The Evolution of Extreme Genetic Variability in a Parasite-Resistance Complex.

Genomic regions that play a role in parasite defense are often found to be highly variable, with the MHC serving as an iconic example. Single nucleotide polymorphisms may represent only a small portion of this variability, with Indel polymorphisms and copy number variation further contributing. In extreme cases, haplotypes may no longer be recognized as orthologous. Understanding the evolution of such highly divergent regions is challenging because the most extreme variation is not visible using reference-assisted genomic approaches. Here we analyze the case of the Pasteuria Resistance Complex (PRC) in the crustacean Daphnia magna, a defense complex in the host against the common and virulent bacterium Pasteuria ramosa. Two haplotypes of this region have been previously described, with parts of it being non-homologous, and the region has been shown to be under balancing selection. Using pan-genome analysis and tree reconciliation methods to explore the evolution of the PRC and its characteristics within and between species of Daphnia and other Cladoceran species, our analysis revealed a remarkable diversity in this region even among host species, with many non-homologous hyper-divergent-haplotypes. The PRC is characterized by extensive duplication and losses of Fucosyltransferase (FuT) and Galactosyltransferase (GalT) genes that are believed to play a role in parasite defense. The PRC region can be traced back to common ancestors over 250 million years. The unique combination of an ancient resistance complex and a dynamic, hyper-divergent genomic environment presents a fascinating opportunity to investigate the role of such regions in the evolution and long-term maintenance of resistance polymorphisms. Our findings offer valuable insights into the evolutionary forces shaping disease resistance and adaptation, not only in the genus Daphnia, but potentially across the entire Cladocera class.

Ecotoxicological and metabolomic investigation of chronic exposure of Daphnia magna (Straus, 1820) to yttrium environmental concentrations.

In order to estimate the effects on aquatic organisms of long-term exposure to low doses of yttrium (Y) as a potential emerging contaminant, ecotoxicological and metabolomic data were collected on the model organism Daphnia magna, a keystone species in freshwater ecosystems. Following an initial acute toxicity assessment, a 21-day chronic exposure experiment was conducted using a sublethal concentration of 27 µg L⁻¹ of Y, corresponding to the effective concentrations inducing 10 % effect (EC10) value for mortality endpoint and simulating the environmental Y level in aquatic systems. Results from the 21-day two-factor experiment combining microcrustacean survival, growth and reproduction bioassays and targeted gas chromatography-mass spectrometry (GC-MS) metabolomics indicated significant adverse effects of chronic exposure to Y on D. magna. Daphnids exposed to Y exhibited a significantly lower survival at day 21, delayed the maturity stage, including their first breeding, and decreased clutch size. On the side of metabolomics, a clear and general increase over time of both the number and the level of detected metabolites in the hydroalcoholic extracts of the whole organisms was observed. However, emerging from this broad temporal pattern, several bioactive metabolites were identified (e.g., 2,4-di­tert­butylphenol, itaconic acid, 3-hydroxybutyric acid, and trehalose) whose levels in extracts are linked to the presence of Y. These results emphasize the necessity of considering low-dose, long-term exposure scenarios in environmental risk assessments of rare earth elements (REEs), which have often been overlooked in favour of higher concentration studies.

Evaluation of arsenic induced genotoxicity and its impact on life processes of Daphnia magna.

Heavy metals like arsenic is ubiquitously present in the environment. Geologic and anthropogenic activities are the root cause behind high concentration of arsenic in natural water bodies demanding strict monitoring of water quality prior to human consumption and utilization. In the present study, we have employed Daphnia magna for studying the biological effects of environmentally relevant high concentration of arsenic in water. In acute toxicity study, the LC50 value for 24hr exposure was found to be 2.504 mg/L, which gradually decreased with increase in time period (24hr- 96hr) to 2.011 mg/ L at 96hr. Sub-chronic toxicity was evaluated over 12 days using sub-lethal concentrations (5 %, 10 %, 15 %, and 20 % of the 24-hr LC50). Survivability in Daphnia showed a decreasing trend from 96 % to 91 % with increase in arsenic concentrations from 5 % of LC50 24 hr value to 20 % of LC 50 24hr value respectively. Alongside decreased survivability, there was a significant reduction in body size, with organisms exposed to the highest concentration of arsenic measuring 0.87±0.01 mm compared to 1.51±0.10 mm in the control group. Reproductive potential declined concentration dependently with exposure, with the highest reduction observed at 20 % of LC50 24hr value, where offspring numbers decreased to 7±1 from 23±5 in the control. Heart rate decreased in concentration and time-dependent manners, with the lowest rates observed at the highest arsenic concentration (279±16 bpm after 24hr and 277±27 bpm after 48hr). Comet assay and micronucleus assay conducted after 48 hrs of exposure revealed concentration-dependent genotoxic effects in Daphnia magna. Our results indicate negative impact on physiology and reproduction of Daphnia magna at environmentally existent concentration of arsenic. Also Daphnia magna could serve as a sensitive test system for investigating arsenic contamination in water bodies.

Rapid Response of Daphnia magna Motor Behavior to Mercury Chloride Toxicity Based on Target Tracking.

A rapid and timely response to the impacts of mercury chloride, which is indispensable to the chemical industry, on aquatic organisms is of great significance. Here, we investigated whether the YOLOX (improvements to the YOLO series, forming a new high-performance detector) observation system can be used for the rapid detection of the response of Daphnia magna targets to mercury chloride stress. Thus, we used this system for the real-time tracking and observation of the multidimensional motional behavior of D. magna. The results obtained showed that the average velocity (v¯), average acceleration (a¯), and cumulative travel (L) values of D. magna exposed to mercury chloride stress changed significantly under different exposure times and concentrations. Further, we observed that v¯, a¯ and L values of D. magna could be used as indexes of toxicity response. Analysis also showed evident D. magna inhibition at exposure concentrations of 0.08 and 0.02 mg/L after exposure for 10 and 25 min, respectively. However, under 0.06 and 0.04 mg/L toxic stress, v¯ and L showed faster toxic response than a¯, and overall, v¯ was identified as the most sensitive index for the rapid detection of D. magna response to toxicity stress. Therefore, we provide a strategy for tracking the motile behavior of D. magna in response to toxic stress and lay the foundations for the comprehensive screening of toxicity in water based on motile behavior.

A proof-of-concept multi-tiered Bayesian approach for the integration of physiochemical properties and toxicokinetic time-course data for Daphnia magna.

The use of in silico and in vitro methods, commonly referred to as New Approach Methodologies (NAMs), has been proposed to support environmental (and human) chemical safety decisions, ensuring enhanced environmental protection. Toxicokinetic models developed for environmentally relevant species are fundamental to the deployment of a NAMs-based safety strategy, enabling the conversion between external and internal chemical concentrations, although they require historical toxicokinetic data and robust physical models to be considered a viable solution. Daphnia magna is a key model organism in ecotoxicology albeit with limited and scattered quantitative toxicokinetic data, as for most invertebrates, resulting in a lack of robust toxicokinetic models. Moreover, current D. magna models are chemical specific, which restricts their applicability domain. One aim of this study was to address the current data availability limitations by collecting toxicokinetic time-course data for D. magna covering a broad chemical space and assessing the dataset's uniqueness. The collated toxicokinetic dataset included 48 time-courses for 30 chemicals from 17 studies, which was developed into an R package named AquaTK, with 11 studies unique to our work when compared to existing databases. Subsequently, a proof-of-concept Bayesian analysis was developed to estimate the steady-state concentration ratio (internal concentration / external concentration) from the data at three different levels of precision given three different data availability scenarios for environmental risk assessment. Specifically, an atrazine case study illustrates the multi-level modelling approach providing improvements (uncertainty reductions) in predictions of ratios for increasing amounts of data availability. Our work provides a consistent and self-contained Bayesian framework that irrespective of the hierarchy or resolution of individual experiments, can utilise the available information to generate optimal predictions of steady-state concentration ratios in D. magna. This approach is paramount to supporting the implementation of a NAMs based environmental safety paradigm shift in environmental risk assessment.

Are UV filters better together? A comparison of the toxicity of individual ultraviolet filters and off-the-shelf sunscreens to Daphnia magna.

Organic ultraviolet filters (UVFs) are known to contaminate many aquatic ecosystems, with much environmental contamination attributed to the use of UVF-containing skin care products such as sunscreens during aquatic recreation. Most studies addressing the impact of sunscreen contamination have focused on the effects of UVFs under the assumption that they are the primary contaminants of concern from sunscreen pollution; however, the extent to which the toxicity of UVFs is representative of the environmental impacts of the whole sunscreen mixture is unknown. To address this knowledge gap, this study compared the mixture toxicity of five off-the-shelf sunscreen spray products containing the UVFs avobenzone, homosalate, octisalate, octocrylene and oxybenzone to the toxicity of each UVF in isolation to the freshwater invertebrate Daphnia magna. It was found that sunscreen toxicity was not proportional to their total UVF content, as the sunscreen containing the fewest UVFs was approximately equivalent to the sunscreen with the most UVFs, causing ≥90 % mortality and inhibiting all daphnid reproduction over 21 d exposures. Sunscreen toxicity was typically lower than expected when compared to the toxicity of each individual UVF within the mixture, as some sunscreens causing ≤20 % mortality contained octocrylene and/or oxybenzone at concentrations exceeding those which caused 90 % mortality during exposure to the UVF alone. Despite sunscreens causing large impairments in reproduction, growth and metabolism, poor correlations existed between the severity of most sublethal endpoints with respect to the measured UVF content of each sunscreen. Overall, these results indicate that potential antagonistic relationships between sunscreen ingredients can greatly reduce the toxicity of UVFs, creating more uncertainty regarding the level of threat that UVFs pose to the environment as a result of sunscreen contamination.

Comparing the effects of pristine and UV-VIS aged microplastics: Behavioural response of model terrestrial and freshwater crustaceans.

Physico-chemical properties of microplastics (MPs) change during weathering in the environment. There is a lack of knowledge about the effects of such environmentally relevant MPs on organisms. We investigated: 1) the physico-chemical changes of MPs due to UV-VIS weathering, and 2) compared the effect of pristine and aged MPs on the behaviour of the water flea Daphnia magna and terrestrial crustacean Porcellio scaber. Dry powders of MPs were produced from widely used polymer types: disposable three-layer polypropylene (PP) medical masks (inner, middle and outer), polyester textile fibres, car tires and low-density polyethylene (LDPE) bags and were subjected to accelerated ultraviolet-visible (UV-VIS) ageing. Our results show that the extent of transformation depends on the type of polymer, with PP showing the most changes, followed by LDPE, textile fibres and tire particles. Obvious fragmentation was observed in PP and textile fibres. In the case of PP, but not polyester textile fibres, changes in FTIR spectra and surface properties were observed. Tire particles and LDPE did not change in size, but clear changes were observed in their FTIR spectra. Most MPs, aged and pristine, did not affect the swimming of daphnids. The only effect observed was a significant increase in path length and swimming speed for the pristine tire particles when the recording was done with particles remaining in the wells. After transfer to a clean medium, this effect was no longer present, suggesting a physical rather than chemical effect. Similarly, woodlice showed no significant avoidance response to the MPs tested, although there was a noticeable trend to avoid soils contaminated with pristine polyester textile fibers and preference towards the soils contaminated with aged MP of the middle mask layer. Overall, the apparent changes in physico-chemical properties of MPs after accelerated ageing were not reflected in their effects on woodlice and daphnids.

Ecotoxicological assessment of waste foundry sands and the application of different classification systems.

The application of a battery of bioassays is widely recognized as a useful tool for assessing environmental hazard samples. However, the integration of different toxicity data is a key aspect of this assessment and remains a challenge. The evaluation of industrial waste leachates did not initially undergo any of the proposed integration procedures. This research addressed this knowledge gap. Twenty-five samples of waste foundry sands were subjected to a leaching test (UNI EN 12457-2) to evaluate waste recovery and landfill disposal. The leachates were evaluated using a battery of standardized toxicity bioassays composed of Aliivibrio fischeri (EN ISO 11348-3), Daphnia magna (UNI EN ISO 6341), and Pseudokirchneriella subcapitata (UNI EN ISO 8692), both undiluted and diluted. Daphnia magna and P. subcapitata were the most affected organisms, with significant effects caused by 68% and 64% of undiluted samples, respectively. The dilution of samples facilitates the calculation of EC50 values, which ranged from greater than the highest concentration tested to 2.5 g/L for P. subcapitata. The data on single-organism toxicity were integrated using three methods: the Toxicity Classification System, the toxicity test battery integrated index, and the EcoScore system. The three classifications were strongly similar. According to all applied systems, three samples were clearly nontoxic (from iron casting plants) and two were highly toxic (from steel casting plants). Moreover, the similar ranking between undiluted and diluted leachates suggests the possibility of using only undiluted leachates for a more cost-effective and time-efficient screening of waste materials. The findings of this study highlight the usefulness of integrating ecotoxicological waste assessment. Integr Environ Assess Manag 2024;00:1-18. © 2024 The Author(s). Integrated Environmental Assessment and Management published by Wiley Periodicals LLC on behalf of Society of Environmental Toxicology & Chemistry (SETAC).

Granulated rubber in playgrounds and sports fields: A potential source of atmospheric plastic-related contaminants and plastic additives after runoff events.

The use of "crumb rubber" coming from recycling materials in outdoor floors like playgrounds has been a frequent practice during the last years. However, these surfaces are object of abrasion and weathering being a potential source of micro and nanoplastics (MNPLs) to the atmosphere and a potential source of human exposure to them. Our main goal has been to expose different crumb rubber materials to summer weathering effects. The released inhalable fractions were sampled for two months with passive samplers and the composition of MNPLs and plastic additives (organic and inorganic) were evaluated. The ecotoxicological effects of leached materials emulating runoff events was evaluated in freshwater micro crustacean Daphnia magna and the green algae Chlorella vulgaris. The analysis of MNPLs showed the presence of polyethylene, polypropylene, polybutadiene, polysiloxanes and polybutylene at concentrations up to 30,426 ng/m3. In the same fraction, we also identified up to 56 plastic additives, including antioxidants, pigments, copolymers, flame retardants, fungicides, lubricants, plasticizers, UV filters and metal ions. Finally, runoff ecotoxicological effects on D. magna and C. vulgaris showed that leached compounds, either from virgin or aged material, would be toxicants for exposed organisms although at concentrations much higher than those expected to be released to the media.

Trehalose mediates salinity-stress tolerance in natural populations of a freshwater crustacean.

Salinization poses an increasing problem worldwide, threatening freshwater organisms and raising questions about their ability to adapt. We explored the mechanisms enabling a planktonic crustacean to tolerate elevated salinity. By gradually raising water salinity in clonal cultures from 185 Daphnia magna populations, we showed that salt tolerance strongly correlates with native habitat salinity, indicating local adaptation. A genome-wide association study (GWAS) further revealed a major effect of the Alpha,alpha-trehalose-phosphate synthase (TPS) gene, suggesting that trehalose production facilitates salinity tolerance. Salinity-tolerant animals showed a positive correlation between water salinity and trehalose concentrations, while intolerant animals failed to produce trehalose. Animals with a non-functional TPS gene, generated through CRISPR-Cas9, supported the trehalose role in salinity stress. Our study highlights how a keystone freshwater animal adapts to salinity stress using an evolutionary mechanism known in bacteria, plants, and arthropods.

Accumulation, depuration, and potential effects of environmentally representative microplastics towards Daphnia magna.

Microplastic risk assessment often characterizes primary plastics, plastics intentionally manufactured at the micro- and nanoscale, or plastics collected within the natural environment, which often lack repeatability and the volume necessary for reliable hazard characterization. There is limited understanding of how environmentally representative plastics prepared at the microscale impact aquatic organisms. The aim of the present study was to create environmentally representative microplastics and characterize their toxicokinetics and hazards. Plastic cups and forks were micronized to <120 µm particles and Daphnia magna were exposed for 48 h at concentrations ranging from 0.01 mg/L to 100 mg/L. Uptake and depuration experiments were conducted at the highest concentration where accumulation was confirmed. Raman spectroscopy identified that both plastics were polystyrene and had similar size distributions. Microplastics were not acutely toxic but accumulated and rapidly depurated. Toxicokinetics demonstrated that cup MPs were consumed at higher rates than fork MPs despite similar physical characteristics. Daphnia magna preferentially selected smaller particles from the heterogenous suspensions. Future research will need to further explore the relationship between physicochemical properties, particularly size, and ecotoxicity. The study focused on mortality as the primary hazard endpoint. However alternative, sublethal biomarkers may be more appropriate in describing the effects of microplastic exposure.

Dragon fruit-derived oligosaccharides alter hemocyte-mediated immunity and expression of genes related to innate immunity and oxidative stress in Daphnia magna.

Dragon fruit oligosaccharide (DFO) is an indigestible prebiotic that enhances the growth and reproduction of Daphnia magna, increases the expression of genes involved in immunity, and reduces oxidative stress. This study investigated the effects of DFO on the expression of innate immunity- (Toll, Pelle, proPO, A2M, and CTL), oxidative stress- (Mn-SOD), and nitric oxide (NO) synthesis-related genes (NOS1, NOS2, and arginase) as well as NO localization and number of hemocytes in D. magna. For this ten-day-old D. magna were treated with 0 or 9 mg l-1 of DFO for 24 and 85 h. Gene expression levels, NO intensity and localization, and total hemocytes were evaluated. After 24 h, the expression of Toll and proPO increased significantly (p < 0.05), while that of C-type lectins (CTL) was reduced (p < 0.05). At 85 h, Mn-SOD and CTL expressions were markedly suppressed (p < 0.05). NO was mostly localized in the foregut, midgut, hindgut, and carapace. The expression of NOS1 was reduced after 24 h (p < 0.05). In addition, NO intensity at 24 h was insignificantly lower than the control (p > 0.05). At 85 h, the expression of NOS1, NOS2, and arginase was higher than control, but NO intensity did not differ significantly (p > 0.05). Furthermore, the total hemocyte count elevated remarkably at 85 h (p < 0.05). Our study suggested that 9 mg l-1 of DFO could alter the expression of the genes related to innate immunity, oxidative stress, and NO synthesis in D. magna and significantly stimulate hemocyte production.

Ecotoxicological assessment, in freshwater environment, of wastewater sludge coupled and uncoupled with micro-polyvinyl chloride on algae and water fleas.

In the frame of bioeconomy and circular economy, wastewater sludge (WS) could be a good candidate for its use in agriculture as fertilizer, due to its high content of organic matter, N and P, but on the other hand, it is full of toxicants such as heavy metal, microplastics, detergent, antibiotics, and so on that can reach groundwater and water bodies in leachate form. In this study, we have investigated different sludge concentrations in the eluate form, combined and not with PVC on two different freshwater organisms Selenastrum capricornutum and Daphnia magna, using ecotoxicity tests. At the endpoint, we have evaluated inhibition growth rate, oxidative stress, and pigments production for S. capricornutum, while in case of D. magna, we have assessed organism immobilization and development. From our results, it emerged that at the higher WS concentration, there was not inhibition growth rate, while at oxidative stress, it was higher in algae treated with WS and PVC. Higher Chl-a production was shown for algae treated with 0.3 g/L of sludge coupled with PVC, where higher phaeopigments production were recorded for algae treated with 0.3 g/L of WS. D. magna has shown an opposite trend when compared with algae, where at the highest WS concentrations supplied was corresponding to an increased mortality explaned as the highest immobility percentage. PRACTITIONER POINTS: Wastewater sludge is used in agriculture as fertilizer. PVC microplastic presence and associate ecotoxicity was tested. PVC presence increased oxidative stress in S. capricornutum. D. magna was significantly affected by sludge concentrations supplied.

Non-chemical stresses do not strongly induce male offspring in Daphnia magna ascertained using the short-term juvenile hormone activity screening assay.

Juvenile hormone (JH), together with ecdysone, regulates molting, metamorphosis, growth, and reproduction in arthropods. The effects of its analogs used as insecticides on nontarget species are of concern. Since JH and JH analogs (JHAs) induce male offspring in daphnids, which generally reproduce by parthenogenesis, short-term JH activity screening assay (JHASA) using the male offspring ratio as an endpoint has been developed as a detection method for JHA. However, the production of male offspring is also induced by environmental stresses such as temperature, short-day length, overcrowding, and food limitation. Thus, it is vital to prevent non-chemical stresses from inducing male offspring during the test to detect chemicals with potential JH activity accurately. Therefore, we investigated the effects of temperature (low and high), hardness, high density with low feeding, and day length on male production utilizing JHASA. Male offspring were not strongly induced by any stresses in JHASA, although the male ratios of 4-12% were observed in the preculture under high density (≥70 daphnid/L) and constant darkness. The Clone A strain was relatively more sensitive to high density and day length compared with the strain from National Institute for Environmental Studies (NIES). The selection of strains that rarely produce males under non-chemical stresses and finding the culturing conditions for each strain appropriate for not-inducing male offspring are recommended to control and prevent male offspring induction during JHASA.

A Novel Method for the Assessment of Feeding Rate as a Phenotypic Endpoint for the Impact of Pollutants in Daphnids.

Traditional approaches for monitoring aquatic pollution primarily rely on chemical analysis and the detection of pollutants in the aqueous environments. However, these methods lack realism and mechanistic insight and, thus, are increasingly supported by effect-based methods, which offer sensitive endpoints. In this context, daphnids, a freshwater species used extensively in molecular ecotoxicology, offer fast and noninvasive approaches to assess the impact of pollutants. Among the phenotypic endpoints used, feeding rate is a highly sensitive approach because it provides evidence of physiological alterations even in sublethal concentrations. However, there has been no standardized method for measuring feeding rate in daphnids, and several approaches follow different protocols. There is a diversity among tests employing large volumes, extensive incubation times, and high animal densities, which in turn utilize measurements of algae via fluorescence, radiolabeling, or counting ingested cells. These tests are challenging and laborious and sometimes require cumbersome instrumentation. In the present study, we optimized the conditions of a miniaturized fast, sensitive, and high-throughput assay to assess the feeding rate based on the ingestion of fluorescent microparticles. The protocol was optimized in neonates in relation to the concentration of microplastic and the number of animals to increase reproducibility. Daphnids, following exposures to nonlethal concentrations, were incubated with microplastics; and, as filter feeders, they ingest microparticles. The new approach revealed differences in the physiology of daphnids in concentrations below the toxicity limits for a range of pollutants of different modes of action, thus proving feeding to be a more sensitive and noninvasive endpoint in pollution assessment. Environ Toxicol Chem 2024;43:2211-2221. © 2024 The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Impacts of UV light on the effects of either conventional or nano-enabled azoxystrobin on Daphnia magna.

Agri-chemicals such as fungicides are applied in natural settings and hence are exposed to the environment's ultraviolet (UV) light. Recently, many fungicides in commerce are being modified as nano-enabled formulations to increase agricultural productivity and reduce potential off-target effects. The present study investigated the impacts of sunlight-grade UV emission on the effects of either conventional or nano-enabled azoxystrobin (Az or nAz, respectively), a commonly applied agricultural fungicide, on Daphnia magna. Daphnids were exposed to increasing concentrations of Az or nAz under either full-spectrum (Vis) or full-spectrum Vis + UV (Vis + UV) lighting regimes to evaluate LC50s. Az LC50 was calculated at 268.8 and 234.2 µg/L in Vis or Vis + UV, respectively, while LC50 for nAz was 485.6 and 431.0 µg/L under Vis or Vis + UV light, respectively. Daphnids were exposed to 10% LC50 of either Az or nAz under Vis or Vis + UV lighting regime for 48 h or 21 d (acute and chronic, respectively). By 48 h, both Az and nAz reduced O2 consumption and increased TBARS. Heart rate was increased in Az-exposed daphnids but not in nAz groups. Neither of the two chemicals impacted thoracic limb activity. In 21 d exposures, Az significantly reduced biomass production and fecundity, but nAz groups were not significantly different from controls. The results of the present study demonstrate that conventional Az is more toxic to D. magna at lethal and sub-lethal levels in acute and chronic exposures, and sunlight strength UV can potentiate both acute and chronic effects of Az and nAz on D. magna.

Inhibitory effects of toxic Dolichospermum flos-aquae and anatoxin-a on inducible defenses of Daphnia magna.

Cyanobacterial blooms, resulting from serious eutrophication, can produce various cyanotoxins and severely disrupt aquatic ecosystems. Inducible defenses are adaptive traits developed by prey in response to predation risks. However, the effects of the increasing proportion of cyanobacteria and cyanotoxins produced during cyanobacterial blooms on the inducible defenses of cladocerans, particularly in terms of behavioral defenses, remain unclear. In this study, we selected Daphnia magna and investigated the defensive traits against predation risks by the predator Rhodeus ocellatus under different ratios of cyanobacteria (Dolichospermum flos-aquae) and green algae (Scenedesmus obliquus), as well as varying concentrations of anatoxin-a (ATX), a cyanotoxin. We recorded the inducible defensive traits involving to morphology, behavior, and offspring production of D. magna. Results showed that the body length of D. magna at sexual maturity and the number of offspring in the first brood were significantly reduced by the presence of D. flos-aquae. Moreover, when the proportion of D. flos-aquae reached 75% and 100%, D. magna did not develop to sexual maturity. Furthermore, D. flos-aquae inhibited the formation of inducible behavioral defense of D. magna, with a stronger inhibitory effect as the proportion of D. flos-aquae increased. In this experiment, the effects of ATX on the morphological traits at sexual maturity and offspring production of D. magna were minor, but ATX still had the potential to inhibit the formation of inducible behavioral defense. We confirmed that changes in the proportion of cyanobacteria and green algae as well as the production of ATX by cyanobacteria during cyanobacterial blooms can affect the growth, development, and inducible defensive traits of cladocerans, potentially altering their population dynamics during such events.

Developing a Passive Dosing Method for Acute Aquatic Toxicity Tests of Cationic Surfactant Benzalkoniums (BACs).

Benzalkonium chlorides (BACs) have been of environmental concern due to their widespread use and potential harm. However, challenges arise in defining and controlling the exposure concentration (Cw) in aquatic toxicity tests involving BACs with a long alkyl chain (i.e., #C > 14). To address this, a novel passive dosing method was introduced in the 48 h-acute ecotoxicity test on Daphnia magna and compared to the conventional solvent-spiking method in terms of Cw stability and toxicity results. Among 13 sorbent materials tested for their sorption capacity, poly(ether sulfone) (PES) membrane was an optimal passive dosing reservoir, with equilibrium desorption of BACs to water achieved within 24 h. The Cw of BACs remained constant in both applied dosing methods during the test period. However, the Cw in solvent-spiking tests was lower than the nominal concentration for long-chain BACs, particularly at low exposure concentrations. Notably, the solvent-spiking tests indicated that the toxicity of BACs increased with alkyl chain length from C6 to 14, followed by a decline in toxicity from C14 to 18. In contrast, the passive dosing method displayed similar or slightly increasing toxicity levels of BACs from C14 to C18, indicating higher toxicity of C16 and C18-BACs than that inferred by the solvent spiking test. These findings emphasize the potential of applying this innovative passive dosing approach in aquatic toxicity tests to generate reliable and accurate toxicity data and support a comprehensive risk assessment of cationic surfactants.

Suspended particulate matter-biofilm aggregates benefit microcystin removal in turbulent water but trigger toxicity toward Daphnia magna.

Suspended particulate matter (SPM) and biofilm are critical in removing contaminants in aquatic environments, but the environmental behavior and ecological toxicity of SPM-biofilm aggregates modulated by turbulence intensities are largely unknown. This study determined the removal pathways of microcystin-LR (MC-LR) by SPM and its biofilm under different turbulence intensities (2.25 × 10-3, 1.01 × 10-2, and 1.80 × 10-2 m2/s3). Then, we evaluated the toxicity of SPM-biofilm aggregates to Daphnia magna. The results revealed that SPM contributed to the adsorption of MC-LR, and the removal of MC-LR can be accelerated with biofilm formation on SPM, with 95.66 % to 97.45 % reduction in MC-LR concentration under the studied turbulence intensities. Higher turbulence intensity triggered more frequent contact of SPM and MC-LR, formed compact but smaller clusters of SPM-biofilm aggregates, and enhanced the abundance of mlrA and mlrB; thus benefiting the adsorption, biosorption, and biodegradation of MC-LR. Furthermore, the SPM-biofilm aggregates formed in turbulent water triggered oxidative stress to Daphnia magna, while a weak lethal toxic effect was identified under moderate turbulence intensity. The results indicate that the toxicity of SPM-biofilm aggregates fail to display a linear relationship with turbulence intensity. These findings offer new perspectives on understanding the environmental behavior and ecological outcomes of SPM and its biofilms in turbulent aquatic environments.

Ecological risks of high-ammonia environment with inhibited growth of Daphnia magna: Disturbed energy metabolism and oxidative stress.

High ammonia pollution is a common problem in water bodies. However, research on the mechanisms underlying the toxic effects on organisms at different nutritional levels is still insufficient. Herein, based on the environmental concentration, the toxic effects of high ammonia pollution on Daphnia magna were investigated. Overall, the feeding and filtration rates of D. magna were significantly decreased by ammonia. Growth inhibition of D. magna by ammonia was confirmed by the decreased body length. After ammonia exposure, the metabolic status of D. magna changed, the correlation network weakened, and the correlations between metabolites were disrupted. Changes occurred in metabolites primarily involved in oxidative stress, fatty acid oxidation, tricarboxylic acid cycle, and protein digestion, absorption, and synthesis, which were validated through alterations in multiple biomarkers. In addition, mitochondrial function was evaluated and was found to inhibit mitochondrial activity, which was accompanied by a decreased marker of mitochondrial activity contents and ATPase activity. Thus, the results suggested that energy metabolism and oxidative stress were involved in ammonia-induced growth toxicity. This study provides new insights into the impact of ammonia on aquatic ecological health.