Bioaccumulation and toxicity of perfluorooctanoic acid and perfluorooctane sulfonate in marine algae Chlorella sp

Antioxidant system alterations and oxidative stress caused by polyfluoroalkyl substances (PFAS) in exposed biota: a review

Contamination of aquatic and terrestrial organisms by Perfluoroalkyl substances (PFAS), emerging contaminants, is widespread, as these compounds are present in water, soil, air, and food, owing to their environmental persistence. PFAS exposure induces biochemical process alterations associated with the disruption of the antioxidant defense system in several species. This review aims to discuss how PFAS-induced antioxidant system alterations lead to changes in biochemical processes in different organisms exposed to these pollutants. This disruption, then leads to an imbalance in antioxidant defense systems, contributing to the formation of reactive oxidative species (ROS), which, in turn, can be exacerbate oxidative stress, induce cellular damage, enhance lipid peroxidation, destabilize lysosomal membranes, and cause genotoxic effects, ultimately compromising DNA integrity. In acute tests, PFAS have led to mortality, growth inhibition, diminished behavioral and locomotor abilities, and reproductive impairment. PFAS-induced effects differ with varying species or types of substances, and further bioaccumulation through food chains exacerbates environmental contamination, carrying considerable risks. These findings demonstrate the complex and enduring impact of PFAS on environmental health, emphasizing the importance of this review in corroborating studies on sub-lethal toxicity in exposed organisms and how these effects reflect on the environment.

Mechanisms of PFBA toxicity in Chlorella vulgaris: Photosynthesis, oxidative stress, and antioxidant impairment

Perfluorobutanoic acid (PFBA), an emerging alternative to perfluorooctanoic acid (PFOA), has become increasingly prevalent in aquatic ecosystems, yet its ecotoxicological impacts remain poorly understood. This study investigated the aquatic toxicity of PFBA using the freshwater algae Chlorella vulgaris (C. vulgaris) as a model organism, employing a 96h pre-exposure assay to determine the median effective concentration followed by acute toxicity experiments analyzing multiple endpoints including growth, photosynthetic parameters, oxidative stress markers, and antioxidant enzyme activities. Computer simulation techniques were utilized to illustrate the underlying molecular mechanisms of PFBA toxicity. The results showed that the 96h-EC50 value of PFBA was 154.88 mg/L, which is comparable to conventional per- and polyfluoroalkyl substances (PFAS). Acute toxicity experiments revealed a biphasic dose-response relationship to the algal growth with the hormetic effects at the lower concentrations (30.97-92.93 mg/L) but inhibition at the higher levels (123.91-185.86 mg/L) of PFBA. High dosages of PFBA significantly decreased the maximum photosynthetic yield (Fv/Fm) and relative electron transfer rate (rETR), while inducing oxidative stress and inhibiting superoxide dismutase (SOD) and catalase (CAT) activities. Future AlphaFold2 modeling and molecular docking simulations demonstrated the potential binding of PFBA to photosystem II D1 C-terminal processing protease (PSII D1 protein), SOD, and CAT. These findings reveal a complex toxicity mechanism of PFBA on C. vulgaris involving photosynthetic disruption, oxidative stress, and antioxidant system impairment, contributing to the understanding of short-chain PFAS alternative ecotoxicity in aquatic ecosystems.

Bioremediation of perfluorooctanoic acid using microalgae with a transcriptomic approach

Microalgal-mediated bioremediation technologies offer sustainable strategies for removal of emerging contaminants in aquatic environments. However, the molecular mechanisms and bioremediation pathways in microalgal species involved in the degradation of persistent organic pollutant perfluorooctanoic acid (PFOA) remain largely unexplored and poorly characterized. This study explored the potential of four microalgal strains for PFOA treatment and examined the expression of key functional genes through transcriptomic analysis. Scenedesmus quadricauda emerged as the most promising candidate for PFOA removal, exhibiting a high removal efficiency of 58.2 % (1.22 mg-PFOA/g-microalgae) at an initial PFOA concentration of 5 ppm. The mass balance analysis of PFOA removal by S. quadricauda revealed that 44.8 % of the PFOA was removed through bioaccumulation, and 12.8 % through biosorption. The chromatographic analysis confirmed that a portion of the bioaccumulated PFOA (0.58 %, 22.7 μg/L) was biodegraded by the biological removal mechanism in microalgae and identified by-products of PFOA. When S. quadricauda was exposed to PFOA, the fatty acid methyl ester yield increased by 178 % through transesterification. The transcriptome analysis revealed key functional genes involved in defense, energy production, and degradation in response to PFOA exposure. These results underscore the need to develop microalgae-mediated bioremediation technology for effectively removing PFOA from polluted aquatic environments.

Unraveling the impact of PFOA toxicity on Zostera marina using a multi-omics approach: Insights from growth, physiological, transcriptomic, and metabolomic signatures

Perfluorooctanoic acid (PFOA), an anthropogenic organic pollutant known for its persistence, resistance to degradation, and toxicity, has raised significant concerns about its potential ecological impacts. Zostera marina, a common submerged seagrass species in temperate offshore areas, is highly vulnerable to pollutant stressors. However, the impact of PFOA on Z. marina remains unclear. In this study, Z. marina was exposed to different concentrations of PFOA (0, 0.5, 1, 5, 10, and 20 μg/L) for 14 days. We subsequently assessed survival rates, growth patterns, physiological indices, transcriptomic profiles, and metabolomic characteristics. The results revealed dose-dependent PFOA accumulation in Z. marina tissues and significant growth inhibition. Furthermore, exposure to PFOA resulted in a significant reduction in photosynthetic pigment content (IBRv2 indices: 2.78-10.29) and elevated enzyme activity (IBRv2 indices: 2.90-8.96). Transcriptomic analysis identified 1511 differentially expressed genes associated with 11 KEGG pathways predominantly affected by PFOA exposure. Weighted gene co-expression network analysis highlighted the crucial role of the hydroxyphenylpyruvate reductase (hppr) gene in antioxidant defense mechanisms and detoxification processes against PFOA-induced stress. Metabolomics identified 412 differentially expressed metabolites, mainly consisting of flavonoids, organic acids, and lipids. In summary, PFOA exposure resulted in the down-regulation of gene expression related to photosynthesis and energy metabolism while also affecting metabolite synthesis. The response of Z. marina to PFOA stress involves modulation of the cytoskeletal dynamics and signal transduction pathways, as well as activation of a suite of genes and metabolites to initiate defense mechanisms.

The acute toxicity of tripropyl phosphate and tributyl phosphate to Microcystis aeruginosa

The mass production and applications of tripropyl phosphate (TPrP) and tributyl phosphate (TBP) have facilitated their widespread distribution in aquatic environments, thereby posing a threat to the ecosystem. Here, the acute toxicity of TPrP and TBP to Microcystis aeruginosa and the underlying mechanisms were investigated. The results demonstrate that both TPrP and TBP can significantly inhibit the growth and reduce cell viability of M. aeruginosa with increasing concentrations and exposure time. Moreover, the treatment with TPrP and TBP result in a notable reduction in the content of chlorophyll a. The content of dissolved organic carbon (DOC) is down-regulated at lower concentrations, and shows a gradual increase with increasing concentrations of TPrP or TBP. Meanwhile, minor discrepancies have been observed in the proportions of DOC components through excitation-emission-matrix (EEM) spectra. The exposure of TPrP and TBP results in the production of excessive reactive oxygen species (ROS) and the increase of antioxidant enzymatic activities, including superoxide dismutase (SOD) and catalase (CAT). TPrP, but not TBP, has been demonstrated to enhance the MDA level, indicating a significant effect on membrane lipid peroxidation. The differences in the respective toxicity mechanisms and biological effects can be attributed to the alkyl chain lengths and physicochemical properties inherent to each compound. Consequently, the study not only offers insights into the acute effects of the two alkyl organophosphate esters on M. aeruginosa, but also provides a scientific basis and framework for assessing their ecological risk in aquatic environments.

Sub-acute exposure of sea urchin (Strongylocentrotus intermedius) to environmentally relevant concentrations of PFOA and GenX influences gonadal development

Perfluorooctanoic acid (PFOA) and its substitute, hexafluoropropylene oxide dimer acid (GenX), are widely used perfluorinated compounds (PFCs) that pose significant risks to marine ecosystems. However, the specific impacts of these contaminants on marine invertebrates, particularly echinoderms, remain poorly understood. Strongylocentrotus intermedius, a globally significant benthic aquacultural species, may be potentially affected by PFCs. This study aimed to assess the reproductive toxicity of PFOA and GenX in S. intermedius. After exposing S. intermedius to either PFOA or GenX for 7 or 14 days, it was observed that even at environmentally relevant concentrations (2 μg/L), both compounds inhibited normal growth and gonadal development in S. intermedius, with effects becoming more pronounced over time. Further analysis revealed that prolonged exposure to PFCs resulted in a significant reduction in energy reserves (glycogen, lipids, and proteins) and caused abnormal changes in metabolic enzyme activities, with PFOA exhibiting more pronounced effects compared to GenX. At the genetic level, the expression of genes related to gonadal development initially increased and then decreased as the concentrations of the compounds rose. Additionally, integrated biomarker response analysis indicated that PFOA had greater reproductive toxicity than GenX, in terms of both concentration and exposure duration. These results provided a preliminary evaluation of the impact of PFCs on marine invertebrates, offering a foundation for further research into their ecological risks and contributing to the development of more comprehensive environmental risk assessments for these contaminants.

How heatwaves impact microalgae in the presence of environmentally relevant PFAS concentration: Metabolic shifts and challenges posed

Per- and polyfluoroalkyl substances (PFAS) are widely distributed in the aquatic environment. While increasing studies have investigated the effects of specific PFAS exposure on microalgae, the impact of environmentally relevant PFAS concentrations, particularly during extreme weather events like heatwaves, remains unclear. For Microcystis aeruginosa, a cyanobacteria causing harmful algal blooms, PFAS exposure promoted growth and photosynthesis by accelerating the TCA cycle, intensifying carbon/nitrogen and nucleotide metabolism, and enhancing antioxidant expression. Moreover, although heatwave exposure alone adversely affected algal growth, co-exposure to PFAS and heatwaves paradoxically enhanced algal growth. This co-exposure also enhanced the expression of photosynthetic pigments and metabolites involved in alanine, aspartate and glutamate metabolism, as well as arginine and proline metabolism (compared to PFAS exposure alone). Nevertheless, co-exposure intensified oxidative stress, leading to differential expression of antioxidants, which may consequently affect the synthesis of membrane lipids. In addition, PFAS adsorption and uptake are primarily influenced by the varying strengths of PFAS molecules in binding with proteins and notably boosted by heatwaves. This study highlights the role of diverse PFAS in microalgae blooms and the influence of heatwave events on pollutant responses, providing scientific foundations for aquatic ecosystem protection against climate and pollution challenges.

Exploring the terrestrial ecosystem hazards of perfluorooctanoic acid: a comparative acute and chronic study of Eisenia fetida responses in different soil types

Human activities predominantly release perfluorooctanoic acid (PFOA) and other fluorinated chemicals, which are highly persistent, leading to long-term accumulation in organisms and posing significant health risks. Therefore, it is essential to study the long-term impacts of PFOA on terrestrial ecosystems using sentinel organisms such as earthworms. This research investigated the toxicity of PFOA on earthworms (Eisenia fetida) across three different soil types. An acute toxicity assay was conducted to assess the effects of PFOA on survival, growth, cellulase activity, lysosomal membrane stability, and avoidance behaviour. Concurrently, a chronic toxicity assay examined the impact on reproduction, specifically focusing on cocoon production and juvenile emergence. For the 14-day acute toxicity study, LC50 values were found to be 823.9 mg/kg, 894.9 mg/kg, and 672.2 mg/kg in alkaline, neutral, and OECD soils, respectively. Although PFOA showed lower toxicity in neutral soils, it still caused significant sublethal effects in all soil types. Chronic exposure to a concentration of 100 mg/kg significantly affected reproduction in all soils tested. Overall, the findings suggested that earthworms were effective sentinel organisms for evaluating the toxic potential of PFOA, with reproductive effects serving as particularly sensitive indicators of PFOA contamination.

Interaction between root exudates and PFOS mobility: Effects on rhizosphere microbial health in wetland ecosystems

Perfluorooctanesulfonate (PFOS), a persistent organic pollutant, poses significant ecological risks. This study investigates the effects of PFOS on rhizosphere microbial communities of two wetland plants, Lythrum salicaria (LS) and Phragmites communis (PC). We conducted microcosm experiments to analyze the physiological status of soil microbes under varying PFOS concentrations and examined the role of root exudates in modulating PFOS mobility. Flow cytometry and soil respiration measurements revealed that PFOS exposure increased microbial mortality, with differential impacts observed between LS and PC rhizospheres. LS root exudates intensified microbial stress, whereas PC exudates mitigated PFOS toxicity. Thin-layer chromatography indicated that LS exudates decreased PFOS mobility, leading to higher local concentrations and increased microbial toxicity, while PC exudates enhanced PFOS mobility, reducing its local impact. Fourier-transform infrared spectroscopy and excitation-emission matrix fluorescence spectroscopy of root exudates identified compositional shifts under PFOS stress, highlighting distinct defense strategies in LS and PC. These findings underscore the importance of plant-microbe interactions and root exudate composition in determining microbial resilience to PFOS contamination.

Assessment of the Variability in the Occurrence of PFAS in Fish Tissues from Selected Fisheries in the Baltic Sea

In this study, the results of a comprehensive assessment of the variability in the occurrence of ten perfluorinated compounds (PFAS) in fish tissues originating from 2014 to 2019 from six fisheries in the Baltic Sea are presented. A total of 360 fish samples of three species (perch, herring and flatfish) were analysed. For the determination of PFAS, both linear and branched stereoisomers, LC-ESI-MS/MS technique preceded by simultaneous SPE isolation was validated and applied. The total concentration of all determined PFAS compounds shows that the highest levels were observed in the Szczecin Lagoon (4.8 ± 0.7 µg/kg) and the lowest in the Pomeranian Bay (1.9 ± 0.1 µg/kg). In most samples, the dominant compound was perfluorooctane sulfonic acid (PFOS). The present research enabled the assessment of the variability in the occurrence of PFAS stereoisomers in marine fish.

Evanescent hormesis effect induced by environmentally relevant PFOS to marine Chlorella sp

Perfluorooctanesulfonic acid (PFOS) is widely detected in the aquatic environment. More attentions were paid to its acute biotoxicity at high-dose concentrations, whereas the actual long-term effect (hormesis or inhibition of growth) of PFOS with environmental concentrations on marine phytoplankton remains unclear. In this study, marine Chlorella sp. was exposed to PFOS at low concentrations (100 ng/L, 10 μg/L, and 1 mg/L) for 26 days. The hormesis effect disappeared at the population level on Day 18, but persisted at the molecular and cellular levels on Day 24, suggesting that the stimulatory hormetic effect induced by low-level PFOS (approximating environmental concentrations) does not persist throughout algal life cycle at population level. The 100 ng/L and 1 mg/L PFOS treatments caused algal cell to swell and shrink, respectively. The low-level PFOS treatments could accelerate cells apoptosis and induce cell necrosis at 100 ng/L. Specifically, the energy metabolism associated with carbohydrate metabolism and amino acid metabolism was significantly up-regulated as well as the reduced chlorophyll content (related to the down-regulation of porphyrin metabolism) to combat the 100 ng/L PFOS rather than be engaged in divide and growth. Additionally, the decreased biomass in the 100 ng/L treatment was also attributed to certain proteins associated with down-regulations of carotenoid biosynthesis, thiamine metabolism, non-homologous end-joining, and nitrogen metabolism along with the increased oxidative stress. Our findings provide a new insight into the long-term ecological effect of PFOS at environmental concentrations.

Revealing the bioavailability and phytotoxicity of different particle size microplastics on diethyl phthalate (DEP) in rye (Secale cereale L.)

Understanding how widely distributed microplastics (MPs) and diethyl phthalate (DEP) interact with crops remains limited, despite their significant implications for human exposure. We used physiology, transcriptomics, adsorption kinetics, and computational chemistry to assess rye's molecular response to two sizes of MPs (200 nm and 5 µm) and DEP, both individually and in combination. Findings systematically highlight potential ecological risks from MPs and DEP, with ecotoxicity ranking as follows: CK (Control Check) < LMPs < SMPs < DEP < LMPs+DEP < SMPs+DEP. Fluorescence and scanning electron microscopy revealed SMP's translocation ability in rye and its potential to disrupt leaf cells. DEP increased the electronegativity on MPs, which enhanced their uptake by rye. DEP adsorption by MPs in hydroponics reduced DEP bioavailability in rye (18.17-46.91 %). Molecular docking studies showed DEP interacted with chlorophyll, superoxide dismutase, and glutathione S-transferases proteins' active sites. Transcriptomic analysis identified significant up-regulation of genes linked to mitogen-activated protein kinase signaling, phytohormones, and antioxidant systems in rye exposed to MPs and DEP, correlating with physiological changes. These findings deepen the understanding of how MPs can accumulate and translocate within rye, and their adsorption to DEP raises crop safety issues of greater environmental risk.

Allelopathy of extracellular chemicals released by Karlodinium veneficum on photosynthesis of Prorocentrum donghaiense

Dinoflagellates Prorocentrum donghaiense and Karlodinium veneficum are the dominant species of harmful algal blooms in the East China Sea. The role of their allelopathy on the succession of marine phytoplankton populations is a subject of ongoing debate, particularly concerning the formation of blooms. To explore the allelopathy of K. veneficum on P. donghaiense, an investigation was conducted into photosynthetic performance (including PSII functional activities, photosynthetic electron transport chain, energy flux, photosynthetic different genes and photosynthetic performance) and photosynthetic damage-induced oxidative stress (MDA, SOD, and CAT activity). The growth of P. donghaiense was strongly restrained during the initial four days (1-6 folds, CK/CP), but the cells gradually resumed activity at low filtrate concentrations from the eighth day. On the fourth day of the strongest inhibition, allelochemicals reduced representative photosynthetic performance parameters PI and ΦPSII, disrupted related processes of photosynthesis, and elevated the levels of MDA content in P. donghaiense. Simultaneously, P. donghaiense repairs these impairments by up-regulating the expression of 13 photosynthetic genes, modifying photosynthetic processes, and activating antioxidant enzyme activities from the eighth day onward. Overall, this study provides an in-depth overview of allelopathic photosynthetic damage, the relationship between genes and photosynthesis, and the causes of oxidative damage induced by photosynthesis. ENVIRONMENTAL IMPLICATIONS: As a typical HAB species, Karlodinium veneficum is associated with numerous fish poisoning events, which have negative impacts on aquatic ecosystems and human health. Allelochemicals produced by K. veneficum can provide a competitive advantage by interfering with the survival, reproduction and growth of competing species. This study primarily investigated the effects of K. veneficum allelochemicals on the photosynthesis and photosynthetic genes of Prorocentrum donghaiense. Grasping the mechanism of allelochemicals inhibiting microalgae is helpful to better understand the succession process of algal blooms and provide a new scientific basis for effective prevention and control of harmful algal blooms.

Insights into the combined toxicity and mechanisms of BDE-47 and PFOA in marine blue mussel: An integrated study at the physiochemical and molecular levels

The coexistence of multiple emerging contaminants imposes a substantial burden on the ecophysiological functions in organisms. The combined toxicity and underlying mechanism requires in-depth understanding. Here, marine blue mussel (Mytilus galloprovincialis L.) was selected and exposed to 2,2',4,4'-tetrabromodiphenyl ether (BDE-47) and perfluorooctanoic acid (PFOA) individually and in combination at environmental related concentrations to elucidate differences in stress responses and potential toxicological mechanisms. Characterization and comparison of accumulation, biomarkers, histopathology, transcriptomics and metabolomics were performed. Co-exposure resulted in differential accumulation patterns, exacerbated histopathological alterations, and different responses in oxidative stress and biomarkers for xenobiotic transportation. Moreover, the identified differentially expressed genes (DEGs) and differential metabolites (DEMs) in mussels were found to be annotated to different metabolic pathways. Correlation analyses further indicated that DEGs and DEMs were significantly correlated with the above biomarkers. BDE-47 and PFOA altered the genes and metabolites related to amino acid metabolism, energy and purine metabolism, ABC transporters, and glutathione metabolism to varying degrees, subsequently inducing accumulation differences and combined toxicity. Furthermore, the present work highlighted the pivotal role of Nrf2-keap1 detoxification pathway in the acclimation of M. galloprovincialis to reactive oxygen species (ROS) stress induced by BDE-47 and PFOA. This study enabled more comprehensive understanding of combined toxic mechanism of multi emerging contaminants pollution.

Mechanism of microplastics effects on the purification of heavy metals in piggery effluents by microalgae

Microalgae is an effective bioremediation technique employed for treating piggery effluent. However, there is insufficient study on how the presence of microplastics (MPs) in wastewater affects the ability of microalgae to remove heavy metals from piggery effluent. This study aims to investigate the influence of two prevalent heavy metals found in piggery wastewater, Cu2+ (2 mg/L) and Zn2+ (2 mg/L), on their removal by microalgae (Desmodesmus sp. CHX1) in the presence of four types of MPs: polyethylene (PE), polyvinyl chloride (PVC), polypropylene (PP), and polyethylene terephthalate (PET). The results revealed that smaller particle size MPs promoted chlorophyll accumulation, while larger particles inhibits it. Additionally, higher concentrations of MPs promoted chlorophyll accumulation, while lower concentrations inhibited it. As for heavy metals, the presence of microplastics reduced the removal efficiency of Cu2+ and Zn2+ by Desmodesmus sp. CHX1. The highest inhibition of Cu2+ was 30%, 10%, 19%, and 16% of the control (CK), and the inhibition of Zn2+ was 7%, 4%, 4%, and 13%, respectively, under the treatments of PE, PVC, PP and PET MPs. Furthermore, Desmodesmus sp. CHX1 can secrete more extracellular polymeric substances (EPS) and form heterogeneous aggregates with MPs to counteract their pressure. These findings elucidate the impact of MPs on microalgae in bioremediation settings and offer useful insights into the complex relationships between microalgae, MPs, and heavy metals in the environment.

Influence of humic acid on the bioaccumulation, elimination, and toxicity of PFOS and TBBPA co-exposure in Mytilus unguiculatus Valenciennes

Tetrabromobisphenol A (TBBPA) and Perfluorooctane sulfonate (PFOS) are emerging contaminants which coexist in marine environments, posing significant risks to ecosystems and human health. The behavior of these contaminants in the presence of dissolved organic matter (DOM), specifically the co-contamination of TBBPA and PFOS, is not well understood. The bioaccumulation, distribution, elimination, and toxic effects of TBBPA and PFOS on thick-shell mussels (Mytilus unguiculatus V.), with the absence and presence of humic acid (HA), a typical DOM, were studied. The results showed that the uptake of TBBPA decreased and the uptake of PFOS increased when exposed to 1 mg/L HA. However, at higher concentrations of HA (5 and 25 mg/L), the opposite effect was observed. Combined exposure to HA, TBBPA, and PFOS resulted in oxidative stress in the digestive gland, with the severity of stress dependent on exposure time and HA dose. Histological analysis revealed a positive correlation between HA concentration and tissue damage caused by TBBPA and PFOS. This study provides insights into the influence of HA on the bioaccumulation-elimination patterns and toxicity of TBBPA and PFOS in marine bivalves, offering valuable data for ecological and health risk assessments of combined pollutants in aquatic environments rich in DOM.

Hormetic effect of a short-chain PFBS on Microcystis aeruginosa and its molecular mechanism

Short-chain Perfluorinated compounds (PFCs), used as substitutes for highly toxic long-chain PFCs, are increasingly entering the aquatic environment. However, the toxicity of short-chain PFCs in the environment is still controversial. This study investigated the effects of short-chain perfluorobutanesulfonic acid (PFBS) at different concentrations (2.5, 6, 14.4, 36, and 90 mg/L) on M. aeruginosa growth under 12-day exposure and explored the molecular mechanism of toxicity using transcriptomics. The results showed that M. aeruginosa exhibited hormetic effects after exposure to PFBS. Low PFBS concentrations stimulated algal growth, whereas high PFBS concentrations inhibited it, and this inhibitory effect became progressively more pronounced with increasing PFBS exposure concentrations. Transcriptomics showed that PFBS promoted the pathways of photosynthesis, glycolysis, energy metabolism and peptidoglycan synthesis, providing the energy required for cell growth and maintaining cellular morphology. PFBS, on the other hand, caused growth inhibition in algae mainly through oxidative stress, streptomycin synthesis, and genetic damage. Our findings provide new insights into the toxicity and underlying mechanism of short-chain PFCs on algae and inform the understanding of the hormetic effect of short-chain PFCs, which are crucial for assessing their ecological risks in aquatic environments.

Polystyrene microplastics enhanced the effect of PFOA on Chlorella sorokiniana: Perspective from the cellular and molecular levels

Microplastics (MPs) commonly coexist with other contaminants and alter their toxicity. Perfluorooctanoic acid (PFOA), an emerging pollutant, may interact with MPs but remain largely unknown about the joint toxicity of PFOA and MPs. Hence, this research explored the single and joint effects of PFOA and polystyrene microplastics (PS-MPs) on microalgae (Chlorella sorokiniana) at the cellular and molecular levels. Results demonstrated that PS-MPs increased PFOA bioavailability by altering cell membrane permeability, thus aggravating biotoxicity (synergistic effect). Meanwhile, the defense mechanisms (antioxidant system modulation and extracellular polymeric substances secretion) of Chlorella sorokiniana were activated to alleviate toxicity. Additionally, transcriptomic analysis illustrated that co-exposure had more differential expression genes (DEGs; 4379 DEGs) than single-exposure (PFOA: 2533 DEGs; PS-MPs: 492 DEGs), which were mainly distributed in the GO terms associated with the membrane composition and antioxidant system. The molecular regulatory network further revealed that PS-MPs and PFOA primarily regulated the response mechanisms of Chlorella sorokiniana by altering the ribosome biogenesis, photosynthesis, citrate cycle, oxidative stress, and antioxidant system (antioxidant enzyme, glutathione-ascorbate cycle). These findings elucidated that PS-MPs enhanced the effect of PFOA, providing new insights into the influences of MPs and PFOA on algae and the risk assessment of multiple contaminants. ENVIRONMENTAL IMPLICATION: MPs and PFAS, emerging contaminants, are difficult to degrade and pose a non-negligible threat to organisms. Co-pollution of MPs and PFAS is ubiquitous in the aquatic environment, while risks of co-existence to organisms remain unknown. The present study revealed the toxicity and defense mechanisms of microalgae exposure to PS-MPs and PFOA from cellular and molecular levels. According to biochemical and transcriptomic analyses, PS-MPs increased PFOA bioavailability and enhanced the effect of PFOA on Chlorella sorokiniana, showing a synergistic effect. This research provides a basis for assessing the eco-environmental risks of MPs and PFAS.

Mechanism of the adverse outcome of Chlorella vulgaris exposure to diethyl phthalate: Water environmental health reflected by primary producer toxicity

As a ubiquitous contaminant in aquatic environments, diethyl phthalate (DEP) is a major threat to ecosystems because of its increasing utilization. However, the ecological responses to and toxicity mechanisms of DEP in aquatic organisms remain poorly understood. To address this environmental concern, we selected Chlorella vulgaris (C. vulgaris) as a model organism and investigated the toxicological effects of environmentally relevant DEP concentrations at the individual, physiological, biochemical, and molecular levels. Results showed that the incorporation of DEP significantly inhibited the growth of C. vulgaris, with inhibition rates ranging from 10.3 % to 83.47 %, and disrupted intracellular chloroplast structure at the individual level, while the decrease in photosynthetic pigments, with inhibition rates ranging from 8.95 % to 73.27 %, and the imbalance of redox homeostasis implied an adverse effect of DEP at the physio-biochemical level. Furthermore, DEP significantly reduced the metabolic activity of algal cells and negatively altered the cell membrane integrity and mitochondrial membrane potential. In addition, the apoptosis rate of algal cells presented a significant dose-effect relationship, which was mainly attributed to the fact that DEP pollutants regulated Ca2+ homeostasis and further increased the expression of Caspase-8, Caspase-9, and Caspase-3, which are associated with internal and external pathways. The gene transcriptional expression profile further revealed that DEP-mediated toxicity in C. vulgaris was mainly related to the destruction of the photosynthetic system, terpenoid backbone biosynthesis, and DNA replication. Overall, this study offers constructive understandings for a comprehensive assessment of the toxicity risks posed by DEP to C. vulgaris.

Perfluorooctane sulfonate causes pyroptosis and lipid metabolism disorders through ROS-mediated NLRP3 inflammasome activation in grass carp hepatocyte

The surfactant perfluorooctane sulfonate (PFOS) is widely produced worldwide. It is a persistent organic pollutant in the aquatic environment and poses a serious threat to aquatic organisms, as PFOS exposure can cause liver injury in a wide range of organisms. However, it is unclear whether PFOS exposure-induced hepatocellular injury in fish is associated with ROS-mediated activation of NLRP3 inflammasome. In this study, various PFOS concentrations were applied to L8824 cells, a cell line of grass carp hepatocytes. The detrimental impacts of PFOS on oxidative stress, pyroptosis, lipid metabolism, and the discharge of inflammatory factors were examined. MCC950 and N-acetylcysteine were employed to hinder the PFOS-stimulated activation of the NLRP3 inflammasome and the excessive generation of reactive oxygen species in L8824 cells, respectively. This study demonstrated that treatment with PFOS resulted in oxidative stress and activation of NLRP3 inflammasome in L8824 cells. This led to increased expression levels of indicators related to pyroptosis, accompanied by the upregulation of pro-inflammatory cytokine expression as well as downregulation of anti-inflammatory factors. In addition, following PFOS exposure, the expression levels of genes related to lipid synthesis were upregulated and lipid catabolism-related genes were downregulated. Surprisingly, both N-acetylcysteine and MCC950 interventions significantly reduced PFOS-induced L8824 cell pyroptosis and lipid metabolism disorders. In conclusion, this research demonstrated that PFOS drives NLRP3 inflammasome activation through oxidative stress induced by reactive oxygen species overload. This in turn leads to pyroptosis and lipid metabolism disorders.

Inhibition of algal blooms by residual antibiotics in aquatic environments: Design, screening, and validation of antibiotic alternatives

Water blooms frequently appear in the aquatic environment with global warming. However, traditional methods for treating water bloom usually require the addition of algaecides, which may lead to secondary environmental pollution problems in the water environment. To solve this problem, researchers have initiated efforts to harness pre-existing chemical substances within aquatic environments to regulate algal blooms, thereby pioneering novel avenues for water body management. Therefore, an integrated approach involving molecular docking, molecular dynamics simulations, three-dimensional quantitative structure-activity relationship (3D-QSAR), and toxicokinetics methods were utilized for the molecular modification of fluoroquinolone antibiotics, to design and screen fluoroquinolone substitutes with improved toxicity of cyanobacteria and green algae, functionality, and environmental friendliness. A total of 143 fluoroquinolone alternatives were designed in this study, and lomefloxacin-6 (LOM6) was found as the optimum alternative to lomefloxacin (LOM), with increased toxicity to cyanobacteria and green algae by 31 % and 72 %. Molecular docking of LOM before and after modification with seven other cyanobacterial and green algal photosynthetic proteins revealed that LOM6 exhibited varying degrees of increased toxicity towards 6 of these photosynthetic proteins, of which 2J96 protein increased the most (136.25 %). It shows that the residual LOM6 in the water environment has a certain inhibitory effect on the algae bloom. In addition, results showed that LOM6 had synergistic toxic effects on cyanobacteria and green algae with other pollutants residual in the aqueous environment, such as trichloroethyl phosphate, triethyl phosphate, perfluorononanoic acid, perfluorooctanoic acid. This indicates that LOM6 has better algal removal effectiveness in aqueous environments where organophosphate flame retardants and perfluorinated compounds exist together. In this paper, a novel method was developed to remove cyanobacteria and green algae in water environment and reduce the secondary pollution through theoretical simulation, which provides theoretical support for the control of water blooms.

Phosphorus conditions change the cellular responses of Microcystis aeruginosa to perfluorooctanoic acid

Perfluorooctanoic acid (PFOA), a widespread and emerging organic contaminant of aquatic environments, has high bioaccumulation potential and high toxicity. Consequently, major concerns have been raised worldwide regarding the management of this pollutant in aquatic ecosystems. To thoroughly understand PFOA's toxic effects on aquatic organisms, systematic investigations were conducted on the cellular responses of Microcystis aeruginosa to the environmental concentrations of PFOA under various concentrations as well as phosphorus (P) conditions (concentrations and forms). The results showed that P conditions remarkably affected cyanobacterial growth as well as photosynthetic pigment content, triggered oxidative stress to disrupt the function and structure of the cell membrane, and caused changes in the extracellular and intracellular contents of microcystin-LR (MC-LR). Furthermore, PFOA (100 μg/L) was absorbed by cyanobacterial cells through the stimulation of the secretion of extracellular polymeric substances (EPS) by M. aeruginosa. After entering the cyanobacterial cells, PFOA inhibited photosynthesis, reduced P absorption, induced oxidative damage, lead to a loss of cell integrity evident in scanning electron microscope images, and increased mcyA gene expression to promote MC-LR production. Moreover, the limited P concentration and forms conditions led to increased PFOA absorption by cyanobacterial cells, which further upregulated mcyA gene expression and increased the risk of MC-LR diffusion into the aquatic environment. Our present study provided a theoretical basis and new ideas for understanding and addressing safety issues related to the presence of PFOA in aquatic environments with varying nutritional statuses.

Interactions between quorum sensing/quorum quenching and virulence genes may affect coral health by regulating symbiotic bacterial community

Quorum sensing (QS) and quorum quenching (QQ) are two antagonistic processes that may regulate the composition, function and structure of bacterial community. In coral holobiont, autoinducers signaling mediate the communication pathways between interspecies and intraspecies bacteria, which regulate the expression of the virulence factors that can damage host health. However, under environmental stressors, the interaction between the QS/QQ gene and virulence factors and their role in the bacterial communities and coral bleaching is still not fully clear. To address this question, here, metagenomics method was used to examine the profile of QS/QQ and virulence genes from a deeply sequenced microbial database, obtained from three bleached and non-bleached corals species. The prediction of bacterial genes of bleached samples involved in functional metabolic pathways were remarkably decreased, and the bacterial community structure on bleached samples was significantly different compared to non-bleached samples. The distribution and significant difference in QS/QQ and virulence genes were also carried out. We found that Proteobacteria was dominant bacteria among all samples, and AI-1 system is widespread within this group of bacteria. The identified specific genes consistently exhibited a trend of increased pathogenicity in bleached corals relative to non-bleached corals. The abundance of pathogenicity-associated QS genes, including bapA, pfoA and dgcB genes, were significantly increased in bleached corals and can encode the protein of biofilm formation and the membrane damaging toxins promoting pathogenic adhesion and infection. Similarly, the virulence genes, such as superoxide dismutase (Mn-SOD gene), metalloproteinase (yme1, yydH and zmpB), glycosidases (malE, malF, malG, and malK) and LodAB (lodB) genes significantly increased. Conversely, QQ genes that inhibit QS activity and virulence factors to defense the pathogens, including blpA, lsrK, amiE, aprE and gmuG showed a significant decrease in bleached groups. Furthermore, the significant correlations were found among virulence, QS/QQ genes, and coral associated bacterial community, and the virulence genes interact with key QS/QQ genes, directly or indirectly influence symbiotic bacterial communities homeostasis, thereby impacting coral health. It suggested that the functional and structural divergence in the symbiont bacteria may be partially attribute to the interplay, involving interactions among the host, bacterial communication signal systems, and bacterial virulence factors. In conclusion, these data helped to reveal the characteristic behavior of coral symbiotic bacteria, and facilitated a better understanding of bleaching mechanism from a chemical ecological perspective.

Low-dose chemical stimulation and pest resistance threaten global crop production

Pesticide resistance increases and threatens crop production sustainability. Chemical contamination contributes to the development of pest resistance to pesticides, in part by causing stimulatory effects on pests at low sub-toxic doses and facilitating the spread of resistance genes. This article discusses hormesis and low-dose biological stimulation and their relevance to crop pest resistance. It highlights that a holistic approach is needed to tackle pest resistance to pesticides and reduce imbalance in accessing food and improving food security in accordance with the UN's Sustainable Development Goals. Among others, the effects of sub-toxic doses of pesticides should be considered when assessing the impact of synthetic and natural pesticides, while the promotion of alternative agronomical practices is needed to decrease the use of agrochemicals. Potential alternative solutions include camo-cropping, exogenous application of phytochemicals that are pest-suppressing or -repelling and/or attractive to carnivorous arthropods and other pest natural enemies, and nano-technological innovations. Moreover, to facilitate tackling of pesticide resistance in poorer countries, less technology-demanding and low-cost practices are needed. These include mixed cropping systems, diversification of cultures, use of 'push-pull cropping', incorporation of flower strips into cultivations, modification of microenvironment, and application of beneficial microorganisms and insects. However, there are still numerous open questions, and more research is needed to address the ecological and environmental effects of many of these potential solutions, with special reference to trophic webs.