mim]Cl) were selected to study their toxic effects on Isatis tinctoria. ILs may affect the germination rate. Fresh weight, dry weight and Hill reaction activity decreased continuously with increasing of IL concentrations, showing an effect-dose relationship. Transmission electron microscopy (TEM) revealed that cell walls were fuzzy, starch granules had accumulated and the chloroplast structure was damaged. These changes will affected the function and electron transport efficiency of photosystemⅡ. Superoxide anion accumulation stimulated the activity of antioxidant enzymes (SOD, POD, CAT) and caused lipid peroxidation as well as an increased malondialdehyde content. ILs also reduced indirubin and total flavonoids contents, which reduced the pharmacological efficacy of Isatis tinctoria. This is demonstrated by three-dimensional fluorescence chromatogram. [C₄mim]Cl was more toxic than [C₄mim]BF₄. ILs caused toxic effects to Isatis tinctoria. The ecological toxicity of ILs should be considered when using them as additives in the textile industry.

Enantioselective effects of the fungicide metconazole on photosynthetic activity in Microcystis flos-aquae

Enantiomers of chiral fungicides usually display different toxic effects on nontarget organisms in the surrounding environment, although there are rare reports on the enantioselective toxicity of metconazole (MEZ) to aquatic organisms, such as Microcystis flos-aquae (M. flos-aquae). To explore the enantioselective toxicity of MEZ in algae, the impact of various concentrations (0.001, 0.003, 0.01, 0.03 and 0.1 mg/L) of MEZ on M. flos-aquae over 8 days was investigated. Significant differences were observed between the four enantiomers in chlorophyll a (Chl a) contents, carotenoids, photochemical efficiency (F_v/F_m), rapid light-response curves (RLCs), utilization efficiency of light energy (α) and protein contents during treatment time. MEZ can enantioselectively stimulate the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α) and carotenoid and Chl a contents of M. flos-aquae, especially at low concentrations (0.001 or 0.003 mg/L). At high concentrations of 0.03 or 0.1 mg/L, the chlorophyll fluorescence parameters (RLCs, F_v/F_m and α), protein and Chl a contents of M. flos-aquae exposed to cis-enantiomers were lower than those of M. flos-aquae exposed to trans-enantiomers. These observations indicated that the enantiomers of MEZ pose different toxicities to M. flos-aquae, with the cis-enantiomers more toxic than the trans-enantiomers. These results are beneficial for understanding the enantioselective effects of MEZ enantiomers on nontarget organisms and helpful for evaluating their eco-environment risk.

Prioritization of Pesticides for Assessment of Risk to Aquatic Ecosystems in Canada and Identification of Knowledge Gaps

Pesticides can enter aquatic environments via direct application, via overspray or drift during application, or by runoff or leaching from fields during rain events, where they can have unintended effects on non-target aquatic biota. As such, Fisheries and Oceans Canada identified a need to prioritize current-use pesticides based on potential risks towards fish, their prey species, and habitats in Canada. A literature review was conducted to: (1) Identify current-use pesticides of concern for Canadian marine and freshwater environments based on use and environmental presence in Canada, (2) Outline current knowledge on the biological effects of the pesticides of concern, and (3) Identify general data gaps specific to biological effects of pesticides on aquatic species. Prioritization was based upon recent sales data, measured concentrations in Canadian aquatic environments between 2000 and 2020, and inherent toxicity as represented by aquatic guideline values. Prioritization identified 55 pesticides for further research nationally. Based on rank, a sub-group of seven were chosen as the top-priority pesticides, including three herbicides (atrazine, diquat, and S-metolachlor), three insecticides (chlorpyrifos, clothianidin, and permethrin), and one fungicide (chlorothalonil). A number of knowledge gaps became apparent through this process, including gaps in our understanding of sub-lethal toxicity, environmental fate, species sensitivity distributions, and/or surface water concentrations for each of the active ingredients reviewed. More generally, we identified a need for more baseline fish and fish habitat data, ongoing environmental monitoring, development of marine and sediment-toxicity benchmarks, improved study design including sufficiently low method detection limits, and collaboration around accessible data reporting and management.

Characterization of the mercury-binding proteins in tuna and salmon sashimi: Implications for health risk of mercury in food

Fish consumption is one of the major ways through which humans receive exposure to mercury (Hg). The existing forms of Hg in food, particularly Hg bound to proteins, may affect the absorption of Hg by humans and subsequently its potentially toxic effects. However, the knowledge regarding Hg-binding proteins in edible fish muscle is scarce. In the present study, salmon and tuna fish muscles, collected from seven different regions and countries, were analyzed using metallomics- and proteomics-based techniques. The concentration of Hg in sashimi samples ranged from 4.4 to 317.4 ng/g. Size exclusion chromatography (SEC) coupled with inductively coupled plasma mass spectrometer (ICP-MS) showed that beta-actin was a novel Hg-binding protein from the fish muscles, and this protein could also bind bismuth (Bi), silver (Ag), and copper (Cu). Hg bound to beta-actin accounted for approximately 30.2-37.6% of the total Hg in the tuna muscles and was significantly correlated to total Hg in the fish muscles (r = 0.98, p < 0.01) and in the fraction of soluble proteins (r = 0.94, p < 0.01). These findings suggest that proteins act as the main Hg accumulation sites in edible fish; thus, increasing human exposure to Hg following gastrointestinal digestion.

Exposure of the alga Pseudokirchneriella subcapitata to environmentally relevant concentrations of the herbicide metolachlor: Impact on the redox homeostasis

This study investigated the effect of the herbicide metolachlor (MET) on the redox homeostasis of the freshwater green alga Pseudokirchneriella subcapitata. At low MET concentrations (≤40 μg L^-1), no effects on algal cells were detected. The exposure of P. subcapitata to 45-235 μg L^-1 MET induced a significant increase of reactive oxygen species (ROS). The intracellular levels of ROS were particularly increased at high (115 and 235 μg L^-1) but environmentally relevant MET concentrations. The exposure of algal cells to 115 and 235 μg L^-1 MET originated a decrease in the levels of antioxidants molecules (reduced glutathione and carotenoids) as well as a reduction of the activity of scavenging enzymes (superoxide dismutase and catalase). These results suggest that antioxidant (non-enzymatic and enzymatic) defenses were affected by the excess of MET. As consequence of this imbalance (ROS overproduction and decline of the antioxidant system), ROS inflicted oxidative injury with lipid peroxidation and damage of cell membrane integrity. The results provide further insights about the toxic modes of action of MET on a non-target organism and emphasize the relevance of toxicological studies in the assessment of the impact of herbicides in freshwater environments.

Computational simulation associated with biological effects of alkyl organophosphate flame retardants with different carbon chain lengths on Chlorella pyrenoidosa

The environmental safety of flame retardants has attracted growing attention. Alkyl organophosphorus flame retardants (OPFRs) have been prevalently applied, but the potential risk and the structure effects of different alkyl chain lengths OPFRs on aquatic microalgae remain unknown. This study investigated the biological response of five alkyl-OPFRs to Chlorella pyrenoidosa by computational simulation together with biological approaches. The reduced docking energy had a significantly positive correlation (R² = 0.9) with the cell inhibition alongside the incremental chain length of alkyl-OPFRs. Molecular docking simulations suggested that the toxicity of alkyl-OPFRs would be highly correlated to their molecular structures. Coincidently, the reactive oxygen species, superoxide dismutase and malondialdehyde were triggered by 85%, 92% and 155% (based on the control group), after exposure to the longest chain length tributyl phosphate (TBP_C12), respectively. Furthermore, combining the ultrastructure scrutiny with the photosynthesis analysis, TBP_C12 was also found to significantly inhibit the chlorophyll biosynthesis (43%) and restrain the photosynthetic efficiency (26%) when compared with the control group. Overall, this is the first study to comprehensively reveal the biological effects of different alkyl-OPFRs on microalgae via the combination of computational simulation and cellular responses, providing a novel insight into targeted predicting the aquatic ecological risks of OPFRs.

Effects of residual S-metolachlor in soil on the phyllosphere microbial communities of wheat (Triticum aestivum L.)

S-metolachlor (S-ME) is a widely used chiral herbicide that can cause potential ecological risks via long-term usage. In this work, we chose a model plant, wheat, as the test material to determine the effects of applying 10 mg/kg S-ME to soil on its fresh weight, chlorophyll and malondialdehyde (MDA) content, and superoxide dismutase (SOD) activity and the diversity and structural composition of the phyllosphere microorganisms after 7 and 14 days of exposure. Our work showed that this concentration of residual S-ME in soil only slightly decreased plant biomass and had little effect on lipid peroxidation, the antioxidant enzyme system and chlorophyll content. Interestingly, although the test concentration of S-ME did not exert strong inhibitory effects on the physiological activities of wheat, it decreased the diversity of phyllosphere microbial communities and changed their structure, indicating that microorganisms were more sensitive stress indicators. S-ME reduced the colonization by some beneficial bacteria related to plant nitrogen fixation among the phyllosphere microorganisms, which influenced the growth and yield of wheat because these bacteria contribute to plant fitness. In addition, S-ME affected the association between the host and the composition of the phyllosphere microbial communities under different growth conditions. Our work provides insights into the ecological implications of the effects of herbicides on the phyllosphere microbiome.

Oxidative stress response mechanism of Scenedesmus obliquus to ionic liquids with different number of methyl-substituents

Ionic liquids (ILs) have become persistent contaminants in water because of their good solubility and low biodegradability. The oxidative stress responses of Scenedesmus obliquus to three imidazole ILs with different number of methyl-substituents, i.e., 1-decyl-imidazolium chloride ([C₁₀IM]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀MIM]Cl), and 1-decyl-2,3-dimethylimidazolium chloride ([C₁₀DMIM]Cl), were studied. There was a positive correlation between ROS level and IL concentration. The activities of antioxidant enzymes, i.e., superoxide dismutase, catalase, peroxidase, ascorbate peroxidase, and glutathione peroxidase, and the content of antioxidants, i.e., ascorbic acid and glutathione, changed in IL treatment with a concentration-dependent effect. Proline accumulation increased with increasing IL concentration. Integrated biomarker response (IBR) index analysis, based on the eight oxidative stress response indicators, revealed that the toxicity order was: [C₁₀IM]Cl < [C₁₀DMIM]Cl < [C₁₀MIM]Cl. Proteomic analysis showed that IL affect the type and distribution of proteins in S. obliquus. Chloroplast and photosystem II were affected as cellular component, and the proteins related to oxidative stress are annotated in GO categories. IBR index and proteomic analysis indicate that oxidative stress response is one of the main biomarkers of IL stress.

The herbicide alachlor severely affects photosystem function and photosynthetic gene expression in the marine dinoflagellate Prorocentrum minimum

Alachlor is one of the most widely used herbicides and can remain in agricultural soils and wastewater. The toxicity of alachlor to marine life has been rarely studied; therefore, we evaluated the physiological and transcriptional responses in the marine dinoflagellate Prorocentrum minimum. The herbicide led to considerable decreases in P. minimum cell numbers and pigment contents. The EC₅₀ was determined to be 0.373 mg/L. Photosynthesis efficiency and chlorophyll autofluorescence dramatically decreased with increasing alachlor dose and exposure time. Real-time PCR analysis showed that the photosynthesis-related genes PmpsbA, PmatpB, and PmrbcL were induced the most by alachlor; the transcriptional level of each gene varied with time. PmrbcL expression increased after 30 min of alachlor treatment, whereas PmatpB and PmpsbA increased after 24 h. The PmpsbA expression level was highest (5.0 times compared to control) after 6 h of alachlor treatment. There was no significant change in PmpsaA expression with varying treatment time or concentration. Additionally, there was no notable change in the expression of antioxidant genes PmGST and PmKatG, or in ROS accumulation. These suggest that alachlor may affect microalgal photosystem function, with little oxidative stress, causing severe physiological damage to the cells, and even cell death.

Reproductive cycle progression arrest and modification of cell morphology (shape and biovolume) in the alga Pseudokirchneriella subcapitata exposed to metolachlor

Metolachlor (MET) is an herbicide widely used and frequently found (at μg L^-1) in aquatic systems. This work aimed to study the modes of action of MET on the green microalga Pseudokirchneriella subcapitata. Algae exposed to 115 or 235 μg L^-1 MET, for 48 or 72 h, presented a reduction of metabolic activity, chlorophyll a and b content and photosynthetic efficiency. The exposure to 115 or 235 μg L^-1 MET also induced growth yield reduction, mean cell biovolume increase and alteration of the typical algae shape (cells lunate or helically twisted) to "French croissant"-type; at these MET concentrations, algal population was mainly composed by multinucleated cells (≥ 4 nuclei), which suggest that MET impairs the normal progression of the reproductive cycle but did not hinder nuclear division. The accumulation of multinucleated cells seems to be the consequence of the incapacity of the parent cell to release the autospores. In conclusion, MET disrupts the physiology of P. subcapitata cells; the disturbance of the progression of the reproductive cycle should be in the origin of growth slowdown (or even its arrest), increase of mean cell biovolume and modification of algal shape. This work contributed to elucidate, in a systematically and integrated way, the toxic mechanism of MET on the non-target organism, the alga P. subcapitata.

Ecotoxicological effects of alpha-cypermethrin on freshwater alga Chlorella sp.: Growth inhibition and oxidative stress studies

Alpha-cypermethrin (ACy) is a synthetic pyrethroid insecticide commonly used in agricultural practices for controlling a broad range of insect pests particularly belonging to the order Lepidoptera and Coleoptera. The present study aims to evaluate the toxic effect of ACy on microalgae by studying its influence on Chlorella sp. According to our knowledge, this is the first detailed study of ACy toxicity on microalgae. Significant growth inhibition of Chlorella sp. was observed at high ACy concentration (6-48 mg L^-1) during the entire 96 h bioassay. The 96 h median effective concentration (EC₅₀) of ACy was estimated to be 11.00 mg L^-1. Flow cytometry analysis showed an enhanced generation of reactive oxygen species (ROS) and intracellular lipid accumulation after 96 h exposure to 11.00 mg L^-1 of ACy. Further, the same ACy concentration showed a significant decrease in photosynthetic pigment content and an increase in antioxidant enzyme activity and malondialdehyde (MDA) content in Chlorella sp.

Four pairs of alkaloid enantiomers from Isatis indigotica Fortune Ex Land with neuroprotective effects against H2O2-induced SH-SY5Y cell injury

In the current study, four pairs of new enantiomeric alkaloids (1a/1b-4a/4b) were obtained from the leaves of Isatis indigotica Fortune Ex Land. Their structures were elucidated through spectroscopic methods and quantum mechanical calculations. Biologically, all isolates were evaluated for their neuroprotective effects against H₂O₂-induced SH-SY5Y cell injury. As a result, 1a and 1b exhibited enantioselective neuroprotective effects, further Annexin V-FITC/PI analysis showed that apoptosis ratios of 1a and 1b were reduced to 20.93% and 17.87%, respectively.

Comparative molecular and metabolic responses of wheat seedlings (Triticum aestivum L.) to the imazethapyr enantiomers S-IM and R-IM

The enantioselective effects of imazethapyr (IM) enantiomers on wheat seedlings in a hydroponic medium were studied. R-IM at 0.05mg/L exerted a stronger inhibitory effect on shoot weight and root weight than 0.05mg/L S-IM, suggesting that R-IM more severely inhibited growth. Oxidative damage, based on the anthocyanin content, malondialdehyde (MDA) content, antioxidant enzyme activities and transcript levels of antioxidant enzyme genes, were studied together with the cellular ultrastructure of wheat leaves. The anthocyanin and MDA contents in the R-IM treatment group were significantly increased compared with those in the control group, but no significant changes were observed in the S-IM treatment group. The antioxidant enzyme activities of CAT and SOD were inhibited by 0.32- and 0.73-fold, respectively, in the 14day R-IM treatment group compared to those in the control. However, the transcript levels of antioxidant enzyme genes, including CuZnSOD, POD and CAT, were downregulated in the 14day R-IM exposure group, but those of DHAR were not. The number and size of starch granules increased and chloroplast swelling was observed in wheat leaf cells after R-IM exposure, which showed that photosynthetic functions were potentially disturbed. These results directly or indirectly imply that R-IM exposure causes more oxidative stress and exerts a stronger negative effect on wheat than S-IM. A metabolomics approach revealed that the tricarboxylic acid cycle was heavily suppressed by R-IM treatment. Some amino acids (proline, threonine, lysine, valine) were increased by only the R-IM treatment, indicating the activation of antioxidant pathways. The decrease in a series of fatty acids implied that the cell membrane composition changed in response to R-IM. These results provide a deeper understanding of the enantioselective effects of IM enantiomers on the molecular and metabolic responses in wheat seedlings.

Physiological responses of Chlorella pyrenoidosa to 1-hexyl-3-methyl chloride ionic liquids with different cations

Ionic liquids (ILs) are massively used in multiple fields of industry, and consequently, they have entered the environment and become potential threats to the respective ecosystems. In this paper, the toxicity of two different cationic types of ILs (1-hexyl-3-methyl pyridine chloride ([C₆Py]Cl) and 1-hexyl-3-methyl imidazole chloride ([C₆MIM]Cl)) to Chlorella pyrenoidosa (C. pyrenoidosa) was investigated. Growth inhibition increased with increasing ILs concentrations. C. pyrenoidosa showed a certain recovery at low ILs concentrations, the growth inhibition decreased from 6.13% to 1.57% of the control from 24 h to 96 h, respectively, in 0.5 mg/L [C₆MIM]Cl treatment. However, growth inhibition was negatively related with exposure time at high concentrations, and the strongest toxic effects were observed after 48 h. The IC₅₀ values (half inhibitory concentration) were 8.47, 6.65, 6.91 and 7.11 mg/L of [C₆MIM]Cl, respectively, in 24, 48, 72, and 96 h, and were 9.05, 6.83, 7.79 and 8.14 mg/L of [C₆Py]Cl, respectively. Chlorophyll content declined with higher concentrations of the ILs. The values of chlorophyll fluorescence parameters: the maximum effective quantum yield of photosystem II (PSII) (F_v/F_m), maximum quantum yield in PSII (F_v/F₀), and photosynthetic efficiency in PSII (Y(II)), decreased, whereas the minimal fluorescence (F₀) increased following the ILs treatment, indicating damage to the photosystem II. [C₆MIM]Cl and [C₆Py]Cl caused deformation of algae cells, plasmolysis, and damage of the cell membrane and cell wall, and affected organelle structure. Reactive oxygen species (ROS) concentrations increased with higher ILs concentrations from, and superoxide dismutase and catalase activity first increased and then decreased, indicating that the antioxidant defense system was activated to counteract ROS. ROS was the main stress in C. pyrenoidosa induced by ILs, and compared with [C₆Py]Cl, [C₆MIM]Cl were more toxic to C. pyrenoidosa.

Effect of differently methyl-substituted ionic liquids on Scenedesmus obliquus growth, photosynthesis, respiration, and ultrastructure

Concerns have been raised regarding the ecotoxicity of ionic liquids (ILs) owing to their wide usage in numerous fields. Three imidazolium chloride ILs with different numbers of methyl substituents, 1-decyl-imidazolium chloride ([C₁₀IM]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀MIM]Cl), and 1-decyl-2,3-dimethylimidazolium chloride ([C₁₀DMIM]Cl), were examined to assess their effects on growth, photosynthesis pigments content, chlorophyll fluorescence, photosynthetic and respiration rate, and cellular ultrastructure of Scenedesmus obliquus. The results showed that algal growth was significantly inhibited by ILs treatments. The observed IC_50,48h doses were 0.10 mg/L [C₁₀IM]Cl, 0.01 mg/L [C₁₀MIM]Cl, and 0.02 mg/L [C₁₀DMIM]Cl. The chlorophyll a, chlorophyll b, and total chlorophyll content declined, and the chlorophyll fluorescence parameters, minimal fluorescence yield (F₀), maximal fluorescence yield (F_m), maximum quantum yield of PSII photochemistry (F_v/F_m), effective quantum yield of PSII [Y(II)], non-photochemical quenching (NPQ) and non-photosynthetic losses yield [Y(NO)] were notably affected by ILs in a dose-dependent manner. ILs affected the primary photosynthetic reaction, impaired heat dissipation capability, and diminished photosynthetic efficiency, indicating negative effects on photosystem II. The photosynthetic and respiration rates of algal cells were also reduced due to the ILs treatments. The adverse effects of ILs on plasmolysis and chloroplast deformation were examined using ultrastructural analyses; chloroplast swelling and lamellar structure almost disappeared after the [C₁₀MIM]Cl treatment, and an increased number of starch grains and vacuoles was observed after all ILs treatments. The results indicated that one-methyl-substituted ILs were more toxic than non-methyl-substituted ILs, which were also more toxic than di-methyl-substituted ILs. The toxicity of the examined ILs showed the following order: [C₁₀IM]Cl < [C₁₀DMIM]Cl ≤ [C₁₀MIM]Cl.

Acute toxicity of triflumizole to freshwater green algae Chlorella vulgaris

Triflumizole is one of imidazole fungicides that works by inhibiting ergosterol biosynthesis, and is widely used for the control of powdery mildew and scabs on various fruits and crops. Triflumizole residue has been frequently detected in soil and aquatic ecosystems. While many studies have focused on its toxic effect on terrestrial and aquatic animals, little attention has been paid to aquatic algae, the primary producers of aquatic environments. Therefore, we evaluated the acute (96 h) toxicity effects of triflumizole on the freshwater algae Chlorella vulgaris, by examining growth, cell morphology, photosynthesis, and oxidative stress. The results showed that the 96 h median inhibition concentration (96 h-EC₅₀) was 0.82 mg/L (95% confidential interval 0.70-0.98 mg/L).The growth of algal cells was conspicuously inhibited by triflumizole exposure, and the cell surfaces appeared to be shrunkThe chlorophyll content (including Chl-a, Chl-b and T-Chl) dramatically decreased at triflumizole concentrations of 0.2 and 1.0 mg/L. In addition, the transcript abundance of photosynthesis-related genes (psaB, psbC and rbcL) showed obvious decreases in above treatments after 96 h of exposure to triflumizole. Moreover, the algal growth inhibition was accompanied by an increase in intracellular reactive oxygen species and malondialdehyde content, as well as increased activity of antioxidant enzymes such as superoxide dismutase and peroxidase, indicating oxidative stress and lipid peroxidation. Our findings reveal that triflumizole has potential toxicity to the primary producers (freshwater algae) in aquatic ecosystems.

Toxic effects of tetracycline and its degradation products on freshwater green algae

Tetracycline antibiotics are the most widely used antibiotics in the world and the most common veterinary drugs and feed additives used in livestock, poultry and aquaculture operations. Because antibiotics cannot be completely removed by currently existing sewage treatment facilities, these materials enter the environment directly via sewage treatment plant discharge, where they degrade. Accordingly, the metabolism and the ecological toxicity of tetracycline degradation products are worthy of attention. Herein, we investigated the effects of tetracycline and its degradation products (anhydrotetracycline and epitetracycline hydrochloride) on the growth, cell structure and algal cell oxidative stress of common Chlorella vulgaris. The results showed that the 96h-EC₅₀ values of tetracycline (TC), anhydrotetracycline (ATC) and epitetracycline (ETC) on algal cells were 7.73, 5.96 and 8.42 mg/L, respectively. Moreover, the permeability of algal cells exposed to high concentrations of these three drugs was significantly enhanced. In addition, there were structural changes in the cells such as plasmolysis and starch granule deposition appeared, the thylakoid lamellae in the chloroplasts became blurred and deformed, and the vacuoles became larger. Exposure to higher concentrations (>5 mg/L) of TC and its degradation products ATC and ETC significantly upregulated the activity of ROS, as well as the antioxidants SOD and CAT. The levels of the lipid peroxidation product MDA also showed the same trend. Finally, ATC had the strongest toxicity toward algal cells, followed by TC and then ETC.

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

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

Enantioselective Oxidative Stress Induced by S- and Rac-metolachlor in Wheat (Triticum aestivum L.) Seedlings

The unfounded use of chiral pesticides has caused widespread concern. In this study, the enantioselective effects of S- and racemic (Rac)-metolachlor on the oxidative stress of wheat seedlings was determined based on physiological and gene transcription differences. Growth inhibition increased with increasing concentrations of tested metolachlor, and S-metolachlor had a stronger inhibitory effect than did Rac-metolachlor. Root growth was also significantly inhibited, but no enantioselective effects from the tested concentrations of the metolachlor enantiomers were observed. At a concentration of 5 mg L^-1, the maximal fresh weight inhibition reached 63.7% and 53.8% for S-metolachlor and Rac-metolachlor, respectively. In response to the S-metolachlor treatment, the maximum level of superoxide anions and malondialdehyde (MDA) increased to 1.73 and 2.55 times that in response to the control treatment, both of which were greater than those in response to the Rac-metolachlor treatment. The activity of superoxide dismutase (SOD) also increased in response to the S-metolachlor treatment, but the activity of peroxidase (POD) decreased. Real-time polymerase chain reaction (PCR) revealed that, compared with the Rac-metolachlor treatment, the S-metolachlor treatment attenuated the expression of several antioxidant genes. Together, these results demonstrate that S-metolachlor has a greater effect than does Rac-metolachlor on wheat seedlings.

Enantioselective thyroid disruption in zebrafish embryo-larvae via exposure to environmental concentrations of the chloroacetamide herbicide acetochlor

Acetochlor (ACT) is a chiral chloroacetamide pesticide that has been heavily used around the world, resulting in its residues being frequently found in surface waters. It has been reported that ACT is an endocrine disrupting chemical (EDC) with strong thyroid hormone-disrupting activity in aquatic organisms. However, the enantioselectivity underlying thyroid disruption has yet to be understood. In this study, using a zebrafish embryo-larvae model, the enantioselective thyroid disruption of ACT was investigated at a series of environmentally relevant concentrations (1, 2, 10 and 50 μg/L). Our results showed that both racemic ACT and its enantiomers significantly increased the malformation rates of embryos at 72 h postfertilization (hpf). Decreased thyroxine (T₄) contents and increased triiodothyronine (T₃) contents were found in larvae at 120 hpf, with (+)-S-ACT exhibiting a greater effect than (-)-R-enantiomer. Similarly, (+)-S-ACT also showed a stronger effect on the mRNA expressions of thyroid hormone receptors (TRα and TRβ), deiodinase2 (Dio2) and thyroid-stimulating hormone-β (TSHβ) genes. The observed enantioselectivity in TR expressions was consistent with that of in silico binding analysis, which suggested that (+)-S-enantiomer binds more potently to the TRs than (-)-R-enantiomer. In general, ACT enantiomers showed different influences on the secretion of THs, expression of TH-related key genes and binding affinity to TRs. Considering the different toxicity of different enantiomers, our study highlights the importance of enantioselectivity in understanding of thyroid disruption effects of chiral pesticides.

Growth inhibition and oxidative stress caused by four ionic liquids in Scenedesmus obliquus: Role of cations and anions

Ionic liquids (ILs) are widely used in various industrial applications. However, they are considered potential toxins in aquatic environments because of their physical stability and solubility. The growth inhibition and oxidative stress induced by four ionic liquids with different cations and anions on the green algae Scenedesmus obliquus was investigated in this study. The order of growth inhibition was 1‑hexyl‑3‑methylimidazolium nitrate ([HMIM]NO₃) > 1‑hexyl‑3‑methylimidazolium chloride ([HMIM]Cl) > N‑hexyl‑3‑metylpyridinium bromide ([HMPy]Br) > N‑hexyl‑3‑metylpyridinium chloride ([HMPy]Cl). Imidazolium IL had a higher growth inhibition effect than pyridinium IL, nitrate IL and bromide IL had a higher effect than chloride IL. Reactive oxygen species (ROS) level in S. obliquus increased with increasing IL concentrations. Green fluorescence in [HMIM]Cl treated algae showed increased brightness compared to the [HMPy]Cl treatment, and [HMIM]NO₃ treatment produced increased brightness compared to the [HMPy]Br treatment, suggesting that higher ROS levels were induced by [HMIM]Cl and [HMIM]NO₃. Soluble protein, catalase (CAT), and superoxide dismutase (SOD) activities were stimulated at lower concentrations but were inhibited at higher concentrations. Regression analysis suggested that ROS level is the main index responsible for oxidative stress induced by the four ILs. The ILs induced oxidative damage on S. obliquus, and ROS in high concentration treatments could not be effectively removed by the antioxidant system, leading to oxidative damage and ultimately resulting in growth inhibition and cell death.

Enantioselective Toxicity of Chiral Herbicide Metolachlor to Microcystis aeruginosa

The enantioselective effects of chiral herbicides on aquatic organisms have received increasing attention. As one kind of freshwater algae responsible for most algal blooms, Microcystis aeruginosa can produce hepatotoxic microcystin and cause serious health concerns for drinking water. Thus, the effects of chiral herbicides on M. aeruginosa are of vital significance but poorly understood, especially as the structures of chiral herbicides become more complex. In this study, the enantioselective effects of four metolachlor enantiomers based on carbon center and axis chirality on M. aeruginosa were investigated for the first time at an enantiomeric level. The results of the investigation into algal growth inhibition, chlorophyll a content, and cell integrity indicated that ( S)-metolachlor [( S)-Met] was significantly more toxic than any other isomer. The toxicity ranking of different enantiomers at the highest concentration (15 mg/L) against M. aeruginosa was ( S)-Met > (α R,1' S)-Met > (α S,1' S)-Met > (α S,1' R)-Met > (α R,1' R)-Met, with (α S,1' S)-Met and (α R,1' S)-Met displaying a synergistic effect. Additionally, the Fe distribution in M. aeruginosa presented distinct enantioselectivity, which may contribute to the enantioselective toxicity of metolachlor. Furthermore, metolachlor upregulated the expression of genes mcyD and mcyH in an enantioselective manner, indicating that this herbicide can potentially promote the synthesis and efflux of microcystin, thus aggravating agricultural water contamination to different extents. Overall, this study will help to understand the ecotoxicity of metolachlor at a deeper level and provide theoretical insights into the enantioselective behaviors of metolachlor.

Temporal variation of oxidative potential of water soluble components of ambient PM2.5 measured by dithiothreitol (DTT) assay

The exposure to ambient fine particulate matter (PM_2.5) can induce oxidative stress, contributing to global burden of diseases. The evaluation of the oxidative potential (OP) of PM_2.5 is thus critical for the health risk assessment. We collected ambient PM_2.5 samples in Hangzhou city, China for four consecutive quarters in the year 2017 and investigated the oxidation property of PM_2.5 components by the dithiothreitol (DTT) assay. The annual mean of ambient PM_2.5 mass concentrations in 2017 was 63.05 μg m^-3 (median: 57.34, range: 6.67-214.33 μg m^-3) with the significant seasonal variations ranking as winter > spring > summer > autumn. Secondary inorganic aerosol (SIA) species including SO₄^2-, NO₃^- and NH₄⁺ totally account for >50% of PM_2.5 mass. The annual mean volume-normalized DTT activity (DTTv) showed a relatively high value of 0.62 nmol/min/m³ (median: 0.62, range: 0.11-1.66 nmol/min/m³) and DTTv of four seasons was roughly at the same level, indicating a high annual exposure level of ambient PM_2.5. SIA species were correlated well with the corresponding DTTv and showed significant diurnal variations with strong or moderate correlations at day and weak correlations at night, suggesting strong secondary formation in daytime with contribution to the particulate OP. The annual mean mass-normalized DTT activity (DTTm) had a relatively low value of 6.39 pmol/min/μg (median: 5.63, range: 1.99-22.70 pmol/min/μg), indicating low intrinsic oxidative toxicity. The DTTm of four seasons ranked as autumn > winter > spring > summer, indicating seasonal variations of the DTT-active components. The PM_2.5 mass concentration is more related to exposure levels than intrinsic properties of components, while OP is determined by the components rather than PM_2.5 mass concentration. Our results provide an insight into reactive oxygen species-induced health risk of PM_2.5 exposure and decision for subsequent emission control.

Acute toxicity of the fungicide azoxystrobin on the diatom Phaeodactylum tricornutum

Azoxystrobin (AZ) is an effective broad-spectrum fungicide. Due to its extensive application, AZ is detectable in aquatic ecosystems and thus influences aquatic organisms. In this study, the acute toxicity (96 h) of AZ at concentrations of 1.0 mg/L and 5.0 mg/L on the diatom Phaeodactylum tricornutum were examined. At the tested concentrations, AZ significantly inhibited P. tricornutum growth and destroyed its cellular structure. Furthermore, the mechanisms of AZ-induced toxicity on P. tricornutum changed as the exposure time extended. Forty-eight hours after exposure, AZ inhibited P. tricornutum growth primarily via inducing oxidative stress, which increased the activity of two main antioxidant enzymes, superoxide dismutase and peroxidase, and inhibited energy metabolism. However, after 96 h of treatment, the decline in the photosynthetic capacity of P. tricornutum demonstrated that the photosystem was the main AZ target. The pigment content and expression levels of genes related to photosynthetic electron transfer reactions were also significantly decreased. The present study describes AZ toxicity in P. tricornutum and is very valuable for assessing the environmental risk of AZ.

Enantioselective effect of glufosinate on the growth of maize seedlings

Glufosinate is a non-selective chiral herbicide, which has been used extensively around the world. However, limited information on the enantioselectivity of Rac- and L-glufosinate against crops. In this study, the enantioselective effects on the growth, antioxidant, and targeted enzyme activities of maize seedlings of chiral glufosinate were investigated. The results showed the enantioselective growth inhibitions were observed at both 1 and 5 mg/L concentration levels. L-Glufosinate induced more growth rate reduction in shoot height and weight compared to Rac-glufosinate. All of the antioxidant enzyme activities increased obviously in the leaves of maize seedlings treated by 1 mg/L of glufosinate. Superoxide dismutase (SOD) activity, catalase (CAT) activity, peroxidase (POD) activity, glutathione reductase (GR) activity, and malondialdehyde (MDA) content induced by L-glufosinate were 1.36, 1.16, 1.51, 1.65, and 1.65 times higher than those by Rac-glufosinate, respectively Notably, the glutamine synthetase (GS) activity was significantly reduced to 80% and 57% in the control group at 1 mg/L treated with Rac- and L-glufosinate, respectively. Our results indicated that Rac- and L-glufosinate showed the obvious enantioselectivity in the growth of maize seedlings, which has shed light on the potential enantioselective phytotoxicity of glufosinate. Data provided here will be helpful to develop the environmentally friendly herbicides.

Toxic effects of boscalid on the growth, photosynthesis, antioxidant system and metabolism of Chlorella vulgaris

Boscalid is one of the most frequently detected pesticides in main coastal estuaries in California, with concentrations as high as 36 μg/L. However, ecotoxicology information about boscalid to aquatic organisms is scarce. To investigate toxic effects and mechanisms of boscalid on freshwater algae Chlorella vulgaris (C. vulgaris), C. vulgaris were exposed to a range of boscalid concentrations (0, 0.8, 1.6, 2.4 and 3.2 mg/L) for 96 h to study the changes in photosynthetic pigment contents, responses of the antioxidant enzyme system and alterations in endogenous substances. Results indicated that the growth of algae and the content of chlorophyll and carotenoids were significantly inhibited by 1.6 mg/L boscalid. Reactive oxygen species (ROS) and oxidative damage of C. vulgaris could be induced by boscalid, in accordance with significant changes in ROS levels and a series of antioxidant enzyme activities. Moreover, the alterations in endogenous substances showed that boscalid could affect photosynthesis and energy metabolism of C. vulgaris. These results demonstrated that boscalid could induce impacts on C. vulgaris mainly through disturbing the photosynthesis, oxidative damage and energy metabolism. The present study provided a better understanding of the negative effects and mechanisms of bosaclid in microalgae.

S-metolachlor promotes oxidative stress in green microalga Parachlorella kessleri - A potential environmental and health risk for higher organisms

The estimation of the toxic influences of herbicide products on non-target aquatic organisms is essential for evaluation of environmental contamination. We assessed the effects of the herbicide S-metolachlor (S-MET) on unicellular green microalga Parachlorella kessleri during 4-72 in vitro exposure to concentrations in the range 2-200μg/L. The results have shown that S-MET had a significant effect on algae, even in doses 10 and 20 times lower than the EC50 values obtained for P. kessleri (EC50-72h=1090μg/L). It generates reactive oxygen species in algae, decreases their growth and photosynthetic pigment concentration, changes their ultrastructure and alters the cellular antioxidant defence capacities. The levels of protein adducts with the reactive aldehyde 4-hydroxy-2-nonenal (HNE), the end-product of lipid peroxidation, were significantly elevated in S-MET treated cells revealing the insufficient effectiveness of P. kessleri antioxidant mechanisms and persistent lipid peroxidation. Since algae are fundamental aquatic food component, the damaged algal cells, still capable of dividing while having persistently increased content of HNE upon S-MET contamination could represent an important environmental toxic factor that might further affect higher organisms in the food chain.

Effect of imidazolium-based ionic liquids with varying carbon chain lengths on Arabidopsis thaliana: Response of growth and photosynthetic fluorescence parameters

As green and novel solvents, ionic liquids (ILs) are popular in many industries, which may threaten ecosystems. The effects of three imidazolium-based ILs with different alkyl chain lengths, including 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl), 1-decyl-3-methylimidazolium chloride ([C₁₀mim]Cl), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) on growth and photosystem of Arabidopsis thaliana were investigated. Root length, fresh weight, cell membrane permeability, and chlorophyll content of whole plant were significantly affected by ILs. Vein clearing, leaf chlorosis, and browning on the A. thaliana leaf abaxial surface occurred, with a dose-response relationship. The effect of ILs on whole plant increased with alkyl chain lengths. Chlorophyll fluorescence parameters of photosynthetic system II (PSII) were all affected in [C₈mim]Cl and [C₁₀mim]Cl treatments, electron-transfer was blocked, and photochemical energy conversion was damaged. There were no significant changes in chlorophyll fluorescence of newly-growing leaves in [C₁₂mim]Cl treatment, but has severe effect on aged leaves. The number and size of starch granules and osmiophilic globules increased, plasmolysis and the chloroplast swelling occurred in [C₈mim]Cl, [C₁₀mim]Cl treatments and on aged leaves in [C₁₂mim]Cl treatment, but no significant damages occurred on newly-growing leaves of [C₁₂mim]Cl treatment, perhaps due to plant self-protection of plant. The results indicating the appropriate use of ILs is needed.

Synergistic effect of co-exposure to cadmium (II) and 4-n-nonylphenol on growth inhibition and oxidative stress of Chlorella sorokiniana

Toxicological effect of freshwater algae co-exposure to Cd and 4-n-nonylphenol (4-n-NP) was seldom reported. In the present study, Chlorella sorokiniana was selected for testing the single and combined effect of Cd and 4-n-NP by detecting the growth inhibition and oxidative stress after exposure for 48 h, 72 h, and 96 h. The combined effects were evaluated by using toxic units (TU) method and concentration addition（CA）model. The synergistic effect of mixture on algal growth inhibition was both observed at 48 h and 72 h, and the additive effect was observed at 96 h. In addition, the significant alterations of superoxide, thiobarbituric acid reactive substances and antioxidant defenses (superoxide dismutase, catalase, glutathione) have been detected. It could be observed that the mixture predominantly lead to synergistic effects in superoxide induction, and the antagonistic effects in the GSH induction. A similar trend between the superoxide induction and growth inhibition were observed, which may indicate that the oxidative effects of Chlorella sorokiniana contributed to the growth inhibition after exposure to Cd and 4-n-NP. These findings may have important implications in the risk assessments of heavy metals and endocrine disruptors in the aquatic environment.

Toxicity evaluation of 4,4'-di-CDPS and 4,4'-di-CDE on green algae Scenedesmus obliquus: growth inhibition, change in pigment content, and oxidative stress

Polychlorinated diphenyl sulfides and polychlorinated diphenyl ethers are two types of dioxin-like pollutants, which are prevalent in aquatic environments. However, to date, limited information is available regarding their toxicity to green algae. In this study, growth inhibition, effect on pigment content, and oxidative stress potentials of 4,4'-di-CDPS and 4,4'-di-CDE on green algae Scenedesmus obliquus were investigated. The results indicate that the EC₅₀ values of 4,4'-di-CDPS after 24, 48, 72, and 96 h of exposure were 1.736, 1.172, 0.994, and 0.820 mg/L, while the corresponding values for 4,4'-di-CDE were 0.697, 1.087, 0.833, and 0.327 mg/L. As compared to the control group, most of the measured pigment content in algal cells significantly decreased after 96-h exposure to these two chemicals, suggesting their suppressive capability on the photosynthesis process in algal cells. Additionally, oxidative stress occurred as demonstrated by the significantly inhibited activities of the antioxidant enzymes (total superoxide dismutase (T-SOD), catalase (CAT), and glutathione peroxidase (GPx)), and high increases in malondialdehyde (MDA) content in all 4,4'-di-CDE-treated groups and some moderate-dose and high-dose treatments with 4,4'-di-CDPS. Acute toxicity tests and biochemical analysis showed that 4,4'-di-CDE was more toxic than 4,4'-di-CDPS on S. obliquus.

The toxicity of ionic liquid 1-decylpyridinium bromide to the algae Scenedesmus obliquus: Growth inhibition, phototoxicity, and oxidative stress

Although ionic liquids (ILs) are unlikely to act as air contaminants, their high solubility and slow degradation make them a potential threat to the aquatic environment. The IL 1-decylpyridinium bromide ([DPy]Br) is a common type of pyridine IL, which has varied applications such as in extraction, separation, and catalytic synthesis. Herein, the toxicity of [DPy]Br to S. obliquus is determined. Growth was inhibited by high-concentration [DPy]Br, whereas it had a hormetic effect at low concentrations. The IC_50-96h was approximately 0.06mg/L. The cell membrane permeability of S. obliquus increased with [DPy]Br concentration, indicating that [DPy]Br can cause damage to the algae cell structure. Chlorophyll content decreased at high [DPy]Br concentration; chlorophyll fluorescence parameters, such as the maximum effective quantum yield of PSII (F_v/F_m), potential activity of PSII (F_v/F₀), yield of the photochemical quantum [Y(II)], and the non-photochemical quenching coefficient (NPQ) were affected, suggesting that [DPy]Br can damage PSII. The ROS fluorescent images revealed that the morphology of cells changed gradually from fusiform to round. High ROS levels were observed with high concentrations of [DPy]Br, indicating that [DPy]Br induced oxidative stress on S. obliquus. The SOD and CAT activities increased when the concentration was lower than IC₅₀, whereas they decreased when the concentration was higher than IC₅₀. The relative ROS content was significantly correlated with growth inhibition rate, cell membrane permeability, chlorophyll content, and SOD and CAT activities. The increase of ROS content in algal cells is an important toxicological mechanism of [DPy]Br to S. obliquus.

Neuroprotective Effects of 1,2-Diarylpropane Type Phenylpropanoid Enantiomers from Red Raspberry against H2O2-Induced Oxidative Stress in Human Neuroblastoma SH-SY5Y Cells

Red raspberry (Rubus idaeus L.) is an edible fruit-producing species belonging to the Rosaceae family. In our search for the health-promoting constituents from this fruit, four pairs of enantiomeric phenylpropanoids (1a/1b-4a/4b), including three new compounds (1a and 2a/2b), were isolated from red raspberry. Their structures were elucidated by a combination of the extensive NMR spectroscopic data analyses, high-resolution electrospray ionization mass spectrometry and comparison between the experimental measurements of electronic circular dichroism (ECD) and calculated ECD spectra by time-dependent density functional theory (TDDFT). In addition, their neuroprotective effects against H₂O₂-induced oxidative stress in human neuroblastoma SH-SY5Y cells were investigated, and the results showed enantioselectivity, in which that 3a exhibited noticeable neuroprotective activity, while its enatiomer 3b exhibited no obvious protective effect. Further study demonstrated that 3a could selectively inhibit the apoptosis induction and reactive oxygen species (ROS) accumulation by enhancing the activity of catalase (CAT) in H₂O₂-treated human neuroblastoma SH-SY5Y cells. These findings shed much light on a better understanding of the neuroprotective effects of these enantiomers and provide new insights into developing better treatment of neurodegenerative diseases in the future.

Enantioselective oxidative stress caused by chiral ionic liquids forms of 1-alkyl-3-methyl imidazolium tartrate on Scenedesmus obliquus

Ionic liquids (ILs) are widely used, but their potential threat to the environment has recently gained more attention. The enantioselective oxidative stress caused by chiral ionic liquids (CILs), such as 1-alkyl-3-methyl imidazolium tartrate (RMIM T), on Scenedesmus obliquus was demonstrated in this study. Stronger green fluorescence was observed in response to l-(+)-RMIM T treatment than to d-(+)-RMIM T treatment, which suggested that more reactive oxygen species (ROS) were stimulated by l-(+)-RMIM T. Significantly higher ROS levels were recorded during the RMIM T treatments than in the control. There were 1.13-, 1.25-, 1.43-, 1.68-, and 1.96-fold increases over levels in the control in the 3, 5, 10, 15, and 25mg/L d-(-)-HMIM T treatments, respectively, and 1.26-, 1.37-, 1.58-, 1.86- and 2.08-fold increases over levels in the control in the 3, 5, 10, 15, and 25mg/L l-(+)-HMIM T treatments, respectively. The total soluble protein content decreased as the RMIM T concentration increased. The SOD and CAT activities were stimulated at lower concentrations, but were inhibited at higher concentrations. Regression analysis implied that ROS is the major factor responsible for the oxidative damage caused by RMIM T. The ultrastructural morphology analysis showed that plasmolysis and damage to the chloroplasts, starch granule decreases, and lipid granule increased, and pyrenoid and nucleoid damage had occurred. These results showed that enantioselective oxidative stress and oxidative damage were caused by d-(+)-RMIM T and l-(+)-RMIM T, and that l-(+)-RMIM T caused more damage than d-(+)-RMIM T.