Linking multiple biomarker responses in Daphnia magna under thermal stress

Zooplankton-based adverse outcome pathways: A tool for assessing endocrine disrupting compounds in aquatic environments

Endocrine disrupting compounds (EDCs) pose a significant ecological risk, particularly in aquatic ecosystems. EDCs have become a focal point in ecotoxicology, and their identification and regulation have become a priority. Zooplankton have gained global recognition as bioindicators, benefiting from rigorous standardization and regulatory validation processes. This review aims to provide a comprehensive summary of zooplankton-based adverse outcome pathways (AOPs) with a focus on EDCs as toxicants and the utilisation of freshwater zooplankton as bioindicators in ecotoxicological assessments. This review presents case studies in which zooplankton have been used in the development of AOPs, emphasizing the identification of molecular initiating events (MIEs) and key events (KEs) specific to zooplankton exposed to EDCs. Zooplankton-based AOPs may become an important resource for understanding the intricate processes by which EDCs impair the endocrine system. Furthermore, the data sources, experimental approaches, advantages, and challenges associated with zooplankton-based AOPs are discussed. Zooplankton-based AOPs framework can provide vital tools for consolidating toxicological knowledge into a structured toxicity pathway of EDCs, offering a transformative platform for facilitating enhanced risk assessment and chemical regulation.

Rapid evolution of consumptive and non-consumptive predator effects on prey population densities, bioenergetics and stoichiometry

Predators can strongly influence prey populations not only through consumptive effects (CE) but also through non-consumptive effects (NCE) imposed by predation risk. Yet, the impact of NCE on bioenergetic and stoichiometric body contents of prey, traits that are shaping life histories, population and food web dynamics, is largely unknown. Moreover, the degree to which NCE can evolve and can drive evolution in prey populations is rarely studied. A 6-week outdoor mesocosm experiment with Caged-Fish (NCE) and Free-Ranging-Fish (CE and NCE) treatments was conducted to quantify and compare the effects of CE and NCE on population densities, bioenergetic and stoichiometric body contents of Daphnia magna, a keystone species in freshwater ecosystems. We tested for evolution of CE and NCE by using experimental populations consisting of D. magna clones from two periods of a resurrected natural pond population: a pre-fish period without fish and a high-fish period with high predation pressure. Both Caged-Fish and Free-Ranging-Fish treatments decreased the body size and population densities, especially in Daphnia from the high-fish period. Only the Free-Ranging-Fish treatment affected bioenergetic variables, while both the Caged-Fish and Free-Ranging-Fish treatments shaped body stoichiometry. The effects of CE and NCE were different between both periods indicating their rapid evolution in the natural resurrected population. Both the Caged-Fish and Free-Ranging-Fish treatments changed the clonal frequencies of the experimental Daphnia populations of the pre-fish as well as the high-fish period, indicating that not only CE but also NCE induced clonal sorting, hence rapid evolution during the mesocosm experiment in both periods. Our results demonstrate that CE as well as NCE have the potential to change not only the body size and population density but also the bioenergetic and stoichiometric characteristics of prey populations. Moreover, we show that these responses not only evolved in the studied resurrected population, but that CE and NCE also caused differential rapid evolution in a time frame of 6 weeks (ca. four to six generations). As NCE can evolve as well as can drive evolution, they may play an important role in shaping eco-evolutionary dynamics in predator-prey interactions.

Mitochondrial metabolism and respiration adjustments following temperature acclimation in Daphnia magna

Seasonal temperature changes and local variations in the water column challenge lentic zooplankton in their habitat. At the cellular level, exposure to varying temperatures affects the mitochondrial functional properties of poikilothermic organisms. Metabolic enzymes that supply reduced substrates to the electron transport chain and elements of the oxidative phosphorylation system must therefore adjust their activity and flux rates to the altered temperature conditions. In the present study, Daphnia magna respiration was analyzed in response to acute and chronic changes in ambient temperature. Oxygen consumption as well as substrate and electron flux rates were measured at the animals' acclimation temperature and at two additional acute temperatures. High activity of citrate synthase (CS) in cold-acclimated animals (10 °C) may have resulted from mitochondrial quantitative adjustments. However, thermal sensitivity of the functional properties of mitochondrial enzymes was greater in warm-acclimated animals (30 °C). In whole animals, temperature-induced changes were partly compensated by acclimation, but these changes were promoted by acclimation in the case of the mitochondrial electron transport chain. Thus, respiration realised in whole animals was limited by the provision of reduced substrates in the tricarboxylic acid cycle rather than by restrictions of the respiratory chain complexes. This may minimize production of reactive oxygen species and resulting damage and reduce waste of substrates from the animals' energy reserves. Still, the integrated biomarker response indicated increased defense against oxidative stress at elevated temperatures.

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.

Is a lower-toxicity strain of Microcystis aeruginosa really less toxic?

Some well-known hazards of blooming cyanobacteria are caused by toxic metabolites such as microcystins (MCs), though many other bioactive chemicals of unknown toxicity are present in their exudates. It is also unclear whether toxicity of cyanobacterial cells depends on growth phases in the life cycle. In this study, we compared toxicity to Daphnia magna of Microcystis aeruginosa - a common cyanobacterial species - exudates (MaE) from two MC-producing strains over both exponential growth and stationary phases in acute and chronic experiments. Specifically, we assessed mitochondrial dysfunction, oxidative stress and lipid peroxidation, and filtering activity and heartbeat rate of Daphnia exposed to MaE. All MaE treatments induced common characteristics of Microcystis toxicity including disorder in the mitochondrial membrane and aberrant heart rate. MaE from cells at stationary growth phase were more toxic than those at exponential phase. Surprisingly, the MC-lower strain had higher toxicity than MC-higher one. Microcystis at different stage of blooms may differentially affect waterfleas owing to variable MaE-induced physiological dysfunction, abundance and grazing rate. Our study suggested that Microcystis strains with lower microcystin-producing ability might release other detrimental chemicals and should not be ignored in harmful bloom monitoring.

Elevated temperature enhanced lethal and sublethal acute toxicity of polyethylene microplastic fragments in Daphnia magna

Microplastic (MP) pollution poses a growing concern in freshwater ecosystems, which are further threatened by global warming. Thus, this study investigated the effect of elevated temperature (25 °C) on acute toxicity of polyethylene MP fragments to Daphnia magna over a 48 h period. At the reference temperature (20 °C), MP fragments (41.88 ± 5.71 µm) induced over 70 times higher lethal toxicity than that induced by MP beads (44.50 ± 2.50 µm), with median effective concentrations (EC50) of 3.89 and 275.89 mg L-1, respectively. Elevated temperature significantly increased (p < 0.05) the lethal (EC50 = 1.88 mg L-1) and sublethal (lipid peroxidation and total antioxidant capacity) toxicity in D. magna exposed to MP fragments compared to those at the reference temperature. Additionally, the elevated temperature led to a significant increase (p < 0.05) in the bioconcentration of MP fragments in D. magna. Overall, the present study increases understanding for the ecological risk assessment of microplastics under global warming, highlights that elevated temperature can be seriously increased bioconcentration of MP fragments, leading to increased acute toxicity in D. magna.

Temperature related toxicity features of acute acetamiprid and thiacloprid exposure in Daphnia magna and implications on reproductive performance

This study investigated the potential for elevated temperature to alter the toxicity of acetamiprid (ACE) and thiacloprid (Thia) in the ecotoxicity model Daphnia magna. The modulation of CYP450 monooxygenases (ECOD), ABC transporter activity (MXR) and incident cellular reactive oxygen species (ROS) overproduction was screened in premature daphnids following acute (48 h) exposure to sublethal concentrations of ACE and Thia (0.1-, 1.0 μM) at standard 21 °C and elevated 26 °C temperatures. Delayed outcomes of acute exposures were further evaluated based on the reproduction performance of daphnids monitored over 14 days of recovery. Exposures to ACE and Thia at 21^o C elicited moderate induction of ECOD activity, pronounced inhibition of MXR activity and severe ROS overproduction in daphnids. In the high thermal regime, treatments resulted in significantly lower induction of ECOD activity and inhibition of MXR activity, suggesting a suppressed metabolism of neonicotinoids and less impaired membrane transport activity in daphnids. Elevated temperature on its own, caused a three-fold rise in ROS levels in control daphnids, while ROS overproduction upon neonicotinoid exposure was less accentuated. Acute exposures to ACE and Thia caused significant decreases also in the reproduction of daphnids, indicating delayed outcomes even at environmentally relevant concentrations. Both the cellular alterations in exposed daphnids and decreases in their reproductive output post exposures evidenced closely similar toxicity patterns and potentials for the two neonicotinoids. While elevated temperature elicited only a shift in baseline cellular alterations evoked by neonicotinoids, it significantly worsened the reproductive performance of daphnids following neonicotinoid exposures.

Risk assessment of bisphenol analogues towards mortality, heart rate and stress-mediated gene expression in cladocerans Moina micrura

Bisphenol A (BPA) is a well-known endocrine-disrupting compound that causes several toxic effects on human and aquatic organisms. The restriction of BPA in several applications has increased the substituted toxic chemicals such as bisphenol F (BPF) and bisphenol S (BPS). A native tropical freshwater cladoceran, Moina micrura, was used as a bioindicator to assess the adverse effects of bisphenol analogues at molecular, organ, individual and population levels. Bisphenol analogues significantly upregulated the expressions of stress-related genes, which are the haemoglobin and glutathione S-transferase genes, but the sex determination genes such as doublesex and juvenile hormone analogue genes were not significantly different. The results show that bisphenol analogues affect the heart rate and mortality rate of M. micrura. The 48-h lethal concentration (LC₅₀) values based on acute toxicity for BPA, BPF and BPS were 611.6 µg L^-1, 632.0 µg L^-1 and 819.1 µg L^-1, respectively. The order of toxicity based on the LC₅₀ and predictive non-effect concentration values were as follows: BPA > BPF > BPS. Furthermore, the incorporated method combining the responses throughout the organisation levels can comprehensively interpret the toxic effects of bisphenol analogues, thus providing further understanding of the toxicity mechanisms. Moreover, the output of this study produces a comprehensive ecotoxicity assessment, which provides insights for the legislators regarding exposure management and mitigation of bisphenol analogues in riverine ecosystems.

Transgenerational effects of benzotriazole on the gene expression, growth, and reproduction of Daphnia magna

Due to its widespread and intensive use as a corrosion inhibitor, benzotriazole is ubiquitously detected from a few parts per billion to several hundred parts per million in aquatic environments. The long-term toxicity of benzotriazole is unclear despite its low acute toxicity. Therefore, we investigated the transgenerational effects of benzotriazole at the genomic and individual levels using the freshwater zooplankton Daphnia magna. Maternal exposure to sublethal concentrations (15 and 30 mg/L) of benzotriazole exerted transgenerational effects on D. magna at the genomic and individual levels even in descendants that have never been exposed to benzotriazole. Significant alterations in the expression of Cyp, GST, Vtg1, and Hb and in neonate size were observed in the unexposed F3 generation, confirming the transgenerational effect of benzotriazole. Interestingly, detoxification related genes Cyp and GST were unaffected or downregulated in the exposed generation but upregulated in the following unexposed generations. Furthermore, continuous multigenerational exposure to an environmental concentration (4.3 μg/L) of benzotriazole also upregulated detoxification genes in decent generations but exerted no individual-level effects in subsequent generations.

Disturbances in growth, oxidative stress, energy reserves and the expressions of related genes in Daphnia magna after exposure to ZnO under thermal stress

The toxicological effects of metal contamination are influenced by the ambient temperature. Therefore, global warming affects the toxicity of metal contamination in aquatic ecosystems. ZnO is widely used as a catalyst in many industries, and causes contamination in aquatic ecosystems. Here, we investigated the effects of ZnO concentration under elevated temperature by observing growth, oxidative stress, energy reserves and related gene expression in exposed Daphnia magna. Body length and growth rate increased in neonates exposed to ZnO for 2 days but decreased at 9 and 21 days under elevated temperature. ZnO concentration and elevated temperature induced oxidative stress in mature D. magna by reducing superoxide dismutase (SOD) activity and increasing malondialdehyde (MDA) levels. In contrast, juveniles were unaffected. Carbohydrate, protein and caloric contents were reduced throughout development in D. magna treated with ZnO and elevated temperature in all exposure periods (2, 9 and 21 days). However, lipid content also decreased in mature D. magna treated with ZnO cultured under elevated temperature, while that of juveniles showed an increase in lipid content. Therefore, energy was perhaps allocated to physiological processes for detoxification and homeostasis. Moreover, expression patterns of genes related to physiological processes changed under elevated temperature and ZnO exposure. Taken together, our results highlight that the combination of temperature and ZnO concentration induced toxicity in D. magna. This conclusion was confirmed by the Integrated Biological Response (IBR) index. This study shows that changes in biological levels of organization could be used to monitor environmental change using D. magna as a bioindicator.

Microplastics increases the heat tolerance of Daphnia magna under global warming via hormetic effects

The ecological risk assessment of microplastics under global warming receives increasing attention. Yet, such studies mostly focused on increased mean temperatures (MT), ignoring another key component of global warming, namely daily temperature fluctuations (DTF). Moreover, we know next to nothing about the combined effects of multigenerational exposure to microplastics and warming. In this study, Daphnia magna was exposed to an environmentally relevant concentration of polystyrene microplastics (5 μg L-1) under six thermal conditions (MT: 20 ℃, 24 ℃; DTF: 0 ℃, 5 ℃, 10 ℃) over two generations to investigate the interactive effects of microplastics and global warming. Results showed that microplastics had no effects on Daphnia at standard thermal conditions (constant 20 °C). Yet, microplastics increased the fecundity, heat tolerance, amount of energy storage, net energy budget and cytochrome P450 activity, and decreased the energy consumption when tested under an increased MT or DTF, indicating a hormesis effect induced by microplastics under warming. The unexpected increase in heat tolerance upon exposure to microplastics could be partly explained by the reduced energy consumption and/or increased energy availability. Overall, the present study highlighted the importance of including DTF and multigenerational exposure to improve the ecological risk assessment of microplastics under global warming.

Elevated temperature alleviates benzophenone-3 toxicity in Daphnia magna

Water temperature rises due to thermal discharge and global warming and the potential resulting impacts on the ecotoxicity of emerging chemicals are a growing concern. Benzophenone-3 (BP-3) is an ultraviolet filter added to personal care and plastic products, which is detected at highest concentrations during the hot summer season. This study aimed to investigate the effect of elevated temperature on acute (48 h) and chronic (21 d) BP-3 toxicity in Daphnia magna. Neonates (<24 h) acclimated at 28 °C showed much lower acute toxicity (EC₅₀ = 3.91 and 2.69 mg L^-1 at 20 and 28 °C, respectively) than those acclimated at 20 °C (EC₅₀ = 2.96 and 2.04 mg L^-1 at 20 and 28 °C, respectively). The body length, embryonic development, and the number of offspring in D. magna offspring exposed to BP-3 for 21 d were significantly decreased after exposure to 0.8 mg L^-1 BP-3 at 20 °C. However, these adverse effects of BP-3 in D. magna were significantly ameliorated at 28 °C. Under these conditions, stress response genes such as Hb (hemoglobin), Hsp70 (heat shock protein), Cyp4 (cytochrome P450), and GST (glutathione-S-transferase) were significantly upregulated. These findings suggest that elevated temperature activated stress responses in D. magna, leading to enhanced protection against BP-3 toxicity. This study will contribute to a better understanding of the ecotoxicological impacts of toxic chemicals on aquatic organisms at elevated temperature.

Role of benzophenone-3 additive in chronic toxicity of polyethylene microplastic fragments to Daphnia magna

Plastic additives may accelerate adverse effects of microplastics (MPs). This study aimed to identify the role of benzophenone-3 (BP-3) additive (10.82 ± 1.20% w/w) in chronic toxicity of polyethylene MP fragments to Daphnia magna (D. magna). MP fragments with and without BP-3 (48.37 ± 6.26 and 44.39 ± 11.16 μm, respectively) were synthesized and 4 d-old D. magna were exposed for 17 d. Daphnids exposed to MP/BP-3 fragments (98%) showed higher survival than those exposed to MP fragments (62%), which can be explained by a significantly low (p < 0.0001) bioconcentration of MP/BP-3 fragments. BP-3 leachate induced significantly low (p < 0.05) phototactic behavior of D. magna, likely leading to the low bioconcentration of MP/BP-3 fragments. Unlike MP fragments, both MP/BP-3 fragments and BP-3 additive inhibited embryonic development and offspring growth in a similar manner. Additionally, only BP-3 additive significantly induced (p < 0.05) higher lipid peroxidation in D. magna. This study suggests the critical role of plastic additives in MPs chronic toxicity to aquatic organisms, which should be further identified for other environmentally relevant plastic additives.

The Uptake of Sporopollenin Exine Capsules and Associated Bioavailability of Adsorbed Oestradiol in Selected Aquatic Invertebrates

Lycopodium clavatum sporopollenin exine capsules (SpECs) are known to both adsorb and absorb chemicals. The aim of the present work was to determine whether oestradiol (E2) is 'bioavailable' to bioindicator species, either pre-adsorbed to, or in the presence of, SpECs. SpEC uptake was confirmed for Daphnia magna and Dreissena bugensis. E2 levels varied among treatments for Caenorhabditis elegans though there was no relationship to SpEC load. E2 was not detected in D. bugensis tissues. Expression changes of general stress and E2-specific genes were measured. For C. elegans, NHR-14 expression suggested that SpECs modulate E2 impacts, but not general health responses. For D. magna, SpECs alone and with E2 changed Vtg1 and general stress responses. For D. bugensis, SpECS were taken up but no E2 or change in gene expression was detected after exposure to E2 and/or SpECs. The present study is the first to investigate SpECs and bound chemical dynamics.

Time-Dependent Naphthalene Toxicity in Anabas testudineus (Bloch): A Multiple Endpoint Biomarker Approach

Polyaromatic compounds are the major, widespread contaminants in the aquatic environment. However, the adverse impacts of these compounds on blood pathophysiology (hematological profiling and serum biochemical responses) are poorly understood. As a consequence, this study was intended to evaluate the toxic effects of naphthalene, one of the polycyclic aromatic hydrocarbons, on the blood pathophysiology of Anabas testudineus using multiple end-point biomarker approach. A. testudineus was exposed to short-term (1 and 5 d) and long-term (10, 15, and 21 d) naphthalene concentrations, that is, T1 (0.71 mg/L indicates 25% of LC₅₀) and T2 (1.42 mg/L indicates 50% of LC₅₀ value). The results disclosed significant decrease in red blood cells, hemoglobin (Hb), packed cell volume, and platelet levels, while other blood parameters, namely, white blood cells, percent lymphocyte, mean cell volume, mean corpuscular Hb, and mean corpuscular Hb concentration showed enhanced levels under naphthalene intoxication. Results were more detrimental under T2 concentration. Cholesterol, glucose, calcium, high-density lipoprotein, and low-density lipoprotein levels gradually increased throughout the different exposure periods under T1 and T2 concentrations, while the triglyceride level gradually decreased during exposure periods. Finally, integrated biomarker responses (IBR) analysis indicated that serum biochemical parameters are more powerful than hematological parameters for determining the naphthalene-induced fish health status. Additionally, the IBR study clearly identified that long-term (>5 d) exposure was more harmful than short-term (<5 d) naphthalene exposure. So, these responses may be derived as biomarkers for monitoring naphthalene pollution in an aquatic ecosystem.

Changes in the Magnitude of the Individual and Combined Effects of Contaminants, Warming, and Predators on Tropical Cladocerans across 11 Generations

A massive challenge in ecotoxicology is assessing how the interaction of contaminants, climate change, and biotic stressors shapes the structure and functions of natural populations. Furthermore, it is not known whether contemporary evolutionary responses to multiple stressors across multigenerations may alter the interaction of these stressors. To address these issues, we exposed Moina dubia to lead (Pb, 50 μg/L) under two temperatures (25 and 28 °C) with/without predator cues from climbing perch (Anabas testudineus) for 11 generations (F1-F11). We assessed changes in M. dubia fitness, including development time, adult size, lifespan, fecundity, and neonate production. We found strong negative effects of Pb, elevated temperature, and predator cues on the fitness of M. dubia. Strikingly, Pb-induced reduction in the performance of M. dubia was stronger at 25 °C and in the absence of predator cues. The individual and interactive effects of Pb, temperature, and predator cues on M. dubia were stronger across F1-F9 and generally leveled off in F10-F11. Our results highlight the high vulnerability of M. dubia to multiple stressors, thus weakening top-down control on algal blooms in eutrophic lakes. Our study underscores the importance of integrating evolutionary responses in realistic ecotoxicological risk assessments of contaminants interacting with climatic and biotic stressors.