Nickel response in function of temperature differences: Effects at different levels of biological organization in Daphnia magna

Long-term adverse effects of microplastics on Daphnia magna reproduction and population growth rate at increased water temperature and light intensity: Combined effects of stressors and interactions

In many ecosystems, the zooplankton community has been pressured simultaneously by microplastic pollution and alterations resulting from global climate changes. The potential influence of light intensity rise (from 10,830 lx to 26,000 lx) and water temperature rise (from 20 °C to 25 °C) on the long term-toxicity of microplastics (MPs) to Daphnia magna were investigated. Three 21-day laboratory bioassays with model MPs (1-5 μm diameter) were carried out at (i) 20 °C/10830 lx, (ii) 20 °C/26000 lx, and (iii) 25 °C/10830 lx. In each bioassay, one control (no MPs) and three MP concentrations (0.04, 0.09, 0.19 mg/L) were tested. In all the bioassays, MPs caused parental and juvenile mortality, and reduced the somatic growth, reproduction and population growth rate. The MP EC₅₀s on living offspring (95% confidence interval within brackets) were 0.146 mg/L (0.142-0.151 mg/L) at 20 °C/10830 lx, 0.102 mg/L (0.099-0.105 mg/L) at 20 °C/26000 lx, and 0.101 mg/L (0.098-0.104 mg/L) at 25 °C/10830 lx. Relatively to the respective control group, 0.19 mg/L of MPs decreased the mean of the population growth rate by 27% at 20 °C/10830 lx, 38% at 20 °C/26000 lx and 59% at 25 °C/10830 lx. Based on the population growth rate and in relation to 20 °C/10830 lx (control, no MPs), the interaction between increased light intensity (26,000 lx) and MPs was synergism (at all the MP concentrations tested). The interaction between water temperature rise (25 °C) and MPs was antagonism at 0.04 mg/L of MPs and synergism at 0.09 and 0.19 mg/L of MPs. In the present scenario of climate changes and global MP pollution such findings raise high concern because zooplankton communities are crucial for aquatic biodiversity conservation, ecosystem functioning and services provided to humans. Further studies on the combined effects of MPs, other common pollutants, and alterations due to climate changes are needed.

Combined effects of ZnO nanoparticles and toxic Microcystis on life-history traits of Daphnia magna

Rise in cyanobacterial blooms and massive discharge of nanoparticles (NPs) in aquatic ecosystems cause zooplankton to be exposed in toxic food and NPs simultaneously, which may impact on zooplankton interactively. Therefore, the present study focused on assessing the combined effects of different ZnO NPs levels (0, 0.10, 0.15, 0.20 mg L^-1) and different proportions of toxic Microcystis (0%, 10%, 20%, 30%) in the food on a model zooplankton, Daphnia magna. The results showed that both toxic Microcystis and ZnO NPs significantly delayed the development of D. magna to maturation, but there was no significant interaction between the two factors on the times to maturation except the body length at maturation. Both ZnO NPs and toxic Microcystis also significantly decreased the number of neonates in the first brood, total offspring, and number of broods per female, and there was a significant interaction between ZnO NPs and food composition on the reproductive performance of D. magna. Specifically, presence of toxic Microcystis reduced the gap among the effects of different ZnO NPs concentrations on the reproductive performance of D. magna. When the ZnO NPs concentration was at 0.15 mg L^-1, the gap of the reproductive performance among different proportions of toxic Microcystis also tended to be narrow. Similar phenomenon also occurred in mortality. Such results suggested that low concentration of ZnO NPs and toxic Microcystis can mutually attenuate their harmful effects on D. magna, which has significantly implications in appropriately assessing the ecotoxicological effects of emerging pollutants in a complex food conditions.

Effect of temperature on nickel uptake and elimination in Daphnia magna

It is well known that temperature can affect the ecotoxicity of chemicals (including metals) to aquatic organisms. It was recently reported that nickel (Ni), a priority substance under the European Water Framework directive, showed decreasing chronic toxicity to Daphnia magna with increasing temperature, between 15 and 25 °C. We performed a toxicokinetic study to contribute to an increased mechanistic understanding of this effect. More specifically, we investigated the effect of temperature on Ni uptake and elimination in D. magna (in 4 clones) using an experimental design that included Ni exposures with different stable isotopic composition and using a one-compartment model for data analysis. Both Ni uptake and elimination were affected by temperature, and some clear interclonal differences were observed. On average (across all clones), however, a similar pattern of the effect of temperature was observed on both Ni uptake and elimination, that is, the uptake rate constant (k_u ) and elimination rate constant (k_e ) during 72 h of Ni exposure were lower at 25 than at 19 °C, by 2.6-fold and 1.6-fold, respectively, and they were similar at 19 and 15 °C. This pattern does not correspond to the effects of temperature on chronic Ni toxicity reported previously, suggesting that Ni compartmentalization and/or toxicodynamics may also be affected by temperature. The data gathered with our specific experimental design also allowed us to infer that 1) the k_u was up-regulated over time, that is, the k_u after 2 d of Ni exposure was significantly higher than the initial k_u , by 1.5- to 2.3-fold, and 2) the k_e decreased significantly when the external Ni exposure was stopped, by 1.2- to 1.9-fold. These 2 findings are in contrast with 2 commonly used assumptions in toxicokinetic models, that is, that k_u is constant during exposure and k_e is independent of external exposure. We suggest that future toxicokinetic studies consider these factors in their experimental designs and data analyses. Overall, our study contributes to the growing body of evidence that temperature affects toxicokinetics of metals (and chemicals in general), but at the same time we emphasize that knowledge of toxicokinetics alone is not necessarily sufficient to explain or predict temperature effects on (chronic) toxicity. Environ Toxicol Chem 2019;38:784-793. © 2019 SETAC.

Toxicological interactions induced by chronic exposure to gold nanoparticles and microplastics mixtures in Daphnia magna

The effects of emerging environmental contaminants on human and environmental health is of high concern, especially those potentially induced by mixtures. The main goal of the present study was to assess the chronic effects of mixtures of citrate stabilized ≈5 nm gold nanoparticles (AuNP) and 1-5μm microplastics (MP) on Daphnia magna. A 21-day bioassay was carried out. The effect criteria were parental mortality, somatic growth and several reproductive parameters. AuNP induced parental mortality, reduced the total offspring and caused immobile juveniles and aborted eggs. MP induced parental mortality, delayed the first brood release, decreased the number of broods released, the total offspring, and caused immobile juveniles. All the mixtures caused higher toxicity than AuNP and MP alone. Based on parental mortality, evidences of antagonism between AuNP and MP were observed at low concentrations of both mixture components, whereas evidences of synergism at high concentrations were found. Chronic (21-day) exposure of D. magna to AuNPs, MP, and their mixtures can impair development, reproduction, ultimately leading to death.

Combined effects of interspecies interaction, temperature, and zinc on Daphnia longispina population dynamics

Under natural conditions, organisms can experience a variety of abiotic (e.g., temperature, pH) and biotic (e.g., species interactions) factors, which can interact with toxicant effects. By ignoring species interactions conventional ecotoxicological studies (i.e., single-species tests) oversimplify the actual field situation. We investigated whether temperature and interspecific competition affected the effects of zinc (Zn) on a Daphnia longispina population. The D. longispina populations were exposed in a full factorial design to 3 different Zn treatments (background, 29, and 110 μg Zn/L), 2 different temperature regimes (cold, 17-18 °C; warm, 21-22 °C), and 2 interspecific competition levels (no interspecific Brachionus competition = no Brachionus calyciflorus added; interspecific Brachionus competition = B. calyciflorus added). Interspecific Brachionus competition and temperature by itself had a limited effect on the Daphnia abundance but significantly interacted with the highest Zn concentration. Without Brachionus competition the D. longispina juvenile and adult abundances under warm conditions were up to 5.5 and 21 times lower, respectively, in the high Zn treatment in comparison with the Zn control, whereas under cold conditions no significant Zn effect was observed. However, with Brachionus competition the highest Zn treatment was on average 2.2 times less toxic to the D. longispina juvenile abundance at higher temperatures. Under cold conditions the highest Zn treatment affected the juvenile abundance sooner and up to 9 times more negatively when simultaneously faced with Brachionus competition. It is possible that the competition for food reduced the amount of energy that could be used by D. longispina for reproduction, and the metabolic costs increased as a result of Zn stress. The present study clearly illustrated the influence of temperature and competition on the effects of a chemical stressor. Thus, not considering such factors in ecological risk assessment may underestimate or overestimate risks in aquatic ecosystems when extrapolating data from standard single-species tests to the field. Environ Toxicol Chem 2018;37:1668-1678. © 2018 SETAC.

Effect of temperature on chronic toxicity of copper, zinc, and nickel to Daphnia magna

Few studies have considered the effect of temperature on the chronic sensitivity of Daphnia magna to other stressors. The present study investigated the effect of temperature on chronic metal toxicity and whether this effect differed among 4 different D. magna clones. Life table experiments were performed with copper, zinc, and nickel at 15 °C, 20 °C, and 25 °C. General linear modeling indicated that chronic Cu, Zn, and Ni toxicity to D. magna were all significantly affected by temperature. When averaged across clones, our results suggest that chronic metal toxicity to D. magna was higher at 15 °C than at 20 °C, which is the temperature used in standard toxicity tests. At 15 °C, the 21-d median effect concentrations (EC50s) of Cu, Zn, and Ni were 1.4 times, 1.1 times, and 1.3 times lower than at 20 °C, respectively. At 25 °C, chronic Cu and Zn toxicity did not change in comparison with 20 °C, but chronic Ni toxicity was lower (21-d EC50 of nickel at 25 °C was 1.6 times higher than at 20 °C). The same trends were observed for Cu and Ni when the 21-d 10% and 20% effect concentrations were considered as the effect estimator, but not for Zn, which warns against extrapolating temperature effects on chemical toxicity across effect sizes. Overall, however, chronic metal toxicity was generally highest at the lowest temperature investigated (15 °C), which is in contrast with the usually observed higher acute metal toxicity at higher temperatures. Furthermore, the effect of temperature on chronic Ni toxicity depended significantly on the clone. This warns against extrapolating results about effect of temperature on chemical toxicity from single clone studies to the population level. Environ Toxicol Chem 2017;36:1909-1916. © 2016 SETAC.

Combined effects of temperature changes and metal contamination at different levels of biological organization in yellow perch

In this study, we measured the effects of temperature (9°C, 20°C, and 28°C), metal contamination (cadmium and nickel) and their interaction on yellow perch (Perca flavescens) using liver enzymatic and transcriptomic endpoints and biometric indices. Kidney metal concentrations increased with a rise of temperature. The biometric indices analysed (Fulton condition factor, pyloric cæca, hepatosomatic and gonadosomatic indices) generally decreased with an increase of temperature but not with metal contamination. At the enzymatic level, the activity of superoxide dismutase (SOD), involved in antioxidant response, was affected by both temperature and metal contamination, whereas the activity of glucose-6-phosphate dehydrogenase (G6PDH), involved in energy accumulation but also in antioxidant response, was only affected by metal exposure. The response of perch to the stressors at the transcriptional level differed from the metabolic response. In particular, the transcription level of the cco and g6pdh genes sharply decreased with increasing temperature, while the activities of the corresponding enzymes remained stable. The normal response of the transcription level of the apoptotic gene (diablo) to heat stress was also altered in metal-contaminated fish. The combination of metal and temperature stresses also modified the response of antioxidant metabolism induced by these stressors individually. This study contributes to a better understanding of the influences of natural stressors like temperature on biomarkers commonly used in ecotoxicological studies and will facilitate their interpretation in the context of multiple stressors characteristic of field situations.

How does exposure to nickel and cadmium affect the transcriptome of yellow perch (Perca flavescens)--results from a 1000 candidate-gene microarray

The molecular mechanisms underlying nickel (Ni) and cadmium (Cd) toxicity and their specific effects on fish are poorly understood. Documenting gene transcription profiles offers a powerful approach toward identifying the molecular mechanisms affected by these metals and to discover biomarkers of their toxicity. However, confounding environmental factors can complicate the interpretation of the results and the detection of biomarkers for fish captured in their natural environment. In the present study, a 1000 candidate-gene microarray, developed from a previous RNA-seq study on a subset of individual fish from contrasting level of metal contamination, was used to investigate the transcriptional response to metal (Ni and Cd) and non metal (temperature, oxygen, and diet) stressors in yellow perch (Perca flavescens). Specifically, we aimed at (1) identifying transcriptional signatures specific to Ni and Cd exposure, (2) investigating the mechanisms of their toxicity, and (3) developing a predictive tool to identify the sublethal effects of Ni and Cd contaminants in fish sampled from natural environments. A total of 475 genes displayed significantly different transcription levels when temperature varied while 287 and 176 genes were differentially transcribed at different concentrations of Ni and Cd, respectively. These metals were found to mainly affect the transcription level of genes involved in iron metabolism, transcriptional and translational processes, vitamin metabolism, blood coagulation, and calcium transport. In addition, a linear discriminant analysis (LDA) made using gene transcription levels yielded 94% correctly reassigned samples regarding their level of metal contamination, which indicates the potential of the microarray to detect perch response to Cd or Ni effects.