The water flea Daphnia magna (Crustacea, Cladocera) as a test species for screening and evaluation of chemicals with endocrine disrupting effects on crustaceans

Acute and chronic effects of the antifouling booster biocide Irgarol 1051 on the water flea Moina macrocopa revealed by multi-biomarker determination

Irgarol 1051 is an herbicide extensively utilized in antifouling paint due to its ability to inhibit photosynthesis. Irgarol and its photodegradation products are highly persistent in waters and sediments, although they are present in low concentrations. However, our understanding of the harmful effects of Irgarol on non-target organisms remains limited. In this study, we assessed the effects of acute (24 h) and chronic (14 days across three generations) exposure to different concentrations (including the 1/10 NOEC, NOEC, and 1/10 LC50 calculated from the 24-h acute toxicity test) of Irgarol using the water flea Moina macrocopa. Acute exposure to 1/10 LC50 significantly decreased survival, feeding rate, thoracic limb activity, heart rate, and acetylcholinesterase activity. Elevated levels of intracellular reactive oxygen species and malondialdehyde, along with a significant increase in catalase and superoxide dismutase activity, suggested the induction of oxidative stress in response to 1/10 LC50. An initial boost in glutathione level and the enzymatic activities of glutathione peroxidase and glutathione reductase, followed by a plunge, implies some compromise in the antioxidant defense system. Upon chronic exposure to the NOEC value, both generations F1 and F2 displayed a significant decrease in survival rate, body length, number of neonates per brood, and delayed sexual maturation, suggesting maternal transfer of potential damage through generations. Taken together, Irgarol induced acute toxicity through physiological and cholinergic damage, accompanied by the induction of oxidative stress, in the water flea. Even its sub-lethal concentrations can induce detrimental effects across generations when consistently exposed.

Synthesis and Characterization of Maghemite Nanoparticles Functionalized with Poly(Sodium 4-Styrene Sulfonate) Saloplastic and Its Acute Ecotoxicological Impact on the Cladoceran Daphnia magna

Using a modified co-precipitation method, 11(2) nm γ-Fe2O3 nanoparticles functionalized with PSSNa [Poly(sodium 4-styrenesulfonate)] saloplastic polymer were successfully synthesized, and their structural, vibrational, electronic, thermal, colloidal, hyperfine, and magnetic properties were systematically studied using various analytic techniques. The results showed that the functionalized γ-Fe2O3/PSSNa nanohybrid has physicochemical properties that allow it to be applied in the magnetic remediation process of water. Before being applied as a nanoadsorbent in real water treatment, a short-term acute assay was developed and standardized using a Daphnia magna biomarker. The ecotoxicological tests indicated that the different concentrations of the functionalized nanohybrid may affect the mortality of the Daphnia magna population during the first 24 h of exposure. A lethal concentration of 533(5) mg L-1 was found. At high concentrations, morphological changes were also seen in the body, heart, and antenna. Therefore, these results suggested the presence of alterations in normal growth and swimming skills. The main changes observed in the D. magna features were basically caused by the PSSNa polymer due to its highly stable colloidal properties (zeta potential > -30 mV) that permit a direct and constant interaction with the Daphnia magna neonates.

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.

A critical review on male-female reproductive and developmental toxicity induced by micro-plastics and nano-plastics through different signaling pathways

It is widely accepted that humans are constantly exposed to micro-plastics and nano-plastics through various routes, including inhalation of airborne particles, exposure to dust, and consumption of food and water. It is estimated that humans may consume thousand to millions of micro-plastic particles, equating to several milligrams per day. Prolonged exposure to micro-plastics and nano-plastics has been linked to negative effects on different living organisms, including neurotoxicity, gastrointestinal toxicity, nephrotoxicity, and hepatotoxicity, and developmental toxicities. The main purpose of this review is to explore the effect of micro-plastics and nano-plastics on the male and female reproductive system, as well as their offspring, and the associated mechanism implicated in the reproductive and developmental toxicities. Micro-plastics and nano-plastics have been shown to exert negative effects on the reproductive system of both male and female mammals and aquatic animals, including developmental impacts on gonads, gametes, embryo, and their subsequent generation. In addition, micro-plastics and nano-plastics impact the hypothalamic-pituitary axes, leading to oxidative stress, reproductive toxicity, neurotoxicity, cytotoxicity, developmental abnormalities, poor sperm quality, diminishes ovarian ovulation and immune toxicity. This study discusses the so many different signaling pathways associated in the male and female reproductive and developmental toxicity induced by micro-plastics and nano-plastics.

Ecotoxicological Properties of Pure and Phosphorus-Containing Graphene Oxide Bidimensional Sheets in Daphnia magna

In this work, the synthesis and structural, thermal, vibrational, morphological, and electronic characterization of 2D-like pure graphene oxide (GO) and phosphorus-containing graphene oxide (GOP) sheets were investigated. The average thicknesses of GO and GOP were 0.8 μm and 3.1 μm, respectively. The electron energy-loss spectroscopy spectra were used to analyze the differences in the C-K and O-K energy edge bands between GO and GOP. In addition, colloidal stability was studied using dynamic light scattering and zeta potential physicochemical techniques, determining that as the concentration increases, the hydrodynamic diameter and electrostatic stability of GO and GOP increase. The colloidal stability was quite important to ensure the interaction between the suspended solid phase and the biomarker. The 2D-like materials were used to determine their ecotoxicological properties, such as the medium lethal concentration, a crucial parameter for understanding ecotoxicity. Acute ecotoxicity experiments (24 h) were conducted in triplicate to obtain robust statistics, with corresponding mean lethal concentration (LC50) of 11.4 mg L-1 and 9.8 mg L-1 for GO and GOP, respectively. The morphological parameters of GO and GOP were compared with a negative control. However, only the case of GO was analyzed, since the Daphnia magna (D. magna) set exposed to GOP died before completing the time required for morphological analysis. The results indicate that the GOP sample is more toxic than the GO, both during and after exposure. Furthermore, the morphological parameters with the greatest statistically significant changes (p<0.05) were associated with the heart and body, while the eye and tail showed less significant changes.

Machine learning-based water quality prediction using octennial in-situ Daphnia magna biological early warning system data

Biological early warning system (BEWS) has been globally used for surface water quality monitoring. Despite its extensive use, BEWS has exhibited limitations, including difficulties in biological interpretation and low alarm reproducibility. This study addressed these issues by applying machine learning (ML) models to eight years of in-situ BEWS data for Daphnia magna. Six ML models were adopted to predict contamination alarms from Daphnia behavioral parameters. The light gradient boosting machine model demonstrated the most significant improvement in predicting alarms from Daphnia behaviors. Compared with the traditional BEWS alarm index, the ML model enhanced the precision and recall by 29.50% and 43.41%, respectively. The speed distribution index and swimming speed were significant parameters for predicting water quality warnings. The nonlinear relationships between the monitored Daphnia behaviors and water physicochemical water quality parameters (i.e., flow rate, Chlorophyll-a concentration, water temperature, and conductivity) were identified by ML models for simulating Daphnia behavior based on the water contaminants. These findings suggest that ML models have the potential to establish a robust framework for advancing the predictive capabilities of BEWS, providing a promising avenue for real-time and accurate assessment of water quality. Thereby, it can contribute to more proactive and effective water quality management strategies.

Combined effects of spinetoram and Microcystis aeruginosa on Daphnia pulex offspring: Maternal effects and multigenerational implications

The increasing occurrence of harmful algal blooms (HABs) in freshwater ecosystems detrimentally affect global water environments. Zooplankton's role in controlling HABs is hindered by contaminant exposure, necessitating research into combined stressors' ecological impacts. The response of Daphnia, a freshwater keystone species, to environmental stressors can be influenced by its maternal effects. Here, we investigated the combined effects of the world-widely used insecticide spinetoram and non-toxic HABs species Microcystis aeruginosa on the life-history traits of D. pulex offspring produced from different maternal food conditions. Four maternal groups were established, with each group receiving a specific blend of C. vulgaris (Ch) and M. aeruginosa (Ma) in varying proportions: A (100% Ch), B (90% Ch + 10% Ma), C (80% Ch + 20% Ma), and D (70% Ch + 30% Ma). The offspring from the third brood were gathered, and a 21-day experiment was carried out, involving various feeding groups (AA, AD, BA, BB, CA, CC, DA, and DD). Results demonstrated that grazing on M. aeruginosa by D. pulex induced maternal effects on their offspring, with the continuous exposure group showing an enhanced tolerance to M. aeruginosa. This study also unveiled that spinetoram could interfere with the molting of D. pulex, leading to developmental retardation. The Recovery Group exhibited an intriguing phenomenon: under the influence of both concentrations of the pesticide spinetoram (0.18, 0.35 μg L-1), D. pulex produced more offspring. This might be due to a combined strategy of allocating more energy towards reproduction in response to low-quality food and a potential hormetic effect from low concentrations of spinetoram. Assessing the interplay of combined stressors across multiple generations, encompassing harmful algal blooms (HABs) and environmental pollutants, is essential for predicting population responses to evolving environmental conditions. This understanding is vital for the protection and management of aquatic environments and ecosystems.

Chronic toxicity of biodegradable microplastic (Polylactic acid) to Daphnia magna: A comparison with polyethylene terephthalate

The increase in the usage of biodegradable microplastics (MPs) as an alternative to conventional plastics has necessitated comprehensive ecotoxicity assessments of biodegradable MPs alongside conventional MPs. This study aimed to assess ecotoxicity of biodegradable polylactic acid (PLA) MPs at concentration of 1 and 5 mgL-1 including a genetic analysis of Daphnia magna, and compared to effects of conventional polyethylene terephthalate (PET) MPs. The survival rate for D. magna exposed to 5 mg L-1 of PLA-MPs declined to 52.4 %, signifying a higher rate of mortality when contrasted with PET-MPs, which exhibited 85.7 % survival rate. Chronic exposure to 1 and 5 mgL-1 PLA-MPs resulted in a decrease of offspring, while increasing the sex ratio and deformed embryo. Interestingly, down-regulation of the SOD and AK genes was observed in D. magna after exposure to 5 mgL-1 of PLA-MPs, while 1 mgL-1 of PLA-MPs up-regulated. These results means that 5 mgL-1 PLA-MP could not produce energy and cope with oxidative stress, resulting in high mortality, and 1 mgL-1 of MP was maintained survival due to energy production and antioxidant action. This study contributes to our understanding of biodegradable microplastics (BMPs) toxic effects on D. magna which could be similar to conventional MPs and provide the importance of ecotoxicological data for risk assessment of BMPs in aquatic organisms.

Using DeepLabCut for markerless cardiac physiology and toxicity estimation in water fleas (Daphnia magna)

Daphnia magna is one species of water flea that has been used for a long time for ecotoxicity studies. In addition, Daphnia has a myogenic heart that is very useful for cardiotoxicity studies. Previous attempts to calculate the cardiac parameter endpoints in Daphnia suffer from the drawback of tedious operation and high variation due to manual counting errors. Even the previous method that utilized deep learning to help the process suffer from either overestimation of parameters or the need for specialized equipment to perform the analysis. In this study, we utilized DeepLabCut software previously used for animal pose tracking and demonstrated that ResNet_152 was the best fit for training the network. The trained network also showed comparable results with ImageJ and Kymograph, which was mostly done manually. In addition to that, several macro scripts in either Excel or Python format were developed to help summarize the data for faster analysis. The trained network was then challenged to analyze the potential cardiotoxicity of imidacloprid and pendimethalin in D. magna, and it showed that both pesticides cause alteration in their cardiac performance. Overall, this method provides a simple and automatic method to analyze the cardiac performance of Daphnia by utilizing DeepLabCut. The method proposed in this paper can contribute greatly to scientists conducting fast and accurate cardiotoxicity measurements when using Daphnia as a model.

Magnetized vermiculite as a tool for the treatment of produced water generated by oil companies: Effects on aquatic organisms before and after treatment

Produced water (PW) generated by oil companies is a highly impacting waste that contains chemicals such as metals and organic and inorganic compounds. Given its polluting potential, PW requires effective treatment before being discharged into the environment. Conventional treatments have limited efficiency in removing PW toxicity, so alternative approaches must be developed and standardized. In this context, treatment with adsorbent materials like magnetized vermiculite (VMT-mag) is highlighted. This work aimed to evaluate the efficiency of treatment with VMT-mag in reducing PW toxicity to aquatic biota. For this purpose, three aquatic species (the midge Chironomus riparius, the planarian Girardia tigrina, and the crustacean Daphnia magna) were exposed to untreated PW and to PW treated with VMT-mag at laboratory conditions. The assessed endpoints included mortality, growth, emergence, and developmental time of C. riparius; mortality, locomotion, feeding, and head regeneration of G. tigrina; and intrinsic population growth rate (r) and reproductive output of D. magna. The results showed that all the species exposed to raw PW were impaired: C. riparius had delayed development, G. tigrina had reduced locomotor activity and delayed head regeneration, and D. magna had reduced reproduction and delayed intrinsic population growth rate (r). Most of the analyzed parameters showed that treatment with VMT-mag diminished PW toxicity. Therefore, using VMT-mag to treat PW may be the key to reducing the PW effects on aquatic organisms.

Toxic Effects of Methylene Blue on the Growth, Reproduction and Physiology of Daphnia magna

Methylene blue (MB) is a disinfectant used in aquaculture to prevent and treat fish diseases. However, the release of MB can pose a risk to the receiving water bodies. Zooplankton are the most sensitive organisms among aquatic life. Hence, this study examined the acute and chronic toxic effects of MB on zooplankton using Daphnia magna (D. magna) as a test organism to provide basic data for risk assessment. The results show that 48 h-EC₅₀ and 24 h-LC₅₀ were 61.5 ± 2.3 and 149.0 ± 2.2 μg/L, respectively. Chronic exposure to MB affected the heart rate, beat frequency of the thoracic limbs, and reproductive ability of D. magna at environmental concentrations higher than 4.7 μg/L. The cumulative molts, time to production of the first brood, and total number of living offspring were affected at different MB concentrations, while "abortions" were observed in high-exposure groups. The activity of superoxide dismutase was increased, while glutathione S-transferase activity was stimulated at low concentrations and inhibited at high concentrations. In addition, the malondialdehyde content increased with increasing concentrations of MB. Our findings demonstrate the impact of MB on the reproduction and growth of freshwater species, as well as their physiological responses. These results have implications for establishing guidelines on the use of MB in aquaculture and setting discharge standards.

Adverse health effects and mechanisms of microplastics on female reproductive system: a descriptive review

Microplastics (MPs), with a diameter of less than 5 mm, include polymers such as polystyrene, polypropylene, and polyethylene. The MPs occur in different morphologies including fragments, beads, fibers, and films that are swallowed by fresh water and land-based animals and enter their food chain, where they produce hazardous effects such as uterine toxicity, infertility, and neurotoxicity. The aim of this review is to explore the effects of polystyrene MPs (PS-MPs) on the female reproductive system and understand the mechanisms by which they produce reproductive toxicity. Several studies suggested that the exposure to PS-MPs increased the probability of larger ovaries with fewer follicles, decreased the number of embryos produced, and decreased the number of pregnancies in female mice. It also changed sex hormone levels and caused oxidative stress, which could have an impact on fertility and reproduction. Exposure to PS-MPs caused the death of granulosa cells through apoptosis and pyroptosis via activation of the NLRP3/caspase pathway and disruption of the Wnt-signaling pathway. Activation of TL4/NOX2 caused the uterine fibrosis resulting in endometrium thinning. The PS-MPs had a negative impact on ovarian capacity, oocyte maturation, and oocyte quality. Furthermore, the PS-MPs disrupted the hypothalamus-pituitary-gonadal axis in marine animals, resulting in a decrease in hatching rate and offspring body size, causing trans-generational effects. It also reduced fecundity and produced germ-line apoptosis. The main focus of this review was to explore the different mechanisms and pathways through which PS-MPs adversely impact the female reproductive system.

Assessment of ecotoxicity effects of aspirin on non-target organism (Daphnia magna) via analysis of the responses of oxidative stress, DNA methylation-related genes expressions and life traits changes

Aspirin (acetylsalicylic acid, ASA), a widely used non-steroidal anti-inflammatory drug, was frequently detected in aquatic environments around the world. However, information on the potential toxic effects of aspirin on non-target aquatic invertebrates is limited. In the present study, we investigated the effects of ASA on the transcriptional expressions of antioxidant genes (Nrf2, Keap1, HO-1, GCLC, GPx, TRX, TrxR and Prx1) and DNA methylation genes (DNMT1, DNMT3 and TET2) in Daphnia magna (D. magna)for 24, 48 and 96 h and the changes of antioxidant enzymatic activity and GSH, MDA content for 48 h. The effects of ASA on the life traits of D. magna were also addressed via a 21-days chronic toxicity test. Results showed that the expressions of Nrf2 and its target genes (HO-1, GPx and TrxR, GCLC, TRX and Prx1) were induced to different degrees at 48 h and/or 96 h. The activity of antioxidant enzymes (SOD, CAT, GST and GPx) and MDA content increased but GSH content decreased, indicating that ASA caused oxidative stress in D. magna. ASA also changed the expression of DNA methylation genes, such as DNMT and TET2, in D. magna. We speculated that ASA may affect the antioxidant system responses through regulation of Nrf2/Keap1 signaling pathway, and/or through indirectly influencing DNA methylation levels by DNMT and TET gene expression, but the detailed mechanism needs further investigations. Chronic exposure to ASA for 21 days caused inhibitions on the growth, reproduction and behavior of D. magna (e.g., delaying days to the first brood and shortening the body length). In summary, ASA significantly affected the antioxidant responses of D. magna, and negatively disturbed its life traits in growth, development and reproduction.

Acute toxicity characterization of organic UV-filters and chronic exposure revealing multigenerational effects in DAPHNIA MAGNA

Organic ultraviolet (UV) filters have often been detected in aquatic ecosystems in concentrations ranging from ng/L to μg/L. However, both their acute and chronic effects on aquatic organisms have been insufficiently explored. This study aimed to evaluate acute toxicity of some of the main UV filters used worldwide (2-ethylhexyl,4-methoxycinnamate/EHMC, avobenzone/AVO, benzophenone-3/BP-3, and octocrylene/OC), in three aquatic organisms (Artemia salina, Desmodesmus subspicatus, and Daphnia magna), and to further investigate multigenerational effects in D. magna. After acute toxicity was confirmed, daphnids were chronically exposed to environmentally relevant concentrations of UV filters for two consecutive generations (F0 and F1), and reproductive endpoints, as well as catalase (CAT) and glutathione-S-transferase (GST) activities, were assessed. EHMC showed the most toxic potential, with the lowest EC₅₀ values for the three organisms. On the other hand, reproductive delays and a decrease in the reproduction rate were observed in the F1 generation exposed to AVO (4.4 µg/L), BP-3 (0.17 µg/L), EHMC (0.2 µg/L), and MIX. An increase of the CAT activity in organisms exposed to BP-3 and EHMC suggested induction of the antioxidant system. Although no reproductive effect was observed in the first generation, toxic effects obtained in the F1 revealed the importance of multigenerational studies and the potential harm of UV filters to the life cycle of D. magna, even at environmentally relevant concentrations. This emphasizes the need for further studies considering these levels of exposure and more realistic experimental designs to better understand their potential risks. Environmentally relevant concentrations of Organic UV filters are not lethal to aquatic organisms, however may affect reproductive parameters in Daphnia magna though multigenerational exposures.

Effects of glyphosate on cladocera: A synthetic review

Glyphosate [N-(phosphonomethyl) glycine] is currently the most widely used herbicide worldwide. Its application in agricultural and urban areas can lead to the dispersion and arrival to aquatic systems causing environmental deterioration with detrimental effects on the inhabiting biota. This is triggered not only by the herbicide per se but also its metabolite aminomethyl-phosphonic acid (AMPA), which can be highly toxic to many aquatic organisms. Water fleas are some of the key components in aquatic food webs, being one of the most sensitive groups to pollutants. Although being often used in standardized toxicity tests, they are comparatively less studied in relation to glyphosate exposition. Here we examine the current scientific literature regarding the acute and sublethal toxicity of glyphosate in the Cladocera taxonomic group, with special comparisons between the active ingredient (A.I) and formulations. Our results document a high variation in the lethal concentrations reported for different cladoceran species, due to the high diversity of products used in the toxicity tests. Most articles accounting for sublethal effects were performed on the standard Daphnia magna species. Reproduction, including decreased fecundity and delayed age of first reproduction, is usually one of the most severely affected individual traits. Although still scarce, studies documenting metabolic and genetic alterations might provide accurate information on the mechanisms of action of the herbicide.

Impacts of endocrine disrupting chemicals on reproduction in wildlife and humans

Endocrine disrupting chemicals (EDCs) are ubiquitous in aquatic and terrestrial environments. The main objective of this review was to summarize the current knowledge of the impacts of EDCs on reproductive success in wildlife and humans. The examples selected often include a retrospective assessment of the knowledge of reproductive impacts over time to discern how the effects of EDCs have changed over the last several decades. Collectively, the evidence summarized here within reinforce the concept that reproduction in wildlife and humans is negatively impacted by anthropogenic chemicals, with several altering endocrine system function. These observations of chemicals interfering with different aspects of the reproductive endocrine axis are particularly pronounced for aquatic species and are often corroborated by laboratory-based experiments (i.e. fish, amphibians, birds). Noteworthy, many of these same indicators are also observed in epidemiological studies in mammalian wildlife and humans. Given the vast array of reproductive strategies used by animals, it is perhaps not surprising that no single disrupted target is predictive of reproductive effects. Nevertheless, there are some general features of the endocrine control of reproduction, and in particular, the critical role that steroid hormones play in these processes that confer a high degree of susceptibility to environmental chemicals. New research is needed on the implications of chemical exposures during development and the potential for long-term reproductive effects. Future emphasis on field-based observations that can form the basis of more deliberate, extensive, and long-term population level studies to monitor contaminant effects, including adverse effects on the endocrine system, are key to addressing these knowledge gaps.

Screening of NaCl salinity sensitivity across eight species of subterranean amphipod genus Niphargus

Secondary salinization of freshwater is becoming a growing environmental problem. Currently, there is few data available on the effects of salinisation on subterranean crustaceans that are vital for the maintenance of groundwater ecosystem functioning. In this study, the sensitivity of subterranean Niphargus amphipods to NaCl was investigated. We expected that cave-dwelling species would be more sensitive as surface-subterranean boundary species. Eight ecologically different Niphargus species were tested: four live at the boundary between the surface and subterranean ecosystems (N. timavi, N. krameri, N. sphagnicolus, N. spinulifemur), three live in cave streams (N. stygius, N. scopicauda, N. podpecanus), and one species (N. hebereri) lives in anchialine caves and wells. The organisms were exposed to five concentrations of NaCl for 96 h and afterwards the immobility, mortality, and electron transfer system (ETS) activity (a measure for metabolic rate of animals) were evaluated. As expected, the most tolerant species was N. hebereri dwelling in naturally high-salinity habitat. However, contrary to our expectations, the species collected at the surface-subterranean boundary were more sensitive as cave stream species when their immobility and mortality were assessed. Interestingly, the majority of Niphargus tested were more NaCl tolerant as can be deduced from currently available data for subterranean and surface crustaceans. We could not observe a clear trend in ETS activity changes between groups of surface-subterranean boundary and cave streams species after exposure to NaCl stress, but it appears that osmotic stress-induced metabolic rate changes are species-specific. This study shows that amphipods Niphargus can be a valuable subterranean environmental research model and further ecotoxicity research is of interest.

Juvenile hormone synthesis and signaling disruption triggering male offspring induction and population decline in cladocerans (water flea): Review and adverse outcome pathway development

Juvenile hormone (JH) are a family of multifunctional hormones regulating larval development, molting, metamorphosis, reproduction, and phenotypic plasticity in arthropods. Based on its importance in arthropod life histories, many insect growth regulators (IGRs) mimicking JH have been designed to control harmful insects in agriculture and aquaculture. These JH analogs (JHAs) may also pose hazards to nontarget species by causing unexpected endocrine-disrupting (ED) effects such as molting and metamorphosis defects, larval lethality, and disruption of the sexual identity. This critical review summarizes the current knowledge of the JH-mediated effects in the freshwater cladoceran crustaceans such as Daphnia species on JHA-triggered endocrine disruptive outputs to establish a systematic understanding of JHA effects. Based on the current knowledge, adverse outcome pathways (AOPs) addressing the JHA-mediated ED effects in cladoceran leading to male offspring production and subsequent population decline were developed. The weight of evidence (WoE) of AOPs was assessed according to established guidelines. The review and AOP development aim to present the current scientific understanding of the JH pathway and provide a robust reference for the development of tiered testing strategies and new risk assessment approaches for JHAs in future ecotoxicological research and regulatory processes.

Induction of carbonyl reductase 1 (CR1) gene expression in Daphnia magna by TNT, but not its key metabolites 2-ADNT and 4-ADNT

2,4,6-trinitrotoluene (TNT) is a known source of reactive oxygen species (ROS), which cause oxidative stress in aquatic ecosystems. Carbonyl reductases (CRs) are one of several possible defense mechanisms induced against ROS products, especially those that result in the 'so-called' carbonyl stress. Daphnia magna, a freshwater organism living in stagnant freshwater bodies, expresses four copies of the CR gene (Dma_CR1, Dma_CR2, Dma_CR3 and Dma_CR4). In this study, induction of all four copies of Dma_CR by 2-amino-4,6-dinitrotoluene (2-ADNT) and 4-amino-2,6-dinitrotoluene (4-ADNT), was investigated. Reverse transcription polymerase chain reaction (RT-PCR) analysis of treated daphnids revealed up-regulation of Dma_CR1 alone in response to TNT, but not 2-ADNT and 4-ADNT (which are key metabolites of TNT). This concentration- and time-dependent up-regulation in mRNA-expression was observed both in the presence and absence of light, in the same magnitude. Moreover, significant change in mRNA-expression could be observed 8 h after treatment with TNT. In the presence of TNT, the antioxidant N-acetylcysteine (NAc) could not reverse TNT-induced up-regulation of Dma_CR1 mRNA-expression. On the other hand, withdrawal of TNT from the culture medium caused a significant reduction in the TNT-induced mRNA-expression of Dma_CR1 within 24 h. These findings highlight the potential of Dma_CR1 as a biomarker for biomonitoring of TNT levels in freshwater bodies.

Effects of water produced by oil segment on aquatic organisms after treatment using advanced oxidative processes

The water produced (PW) by the petroleum industry is a potential contaminant to aquatic biota, due to its complex mixture that may contain polycyclic aromatic hydrocarbons (PAHs), organic chemical compounds, including benzene, toluene, ethylbenzene and xylene (BTEX), metals and other components that are known to be toxic. The aim of this investigation was to examine the acute toxicity produced by a PW sample in aquatic organisms Vibrio fischeri and Daphnia similis prior to and after 4 treatments using advanced oxidative processes such as photocatalysis, photoelectrocatalysis, ozonation and photoelectrocatalytic ozonation. Data demonstrated that exposure to PW was toxic to both organisms, as evidenced by reduced luminescence in bacterium Vibrio fischeri and induced immobility in Daphnia similis. After treatment of PW with 4 different techniques, the PW remained toxic for both tested organisms. However, photoelectrocatalysis was more efficient in decreasing toxicity attributed to PW sample. Therefore, data demonstrate the importance of treating PW for later disposal in the environment in order to mitigate ecotoxicological impacts. Further photoelectrocatalysis appeared to be a promising tool for treating PW samples prior to disposal and exposure of aquatic ecosystems.

Combined exposure to microplastics and zinc produces sex-specific responses in the water flea Daphnia magna

Microplastics are ubiquitous environmental pollutants and a great threat to the aquatic environment. Due to their small size (ranging from 1 µm to 5 mm), microplastics be easily ingested by a wide range of organisms and can serve as a vector for various contaminants. In this study, additive or possible synergistic effects of microplastics and zinc were demonstrated through sex-specific alterations in behavior, redox status, and modulation of detoxification-related genes in Daphnia magna, with males being more sensitive than females with stronger modulations of antioxidant responses, particularly on glutathione S-transferases expressions. Furthermore, we demonstrated microplastics may act as vectors for metals (Zn²⁺) in the aquatic environment in D. magna, with reduced bio-concentration of the total Zn concentration, inducing greater toxicity. Our findings demonstrated synergistic toxicity of the heavy metal Zn and microplastics and could contribute to greater understanding of sex-specific effects of microplastics in aquatic organisms.

Evaluation of silver nanowires (AgNWs) toxicity on reproductive success of Daphnia magna over two generations and their teratogenic effect on embryonic development

This study assessed the reproductive toxicity of silver nanowires (AgNWs) in Daphnia magna over two consecutive generations. An acute immobilization test was conducted according to the ΟECD 202 guidelines. To perform reproductive toxicity tests in both F0 and F1 generations, the animals were exposed to different concentrations of AgNWs (0, 0.4, 2, 10, and 50 µg L^-1) and pyriproxyfen (0.4 µg L^-1), as a positive control, based on the ΟECD 211 principles. Overall, AgNWs were acutely toxic to D. magna with EC₅₀ value of 0.063 mg L^-1. Compared to the control groups, AgNWs disrupted reproductive performances of D. magna through increasing the egg development time and time to production of first brood as well as decreasing the total offspring production and molting frequency in both F0 and F1 generations. After exposure to AgNWs, the number of male neonates and non-reproductive females increased in the F0 generation, whereas just male neonates raised in the F1 generation. Moreover, AgNWs caused several congenital anomalies including underdeveloped antennae, 2nd antennae, malpighian tube, rostrum, sensory bristles, tail spine, and malformed eyes. Together, AgNWs could disrupt reproductive health of D. magna, and these types of bioperturbations could dramatically change the good health state of aquatic ecosystems.

Daphnia magna model in the toxicity assessment of pharmaceuticals: A review

Daphnia magna is one of the most commonly used model organism to assess toxicity of wide range of pharmaceuticals such as antibiotics, anticancer drugs, antidepressants, anti-inflammatory drugs, beta-blockers and lipid-regulating agents. Currently, daphnia toxicity tests based on immobilisation and lethality standardised by OECD, acute immobilisation test and reproduction test, are mainly used in toxicological studies. Detailed analysis of Daphnia biology allows distinguishing the swimming behaviour and physiological endpoints such as swimming speed, distance travelled, hopping frequency, heart rate, ingestion rate, feeding rate, oxygen consumption, thoracic limb activity which could be also useful in assessment of toxic effects. The advantage of behavioural and physiological parameters is the possibility to observe sublethal effects induced by lower concentrations of pharmaceuticals which would not be possible to notice by using OECD tests. Additionally, toxic effects of tested drugs could be assessed using enzymatic and non-enzymatic biomarkers of daphnia toxicity. This review presents scientific data considering characteristics of D. magna, analysis of immobilisation, lethality, reproductive, behavioural, physiological and biochemical parameters used in the toxicity assessment of pharmaceuticals. The aim of this paper is also to emphasize usefulness, advantages and disadvantages of these invertebrate model organisms to assess toxicity of different therapeutic classes of pharmaceuticals. Also, various examples of application of D. magna in studies on pharmaceutical toxicity are presented.

Auramine dyes induce toxic effects to aquatic organisms from different trophic levels: an application of predicted non-effect concentration (PNEC)

The dyes Auramine and Auramine O are used in several industrial products, despite the scarce information regarding their ecotoxicity. The aim of the present study was to assess the acute and chronic toxicity of both dyes to aquatic organisms from different trophic levels (Raphidocelis subcapitata, Daphnia similis, Hydra attenuata, and Danio rerio) and calculate their predicted non-effect concentrations (PNEC). Auramine and Auramine O induced toxicity to all selected test organisms with L(E)C50 values ranging from 300 to 4800 ug/L. Both dyes induced inhibition in the growth rate of exposed algae, negatively affecting the reproduction of D. similis and induced deformities in H. attenuata (clubbed tentacles and shortened tentacles) and D. rerio (edemas, tail malformation and delay in yolk sac absorption). PNEC values of 0.92 μg/L and 4.0 μg/L were obtained for Auramine and Auramine O, respectively, based on results of the most sensitive test system (algae). Test results were analyzed using the Criteria of Reporting and Evaluating Ecotoxicity Data (CRED), confirming their reliability and relevance. Thus, PNEC values can be used in future risk assessments of those substances in freshwater systems.

Molecular Insights into Structural and Ligand Binding Features of Methoprene-Tolerant in Daphnids

Juvenile hormone (JH) is an important endocrine factor regulating many biological activities in arthropods. In daphnids, methoprene-tolerant (Met) belongs to a basic helix-loop-helix/Per-Arnt-Sim (bHLH/PAS) family protein which has recently been confirmed as a JH receptor and can bind and be activated by JHs and JH agonists. Although the activation of the JH signaling pathway causes many physiological effects, the molecular basis for the structural feature and ligand binding properties of Daphnia Met are not fully understood. To study the ligand preference in terms of structural features of Daphnia Met, we built in silico homology models of the PAS-B domain of Daphnia Mets from cladoceran crustaceans, Daphnia pulex and D. magna. Structural comparison of two Daphnia Met PAS-B domain models revealed that the volume in the main cavity of D. magna Met was larger than that of D. pulex Met. Compared with insect Met, Daphnia Met had a less hydrophobic cavity due to polar residues in the core-binding site. Molecular docking simulations of JH and its analogs with Daphnia Met indicated that the interaction energies were correlated with each of the experimental values of in vivo JH activities based on male induction and in vitro Met-mediated transactivation potencies. Furthermore, in silico site-directed mutagenesis supported experimental findings that Thr292 in D. pulex Met and Thr296 in D. magna Met substitution to valine contribute to JH selectivity and differential species response. This study demonstrates that in silico simulations of Daphnia Met and its ligands may be a tool for predicting the ligand profile and cross species sensitivity.

Cascading effects caused by fenoxycarb in freshwater systems dominated by Daphnia carinata and Dolerocypris sinensis

To evaluate the aquatic hazards of the insect juvenile hormone analogue fenoxycarb, a single application (0, 48.8, 156.3, 500, 1600, and 5120 μg/L) of it was done in indoor freshwater systems dominated by Daphnia carinata (daphnid) and Dolerocypris sinensis (ostracoda). The responses of zooplankton (counted by abundance and the activity and immuno-reactive content of free N-Acetyl-β-D-glucosaminidase (NAGase)), phytoplankton (counted by chlorophyll and phycocyanin), planktonic bacteria and fungi, and some water quality parameters were investigated in a period of 35 d. Results of the study showed that the ostracoda was more sensitive than daphnid, with time-weighted average (TWA)-based no observed effect concentrations (NOECs) to be 8.45 and 12.66 μg/L in systems without humic acid addition (HA-) and to be 6.37 and 9.54 μg/L in systems with humic acid addition (HA+). The duration of treatment-related effects in the ostracoda population was longer than the daphnid population (21 vs. 14 days). Besides, the data analysis indicated that the toxicity of fenoxycarb was significantly enhanced in the HA+ systems. Owing to the reduced grazing pressure, the concentrations of chlorophyll and phycocyanin increased in the two highest treatments. The increase in photosynthesis along with a reduced animal excretion led to an increase in pH and a decrease in nutrient contents. These changes seemed to have an effect on the microbial communities. For example, the abundances of some opportunistic pathogens of aquatic animals (e.g. Aeromonas and Cladosporium) and organic-pollutant-degrading microorganisms (e.g. Ancylobacter and Azospirillum) increased significantly in microbial communities, but the abundances of Pedobacter, Candidatus Planktoluna, and Rhodobacter (photosynthetic bacteria) markedly decreased. This study provides useful information to understand the ecotoxicological impacts of fenoxycarb at the population and community levels while integrating the effects of HA on toxicity.

Toxicokinetic modeling of octylphenol bioconcentration in Chlorella vulgaris and its trophic transfer to Daphnia magna

Bioconcentration of 4-tert-Octylphenol (OP) in freshwater algae Chlorella vulgaris was investigated by considering the effects of algal growth and exudate excretion. The OP uptake in algae was approximately 113 mg kg^-1 after 24 h, and the uptake rate constant was estimated as 2.4 × 10⁴ L kg^-1 d^-1. The OP sorption onto exudates reduced OP bioavailability to C. vulgaris to 11% after 24 h, with a sorption coefficient of 9.7 × 10³ L kg^-1. The elimination of OP by algae growth (0.80 d^-1) was dominant over real elimination (0.60 d^-1). The calculated bioconcentration factor of OP in C. vulgaris following uptake and elimination rate constants was 4.0 × 10⁴ L kg^-1. Further, bioaccumulation of OP in Daphnia magna was investigated by considering both aqueous and dietary (C. vulgaris) exposures. Uptake and elimination rates of OP via water were 1.6 × 10⁴ L kg^-1 d^-1 and 0.95 d^-1, respectively, while ingestion rate and assimilation efficiency via diet were 0.41 d^-1 and 58%, respectively. The OP accumulation in D. magna predominantly occurred via water (63%) relative to diet (37%), resulting in a bioaccumulation factor of 2.7 × 10⁴ L kg^-1. The estimated trophic transfer factor was 0.25, suggesting that OP biomagnification was unlikely in the C. vulgaris-D. magna trophic relationship.

Toxic effect of different types of titanium dioxide nanoparticles on Ceriodaphnia dubia in a freshwater system

In the current study, the effect of different types of titanium dioxide (TiO₂) nanoparticles (NPs) (rutile, anatase, and mixture) was analyzed on Ceriodaphnia dubia in the presence of algae under distinct irradiation conditions such as visible and UV-A. The toxicity experiments were performed in sterile freshwater to mimic the chemical composition of the freshwater system. In addition, the oxidative stress biomarkers such as MDA, catalase, and GSH were analyzed to elucidate the stress induced by the NPs on daphnids. Individually, both rutile and anatase NPs induced similar mortality under both visible and UV-A irradiations at all the test concentrations except 600 and 1200 μM where rutile induced higher mortality under UV-A. Upon visible irradiation, the binary mixture exhibited a synergistic effect at their lower concentration and an additive effect at higher concentrations. In contrast, UV-A irradiation demonstrated the additive effect of mixture except for 1200 μM which elucidated antagonistic effect. Mathematical model confirmed the effects of the binary mixture. The surface interaction between the individual NPs in the form of aggregation played a pivotal role in the induction of specific effects exhibited by the binary mixture. Oxidative stress biomarkers were highly increased upon NPs exposure especially under visible irradiation. These observations elucidated that the irradiation and crystallinity effect of TiO₂ NPs were noted only on certain biomarkers and not on the mortality.

Comparison in the response of three European Gammarid species exposed to the growth regulator insecticide fenoxycarb

Growth regulator insecticides with juvenoid activity can affect the development and reproduction of non-target organisms such as crustaceans. In this perspective, our previous studies revealed deleterious effects of the juvenoid fenoxycarb at 5 μg L^-1 on the embryogenesis and at 50 μg L^-1 on the reproductive behavior of the amphipod Gammarus fossarum. In the present study, to determine whether data generated with one amphipod species can be extended to other gammarid species, we tested the effects of a 5 μg L^-1 fenoxycarb exposure on three European amphipod species: G. fossarum, Gammarus roeseli, and Echinogammarus longisetosus. We exposed individually 60 freshly fertilized females to fenoxycarb throughout the entire oogenesis/embryogenesis cycle (i.e., 19 days). In newborn individuals from exposed embryos, we measured both pigmentation and lipid reserve impairments while in exposed females, we observed reproductive behavior. At 5 μg L^-1 fenoxycarb, reproductive behavior was only altered in G. fossarum. This study demonstrates the variability of the toxic response among the three gammaridae species, underlining the need for acquiring data with a broad phylogenetic representation to better predict toxic effects on freshwater ecosystems.

Evaluation of the subtle effects and oxidative stress response of chloramphenicol, thiamphenicol, and florfenicol in Daphnia magna

Phenicol antibiotics, such as chloramphenicol, thiamphenicol, and florfenicol, are commonly used in the veterinary and aquaculture fields to treat diseases and have frequently been detected in aquatic environments. Nevertheless, there is limited information regarding the effects of phenicol antibiotics on aquatic nontarget species. Thus, the present study aims to investigate the long-term (21-d) influence on the reproduction and growth of and the acute (24-h) oxidative response and tissue damage in the crustacean Daphnia magna after exposure to phenicol drugs, including their environmental concentrations. The results indicate that D. magna exposed to florfenicol are likely to cause more adverse effects than those exposed to chloramphenicol and thiamphenicol over long-term (21-d) exposures. Furthermore, changes in biochemical biomarkers such as malondialdehyde (MDA), catalase (CAT), and reduced glutathione (GSH) induced by individual and mixtures of phenicol antibiotics were also observed. Low concentrations of chloramphenicol, thiamphenicol + florfenicol, and chloramphenicol + thiamphenicol significantly increased the MDA levels of D. magna after 24-h exposures, causing cellular oxidative damage in the animals. In addition, discrepancies between CAT activities and GSH levels were observed, underscoring the need to evaluate multiple indicators of oxidative stress in toxicological studies using D. magna as a model. Environ Toxicol Chem 2019;38:575-584. © 2018 SETAC.

Establishment of a high-sensitivity reporter system in mammalian cells for detecting juvenoids using juvenile hormone receptors of Daphnia pulex

Environmental waters are polluted by various chemicals originating from human activities. Recently, the environmental risk of juvenile hormones (JHs) to aquatic microcrustaceans has been recognized by risk assessors and researchers. JH is a major arthropod hormone that regulates molting and reproduction and has analogs that have been used as insect growth regulators. JHs are known to disturb the sex determination system of Daphnia, which is a keystone animal in limnetic ecosystems and is not the target of extermination. To assess the risk of contaminant chemicals and to protect biodiversity, reliable methods for detecting such chemicals are essential. In this study, we attempted to establish a practical in vitro reporter assay system for detecting chemicals with JH activity. Using a newly constructed reporter vector (modified from the JH response element of Tribolium castaneum Krüppel homolog 1, which is a major JH responsive gene in insects), strong JH-dependent transcriptional activity (>40-fold activation) was found in Chinese hamster ovary cells that express JH receptors of Daphnia pulex. Dose-response analysis conducted on several JH and non-JH chemicals revealed that the established reporter assay system has strict specificity to JH chemicals, and the half maximum effective concentration (EC₅₀ ) was between 10^-7 and 10^-9  m. These results suggest that the new system is a rapid and economical method for assessing the environmental risk of JH-active chemicals.

Life history traits and genotoxic effects on Daphnia magna exposed to waterborne uranium and to a uranium mine effluent - A transgenerational study

Assessing the impact of uranium mining industry on aquatic ecosystems near mining areas is critical to ensure the long-term health and sustainability of ecosystem services. As so, a transgenerational study with Daphnia magna has been conducted to perceive to what extent intermittent discharges of uranium mine effluents into watercourses may impact the DNA integrity and life history traits of cladocerans. Organisms were exposed for 48 h to a 2% dilution of an uranium mine effluent (UME) and to a corresponding dose of waterborne uranium (WU) that, according to our preliminary studies, induces significant DNA damage in daphnids. After exposure, organisms were transferred to clean medium, where three successive generations were monitored for genotoxicity and other effects at the individual and population level. Despite some differences between WU and UME data, our results revealed that the negative impacts of the short-term exposure gradually disappeared after placing the organisms in clean medium. These results suggest that, under intermittent stress, daphnids are able to recover, since after the 3^rd brood release, DNA damage (measured as DNA strand breaks) is no longer observed and has no significant impact on the detectable life traits of offspring. Although our results indicate that populations of D. magna are not affected by intermittent and highly diluted discharges from uranium mining, aquatic systems under this kind of pressure should not be seen as hazardous-free. Future studies in this field are recommended and these should consider radionuclides in the water column, their accumulation in the sediments and also multiple life stages.

Estimation of population-level effect of the endocrine disruptor pyriproxyfen in Daphnia magna by using changes in sex ratio and reproductive output

Here we developed an analytical means of estimating population-level effects of endocrine disruptors on Daphnia magna. Our approach was based on the fact that the endocrine-disrupting juvenile hormone analogs induce the production of male neonates if they are exposed to the analogs during a particular period in their prenatal development; the method also assumed that the abnormal production of male neonates in the sake of production of female neonates reduces population growth. We constructed a linear toxicodynamics model to elucidate the period in which D. magna neonates are sensitive to exposure to the analog and also the probability of an individual neonate changing sex under specific exposure concentrations. The proposed model was applied to D. magna reproduction test data obtained under time-varying exposure to pyriproxyfen to derive the maximum-likelihood estimates and the posterior distributions of the model parameters. To quantitatively assess the ecological risk at the population level, we conducted a population dynamics simulation under two time-varying exposure scenarios (i.e., constant or pulsed exposure) by using an age-structured population model. When the change in sex ratio was based on the time-weighted average concentration during the period of sensitivity, change in sex ratio caused approximately equivalent population-level effects as did reproductive inhibition (i.e., reduction in the total number of neonates per female parent) regardless of the exposure scenario. In contrast, when change in sex ratio was based on maximum concentration during the sensitive period, change in sex ratio caused only half the population-level effects as did reproductive inhibition under constant exposure, whereas it caused a much larger population-level effect than did reproductive inhibition under pulsed exposure.

Acute and chronic effects of exposure to the juvenile hormone analog fenoxycarb during sexual reproduction in Daphnia magna

Recent studies have demonstrated that insect growth regulating insecticides are able to affect reproductive endpoints in zooplankton species at very low levels. For the cyclic parthenogenetic water flea Daphnia, most of this research has focused on the asexual part of the life cycle and induction of male offspring. Even though Daphnia and many other aquatic invertebrates rely on sexual reproduction and subsequent production of dormant eggs to recover from environmentally harsh conditions, much less is known about the effects of toxicants on the sexual reproductive phase. Using fenoxycarb as a model pesticide, we exposed male and female neonate Daphnia magna, under conditions inducing a switch to sexual reproduction, and tested for effects on dormant egg (ephippia) production and sex ratio of parthenogenetic offspring. Subsequently, we assessed whether fenoxycarb exposure affected the quality of the produced dormant eggs and viability of the hatchlings. Our results showed that exposure to sub-lethal concentrations of fenoxycarb caused a sharp decrease in parthenogenetic reproduction, while inducing male offspring. Dormant egg production was marginally negatively affected, but survival and fitness of the hatched individuals were not significantly affected. This indicates that under pesticide stress, surviving adult females invested in sexual reproduction at the expense of parthenogenetic reproduction. Exposure to toxicants during the sexual reproductive phase, could affect the active aquatic phase as well as the dormant phase in natural zooplankton populations. This indicates the need for further ecotoxicological research and development of test protocols taking into account the full life cycle of zooplankton species.

Ecotoxicological assessment of perchlorate using in vitro and in vivo assays

Perchlorate is an inorganic ion widespread in the environment, generated as a natural and anthropogenic pollutant, with known endocrine disruption properties in the thyroid gland. Nonetheless, there are few reports of its ecotoxicological impact on wildlife. The aim of this study was to evaluate the adverse effects of KClO₄ exposure on different cell lines, HEK, N2a, and 3T3, as well as in ecological models such as Vibrio fischeri, Pseudokirchneriella subcapitata, Daphnia magna, and Eisenia fetida. Perchlorate exhibited similar toxicity against tested cell lines, with LC₅₀ values of 19, 15, and 19 mM for HEK, N2a, and 3T3, respectively; whereas in V. fischeri, the toxicity, examined as bioluminescence reduction, was considerably lower (EC₅₀ = 715 mM). The survival of the freshwater algae P. subcapitata was significatively impaired by perchlorate (LC₅₀ = 72 mM), and its effect on the lethality in the crustacean D. magna was prominent (LC₅₀ = 5 mM). For the earthworm E. fetida, the LC₅₀ was 56 mM in soil. In this organism, perchlorate induced avoidance behavior, weight loss, and decreased egg production and hatchling, as well as morphological and histopathological effects, such as malformations, dwarfism, and necrosis. In conclusion, perchlorate toxicity varies according to the species, although E. fetida is a sensitive model to generate information regarding the toxicological impact of KClO₄ on biota.

Aquatic toxicity of several textile dye formulations: Acute and chronic assays with Daphnia magna and Raphidocelis subcapitata

Dyes are widely used in various sectors and can be released into the environment where they persist for a long time because of their high stability to light or temperature and their resistance to environmental degradation. Dyes are often poorly characterized and toxicological/ecotoxicological data are available only for a few. These features, coupled with their toxicity, make dyes a possible source of ecological concern, particularly for freshwater aquatic ecosystems. Therefore, new data may be very useful for their risk assessment. In the present study, we investigated the aquatic toxicity of 42 commercial dye formulations using the application of in silico tools and ecological bioassays. The in silico approach was used to assess the similarities among the dyes, highlighting that dyes from the same chemical class are generally similar. No correlation was found among dyes with the same color. Acute and long-term ecotoxicological assays with daphnids and algae were applied to evaluate the potential impact of these products, according to the OECD guidelines 201 and 202. The bioassays were able to identify structures with potential ecotoxicity: only 9 formulations showed toxicity lower than 100mg/L for daphnids while 30 dyes were toxic for algae. In our experimental conditions, algae were more sensitive to dye toxicity, particularly when the effects on cell number were considered.

Toxic potential of the emerging contaminant nicotine to the aquatic ecosystem

Nicotine is a "life-style compound" widely consumed by human populations and, consequently, often found in surface waters. This fact presents a concern for possible effects in the aquatic ecosystems. The objective of this study was to assess the potential lethal and sublethal toxicity of nicotine in aquatic organisms from different trophic levels (Vibrio fischeri, Pseudokirchneriella subcapitata, Thamnocephalus platyurus, and Daphnia magna). The bioassays were performed by exposing the organisms to concentrations of nicotine in a range of 0.5-1000 μg/L. Results showed that nicotine, at tested concentration, was not acutely toxic to V. fischeri and T. platyurus. On the contrary, this substance exhibited toxicity to P. subcapitata and Daphnia magna. Thus, concentrations of nicotine of 100 and 200 μg/L promoted an inhibition in the growth of P. subcapitata. In addition, a concentration of 100 μg/L nicotine acted on the reproduction of the crustacean D. magna, by decreasing the number of juveniles produced by female. On the other hand, the results showed that concentrations equal to or greater than 10 μg/L induced the production of daphnids male offspring, which may indicate that nicotine is a weak juvenoid compound of the D. magna endocrine system. Furthermore, the result showed that concentrations tested of this chemical have the capacity to revert the effect of fenoxycarb, a strong juvenoid chemical insecticide. The results of the study revealed that nicotine can induce several changes in some of the most important key groups of the aquatic compartment, which can compromise, in a short time, the balance of aquatic ecosystem. Finally, a preliminary environmental risk assessment of this stimulant was performed from the highest measured concentration in surface water and the no observable effect concentration value in the most sensitive species, i.e., D. magna. This process revealed that nicotine can produce an important risk to aquatic organisms.

Sublethal and Reproductive Effects of Acute and Chronic Exposure to Flowback and Produced Water from Hydraulic Fracturing on the Water Flea Daphnia magna

Hydraulic fracturing is an industrial process allowing for the extraction of gas or oil. To fracture the rocks, a proprietary mix of chemicals is injected under high pressure, which later returns to the surface as flowback and produced water (FPW). FPW is a complex chemical mixture consisting of trace metals, organic compounds, and often, high levels of salts. FPW toxicity to the model freshwater crustacean Daphnia magna was characterized utilizing acute (48 h median lethal concentrations; LC₅₀) and chronic (21 day) exposures. A decrease in reproduction was observed, with a mean value of 18.5 neonates produced per replicate over a 21 day chronic exposure to 0.04% FPW, which was a significant decrease from the average of 64 neonates produced in the controls. The time to first brood was delayed in the highest FPW (0.04%) treatment. Neonates exhibited an LC₅₀ of 0.19% of full-strength FPW, making them more sensitive than adults, which displayed an LC₅₀ value of 0.75%. Quantitative PCR highlighted significant changes in expression of genes encoding xenobiotic metabolism (cyp4) and moulting (cut). This study is the first to characterize chronic FPW toxicity and will help with the development of environmental monitoring and risk assessment of FPW spills.

Degradation and ecotoxicity of dye Reactive Black 5 after reductive-oxidative process : Environmental Science and Pollution Research

This research paper describes the study of a reduction-oxidation system using commercial steel wool (Fe0) and H2O2 for degradation of the dye Reactive Black 5 and aromatic compounds in water. The reductive process alone allowed the almost complete removal of color (97 ± 1 %) after 60 min of reaction. The decrease in spectral area (λ = 599 nm) associated with the chromophore group indicates breakage of the azo bonds. Moreover, the significant change in UV spectra can be associated with the formation of aromatic amines. Regarding the transformation products, a spectrophotometric method based on the diazotization reaction was employed to identify aromatic amines after reductive process, using sulfanilic acid as a model of aromatic amines. In addition, association with Fenton reagents improved the efficiency in the system with 93 ± 1 % degradation of intermediates formed during the reductive process. Ecotoxicological analysis revealed that the dye solution, after the reductive and oxidative processes, was not toxic to Lactuca sativa seeds. For Daphnia magna, the EC50 (%) values observed revealed that dye solution has an EC50(%) = 74.1 and after reductive process, the toxicity increased (EC50(%) = 63.5), which might be related to the formation of aromatic amines. However, after the Fenton process, the EC50 (%) was >100. These results demonstrated that the Fenton reaction using steel wool as an iron source was very efficient to decrease color, aromatic transformation products, and the ecotoxicity of Reactive Black 5 in solution.

Whole-Organism Transcriptomic Analysis Provides Mechanistic Insight into the Acute Toxicity of Emamectin Benzoate in Daphnia magna

Emamectin benzoate (EMB) is an antisea lice chemical widely used in the aquaculture that may also unintentionally affect nontarget crustaceans in the environment. Although the adverse effects of this compound are well documented in various species, the full modes of action (MoAs) are still not well characterized. The current study was therefore conducted to characterize the MoAs of EMB and link perturbations of key toxicological pathways to adverse effects in the model freshwater crustacean Daphnia magna. Effects on molting and survival were determined after 48 h exposure to EMB, whereas global transcriptional changes and the ecdysone receptor (EcR) binding potency was determined to characterize the MoA. The results showed that the molting frequency and survival of D. magna decreased in a concentration-dependent manner, and the observed changes could not be attributed to direct interactions with the EcR. Major MoAs such as activation of glutamate-gated chloride channels and gamma-aminobutyric acid signaling, disruption of neuroendocrine regulation of molting, perturbation of energy homeostasis, suppression of DNA repair and induction of programmed cell death were observed by transcriptional analysis and successfully linked to the adverse effects. This study has demonstrated that acute exposure to intermediate and high pM levels of EMB may pose hazards to nontarget crustaceans in the aquatic environment.

Assessment of the effects of the carbamazepine on the endogenous endocrine system of Daphnia magna

In the present study, the endocrine activity of the antiepileptic pharmaceutical carbamazepine (CBZ) in the crustacean Daphnia magna was assessed. To assess the hormonal activity of the drug, we exposed maternal daphnids and embryos to environmental relevant concentrations of CBZ (ranging from 10 to 200 μg/L) and to mixtures of CBZ with fenoxycarb (FEN; 1 μg/L). Chronic exposure to CBZ significantly decreased the reproductive output and the number of molts of D. magna at 200 μg/L. This compound induced the production of male offspring (12 ± 1.7 %), in a non-concentration-dependent manner, acting as a weak juvenile hormone analog. Results showed that this substance, at tested concentrations, did not antagonize the juvenoid action of FEN. Further, CBZ has shown to be toxic to daphnid embryos through maternal exposure interfering with their normal gastrulation and organogenesis stages but not producing direct embryo toxicity. These findings suggest that CBZ could act as an endocrine disruptor in D. magna as it decreases the reproductive output, interferes with sex determination, and causes development abnormality in offspring. Therefore, CBZ could directly affect the population sustainability.

Transcriptomic alterations in Daphnia magna embryos from mothers exposed to hypoxia

Hypoxia occurs when dissolved oxygen (DO) falls below 2.8mgL(-1) in aquatic environments. It can cause trans-generational effects not only in fish, but also in the water fleas Daphnia. In this study, transcriptome sequencing analysis was employed to identify transcriptomic alterations induced by hypoxia in embryos of Daphnia magna, with an aim to investigate the mechanism underlying the trans-generational effects caused by hypoxia in Daphnia. The embryos (F1) were collected from adults (F0) that were previously exposed to hypoxia (or normoxia) for their whole life. De novo transcriptome assembly identified 18270 transcripts that were matched to the UniProtKB/Swiss-Prot database and resulted in 7419 genes. Comparative transcriptome analysis showed 124 differentially expressed genes, including 70 up- and 54 down-regulated genes under hypoxia. Gene ontology analysis further highlighted three clusters of genes which revealed acclimatory changes of haemoglobin, suppression in vitellogenin gene family and histone modifications. Specifically, the expressions of histone H2B, H3, H4 and histone deacetylase 4 (HDAC4) were deregulated. This study suggested that trans-generational effects of hypoxia on Daphnia may be mediated through epigenetic regulations of histone modifications.

Diapause as escape strategy to exposure to toxicants: response of Brachionus calyciforus to arsenic

Invertebrate organisms commonly respond to environmental fluctuation by entering diapause. Production of diapause in monogonont rotifers involves a previous switch from asexual to partial sexual reproduction. Although zooplankton have been used in ecotoxicological assays, often their true vulnerability to toxicants is underestimated by not incorporating the sexual phase. We experimentally analyzed traits involved in sexual reproduction and diapause in the cyclically parthenogenetic freshwater rotifer, Brachionus calyciflorus, exposed to arsenic, a metalloid naturally found in high concentrations in desert zones, focusing on the effectiveness of diapause as an escape response in the face of an adverse condition. Addition of sublethal concentrations of arsenic modified the pattern of diapause observed in the rotifer: investment in diapause with arsenic addition peaked earlier and higher than in non-toxicant conditions, which suggests that sexual investment could be enhanced in highly stressed environmental conditions by increased responsiveness to stimulation. Nevertheless, eggs produced in large amount with arsenic, were mostly low quality, and healthy-looking eggs had lower hatching success, therefore it is unclear whether this pattern is optimum in an environment with arsenic, or if rather arsenic presence in water bodies disturbs the optimal allocation of offspring entering diapause. We observed high accumulation of arsenic in organisms exposed to constant concentration after several generations, which suggests that arsenic may be accumulated transgenerationally. The sexual phase in rotifers may be more sensitive to environmental conditions than the asexual one, therefore diapause attributes should be considered in ecotoxicological assessment because of its ecological and evolutionary implications on lakes biodiversity.

Mechanism-specific and whole-organism ecotoxicity of mono-rhamnolipids

Biosurfactants like rhamnolipids are promising alternatives to chemical surfactants in a range of applications. A wider use requires an analysis of their environmental fate and their ecotoxicological potential. In the present study mono-rhamnolipids produced by a recombinant Pseudomonas putida strain were analyzed using the Green Toxicology concept for acute and mechanism-specific toxicity in an ecotoxicological test battery. Acute toxicity tests with the invertebrate Daphnia magna and with zebrafish embryos (Danio rerio) were performed. In addition, microbial and fungicidal effectiveness was investigated. Mutagenicity of the sample was tested by means of the Ames fluctuation assay. A selected mono-rhamnolipid was used for model simulations regarding mutagenicity and estrogenic activity. Our results indicate that mono-rhamnolipids cause acute toxicity to daphnids and zebrafish embryos comparable to or even lower than chemical surfactants. Rhamnolipids showed very low toxicity to the germination of Aspergillus niger spores and the growth of Candida albicans. No frameshift mutation or base substitutions were observed using the Ames fluctuation assay with the two tester strains TA98 and TA100. This result was confirmed by model simulations. Likewise it was computed that rhamnolipids have no estrogenic potential. In conclusion, mono-rhamnolipids are an environmental friendly alternative to chemical surfactants as the ecotoxicological potential is low.

Heterodimeric TALENs induce targeted heritable mutations in the crustacean Daphnia magna

Transcription activator-like effector nucleases (TALENs) are artificial nucleases harboring a customizable DNA-binding domain and a FokI nuclease domain. The high specificity of the DNA-binding domain and the ease of design have enabled researchers to use TALENs for targeted mutagenesis in various organisms. Here, we report the development of TALEN-dependent targeted gene disruption in the crustacean Daphnia magna, the emerging model for ecological and toxicological genomics. First, a reporter transgene DsRed2 (EF1α-1::DsRed2) was targeted. Using the Golden Gate method with a GoldyTALEN scaffold, we constructed homodimeric and heterodimeric TALENs containing wild-type and ELD/KKR FokI domains. mRNAs that coded for either the customized homodimeric or heterodimeric TALENs were injected into one-cell-stage embryos. The high mortality of embryos injected with homodimeric TALEN mRNAs prevented us from detecting mutations. In contrast, embryos injected with heterodimeric TALEN mRNAs survived and 78%–87% of the adults lost DsRed2 fluorescence in a large portion of cells throughout the body. In addition, these adults produced non-fluorescent progenies, all of which carried mutations at the dsRed2 locus. We also tested heterodimeric TALENs targeted for the endogenous eyeless gene and found that biallelic mutations could be transmitted through germ line cells at a rate of up to 22%. Both somatic and heritable mutagenesis efficiencies of TALENs were higher than those of the CRISPR/Cas9 system that we recently developed. These results suggest that the TALEN system may efficiently induce heritable mutations into the target genes, which will further contribute to the progress of functional genomics in D. magna.

Timing matters: sensitivity of Daphnia magna dormant eggs to fenoxycarb exposure depends on embryonic developmental stage

Although Daphnia magna is a key species in many lentic freshwater ecosystems and is commonly used as model organism in ecology and ecotoxicology, very little is known about the effects of chemicals on their dormant life stages. Dormant eggs (ephippia) are produced when environmental conditions deteriorate, and Daphnia switch from clonal to sexual reproduction. Ephippia produced over different growing seasons can accumulate in the sediment of ponds and lakes, where they can be exposed to pesticides and other (anthropogenic) stressors. In the present study, we have investigated the effects of pesticide exposure on dormant eggs at different embryonic developmental stages and evaluated the degree of protection against pollution provided by the ephippial case. We therefore conducted a hatching experiment in which decapsulated and encapsulated dormant eggs were exposed to an insect growth regulator (fenoxycarb) at different stages during their development, both before and after activation of the eggs. In addition, we developed an analytical method to measure fenoxycarb concentrations in the dormant eggs. Fenoxycarb negatively affected development and hatching success and changed the timing of hatching in activated and in dormant eggs. Hatching characteristics as well as fenoxycarb concentrations inside the eggs differed significantly between exposure treatments. Final stages of embryonic development were most sensitive to pesticide exposure and had the highest tissue concentrations of fenoxycarb. Tissue concentrations did not differ significantly between decapsulated and encapsulated eggs, suggesting that the ephippial case offers limited or no direct protection against pesticide exposure. With this study we provide new evidence showing that pesticides can bioconcentrate in and affect D. magna dormant eggs. The severity of the effects on developing embryos depends on the timing of pesticide exposure. Our results stress the importance of considering the full life-cycle of model organisms used in ecotoxicological studies, since these are ultimately aimed at assessing risks of chemical exposure on natural aquatic ecosystems.

Diofenolan induces male offspring production through binding to the juvenile hormone receptor in Daphnia magna

Juvenile hormone (JH) and JH agonists have been reported to induce male offspring production in various daphnid species including Daphnia magna. We recently established a short-term in vivo screening assay to detect chemicals having male offspring induction activity in adult D. magna. Diofenolan has been developed as a JH agonist for insect pest control, but its male offspring induction activity in daphnids has not been investigated yet. In this study, we found that the insect growth regulator (IGR) diofenolan exhibited a potent male offspring induction activity at low ng/L to μg/L concentrations, as demonstrated by the short-term in vivo screening assay and the recently developed TG211 ANNEX 7 test protocol. A two-hybrid assay performed using the D. magna JH receptor confirmed that diofenolan had a strong JH activity. Global whole body transcriptome analysis of D. magna exposed to 10 ng/L diofenolan showed an up-regulation of JH-responsive genes and modulation of several genes involved in the ecdysone receptor signaling pathway. These results clearly demonstrate that diofenolan has strong JH activity and male offspring induction activity, and that a combination of modified standardized regulatory testing protocols and rapid in vitro and in vivo screening assays are able to identify potential endocrine disruptors in D. magna. The observation that diofenolan modulates multiple endocrine signaling pathways in D. magna suggests that further investigation of potential interference with growth, development and reproduction is warranted.

Transgenerational effects of two antidepressants (sertraline and venlafaxine) on Daphnia magna life history traits

The low levels of antidepressants detected in surface waters currently raise concern about their potential long-term risks to nontarget aquatic organisms. We investigated the transgenerational effects of sertraline, a selective serotonin reuptake inhibitor, and venlafaxine, a serotonin-norepinephrine reuptake inhibitor, on the life traits of Daphnia magna over two generations under environmentally realistic concentrations. We also studied the reversibility of the effect using recovery experiments. We assessed daphnid survival, growth, and reproduction over 21 days and evidenced detectable effects of the antidepressants. Sertraline increased the F0-daphnid fecundity whereas it decreased the offspring number of F1-daphnids. Transfer to clean medium caused negative effects on the offspring of daphnids exposed to 0.3 μg L(–1), but improved the fecundity of offspring of daphnids exposed to 100 μg L(–1). Venlafaxine exposure decreased the offspring number of F0-daphnids and resulted in drug tolerance in the F1 generation. Sertraline, unlike venlafaxine, may turn out to be a true environmental threat due to its accumulation in algae and the physiological weakness observed over generations. These effects across generations point out to the need to perform multigeneration tests to assess the environmental risk of pharmaceuticals in nontarget organisms.