Whole-organism and biomarker endpoints in Daphnia magna show uncoupling of oxidative stress and endocrine disruption in phenolic derivatives

Toxicity of butylone and its enantiomers to Daphnia magna and its degradation/toxicity potential using advanced oxidation technologies

Butylone (BTL) is a chiral synthetic cathinone available as a racemate and reported as contaminant in wastewater effluents. However, there are no studies on its impact on ecosystems and possible enantioselectivity in ecotoxicity. This work aimed to evaluate: (i) the possible ecotoxicity of BTL as racemate or its isolated (R)- and (S)- enantiomers using Daphnia magna; and (ii) the efficiency of advanced oxidation technologies (AOTs) in the removal of BTL and reduction of toxic effects caused by wastewaters. Enantiomers of BTL were obtained by liquid chromatography (LC) using a chiral semi-preparative column. Enantiomeric purity of each enantiomer was > 97 %. For toxicity assessment, a 9-day sub-chronic assay was performed with the racemate (at 0.10, 1.0 or 10 μg L-1) or each enantiomer (at 0.10 or 1.0 μg L-1). Changes in morphophysiological, behavioural, biochemical and reproductive endpoints were observed, which were dependent on the form of the substance and life stage of the organism (juvenile or adult). Removal rates of BTL in spiked wastewater (10 μg L-1) treated with different AOTs (ultraviolet, UV; ozonation, O3; and UV/O3) were similar and lower than 29 %. The 48 h D. magna acute toxicity assays demonstrated a reduction in the toxicity of the treated spiked effluents, but no differences were found amongst AOTs treatments. These results warn for the contamination and negative impact of BTL on ecosystems and highlight the need for efficient removal processes.

A combined toxicological impact on Artemia salina caused by the presence of dust particles, microplastics from cosmetics, and paracetamol

Environmental pollution poses a significant and pressing threat to the overall well-being of aquatic ecosystems in modern society. This study showed that pollutants like dusts from AC filter, fan wings and Traffic dust PM 2.5 were exposed to Artemia salina in pristine form and in combination. The findings indicated that exposure to multi-pollutants had a detrimental effect on the hatching rates of A. salina cysts. Compared to untreated A. salina, the morphology of adult (7th day old) A. salina changed noticeably after each incubation period (24-120 h). Oxidative stress increased considerably as the exposure duration increased from 24 to 120 h compared to the control group. There was a time-dependent decline in antioxidant enzyme activity and total protein concentration. When all particles were used all together, the total protein content in A. salina decreased significantly. All particles showed a considerable decline in survival rate. Those exposed to traffic dust particles showed significantly higher levels of oxidative stress and antioxidant activity than those exposed to other particles.

Endocrine disruption in crustaceans: New findings and perspectives

A significant advance has been made, especially during the last two decades, in the knowledge of the effects on crustacean species of pollutants proven to be endocrine disruptors in vertebrates. Such effects have been also interpreted in the light of recent studies on crustacean endocrinology. Year after year, the increased number of reports refer to the effects of endocrine disruptors on several processes hormonally controlled. This review is aimed at summarizing and discussing the effects of several kinds of endocrine disruptors on the hormonal control of reproduction (including gonadal growth, sexual differentiation, and offspring development), molting, and intermediate metabolism of crustaceans. A final discussion about the state of the art, as well as the perspective of this toxicological research line is given.

Are biopesticides safe for the environment? Effects of pyrethrum extract on the non-target species Daphnia magna

Biopesticides are natural compounds considered more safe and sustainable for the environment. However, it is also important to evaluate the potential risk in non-target organisms. Pyrethrum extract (PE) is a biopesticide, widely used for agriculture, veterinary, and aquaculture. This work aimed to evaluate acute (0.6 - 40.0 µg/L; 96 h; E(L)C₅₀ toxicity) and sub-chronic (0.7 - 1.1 µg/L; 10 d; life-history parameters) effects of PE on Daphnia magna. Moreover, a biomarkers approach using antioxidant and biotransformation capacity, lipid peroxidation (LPO), neurotoxicity, and energy reserves content were evaluated. Acute effects (mortality, changes in swimming behavior, oxidative stress, lipid peroxidation, neurotoxicity) were recorded with the increase in PE concentration. Sub-chronic assay showed an increase in energy reserves content, antioxidant parameters, and LPO demonstrating that PE unbalances oxidative metabolism. This study can conclude that PE potentiates toxic effects in D. magna and demonstrates the vulnerability of a non-target organism to PE that is considered environmentally safe.

Integrated Approach for Synthetic Cathinone Drug Prioritization and Risk Assessment: In Silico Approach and Sub-Chronic Studies in Daphnia magna and Tetrahymena thermophila

Synthetic cathinones (SC) are drugs of abuse that have been reported in wastewaters and rivers raising concern about potential hazards to non-target organisms. In this work, 44 SC were selected for in silico studies, and a group of five emerging SC was prioritized for further in vivo ecotoxicity studies: buphedrone (BPD), 3,4-dimethylmethcathinone (3,4-DMMC), butylone (BTL), 3-methylmethcathinone (3-MMC), and 3,4-methylenedioxypyrovalerone (MDPV). In vivo short-term exposures were performed with the protozoan Tetrahymena thermophila (28 h growth inhibition assay) and the microcrustacean Daphnia magna by checking different indicators of toxicity across life stage (8 days sublethal assay at 10.00 µg L^-1). The in silico approaches predicted a higher toxic potential of MDPV and lower toxicity of BTL to the model organisms (green algae, protozoan, daphnia, and fish), regarding the selected SC for the in vivo experiments. The in vivo assays showed protozoan growth inhibition with MDPV > BPD > 3,4-DMMC, whereas no effects were observed for BTL and stimulation of growth was observed for 3-MMC. For daphnia, the responses were dependent on the substance and life stage. Briefly, all five SC interfered with the morphophysiological parameters of juveniles and/or adults. Changes in swimming behavior were observed for BPD and 3,4-DMMC, and reproductive parameters were affected by MDPV. Oxidative stress and changes in enzymatic activities were noted except for 3-MMC. Overall, the in silico data agreed with the in vivo protozoan experiments except for 3-MMC, whereas daphnia in vivo experiments showed that at sublethal concentrations, all selected SC interfered with different endpoints. This study shows the importance to assess SC ecotoxicity as it can distress aquatic species and interfere with food web ecology and ecosystem balance.

Interactions of Bisphenol A with Artemia franciscana and the ameliorative effect of probiotics

In the present study, the bidirectional interactions of Artemia franciscana with BPA, administered either alone or following treatment with the probiotics Bacillus subtilis, Lactococcus lactis or Lactobacillus plantarum, were evaluated. A 24 h exposure to BPA below LC₅₀ induced oxidative stress to Artemia, indicated by diminished activity of superoxide dismutase, glutathione reductase, glutathione transferase and phenoloxidase, increased lipid peroxidation and decreased survival. Probiotic treatment prior to BPA exposure, led to increased survival, reduced lipid peroxidation and increased enzyme activities. BPA quantification in Artemia and its culture medium, showed a time dependent reduction in its levels, more evident in probiotic series, indicating its biotransformation. ESI-MS analysis confirmed the presence of the tentative BPA metabolites hydroquinone and BPA-sulfate, while BPA-disulfate formation was confirmed in only in the probiotic series. Our results provide evidence that probiotics alleviate the oxidative stress response induced by BPA, by enhancing the BPA biotransformation ability of Artemia.

Toxicity of the 3,4-Methylenedioxymethamphetamine and Its Enantiomers to Daphnia magna after Isolation by Semipreparative Chromatography

MDMA (3,4-methylenedioxymethamphetamine) is a chiral psychoactive recreational drug sold in illicit markets as racemate. Studies on the impact of MDMA on aquatic organisms are scarce. While enantioselectivity in toxicity in animals and humans has been reported, none is reported on aquatic organisms. This study aimed to investigate the ecotoxicological effects of MDMA and its enantiomers in Daphnia magna. For that, enantiomers (enantiomeric purity > 97%) were separated by liquid chromatography using a homemade semipreparative chiral column. Daphnids were exposed to three concentrations of (R,S)-MDMA (0.1, 1.0 and 10.0 µg L^-1) and two concentrations of (R)- and (S)-enantiomers (0.1 and 1.0 µg L^-1) over the course of 8 days. Morphophysiological responses were dependent on the substance form and daphnia development stage, and they were overall not affected by the (R)-enantiomer. Changes in swimming behaviour were observed for both the racemate and its enantiomers, but enantioselective effects were not observed. Reproductive or biochemical changes were not observed for enantiomers whereas a significant decrease in acetylcholinesterase and catalase activity was noted at the highest concentration of (R,S)-MDMA (10 µg L^-1). Overall, this study showed that sub-chronic exposure to MDMA racemate and its enantiomers can interfere with morphophysiological and swimming behaviour of D. magna. In general, the (R)-enantiomer demonstrated less toxicity than the (S)-enantiomer.

Metabolomic analysis predicted changes in growth rate in Daphnia magna exposed to acetaminophen

As urbanization and the global population increases, pollutants associated with municipal wastewater such as pharmaceuticals are becoming more prevalent in aquatic environments. Acetaminophen (paracetamol) is a widely used drug worldwide and one of the most frequently detected pharmaceuticals in freshwater ecosystems. This study investigated the impact of acetaminophen on the metabolite profile of Daphnia magna at two life stages; and used these metabolomic findings to hypothesize a potential impact at a higher organismal level which was subsequently tested experimentally. Targeted polar metabolite analysis by liquid chromatography-tandem mass spectrometry (LC-MS/MS) was used to measure changes in the concentration of 51 metabolites in the neonate (> 24 h old) and adult (8 day-old) daphnids following a 48-h exposure to sub-lethal concentrations of acetaminophen. The impact of acetaminophen on the metabolic profile of neonates was widely different from adults. Also, acetaminophen exposure perturbed the abundance of nucleotides more extensively than other metabolites. The acute metabolomic experimental results led to the hypotheses that exposure to sub-lethal concentrations of acetaminophen upregulates protein synthesis in D. magna and subsequently increases growth during early life stages and has an opposite impact on adults. Accordingly, a 10 day growth rate experiment indicated that exposure to acetaminophen elevated biomass production in neonates but not in adults. These novel findings demonstrate that a targeted analysis and interpretation of the changes in the polar metabolic profile of organisms in response to environmental stressors could be used as a tool to predict changes at higher biological levels. As such, this study further emphasizes the incorporation of molecular-level platforms as critical and robust tools in environmental assessment frameworks and biomonitoring of aquatic ecosystems.

Psychoactive drugs citalopram and mirtazapine caused oxidative stress and damage of feeding behavior in Daphnia magna

As the emerging contaminants, the environmental risks of drug-derived pollutants have attracted extensive attention. Citalopram (CTP) and mirtazapine (MTP) are commonly used as modern antidepressant drugs. Previous studies had proved that CTP and MTP entered the aquatic environment, but less reported the negative effects of the drugs on aquatic organisms. Herein, the effects on the feeding rate of Daphnia magna (D. magna) induced by psychotropic drugs CTP and MTP were investigated, which the possible mechanisms were analyzed with the oxidative stress and damage. Generally, the feeding rates of exposed D. magna under all concentrations of CTP and 1.03 mg/L of MTP were significantly decreased after exposure (p < 0.05 or p < 0.01). The inhibitory effect of CTP on the feeding rate of D. magna was time- and dose-dependent. The levels of reactive oxygen species (ROS) were particularly increased in D. magna after CTP and MTP exposure (p < 0.05 or p < 0.01). The level of antioxidant molecules glutathione S-transferase (GST) and the activity of scavenging enzymes superoxide dismutase (SOD), catalase (CAT), and glutathione peroxidase (GPX) of D. magna were increased (p < 0.05 or p < 0.01). In consequence, the levels of malondialdehyde (MDA), protein carbonyl, and 8-hydroxydeoxyguanosine (8-OHdG) were increased (p < 0.05 or p < 0.01), which indicated oxidative damage caused by MTP and CTP, due to the imbalance of antioxidative stress system. These findings indicated that psychoactive drugs posed a high toxic threat to the aquatic organisms, and the aquatic environmental risks caused by using psychoactive drugs deserve more attention.

Dangerous connections: biochemical and behavioral traits in Daphnia magna and Daphnia longispina exposed to ecologically relevant amounts of paracetamol

Exposure of nontarget organisms to therapeutic agents can cause distinct toxic effects, even at low concentrations. Paracetamol is a painkiller drug, widely used in human and veterinary therapies, being frequently found in the aquatic compartment in considerable amounts. Its toxicity has already been established for some species, but its full ecotoxicological potential is still not sufficiently described. To characterize the ecotoxicity of paracetamol, the present study evaluated several parameters, such as acute immobilization (EC₅₀ calculation), biochemical alterations, and behavioral effects, in two species of freshwater microcrustaceans of the genus Daphnia (D. magna and D. longispina). To increase the relevance of the data obtained, animals were exposed to levels of paracetamol similar to those already reported to occur in the wild. Data showed antioxidant responses in both species, namely an increase of catalase and GSTs activities in D. magna. On the contrary, effects of paracetamol on D. longispina included only an impairment of GSTs activity. Despite the absence of anticholinesterasic effects, behavioral modifications were also observed. This set of data indicates that realistic levels of paracetamol may trigger the activation of the antioxidant defense system of freshwater crustaceans, causing changes in behavioral traits (increase in swimming time, but with a reduction in swimming distance) of unknown etiology that are likely to affect normal life traits of wild populations.

Study of phenol biodegradation in different agitation systems and fixed bed column: experimental, mathematical modeling, and numerical simulation

Phenol degradation was studied in two different agitation systems in a batc h reactor (mechanical agitation and orbital agitation) and the support of the most efficient system was used for fixed bed bioreactor studies. The support used was coconut shell charcoal. The results showed that the mechanical agitation bioreactor was more effective in phenol removal, due to the amount of biomass adhered to the support (8.56 mg g_support^-1), running at approximately 100% of the phenol biodegradation in 300 min. The toxicity analysis of the waters was moderate, because the EC_50,48h values in the analyzed samples are higher than 50%. Within the experimental data obtained from the batch system, it was possible to find the parameters of the kinetic model of Michaelis-Menten, which was used to simulate the bioreactor in a fixed bed. A mathematical model of a one-equation, which considers the effects of dispersion, convection, and reaction in the liquid phase, and diffusion and reaction inside the biofilm was used and the results obtained through numerical simulation were compared with the experimental results of the bioreactor in a fixed bed, and new operational conditions in the bed were simulated with good accuracy.

Standard and biochemical toxicological effects of zinc pyrithione in Daphnia magna and Daphnia longispina

Chemical toxicity in the environment may be the consequence of exposure of living organisms to multiple substances, with distinct putative effects. Among this mulytiplicity of chemicals that occur in the wild, pharmaceutical drugs and antifoulers are prone to exert toxic effects on non-target organisms. To characterize the toxicity elicited by a compound of this specific class, the present study used standard and biochemical-based tools to quantify the toxic response of the antifouler and antidandruff zinc pyrithione in Daphnia magna and Daphnia longispina. The analised parameters were immobility, reproduction, behavioral alteration (swimming patterns), anti-oxidant defense (catalase activity), metabolism (GSTs activities), and neurotoxicity (ChE activity) after exposure to sublethal concentrations of this drug. Exposure to zinc pyrithione has been shown to have neurotoxic and oxidative effects, with changes in swimming behavior. There were no changes in reproductive traits of exposed individuals, from both species. The obtained data demonstrate that ecologically relevant levels of zinc pyrithione can deleteriously alter critical parameters in two distinct freshwater microcrustacean species, although with distinct toxicity patterns and outcomes.

Multilevel ecotoxicity assessment of environmentally relevant bisphenol F concentrations in Daphnia magna

With the pressure to ban or limit the use of Bisphenol A (BPA), substitutes such as bisphenol F (BPF) are applied to various commodities and generally detected in aquatic systems worldwide. To understand the potential ecological risk of BPF, the acute toxicity as well as behavioural, physiological and biochemical parameters of the water flea Daphnia magna were assessed. Following BPF exposure at concentrations ranging from 0.1 μg L^-1 to 100 μg L^-1, phenotypic traits including growth development, fecundity and swimming activity were significantly inhibited in response to exposure to sublethal concentrations (1-100 μg L^-1) of BPF, which had a positive relationship with the activity of antioxidant enzymes. Moreover, the acetylcholinesterase (AChE) activity, which was strictly associated with the behavioural changes, was clearly inhibited, which was also obviously related to the heart rate and thoracic limb activity. Compared to the toxicity of BPA, BPF induces similar toxic effects, and the health concerns regarding the use of these alternatives should be highlighted.

The Toxicity of Nonaged and Aged Coated Silver Nanoparticles to Freshwater Alga Raphidocelis subcapitata

The transformation of coated silver nanoparticles (AgNPs) and their impacts on aquatic organisms require further study. The present study investigated the role of aging on the transformation of differently coated AgNPs and their sublethal effects on the freshwater alga Raphidocelis subcapitata. The stability of AgNPs was evaluated over 32 d, and the results indicated that transformation of AgNPs occurred during the incubation; however, coating-specific effects were observed. Fresh AgNPs increased reactive oxygen species (ROS) formation, whereas aged AgNPs induced excessive ROS generation compared with their fresh counterparts. Increased ROS levels caused increased lipid peroxidation (LPO) in treatment groups exposed to both fresh and aged NPs, although LPO was comparatively higher in algae exposed to aged AgNPs. The observed increase in catalase (CAT) activity of algal cells was attributed to early stress responses induced by excessive intracellular ROS generation, and CAT levels were higher in the aged NP treatment groups. In conclusion, AgNPs increased ROS levels and LPO in algae and caused the activation of antioxidant enzymes such as CAT. Overall, the results suggest that aging and coating of AgNPs have major impacts on AgNP transformation in media and their effects on algae. Environ Toxicol Chem 2019;38:2371-2382. © 2019 SETAC.

Effects of commonly used therapeutic drugs, paracetamol, and acetylsalicylic acid, on key physiological traits of the sea snail Gibbula umbilicalis

Over time, the consumption of pharmaceutical drugs has highly augmented, directly contributing for an increase of the discharges of these substances into sewage water due to excretion, and their direct release to the environment, with or without adequate treatment. Considering that part of the sewage water is dumped into rivers and seas, this is the major source of contamination of the aquatic environment. Paracetamol and acetylsalicylic acid are among the most worldwide consumed pharmaceutical drugs, frequently found in wastewater discharges and consequently in the aquatic environment in considerable amounts, posing ecotoxicity concerns especially towards aquatic non-target species. Thus, it is important to study the ecotoxicological implications that these drugs might pose to organisms from aquatic environments. The objective of this study was to assess the toxic effects of these two compounds on key biochemical features (antioxidant defenses and damage, metabolism, and cholinergic neurotoxicity) of the marine snail species Gibbula umbilicalis after an acute (96 h) exposure, simulating pulses of contamination. In order to understand the effects that those drugs have on this species, the biochemical biomarkers analyzed were the activities of catalase (CAT), glutathione-S-transferases (GSTs), cholinesterases (ChEs), and the levels of lipid peroxidation (TBARS). After acute exposure to paracetamol, catalase activity decreased significantly in organisms exposed to both highest concentrations; no significant alterations were observed for glutathione-S-transferases activity; TBARS concentration decreased significantly in organisms exposed to the intermediate and both highest concentrations, and cholinesterase activity increased significantly in animals exposed to the lowest concentration. However, after acute exposure to acetylsalicylic acid, catalase activity increased significantly; no significant alterations were observed for glutathione-S-transferases activity, and TBARS concentrations and cholinesterase activity increased. This set of data shows that G. umbilicalis is highly responsive to the presence of the tested drugs, and may thus be a promising species to serve as test organism in future marine ecotoxicological testing. The adoption of this species may broaden the offer of highly ecologically representative test organisms to be included in biomonitoring projects of the coastal and marine environment. Furthermore, it is possible to suggest that both drugs may pose significant deleterious effects of pro-oxidative origin to the physiology of the selected species, with potential adverse ecological consequences, even after short periods of exposure. The absence of neurotoxicity showed that despite being able to trigger antioxidant mechanisms, both drugs did not affect neurotransmission.

Food up-take and reproduction performance of Daphnia magna under the exposure of Bisphenols

Because the application of Bisphenol A (BPA) was restricted, many substitutes, such as Bisphenol F (BPF) and Bisphenol S (BPS), were developed as BPA substitutes. Therefore, environmental impacts of BPA and its substitutes on aquatic organisms should be concerned, especially their combined toxicity. In this study, the impacts of BPA, BPF, BPS and their mixture on the feeding behavior, reproduction and physiological function of daphnids were synthetically evaluated, involving the duration and mode of exposure. In short-term exposure tests, feeding rates of D. magna decreased after exposure to BPA, BPF, BPS and their mixture, while the inhibition reversed into stimulation in the recovery period. It may benefit from overcompensation of D. magna. In long-term exposure tests, the inhibition effect on the reproduction and growth of the exposed D. magna was difficult to recover, and only some experimental groups have a certain recovery. In conclusion, environmental risk of BPA, BPF, BPS and their mixture on the behavior of D. magna increased with prolonged exposure time. Moreover, relative activities of trypsin, amylase (AMS), acetylcholinesterase (AChE), carbonic anhydrase (CA), glutathione peroxidase (GPx) and super oxidase dimutase (SOD) of the exposed daphnids decreased in most treatment groups, indicating the disorder of digestive, nervous and antioxidative system of D. magna. Interestingly, inhibition of enzymes activities decreased with the increase of the exposure time, which implied the tolerance may be occurred.

Comprehensive analysis of antagonistic endocrine activity during ozone treatment of hospital wastewater

To reduce the discharge of micropollutants, advanced wastewater treatment methods were investigated in the last years. Estrogenic effects were found to be reduced by ozonation. These activities are usually measured using genetically modified cell-based tests. As these bioassays are representing a sum parameter, also inhibitory effects such as antagonistic effects need to be further investigated as they are potentially reducing the detected activities. Therefore, a direct comparison of chemical target analysis and biological equivalent concentrations measured by bioassays is often difficult. To investigate the fate of antagonistic activities and their role in mixtures with agonistic activities, two hospital wastewater treatment plants were studied after different treatment steps. Thereby highly enriched samples were analyzed by a combination of bioassays with chemical target and non-target analyses. In order to achieve an in-depth characterization of the antagonistic activities a fractionation of the enriched samples was performed. To identify relevant compounds an effect directed identification approach was used by combining high-resolution mass spectrometry and bioassays. The results showed a high reduction for estrogene and androgene activities. However, a constant antagonistic activity after membrane bioreactor and ozone treatment was observed. A reduction of the antagonistic activity was observed after passing an activated carbon filter. The fractionation approach showed a specific finger-print of each sample of the different treatment steps. Hereby we could show that the composition of agonistic and antagonistic active compounds is changing after each treatment step while the overall measured activity stays the same. Using fractionation and the combination of bioassays the number of relevant features detected by chemical non-target screening could be reduced by >85%. As a result the phosphorous flame retardant TCEP could be identified as anti-estrogene active. Future research should be done to identify more antagonistic active compounds and potentially active transformation products after ozone treatment.

Transgenerational Effects of Toxicants: An Extension of the Daphnia 21-day Chronic Assay?

The assessment of transgenerational effects should be incorporated in standard chronic toxicity protocols for the sake of a realistic extrapolation of contaminant effects to the population level. We propose a simple add-on to the standard 21-day chronic Daphnia magna assay, allowing the assessment of the reproductive performance of the offspring (F₁ generation) born from the first clutch of the parental (F₀) generation. The extended generational assay was performed simultaneously with the standard reproduction assay. With this design, we evaluated the lethal, reproductive, and transgenerational effects of four widespread and extensively used substances: a biocide/anti-fouling (copper sulphate), an industrial oxidizing agent (potassium dichromate), a pharmaceutical (paracetamol), and a quaternary ammonium compound (benzalkonium chloride). Benzalkonium chloride was the most toxic in terms of lethality, whereas paracetamol, copper sulphate, and potassium dichromate caused deleterious effects in the reproductive performance of exposed D. magna. Adverse effects in the fitness of the daughter (F₁) generation were observed in the case of maternal exposure to paracetamol and copper sulphate, although they were not very pronounced. These findings highlight the usefulness of our approach and reinforce the view-shared by other authors-of the need for a generalised formal assessment of the transgenerational effects of pollutants.

Single and mixture toxicities of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 on the feeding activity of Daphnia magna: From behavior assessment to neurotoxicity

Although 2,2',4,4'-tetrabrominated diphenyl ether (BDE-47), 6-hydroxy-2,2',4,4'-tetrabromodiphenyl ether (6-OH-BDE-47) and 6-methoxy-2,2',4,4'-tetrabromodiphenyl ether (6-MeO-BDE-47) clearly disrupt the endocrine system, current knowledge of their single and/or mixture toxicities on other behaviors of aquatic organisms remains limited. In the present study, Daphnia magna was used to investigate the single and mixture toxicities of BDE-47, 6-OH-BDE-47 and 6-MeO-BDE-47 as measured by inhibition of feeding during exposure and post-exposure periods. Additionally, the biochemical performance, i.e., the activities of super oxidase dismutase (SOD), glutathione peroxidase (GPx) and acetylcholinesterase (AChE) of the test organism was studied to investigate the potential mechanisms of the toxicity of the target compounds. The three target compounds produced an obvious depressive effect on feeding behavior during the exposure period, and the effect increased with increasing concentrations. D. magna was most sensitive to 6-OH-BDE-47. The toxicity of the ternary mixture showed an obvious concentration-dependent effect, whereas the binary mixture toxicity showed the characteristics of hormesis. During the post-exposure period, overcompensation occurred, indicating a short-term effect of the target compounds on D. magna. Additionally, significant changes occurred in neurological responses, indicating that these compounds might have neurobehavioral toxicity in D. magna. The decrease in oxidative stress enzymes (SOD and GPx) indicated that the antioxidant response of D. magna was destroyed.

Novel approach for evaluating pharmaceuticals toxicity using Daphnia model: analysis of the mode of cytochrome P450-generated metabolite action after acetaminophen exposure

Because of its widespread use, the pharmaceutical acetaminophen (APAP) is frequently detected in aquatic environments. APAP can have serious physiological effects, such as reduced reproduction, low growth rates, and abnormal behavior, in aquatic organisms. However, the methods available for evaluation of the aquatic toxicity of APAP are of limited usefulness. The present study aimed to develop reliable and sensitive markers for evaluation of APAP toxicity using Daphnia as a model organism. We focused on N-acetyl-p-benzoquinoneimine (NAPQI) production from APAP via cytochrome P450 metabolism because NAPQI causes APAP toxicity. Daphnia magna were exposed to APAP (0, 50, or 100 mg/L for 12 h or 24 h), and the total metabolites were extracted and analyzed for NAPQI. Direct detection of NAPQI was difficult because of its high reactivity, and its peak was close to that for APAP. Therefore, we tried to identify molecular and biochemical indicators associated with NAPQI generation, elimination, and its interactions with macromolecules. We identified changes in CYP370A13 gene expression, glutathione depletion, inhibition of thioredoxin reductase activity, and production of reactive oxygen species as indicators of D. magna exposure to APAP. These indicators could be used to develop sensitive and accurate techniques to evaluate the environmental toxicity of APAP.