Chronic effects of temperature and nitrate pollution on Daphnia magna: Is this cladoceran suitable for widespread use as a tertiary treatment?

Feeding on stressed algae exerts important effects on life history traits of Daphnia magna in a multi-stressor environment

Freshwater ecosystems are increasingly exposed to anthropogenic eutrophication, including high nitrogen. In addition, climate change is leading to more intense and frequent heatwaves, which have enormous impacts on all trophic levels of the ecosystem. Any change in the lower trophic levels, e.g., the phytoplankton, also introduces stress to higher trophic levels e.g., the zooplankton crustacean Daphnia. Individual effects of heatwaves, high nitrate, and changing feed quality have been studied in daphnia, but less is known about their interactive effects. This study used a 3 × 3 × 2 factorial design in which daphnia were exposed to combinations of ecologically relevant nitrate concentrations (0, 50, or 200 mg/L) and different heatwave scenarios (no, short-moderate, or long-intense) in which individuals were either fed with microalgae (P. subcapitata and C. reinhardtii) grown at 20 °C and 50 mg/L nitrate (control feed) or the same conditions as daphnia was exposed to (experimental feed). Throughout the experiment, the interactive effects of high nitrate, heatwave, and feed on mortality, maturation, offspring, and body size were evaluated. In general, heatwaves shorten the lifespan of daphnia. Exposing daphnia to a long-intense heatwave combined with high nitrate resulted in poor performance. In the nitrate-limited condition, however, the restricted proliferation of microalgae reduced feed availability, which also had a major impact on daphnia's life history traits. Daphnia cultured in high nitrate and fed control feed performed better than when fed experimental feed, suggesting that in a high nitrate condition, the microalgae grown under the same experimental conditions was either unable to meet energy requirements or introduced extra stress for the daphnia. Most importantly, the effect of nitrate and heatwave as stressors on the availability and quality of the feed had a greater impact on daphnia than its direct impact. Interestingly, a transgenerational adaptation to nitrate was observed which may help to maintain ecological balance in the long run.

Deep dive into the chronic toxicity of tyre particle mixtures and their leachates

Particles from the tread of vehicle tyres are a global pollutant, which are emitted into the environment at an approximate rate of 1.4 kg.year-1 for an average passenger-car. In this study, popular tyre brands were used to generate a tyre tread microparticle mixture. The chronic toxicity of both particles and chemical leachates were compared on a planktonic test species (Daphnia magna). Over 21 days of exposure, pristine tyre tread microparticles were more toxic (LC50 60 mg.L-1) than chemical lechates alone (LC50 542 mg.L-1). Microparticles and leachates showed distinct effects on reproduction and morphological development at environmentally relevant concentrations, with dose-dependent uptake of particles visible in the digestive tract. Chemical characterization of leachates revealed a metal predominance of zinc, titanium, and strontium. Of the numerous organic chemicals present, at least 54 were shared across all 5 tyre brands, with many classified to be very toxic. Our results provide a critically needed information on the toxicity of tyre tread particles and the associated chemicals that leach from them to inform future mitigation measures. We conclude that tyre particles are hazardous pollutants of particular concern that are close to or possibly above chronic environmental safety limits in some locations.

Zooplankton vulnerability to glyphosate exacerbated by global change

Anthropogenic activities generate a severe footprint at a global scale. Intensive agriculture is a global change driver that affects aquatic systems due to the discharge of pollutants. This situation can be modified or aggravated by other aspects, such as the disturbance history and other global change factors. Following our study line, it is necessary to evaluate how the disturbance history combined with temperature changes can affect the functioning of aquatic systems. The objectives of this study were divided into two phases. The objectives of phase 1 were to induce vulnerability in Daphnia magna populations through a disturbance history based on sublethal glyphosate concentration exposure under different temperature conditions (20 °C and 25 °C). In phase 2, vulnerability was assessed through the exposure to subsequent stressors (starvation, increased salinity and paracetamol) combined with changes in temperature. During the glyphosate exposure period in phase 1, differences were observed in the D. magna populations with respect to temperature, with lower abundance at 25 °C than at 20 °C. However, no differences were observed in abundance regarding glyphosate treatment. The results obtained in phase 2 with the new stressors combined with temperature changes in both directions, revealed stronger effects in vulnerable populations than in control populations. In addition, the temperature changes modulated the effects in the starvation and increased salinity tests. Agrochemical sublethal concentrations induce vulnerability in D. magna populations and inflicted temperature changes can act as a modulating factor for this vulnerability, showing the complexity in assessing the responses under the multiple scenarios associated with global change.

Ecotoxicity characterization assisted performance assessment of electro-bioremediation reactors for nitrate and arsenite elimination

The performance of combined reduction of nitrate (NO3 - ) to dinitrogen gas (N2 ) and oxidation of arsenite (As[III]) to arsenate (As[V]) by a bioelectrochemical system was assessed, supported by ecotoxicity characterization. For the comprehensive toxicity characterization of the untreated model groundwater and the treated reactor effluents, a problem-specific ecotoxicity test battery was established. The performance of the applied technology in terms of toxicity and target pollutant elimination was compared and analyzed. The highest toxicity attenuation was achieved under continuous flow mode with hydraulic retention time (HRT) = 7.5 h, with 95%, nitrate removal rate and complete oxidation of arsenite to arsenate. Daphnia magna proved to be the most sensitive test organism. The results of the D. magna lethality test supported the choice of the ideal operational conditions based on chemical data analysis. The outcomes of the study demonstrated that the applied technology was able to improve the groundwater quality in terms of both chemical and ecotoxicological characteristics. The importance of ecotoxicity evaluation was also highlighted, given that significant target contaminant elimination did not necessarily lower the environmental impact of the initial, untreated medium, in addition, anomalies might occur during the technology operational process which in some instances, could result in elevated toxicity levels.

Environmental safety of second and third generation bioplastics in the context of the circular economy

Bioplastics derived from organic materials other than crude oil are often suggested as sustainable solutions for tackling end-of-life plastic waste, but little is known of their ecotoxicity to aquatic species. Here, we investigated the ecotoxicity of second and third generation bioplastics toward the freshwater zooplankton Daphnia magna. In acute toxicity tests (48 h), survival was impacted at high concentrations (g.L^-1 range), within the range of salinity-induced toxicity. Macroalgae-derived bioplastic induced hormetic responses under chronic exposure (21 d). Most biological traits were enhanced from 0.06 to 0.25 g.L^-1 (reproduction rate, body length, width, apical spine, protein concentration), while most of these traits returned to controls level at 0.5 g.L^-1. Phenol-oxidase activity, indicative of immune function, was enhanced only at the lowest concentration (0.06 g.L^-1). We hypothesise these suggested health benefits were due to assimilation of carbon derived from the macroalgae-based bioplastic as food. Polymer identity was confirmed by infra-red spectroscopy. Chemical analysis of each bioplastic revealed low metal abundance whilst non target exploration of organic compounds revealed trace amounts of phthalates and flame retardants. The macroalgae-bioplastic disintegrated completely in compost and biodegraded up to 86 % in aqueous medium. All bioplastics acidified the test medium. In conclusion, the tested bioplastics were classified as environmentally safe. Nonetheless, a reasonable end-of-life management of these safer-by-design materials is advised to ensure the absence of harmful effects at high concentrations, depending on the receiving environment.

Effects of two submerged macrophyte species on microbes and metazoans in rooftop water-storage ponds with different labile carbon loadings

Nature-based solutions including rooftop-water storage ponds are increasingly adopted in cities as new eco-designs to address climate change issues, such as water scarcity and storm-water runoff. Macrophytes may be valuable additions for treating stored rooftop waters and provisioning other services, including aquaponics, esthetic and wildlife-conservation values. However, the efficacy of macrophyte treatments has not been tested with influxes of different labile carbon loadings such as those occurring in storms. Moreover, little is known about how macrophytes affect communities of metazoans and microbes, including protozoans, which are key players in the water-treatment process. Here, we experimentally investigated the effectiveness of two widely distributed macrophytes, Ceratophyllum demersum and Egeria densa, for treating drained rooftop water fed with two types of leaf litter, namely Quercus robur (high C lability) and Quercus rubra (low C lability). C. demersum was better than E. densa at reducing water conductivity (by 10 ̶ 40 µS/cm), TDS (by 10-18 mg/L), DOC (by 4-5 mg/L) and at increasing water transparency (by 4-9%), water O₂ levels (by 19-27%) and daylight pH (by 0.9-1.3) compared to leaf-litter only microcosms after 30 days. Each treatment developed a different community of algae, protozoa and metazoa. Greater plant mass and epiphytic chlorophyll-a suggested that C. demersum was better at providing supporting habitat than E. densa. The two macrophytes did not differ in detritus accumulation, but E. densa was more prone to develop filamentous bacteria, which cause sludge bulking in water-treatment systems. Our study highlights the superior capacity of C. demersum and the usefulness of whole-ecosystem experiments in choosing the most adequate macrophyte species for nature-based engineered solutions.

Zooplankton-based reactors for tertiary wastewater treatment: A pilot-scale case study

Nature-based wastewater treatments are an economic and sustainable alternative to intensive technologies in rural areas, although their efficiency needs to be improved. This study explores technological co-operation between zooplankton (e.g., Daphnia magna) and bacterial and algal biofilms in a 1.5 m³ zooplankton-based reactor for the on-site treatment of secondary urban wastewater. The efficiency of the reactor was evaluated over a 14-month period without any maintenance. The results suggest a low seasonality effect on nutrient polishing (organic matter and nitrogen) and the removal of solids (TSS and turbidity). The best performance, involving a decrease in organic carbon, nitrogen, E. coli loads, and solid content was achieved in winter when operating the reactor at 750 L d^-1. Under these conditions, the quality of the effluent water was suitable for its reuse for six different purposes in conformance with Spanish legislation. These results demonstrate that the zooplankton-based reactor presented here can be used as an eco-sustainable tertiary treatment to provide water suitable for reuse. On-site research revealed that the robustness of the reactor against temperature and oxygen fluctuations needs to be improved to ensure good performance throughout the year.

Mixture toxicity effects of chloramphenicol, thiamphenicol, florfenicol in Daphnia magna under different temperatures

Acute toxicities of chloramphenicol (CAP), thiamphenicol (TAP), and florfenicol (FLO) and their mixtures on Daphnia magna under two representative temperatures of the aquatic environment (20 and 25 °C) have been examined. Their toxicities depicted with an order of 72-h EC₅₀ values were as follows: CAP > FLO > TAP and CAP ≈ FLO > TAP under 20 and 25 °C, separately. Furthermore, the acute toxicity significantly increased with the rise of temperature from 20 to 25 °C in nearly all separate and mixture phenicol antibiotics. Meanwhile, the most toxic combination under two different temperatures was diverse. The nature of toxicological interactions of phenicol antibiotic mixtures was analyzed by Combination Index (CI) equation. In general, a dual synergism-antagonism effect was dominant in nearly all mixtures at both temperatures. The prediction suitability of Concentration Addition (CA), Independent Action (IA) models, and CI method was compared, suggesting that the CI equation seems to be more appropriate for predicting the toxicity values of phenicol drugs than CA and IA models. In brief, phenicol antibiotic mixtures with temperature variation may pose more significant hazards and risks to aquatic organisms; hence, the environment.

Synergistic effects of water temperature, microplastics and ammonium as second and third order stressors on Daphnia magna

Daphnids, including the water flea Daphnia magna, can be exploited for wastewater treatment purposes, given that they are filter feeder organisms that are able to remove suspended particles from water. The presence of pollutants, such as microplastics and chemicals, might be considered stressors and modify the behaviour and survival of D. magna individuals. The impact of the cumulative pollutants that regulate the fate of living organisms has yet to be fully determined. Here we present the effect of double and triple combinations of stressors on the behaviour of D. magna. The impact of water temperature, ammonium and polystyrene microplastics on the filtration capacity and survival of D. magna is studied. Water temperatures of 15 °C, 20 °C and 25 °C, microplastic-to-food ratios of 25% and 75%, and ammonium concentrations of 10 and 30 mg N-NH₄⁺ L^-1 are tested after making dual and triple combinations of the parameters. A synergistic effect between water temperature and ammonium is normally observed but not in the case of the lower values of ammonium concentration and temperature. The combination of three stressors (water temperature, microplastics and ammonium) is also found to be synergistic, producing the greatest impact on D. magna filtration capacity and reducing their survival. In comparison with the effect of the two stressor conditions, the combination of the three stressors caused a reduction of between 13.1% and 91.7% in the t_50% time (the time required for a 50% reduction in the D. magna filtration capacity) and a reduction of between 4.8% and 54.5% in TD50 (the time for 50% mortality).

Assessment of zooplankton-based eco-sustainable wastewater treatment at laboratory scale

The combination of the filtration capacity of zooplankton (e.g. Daphnia) with the nutrient removal capacity of bacterial/algal biofilm in a zooplankton-containing reactor could provide a natural-based alternative for wastewater treatment. A laboratory-scale zooplankton-based reactor was tested at different HRTs resulting in a significant reduction in nutrient concentrations in wastewater when the system was operated at HRTs longer than 1.1 days (preferably of between 2 and 4 days). However, the presence of high concentrations of organic matter (>250 mg COD L^-1) in the wastewater inhibited zooplankton activity, limiting its use to tertiary treatment. Therefore, in combination with other natural treatments that can perform primary and secondary treatments, zooplankton may provide a solution for wastewater clarification and nutrient polishing. The effect of a common metal such as copper on the filtration capacity of Daphnia was also evaluated. Daphnia, as well as the whole zooplankton-based reactor, adapted to copper concentrations of up to 70 μg Cu L^-1 but an overload of 380 μg Cu L^-1 for two-weeks severely affected the biological system.

Microbial levan and pullulan as potential protective agents for reducing adverse effects of copper on Daphnia magna and Vibrio fischeri

Microbial polysaccharides, due to their unique physiochemical properties, have found application in the food industry, cosmetics, pharmacy and medicine. In the environment, microbes can use polysaccharides to alleviate the adverse effects of heavy metals in their close proximity. This adaptive property shows interesting potential for bioremediation. Herein, the effects of the exopolysaccharides (EPS) levan, produced by the bacterium Bacillus licheniformis NS032 and pullulan, produced by the fungus Aureobasidium pullulans CH-1 in the presence of copper (Cu²⁺) have been investigated for the first time on antioxidant enzyme activity, respiration and Cu²⁺ bioaccumulation of Daphnia magna as well as the bioluminescence of Vibrio fischeri. Both EPS decreased toxicity of Cu²⁺ in the acute test with D. magna. The activity of catalase (CAT) was significantly diminished after acute exposure to Cu²⁺ in comparison to treatments with Cu²⁺ and EPS, while in the prolonged acute exposure the CAT activity did not show statistically significant (P ≤ 0.05) differences between treatments with and without the EPS. According to ICP-MS results, during prolonged acute exposure of neonates, the bioaccumulation of Cu²⁺ in treatments without the EPS was 52.03 μg/g of biomass (wet), while in treatments with EPS, the bioaccumulation was lower by one order of magnitude. The respiration of neonates during acute exposure to Cu²⁺ with or without the EPS was monitored using the MicroOxymax respirometer, and the results show the EPS can positively effect the respiration. In the case of bacterial bioluminescence, the toxicity of Cu²⁺ decreased in treatments with EPS (30 min EC₁₀) from 3.54 mg/L to 140.61 mg/L (levan) and 45.00 mg/L (pullulan). This study demonstrates protective effect of EPS against Cu²⁺ toxicity on D. magna and V. fischeri, and opens the door for further investigation of potential application of levan and pullulan in bioremediation of heavy metals and mitigation of their adverse effects in the aquatic environment.

Effects of Silver Nitrate are a Conservative Estimate for the Effects of Silver Nanoparticles on Algae Growth and Daphnia magna Reproduction

Silver (Ag) salts have been shown to be highly toxic to freshwater organisms. There is nevertheless still a high level of uncertainty as to the aquatic effects of Ag nanoparticles (AgNPs), and how these relate to the effects of soluble Ag salts. As part of the substance evaluation for Ag of the European Union Registration, Evaluation, Authorisation, and Restriction of Chemicals regulation, we have generated new data to justify read-across from soluble Ag salts to AgNPs. The aquatic toxicity to algae growth and Daphnia magna reproduction, fate, and behavior of AgNO₃ versus AgNPs were tested and compared. Chloride salts in the test media were replaced with equimolar concentrations of nitrate salts. Total Ag, "conventionally" dissolved Ag (0.45 µm), and "truly" dissolved Ag (3 kDa) were determined. Algae were the most sensitive test species to AgNO₃ (10% effect concentration [EC10] 0.10 µg Ag/L) when expressed as conventionally dissolved Ag. The corresponding value for AgNPs was 0.26 µg/L. For D. magna reproduction, the lowest EC10 values were 3.49 µg Ag/L for AgNO₃ and 33.4 µg Ag/L for AgNPs. Using measured Ag concentrations, AgNO₃ was experimentally shown to be more toxic than AgNPs for all Ag fractions. We explain these observations by a different dissolution behavior of AgNO₃ versus AgNPs. The results provide experimental confirmation that AgNO₃ can be used as a conservative estimate for the aquatic effects of AgNPs at comparable Ag concentrations. Environ Toxicol Chem 2019;38:1701-1713. © 2019 SETAC.

Daphnia magna filtration, swimming and mortality under ammonium, nitrite, nitrate and phosphate

Biological methods are a promising approach to treating wastewater in order to produce water of an appropriate quality for sub-potable water purposes, thus reducing pressure on potable water sources. Daphnia magna are organisms that filter on small suspended particles and bacteria and so may be able to clarify and disinfect wastewater. However, Daphnia magna are sensitive to common chemicals and might be vulnerable to the quality of the wastewater. This study analyses the filtration, mobility and mortality rates of Daphnia magna exposed to seven days of changing concentrations of ammonium, nitrite, nitrate and phosphate. Inactivation increased with the time of exposure for both nitrite and ammonium, with a 50% inactivation in Daphnia magna filtrations after 7 days of exposure at nitrite concentrations above 6 ppm and ammonium concentrations above 40 ppm. The Daphnia filtration remained unaltered in the nitrate and phosphate concentrations. Mortality increased with nitrite and ammonium concentrations, but not with phosphate or nitrate. The swimming velocity of Daphnia magna individuals decreased when both nitrite and ammonium concentrations increased and also with phosphate concentrations above 30 ppm. However, Daphnia magna swimming velocities remained unaltered in the presence of nitrate concentrations below 100 ppm.

Functional responses of Daphnia magna to zero-mean flow turbulence

Daphnia are important to understanding the biogeochemistry of aquatic ecosystems, mainly because of their ability to filter bacteria, algae and inorganic particles as well. Although there are many studies on the general effects that biotic and abiotic stressors, increased temperature and hypoxia, salinity, metals, pharmaceuticals, pesticides, etc., have on Daphnia populations, little is known about the impact elevated turbulence has. Here, we show that turbulence affects Daphnia magna survival, swimming behaviour and filtering capacity. Our data demonstrate that altering their habitat by induced mixing from turbulence, induces an increased filtering capacity of the Daphnia magna individuals, provided the level of background turbulence (defined by the dissipation of turbulent kinetic energy) is lower than ε = 0.04 cm² s⁻³. The filtering capacity reduced exponentially with increasing ε, and at ε > 1 cm² s⁻³ both mobility and filtration were suppressed and eventually led to the death of all the Daphnia magna individuals.

Temperature-driven response reversibility and short-term quasi-acclimation of Daphnia magna

Analysing the effect water temperature has on Daphnia magna is essential in anticipating the impact climate change will have on this freshwater zooplanktonic keystone species. While many authors have followed this line of research, few have covered an extensive temperature range or complex temperature change scenarios. Global warming is mostly associated with increased extreme temperature events, such as heat waves, as well as earlier and more intense thermal stratification. Both of these events may directly influence D. magna fitness, especially in those populations performing diel vertical migration (DVM). We analysed the effect water temperatures, ranging from 11 to 29°C, have on the filtration capacity (FC) of D. magna, to anticipate the effects of acclimation, temperature change rate (TCR) and potential reversibility of responses to such conditions. Results show that sudden temperature changes have an immediate negative impact on the FC of D. magna and is more severe at higher temperatures and higher TCRs. However, D. magna individuals have shown themselves to be capable of quasi-acclimating to temperatures ranging from 11 to 25°C in around a week and achieving much higher FCs; albeit never reaching the optimal FC achieved at 20°C. That said, 29°C is lethal for D. magna individuals within approximately five days. Finally, non-optimal temperature acclimated individuals can recover maximal FC within 2–4 days of the optimal long-term acclimation temperature (20°C) being re-established, thus proving temperature responses to be reversible.

Daphnia magna filtration efficiency and mobility in laminar to turbulent flows

Daphnia are filter feeder organisms that prey on small particles suspended in the water column. Since Daphnia individuals can feed on wastewater particles, they have been recently proposed as potential organisms for tertiary wastewater treatment. However, analysing the effects of hydrodynamics on Daphnia individuals has scarcely been studied. This study focuses then, on quantifying the filtration and swimming velocities of D. magna individuals under different hydrodynamic conditions. Both D. magna filtration and movement responded differently if the flow was laminar or if it was turbulent. In a laminar-dominated flow regime Daphnia filtration was enhanced up to 2.6 times that of a steady flow, but in the turbulent-dominated flow regime D. magna filtration was inhibited. In the laminar flow regime D. magna individuals moved freely in all directions, whereas in the turbulent flow regime they were driven by the streamlines of the flow. A model based on Daphnia-particle encountering revealed that the filtration efficiency in the laminar regime was driven by the length of the D. magna individuals and the shear rate imposed by the system.

Ecological impact and recovery of a Mediterranean river after receiving the effluent from a textile dyeing industry

The textile industry is one of the largest sectors globally, representing up to 20% of industrial water pollution. However, there is limited insight into how fluvial ecosystems respond and recover from this impact. From summer 2012 to spring 2013, we examined water quality and ecological status upstream and 1.5km downstream the input of a textile industry wastewater treatment plant (WWTP) in Ripoll River, NE Spain. The ecological status was determined via diversity measures and 10 biotic indices based on diatoms, macrophytes, macroinvertebrates and fish. Our results showed that the WWTP severely deteriorated water quality and biological communities at the discharge site, but that they improved at 1.5km downstream. Severity also varied across taxa and seasons, being fish the most affected taxa and spring the season with the best ecological status. The strong correlation amongst water quality variables and many biotic indices across taxa indicated that this is a chronic pollution event affecting multiple trophic levels. Thus, this study suggests that there is an urgent need to invest in wastewater treatment in this industry to preserve the ecological integrity of Ripoll River and especially its fish fauna. Likewise, it illustrates the diagnostic power of biotic indices based on diatoms, macroinvertebrates and fish, as driven by the European Water Framework Directive.

Chronic nitrate enrichment decreases severity and induces protection against an infectious disease

Excessive fertilisation is one of the most pernicious forms of global change resulting in eutrophication. It has major implications for disease control and the conservation of biodiversity. Yet, the direct link between nutrient enrichment and disease remains largely unexplored. Here, we present the first experimental evidence that chronic nitrate enrichment decreases severity and induces protection against an infectious disease. Specifically, this study shows that nitrate concentrations ranging between 50 and 250mgNO3(-)/l reduce Gyrodactylus turnbulli infection intensity in two populations of Trinidadian guppies Poecilia reticulata, and that the highest nitrate concentration can even clean the parasites from the fish. This added to the fact that host nitrate pre-exposure altered the fish epidermal structure and reduced parasite intensity, suggests that nitrate protected the host against the disease. Nitrate treatments also caused fish mortality. As we used ecologically-relevant nitrate concentrations, and guppies are top-consumers widely used for mosquito bio-control in tropical and often nutrient-enriched waters, our results can have major ecological and social implications. In conclusion, this study advocates reducing nitrate level including the legislative threshold to protect the aquatic biota, even though this may control an ectoparasitic disease.