Toxicity effects of p-choroaniline on the growth, photosynthesis, respiration capacity and antioxidant enzyme activities of a diatom, Phaeodactylum tricornutu

Insight into the mechanism of chlorinated nitroaromatic compounds anaerobic reduction with mackinawite (FeS) nanoparticles

Anaerobic biotechnology for wastewaters treatment can nowadays be considered as state of the art methods. Nonetheless, this technology exhibits certain inherent limitations when employed for industrial wastewater treatment, encompassing elevated substrate consumption, diminished electron transfer efficiency, and compromised system stability. To address the above issues, increasing interest is being given to the potential of using conductive non-biological materials, e,g., iron sulfide (FeS), as a readily accessible electron donor and electron shuttle in the biological decontamination process. In this study, Mackinawite nanoparticles (FeS NPs) were studied for their ability to serve as electron donors for p-chloronitrobenzene (p-CNB) anaerobic reduction within a coupled system. This coupled system achieved an impressive p-CNB removal efficiency of 78.3 ± 2.9% at a FeS NPs dosage of 1 mg/L, surpassing the efficiencies of 62.1 ± 1.5% of abiotic and 30.6 ± 1.6% of biotic control systems, respectively. Notably, the coupled system exhibited exclusive formation of aniline (AN), indicating the partial dechlorination of p-CNB. The improvements observed in the coupled system were attributed to the increased activity in the electron transport system (ETS), which enhanced the sludge conductivity and nitroaromatic reductases activity. The analysis of equivalent electron donors confirmed that the S2- ions dominated the anaerobic reduction of p-CNB in the coupled system. However, the anaerobic reduction of p-CNB would be adversely inhibited when the FeS NPs dosage exceeded 5 g/L. In a continuous operation, the p-CNB concentration and HRT were optimized as 125 mg/L and 40 h, respectively, resulting in an outstanding p-CNB removal efficiency exceeding 94.0% after 160 days. During the anaerobic reduction process, as contributed by the predominant bacterium of Thiobacillus with a 6.6% relative abundance, a mass of p-chloroaniline (p-CAN) and AN were generated. Additionally, Desulfomonile was emerged with abundances ranging from 0.3 to 0.7%, which was also beneficial for the reduction of p-CNB to AN. The long-term stable performance of the coupled system highlighted that anaerobic technology mediated by FeS NPs has a promising potential for the treatment of wastewater containing chlorinated nitroaromatic compounds, especially without the aid of organic co-substrates.

Toxic interactions at the physiological and biochemical levels of green algae under stress of mixtures of three azole fungicides

Assessing the interactions between environmental pollutants and these mixtures is of paramount significance in understanding their negative effects on aquatic ecosystems. However, existing research often lacks comprehensive investigations into the physiological and biochemical mechanisms underlying these interactions. This study aimed to reveal the toxic mechanisms of cyproconazole (CYP), imazalil (IMA), and prochloraz (PRO) and corresponding these mixtures on Auxenochlorella pyrenoidosa by analyzing the interactions at physiological and biochemical levels. Higher concentrations of CYP, IMA, and PRO and these mixtures resulted in a reduction in chlorophyll (Chl) content and increased total protein (TP) suppression, and malondialdehyde (MDA) content exhibited a negative correlation with algal growth. The activity of catalase (CAT) and superoxide dismutase (SOD) decreased with increasing azole fungicides and their mixture concentrations, correlating positively with growth inhibition. Azole fungicides induced dose-dependent apoptosis in A. pyrenoidosa, with higher apoptosis rates indicative of greater pollutant toxicity. The results revealed concentration-dependent toxicity effects, with antagonistic interactions at low concentrations and synergistic effects at high concentrations within the CYP-IMA mixtures. These interactions were closely linked to the interactions observed in Chl-a, carotenoid (Car), CAT, and cellular apoptosis. The antagonistic effects of CYP-PRO mixtures on A. pyrenoidosa growth inhibition can be attributed to the antagonism observed in Chl-a, Chl-b, Car, TP, CAT, SOD, and cellular apoptosis. This study emphasized the importance of gaining a comprehensive understanding of the physiological and biochemical interactions within algal cells, which may help understand the potential mechanism of toxic interaction.

The toxic effects of petroleum pollutants to microalgae in marine environment

Marine oil pollution is one of the major global environmental pollution problems. Marine microalgae are the foundation of the marine food chain, providing the main primary productivity of the ocean. They not only maintain the energy flow and material cycle of the entire marine ecosystem, but also play an important role in regulating global climate change. Exploring the impact of petroleum pollutants on marine microalgae is extremely important for studying marine environmental pollution. This review first introduced the sources, compositions, and forms of petroleum pollutants and their migration and transformation processes in the ocean. Then, the toxic effects of petroleum pollutants on marine microalgae were summarized. The growth of marine microalgae showed low-concentration promotion and high-concentration inhibition. The population growth and interspecific relationships of marine microalga was changed and the photosynthesis of marine microalgae was influenced. Finally, potential research directions and suggestions for marine microalgae in the future were proposed.

Effects of Enhanced Resistance and Transcriptome Analysis of Twig Blight Disease by Exogenous Brassinolide in Myrica rubra

Twig blight disease is the primary disease that affects the production of Myrica rubra in China. It was reported that exogenous brassinolide (BL) can improve disease resistance in plants. Here, we examined the effects of exogenous BL on disease resistance, chlorophyll contents, antioxidant enzyme activity, ROS accumulation, and key gene expression of M. rubra to analyze the mechanism of BR-induced resistance of twig blight disease in M. rubra. The results demonstrated that 2.0 mg·L-1 of BL could significantly lessen the severity of twig blight disease in M. rubra. Exogenous BL increased the contents of chlorophyll a, chlorophyll b, carotenoids, and total chlorophyll. Moreover, exogenous BL also significantly enhanced the activity of antioxidant enzymes such as superoxide dismutase (SOD), peroxidase (POD), and catalase (CAT), and decreased malondialdehyde (MDA) content and reactive oxygen species (ROS) accumulation in leaves, such as H2O2 and O2·-. Additionally, exogenous BL dramatically up-regulated the expression of pathogenesis-related (PR) genes such as MrPR1, MrPR2, and MrPR10, as well as important genes such as MrBAK1, MrBRI1, and MrBZR1 involved in brassinosteroid (BR) signaling pathway. The transcriptome analysis revealed that a total of 730 common differentially expressed genes (DEGs) under BL treatment were found, and these DEGs were primarily enriched in four Kyoto Encyclopedia of Genes and Genomes (KEGG) pathways. Based on these findings, nine important candidate genes related to the resistance of twig blight disease under BL treatment were further identified. In this study, we elucidated the effects of exogenous BL on enhancing the resistance of M. rubra to twig blight disease and preliminary analyzed the potential mechanism of resistance induction, which will provide a crucial foundation for the management and prevention of twig blight disease in M. rubra.

Evaluation of the toxicity of clozapine on the freshwater diatom Navicula sp. using the FTIR spectroscopy

Clozapine is an often prescribed neuroactive pharmaceutical and frequently detected in the aquatic environments. However, its toxicity on low trophic level species (i.e., diatoms) and associated mechanisms are seldom reported. In this study, the toxicity of clozapine on a widely distributed freshwater diatom Navicula sp. was evaluated using the FTIR spectroscopy along with biochemical analyses. The diatoms were exposed to various concentrations of clozapine (0, 0.01, 0.05, 0.10, 0.50, 1.00, 2.00, 5.00 mg/L) for 96 h. The results revealed that clozapine reached up to 392.8 μg/g in the cell wall and 550.4 μg/g within the cells at 5.00 mg/L, suggesting that clozapine could be adsorbed extracellularly and accumulated intracellularly in diatoms. In addition, hormetic effects were displayed on the growth and photosynthetic pigments (chlorophyll a and carotenoid) of Navicula sp., with a promotive effect at concentrations less than 1.00 mg/L while an inhibited effect at concentrations over 2 mg/L. Clozapine induced oxidative stress in Navicula sp., accompanied by decreased levels of total antioxidant capacity (T-AOC) (>0.05 mg/L), in which, the activity of superoxide dismutase (SOD) (at 5.00 mg/L) was increased whereas the activity of catalase (CAT) (>0.05 mg/L) was decreased. Furthermore, FTIR spectroscopic analysis showed that exposure to clozapine resulted in accumulation of lipid peroxidation products, increased sparse β-sheet structures, and altered DNA structures in Navicula sp. This study can facilitate the ecological risk assessment of clozapine in the aquatic ecosystems.

Mechanism of time-dependent toxicity of quinolone antibiotics on luminescent bacteria Vibrio qinghaiensis sp.-Q67

Four quinolone antibiotics (ciprofloxacin (CIP), enrofloxacin (ENR), sparfloxacin (SPA), gatifloxacin (GAT)) and their binary mixtures at environmentally relevant concentrations exhibited time-dependent hormesis on Vibrio qinghaiensis sp.-Q67 (Q67). The study aims to investigate the time-dependent toxicity of low-dose pollutants and the occurrence of hormesis. These indicators, total protein (TP), reactive oxygen species (ROS), superoxide dismutase (SOD), catalase (CAT), malondialdehyde (MDA) and luminescence-related chemicals flavin mononucleotide (FMN), nicotinamide adenine dinucleotide (NADH), were measured to explore the mechanism of hormesis. The results showed a trend of increases in all indicators after 12 h of exposure, reaching maximal effects at 60 h and then decreasing as time progressed. At 36 h, 60 h and 84 h, the results showed a gradual increase followed by a decreasing trend in TP, FMN and NADH as the concentration in the group increased, whereas ROS, CAT, SOD and MDA showed the opposite trend. Notably, the degree of changes was related to the magnitude of hormesis. At low concentrations, the content of ROS and MDA decreased, the activity of CAT and SOD was lower, but the content of TP, FMN, NADH gradually increased, positively correlated with the promotion of Q67. At high concentrations, ROS and MDA content in Q67 increased, triggering the antioxidant defense mechanism (CAT and SOD activity increased), but TP, FMN, NADH content decreased, negatively correlated with the inhibited Q67. Therefore, our findings demonstrated two common patterns in these seven biochemical indicators on Q67. These findings have important practical implications for the ecological risk assessment of antibiotics in aquatic environment.

Altering autotrophic carbon metabolism of Nitzschia closterium to mixotrophic mode for high-value product improvement

An adaptive laboratory evolution (ALE) strategy was designed to evolve autotrophic Nitzschia closterium to mixotrophic growth for high productivity of essential amino acid (EAA), eicosapentaenoic acid (EPA) and fucoxanthin. The N. closterium growth was limited under glucose initially, but a red light emitting diode was innovatively applied to modify carbon metabolism and obtain mixotrophic strain of N. closterium GM. The N. closterium GM biomass concentration was improved by 65.07% comparing with wild type, but exhibited weak photosynthesis and strong glucose metabolism. At carbon metabolism levels, ALE promoted NADPH oxidase activity and induced protein degradation to lipid biosynthesis by elevating acetyl-CoA and pyruvate contents. It also improved carbon flux to TCA cycle, and elevated contents of glucose-6-phosphate, fructose-6-phosphate, glyceraldehyde-3-phosphate for providing sufficient ATP and NADPH. Productivities of EPA, EAA and fucoxanthin were increased by 41.0%, 18.8% and 20.4%, respectively. This ALE strategy was promising in microalgal production of high-value products.

Production and use of Scenedesmus acuminatus biomass in synthetic municipal wastewater for integrated biorefineries

Bioethanol production from algal biomass is a promising alternative for sustainable biofuel production. Algae possess a high photosynthetic capacity and an adaptive ability to thrive under harsh environmental conditions. The potential properties of Scenedesmus acuminatus CCALA 436 were assessed in this research for its bioethanol efficiency, and the effects of growing the algae in wastewater and at different concentrations of mepiquat chloride were studied. Also, pre-treatment efficiencies of different concentrations of calcium oxide were carried out on microalgae biomass. Superoxide dismutase, catalase activity, glutathione, and malondialdehyde contents of microalgae were examined, and the changes in chlorophyll, photoprotective carotenoid contents, and protein concentrations were determined. The results revealed that the maximum sugar and ethanol contents of Scenedesmus acuminatus CCALA 436 were 44.7 ± 1.5% and 20.32 g/L, respectively, for 50% wastewater and mepiquat chloride (2.5 mg/L) after pre-treatment with calcium oxide (0.08%). Additionally, the levels of oxidative enzymes varied depending on the wastewater concentrations. These findings indicate Scenedesmus acuminatus CCALA 436 grown in wastewater and mepiquat chloride can be used for the treatment of wastewater and the production of ethanol and high-value products such as carotenoid.

Weighted gene Co-expression network analysis (WGCNA) reveals a set of hub genes related to chlorophyll metabolism process in chlorella (Chlorella vulgaris) response androstenedione

Androstenedione (ADSD) was the main androgen detected in wastewaters. Chlorella was the most widely used plant in biological wastewater treatment process. In order to understand the toxicological response of chlorella to ADSD contamination, we used the weighted gene co-expression network analysis (WGCNA) method to systematically analyze the gene regulatory networks of chlorella after ADSD treatments. Total of 25 modules was identified from gene co-expression networks, and the turquoise module were selected for GO and KEGG enrichment analysis. Results showed that most hub genes were associated with chloroplast organizations or photosystems processes. Among them, the expressions profiles of hcar, nol, pao and sgr genes were highly correlated to the content fluctuations of chlorophylls after different ADSD treatments. All these results demonstrated that chlorophylls play a key role in preventing cell damage of chlorella caused by ADSD contamination. Besides, we proposed a possible chlorophyll metabolism pathway in chlorella response to ADSD contamination.

Impact of P-Chloroaniline on Oxidative Stress and Biomacromolecules Damage in the Clam Ruditapes philippinarums: A Simulate Toxicity Test of Spill Incident

As a hazardous chemical, p-chloroaniline (PCA) shows intensive adsorption and accumulation after entering the aquatic ecosystem, which can be enriched in organisms and cause damage. With the objective of achieving an integrated and mechanistic view of the toxic effects of PCA in the marine sentinel organism Ruditapes philippinarum, Manila clams were exposed to different concentration of PCA (0.5, 2 and 5 mg/L) for 15 days. Focusing on the gills, first targeting the toxic and digestive gland, the metabolic detoxification organ, we detected dose- and time-related changes inantioxidase activities and biomacromolecular damages in treated clams. Glutathione S-transferase (GST) activity and glutathione (GSH) contents were significantly induced, and superoxide dismutase (SOD) activity increased at the beginning of exposure and then decreased. The malondialdehyde (MDA) and protein methylation (PC) contents which represent lipid peroxidation and carbonylation of proteins, increased first with exposure time and then decreased in the digestive gland. DNA strand break levels were consistently higher than those in the control group. The digestive gland showed more sensitivity to the stress of PCA than the gills. GST and MDA in the gill and GST, GSH, SOD, DNA strand break level in the digestive gland showed significant correlation with PCA exposure, which indicated that these parameters can be used as sensitive biomarkers to indicate toxic effects from chloraniline leakage.

Intermediates formed during natural attenuation of C9 aromatics under simulated marine conditions: Identification, transformation pathway, and toxicity to microalgae

C9 aromatics - benzene hydrocarbon containing nine carbon atoms among - leakage accident has caused serious damage to the marine ecology near Quangang District, Fujian Province, China. The ecological restoration of the accident sea area is basically realized through natural attenuation. To determine whether the natural attenuation of C9 aromatics in the marine environment will generate highly toxic intermediates, and thus cause more serious harm to marine ecology, the intermediates of C9 aromatics (n-propylbenzene, isopropylbenzene, 2-ethyltoluene, 3-ethyltoluene, 4-ethyltoluene, 1,2,3-trimethylbenzene, 1,2,4-trimethylbenzene, 1,3,5-trimethylbenzene, and indene) in the process of natural attenuation were studied under the marine conditions simulated by a microcosm. The acute toxic effects of 12 intermediates with longer residual time on Phaeodactylum tricornutum were also ascertained. Twenty natural attenuation intermediates of C9 aromatics were identified. These products primarily include the derivatives of phenols, aromatic alcohols, aromatic aldehydes, aromatic ketones, and aromatic acids, as well as an aromatic lactone compound. No intermediates of 1,3,5-trimethylbenzene and indene during the attenuation process were determined. The indirect photooxidation initiated by hydroxyl radical might play an essential role in the formation of intermediates of C9 aromatic. Based on the 96-h EC₅₀ values for P. tricornutum, the toxicity of the 12 intermediates, in descending order, was: 4-ethylphenol, 2-methylacetophenone, 2,3-dimethylbenzyl alcohol, 4-methylacetophenone, 3-methylacetophenone, 1-phenyl-1-propanol, 1-(2-methylphenyl) ethanol, 2-phenyl-2-propanol, 3,4-dimethylbenzoic acid, 2,4-dimethylbenzoic acid, 2,5-dimethylbenzoic acid, then 4-tolylacetic acid. The 96-h EC₅₀ values of the intermediates of C9 aromatics to P. tricornutum ranged from 8.4 to 199.1 mg/L, which were lower than that of their corresponding parent compound. The findings provided essential fundamental insights for the assessment of marine environmental risk of C9 aromatics leakage accidents, and subsequent emergency disposal countermeasures.

Using Caenorhabditis elegans to assess the ecological health risks of heavy metals in soil and sediments around Dabaoshan Mine, China

Heavy metal pollution is a global environmental problem, and the potential risks associated with heavy metals are increasing. The acid mine drainage (AMD) which is generated by mining activities at Dabaoshan Mine, the largest polymetallic mine in southern China, is harmful to local residents. A detailed regional survey of the ecological and human health risks of this polluted area is urgently needed. In this study, eight sediments and farmland samples were collected along the flow direction of tailing wastewater and Fandong Reservoir; the content of multiple heavy metals in these samples was determined by inductively coupled plasma mass spectrometry. The biological toxicity of water-soluble extracts from the samples was further assessed by referring to different endpoints of Caenorhabditis elegans (C. elegans). The relationship between specific heavy metals and biological toxicity was estimated by partial least squares regression. The results indicated that the risk of heavy metals in Dabaoshan mining area was very high (potential ecological risk index = 721.53) and was related to geographical location. In these samples, the carcinogenic risk (the probability that people are induced carcinogenic diseases or injuries when exposed to carcinogenic pollutants) of arsenic (As) for adults exceeded the standard value 1 × 10^-4 and indicated that As presented a high carcinogenic risk to adults, while the high risk of non-carcinogenic effects (the hazard degree of human exposure to non-carcinogenic pollutants) in children was related to lead exposure (hazard index = 1.24). In addition, the heavy metals at high concentration in the water-soluble fraction of sediment and farmland soil extracts, which might easily distribute within the water cycle, inhibited the survival rate and growth of C. elegans. Gene expression and enzymatic activity related to oxidative stress were increased and genes related to apoptosis and metallothionein were also affected. In conclusion, the results of chemical analysis and biological assays provided evidence on the toxicity of soil and sediment extracts in the Dabaoshan mining area and advocated the control and remediation of heavy metal pollution around Dabaoshan Mine.

Risk assessments of emerging contaminants in various waters and changes of microbial diversity in sediments from Yangtze River chemical contiguous zone, Eastern China

Over recent decades, increasing chemical contamination has greatly affected aquatic life and human health, even though most contaminants are present at low concentrations. The large-scale chemical industrial parks (CIPs) concentrated in the Yangtze River Delta account for over half of the total in China, and Jiangsu Province occupies one fifth of the Yangtze River Delta. Inevitably, the ecosystems could be affected by these CIPs. In this study, we collected 35 water and 12 sediment samples from the Yangtze River (Taizhou section) surrounding waters adjacent to concentrated CIPs and determined their cumulative chemical levels to be 0.2 to 28.4 μg/L and cumulative detections to be 11 to 39 contaminants with a median of 20 contaminants. 61 out of 153 screened chemicals were detected from at least one sampling site, and 6 contaminants, mostly semi-volatile organic compounds, appeared at all sites. Among these detected chemicals, di-n-octyl phthalate and dibutyl phthalate were at the highest levels. Ecological assessment revealed that 4-chloroaniline, phenol and dibutyl phthalate possibly would induce adverse effects on Yangtze River (Taizhou) ecosystems. Further aided with an evaluation of integrated biomarker response (IBR) index, it was found that site W06 (downstream of Binjiang CIP wastewater inlet) was the location in greatest need of urgent action. As a result, the microbial diversity of sediments in the Yangtze River mainstream was significantly higher than that of tributaries, where CIPs wastewater entered.

Abundant Allelochemicals and the Inhibitory Mechanism of the Phenolic Acids in Water Dropwort for the Control of Microcystis aeruginosa Blooms

In recent years, with the frequent global occurrence of harmful algal blooms, the use of plant allelopathy to control algal blooms has attracted special and wide attention. This study validates the possibility of turning water dropwort into a biological resource to inhibit the growth of harmful Microcystis aeruginosa blooms via allelopathy. The results revealed that there were 33 types of allelopathic compounds in the water dropwort culture water, of which 15 were phenolic acids. Regarding water dropwort itself, 18 phenolic acids were discovered in all the organs of water dropwort via a targeted metabolomics analysis; they were found to be mainly synthesized in the leaves and then transported to the roots and then ultimately released into culture water where they inhibited M. aeruginosa growth. Next, three types of phenolic acids synthesized in water dropwort, i.e., benzoic, salicylic, and ferulic acids, were selected to clarify their inhibitory effects on the growth of M. aeruginosa and their mechanism(s) of action. It was found that the inhibitory effect of phenolic acids on the growth of M. aeruginosa increased with the increase of the exposure concentration, although the algae cells were more sensitive to benzoic acid than to salicylic and ferulic acids. Further study indicated that the inhibitory effects of the three phenolic acids on the growth of M. aeruginosa were largely due to the simultaneous action of reducing the number of cells, damaging the integrity of the cell membrane, inhibiting chlorophyll a (Chl-a) synthesis, decreasing the values of F₀ and F_v/F_m, and increasing the activity of the antioxidant enzymes (SOD, POD, and CAT) of M. aeruginosa. Thus, the results of this study indicate that both culture water including the rich allelochemicals in water dropwort and biological algae inhibitors made from water dropwort could be used to control the growth of noxious algae in the future.

Toxicities of three metal oxide nanoparticles to a marine microalga: Impacts on the motility and potential affecting mechanisms

With the fast growth of the production and application of engineered nanomaterials (ENMs), nanoparticles (NPs) that escape into the environment have drawn increasing attention due to their ecotoxicological impacts. Motile microalgae are a type of primary producer in most ecosystems; however, the impacts of NPs on the motility of microalgae have not been studied yet. So the toxic impacts of three common metal oxide NPs (nTiO₂, nZnO, and nFe₂O₃) on swimming speed and locomotion mode of a marine microalgae, Platymonas subcordiformis, were investigated in this study. Our results demonstrated that both the velocity and linearity (LIN) of swimming were significantly decreased after the exposure of P. subcordiformis to the tested NPs. In addition, the obtained data indicate that NPs may suppress the motility of P. subcordiformis by constraining the energy available for swimming, as indicated by the significantly lower amounts of intracellular ATP and photosynthetic pigments and the lower activities of enzymes catalyzing glycolysis. Incubation of P. subcordiformis with the tested NPs generally resulted in the overproduction of reactive oxygen species (ROS), aggravation of lipid peroxidation, and induction of antioxidant enzyme activities, suggesting that imposing oxidative stress, which may impair the structural basis for swimming (i.e. the membrane of flagella), could be another reason for the observed motility suppression. Moreover, NP exposure led to significant reductions in the cell viability of P. subcordiformis, which may be due to the disruption of the energy supply (i.e., photosynthesis) and ROS-induced cellular damage. Our results indicate that waterborne NPs may pose a great threat to motile microalgae and subsequently to the health and stability of the marine ecosystem.

Toxicity evaluation of butyl acrylate on the photosynthetic pigments, chlorophyll fluorescence parameters, and oxygen evolution activity of Phaeodactylum tricornutum and Platymonas subcordiformis

Butyl acrylate is a hazardous and noxious substance (HNS) listed in the top 50 chemicals that is most likely to be involved in HNS spilling incident. At present, information about toxicity effect of butyl acrylate on marine organisms was insufficient, especially on marine microalgae. Phaeodactylum tricornutum (P. tricornutum) and Platymonas subcordiformis (P. subcordiformis) were used as test organism to evaluate the toxic effect of butyl acrylate on their photosynthetic system. Results showed that chlorophyll a (Chl-a) content, the net photosynthetic oxygen evolution rate (NOR), and chlorophyll fluorescence parameters including maximal photochemical efficiency (Fv/Fm), electron transfer rate (ETR), photochemical quenching (qP), and non-photochemical quenching (NPQ) were all stimulated in the toxic dose of 5,10, and 25 mg/L while those were significantly inhibited in the highest concentration of 25 mg/L groups after 96 h. Meanwhile, it was also found that Fv/Fm would be a suitable indicator for evaluating the toxicity of butyl acrylate on the photosynthetic system of two marine microalgae according to the analysis of Pearson correlation coefficient and integrated biomarker response (IBR). Once butyl acrylate enters the marine ecosystem, the toxicity data obtained in this study could be used as a reference for evaluating the effect of butyl acrylate on the photosynthetic capacity of marine microalgae.

Biochar-mediated reduction of m-nitrotoluene: Interaction between reduction of m-nitrotoluene and sequestration of contaminants

Biochar is a highly effective adsorbent for nitroaromatic compounds (NACs), and acts as an electron shuttle that mediates the reduction of NACs. Hence, when biochar is used to mediate NAC reduction, adsorption and reduction will occur simultaneously and affect each other. However, the effect of biochar-mediated NAC reduction on sorption remains unknown. Eight biochars with different physicochemical properties were used to adsorb m-nitrotoluene and mediate its reduction. The results showed that the adsorption of m-nitrotoluene onto the various biochars facilitated its reduction, whereas biochar-mediated reduction retarded and weakened contaminant adsorption, which increased the environmental risk posed by m-nitrotoluene. Nevertheless, biochars with a high graphitization degree and developed porosity not only had a great catalytic ability, but also significantly alleviated the negative effect of reduction on adsorption. This was ascribed to the π-π interaction and pore-filling effect, which played more important roles than the hydrophobic effect in adsorbing the reduction product (m-toluidine) onto the studied biochars during reduction. Furthermore, the methanol extraction results indicated that the eight biochars presented significantly stronger sequestration abilities for adsorbed m-toluidine than for adsorbed m-nitrotoluene. This resulted from the hydrogen bonding and the Lewis acid-base effect between m-toluidine and each biochar, which were absent for m-nitrotoluene. These results suggest that biochars with a high graphitization degree and developed porosity are applicable for mediating reduction-enhancing sequestration of NACs, which could be a novel strategy for NAC remediation.

Toxic effect of p-chloroaniline and butyl acrylateon Nannochloropsis oculata based on water samples from two sea areas

To compare the influence of water samples collected from various areas on toxic effect of HNS, we examined the toxic effect of two commonly found HNS: p-chloroaniline and butyl acrylate, on Nannochloropsis oculata cultured in seawater collected from Laizhou bay and Jiaozhou bay (China). The results showed that both p-chloroaniline and butyl acrylate had significant toxic effect on N. oculata cultured in both water samples. P-chloroaniline inhibited its net oxygenation rate and oxygen consumption rate. Butyl acrylate inhibited the net oxygenation rate whereas significantly stimulated oxygen consumption rate. Performance of N. oculata changed between two water samples under same level of p-chloroaniline and butyl acrylate. The net oxygenation rate of N. oculata cultured in the seawater from the Jiaozhou bay increased by 11.60 %, the oxygen consumption rate increased by 26.91 %, algae cell growth decreased by 16.83 %, compared to those from Laizhou bay. The Fv/Fm of N. oculata cultured in Jiaozhou bay was more significantly inhibited at 0.5 and 2.0 mg L^-1 p-chloroaniline, while it was significantly inhibited at 5. 0 mg L^-1 of butyl acrylate, compared to those from Laizhou bay. Moreover, the toxic effect of both HNS on net oxygenation rate and oxygen consumption rate were significantly attenuated as the concentration increased. The growth inhibition of microalgae cultured in two seawater samples was more evident at 0.5 and 5.0 mg L^-1 p-chloroaniline than at 2.0 mg L^-1 p-chloroaniline,and the growth inhibition of microalgae cultured in two seawater samples was more evident at 2.0 and 5.0 mg L^-1 butyl acrylate than at 0.5 mg L^-1 butyl acrylate. These results indicated that toxic effect of p-chloroaniline and butyl acrylate on the growth of N. oculata was influenced by the pollutants in the two water samples. Consequently, a corresponding research on water sample is required in advance to increase accuracy of future ecological risk assessment of HNS.

Microalgal biosorption of heavy metals: A comprehensive bibliometric review

Heavy metals in the effluents released from industrial establishments pose risks to the environment and society. Prevalent organisms such as microalgae in industrial wastes can thrive in this harmful environment. The connection of the metal-binding proteins of the microalgal cell wall to the metal ions of the heavy metals enables microalgae as an ideal medium for biosorption. The current literature lacks the review of various microalgae used as biosorption of heavy metals from industrial effluents. This work aims to comprehensively review the literature on the use of microalgae as a biosorption for heavy metals. The study summarizes the application of different microalgae for heavy metals removal by identifying the various factors affecting the biosorption performance. Approaches to quantifying the heavy metals concentration are outlined. The methods of microalgae to generate biocompounds to enable biosorption of heavy metals are itemized. The study also aims to identify the materials produced by microalgae to facilitate biosorption. The industrial sectors with the potential benefit from the adoption of microalgal biosorption of heavy metals are recognized. Moreover, the current challenges and future perspectives of microalgal biosorption are discussed.

Using a freshwater green alga Chlorella pyrenoidosa to evaluate the biotoxicity of ionic liquids with different cations and anions

With the extensive use of ionic liquids (ILs) in various industrial fields, their potential toxicity to aquatic ecosystem has attracted considerable attention. In this work, biotoxicity of ILs with different cations and anions was evaluated by using a freshwater green alga Chlorella pyrenoidosa. Results showed that 1-butyl-3-methylimidazolium chloride ([C₄mim]Cl), 1-octyl-3-methylimidazolium chloride ([C₈mim]Cl), 1-octyl-3-methylimidazolium nitrate ([C₈mim]NO₃), 1-octyl-3-methylimidazolium tetrafluoroborate ([C₈mim]BF₄), and 1-dodecyl-3-methylimidazolium chloride ([C₁₂mim]Cl) had a significant inhibition on the algal growth with EC₅₀ values of 23.48, 4.72, 3.80, 4.44, and 0.10 mg L^-1 at the 72 h of exposure, respectively. These data suggested that the toxicity of ILs increased with the increase of side alkyl chain length, while anions had little influences on their toxicity to this alga. Moreover, changes in chlorophyll a content and chlorophyll fluorescence parameters (F_v/F_m and Φ_PSII) indicated that the five ILs could damage the photosynthetic system of this alga resulting in the decrease of photosynthetic efficiency. The increased soluble protein content and antioxidase activity could be considered as an active response mechanism of this alga against the exposure of ILs. Content of malondialdehyde (MDA) in this alga increased significantly when it was exposed to ILs, suggesting that reactive oxygen species (ROS) were accumulated in the algal cells, which would cause injury of the algal biofilm and chloroplast. Therefore, results obtained in this work would help to explain the possible underlying toxic mechanisms of ILs to C. pyrenoidosa, and provide a significant theoretical support for assessing the toxicity of ILs to aquatic organisms.

The allelopathic effects of aqueous extracts from Spartina alterniflora on controlling the Microcystis aeruginosa blooms

The Microcystis aeruginosa (M. aeruginosa) blooms and Spartina alterniflora (S. alterniflora) invasion have caused serious damage to local ecological environment. This study validated the possibility of transforming the abandoned S. alterniflora into a biological resource to inhibit M. aeruginosa blooms through allelopathy. The results showed that the inhibitory effect became stronger with the increasing S. alterniflora concentration by decreasing chlorophyll a and weakening photosynthesis when S. alterniflora aqueous extract concentration was over 0.05 g/mL. The results of GC-MS showed that Cyclohexane, Heptane, 2-Cyclohexen-1-one, Hexadecanoic acid, 2,4-Di-tert-butylphenol and Hydrocinnamic acid may be the main allelochemicals. In addition, the S. alterniflora aqueous extract had little effect on the relative abundance and diversity of microbial communities in the culture system. This study provided a novel idea of controlling the M. aeruginosa blooms using the rapidly expanding S. alterniflora.

Effects of transient 3-chloroaniline shock loading on the performance, microbial community and enzymatic activity of sequencing batch reactor

Chloroanilines from industrial wastewater can produce adverse effects on biological wastewater treatment systems due to their potential biotoxicity. The performance, nitrogen removal rate, microbial community and enzymatic activity of a sequencing batch reactor (SBR) were evaluated under transient 3-chloroaniline shock loading. After 40 mg/L 3-chloroaniline shock loading of 24 h on day 9, the chemical oxygen demand (COD) removal efficiency decreased from 90.71% on day 8 to 80.57% on day 11, and the NH₄⁺-N removal efficiency reduced from 98.96% on day 8 to 35.51% on day 12. Subsequently, the COD and NH₄⁺-N removal efficiencies gradually recovered to normal value. Compared with the absence of 3-chloroaniline shock loading, the ammonia-oxidizing rate (SAOR), nitrite-oxidizing rate (SNOR), nitrite-reducing rate (SNIRR) and nitrate-reducing rate (SNRR) decreased by 66.19%, 14.49%, 16.20% and 49.38% on day 11, respectively, and then they gradually recovered to normal value. The SAOR, SNOR, SNIRR and SNRR displayed the similar varying trends to the activities of ammonia monooxygenase, nitrite oxidoreductase, nitrite reductase and nitrate reductase, respectively. The appearance of 3-chloroaniline promoted the microbial reactive oxygen species production and lactate dehydrogenase release. The transient 3-chloroaniline shock loading distinctly impacted the microbial richness and diversity. The present research results can provide theoretical basis and technical support for evaluating the effects of transient 3-chloroaniline shock on biological wastewater treatment systems, which is beneficial to take reasonable preventable measures to decrease the adverse effects on the bioreactor performance.

Toxicity assessment of p-choroaniline on Platymonas subcordiformis and its biodegradation

The use of p-chloroaniline (PCA) in various aspects leads to its existence and accumulation in the environment. Relevant researches showed that PCA was a prime toxic pollutant that had imposed a serious risk to public health and the environment. This paper investigated the toxicity effects of PCA on Platymonas subcordiformis (P. subcordiformis) and the biodegradation of PCA by the marine microalga. In the toxicity experiments, the EC₅₀ of PCA on P. subcordiformis at 24 h, 48 h, 72 h and 96 h was 41.42, 24.04, 17.15 and 13.05 mg L^-1, respectively. The pigment parameters including chlorophyll a, chlorophyll b, carotenoids, photosynthetic O₂ release rate, respiration O₂ consumption rate and the chlorophyll fluorescence parameters including Fv/Fm, ETR and qP decreased greatly while antioxidant enzyme activities (SOD, CAT) and the chlorophyll fluorescence parameter NPQ increased when P. subcordiformis exposed to PCA compared with the control group. Fv/Fm would be a suitable indicator for assessing the toxicity of PCA in marine environment based on the analysis of Pearson's correlation coefficient and Integrated Biomarker Response (IBR). The degradation assay in P. subcordiformis indicated that the green marine microalga had the ability to remove and degrade PCA, and the order of removal and degradation proportion of PCA was 2 mg L^-1 > 5 mg L^-1>10 mg L^-1. The maximum removal and biodegradation percentage was 54% and 34%, respectively.

Biodegradation and metabolic fate of thiamphenicol via Chlorella sp. UTEX1602 and L38

Thiamphenicol (TAP) is a typical medicament in animal husbandry and aquaculture for treating diverse infections. In this work, thiamphenicol biodegradation performance via microalgae was tested. The cultivation results showed that TAP could be biodegraded via the target algae. Chlorella sp. L38 presented strong adaptive ability to high concentration TAP. Biodegradation, biosorption and bioaccumulation were the dominant metabolic fates. Biodegradation contributed around 97% of the total removal efficiency at the TAP concentration of 46.2 mg·L^-1. The removal of TAP by Chlorella L38 and UTEX1602 agreed with the kinetic range of zero-order reaction, and the shortest half-lives were 3.2 d and 5.0 d. Based on the identification of metabolites, the metabolic pathway of TAP by microalgae was proposed, including chlorination, chlorine substitution, dehydration and hydroxylation. Therefore, biological treatment via microalgae has the potential for TAP purification.

Formation mechanism of the Microcystis aeruginosa bloom in the water with low dissolved phosphorus

The utilization of phosphorus by algae in the low-phosphorus state has drawn wide concerns due to the high risk of forming algal blooms. The cyanobacteria Microcystis aeruginosa (M. aeruginosa) grew well under low-phosphorus condition by hydrolyzing dissolved organic phosphorus (DOP) to dissolved inorganic phosphorus (DIP) through alkaline phosphatase (AP). There was a negative correlation between DIP concentration and AP activity of algae. AP activity significantly increased at 0-3 d (p < 0.05), and reached the peak values of 43.06 and 49.11 King unit/gprot on day 5 for DIP (0.1 mg/L) and DOP (4.0 mg/L), respectively. The relative expression of phosphate transporter gene increased with decreasing phosphorus concentrations. The catalase activity under low-phosphorus condition increased significantly (p < 0.05) after one week, and was generally higher than 0.15 U/mgprot on day 14. Understanding the utilization efficiency and mechanism of DIP and DOP in the low-phosphorus state would help to inhibit the formation of algal blooms.