Aging of TiO2 Nanoparticles Transiently Increases Their Toxicity to the Pelagic Microcrustacean Daphnia magna

During their aquatic life cycle, nanoparticles are subject to environmentally driven surface modifications (e.g. agglomeration or coating) associated with aging. Although the ecotoxicological potential of nanoparticles might be affected by these processes, only limited information about the potential impact of aging is available. In this context, the present study investigated acute (96 h) and chronic (21 d) implications of systematically aged titanium dioxide nanoparticles (nTiO₂; ~90 nm) on the standard test species Daphnia magna by following the respective test guidelines. The nTiO₂ were aged for 0, 1, 3 and 6 d in media with varying ionic strengths (Milli-Q water: approx. 0.00 mmol/L and ASTM: 9.25 mmol/L) in the presence or absence of natural organic matter (NOM). Irrespective of the other parameters, aging in Milli-Q did not change the acute toxicity relative to an unaged control. In contrast, 6 d aged nTiO₂ in ASTM without NOM caused a fourfold decreased acute toxicity. Relative to the 0 d aged particles, nTiO₂ aged for 1 and 3 d in ASTM with NOM, which is the most environmentally-relevant setup used here, significantly increased acute toxicity (by approximately 30%), while a toxicity reduction (60%) was observed for 6 d aged nTiO₂. Comparable patterns were observed during the chronic experiments. A likely explanation for this phenomenon is that the aging of nTiO₂ increases the particle size at the start of the experiment or the time of the water exchange from <100 nm to approximately 500 nm, which is the optimal size range to be taken up by filter feeding D. magna. If subjected to further agglomeration, larger nTiO₂ particles, however, cannot be retained by the daphnids’ filter apparatus ultimately reducing their ecotoxicological potential. This non-linear pattern of increasing and decreasing nTiO₂ related toxicity over the aging duration, highlights the knowledge gap regarding the underlying mechanisms and processes. This understanding seems, however, fundamental to predict the risks of nanoparticles in the field.     

The use of spontaneous behavior,swimming performances and metabolic rate to evaluate toxicity of PFOS on topmouth gudgeon Pseudorasbora parva

Perfluorooctane sulfonate (PFOS) is a ubiquitous environmental contaminant that has been found to pose various risks to fish health and the safety of aquatic ecosystem. Swimming performance is an integrated index of fitness in fish. However, little research has sought on the effects of PFOS on swimming performances of fish. Experiments were carried out to clarify the impacts of acute exposure to PFOS on behavior, swimming ability and metabolic rate in topmouth gudgeon (Pseudorasbora parva), to understand the underlying ecotoxicological effects of waterborne PFOS exposure on fish physiology and behavior. Fish were exposed to PFOS (0, 0.5, 2, 8 or 32 mg/L) for 96 h. Afterwards, the routine metabolic rate (RMR), spontaneous swimming behavior (SSB), fast-start swimming performance (FSP) and critical swimming speed (U_crit) of the topmouth gudgeon were examined. The results show reduced behavioral performance and increased physiological stress with increasing PFOS concentration. Both RMR, SSB and U_crit were significantly affected by PFOS exposure (p < 0.05). The lowest observed effect concentration (LOEC) is 2 mg/L for SSB. PFOS treatment resulted in increased RMR (p = 0.001) and decreased U_crit (p = 0.005), whereas FSP was not influenced by PFOS (p > 0.05). The results indicate that the anaerobic swimming capacity was conserved, but the metabolic level, SSB and aerobic swimming performance in topmouth gudgeon were susceptible to PFOS contamination, and hence might be useful as considerable potential biomarkers of pollution.     

Titanium Dioxide Nanoparticles Affect the Percentage of Free Radical Scavenging,Protein Content and DNA Mismatch Repair Genes in <Emphasis Type="Italic">Zea mays</Emphasis> L. and <Emphasis Type="Italic">Triticum aestivum</Emphasis> L.

This paper identifies the potential molecular markers predicting the impact of nTiO₂ on plants and explores the new statistical correlations between the biomarkers and growth parameters. The quantitative mRNA expression of the three genes involved in DNA mismatch repair (MLH1) and cell division (PCNA1 and PCNA2) in Zea mays and Triticum aestivum seedlings were related to the growth parameters measured in response to five nTiO2 treatments. The results indicated that the higher concentrations were harmless to Z. mays but not to T. aestivum. nTiO₂ treatments increased the total protein levels in both species and significantly inhibited the percentage of DPPH radical scavenging in Z. mays compared with T. aestivum seedlings. The exposure to both 50 μg/ml and 30 μg/ml concentrations of nTiO₂ significantly induced the expression of MLH1 and PCNA1 genes in both species; however, the exposure to 30 μg/ml of nTiO₂ also significantly induced the expression of PCNA2 genes in T. aestivum. The exposure to 50, 70 and 140 μg/ml significantly inhibited the expression of PCNA2 in both species, while 70 and 140 μg/ml repressed the expression of MLH1 and PCNA1 in the seedlings of Z. mays. The induction and repression of the expression of the three genes were correlated with some growth parameters and biological indices in both species. This key finding suggests that the above genes may play a vital role in mediating plant stress response to nTiO₂ and could be used as sensitive molecular biomarkers indicative of the oxidative stress of nTiO₂ exposure.     

Habitat uncertainty explains variation in offspring provisioning strategies in a temporary pond crustacean

Along with the development of nanotechnology, an increase in production and application of nanosized magnetite (Fe₃O₄) is expected. Though magnetite is considered relatively safe, information concerning potential hazards of synthetic magnetite nanoparticles with unique physico-chemical characteristics to aquatic organisms is still limited. In this study, we evaluated the toxicity of nanosized (27.2 ± 9.8 nm) and bulk (144.2 ± 67.7 nm) magnetite particles to different life stages of the aquatic crustacean Daphnia magna. In addition, phytotoxicity of the magnetite was evaluated using duckweed Lemna minor. The study did not reveal any statistically significant differences between the biological effects of nanosized and bulk magnetite particles. Both forms of magnetite induced very low toxicity (EC50 > 100 ppm) to D. magna and L. minor in the standard acute assays. However, it was demonstrated that at acutely subtoxic magnetite concentrations (10 and 100 ppm), the number of neonates hatched from D. magna ephippia was decreased. Moreover, short-term (48 h) exposure of neonate daphnids to these concentrations may significantly affect the long-term survival and reproductive potential of daphnids. These results indicate that substantial contamination of aquatic ecosystems by magnetite may disrupt the stability of cladoceran populations.     

Protective effects of ectoine on heat-stressed Daphnia magna

Ectoine (ECT) is an amino acid produced and accumulated by halophilic bacteria in stressful conditions in order to prevent the loss of water from the cell. There is a lack of knowledge on the effects of ECT in heat-stressed aquatic animals. The purpose of our study was to determine the influence of ECT on Daphnia magna subjected to heat stress with two temperature gradients: 1 and 0.1 °C/min in the range of 23–42 °C. Time to immobilisation, survival during recovery, swimming performance, heart rate, thoracic limb movement and the levels of heat shock protein 70 kDa 1A (HSP70 1A), catalase (CAT) and nitric oxide species (NOx) were determined in ECT-exposed and unexposed daphnids; we showed protective effects of ECT on Daphnia magna subjected to heat stress. Time to immobilisation of daphnids exposed to ECT was longer when compared to the unexposed animals. Also, survival rate during the recovery of daphnids previously treated with ECT was higher. ECT significantly attenuated a rapid increase of mean swimming velocity which was elevated in the unexposed daphnids. Moreover, we observed elevation of thoracic limb movement and modulation of heart rate in ECT-exposed animals. HSP70 1A and CAT levels were reduced in the presence of ECT. On the other hand, NOx level was slightly elevated in both ECT-treated and unexposed daphnids, however slightly higher NOx level was found in ECT-treated animals. We conclude that the exposure to ectoine has thermoprotective effects on Daphnia magna, however their mechanisms are not associated with the induction of HSP70 1A.     

Lead toxicity at different life stages of the giant prawn (Macrobrachium rosenbergii,de Man): considerations of osmoregulatory capacity and histological changes in adult gills

This study evaluated the acute toxicity of lead in different life stages of the freshwater prawn Macrobrachium rosenbergii, determined the effect of sublethal Pb concentrations on osmoregulatory capacity (OC), measured the Pb level in gills, and investigated the effect of Pb on the structure of the gills of adult prawns. The 24-, 48-, and 96-h LC₅₀ values for Pb to M. rosenbergii increased progressively with increasing life stage, from post-larvae (PL), juvenile to adult. The 24- and 48-h LC₅₀ values for post-larvae ranged from 0.01- to 0.09-mg Pb/L. The 24-, 48-, and 96-h LC₅₀ values for Pb were lower at 12 ppt than those at 0 ppt for either the juveniles or the adults. At 12 ppt, the 96-h LC₅₀ values in PL11, juvenile and adult were 0.47-, 0.58-, and 2.03-mg Pb/L, respectively. Meanwhile, at 12 ppt, the 96-h LC₅₀ values in PL11, juvenile and adult were 0.63-, 4.44-, and 7.98-mg Pb/L, respectively. In adults, the OC values of controls and prawns exposed to 2- and 4-mg Pb/L at 0 ppt were not significantly different. The OC of prawns exposed to and 2-mg Pb/L at 12 ppt increased by 72 and 109% from the OC of the control prawns. At media 12 ppt, the OC value of prawns exposed to 1-mg Pb/L was significantly different from that of prawns exposed to 2-mg Pb/L. The concentrations of Pb in gill tissues increased significantly in Pb exposed prawns both at 0 and 12 ppt. The level of Pb in gills of prawns exposed to 2-mg Pb/L at 12 ppt was not significantly different from those exposed at 0 ppt. The severe toxic actions of Pb were noted in gills of prawns exposed in media 12 ppt. Hyperplasia and necrosis were observed in gill lamellae, resulting in abnormal gill tips after Pb exposure at media 12 ppt. Since the effect of Pb is more pronounced in higher salinity (12 ppt) than in freshwater (0 ppt) it is clear that aquaculture of M. rosenbergii should be conducted in freshwater ponds.     

Feeding behavior as an index of copper stress in Daphnia magna and Brachionus calyciflorus

1. The effect of short-term exposure to the fungicide copper sulfate, on the feeding behavior of two freshwater zooplankters, the rotifer Brachionus calyciflorus and the cladocera Daphnia magna, was studied.2. Both species were exposed to sublethal levels (0.01, 0.02, 0.05 and 0.08 mg/l) of copper sulfate during 24 hr in order to determine the effect of this toxicant on filtration and ingestion rates.3. The experiments were performed using the unicellular algae Nannochloris oculata in a density of 5 × 10⁵ cells/ml, as food for both organisms.4. Rates of filtration and ingestion declined on B. calyciflorus and D. magna with increasing toxicant concentrations.5. The effective copper sulfate concentration at which feeding rate was reduced to 50% of that in controls (ec₅₀) was 0.043 and 0.090 mg/1 for B. calyciflorus and D. magna, respectively.     

Reduction in swimming performance in juvenile rainbow trout (Oncorhynchus mykiss) following sublethal exposure to pyrethroid insecticides

While the lethal toxicity of pyrethroid insecticides to fish is well documented, their sublethal physio-behavioral effects remain poorly characterized. Known pyrethroid-associated changes to insect neuromuscular function may translate into similar effects in fish, thereby altering swimming ability and affecting foraging, predator avoidance, and migration. Three experiments were conducted using critical (U_crit) and burst (U_max) swimming speeds to assess the sublethal effects of the pyrethroids permethrin and deltamethrin in juvenile rainbow trout (Oncorhynchus mykiss). Fish were exposed to deltamethrin (100, 200, or 300 ng/L) or permethrin (1, 2, or 3 μg/L) in water for 4 d, and assessed for swimming performance. Deltamethrin (200 and 300 ng/L) reduced U_crit, but not U_max, while both swim performance measurements were unaffected by permethrin. Subsequent experiments used only U_crit to assess deltamethrin exposure. In a time course experiment, deltamethrin (300 ng/L) reduced U_crit after 1 and 4 d of exposure, but after 7 d of exposure U_crit was fully recovered. Finally, deltamethrin (1, 2, or 3 μg/L) reduced U_crit after 1 h bath exposures similar to recommended protocols for deltamethrin based sea-lice treatment in aquaculture. The real-world implications of the revealed pyrethroid-associated swimming ability reductions in salmon may be important in areas close to aquaculture facilities.     

Increases of Chamber Height and Base Diameter Have Contrasting Effects on Grazing Rate of Two Cladoceran Species: Implications for Microcosm Studies

Aquatic microcosm studies often increase either chamber height or base diameter (to increase water volume) to test spatial ecology theories such as “scale” effects on ecological processes, but it is unclear whether the increase of chamber height or base diameter have the same effect on the processes, i.e., whether the effect of the shape of three-dimensional spaces is significant. We orthogonally manipulated chamber height and base diameter and determined swimming activity, average swimming velocity and grazing rates of the cladocerans Daphnia magna and Moina micrura (on two algae Scenedesmus quadricauda and Chlorella vulgaris; leading to four aquatic algae-cladoceran systems in total) under different microcosm conditions. Across all the four aquatic systems, increasing chamber height at a given base diameter significantly decreased the duration and velocity of horizontal swimming, and it tended to increase the duration but decrease the velocity of vertical swimming. These collectively led to decreases in both average swimming velocity and grazing rate of the cladocerans in the tall chambers (at a given base diameter), in accordance with the positive relationship between average swimming velocity and grazing rate. In contrast, an increase of base diameter at a given chamber height showed contrasting effects on the above parameters. Consistently, at a given chamber volume increasing ratio of chamber height to base diameter decreased the average swimming velocity and grazing rate across all the aquatic systems. In general, increasing chamber depth and base diameter may exert contrasting effects on zooplankton behavior and thus phytoplankton-zooplankton interactions. We suggest that spatial shape plays an important role in determining ecological process and thus should be considered in a theoretical framework of spatial ecology and also the physical setting of aquatic microcosm experiments.     

Direct and transgenerational impact on Daphnia magna of chemicals with a known effect on DNA methylation

The purpose of this study is to investigate (1) the induction of epigenetic effects in the crustacean Daphnia magna using DNA methylation as an epigenetic mark and (2) the potential stable transfer of such an epigenetic effect to non-exposed subsequent generations. Daphnids were exposed to chemical substances known to affect DNA methylation in mammals: vinclozolin, 5-azacytidine, 2′-deoxy-5-azacytidine, genistein and biochanin A. Effects on overall DNA cytosine methylation, body length and reproduction were evaluated in 21 day experiments. Using a multi-generational experimental design these endpoints were also evaluated in the F₁ and F₂ generation of both exposed and non-exposed offspring from F₀ daphnids exposed to 5-azacytidine, genistein or vinclozolin. A reduction in DNA methylation was consistently observed in daphnids exposed to vinclozolin and 5-azacytidine. Only in organisms exposed to 5-azacytidine was this effect transferred to the two subsequent non-exposed generations. A concurrent reduction in body length at day 7 was observed in these treatments. For the first time, exposure to environmental chemicals was shown to affect DNA methylation in the parental generation of D. magna. We also demonstrated a transgenerational alteration in an epigenetic system in D. magna, which indicates the possibility of transgenerational inheritance of environment-induced epigenetic changes in non-exposed subsequent generations.     

Exposure to Cerium Dioxide Nanoparticles Differently Affect Swimming Performance and Survival in Two Daphnid Species

The CeO₂ NPs are increasingly used in industry but the environmental release of these NPs and their subsequent behavior and biological effects are currently unclear. This study evaluates for the first time the effects of CeO₂ NPs on the survival and the swimming performance of two cladoceran species, Daphnia similis and Daphnia pulex after 1, 10 and 100 mg.L⁻¹ CeO₂ exposures for 48 h. Acute toxicity bioassays were performed to determine EC₅₀ of exposed daphnids. Video-recorded swimming behavior of both daphnids was used to measure swimming speeds after various exposures to aggregated CeO₂ NPs. The acute ecotoxicity showed that D. similis is 350 times more sensitive to CeO₂ NPs than D. pulex, showing 48-h EC₅₀ of 0.26 mg.L⁻¹ and 91.79 mg.L⁻¹, respectively. Both species interacted with CeO₂ NPs (adsorption), but much more strongly in the case of D. similis. Swimming velocities (SV) were differently and significantly affected by CeO₂ NPs for both species. A 48-h exposure to 1 mg.L⁻¹ induced a decrease of 30% and 40% of the SV in D. pulex and D. similis, respectively. However at higher concentrations, the SV of D. similis was more impacted (60% off for 10 mg.L⁻¹ and 100 mg.L⁻¹) than the one of D. pulex. These interspecific toxic effects of CeO₂ NPs are explained by morphological variations such as the presence of reliefs on the cuticle and a longer distal spine in D. similis acting as traps for the CeO₂ aggregates. In addition, D. similis has a mean SV double that of D. pulex and thus initially collides with twice more NPs aggregates. The ecotoxicological consequences on the behavior and physiology of a CeO₂ NPs exposure in daphnids are discussed.     

Fatty acid retention under temporally heterogeneous dietary intake in a cladoceran

Omega‐3 (ω3) and ‐6 (ω6) polyunsaturated fatty acids (PUFA) are essential for all aquatic animals, but their dietary availability can be highly heterogeneous in space and time. The way consumers retain PUFA across such heterogeneous feeding conditions remains poorly understood. In a series of feeding experiments, we investigated how retention efficiencies (i.e. amount in consumer biomass/amount ingested) of PUFA and bulk carbon responded to heterogeneous PUFA intake in Daphnia magna. Heterogeneous PUFA intake was achieved by exposing D. magna to algal diets of different PUFA content and composition for specific time periods. The retention efficiency of carbon did not change among dietary treatments. At shorter exposure to PUFA‐rich diet, retention efficiencies of most PUFA were 2–3 times higher than that of bulk carbon, clearly indicating PUFA bioaccumulation in D. magna. Increasing exposure to PUFA‐rich diet caused exponential decrease of retention efficiencies for most PUFA. However, D. magna receiving more PUFA were richer in these compounds despite lower retention efficiency. Eicosapentaenoic (20:5ω3) and arachidonic acid (20:4ω6) and their precursors were always supplied in the same proportions (3.6:1), but the 20:5ω3/20:4ω6 ratio in D. magna (an important measure of nutritional quality for consumers) increased with exposure time to these PUFA from 2.2:1 to 3.8:1, thus eventually matching the diet. Our results suggest that D. magna is an efficient gatherer, accumulator, and repository of PUFA under low/fragmented dietary availability. However, at higher availabilities, PUFA are not always bioaccumulated in D. magna. Hence, the efficiency of PUFA transfer by daphnids in food webs may depend on temporal PUFA availability and its range of variation. Finally, we show that heterogeneity in PUFA intake may also affect higher trophic levels by influencing nutritionally critical PUFA ratios of zooplankton.     

Toxic Effects of Cobalt Chloride on Hematological Factors of Common Carp (Cyprinus carpio)

In this study, we investigate the toxic effects of cobalt chloride on some hematological factors of the carp Cyprinus carpio, such as white blood cell count, red blood cell count, hemoglobin, hematocrit, mean corpuscular volume, mean corpuscular hemoglobin, and mean corpuscular hemoglobin concentration. At first, LC₅₀ of cobalt in C. carpio was measured during 96 h after exposure. Also, physicochemical parameters of water including pH, dissolved oxygen, viscosity, temperature, and conductivity were monitored, continuously. The results showed that LC₅₀ values of cobalt in C. carpio were 327 and 328 mg/L in two replicates, respectively. Then, the changes in some hematological factors in the five treatment groups placed under concentration of 100, 200, 300, 400, and 500 mg/L cobalt were compared with the control group. Based on hematological tests conducted in this research, exposure of carp to 500- and 300-mg/L concentrations of cobalt in 48 h showed significant difference (p?<?0.05) in white blood cell count. The concentration of 500 mg/L cobalt in 24 h showed a significant difference in the amount of hemoglobin, number of red blood cells, and hematocrit level as compared with the control group. The concentration of 100 mg/L cobalt in 48 h did not show a significant difference in comparison with the control group (p?>?0.05). Also, the concentration of 500 mg/L cobalt in 24 h showed a significant difference in the amount of mean corpuscular volume and mean corpuscular hemoglobin as compared with the control group and other treatments. Also, the percentage of mean corpuscular hemoglobin concentration in a concentration of 200 mg/L cobalt in 24 h showed a significant difference as compared with the control group and other treatments.     

pH alters the swimming behaviors of the raphidophyte Heterosigma akashiwo: Implications for bloom formation in an acidified ocean

We investigated the effects of pH on movement behaviors of the harmful algal bloom causing raphidophyte Heterosigma akashiwo. Motility parameters from >8000 swimming tracks of individual cells were quantified using 3D digital video analysis over a 6-h period in 3 pH treatments reflecting marine carbonate chemistry during the pre-industrial era, currently, and the year 2100. Movement behaviors were investigated in two different acclimation-to-target-pH conditions: instantaneous exposure and acclimation of cells for at least 11 generations. There was no negative impairment of cell motility when exposed to elevated PCO₂ (i.e., low pH) conditions but there were significant behavioral responses. Irrespective of acclimation condition, lower pH significantly increased downward velocity and frequency of downward swimming cells (p < 0.001). Rapid exposure to lower pH resulted in 9% faster downward vertical velocity and up to 19% more cells swimming downwards (p < 0.001). Compared to pH-shock experiments, pre-acclimation of cells to target pH resulted in ~30% faster swimming speed and up to 46% faster downward velocities (all p < 0.001). The effect of year 2100 PCO₂ levels on population diffusivity in pre-acclimated cultures was >2-fold greater than in pH-shock treatments (2.2 × 10⁵ μm² s⁻¹ vs. 8.4 × 10⁴ μm² s⁻¹). Predictions from an advection-diffusion model, suggest that as PCO₂ increased the fraction of the population aggregated at the surface declined, and moved deeper in the water column. Enhanced downward swimming of H. akashiwo at low pH suggests that these behavioral responses to elevated PCO₂ could reduce the likelihood of dense surface slick formation of H. akashiwo through reductions in light exposure or growth independent surface aggregations. We hypothesize that the HAB alga's response to higher PCO₂ may exploit the signaling function of high PCO₂ as indicative of net heterotrophy in the system, thus indicative of high predation rates or depletion of nutrients.     

Fitness cost from fluctuating ultraviolet radiation in Daphnia magna

Solar ultraviolet radiation (UVR) is an important environmental threat for organisms in aquatic systems, but its temporally variable nature makes the understanding of its effects ambiguous. The aim of our study was to assess potential fitness costs associated with fluctuating UVR in the aquatic zooplankter Daphnia magna. We investigated individual survival, reproduction and behaviour when exposed to different UVR treatments. Individuals exposed to fluctuating UVR, resembling natural variations in cloud cover, had the lowest fitness (measured as the number of offspring produced during their lifespan). By contrast, individuals exposed to the same, but constant UVR dose had similar fitness to control individuals (not exposed to UVR), but they showed a significant reduction in daily movement. The re-occurring threat response to the fluctuating UVR treatment thus had strong fitness costs for D. magna, and we found no evidence for plastic behavioural responses when continually being exposed to UVR, despite the regular, predictable exposure schedule. In a broader context, our results imply that depending on how variable a stressor is in nature, populations may respond with alternative strategies, a framework that could promote rapid population differentiation and local adaptation.     

Deltamethrin-Mediated Toxicity and Cytomorphological Changes in the Midgut and Nervous System of the Mayfly Callibaetis radiatus

Immature instars of mayflies are important constituents of the food web in aquatic ecosystems (especially in Neotropical regions) and they are among the most susceptible arthropods to pyrethroid insecticides. These insecticides have been recognized as important stressors of freshwater ecosystems, but their cellular effects in aquatic insects have been neglected. Here, we assessed the susceptibility to deltamethrin (a typical type II pyrethroid) as well as the deltamethrin-mediated cytomorphological changes in the central nervous system and midgut of the mayfly Callibaetis radiatus. While the deltamethrin LC₅₀ for 24h of exposure was of 0.60 (0.46–0.78) μg of a.i/L, the survival of C. radiatus was significantly reduced in deltamethrin concentrations ≥ 0.25 μg a.i/L at 96h of exposure. Sub-lethal deltamethrin exposure severely affected the cytomorphology of C. radiatus midgut (e.g., muscle layer retraction, cytoplasm vacuolation, nucleus and striated border disorganization) and also induced slight cytomorphological changes in the brain (e.g., presence of pyknotic nuclei) and in the thoracic ganglia (e.g., vacuolation of neurons and presence of pyknotic nuclei) of these insects. However, DNA damage was absent in all of these organs, suggesting that the sublethal cellular stress induced by deltamethrin might disrupt physiological processes (e.g., metabolism or electrical signal transmission) rather than cause cell death (e.g., apoptosis) in C. radiatus. Thus, our findings indicated that deltamethrin actions at cellular levels represent a clear indication of sublethal effects on the C. radiatus survival abilities.     

Combined exposure to parasite and pesticide causes increased mortality in the water flea Daphnia

Organisms are exposed to multiple biotic and abiotic environmental stressors, which can influence the dynamics of individual populations and communities. Populations may also genetically adapt to both natural (e.g. disease) and anthropogenic (e.g. chemical pollution) stress. In the present study, we studied fitness consequences of exposure to both a parasite (i.e. biotic) and a pesticide (i.e. abiotic) for the water flea Daphnia. In addition, we investigated whether these fitness consequences change through time as a population evolves. Thus, we exposed Daphnia magna clones, hatched from dormant eggs isolated from different time layers of a natural dormant egg bank, to the parasite Pasteuria ramosa and the insecticide diazinon in a multifactorial experiment. While our experimental treatments for unknown reasons failed to induce disease symptoms in the Daphnia, we did observe a reduced survival of D. magna when simultaneously exposed to both the parasite and the pesticide. No increased mortality upon exposure to individual stressors was observed. We did not observe an evolutionary change in fitness response of the Daphnia clones hatched from different time horizons upon exposure to stressors.     

Titanium Dioxide Nanoparticles Increase Sensitivity in the Next Generation of the Water Flea Daphnia magna

The nanoparticle industry is expected to become a trillion dollar business in the near future. Therefore, the unintentional introduction of nanoparticles into the environment is increasingly likely. However, currently applied risk-assessment practices require further adaptation to accommodate the intrinsic nature of engineered nanoparticles. Combining a chronic flow-through exposure system with subsequent acute toxicity tests for the standard test organism Daphnia magna, we found that juvenile offspring of adults that were previously exposed to titanium dioxide nanoparticles exhibit a significantly increased sensitivity to titanium dioxide nanoparticles compared with the offspring of unexposed adults, as displayed by lower 96 h-EC₅₀ values. This observation is particularly remarkable because adults exhibited no differences among treatments in terms of typically assessed endpoints, such as sensitivity, number of offspring, or energy reserves. Hence, the present study suggests that ecotoxicological research requires further development to include the assessment of the environmental risks of nanoparticles for the next and hence not directly exposed generation, which is currently not included in standard test protocols.