48-h EC50 Values Research Articles

Toxicity of polystyrene nanoplastic and copper oxide nanoparticle in Artemiasalina: Single and combined effects on stress responses

Nanoparticles, such as copper oxide nanoparticle (CuO NP) and polystyrene nanoplastic (PSNP), are increasingly released into aquatic environments, and pose potential risks to aquatic animals such as brine shrimps. Understanding the toxicity of these nanoparticles, especially when combined, is very important to assess their environmental effects. Therefore, this work describes the toxicity of polystyrene nanoplastic (PSNP) and CuO nanoparticles (CuO NPs) for brine shrimp (Artemiasalina). The body length and stress biomarkers, including the activity of SOD, CAT, GST, Acid phosphatase, AChE, level of MDA and GSH, and expression of the hsp70 gene were quantified. The 48h-EC50 values for PSNP, CuO NPs, and their combination were determined as 1.024 and 5.089, and 0.512 mg L−1, respectively. The combined exposure groups showed the highest growth inhibition. This was associated with increased activity of SOD and GST, decreased activity of CAT, a significant decrease in the level of GSH, a significant increase in the MDA level, and expression of the hsp70 gene (P < 0.05). Moreover, an increased ACP and reduced AChE activity were observed in exposure groups. This study indicated that PSNP and CuO NPs have synergistic toxicity for A.salina, underscoring the importance of further investigation into their combined effect on aquatic animals.

Toxicity of Silver-Chitosan Nanocomposites to Aquatic Microcrustaceans Daphnia magna and Thamnocephalus platyurus and Naturally Luminescent Bacteria Vibrio fischeri.

All novel materials should be analyzed for their potential environmental hazard. In this study, the toxicity of different silver-chitosan nanocomposites-potential candidates for wound dressings or antimicrobial surface coatings-was evaluated using environmentally relevant aquatic microcrustaceans Daphnia magna and Thamnocephalus platyurus and naturally luminescent bacteria Vibrio fischeri. Three silver-chitosan nanocomposites (nAgCSs) with different weight ratios of Ag to CS were studied. Citrate-coated silver nanoparticles (nAg-Cit), AgNO3 (ionic control) and low molecular weight chitosan (LMW CS) were evaluated in parallel. The primary size of nAgCSs was ~50 nm. The average hydrodynamic sizes in deionized water were ≤100 nm, and the zeta potential values were positive (16-26 mV). The nAgCSs proved very toxic to aquatic crustaceans: the 48-h EC50 value for D. magna was 0.065-0.232 mg/L, and the 24-h LC50 value for T. platyurus was 0.25-1.04 mg/L. The toxic effect correlated with the shedding of Ag ions (about 1%) from nAgCSs. Upon exposure of V. fischeri to nAgCSs for 30 min, bacterial luminescence was inhibited by 50% at 13-33 mg/L. However, the inhibitory effect (minimum bactericidal concentration, MBC) on bacterial growth upon 1 h exposure was observed at higher concentrations of nAgCSs, 40-65 mg/L. LMW CS inhibited bacterial luminescence upon 30-min exposure at 5.6 mg/L, but bacterial growth was inhibited at a much higher concentration (1 h MBC > 100 mg/L). The multi-trophic test battery, where D. magna was the most sensitive test organism, ranked the silver-chitosan nanocomposites from 'extremely toxic' [L(E)C50 ≤ 0.1 mg/L] to 'very toxic' [L(E)C50 > 0.1-1 mg/L]. Chitosan was toxic (EC(L)50) to crustaceans at ~12 mg/L, and ranked accordingly as 'harmful' [L(E)C50 > 10-100 mg/L]. Thus, silver-chitosan nanocomposites may pose a hazard to aquatic organisms and must be handled accordingly.

Combining QSAR and SSD to predict aquatic toxicity and species sensitivity of pyrethroid and organophosphate pesticides

ABSTRACT The widespread use of pyrethroid and organophosphate pesticides necessitates accurate toxicity predictions for regulatory compliance. In this study QSAR and SSD models for six pyrethroid and four organophosphate compounds using QSAR Toolbox and SSD Toolbox have been developed. The QSAR models, described by the formula 48 h-EC50 or 96 h-LC50 = x + y * log Kow, were validated for predicting 48 h-EC50 values for acute Daphnia toxicity and 96 h-LC50 values for acute fish toxicity, meeting criteria of n ≥10, r 2 ≥0.7, and Q 2 >0.5. Predicted 48 h-EC50 values for pyrethroids ranged from 3.95 × 10−5 mg/L (permethrin) to 8.21 × 10−3 mg/L (fenpropathrin), and 96 h-LC50 values from 3.89 × 10−5 mg/L (permethrin) to 1.68 × 10−2 mg/L (metofluthrin). For organophosphates, 48 h-EC50 values ranged from 2.00 × 10−5 mg/L (carbophenothion) to 3.76 × 10−2 mg/L (crufomate) and 96 h-LC50 values from 3.81 × 10−3 mg/L (carbophenothion) to 12.3 mg/L (crufomate). These values show a good agreement with experimental data, though some, like Carbophenothion, overestimated toxicity. HC05 values, indicating hazardous concentrations for 5% of species, range from 0.029 to 0.061 µg/L for pyrethroids and 0.030 to 0.072 µg/L for organophosphates. These values aid in establishing environmental quality standards (EQS). Compared to existing EQS, HC05 values for pyrethroids were less conservative, while those for organophosphates were comparable.

Increased extinction probability and altered physiological characteristics in pirimicarb-tolerant Daphnia magna.

We evaluated the physiological characteristics of chemical-tolerant cladocerans. Over the course of 26 generations (F25), Daphnia magna was continuously exposed to pirimicarb (carbamate) solutions (0, 3.8, 7.5, and 15µg/L) in sub-lethal or lethal levels. The 48h EC50 values (29.2-29.9µg/L) for 7.5 and 15µg/L exposure groups were found to be nearly two times higher than that in the control (17.2µg/L). Subsequently, we investigated whether the extinction probability changed when the chemical-tolerant daphnids were fed two different types of food, Chlorella vulgaris and Synechococcus leopoliensis. Furthermore, we ascertained how chemical tolerance influences respiration and depuration rates. The 48h EC50 value was positively related to the extinction probability when the daphnids were fed S. leopoliensis. Because the measured lipid content of S. leopoliensis was three times lower than that of C. vulgaris, the tolerant daphnids struggled under nutrient-poor conditions. Respiration rates across all pirimicarb treatment groups were higher than those in the control group, suggesting that they may produce large amounts of energy through respiration to maintain the chemical tolerance. Since the pirimicarb depuration rate for 7.5µg/L exposure groups was higher than that in the control, the altered metabolic/excretion rate may be one factor for acquiring chemical tolerance. These altered physiological characteristics are crucial parameters for evaluating the mechanisms of chemical tolerance and associated fitness costs.

Chemical tolerance related to the ABC transporter gene and DNA methylation in cladocera (Daphnia magna).

We performed multigenerational tests to clarify the chemical tolerance mechanisms of a nontarget aquatic organism, Daphnia magna. We continuously exposed D. magna to a carbamate insecticide (pirimicarb) at lethal or sublethal concentrations (0, 3.8, 7.5, and 15 μg/L) for 15 generations (F0-F14). We then determined the 48 h-EC50 values and mRNA expression levels of acetylcholinesterase, glutathione S-transferase, and ATP (Adenosine triphosphate)-binding cassette transporter (ABCt) in neonates (<24 h old) from F0, F4, F9, and F14. To ascertain the effects of DNA methylation on pirimicarb sensitivity, we measured 5-methylcytosine levels (DNA methylation levels) in neonates of parents in the last generation (F14). In addition, we cultured groups exposed to 0 and 7.5 μg/L (the latter of which acquired chemical tolerance to pirimicarb) with or without 5-azacytidine (de-methylating agent) and determined methylation levels and 48 h-EC50 values in neonates (<24 h old) from the treated parents. The EC50 values (30.3-31.6 μg/L) in F14 of the 7.5 and 15 μg/L groups were approximately two times higher than that in the control (16.0 μg/L). A linear mixed model analysis showed that EC50 and ABCt mRNA levels were significantly increased with generational alterations; further analysis showed that the ABCt mRNA level was positively related to the EC50 . Therefore, ABCt may be associated with altered pirimicarb sensitivity. In addition, the EC50 value and DNA methylation levels in pirimicarb-tolerant clones decreased after exposure to 5-azacytidine, suggesting that DNA methylation contributes to chemical tolerance. These findings improved our knowledge regarding the acquisition of chemical tolerance in aquatic organisms.

First report on adverse effects of cyanobacterial anabaenopeptins, aeruginosins, microginin and their mixtures with microcystin and cylindrospermopsin on aquatic plant physiology: An experimental approach

Cyanobacteria produce a variety of oligopeptides beyond microcystins and other metabolites. Their biological activities are not fully recognized especially to aquatic plants. Acute toxicity tests on Spirodela polyrhiza and Lemna minor exposed to a range of concentrations of cyanobacterial metabolites: anabaenopeptins (ANA-A, ANA-B), aeruginosins 98 (Aer-A, Aer-B), microginin-FR1 (MG-FR1), microcystin-LR (MC-LR) and cylindrospermopsin (Cyl) were carried out to compare their influence on plant physiology. Effects of their binary mixtures were determined by isobole approach and calculation of the combination index (CI) that indicates a type of metabolites' interaction. Cyclic oligopeptides microcystin-LR and anabaenopeptin-A revealed the strongest inhibition of S. polyrhiza growth while other metabolites appeared less toxic. Oxygen evolution was inhibited by Cyl, MC-LR, ANA-A, ANA-B, while both variants of aeruginosins and MG-FR1 did not affect this process. Photosynthetic pigments' contents decreased in S. polyrhiza exposed to ANA-A and Cyl, while MC-LR and Aer-A caused their slight increase. 96 h-EC50 values showed that the growth of L. minor was more sensitive to MC-LR, ANA-A, MG-FR1 and Cyl than the growth of S. polyrhiza. In S. polyrhiza synergistic effects of all the binary mixtures of peptides with MC-LR on oxygen evolution were observed, while antagonistic one on the growth of S. polyrhiza exposed to the mixtures with aeruginosins and ANA-A. The mixtures of MC-LR and MG-FR1 with cylindrospermopsin revealed synergistic effects on the growth but antagonistic one to the O2 evolution. Quadruple mixtures (ANA-A + MC-LR + MG-FR1+Cyl) did not reveal any inhibitive effect on the plant growth and very slight on the oxygen evolution, irrespectively of their total concentrations. Various effects caused by ANA-A and ANA-B suggest the importance of molecule structures of metabolites for toxicity. Composition of the mixtures of cyanobacterial metabolites was essential for the observed effects.

Anthelmintic efficacy of febantel against a monogenean parasite, Gyrodactylus kobayashii

Monogenean parasites pose a significant challenge to aquaculture, leading to adverse effects on fish health and yields. Current anthelmintic treatments for monogeneans have demonstrated limited efficacy and are further complicated by potential issues, which emphasize the necessity for effective and safe therapeutic strategies to manage monogeneans in aquaculture. In this study, in vivo and in vitro anthelmintic activity of febantel against Gyrodactylus kobayashii on goldfish (Carassius auratus), as well as its toxicity to goldfish were evaluated. In vivo assays indicated that febantel exhibited potent anthelmintic activity against G. kobayashii with an EC50 value of 0.03 mg/L and 100 % anthelmintic efficacy at 0.1 mg/L after 48 h of exposure. Moreover, in vivo trials also revealed a notable post-treatment effect of febantel, where infected goldfish transferred to drug-free water after short 6-h exposure could still result in full eradication of the worms, indicating febantel might induce persistent perturbations in parasite physiology. In vitro assays showed a negative correlation between febantel concentrations and the survival of G. kobayashii. However, increasing the febantel concentration to 2.0 mg/L did not result in the complete death of all worms. Oral administration of febantel demonstrated limited anthelmintic activity, with only 49 % efficacy at a dosage of 200 mg/kg body weight daily over five days. Acute toxicity assays revealed the 48-h LC50 value of febantel was 5.47 mg/L, which was 182.23 times higher than the 48-h EC50 value, indicating that febantel has a favorable safety profile. However, febantel exposure potentially interfered with hepatic metabolism and oxidative status, as indicated by variations in SOD, GST, and P450 gene expression. In conclusion, treatment with 0.1 mg/L febantel for 24 h completely eradicated G. kobayashii infection on goldfish, demonstrating febantel’s potent anthelmintic activity. Coupled with its safety profile and extended post-treatment effectiveness, febantel is a promising candidate for controlling Gyrodactylus infections in aquaculture.

Effects of Enrofloxacin and Ciprofloxacin on Growth and Toxin Production of Microcystis aeruginosa

Microcystis aeruginosa is a common cyanobacterium found in water blooms and often causes ecological harm. Antibiotics are also increasingly used for the prevention and treatment of bacterial infections in aquaculture. However, since most antibiotics cannot be fully metabolized, they enter the water environment and cause ecological impacts. In this paper, the effects of the two fluoroquinolone antibiotics (enrofloxacin and ciprofloxacin) on the population density and microcystins (MCs) production of M. aeruginosa were studied. It is of great significance for the ecological risk assessment of antibiotics in the water environment. The results showed that the 96h EC50 values of enrofloxacin and ciprofloxacin to M. aeruginosa were 56.10 mg/L and 49.80 mg/L, respectively, and the toxicity of ciprofloxacin to M. aeruginosa was slightly stronger than that of enrofloxacin. With the increase in the two antibiotic concentration, the growth inhibition rate (IR) increased, but when the concentration reached a certain level, the IR would reach its threshold. Long-term exposure to low concentrations of these two antibiotics is not only more likely to lead to the outbreak of M. aeruginosa, but also increase its toxin production capacity. The highest contents of MCs in enrofloxacin and ciprofloxacin groups were 95.539 μg/g and 93.720 μg/g, respectively. The MCs value of these three enrofloxacin treatment groups was more than above 51.8 times that of control group (CK) on the 4th day; from 8th day to 14th day, the MCs value of these three enrofloxacin treatment groups was more than above 3.2 times that of CK group. For ciprofloxacin, the MCs value of the treatment group was more than 64.98 times that of the CK group on the 4th day, and from 8th day to 14th day, the MCs value of the treatment group was more than 2.7 times that of the CK group. These findings provide crucial management rationale.

Effects of o-cresol on the growth and biochemical compositions in marine microalgae

To assess the toxic effects of o-cresol on marine organisms, Skeletonema costatum and Phaeodactylum tricornutum were chosen as test subjects to investigate its impact on growth and biochemical compositions. The results indicated that the 96-h EC50 values for o-cresol in S. costatum and P. tricornutum were 7.99 mg/L and 13.28 mg/L, respectively, demonstrating a moderate and slight toxicity level. Conversely, the maximum no-effect concentration (NOEC) for o-cresol in S. costatum and P. tricornutum were 2.43 mg/L and 0.43 mg/L, respectively, classifying their chronic toxicity grades as negligible and low toxic. Following a 96-h exposure period, the content of photosynthetic pigments in S. costatum did not significantly differ from the control group (P > 0.05). Conversely, the levels of total protein, total lipid, and carbohydrate in microalgae were significantly induced (P < 0.05) as the concentration of o-cresol increased. Higher concentrations of o-cresol generally stimulated the synthesis of biochemical compositions in algae cells, which serves as an active defense mechanism in response to pollution stress. To comprehensively evaluate the potential risk of o-cresol to marine ecosystems, it is crucial to strengthen its toxicity studies on marine fish and crustaceans in the future.

Evaluation of growth and antioxidant responses of freshwater microalgae Chlorella sorokiniana and Scenedesmus dimorphus under exposure of moxifloxacin

As one of the fourth-generation fluoroquinolone antibiotics, moxifloxacin (MOX) has been frequently released to the aquatic environment, threatening local organisms. However, researches on its ecotoxicity to aquatic organisms are still limited. This study analyzed effects of MOX on the growth, photosynthesis and oxidative stress of two common types of freshwater microalgae, Chlorella sorokiniana and Scenedesmus dimorphus. The 96 h-EC50 values of MOX for C. sorokiniana and S. dimorphus were 28.42 and 26.37 mg/L, respectively. Although variations of specific indicators for photosynthetic fluorescence intensity were different, photosystems of two types of microalgae were irreversibly damaged. The malondialdehyde content and superoxide dismutase of C. sorokiniana and S. dimorphus evidently increased, indicating that the exposure of MOX caused serious oxidative stress. Chlorophyll a, b and carotenoids contents of C. sorokiniana increased, probably resulting from the resistance to oxidative stress, whereas they were inhibited due to oxidation damage as for S. dimorphus. Risk quotients (RQs) of MOX for C. sorokiniana and S. dimorphus in wastewater were 7.882 and 8.495, respectively, which demonstrated that MOX had a considerable risk to aquatic environment, especially in the context of its increasing use in practice.

Evaluation of acute toxicity response to the algae Chlorella pyrenoidosa of biosynthetic silver nanoparticles catalysts.

Biosynthetic of silver nanoparticles (AgNPs) by using fungi has attracted much attention due to its high catalytic efficiency and environmentally friendly characteristic. However, a few studies have focused on the ecological toxicity effects of biogenic AgNPs on algae. Here, we first investigated the catalytic reduction of 4-nitrophenol (4-NP) by WZ07-AgNPs biosynthesized by Letendraea sp. WZ07. WZ07-AgNPs had significant catalytic activity with 97.08% degradation of 4-NP in 3.5 min. Then, the toxic effects of WZ07-AgNPs and commercial-AgNPs were compared by Chlorella pyrenoidosa growth, chlorophyll content, protein content, physiological, and biochemical indexes. The results demonstrated that the algal cell biomass of C. pyrenoidosa was differentially inhibited after exposure to different concentrations of AgNPs, which showed concentration dependence and time dependence. The 96h-EC50 values of WZ07-AgNPs and commercial-AgNPs on C. pyrenoidosa were 15.99 mg/mL and 12.69 mg/mL, respectively. With the increase concentration of AgNPs, the chlorophyll content was gradually decreased, the protein content was first increased and then decreased, the activities of superoxide dismutase (SOD) and catalase (CAT) were decreased, and the level of malondialdehyde (MDA) was increased significantly of C. pyrenoidosa. In general, AgNPs affect the growth of algae to some extent. However, compared with commercial-AgNPs, WZ07-AgNPs is less toxic to C. pyrenoidosa, which could be used as a potential and an eco-friendly catalyst. This study provides a basis for the safe application of biosynthetic AgNPs.

Application of Microalgal Physiological Response as Biomarker for Evaluating the Toxicity of the Textile Dye Alizarin Red S.

Textile dyes are becoming a growing threat to the environment. This report presents the findings of the study on the toxicity of the textile dye Alizarin Red S on two freshwater microalgae. The acute toxicity assay revealed that 96-h EC50 values of Chlorella vulgaris and Spirulina platensis were 29.81mg/L and 18.94mg/L respectively. The pigments chlorophyll-a, b and carotenoids in C. vulgaris on 96-h exposure to the dye were 2.91, 3.29 and 3.01 times lower in analogy to control whereas Spirulina platensis showed 2.89and 2.56 fold decrease in chlorophyll-a and carotenoid content than control. After the test period of 96-h with dye, the protein content of C. vulgaris and S. platensis were 2.33 and 1.77 times lower compared to the control. The growth inhibition rate, pigment as well as the protein content declined in compliance with the rise in dye concentration, which anticipate paradigm about the toxic effects of the textile dye.

Enantioselective toxicity, degradation and transformation of the chiral insecticide fipronil in two algae culture

The occurrence of pesticides and their metabolites in the environment can alter the ecological relationships between aquatic food chains. Fipronil is a broad-spectrum insecticide which release in the environment may harm the non-target organisms. However, the toxicity and biotransformation of its two enantiomers are far from fully understood. The present study aimed to investigate the aquatic toxicity and environmental behavior of fipronil at enantiomeric level using two freshwater algae, Scenedesmus quaclricauda (S. quaclricauda), and Chlorella vulgaris (C. vulgaris) through an integrative approach the transformation process of the individual enantiomer isolated and in racemic form. The 72 h-EC50 values of rac-, R-, S-fipronil varied from 3.27 to 7.24 mg L−1 with R-fipronil posing a more significant effect on algal growth inhibition. Chlorophyll a was more susceptible to fipronil exposure than chlorophyll b and carotenoids. Enantioselective alterations on physiological and biochemical parameters (chlorophyll a, chlorophyll b, carotenoids, and the activities of antioxidant enzyme catalase (CAT) and superoxide dismutase (SOD)) were also observed. The half-lives (T1/2) of R-fipronil and S-fipronil in algae culture were 3.4–3.5 d and 4.0–4.9 d, respectively. By the end of the 17-d exposure, the enantiomer fractions (EFs) increased to 0.59, indicating a preferential depuration of R-fipronil. The metabolites monitoring showed the fipronil sulfide was the main metabolite followed by fipronil sulfone. The results revealed that the enantiomers of fipronil pose enantiospecific behaviors induced by these two algae, with the R-enantiomer more toxic to algal growth and favorable in degradation. These analyses are beneficial for understanding the ecological effect of chiral pesticide in aquatic environment, and the enantiomeric differences of the toxicity, degradation and the formation of toxic metabolites could be helpful for the eco-environmental risk evaluation.

Comparing toxicity and biodegradation of racemic glufosinate and L-glufosinate in green algae Scenedesmus obliquus

Glufosinate-ammonium, a widely used chiral herbicide, has become the focus of attention because of its toxicity toward non-target organisms and its degradation behavior in the environment. With the introduction of L-glufosinate-ammonium products, the toxicity and environmental behavior of rac-glufosinate-ammonium and L-glufosinate-ammonium have become the subject of increasing interest. The overall goal of this study was to investigate the differences in toxicity and biodegradation of rac-glufosinate-ammonium and L-glufosinate-ammonium in an aquatic organism, Scenedesmus obliquus. The toxicity of rac-glufosinate-ammonium and L-glufosinate-ammonium to S. obliquus was compared by measuring EC50, malondialdehyde (MDA) content, protein content and antioxidant enzyme activity. The 96-h EC50 values of rac-glufosinate-ammonium and L-glufosinate-ammonium were 57.22 μg/mL and 25.55 μg/mL, respectively, which indicated that L-glufosinate-ammonium was more toxic to S. obliquus than rac-glufosinate-ammonium. Based on the MDA content, protein content, and antioxidant enzyme (SOD and CAT) activity, we found that L-glufosinate-ammonium could cause more serious oxidative damage than rac-glufosinate-ammonium. The residual amount of glufosinate-ammonium and its metabolites in the culture medium and S. obliquus were determined by HPLC-HRMS. Comparison of glufosinate-ammonium concentrations in algae-free and algae-containing media, showed that glufosinate-ammonium degradation in the S. obliquus system was significantly increased, and the degradation rate of L-glufosinate-ammonium was faster than that of D-glufosinate-ammonium. No enantiomerization was observed for pure L-glufosinate-ammonium treatment. N-acetyl-glufosinate was identified as the main metabolite of glufosinate-ammonium.

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.

Benzalkonium chlorides (C12) inhibits growth but motivates microcystins release of Microcystis aeruginosa revealed by morphological, physiological, and iTRAQ investigation

Due to the large-scale outbreak of Corona Virus Disease (2019), amounts of disinfecting agents was regularly used in public environments and their potential toxicity towards organisms needed to be appreciated. Thus, one mostly used cationic disinfectant, benzalkonium chlorides (BAC(C12)), was selected to assess its potential toxicity one common cyanobacteria Microcystis aeruginosa (M. aeruginosa) in this study. The aims were to explore the toxic effect and mechanism of BAC (C12) on M. aeruginosa growth within 96 h via morphological, physiological, and the relative and absolute quantification (iTRAQ)-based quantitative proteomics variations. The results found that BAC(C12) significantly inhibited cell density of M. aeruginosa at concentrations from 1 mg/L to 10 mg/L, and the 96-h EC50 value was identified to be 3.61 mg/L. Under EC50 concentration, BAC(C12) depressed the photosynthesis activities of M. aeruginosa exhibited by 36% decline of the maximum quantum yield for primary photochemistry (Fv/Fm) value and denaturation of photosynthetic organelle, caused oxidative stress response displayed by the increase of three indexes including superoxide dismutase (SOD), malondialdehyde (MDA), and the intracellular reactive oxygen species (ROS), and destroyed the integrity of cell membranes demonstrated by TEM images and the increase of ex-cellular substances. Then, the iTRAQ-based proteomic analysis demonstrated that BAC(C12) depressed photosynthesis activities through inhibiting the expressions of photosynthetic protein and photosynthetic electron transport related proteins. The suppression of electron transport also led to the increase of superoxide radicals and then posed oxidative stress on cell. Meantime, the 63.63% ascent of extracellular microcystin production of M. aeruginosa was observed, attributing to the high expression of microcystin synthesis proteins and the damage of cell membrane. In sum, BAC(C12) exposure inhibited the growth of M. aeruginosa mainly by depressing photosynthesis, inducing oxidative stress, and breaking the cell membrane. And, it enhanced the release of microcystin from the cyanobacterial cells via up-regulating the microcystin synthesis proteins and inducing the membrane damage, which could enlarge its toxicity to aquatic species.

Interspecies competition between Scrippsiella acuminata and three marine diatoms: Growth inhibition and allelopathic effects.

Interactions between Scrippsiella acuminata and three diatoms, Chaetoceros curvisetus, Phaeodactylum tricornutum, and Skeletonema dohrnii, were investigated using bi-algal co-cultures and cell-free and sonicated-cell filtrates in this study. Volatile aldehydes in sonicated filtrates of the three diatoms were analyzed by GC/MS. Furthermore, effects of 2E, 4E-decadienal (2,4-D) on the growth and the photosynthetic efficiency of the four microalgal species were studied. The growth of Sc. acuminata was significantly inhibited by the three diatoms in all co-cultures, and the inhibitory effects were higher under nutrient-rich conditions. Both cell-free and sonicated-cell filtrates of the three diatoms showed significant inhibitions on the growth of Sc. acuminata, which highlighted that diatoms produce allelopathic compounds not only to the surrounding environments but also inside the cells. Fifteen aldehydes were detected in the sonicated-cell filtrates of the three diatoms, and 5, 5, and 12 types of aldehydes were detected in C. curvisetus, P. tricornutum, and Sk. dohrnii, respectively. Polyunsaturated aldehydes (PUAs) composition differed among the three diatom species. Phenylglyoxal (C8H6O2) dominated in C. curvisetus, 2,4-D (C10H16O) predominated in P. tricornutum, and high proportions of 2-hexenal (C6H10O), 2E, 4E-heptadienal (C7H10O), and 2,4-D were detected in Sk. dohrnii. 2,4-D showed significantly inhibitory effects on the growth of algal cells including diatoms themselves in a dose-dependent manner, and photosynthetic efficiency was significantly decreased as well. Sc. acuminata was the most sensitive species. The 96h EC50 values of 2,4-D on the growth of the four microalgae were 1.64 μmol/L for Sc. acuminata, 3.09 μmol/L for C. curvisetus, 4.93 μmol/L for P. tricornutum, and 8.54 μmol/L for Sk. dohrnii, respectively. The results suggest that PUAs produced by diatoms may help them to take the competitive advantages in phytoplankton community, and thus to sustain diatom-dominated community structure in nutrient rich coastal waters.

Biodegradability and toxicity of dodecyl trimethyl ammonium chloride in sea water.

Studies were conducted to assess the biodegradability and toxicity of the cationic surfactant dodecyl trimethyl ammonium chloride (DTMAC) in sea water samples collected from the Gulf of Cadiz (Spain). Ultimate biodegradation was studied following the guideline proposed by the United States Environmental Protection Agency (USEPA). Growth inhibition tests on five marine microalgae species and mortality tests on a marine crustacean (Artemia franciscana) were carried out. Biodegradation process was modelled according to a logistic kinetic model. Lag time and half-life were 15.17 and 26.95 days, respectively. Depending on the microalgae, 96-h EC50 values ranged from 0.69 to 6.34 mg L-1 DTMAC, respectively. 48-h and 72-h LC50 to A. franciscana were 46.74 and 34.19 mg L-1 DTMAC, respectively. The results indicate that DTMAC can be mineralised in sea water. Marine crustacean was more resistant than the microalgae. Surfactant tolerance on microalgae followed this order: T. chuii > N. gaditana > C. gracilis ≈ I. galbana ≈ D. salina, being the Green microalgae T. chuii the most tolerant.

Acute toxicity and ecological risk assessment of 4,4'-dihydroxybenzophenone, 2,4,4'-trihydroxybenzophenone and 4-MBC in ultraviolet (UV)-filters.

Ultraviolet (UV) filters are used in cosmetics, personal care products and packaging materials to provide sun protection for human skin and other substances. Little is known about these substances, but they continue to be released into the environment. The acute toxicity of 4,4’-dihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC to Chlorella vulgaris and Daphnia magna were analyzed in this study. The 96 h-EC50 values of 4,4’-dihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC on C. vulgaris were 183.60, 3.50 and 0.16874 mg/L, respectively. The 48 h-LC50 of 4,4’-dihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC on D. magna were 12.50, 3.74 and 0.54445 mg/L, respectively. The toxicity of a mixture of 4,4’-dihydroxybenzophenone and 4-MBC showed addictive effect on C. vulgaris, while the toxicity of mixtures of 4,4’-dihydroxybenzophenone and 2,4,4’-trihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC as well as 4,4’-dihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC all showed antagonistic effect on C. vulgaris. The induced no-effect concentrations of 4,4’-dihydroxybenzophenone, 2,4,4’-trihydroxybenzophenone and 4-MBC by the assessment factor (AF) method were 0.0125, 0.00350 and 0.000169 mg/L, respectively.

Oxidative stress responses caused by dimethyl phthalate (DMP) and diethyl phthalate (DEP) in a marine diatom Phaeodactylum tricornutum

A marine diatom (Phaeodactylum tricornutum) was exposed to different concentrations of dimethyl phthalate (DMP) and diethyl phthalate (DEP) for 96 h within a batch-culture system to investigate their toxicities. Results showed that P. tricornutum could remove DMP and DEP effectively with removal rates of 0.20–0.30 and 0.14–0.21 mg L−1 h−1, respectively. In addition, DMP and DEP significantly inhibited the photosynthesis and chlorophyll a biosynthesis of P. tricornutum with 96-h EC50 values of 390.5 mg L−1 and 74.0 mg L−1, respectively. Results of reactive oxygen species (ROS) level suggested that the two PAEs could induce excessive ROS production in the diatom. Moreover, activities of antioxidant enzymes (i.e., SOD and POD) in the diatom increased with the increase of DMP and DEP concentrations. The results will help to understand the toxic mechanisms of PAEs, and provide strong evidences for evaluating their ecological risks in the marine environment.