Physiological endpoints in daphnid acute toxicity tests

Local thermal adaption mediates the sensitivity of Daphnia magna to nanoplastics under global warming scenarios

The toxicity of nanoplastics at environmentally relevant concentrations has received widespread attention in the context of global warming. Despite numerous studies on the impact of mean temperature (MT), the effects of daily temperature fluctuations (DTFs) on the ecotoxicity of nanoplastics remains largely unexplored. Moreover, the role of evolutionary adaptation in assessing long-term ecological risks is unclear. Here, we investigated the effects of polystyrene nanoplastics (5 μg L-1) on Daphnia magna under varying MT (20 °C and 24 °C) and DTFs (0 °C, 5 °C, and 10 °C). Capitalizing on a space-for-time substitution approach, we further assessed how local thermal adaptation affect the sensitivity of Daphnia to nanoplastics under global warming. Our results indicated that nanoplastics exposure in general reduced heartbeat rate, thoracic limb activity and feeding rate, and increased CytP450, ETS activity and Hgb concentrations. Higher MT and DTFs enhanced these effects. Notably, clones originating from their respective sites performed better under their native temperature conditions, indicating local thermal adaptation. Warm-adapted low-latitude D. magna showed stronger nanoplastics-induced increases in CytP450, ETS activity and Hgb concentrations under local MT 24 °C, while cold-adapted high-latitude D. magna showed stronger nanoplastics-induced decreases in heartbeat rate, thoracic limb activity and feeding rate under high MT than under low MT.

Zooplankton as a model to study the effects of anthropogenic sounds on aquatic ecosystems

There is a growing interest in the impact of acoustic pollution on aquatic ecosystems. Currently, research has primarily focused on hearing species, particularly fishes and mammals. However, species from lower trophic levels, including many invertebrates, are less studied despite their ecological significance. Among these taxa, studies examining the effects of sound on holozooplankton are extremely rare. This literature review examines the effects of sound on both marine and freshwater zooplankton. It highlights two differences: the few used organisms and the types of sound source. Marine studies focus on the effects of very intense acute sound on copepods, while freshwater studies focus on less intense chronic sound on cladocerans. But, in both, various negative effects are reported. The effects of sound remain largely unknown, although previous studies have shown that zooplankton can detect vibrations using mechanoreceptors. The perception of their environment can be affected by sounds, potentially causing stress. Limited research suggests that sound may affect the physiology, behaviour, and fitness of zooplankton. Following this review, I highlight the potential to use methods from ecology, ecotoxicology, and parasitology to study the effects of sound at the individual level, including changes in physiology, development, survival, and behaviour. Responses to sound, which could alter species interactions and population dynamics, are expected to have larger-scale implications with bottom-up effects, such as changes in food web dynamics and ecosystem functioning. To improve the study of the effect of sound, to better use zooplankton as biological models and as bioindicators, researchers need to better understand how they perceive their acoustic environment. Consequently, an important challenge is the measurement of particle motion to establish useable dose-response relationships and particle motion soundscapes.

Comparative toxicology of algal cell extracts and pure cyanotoxins: insights into toxic effects and mechanisms of harmful cyanobacteria Raphidiopsis raciborskii

Ongoing research on cyanotoxins, driven by the socioeconomic impact of harmful algal blooms, emphasizes the critical necessity of elucidating the toxicological profiles of algal cell extracts and pure toxins. This study comprehensively compares Raphidiopsis raciborskii dissolved extract (RDE) and cylindrospermopsin (CYN) based on Daphnia magna assays. Both RDE and CYN target vital organs and disrupt reproduction, development, and digestion, thereby causing acute and chronic toxicity. Disturbances in locomotion, reduced behavioral activity, and weakened swimming capability in D. magna have also been reported for both RDE and CYN, indicating the insufficiency of conventional toxicity evaluation parameters for distinguishing between the toxic effects of algal extracts and pure cyanotoxins. Additionally, chemical profiling revealed the presence of highly active tryptophan-, humic acid-, and fulvic acid-like fluorescence compounds in the RDE, along with the active constituents of CYN, within a 15-day period, demonstrating the chemical complexity and dynamics of the RDE. Transcriptomics was used to further elucidate the distinct molecular mechanisms of RDE and CYN. They act diversely in terms of cytotoxicity, involving oxidative stress and response, protein content, and energy metabolism, and demonstrate distinct modes of action in neurofunctions. In essence, this study underscores the distinct toxicity mechanisms of RDE and CYN and emphasizes the necessity for context- and objective-specific toxicity assessments, advocating nuanced approaches to evaluate the ecological and health implications of cyanotoxins, thereby contributing to the precision of environmental risk assessments.

QSAR assessment of aquatic toxicity potential of diverse agrochemicals

The fast-increasing number of commercially produced chemicals challenges the experimental ecotoxicity assessment methods, which are costly, time-consuming, and dependent on the sacrifice of animals. In this regard, Quantitative Structure-Property/Activity Relationships (QSPR/QSAR) have led the way in developing ecotoxicity assessment models. In this study, QSAR models have been developed using the pEC50 values of 82 diverse agrochemicals or agro-molecules against a planktonic crustacean Daphnia magna with easily interpretable 2D descriptors. Moreover, a link among octanol-water partition coefficient (KOW), bio-concentration factor (BCF), and critical body residue (CBR) has been addressed, and their imputation for the prediction of the toxicity endpoint (EC50) has been done with an objective of the advanced exploration of several ecotoxicological parameters for toxic chemicals. The developed partial least squares (PLS) models were validated rigorously and proved to be robust, sound, and immensely well-predictive. The final Daphnia toxicity model derived from experimental derived properties along with computed descriptors emerged better in statistical quality and predictivity than those obtained solely from computed descriptors. Additionally, the pEC50 and other important properties (log KOW, log BCF, and log CBR) for a set of external agro-molecules, not employed in model development, were predicted to show the predictive ability of the models.

Plausibility of Daphnia magna as an alternative experimental model to evaluate effects on eicosanoid synthesis

Eicosanoids play important roles in inflammation, allergy, fever, and immune responses. In the eicosanoid pathway, cyclooxygenase (COX) catalyzes the conversion of arachidonic acid to prostaglandins and is a crucial target of nonsteroidal anti-inflammatory drugs (NSAIDs). Thus, toxicological studies on the eicosanoid pathway are important for drug discovery and the evaluation of adverse health outcomes due to environmental contaminants. However, experimental models are limited owing to concerns regarding ethical standards. Thus, new alternative models for evaluating toxic effects on the eicosanoid pathway must be developed. To this end, we adopted an invertebrate species, Daphnia magna, as an alternative model. D. magna was exposed to ibuprofen, a major NSAID, for 6 and 24 h. Transcription of eicosanoid-related genes (pla2, cox, pgd synthase, pgd2r2, ltb4dh, and lox) was analyzed by qPCR, eicosanoids (arachidonic acid, prostaglandin F2, dihydroxy prostaglandin F2, and 5-hydroxyeicosatetraenoate) were quantified by multiple reaction monitoring, and enzyme-linked immunosorbent assay was used to determine protein levels of arachidonic acid and prostaglandin E2 (PGE2). After 6 h of exposure, transcription of the pla2 and cox genes was downregulated. In addition, the whole-body level of arachidonic acid, an upstream of COX pathway, increased by over 1.5-fold. The levels of PGE2, a downstream of COX pathway, decreased after 24 h of exposure. According to our results, it is expected that the eicosanoid pathway might be conserved in D. magna, at least partially. This indicates the plausibility of D. magna as an alternative model for the screening of new drugs or chemical toxicity.

Cyanobacterial metabolites: aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin and their mixtures affect behavioral and physiological responses of Daphnia magna

We determined the effects influence of cyanobacterial products metabolites: aeruginosin-A (AER-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A), cylindrospermopsin (CYL) and their binary and quadruple mixtures on swimming behavior, heart rate, thoracic limb activity, oxygen consumption and in vivo cell health of Daphnia magna. The study showed that CYL induced mortality of daphnids at the highest concentrations, however three oligopeptides had no lethal effect. All the tested Each single metabolites inhibited swimming speed. The mixtures AER+MG-FR1 and AER-A+ANA-A induced antagonistic and the quadruple mixture synergistic effects. Physiological endpoints were depressed by CYL, however they were simulated by the oligopeptides and their binary mixtures. The quadruple mixture inhibited the physiological parameters with antagonistic interactions between the components were antagonistic. Single CYL, MG-FR1 and ANA-A induced cytotoxicity with synergistic interactions and the metabolites in mixtures showed. The study suggests that swimming behavior and physiological parameters may be affected by single cyanobacterial oligopeptides, however their mixtures may induce different total effects.

Biotests in Cyanobacterial Toxicity Assessment-Efficient Enough or Not?

Cyanobacteria are a diverse group of organisms known for producing highly potent cyanotoxins that pose a threat to human, animal, and environmental health. These toxins have varying chemical structures and toxicity mechanisms and several toxin classes can be present simultaneously, making it difficult to assess their toxic effects using physico-chemical methods, even when the producing organism and its abundance are identified. To address these challenges, alternative organisms among aquatic vertebrates and invertebrates are being explored as more assays evolve and diverge from the initially established and routinely used mouse bioassay. However, detecting cyanotoxins in complex environmental samples and characterizing their toxic modes of action remain major challenges. This review provides a systematic overview of the use of some of these alternative models and their responses to harmful cyanobacterial metabolites. It also assesses the general usefulness, sensitivity, and efficiency of these models in investigating the mechanisms of cyanotoxicity expressed at different levels of biological organization. From the reported findings, it is clear that cyanotoxin testing requires a multi-level approach. While studying changes at the whole-organism level is essential, as the complexities of whole organisms are still beyond the reach of in vitro methodologies, understanding cyanotoxicity at the molecular and biochemical levels is necessary for meaningful toxicity evaluations. Further research is needed to refine and optimize bioassays for cyanotoxicity testing, which includes developing standardized protocols and identifying novel model organisms for improved understanding of the mechanisms with fewer ethical concerns. In vitro models and computational modeling can complement vertebrate bioassays and reduce animal use, leading to better risk assessment and characterization of cyanotoxins.

Toxicity of fipronil and 2,4-D pesticides in Daphnia similis: a multiple endpoint approach

In Brazil, among the pesticides widely applied simultaneously in sugarcane monocultures are the Regent® 800 WG insecticide (active ingredient (a.i.) fipronil) and the DMA® 806 BR herbicide (a.i. 2,4-D). Thus, this study aimed to investigate, through different endpoints, the effects of the fipronil and 2,4-D pesticides, isolated and as mixtures, on the cladoceran Daphnia similis. To do this, acute toxicity tests were carried out with the compounds acting in isolation and in mixture, where the survival of the organisms was evaluated, and chronic toxicity tests with the isolated compounds, where reproduction and maternal and neonatal body length were evaluated. In this study, the physiological endpoints of D. similis were also analyzed, through the analysis of feeding rates (filtration and ingestion) in exposure and post-exposure scenarios, in order to verify the cladoceran food recovery capacity. In addition, D. similis data were compared with other species when exposed to the studied pesticides, using species sensitivity distribution curves. Acute toxicity tests of the fipronil and 2,4-D showed an average EC₅₀-48 h of 66.68 μg a.i./L and 327.07 mg a.i./L, respectively. In both cases, D. similis showed lower sensitivity compared to other species. For the mixture test, the evaluation by the IA model (independent action) and deviation DR (dose ratio dependent) indicated the occurrence of mostly antagonistic effects. The chronic test with fipronil showed a decrease in the fecundity of the organism at a concentration of 16 μg a.i./L, a concentration already found in aquatic environments. For 2,4-D, no significant differences were observed for reproduction at the concentrations tested. Regarding the maternal body length, there were no significant changes when D. similis were exposed to both fipronil and 2,4-D, but these differences were observed in the body length of the neonates only for 2,4-D. There were no significant changes in the feeding rates of the organisms when exposed to both pesticides.

Combined methods elucidate the multi-organ toxicity of cylindrospermopsin (CYN) on Daphnia magna

Global water bodies are now at risk from inevitable cyanobacterial blooms and their production of multiple cyanotoxins, in particular cylindrospermopsin (CYN). However, research on the CYN toxicity and its molecular mechanisms is still limited, whilst the responses of aquatic species against CYN are uncovered. By integrating behavioral observations, chemical detections and transcriptome analysis, this study demonstrated that CYN exerted multi-organ toxicity to model species, Daphnia magna. The present study confirmed that CYN could cause protein inhibition by undermining total protein contents, and altered the gene expression related to proteolysis. Meantime, CYN induced oxidative stress by increasing reactive oxygen species (ROS) level, decreasing the glutathione (GSH) concentration, and interfered with protoheme formation process molecularly. Neurotoxicity led by CYN was solidly determined by abnormal swimming patterns, reduced acetylcholinesterase (AChE), and downward expression of muscarinic acetylcholine receptor (CHRM). Importantly, for the first time, this research determined CYN directly interfered with energy metabolism in cladocerans. CYN distinctively reduced filtration and ingestion rate by targeting on heart and thoracic limbs, which declined the energy intake, and could be further displayed by the reduction of motional strength and the trypsin concentration. These phenotypic alterations were supported by transcriptomic profile, including the down-regulation of oxidative phosphorylation and ATP synthesis. Moreover, CYN was speculated to trigger the self-defense responses of D. magna, known as "abandon-ship" by moderating lipid metabolism and distribution. This study, overall, comprehensively demonstrated the CYN toxicity and the responses of D. magna against it, which is of great significance to the advancements of CYN toxicity knowledge.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Ecotoxicological study of glucose:choline chloride and sorbitol:choline chloride at different contents of water

The search of new solvents is currently focused on deep eutectic solvents (DES). However, there are not many ecotoxicological studies in different biomodels of DES that allow knowing how these chemicals affect to the environment along the trophic chain. In this manuscript, two DES at different proportion of water have been prepared and characterized from the ecotoxicological point of view. These solvents are glucose:choline chloride (2:5) and sorbitol:choline chloride (3:2) at different contents of water. To carry out the ecotoxicological study, three biomodels have been used: bacteria Aliivibrio fisheri (A. fisheri), crustacean Daphnia magna (D. magna) and algae Raphidocelis subcapitata (R. subcapitata). The obtained results show that the ecotoxicity of these chemicals depends on the biomodel used and the amount of water, being toxicity values lower for chemicals with higher water content. However, it is important to highlight that the ecotoxicity for all chemicals is quite low with effective concentrations, EC₅₀ values above 1000 mg/L in all the studied cases.

Freshwater crustacean exposed to active pharmaceutical ingredients: ecotoxicological effects and mechanisms

Concerns over the ecotoxicological effects of active pharmaceutical ingredients (APIs) on aquatic invertebrates have been raised in the last decade. While numerous studies have reported the toxicity of APIs in invertebrates, no attempt has been made to synthesize and interpret this dataset in terms of different exposure scenarios (acute, chronic, multigenerational), multiple crustacean species, and the toxic mechanisms. In this study, a thorough literature review was performed to summarize the ecotoxicological data of APIs tested on a range of invertebrates. Therapeutic classes including antidepressants, anti-infectives, antineoplastic agents, hormonal contraceptives, immunosuppressants, and neuro-active drugs exhibited higher toxicity to crustaceans than other API groups. The species sensitivity towards APIs exposure is compared in D. magna and other crustacean species. In the case of acute and chronic bioassays, ecotoxicological studies mainly focus on the apical endpoints including growth and reproduction, whereas sex ratio and molting frequency are commonly used for evaluating the substances with endocrine-disrupting properties. The multigenerational and "Omics" studies, primarily transcriptomics and metabolomics, were confined to a few API groups including beta-blocking agents, blood lipid-lowing agents, neuroactive agents, anticancer drugs, and synthetic hormones. We emphasize that in-depth studies on the multigenerational effects and the toxic mechanisms of APIs on the endocrine systems of freshwater crustacean are warranted.

Behavioral disturbances induced by cyanobacterial oligopeptides microginin-FR1, anabaenopeptin-A and microcystin-LR are associated with neuromotoric and cytotoxic changes in Brachionus calyciflorus

Aquatic animals are exposed to various cyanobacterial products released concomitantly to the environment by decaying blooms. Although there exist results on the toxicity of cyanobacterial extracts little is known on the influence of pure oligopeptides or their mixtures and elucidated mechanisms of behavioral toxicity in zooplanktonic organisms. Therefore, the aim of the present study was to assess the effects of single and mixed pure cyanobacterial oligopeptides: microginin FR-1 (MG-FR1), anabaenopeptin-A (ANA-A) and microcystin-LR (MC-LR) at various concentrations on the swimming behavior and catecholamine neurotransmitter activity, muscular F-actin structure, DNA nuclear content and cell viability of a model rotifer Brachionus calyciflorus. Swimming behavior was analyzed with the use of video digital analysis. Fluorescent microscopy imaging was used to analyze neuromotoric biomarkers in the whole organisms: neuromediator release (by staining with EC517 probe), muscle F-actin filaments (by staining with blue phalloidin dye). DNA content and cytotoxicity was also determined by Hoechst 34580 and propidium iodide double staining, respectively. The results showed that single oligopeptides inhibited all the tested endpoints. The binary mixtures induced synergistic interaction on swimming speed except for MG-FR1 +MC-LR which was nearly additive. Both binary and ternary mixtures also synergistically degraded F-actin and triggered cytotoxic effects visible in the whole organisms. Antagonistic inhibitory effects of all the binary mixtures were found on catecholamine neurotransmitter activity, however the ternary mixture induced additive toxicity. Antagonistic effects of both binary and ternary mixtures were also noted on nuclear DNA content. The results of the study suggest that both depression of neurotransmission and impairment of muscle F-actin structure in muscles may contribute to mechanisms of Brachionus swimming speed inhibition by the tested single cyanobacterial oligopeptides and their mixtures. The study also showed that natural exposure of rotifers to mixtures of these cyanobacterial metabolites may result in different level of interactive toxicity with antagonistic, additive synergistic effects depending on the variants and concentrations present in the environment.

Physiological response of Simocephalus vetulus to five antibiotics and their mixture under 48-h acute exposure

Antibiotics, widely known as major environmental xenobiotics, are increasingly being released into ecosystems due to their essential functions in human health and production. During the COVID-19 pandemic waves, antibiotic use increases remarkably in treating bacterial coinfections. Antibiotics were initially expected only to affect prokaryotes, but recent research has shown that they can disturb the biological systems of eukaryotes, especially vulnerable aquatic creatures, through both direct and indirect processes. However, their toxicity to the freshwater cladoceran Simocephalus vetulus, an essential link in the aquatic food web, has never been evaluated. The effects of four fluoroquinolones (ciprofloxacin: CFX, ofloxacin: OFX, gatifloxacin: GFX, delafloxacin: DFX), tetracycline (TET), and a mixture of these medicines (MIX) on S. vetulus thoracic limb rate (TLR) were examined in this study. After S. vetulus was exposed to 20 and 40 mg GFX L^-1, 90% and 100% mortality rates were recorded. At 2.5-10 mg L^-1, GFX dramatically lowered the TLR of S. vetulus, resulting in a median effective concentration of 9.69 mg L^-1. TLRs increased when the organisms were exposed to 10-40 mg L^-1 of CFX and 1.25-40 mg L^-1 of OFX. However, DFX and TET exposures did not affect TLRs. Exposure to MIX reduced TLR only at 40 mg L^-1, suggesting an antagonistic interaction among the five pharmaceuticals. This study demonstrated that S. vetulus physiological responses to antibiotics, even in the same class, are complex and elusive. Beyond a common additive concentration principle, the antagonistic interaction of antibiotic mixture indicates a high level of uncertainty in terms of ecological dangers. We initially introduce S. vetulus to ecotoxicological studies of antibiotics, presenting the species as a low-cost model for physiological investigations of environmental xenobiotics.

Automated Cardiac Chamber Size and Cardiac Physiology Measurement in Water Fleas by U-Net and Mask RCNN Convolutional Networks

Simple Summary

With the rapid development of technology, artificial intelligent become a major breakthrough that can help human with laborious job. Previously cardiac imaging in Daphnia was also suffer from laborious and tedious process to extract some information from it. Thus the aim of this study was to develop a simple artificial intelligent based method to help anyone in this field to perform analysis in fast, reliable, and less tedious manner. In this study, we compare U-Net and Mask RCNN and found out that Mask RCNN was perform better than U-Net in cardiac chamber area estimation. From this data, several parameter like heart rhythm, stroke volume, ejection fraction, fractional shortening, and cardiac output can be extracted. The validation was done by comparing the normal and Roundup exposed group and it show that Roundup can increase the stroke volume, cardiac output, and the shortening fraction of Daphnia magna.

Abstract

Water fleas are an important lower invertebrate model that are usually used for ecotoxicity studies. Contrary to mammals, the heart of a water flea has a single chamber, which is relatively big in size and with fast-beating properties. Previous cardiac chamber volume measurement methods are primarily based on ImageJ manual counting at systolic and diastolic phases which suffer from low efficiency, high variation, and tedious operation. This study provides an automated and robust pipeline for cardiac chamber size estimation by a deep learning approach. Image segmentation analysis was performed using U-Net and Mask RCNN convolutional networks on several different species of water fleas such as Moina sp., Daphnia magna, and Daphnia pulex. The results show that Mask RCNN performs better than U-Net at the segmentation of water fleas’ heart chamber in every parameter tested. The predictive model generated by Mask RCNN was further analyzed with the Cv2.fitEllipse function in OpenCV to perform a cardiac physiology assessment of Daphnia magna after challenging with the herbicide of Roundup. Significant increase in normalized stroke volume, cardiac output, and the shortening fraction was observed after Roundup exposure which suggests the possibility of heart chamber alteration after roundup exposure. Overall, the predictive Mask RCNN model established in this study provides a convenient and robust approach for cardiac chamber size and cardiac physiology measurement in water fleas for the first time. This innovative tool can offer many benefits to other research using water fleas for ecotoxicity studies.

Warming alters the metabolic rates and life-history parameters of Ceriodaphnia silvestrii (Cladocera)

Temperature rise has effects on the metabolic process of organisms, population structure, and ecosystem functioning. Here, we tested the effects of warming on the metabolic rates and life-history parameters of the widespread cladoceran Ceriodaphnia silvestrii. Two scenarios of global warming were established, an increase of 2 °C and an increase of 4 °C; the control temperature was 22°C. Our results showed that warming altered C. silvestrii metabolic rates, by increasing the rates of assimilation and secondary production, and decreasing the rates of filtration and ingestion. Warming also increased C. silvestrii fecundity and the body size of neonates and juveniles, and decreased the embryonic and post-embryonic time of development. C. silvestrii might be an important food resource at intermediary temperature as it had higher assimilation rates, even filtering fewer algae. At the highest temperature, we observed a substantial decrease in assimilation and secondary production, which could be a sign of stress starting. The increase in temperature by global warming will affect the cladocerans' metabolic processes and the population survival, even a small increase (2°C) might induce drastic fluctuations in such processes and affect the carbon and energy availability inside aquatic food-webs.

Gene expression changes in Daphnia magna following waterborne exposure to cyanobacterial strains from the genus Nostoc

Cyanobacteria can produce highly potent cyanotoxins, however, limited information is provided about their toxicity mechanisms in exposed aquatic invertebrates at the molecular level. In the present study, the effects of cyanobacterial strains from the genus Nostoc (Nostoc Z1 and Nostoc 2S3B) in Daphnia magna after waterborne exposure were investigated. Examined endpoints included immobilization (survival) in acute toxicity tests and selected gene expression changes (cyp314, cyp360A8, gst, p-gp, vtg) analyzed by the quantitative real-time polymerase chain reaction (RT-PCR). In addition, enzyme-linked immunosorbent assay (ELISA) was performed to determine whether the observed changes could be due to the presence of microcystins, the most widespread group of cyanotoxins. The results of acute toxicity tests have shown only minor changes in survival rates, which have not exceeded 20% after 48 h of exposure to either strain. On the other hand, significant changes were recorded in molecular responses of Daphnia to tested strains. Treatment with the aquatic strain Nostoc Z1 altered the expression levels of all analyzed genes. Both strains caused a significant p-glycoprotein (p-gp) induction at 75 µg ml^-1 which suggests the involvement of p-gp mediated multixenobiotic resistance mechanism (MXR) in facilitating excretion of toxic cyanobacterial compounds in daphnids. Additionally, these strains caused an increase in the expression levels of cyp360A8, indicating that genes related to detoxification processes could be sensitive indicators of cyanobacterial toxicity. Statistically significant induction of cyp314, as well as increases in expression of gst and vtg, were observed only after exposure to Nostoc Z1. This study indicates the potential of certain cyanobacterial metabolites to modify the expression of toxicant responsive genes involved in phase I and phase III of the xenobiotic metabolism, as well as possible interference with growth and reproduction in D. magna. Low microcystin concentrations found in both samples suggest that these cyanotoxins were not responsible for the detected toxic effects.

Physiological and metabolic alterations induced by commercial neonicotinoid formulations in Daphnia magna

Neonicotinoid insecticides are widely used agents in agriculture to control a broad range of insect pests. Although use of neonicotinoid pesticides has resulted in the widespread contamination of surface waters, sublethal toxicity data of these products in relation to non-target aquatic biota are still poor. Therefore, the objective of this study was to assess the effects of two neonicotinoid pesticides with widespread use on the basic physiological functions: the thoracic limb activity and heart rate of Daphnia magna, and to screen for their potential to affect the cytochrome P450 monooxygenase system (ECOD activity) of daphnids. The considered pesticides were the acetamiprid- and thiacloprid based products Mospilan 20 SG and Calypso 480 SC, respectively. The dose-dependent variation in the three biological endpoints considered were assessed following 24 h exposures. The two neonicotinoid formulations elicited significant depression on the thoracic limb activity and heart rate of daphnids at doses close to the immobility thresholds of formulations (48h-EC₅₀: Mospilan 20 SG = 190 mg L^-1; Calypso 480 SC = 120 mg L^-1), an effect mainly attributable to the overall drop in the general health status of the organisms. The alterations in the physiological traits were significant at exposures to 190 mg L^-1 for Mospilan 20 SG and 48 mg L^-1 for Calypso 480 SC. The dose related variation in the ECOD activity of daphnids exposed to the selected neonicotinoid formulations followed a biphasic pattern, with starting effective doses for Mospilan 20 SG of 6.3 mg L^-1 (=1/20 of 48h-EC₅₀ for Daphnia neonates), and for Calypso 480 SC of 0.034 mg L^-1 (=1/4000 of 48h-EC₅₀). Maximal ECOD activity (2.2 fold increase vs. controls) was induced by Mospilan 20 SG in daphnids exposed to 114 mg L^-1 product (=48 h-EC₂₀), and by Calypso 480 SC (1.8 fold increase) at 5.2 mg L^-1 dose (=1/20 of 48 h-EC₅₀). Our results outlined significant alterations in the physiological traits and ECOD activity in exposed daphnids at concentrations below the immobility thresholds (48 h-EC₅₀) of the products used as benchmarks to rate their toxicity risks to aquatic biota. Therefore, we think our findings might deserve consideration in the environmental risk evaluation of these products.

Synergistic toxicity of some cyanobacterial oligopeptides to physiological activities of Daphnia magna (Crustacea)

Anabaenopeptins and microcystins are oligopeptides produced by bloom-forming cyanobacteria. We determined in vivo effects of anabaenopeptin-B (AN-B) and two variants of microcystins of different hydrophobicity (MC-LR and MC-LF) on the physiology of Daphnia magna. Heart rate, thoracic limb activity and post-abdominal claw activity were determined by digital video analysis and oxygen consumption by Oxygraph + system. EC50 calculation and isobole methodology for interactive effects of AN-B and MC-LR mixture were used. Daphnids' responses to all three oligopeptides were concentration- and time-dependent. MC-LF was the most potent inhibitor of heart rate, thoracic limb activity, post-abdominal claw activity and oxygen consumption. AN-B was more toxic than MC-LR toward oxygen consumption; it inhibited the movements of limbs and post-abdominal claw similarly to MC-LR, but did not inhibit heart rate. The strongest toxic effects were induced by the binary mixture of AN-B with MC-LR at the sum concentration equal to the concentration of the single compounds. First time direct synergistic toxic effects of the cyanopeptides on all the physiological parameters were found. The obtained results explain stronger disturbances in aquatic organisms caused by cyanobacterial cell contents than the individual cyanopeptides present even at higher concentrations. Other metabolites and their interactions need further studies.

Alteration of acute toxicity of inorganic and methyl mercury to Daphnia magna by dietary addition

Acute toxicity of inorganic mercury [Hg(II)] and methylmercury (MeHg) to Daphnia magna was characterized using a 48-h static, non-renewal acute toxicity test, in which we compared the toxicity of Hg(II) and MeHg in the absence (water-only) and presence of diet [green alga (Raphidocelis subcapitata), yeast, Cerophyll, and trout chow (YCT), or both]. Overall, Hg(II) is more toxic to D. magna than MeHg, with 48-h median lethal concentrations (LC50s) being 4.3 µg/L (95% confidence interval: 4.1–4.5 µg/L) for Hg(II) and 14.3 µg/L (13.2–15.3 µg/L) for MeHg. For Hg(II), the addition of any diet would significantly increase its 48-h LC50, but the 48-h LC50 for MeHg decreased significantly to 7.1 µg/L (6.4–7.8 µg/L) with the algal addition. We also show that the addition of diets significantly influenced the levels and speciation (dissolved vs. particulate) of both Hg forms in the test solution. The bioaccumulation of Hg(II) and MeHg was impacted by the dietary addition, and it appears that the body residue level triggering mortality varied widely among treatments. The results suggest that standard short-term toxicity tests (water-only) should be supplemented with extra tests with dietary addition to provide a more environmentally relevant estimation of short-term toxicity of chemical compounds.

Ecotoxicological QSAR modeling of the acute toxicity of organic compounds to the freshwater crustacean Thamnocephalus platyurus

Growing interest in environmental toxicity assessment using Thamnocephalus platyurus as organism has led to an increased availability of acute toxicity data. Despite this growing interest in tests with this organism, however, to the best of our knowledge there are no computational models to predict the acute toxicity in T. platyurus. In view of the limited number of in silico models for this crustacean, we developed Quantitative Structure-Activity Relationship (QSAR) models for the prediction of acute toxicity towards T. platyurus, reflected by the 24h LC_50, using publicly available data according to the ISO 14380:2011 guideline. Two models were developed following the principles of QSAR modeling recommended by the Organization for Economic Cooperation and Development (OECD). We used partial least squares and gradient boosting machine techniques, which gave encouraging statistical quality in our data set.

Physiological and Behavioral Effects of SiO2 Nanoparticle Ingestion on Daphnia magna

The increasingly widespread use of engineered nanoparticles in medical, industrial, and food applications has raised concerns regarding their potential toxicity to humans and the environment. Silicon dioxide nanoparticles (SiO2 NPs), which have relatively low direct toxicity, have been increasingly applied in both consumer products and biomedical applications, leading to significantly higher exposure for humans and the environment. We carried out a toxicity assessment of SiO2 NPs using the common water flea D. magna by focusing on physiological and behavioral indicators such as heart rate, swimming performance, and growth. Exposure to SiO2 NPs did not produce acute or chronic toxicity at limited concentrations (<100 μg/mL), but did have statistically significant negative effects on heart rate, swimming distance, and body size. The use of fluorescein isothiocyanate in a silica matrix allowed the tracing and visualization of clear SiO2 NP accumulation in D. magna, which was confirmed by ICP-MS. Although exposure to SiO2 NPs seemed to affect cardiac and swimming performance, such end-point experiments may be insufficient to fully understand the toxicity of these nanoparticles. However, the physiological and behavioral changes shown here suggest potential adverse effects on the aquatic environment by substances previously considered nontoxic.

Direct and Delayed Mortality of Ceriodaphnia dubia and Rainbow Trout Following Time-Varying Acute Exposures to Zinc

The potential for delayed mortality following short-term episodic pollution events was evaluated by exposing cladocerans (Ceriodaphnia dubia) and rainbow trout (Oncorhynchus mykiss) to zinc (Zn) in various 1- to 48-h and 1- to 96-h exposures, respectively, followed by transferring the exposed organisms to clean water for up to 47 h for C. dubia and up to 95 h for trout for additional observation. For C. dubia, 1-h exposures of up to 3790 µg Zn/L never resulted in mortality during the actual Zn exposures, but by 48 h, a 1-h exposure to 114 µg/L, a concentration similar to the present US national water quality acute criterion for the test water conditions, ultimately killed 70% of C. dubia. With C. dubia, the speed of action of Zn toxicity was faster for intermediate concentrations than for the highest concentrations tested. For rainbow trout, pronounced delayed mortalities by 96 h only occurred following ≥8-h exposures. For both species, ultimate mortalities from Zn exposures ≤8 h mostly presented as delayed mortalities, whereas for exposures ≥24 h, almost all ultimate mortalities presented during the actual exposure periods. With Zn, risks of delayed mortality following exposures to all concentrations tested were much greater for the more sensitive, small-bodied invertebrate (C. dubia) than for the less sensitive, larger-bodied fish (rainbow trout). These results, along with previous studies, show that delayed mortality is an important consideration in evaluating risks to aquatic organisms from brief, episodic exposures to some substances. Environ Toxicol Chem 2021;40:2484-2498. © 2021 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA.

Evaluation of the Acute Effects and Oxidative Stress Responses of Phenicol Antibiotics and Suspended Particles in Daphnia magna

Suspended particles (SP) exist widely in various water systems and are able to adsorb other pollutants in water, producing ecotoxic effects on aquatic nontarget species. Until now, however, few studies have focused on the effects of SP on antibiotics. Therefore, the present study investigated the effects of the mixtures of SP and phenicol antibiotics (chloramphenicol [CAP], thiamphenicol [TAP]) on acute toxicity and oxidative stress responses in Daphnia magna. The results indicated that the acute toxicity of phenicol antibiotics in D. magna was increased when combined with SP. Besides, the immobilization of daphnids caused by phenicol drugs in the presence of 10 mg/L of SP was more intense than that with 200 mg/L of SP. Furthermore, the impact of SP with diverse concentrations on the activity of catalase and the level of reduced glutathione in D. magna was different. Notably, almost all CAP + TAP + SP treatments markedly increased malondialdehyde content in D. magna, causing potential cellular oxidative damage in D. magna. In summary, the present study provides insights into the toxic effects of phenicol antibiotic and SP mixtures on aquatic organisms. Environ Toxicol Chem 2021;40:2463-2473. © 2021 SETAC.

Beef cattle feedlot surface water containing multi-class agrochemicals elicits physiological and behavioral responses among Daphnia pulex

Despite increasing public concern about air and water pollution risks posed by concentrated animal feeding operation areas (CAFOs), there is little information about bioavailability and ecosystem impacts of agrochemicals used to increase productivity. In this study, we investigated the toxicity of wastewaters originating from beef cattle feeding operation on Daphnia pulex. Specifically, we assessed lethal and chronic sublethal exposure effects using various endpoints including survival, oxygen consumption, morphology, reproduction, and swimming behavior. Exposure assessments (acute and chronic) were performed with ten (10) surface water samples collected from on-site retention ponds designated as A, B, C, D, E, F, G, H, I, and R (reference site). Surface water samples were diluted to yield five concentrations (stock, 1 × , 2 × , 3 × , and 4 ×) as treatments and deionized water was used as control. Results showed site-specific and concentration-related effects on toxicity endpoints. Among treatments, significant (p < 0.05) increase in mortality rate (for A, E, F, and H) and decreasing total body length and width (for B, C, D, and G) of D. pulex were observed with increasing wastewater concentration. However, treatments did not have significant effect on swimming behavior (average speed) after exposure to the wastewater samples from all sites except for site E. Evidence from this study suggested that surface waters near beef cattle feed yards affected physiological responses in D. pulex and therefore may similarly affect organisms in the surrounding aquatic ecosystems.

Behavioral and physiological responses of Daphnia magna to salicylic acid

Salicylic acid (SA), a metabolite of acetylsalicylic acid is a monohydroxybenzoic acid a common non-steroidal analgesic and anti-inflammatory drug (NSAID) frequently detected in various aquatic ecosystems at concentrations up to 19.50 μg L^-1 in surface waters near livestock farms and 59.6 μg L^-1 in wastewaters. Little is known on the effects of short-term exposure of freshwater crustaceans to salicylic acid. Therefore, the aim of our study was to determine the effects of SA at concentrations of 5 μg L^-1, 500 μg L^-1, 5 mg L^-1, 50 mg L^-1 and 500 mg L^-1 on the behavior (swimming speed, swimming height, distance travelled) and physiological endpoints (heart rate, mandible movement) of Daphnia magna exposed for 24 h, 48 h and 72 h. The results showed that SA inhibited the swimming speed, swimming height and distance travelled, heart rate and mandible movement at 5 mg L^-1, 50 mg L^-1 and 500 mg L^-1 when compared to the control. On the other hand, SA at 5 μg L^-1 and 500 μg L^-1 transiently increased swimming speed and distance travelled after 24 h of the exposure, except for swimming height. Behavioral and physiological disturbances were observed much earlier than lethality. Our study showed SA at environmental levels may be an ecotoxicological agent imparing behavior and physiology of freshwater crustaceans.

Ecotoxicity Assessment of Graphene Oxide by Daphnia magna through a Multimarker Approach from the Molecular to the Physiological Level including Behavioral Changes

The extensive use of engineered nanomaterials, such as graphene oxide (GO), is stimulating research about its potential environmental impacts on the aquatic ecosystem. This study is aimed to comprehensively assess the acute toxicity of a well-characterized GO suspension to Daphnia magna. Conventional ecotoxicological endpoints (lethality, immobilization) and more sensitive, sublethal endpoints (heartbeat rate, feeding activity, and reactive oxygen species (ROS)) production were used. The possible normalization of the heartbeat rate and feeding activity in clean test medium was also investigated. The fate, time-dependent, and concentration-dependent aggregation behaviour of GO was followed by dynamic light scattering, UV-Vis spectroscopy, and zeta potential measurement methods. The EC₂₀ value for immobilization was 50 mg/L, while, for physiological and behavioural endpoints, it ranged from 8.1 mg/L (feeding activity) to 14.8 mg/L (immobilization). The most sensitive endpoint was the ROS production with EC₂₀ = 4.78 mg/L. 24-h recovery experiments revealed that feeding activity was restored only up to a certain level at higher concentrations, indicating that the potential environmental health effects of GO cannot be neglected. Alterations of normal physiology (heart rate) and feeding activity may be associated with increased risk of predation and reproductive decline, highlighting that GO may have impacts on population and food web dynamics in aquatic ecosystems.

Oxygen consumption rate of Caenorhabditis elegans as a high-throughput endpoint of toxicity testing using the Seahorse XFe96 Extracellular Flux Analyzer

Caenorhabditis elegans presents functioning, biologically relevant phenotypes and is frequently used as a bioindicator of toxicity. However, most C. elegans in vivo effect-assessment methods are laborious and time consuming. Therefore, we developed a novel method to measure the oxygen consumption rate of C. elegans as a sublethal endpoint of toxicity. This protocol was tested by exposing 50 larval stage one C. elegans individuals for 48 h (at 20 °C) to different concentrations of two toxicants i.e. benzylcetyldimethylammonium chloride (BAC-C16) and cadmium (Cd). Following exposures, the oxygen consumption rate of the C. elegans individuals were measured using the high-throughput functionality of the Seahorse XFe96 Extracellular Flux Analyzer. Dose-response curves for BAC-C16 (R2 = 0.93; P = 0.001) and Cd (R2 = 0.98; P = 0.001) were created. Furthermore, a strong, positive correlation was evidenced between C. elegans oxygen consumption rate and a commonly used, ecologically relevant endpoint of toxicity (growth inhibition) for BAC-C16 (R2 = 0.93; P = 0.0001) and Cd (R2 = 0.91; P = 0.0001). The data presented in this study show that C. elegans oxygen consumption rate can be used as a promising functional measurement of toxicity.

Saxitoxin-producing Raphidiopsis raciborskii (cyanobacteria) inhibits swimming and physiological parameters in Daphnia similis

In this study we tested the effects of a neurotoxic strain of the cyanobacterium Raphidiopsis raciborskii (CYRF-01) on the swimming activity and physiological parameters of Daphnia similis such as movements of the antennae, thoracic limbs, post-abdominal claw and heart rate. An acute assay was performed to test the effect on swimming activity, exposing newborns (<24 h) to different concentrations of live cells and observing the number of immobilized animals over a period of 48 h. For testing the effects on physiological parameters adult females (10-15 days) were exposed in a flow-through system and recorded with a digital camera. Results showed rapid effect of the strain CYRF on all parameters. Animals started to be immobilized in the first 30 min exposure and showed complete paralysis after 2 h in 500 μg L^-1 and after 24 h in the other concentrations. Physiological parameters accompanied the same response pattern with effects starting after 30 min and some recovery at the end of 6 h exposure. Antennae stopped moving after 2-3 h at 250-500 μg L^-1, explaining the paralysis of the swimming activity in Daphnia. Thoracic limbs movements were significantly inhibited after 30 min in all concentrations, staying at lower levels than control through the experiment. Post-abdominal claw movement were completely ceased after 30 min and remained stopped until the end of the trial. Heart rate showed a tendency to decrease abruptly in the first 30 min exposure in all concentrations, but showed significant lower values than control only at 500 μg L^-1, between 3 and 4 h exposure, and a recovery at the end of 6 h. In conclusion, results show that neurotoxic cyanobacteria can impose severe constrains on the physiology of daphniids, which can have consequences to the oxygen uptake, swimming and feeding behavior and to the overall fitness of those organisms.