Toxicity of the new pyrethroid insecticide,deltamethrin, to Daphnia magna

The toxicity of deltamethrin, a synthetic pyrethroid insecticide, was determined under standardized conditions (ISO, 1982) in neonates and juveniles of Daphnia magna. Neonates (6 to 24 h old) were more sensitive than juveniles (48 to 72 h old). The 24- and 48-h EC₅₀s (immobilization) in neonates were 0.113 and 0.031 µg l^–1, respectively. The toxicity of deltamethrin was highly toxic. The 96-h EC₅₀ was in the ppt (µg l^–1) range. Toxicity tests with Daphnia may be used to detect toxic residues in water and sediment in areas treated with deltamethrin and other highly toxic pyrethroid pesticides.     

Toxicity of metal polluted sediments to Daphnia magna and Tubifex tubifex

Sediments from four lakes polluted by effuents from steel industries and from two reference lakes were investigated. The sediments contained elevated concentrations of oil, Pb, Cd, Hg, Zn, Ni and Cr in different combinations. The toxicity of the polluted sediments to Daphnia was much higher than reported elsewhere (24-h LC50 0.5–1.5 vol%). Tubifex survived more than 3 months in the polluted sediments, but growth and reproduction were inhibited.     

Biological surface coating and molting inhibition as mechanisms of TiO2 nanoparticle toxicity in Daphnia magna

The production and use of nanoparticles (NP) has steadily increased within the last decade; however, knowledge about risks of NP to human health and ecosystems is still scarce. Common knowledge concerning NP effects on freshwater organisms is largely limited to standard short-term (≤48 h) toxicity tests, which lack both NP fate characterization and an understanding of the mechanisms underlying toxicity. Employing slightly longer exposure times (72 to 96 h), we found that suspensions of nanosized (～100 nm initial mean diameter) titanium dioxide (nTiO(2)) led to toxicity in Daphnia magna at nominal concentrations of 3.8 (72-h EC(50)) and 0.73 mg/L (96-h EC(50)). However, nTiO(2) disappeared quickly from the ISO-medium water phase, resulting in toxicity levels as low as 0.24 mg/L (96-h EC(50)) based on measured concentrations. Moreover, we showed that nTiO(2) (～100 nm) is significantly more toxic than non-nanosized TiO(2) (～200 nm) prepared from the same stock suspension. Most importantly, we hypothesized a mechanistic chain of events for nTiO(2) toxicity in D. magna that involves the coating of the organism surface with nTiO(2) combined with a molting disruption. Neonate D. magna (≤6 h) exposed to 2 mg/L nTiO(2) exhibited a "biological surface coating" that disappeared within 36 h, during which the first molting was successfully managed by 100% of the exposed organisms. Continued exposure up to 96 h led to a renewed formation of the surface coating and significantly reduced the molting rate to 10%, resulting in 90% mortality. Because coating of aquatic organisms by manmade NP might be ubiquitous in nature, this form of physical NP toxicity might result in widespread negative impacts on environmental health.     

Cellular Toxicity of TiO2 Nanoparticles in Anatase and Rutile Crystal Phase

Titanium dioxide nanoparticles are massively produced and widely used in daily life, which has posed potential risk to human health. However, the molecular mechanism of TiO₂ nanoparticles (NPs) with different crystal phases is not clear. In this study, the characterization of two crystalline phases of TiO₂ NPs is evaluated by transmission electron microscopy and X-ray absorption fine structure spectrum; an interaction of these TiO₂ NPs with HaCaT cells is studied in vitro using transmission electron microscopy, chemical precipitation method, and X-ray absorption fine structure spectrometry. The coordination and surface properties indicate that only the anatase–TiO₂ NPs allow spontaneous reactive oxygen species (ROS) generation, but rutile–TiO₂ NPs do not after dispersion. The interaction between TiO₂ NPs and cellular components might also generate ROS for both anatase–TiO₂ NPs and rutile–TiO₂ NPs. The ROS generation could lead to cellular toxicity if the level of ROS production overwhelms the antioxidant defense of the cell or induces the mitochondrial apoptotic mechanisms. Furthermore, Ti had a direct combination with some protein or DNA after NPs enter the cell, which could also lead to cellular toxicity.     

A comparison of the sensitivities of Daphnia magna and Daphnia pulex to six different cyanobacteria

Cyanobacteria have become an important environmental concern due to their ability to produce a wide range of natural toxins. At present, very few studies describe concentration response curves for cyanobacteria other than Microcystis. However, field evidence highlights that both cyanobacterial concentration as well as cyanobacterial species composition vary considerably with season and year. Therefore, the aim of this study was to investigate the effects of different cyanobacteria at various concentrations of these cyanobacteria in the diet on the reproduction of Daphnia pulex and Daphnia magna. Those two species were chosen to assess whether the cyanobacteria-daphnid dynamics could be generalized for the Daphnia genus. Results demonstrated that both slope and EC50 of the concentration response curves depend upon the Daphnia species, the cyanobacteria species and the potential interaction between the two. This has two major consequences. First, the differences in sensitivity to cyanobacteria between D. magna and D. pulex depend upon concentration of the specific cyanobacteria. Second, we noted different mechanisms of toxicity for the two zooplankton species, a more general mechanism of toxicity for D. pulex and a more specific one for D. magna. Our data therefore suggest that results of studies investigating effects of cyanobacteria at different concentrations cannot be generalized across species. Furthermore, mechanisms of toxicity are not only cyanobacteria specific, but also dependent on the exposed species, even for rather closely related species such as in the Daphnia genus. Whenever possible, we therefore propose to combine a multi-species approach together with a full concentration response analysis to reach more general conclusions concerning the effects of cyanobacteria on zooplankton.     

Acclimation of Daphnia magna to environmentally realistic copper concentrations

It may be hypothesised that as the bioavailable background concentration of an essential metal increases (within natural limits), the natural tolerance (to the metal) of the acclimated/adapted organisms and communities will increase. In this study the influence of acclimation to different copper concentrations on the sensitivity of the freshwater cladoceran Daphnia magna Straus was investigated. D. magna was acclimated over three generations to environmentally relevant copper concentrations ranging from 0.5 to 100 microg Cu/l (copper activity: 7.18 x 10(-15) to 3700 x 10(-12) M Cu2+). A modified standard test medium was used as culture and test medium. Medium modifications were: reduced hardness (lowered to 180 mg CaCO3/l) and addition of Aldrich humic acid at a concentration of 5 mg DOC/l (instead of EDTA). The effects of acclimation on these organisms were monitored using acute mortality assays and long-term assays in which life table parameters, copper body concentrations and energy reserves were used as test endpoints. Our results showed a two-fold increase in acute copper tolerance with increasing acclimation concentration for second and third generation organisms. Copper acclimation concentrations up to 35 microg Cu/l (80 pM Cu2+) did not affect the net reproduction and the intrinsic growth rate. The energy reserves of the acclimated daphnids revealed an Optimal Concentration range (OCEE) and concentrations between 5 and 12 microg Cu/l (0.5-4.1 pM Cu2+) and 1 and 35 microg Cu/l (0.023-80 pM Cu2+) seemed to be optimal for first and third generation daphnids, respectively. Lower and higher copper concentrations resulted in deficiency and toxicity responses. It was also demonstrated that up to 35 microg Cu/l, third generation daphnids were able to regulate their total copper body concentration. These results clearly indicate that bioavailable background copper concentrations present in culture media have to be considered in the evaluation of toxicity test results, especially when the toxicity data are used for water quality guideline derivation and/or ecological risk assessment for metals.     

Reproducibility of short-term and reproduction toxicity experiments with Daphnia magna and comparison of the sensitivity of Daphnia magna with Daphnia pulex and Daphnia cucullata in short-term experiments

Short-term toxicity tests with Daphnia magna are reasonably reproducible. The sensitivity of Daphnia pulex, Daphnia cucullata and Daphnia magna proved to be about the same in short-term tests with 15 different chemical compounds.Reproduction toxicity experiments with Daphnia magna can easily be carried out within three weeks. At least duplicate experiments are necessary to arrive at an approximate no-effect level.     

Detection of triclosan using 2-domain hemoglobin promoter of Daphnia magna

Triclosan has been widely used as an antimicrobial agent. However, triclosan was found to cause toxicity, including muscle contraction disturbances, carcinogenesis, and endocrine disorders. In addition, it was found to affect central nervous system function adversely and even have ototoxic effects. Conventional methods for detecting such triclosan can be performed easily. However, the conventional detection methods are inadequate in precisely reflecting the impact of toxic substances on stressed organisms. Therefore, a test model for the toxic environment at the molecular level through the organism is needed. From that point of view, Daphnia magna is being used as a ubiquitous model. D. magna has the advantages of easy cultivation, a short lifespan and high reproductive capacity, and high sensitivity to chemicals. Therefore, the protein expression pattern of D. magna that appear in response to chemicals can be utilized as biomarkers for detecting specific chemicals. In this study, we characterized the proteomic response of D. magna following triclosan exposure via two-dimensional (2D) gel electrophoresis. As a result, we confirmed that triclosan exposure completely suppressed D. magna 2-domain hemoglobin protein and evaluated this protein as a biomarker for triclosan detection. We constructed the HeLa cells in which the GFP gene was controlled by D. magna 2-domain hemoglobin promoter, which under normal conditions, expressed GFP, but upon triclosan exposure, suppressed GFP expression. Consequently, we consider that the HeLa cells containing the pBABE-HBF3-GFP plasmid developed in this study can be used as novel biomarkers for triclosan detection.     

不同种类农药表面活性剂对大型溞的急性毒性

运用评价化学品对水生生物毒性的标准试验方法,比较了39种非离子型、6种阴离子型和3种阳离子型的常用代表性表面活性剂对大型溞的急性毒性.结果表明:3种阳离子型表面活性剂1427、1227及C8-10的急性毒性均为剧毒,其中1427毒性最高,EC50值为0.97×10-2 mg·L-1;非离子型表面活性剂中蓖麻油聚氧乙烯醚、吐温和斯潘系列乳化剂均为低毒,而烷基酚聚氧乙烯醚系列和脂肪醇聚氧乙烯醚系列表面活性剂的毒性稍偏高,而AEO-7和AEO-5的毒性达到高毒水平,EC50值分别为0.82和0.97 mg·L-1,且此类表面活性剂脂溶性越大,对大型溞的毒性越大;大部分阴离子表面活性剂的毒性为中毒,但NNO表现为高毒,EC50值为0.17 mg·L-1.     

Genetic diversity of Daphnia magna populations enhances resistance to parasites

The diversity-disease hypothesis states that decreased genetic diversity in host populations increases the incidence of diseases caused by pathogens (= monoculture effect) and eventually influences ecosystem functioning. The monoculture effect is well-known from crop studies and may be partially specific to the artificial situation in agriculture. The effect received little attention in animal populations of different diversities. Compared with plants, animals are mobile and exhibiting social interactions. We followed the spread of a microsporidian parasite in semi-natural outdoor Daphnia magna populations of low and high genetic diversity. We used randomly selected, naturally occurring host genotypes. Host populations of low diversity were initially monoclonal, while the host populations of high diversity started with 10 genotypes per replicate. We found that the parasite spread significantly better in host populations of low diversity compared with host populations of high diversity, independent of parasite diversity. The difference was visible over a 3-year period. Host genotypic diversity did not affect host population density. Our experiment demonstrated a monoculture effect in independently replicated semi-natural zooplankton populations, indicating that the monoculture effect may be relevant beyond agriculture.     

Application of individual growth and population models of Daphnia pulex to Daphnia magna, Daphnia galeata and Bosmina longirostris

Daphnia models for individual growth and population dynamics have been developed in the manner of models developed by Gurney, McCauley, Andersen and others. All or most of the earlier models were parameterized for Daphnia pulex; we have used the D. pulex model as a baseline model for other species of Daphnia such as magna, galeata and also Bosmina longirostris. Because of the lack of ample data for D. magna, D. galeata and B. longirostris, some of the physiological data had to be relied on the other species whose data were available and in some case calibrated. We were able to produce reasonable results for individual growth as well as population dynamics under the controlled laboratory conditions. Most of the results were compared with the available laboratory data for population as well as growth. All the simulations have been done under high and low food concentrations. The animals are assumed to be feeding on green algae (Chlamydomonas reinhardtti) under the laboratory conditions of 18–20°C. The continuous growth until the end of the life was observed in smaller B. longirostris, whereas rapid growth in the beginning and slower after the start of the reproduction was observed in Daphnia species. The smaller species matured earlier than larger species. B. longirostris population sustained better than Daphnia species in medium food concentrations.     

Response of the respiratory rate of Daphnia magna to changing food conditions

Summary The respiratory rate of the cladoceran Daphnia magna was measured at varying concentrations of a green alga in a flow-through respirometer. Daphnids were either preconditioned to the respective food concentration or the food concentration was suddenly changed during the experiment and the response of the respiratory rate monitored. Previously starved animals were provided with food or prefed animals were deprived of food. The respiratory rate increased considerably with increasing concentrations of algae until a maximum rate was reached at a critical algal concentration corresponding to the incipient limiting level for feeding. The response of the respiratory rate to changing food conditions was fast, lagging only a few minutes behind the change in food. The respiratory rate of starved daphnids increased quickly when they received food, even at low concentrations. Prefed daphnids responded to the replacement of the food suspension by filtered water with reductions in their respiratory rates. A linear relationship between the assimilation rate and the respiration rate was found, indicating that the more than twofold range of the respiratory rate was due to specific dynamic action. The SDA coefficients of 0.15–0.24 found for Daphnia are consistent with values for marine zooplankton.     

Mechanisms of energy allocation to reproduction in the cladoceran Daphnia magna Straus

Understanding rules of resource allocation within individuals is helpful in explaining population dynamics. This is particularly the case under the conditions of resource limitation that are commonly experienced by zooplankton. Here, we evaluate assumptions underlying models of resource allocation in Daphnia and test the predictions of two models of response to starvation.
We also test the predictions of two simple models concerning the mechanisms of egg provisioning in Daphnia magna. Our results: (1) demonstrate that provisioning is discontinuous, occurring over a discrete period of the instar; (2) support the hypothesis that egg production occurs in a serial fashion; (3) show that Daphnia magna responds to starvation by ceasing egg production but that there is an increase in mean size of eggs provisioned during the instar, prior to starvation; and (4) broadly support predictions that the response of Daphnia to starvation is an instantaneous cessation of reproduction but that there is a time lag before death.     

Bacterial infection changes the elemental composition of Daphnia magna

1. An animal's elemental composition can be an important indicator of its physiological state and role in ecosystem nutrient cycling. We examined the interactive effects of bacterial (Pasteuria ramosa) infection and phosphorus (P)-poor food on the body stoichiometry of Daphnia magna. Daphnia were exposed to or held free of a bacterial parasite and fed algal food of different C:P ratios (100-500) over a 28-day period. 2. To assess the effects of exposure and infection on Daphnia stoichiometry, we measured their whole body content of carbon (C), nitrogen (N), and P on four different days (4, 8, 15, and 28) during the experiment. 3. We found strong effects of infection, food quality, and/or their interactions on the C, N, and P content of Daphnia, especially as the infectious disease progressed. At the end of the experiment, infected animals had significantly more C and less P in their bodies than uninfected conspecifics. Body N content of Daphnia consuming P-rich food was reduced by bacterial infection whereas Daphnia consuming P-poor algae showed increased body N content from infection. 4. Using a mass-balance model, we found that changes in N and P content of host bodies were largely accountable by disease-induced alterations to Daphnia reproduction (i.e. bacterial induced sterility) and the accumulation of Pasteuria spores in the body cavity. Our calculations also show that the observed increase in host C content could not be accounted for by loss of eggs or accumulation of bacterial spores. This instead must result from unidentified changes to underlying daphnid tissue C content. 5. These results demonstrate that intraspecific variation in zooplankton body stoichiometry can be caused by exposure to and infection by bacterial parasites. In addition, these effects were found to depend both upon the stage of the disease and upon the food quality consumed by the host.     

In Vitro Toxicity Evaluation of 25-nm Anatase TiO2 Nanoparticles in Immortalized Keratinocyte Cells

Titanium dioxide (TiO(2)) nanoparticles (NPs) are massively fabricated and widely used in daily life, and thus potential risk has been posed to human health. However, the mechanism of the interaction between TiO(2) NPs and cells is still unclear. In this study, the interaction of anatase TiO(2) NPs with HaCaT cells is studied in vitro with multi-techniques. The TiO(2) NPs not only insert into cells through endocytic pathway but also penetrate into the cell. The TiO(2) NPs could produce reactive oxygen species (ROS) after dispersion spontaneously. Furthermore, the interaction between TiO(2) NPs and cellular components might also generate ROS. The ROS generation could lead to cellular toxicity if the level of ROS production overwhelms the antioxidant defense. Cytoskeletal components, particularly the microfilaments and microtubules, cause modifications upon exposure to TiO(2) NPs. With all results, the toxicological effects of TiO(2) NPs on HaCaT cell can be simplified into six events.     

Toxicity of TiO2 Nanoparticles to Escherichia coli: Effects of Particle Size,Crystal Phase and Water Chemistry

Controversial and inconsistent results on the eco-toxicity of TiO₂ nanoparticles (NPs) are commonly found in recorded studies and more experimental works are therefore warranted to elucidate the nanotoxicity and its underlying precise mechanisms. Toxicities of five types of TiO₂ NPs with different particle sizes (10∼50 nm) and crystal phases were investigated using Escherichia coli as a test organism. The effect of water chemistry on the nanotoxicity was also examined. The antibacterial effects of TiO₂ NPs as revealed by dose-effect experiments decreased with increasing particle size and rutile content of the TiO₂ NPs. More bacteria could survive at higher solution pH (5.0–10.0) and ionic strength (50–200 mg L⁻¹ NaCl) as affected by the anatase TiO₂ NPs. The TiO₂ NPs with anatase crystal structure and smaller particle size produced higher content of intracellular reactive oxygen species and malondialdehyde, in line with their greater antibacterial effect. Transmission electron microscopic observations showed the concentration buildup of the anatase TiO₂ NPs especially those with smaller particle sizes on the cell surfaces, leading to membrane damage and internalization. These research results will shed new light on the understanding of ecological effects of TiO₂ NPs.     

Acute Toxicity of TiO2 Nanoparticles to Ceriodaphnia dubia under Visible Light and Dark Conditions in a Freshwater System

The ever increasing industrial and consumer applications of titanium dioxide nanoparticles (TiO₂ NPs) raise concern over the possible risk associated with their environmental exposure. Still, the knowledge regarding nanoparticle behavior in a freshwater ecosystem is lacking. The current study focuses on the toxicity of TiO₂ NPs towards Ceriodaphnia dubia (a dominant daphnid isolated from the freshwater) under two different conditions; (1) light and dark photoperiod (16:8 h) and (2) continuous dark conditions, for a period of 48 h. An increase in toxicity was observed with an increase in the concentration, until a certain threshold level (under both photoperiod and dark conditions), and beyond which, reduction was noted. The decrease in toxicity would have resulted from the aggregation and settling of NPs, making them less bioavailable. The oxidative stress was one of the major contributors towards cytotoxicity under both photoperiod and dark conditions. The slow depuration of TiO₂ NPs under the photoperiod conditions confirmed a higher NP bioaccumulation and thus a higher bioconcentration factor (BCF) compared to dark conditions. The transmission electron micrographs confirmed the bioaccumulation of NPs and damage of tissues in the gut lining.