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Magna
Kinds of Magna Selected AbstractsExpulsion of a geopressured hydrothermal system associated with destructive earthquakes and buried active faults in the Shinanogawa Seismic Belt, JapanISLAND ARC, Issue 2 2004Huilong Xu Abstract The Shinanogawa Seismic Belt in the Northern Fossa Magna, Honshu Island, Japan, extends along the Shinano River, bounding the Eurasian Plate and the Okhotsk Plate. The geopressured hydrothermal system occurs widely in the Northern Fossa Magna region. Many destructive earthquakes are related to the activity of this system in the Shinanogawa Seismic Belt. Expulsion of a geopressured hydrothermal system and rising from depth along an active fault triggers the occurrence of an earthquake and opens the fault as a pathway. Anomalous areas in temperature, electrical conductivity and Cl, concentration of groundwater trend north,east in a linear distribution, and convincingly demonstrate the presence of a buried active fault at the epicentral area of the destructive earthquake in the Shinanogawa Seismic Belt. The distribution of the major axis of the anomalous area in groundwater temperature shows a strong positive relationship with earthquake magnitude, which means that the distribution of this area may indicate the scale of earthquake fault. The linearly anomalous areas in groundwater temperature, resulting from the percolation of a geopressured hydrothermal system, that have no record of previous destructive earthquake are predicted to be areas where destructive earthquakes could occur in the future. Four potential earthquake areas are proposed and discussed in this paper, based on re-examination of active faults and seismicity in the Shinanogawa Seismic Belt. [source] Risk factors and ultrasonographic profile of posterior fossa haemorrhages in preterm infantsJOURNAL OF PAEDIATRICS AND CHILD HEALTH, Issue 4 2009Arvind Sehgal Aims: While preterm infants are known to be at risk of intracranial haemorrhages, advances in ultrasound imaging of preterm babies have facilitated recognition of presence of haemorrhages in the posterior fossa, which include cerebellar and Cisterna Magna haemorrhages. There are limited data on the profile and predisposing risk factors. The objective was to identify antenatal, intrapartum and post-natal risk factors for and to define the clinical spectrum. The study was designed as a retrospective case-control study in the setting of a tertiary level neonatal intensive care unit. Preterm babies ,30 weeks gestation age admitted between January 2005 and December 2006, with an ultrasound diagnosis of posterior fossa haemorrhage and an equal number of controls matched for gestation age, gender and month of birth with normal cranial scans were selected. Systematic chart and radiographic review was done. All cranial ultrasounds in both groups were reviewed. Results: Eighteen babies had documented posterior fossa haemorrhage (13 cerebellar, 5 isolated Cisterna Magna, 10 both), the median time of detection being 2.5 days. Eleven babies had either no or grade I/II supratentorial bleeds, while half of all cerebellar bleeds were bilateral. All haemorrhages were visualised from mastoid view and none from anterior fontanel. On univariate analysis, multiple gestations, lack of antenatal steroids, foetal heart rate abnormalities, need for volume expanders and cardiotrophins and sepsis were associated with a higher risk for having posterior fossa bleeds. Conclusions: Posterior fossa haemorrhages in preterm babies are being increasingly recognised. Antenatal, intrapartum and post-natal factors may predispose towards haemorrhages in the cerebellum or Cisterna Magna. [source] The effect of a pathogen epidemic on the genetic structure and reproductive strategy of the crustacean Daphnia magnaECOLOGY LETTERS, Issue 9 2004Suzanne E. Mitchell Abstract Host,parasite coevolution is potentially of great importance in producing and maintaining biological diversity. However, there is a lack of evidence for parasites directly driving genetic change. We examined the impact of an epidemic of the bacterium Pasteuria ramosa on a natural population of the crustacean Daphnia magna through the use of molecular markers (allozymes) and laboratory experiments to determine the susceptibility of hosts collected during and after the epidemic. Some allozyme genotypes were more heavily infected than others in field samples, and the population genetic structure differed during and after the epidemic, consistent with a response to parasite-mediated selection. Laboratory studies showed no evidence for the evolution of higher resistance, but did reveal an intriguing life-history pattern: host genotypes that were more susceptible also showed a greater tendency to engage in sex. In light of this, we suggest a model of host,parasite dynamics that incorporates the cycles of sex and parthenogenesis that Daphnia undergo in the field. [source] Effects of predator-induced visual and olfactory cues on 0+ perch (Perca fluviatilis L.) foraging behaviourECOLOGY OF FRESHWATER FISH, Issue 2 2006V. N. Mikheev Abstract,,, Foraging juvenile fish with relatively high food demands are usually vulnerable to various aquatic and avian predators. To compromise between foraging and antipredator activity, they need exact and reliable information about current predation risk. Among direct predator-induced cues, visual and olfactory signals are considered to be most important. Food intake rates and prey-size selectivity of laboratory-reared, naive young-of-the-year (YOY) perch, Perca fluviatilis, were studied in experiments with Daphnia magna of two size classes: 2.8 and 1.3 mm as prey and northern pike, Esox lucius, as predator. Neither total intake rate nor prey-size selectivity was modified by predator kairomones alone (water from an aquarium with a pike was pumped into the test aquaria) under daylight conditions. Visual presentation of pike reduced total food intake by perch. This effect was significantly more pronounced (synergistic) when visual and olfactory cues were presented simultaneously to foraging perch. Moreover, the combination of cues caused a significant shift in prey-size selection, expressed as a reduced proportion of large prey in the diet. Our observations demonstrate that predator-induced olfactory cues alone are less important modifiers of the feeding behaviour of naive YOY perch than visual cues under daylight conditions. However, pike odour acts as a modulatory stimulus enhancing the effects of visual cues, which trigger an innate response in perch. [source] Difference in the sensitivity to chemical compounds between female and male neonates of Daphnia magnaENVIRONMENTAL TOXICOLOGY, Issue 5 2008Erika Ikuno Abstract Daphnia magna usually produce female offspring by parthenogenesis, and thus only female neonates are used to evaluate the environmental toxicity to chemicals. Additionally, it is known that male daphnids are induced by exposure to a juvenile hormone, methyl farnesoate, during late ovarian development. In this study, we investigated the concentration of methyl farnesoate in a 24-h exposure producing 100% males, and the difference in sensitivity to chemical compounds, potassium dichromate, pentachlorophenol, and paraquat, between females and males, referring to OECD Test Guideline 202. The results show that the minimum concentration for 100%-male induction of methyl farnesoate in adult females was 50 ,g/L. In addition, acute toxicity tests (immobility test) with the other chemicals showed that male neonates have higher tolerance to potassium dichromate and pentachlorophenol than females for at least 24 h after birth, while no sex difference was observed in the sensitivity to paraquat. The differences in the median effective concentrations in these compounds between female and male neonates suggest two different overall modes of action. Using female daphnids for environmentally toxicity testing seems reasonable, since the females are more sensitive to chemicals than males. Furthermore, the method of male induction established in this study could be used for screening of endocrine disruptors. © 2008 Wiley Periodicals, Inc. Environ Toxicol, 2008. [source] Chronic toxicity and responses of several important enzymes in Daphnia magna on exposure to sublethal microcystin-LRENVIRONMENTAL TOXICOLOGY, Issue 3 2005Wei Chen Abstract In the current study, the toxicological mechanisms of microcystin-LR and its disadvantageous effects on Daphnia magna were examined. Survival rate, number of newborn, activity of several important enzymes [glutathione S-transferase (GST), lactate dehydrogenase (LDH), phosphatases, and glutathione], accumulated microcystins, and ultrastructural changes in different organs of Daphnia were monitored over the course of 21-day chronic tests. The results indicated that low concentrations of dissolved microcystin had no harmful effect on Daphnia. On the contrary, stimulatory effects were detected. In the presence of toxin at high dosage and for long-term exposure, GST and glutathione levels decreased significantly. The decreased enzyme activity in the antioxidant system probably was caused by detoxification reactions with toxins. And these processes of detoxification at the beginning of chronic tests may enable phosphatases in Daphnia magna to withstand inhibition by the toxins. At the same time, we also found that the LDH activity in test animals increased with exposure to microcystin-LR, indicating that adverse effects occurred in Daphnia. With microcystin given at a higher dosage or for a longer exposure, the effect on Daphnia magna was fatal. In the meantime, microcystin began to accumulate in Daphnia magna, and phosphatase activity started to be inhibited. From the ultrastructure results of cells in D. magna, we obtained new information: the alimentary canal may be the target organ affected by exposure of microcystins to D. magna. The results of the current study also suggested that the oxidative damage and PPI (protein phosphatase inhibition) mechanisms of vertebrates also are adapted to Daphnia. © 2005 Wiley Periodicals, Inc. Environ Toxicol 20: 323,330, 2005. [source] Application of Toxkit microbiotests for toxicity assessment in soil and compostENVIRONMENTAL TOXICOLOGY, Issue 4 2004L. Dubova Abstract The potential of Toxkit microbiotests to detect and analyze pollution in agricultural soil and the quality of compost was studied. The toxicity tests used included seed germination biotests using cress salad (Lepidum sativum L.), tomato (Lycopersicum esculentum L.), and cucumber (Cucumis sativus L.), and the Toxkit microbiotests included those with microalgae (Selenastrum capricornutum), protozoa (Tetrahymena thermophila), crustaceans (Daphnia magna, Thamnocephalus platyurus, and Heterocypris incongruens), and rotifers (Brachionus calyciflorus). Experiments on compost were undertaken in a modified solid-state fermentation system (SSF) and under field conditions (in a windrow). To promote the composting process, two strains of Trichoderma (Trichoderma lignorum and Trichoderma viride), as well as a nitrification association that regulated the nitrogen-ammonification and nitrification processes were applied. © 2004 Wiley Periodicals, Inc. Environ Toxicol 19: 274,279, 2004. [source] Tests for the toxicity assessment of cyanobacterial bloom samplesENVIRONMENTAL TOXICOLOGY, Issue 5 2001gorzata Tarczynska Abstract Cyanobacterial (blue,green algal) blooms are one of the common consequences of the increasing eutrophication of surface waters. The production of cyanobacterial toxins and their presence in drinking and recreational waters represents a growing danger to human and animal health. Due to a lack of toxin standards and to resource limitations on the wide-scale use of analytical methods (e.g., high-performance liquid chromatography, enzyme-linked immunosorbent assay (ELISA)) in cyanobacterial toxin monitoring, it is necessary to assess and to develop additional methods for their detection and estimation. Microbiotests using invertebrates offer a possible approach for the inexpensive and straightforward detection and assessment of cyanobacterial bloom toxicity. Three microbiotests with: Thamnocephalus platyurus, Daphnia magna, and Spirostomum ambiguum were examined with bloom samples containing hepatotoxic microcystin-LR and up to five additional microcystin variants. Two kinds of cyanobacterial bloom sample preparations were tested: crude extracts (CE) and purified extracts (PE). The highest toxicity was found when CE was used for microbiotests. The sensitivity of microorganisms decreased from S. ambiguum to T. platyurus and to D. magna. A statistically significant correlation was found between microcystin concentration and T. platyurus biotest, and between mouse bioassay and S. ambiguum results. Addition of Me2SO (1%, v/v) is a possible method to increase the sensitivity of the microorganisms for microcystin-LR. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 383,390, 2001 [source] Factors affecting biodegradation of 2-chlorophenol by Alcaligenes sp. in aerobic reactorsENVIRONMENTAL TOXICOLOGY, Issue 4 2001A. Gallego Abstract The influence of variations in carbon source concentration, cell inocula, pH, presence of other substrates, and other organisms on the biodegradation of 2-chlorophenol (2-CP) was studied for Alcaligenes sp. isolated from natural sources. Assays of biodegradation were performed in batch and continuous-flow fluidized-bed aerobic reactors. Evaluation of biodegradation was performed by determining total phenols, chemical oxygen demand (COD), and 2-CP by ultraviolet (UV) spectrophotometry. Measurement of microbial growth was carried out by the plate count method. Bioassays of acute toxicity were performed to evaluate detoxification by using Daphnia magna. Results obtained show that under batch conditions with initial inocula of 106 cells/mL the strain grew exponentially with 100, 200, and 300 mg/L of 2-CP within 48 hr. A lag period was observed with low cell density inocula (105 cells/mL). The strain showed marked delay in the biodegradation of 2-CP at pH 5. Removal of target substrate from mixtures containing other carbon sources demonstrated the possibility of concurrent growth. Mineralization of 2-CP was assessed by gas chromatography carried out at the end of the batch assays and at the exit of the continuous-flow reactor. The presence of other organisms (bacteria, rotifers, ciliate, and algae) that developed in the fluidized-bed reactor did not affect the efficacy of the biodegradation of 2-CP. The removal of 2-CP in the two assayed systems was over 97% in all cases. Toxicity was not detected at the exit of the continuous reactor. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 306,313, 2001 [source] Toxicity tests to assess pollutants removal during wastewater treatment and the quality of receiving waters in ArgentinaENVIRONMENTAL TOXICOLOGY, Issue 3 2001Carlos E. Gómez Abstract In Argentina, legislation to control adverse impacts of effluent discharges and the quality of receiving waters is scant and relies mainly on the physicochemical characteristics of the effluents and receiving waters. Objectives of this study were to use standardized acute toxicity tests to assess treatment of petrochemical industry effluents and the toxicity of various treated industrial effluents in the Buenos Aires metropolitan area and their receiving waters. Tests for the first objective used Daphnia magna and Ceriodaphnia dubia; those for the second used D. magna, Spirillum volutans, and Scenedesmus spinosus. Chemical analyses demonstrated that the removal of aromatic hydrocarbon compounds (benzene, toluene, ethylbenzene, xylene, styrene, and naphthalene) from the petrochemical effluents ranged between 77 and 93%, but toxicity removal was significantly lower: untreated effluents were very toxic and treated effluents were very toxic to toxic [acute toxicity units (TUa)>3]. Physicochemical parameters measured according to current Argentinian regulations indicated that industrial effluents (e.g., from textile and paper industries) were within established guidelines, but 25% of the samples were moderately to highly toxic (TUa>1.33). However, for the receiving waters, toxicity tests were moderate to very toxic. The results show the need of including tests for toxicity of discharged effluents, and their effects on receiving waters of Argentina, especially for regulatory purposes. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 217,224, 2001 [source] Toxicity evaluation of metal plating wastewater employing the Microtox® assay: A comparison with cladocerans and fishENVIRONMENTAL TOXICOLOGY, Issue 2 2001Kyungho Choi Abstract The relative sensitivity of the Microtox assay is closely related to the type of toxicant, and hence its utility in biomonitoring effluents is better evaluated on a case-by-case basis. The Microtox® assay, employing the marine bacterium Vibrio fischeri, was evaluated for its applicability in monitoring metal plating wastewater for toxicity. The results of the Microtox assay after 5, 15, and 30 min of exposure, were compared with data obtained from conventional whole effluent toxicity testing (WET) methods that employed Daphnia magna, Ceriodaphnia dubia, and the fathead minnow (Pimephales promelas). The Microtox assay produced notably comparable EC50 values to the LC50 values of the acute fathead minnow toxicity test (<0.5 order of difference). The Spearman's rank correlation analyses showed that the bacterial assay, regardless of exposure duration, correlated better with the acute fish than the daphnid results (p<0.05). These observations were consistent to other studies conducted with inorganic contaminants. The relative sensitivity of the 30-min Microtox assay was within the range of the two frequently used acute daphnid/fish toxicity tests. In conclusion, the Microtox assay correlated well with the acute fathead minnow data and is well suited for toxicity monitoring for these types of industrial wastes. © 2001 John Wiley & Sons, Inc. Environ Toxicol 16: 136,141, 2001 [source] Early signs of lethal effects in Daphnia magna (Branchiopoda, Cladocera) exposed to the insecticide cypermethrin and the fungicide azoxystrobinENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 10 2010Ursula Friberg-Jensen Abstract This study presents the effects of sublethal concentrations of pesticides cypermethrin and azoxystrobin on the activity of several physiological parameters of egg-carrying Daphnia magna studied using a video-image technique. Single tethered daphnids were continuously recorded for 24,h of pesticide exposure, and the activity of the heart, the filtering limbs, the mandibles, and the focal spine were subsequently analyzed. Acute toxicity tests based on the criteria of immobilization were performed on egg-carrying D. magna, and sublethal concentrations of 0.1, 1.0, and 10,µg/L cypermethrin and 0.5, 1.0, and 2.0,mg/L azoxystrobin were established. At a concentration as low as 0.1,µg/L cypermethrin, the 5% effective concentration after 24,h of exposure (EC5,24h), the activity of the focal spine increased and the filtering limb activity decreased. The activity of the mandibles was reduced by exposure to 1.0 (EC18,24,h) and 10,µg/L (EC41,24,h) cypermethrin, whereas heart activity increased at a concentration of 10,µg/L (EC41,24,h). With regard to azoxystrobin, the activity of all response parameters except the focal spine decreased by exposure to 0.5,mg/L (EC4,24h) azoxystrobin. The focal spine was not affected by azoxystrobin. The results show that physiological mechanisms important for ingestion of food in D. magna may be impaired by low concentrations of commonly used pesticides. Environ. Toxicol. Chem. 2010;29:2371,2378. © 2010 SETAC [source] Subcellular distribution of zinc in Daphnia magna and implication for toxicityENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 8 2010Wen-Xiong Wang Abstract We examined the subcellular partitioning of zinc (Zn) in Daphnia magna both under acute and chronic exposures. In the acute Zn toxicity tests, the daphnids were exposed to different Zn concentrations for 48,h or to one lethal concentration (1,000,µg/L) for different durations (time to death for up to 47,h). Significant mortality of daphnids was observed when the newly accumulated Zn concentration reached a threshold level of approximately 40,µg/g wet weight (or 320,µg/g dry wt), approximately 3.5 times higher than the background tissue concentration (92,µg/g dry wt). Chronic exposure (14 d) to Zn resulted in nonobservable effect on survivorship and growth at newly accumulated tissue concentration of over 40,µg/g wet weight. With increasing Zn acute exposure, more Zn was partitioned into the cellular debris fraction, indicating that this fraction was presumably the first targeted site of binding for Zn upon entering the animals. The importance of other subcellular fractions either decreased accordingly or remained comparable. We found that the metal-sensitive fraction (Zn distribution in the organelles and heat-denatured proteins) did not predict the acute Zn toxicity in Daphnia. During chronic exposure, however, no major change of the subcellular partitioning of Zn with increasing Zn exposure was documented. Zinc was mainly found in the organelles and heat-stable protein fractions during chronic exposure, suggesting that any subcellular repartitioning occurred primarily during acute exposure. Metallothioneins were induced upon chronic Zn exposure, but its induction evidently lagged behind the Zn accumulation. Our present study showed that the subcellular fractionation approach could not be readily used to predict the acute and chronic toxicities of Zn in Daphnia. A tissue-based Zn accumulation approach with a threshold Zn tissue concentration was better in predicting acute Zn toxicity. Environ. Toxicol. Chem. 2010; 29:1841,1848. © 2010 SETAC [source] Influence of stability on the acute toxicity of CdSe/ZnS nanocrystals to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2010Heather E. Pace Abstract The acute toxicity of polymer-coated CdSe/ZnS quantum dots (QDs) to Daphnia magna was investigated using 48-h exposure studies. The principal objective was to relate the toxicity of QDs to specific physical and chemical aspects of the QD. As such, two different CdSe core diameters, 2,nm QDs (green-emitting) and 5,nm QDs (red-emitting), and two different surface coatings, polyethylene oxide (PEO) and 11-mercaptoundecanoic acid (MUA) were studied. The QDs were characterized before and after the 48-h exposure using fluorescence, ultrafiltrations (3 kDa), and inductively coupled plasma-atomic emission spectrometry (ICP-AES) metal analysis. In addition, flow field flow fractionation-inductively coupled plasma-mass spectrometry (Fl FFF-ICP-MS) was used as a more extensive characterization technique to determine particle size and composition as well as identify other potential constituents in the QD solutions. The more stable QDs (PEO) were found to be less acutely toxic than the QDs with accelerated dissolution (MUA), suggesting QD stability has significant impact on the nanoparticles' short-term toxicity. The emergence of dissolved Cd2+ in solution indicates that the toxicity of the MUA QDs is likely due to Cd poisoning, and a mass-based dose response occurred as a consequence of this mode of action. Alternatively, the PEO QDs caused acute toxicity without observed particle dissolution (i.e., no detectable metals were solubilized), suggesting an alternative mode of toxic action for these nanoparticles. Results of the present study suggest that using particle number, instead of mass, as a dose metric for the PEO QDs, produces markedly different conclusions, in that smaller core size does not equate to greater toxicity. Environ. Toxicol. Chem. 2010;29:1338,1344. © 2010 SETAC [source] Quick assessment of cytotoxins effect on Daphnia magna using in vivo fluorescence microscopyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2010Vera V. Teplova Abstract A novel approach to contaminant toxicity screening is proposed. The use of fluorescent microscopy with fluorescent dyes allows for assessing intoxication of Daphnia magna tissues, at various stages of exposure, to contaminants present in water. As shown, D. magna may not only be used as a test species in toxicity tests based on its lethality, but due to its translucency and application of fluorescent probes, separate steps of its intoxication and dying can be visualized. Using a variety of fluorescent probes, the present study also contributes to a better understanding of the toxicity mechanisms. Environ. Toxicol. Chem. 2010;29:1345,1348. © 2010 SETAC [source] The effects of continuous and pulsed exposures of suspended clay on the survival, growth, and reproduction of Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2010Sarah E. Robinson Abstract Suspended sediments are a natural component of aquatic ecosystems, but anthropogenic activity such as land development can result in significant increases, especially after rain events. Continuous exposures of suspended clay and silt have been shown to affect growth and reproduction of Cladocera, leading to a decrease in population growth rate. The mechanism of clay toxicity in these filter-feeding organisms is clogging of the gut tract, resulting in decreased food uptake and assimilation. When placed in clean water, daphnids can purge clay from their gut and recover. In many surface waters, aquatic organisms experience episodic exposures of high concentrations of suspended solids driven by rain events. However, little is known about the consequences of pulsed exposures on individuals and populations. The objective of the present study was to characterize the effects of continuous and pulsed exposures of natural and defined clays on survival, growth, and reproduction of Daphnia magna. Two defined clays, montmorillonite and kaolinite, as well as clay isolated from the Piedmont region of South Carolina, USA, were used. Continuous exposures of clays elicited a dose dependent decrease in survival. Toxicity varied depending on clay source with montmorillonite,>,natural clay,>,kaolinite. Pulsed exposures caused a decrease in survival in a 24 h exposure of 734 mg/L kaolinite. Exposure to 73.9 mg/L also caused an increase in the time to gravidity, although there was not a corresponding decrease in neonate production over 21 d. No significant effects resulted from 12 h exposures even at 730 mg/L, almost 10 times the 24-h reproductive effects concentration. This suggests that exposure duration impacted toxicity more than exposure concentration in these pulsed exposures. Environ. Toxicol. Chem. 2010;29:168,175. © 2009 SETAC [source] Chronic toxicity of five structurally diverse demethylase-inhibiting fungicides to the crustacean Daphnia magna: A comparative assessmentENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2009Enken Hassold Abstract Demethylase inhibitors (DMIs) are broad-spectrum fungicides that are ubiquitously used in agriculture and medicine. They comprise chemically heterogeneous substances that share a common biochemical target in fungi, the inhibition of a specific step in sterol biosynthesis. Several DMIs are suspected to disrupt endocrine-mediated processes in a range of organisms and to inhibit ecdysteroid biosynthesis in arthropods. It is unclear, however, whether and, if so, to what extent different DMI fungicides have a similar mode of action in nontarget organisms, which in turn would lead to a common chronic toxicity profile. Therefore, we selected a representative of each of the major DMI classes,-the piperazine triforine, the pyrimidine fenarimol, the pyridine pyrifenox, the imidazole prochloraz, and the triazole triadimefon,-and comparatively investigated their chronic toxicity to Daphnia magna. No toxicity was detectable up to the limit of solubility of triforine (61 ,mol/L). All other DMIs reduced reproductive success by delaying molting and development and by causing severe developmental abnormalities among offspring. Prochloraz was most toxic (median effective concentration [EC50] for fecundity reduction, 0.76 ,mol/L), followed by fenarimol (EC50, 1.14 ,mol/L), pyrifenox (EC50, 3.15 ,mol/L), and triadimefon (EC50, 5.13 ,mol/L). Mean effect concentrations for fecundity reduction were related to lipophilicity and followed baseline toxicity. However, triadimefon and fenarimol (but none of the other tested DMIs) caused severe eye malformations among exposed offspring. Affected neonates did survive, but a reduced ecological fitness can be assumed. Offspring exposed to fenarimol in mater matured earlier. The investigated different life-history parameters were affected in a substance-specific manner. These qualitatively different toxicity profiles suggest additional, substance-specific mechanisms of action in D. magna that probably are related to an antiecdysteroid action. [source] Assessment of the toxicity of mixtures of nickel or cadmium with 9,10-phenanthrenequinone to Daphnia magna: Impact of a reactive oxygen-mediated mechanism with different redox-active metalsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 7 2007Fangli Xie Abstract Recently, we showed that reactive oxygen species (ROS) formation was involved in the toxicity of the redox-active metal Cu and mixtures of Cu plus a photomodified polycyclic aromatic hydrocarbon (PAH), phenanthrenequinone (PHQ), to Daphnia magna. It is unknown, however, if similar results can be observed for metals with lower or no redox activity and their mixtures with PHQ. In the present study using D. magna, the toxicity of Ni, a weakly redox-active metal, and of Cd, a non-redox active metal, was examined with or without PHQ. The abilities of Ni, Cd, PHQ, and binary mixtures of metal plus PHQ to generate ROS were measured using a 2,,7,-dichlorofluorescein fluorescence assay. The results were compared with the results of Cu and mixtures of Cu plus PHQ from a recent study by our group. The order of metal toxicity to D. magna was found to be Cd , Cu > Ni. As with Cu/PHQ mixtures, synergistic toxicity was observed for mixtures of Ni and PHQ, whereas additive toxicity was observed for mixtures of Cd and PHQ. Alone, PHQ had no impact on ROS levels in D. magna. Nickel alone caused elevated ROS, which was further enhanced in the presence of PHQ. Neither Cd nor Cd/PHQ mixtures increased ROS production. Attenuation of toxicity and ROS production was observed in response to treatment with low concentrations of L -ascorbic acid. These results indicate potential toxic interactions between metals and modified PAHs. With redox-active metals, such as Cu and Ni, and modified PAHs, such as PHQ, these interactions can involve ROS formation. [source] Development of a daphnia magna DNA microarray for evaluating the toxicity of environmental chemicalsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2007Hajime Watanabe Abstract Toxic chemical contaminants have a variety of detrimental effects on various species, and the impact of pollutants on ecosystems has become an urgent issue. However, the majority of studies regarding the effects of chemical contaminants have focused on vertebrates. Among aquatic organisms, Daphnia magna has been used extensively to evaluate organism- and populationlevel responses of invertebrates to pollutants in acute toxicity or reproductive toxicity tests. Although these types of tests can provide information concerning hazardous concentrations of chemicals, they provide no information about their mode of action. Recent advances in molecular genetic techniques have provided tools to better understand the responses of aquatic organisms to pollutants. In the present study, we adapted some of the techniques of molecular genetics to develop new tools, which form the basis for an ecotoxicogenomic assessment of D. magna. Based on a Daphnia expressed sequence tag database, we developed an oligonucleotide-based DNA microarray with high reproducibility. The DNA microarray was used to evaluate gene expression profiles of neonatal daphnids exposed to several different chemicals: Copper sulfate, hydrogen peroxide, pentachlorophenol, or ,-naphthoflavone. Exposure to these chemicals resulted in characteristic patterns of gene expression that were chemical-specific, indicating that the Daphnia DNA microarray can be used for classification of toxic chemicals and for development of a mechanistic understanding of chemical toxicity on a common freshwater organism. [source] Mixture and single-substance toxicity of selective serotonin reuptake inhibitors toward algae and crustaceansENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2007Anne Munch Christensen Abstract Selective serotonin reuptake inhibitors (SSRIs) are used as antidepressant medications, primarily in the treatment of clinical depression. They are among the pharmaceuticals most often prescribed in the industrialized countries. Selective serotonin reuptake inhibitors are compounds with an identical mechanism of action in mammals (inhibit reuptake of serotonin), and they have been found in different aqueous as well as biological samples collected in the environment. In the present study, we tested the toxicities of five SSRIs (citalopram, fluoxetine, fluvoxamine, paroxetine, and sertraline) as single substances and of citalopram, fluoxetine, and sertraline in binary mixtures in two standardized bioassays. Test organisms were the freshwater algae Pseudokirchneriella subcapitata and the freshwater crustacean Daphnia magna. In algae, test median effect concentrations (EC50s) ranged from 0.027 to 1.6 mg/L, and in daphnids, test EC50s ranged from 0.92 to 20 mg/L, with sertraline being one of the most toxic compounds. The test design and statistical analysis of results from mixture tests were based on isobole analysis. It was demonstrated that the mixture toxicity of the SSRIs in the two bioassays is predictable by the model of concentration addition. Therefore, in risk assessment based on chemical analysis of environmental samples, it is important to include the effect of all SSRIs that are present at low concentrations, and the model of concentration addition may be used to predict the combined effect of the mixture of SSRIs. [source] Population growth of Daphnia magna under multiple stress conditions: Joint effects of temperature, food, and cadmiumENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 5 2006Evelyn H. W. Heugens Abstract Aquatic organisms in the field often are exposed to combinations of stress factors of variousorigins. Little is known of the interaction between different types of stressors; hence, the predictability of their joint effects is low. Therefore, the present study analyzed the joint effects of temperature, food, and cadmium on the population growth rate of the water flea Daphnia magna. The results revealed that temperature, food, and cadmium, as well as their interactions, were important factors that influenced life-history parameters and, as a consequence, the population growth rate of D. magna. In general, population growth rate increased at high temperature and food level but decreased when cadmium was present. The positive effect of temperature on population growth rate was smallest at limiting food levels. Negative effects of cadmium on the growth rate were enhanced at elevated temperatures, whereas high food levels protected the daphnids from adverse effects of cadmium. To avoid over- or underestimation regarding the toxicity of substances to field populations, results of standard toxicity tests should be applied in a location-specific way. [source] Comparative toxicity of cadmium, zinc, and mixtures of cadmium and zinc to daphnidsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2006Joseph R. Shaw Abstract Investigations were conducted to determine acute (48-h) effects of cadmium and zinc presented individually and in combination on Ceriodaphnia dubia, Daphnia magna, Daphnia ambigua, and Daphnia pulex. Toxicity tests were conducted with single metals to determine lethal effects concentrations (lethal concentrations predicted for a given percent [x] of a population, LCx value). These were used to derive metal combinations that spanned a range of effects and included mixtures of LC15, LC50, and LC85 values calculated for each metal and species. In single-metal tests, 48-h LC50 values ranged from 0.09 to 0.9 ,mol/L and 4 to 12.54 ,mol/L for cadmium and zinc, respectively. For each metal, D. magna was most tolerant and showed a different pattern of response from all others as determined by slope of concentration,response curves. In the combined metal treatments, all daphnids showed a similar pattern of response when LC15 concentrations were combined. This trend continued with few exceptions when LC15 concentrations of cadmium were combined with LC50 or LC85 values for zinc. However, when this treatment was reversed (LC15, zinc + LC50 or LC85, cadmium), responses of all species except D. magna indicated less-than-additive effects. For C. dubia, a near complete reduction in toxicity was observed when the LC15 for zinc was combined with LC85 for cadmium. Multimetal tests with D. magna did not differ from additive. Collectively, these studies suggest that D. magna may not be representative of other cladocerans. [source] Toxicity of fluoroquinolone antibiotics to aquatic organismsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 2 2005April A. Robinson Abstract Toxicity tests were performed with seven fluoroquinolone antibiotics, ciprofloxacin, lomefloxacin, ofloxacin, levofloxacin, clinafloxacin, enrofloxacin, and flumequine, on five aquatic organisms. Overall toxicity values ranged from 7.9 to 23,000 ,g/L. The cyanobacterium Microcystis aeruginosa was the most sensitive organism (5-d growth and reproduction, effective concentrations [EC50s] ranging from 7.9 to 1,960 ,g/L and a median of 49 ,g/L), followed by duckweed (Lemna minor, 7-d reproduction, EC50 values ranged from 53 to 2,470 ,g/L with a median of 106 ,g/L) and the green alga Pseudokirchneriella subcapitata (3-d growth and reproduction, EC50 values ranged from 1,100 to 22,700 ,g/L with a median 7,400 ,g/L). Results from tests with the crustacean Daphnia magna (48-h survival) and fathead minnow (Pimephales promelas, 7-d early life stage survival and growth) showed limited toxicity with no-observed-effect concentrations at or near 10 mg/L. Fish dry weights obtained in the ciprofloxacin, levofloxacin, and ofloxacin treatments (10 mg/L) were significantly higher than in control fish. The hazard of adverse effects occurring to the tested organisms in the environment was quantified by using hazard quotients. An estimated environmental concentration of 1 ,g/L was chosen based on measured environmental concentrations previously reported in surface water; at this level, only M. aeruginosa may be at risk in surface water. However, the selective toxicity of these compounds may have implications for aquatic community structure. [source] Acute and chronic toxicity of imidazolium-based ionic liquids on Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2005Randall J. Bernot Abstract Room-temperature ionic liquids (ILs) are considered to be green chemicals that may replace volatile organic solvents currently used by industry. However, IL effects on aquatic organisms and ecosystems are currently unknown. We studied the acute effects of imidazolium-based ILs on survival of the crustacean Daphnia magna and their chronic effects on number of first-brood neonates, total number of neonates, and average brood size. Lethal concentrations of imidazolium ILs with various anions (X,) ranged from a median lethal concentration (LC50) of 8.03 to 19.91 mg L,1, whereas salts with a sodium cation (Na+ X,) were more than an order of magnitude higher (NaPF6 LC50, 9,344.81 mg L,1; NaBF4 LC50, 4765.75 mg L,1). Thus, toxicity appeared to be related to the imidazolium cation and not to the various anions (e.g., CI,, Br,, PF,6, and BF,4). The toxicity of imidazolium-based ILs is comparable to that of chemicals currently used in manufacturing and disinfection processes (e.g., ammonia and phenol), indicating that these green chemicals may be more harmful to aquatic organisms than current volatile organic solvents. We conducted 21-d chronic bioassays of individual D. magna exposed to nonlethal IL concentrations at constant food-resource levels. Daphnia magna produced significantly fewer total neonates, first-brood neonates, and average neonates when exposed to lower concentrations (0.3 mg L,1) of imidazolium-based ILs than in the presence of Na-based salts at higher concentrations (400 mg L,1). Such reductions in the reproductive output of Daphnia populations could cascade through natural freshwater ecosystems. The present study provides baseline information needed to assess the potential hazard that some ILs may pose should they be released into freshwater ecosystems. [source] Copper toxicity in relation to surface water-dissolved organic matter: Biological effects to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 12 2004Kees J.M. Kramer Abstract Water quality standards for copper are usually stated in total element concentrations. It is known, however, that a major part of the copper can be bound in complexes that are biologically not available. Natural organic matter, such as humic and fulvic acids, are strong complexing agents that may affect the bioavailable copper (Cu2+) concentration. The aim of this study was to quantify the relation between the concentration of dissolved natural organic matter and free Cu2+ in surface waters, and the biological effect, as measured in a standardized ecotoxicological test (48 h-median effective concentration [EC50] Daphnia magna, mobility). Six typical Dutch surface waters and an artificial water, ranging from 0.1 to 22 mg/L dissolved organic carbon (DOC), were collected and analyzed quarterly. Chemical speciation modeling was used as supporting evidence to assess bioavailability. The results show clear evidence of a linear relation between the concentration of dissolved organic carbon (in milligrams DOC/L) and the ecotoxicological effect (as effect concentration, EC50, expressed as micrograms Cu/L): 48-h EC50 (Daphnia, mobility) = 17.2 × DOC + 30.2 (r2 = 0.80, n = 22). Except for a brook with atypical water quality characteristics, no differences were observed among water type or season. When ultraviolet (UV)-absorption (380 nm) was used to characterize the dissolved organic carbon, a linear correlation was found as well. The importance of the free copper concentration was demonstrated by speciation calculations: In humic-rich waters the free Cu2+ concentration was estimated at ,10,11 M, whereas in medium to low dissolved organic carbon waters the [Cu2+] was ,10,10 M. Speciation calculations performed for copper concentrations at the effective concentration level (where the biological effect is considered the same) resulted in very similar free copper concentrations (,10,8 M Cu) in these surface waters with different characteristics. These observations consistently show that the presence of organic matter decreases the bioavailability, uptake, and ecotoxicity of copper in the aquatic environment. It demonstrates that the DOC content must be included in site-specific environmental risk assessment for trace metals (at least for copper). It is the quantification of the effects described that allows policy makers to review the criteria for copper in surface waters. [source] Development and field validation of a biotic ligand model predicting chronic copper toxicity to Daphnia magnaENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 6 2004Karel A.C. De Schamphelaere Abstract In this study, we developed a toxicity model predicting the long-term effects of copper on the reproduction of the cladoceran Daphnia magna that is based on previously reported toxicity tests in 35 exposure media with different water chemistries. First, it was demonstrated that the acute copper biotic ligand model (BLM) for D. magna could not serve as a reliable basis for predicting chronic copper toxicity. Consequently, BLM constants for chronic exposures were derived by multiple regression analysis of 21-d median effective concentrations (EC50s; expressed as Cu2+ activity) versus physicochemistry from a large toxicity dataset and the results of an additional experiment in which the individual effect of sodium on copper toxicity was investigated. The effect of sodium on chronic toxicity (log KNaBL = 2.91) seemed to be similar to its effect on acute toxicity (log KNaBL = 3.19). However, in contrast to the acute BLM, no significant calcium, magnesium, or combined competition effect was observed, and an increase in proton competition and bioavailability of CuOH+ and CuCO3 complexes was noted. Some indirect evidence was also found for some limited toxicity of complexes of copper with two of three tested types of dissolved organic matter. Because the latter was only a minor effect, this factor was not included in the chronic Cu BLM. The newly developed model performed well in predicting 21-d EC50s and no-observed-effect concentrations in natural water samples: 79% of the toxicity threshold values were predicted within a factor of two of the observed values. It is clear, however, that more research is needed to provide information on the exact mechanisms that have resulted in different BLM constants for chronic exposures (as opposed to acute exposures). It is suggested that the developed model can contribute to the improvement of risk assessment procedures of copper by incorporating bioavailability of copper in these regulatory exercises. [source] Synergistic interaction of endocrine-disrupting chemicals: Model development using an ecdysone receptor antagonist and a hormone synthesis inhibitorENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 4 2004Xueyan Mu Abstract Endocrine toxicants can interfere with hormone signaling through various mechanisms. Some of these mechanisms are interrelated in a manner that might result in synergistic interactions. Here we tested the hypothesis that combined exposure to chemicals that inhibit hormone synthesis and that function as hormone receptor antagonists would result in greater-than-additive toxicity. This hypothesis was tested by assessing the effects of the ecdysteroid-synthesis inhibitor fenarimol and the ecdysteroid receptor antagonist testosterone on ecdysteroid-regulated development in the crustacean Daphnia magna. Both compounds were individually characterized for effects on the development of isolated embryos. Fenarimol caused late developmental abnormalities, consistent with its effect on offspring-derived ecdysone in the maturing embryo. Testosterone interfered with both early and late development of embryos, consistent with its ability to inhibit ecdysone provided by maternal transfer (responsible for early developmental events) or de novo ecdysone synthesis (responsible for late developmental events). We predicted that, by decreasing endogenous levels of hormone, fenarimol would enhance the likelihood of testosterone binding to and inhibiting the ecdysone receptor. Indeed, fenarimol enhanced the toxicity of testosterone, while testosterone had no effect on the toxicity of fenarimol. Algorithms were developed to predict the toxicity of combinations of these two compounds based on independent joint action (IJA) alone as well as IJA with fenarimol-on-testosterone synergy (IJA+SYN). The IJA+SYN model was highly predictive of the experimentally determined combined effects of the two compounds. These results demonstrate that some endocrine toxicants can synergize, and this synergy can be accurately predicted. [source] Relative sensitivity distribution of aquatic invertebrates to organic and metal compoundsENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 1 2004Peter Carsten von der Ohe Abstract In the field, a multitude of species can be exposed to numerous toxicants; thus, the sensitivity of individual species to particular toxicants must be known to predict effects and to analyze changes in species composition. For most species, no information about their toxicant sensitivity is available. To address this limitation, we have grouped the available information to assign sensitivities to aquatic invertebrate taxa relative to Daphnia magna. With respect to organic compounds, most taxa of the orders Anisoptera, Basommatophora, Coleoptera, Decapoda, Diptera, Ephemeroptera, Eulamellibranchiata, Heteroptera, Hirudinea, Isopoda, Oligochaeta, Prosobranchia, Trichoptera, Tricladida, and Zygoptera are less sensitive than D. magna. Some taxa of the Amphipoda, Plecoptera, and Cladocera (other than D. magna) are significantly more sensitive. For organic compounds, approximately 22% of the investigated taxa were more sensitive than D. magna. Most taxa of the orders Amphipoda, Basommatophora, Diptera, Ephemeroptera, Eulamellibranchiata, Heteroptera, Isopoda, Oligochaeta, and Tricladida are significantly less sensitive than D. magna to metal compounds. The taxa belonging to the Crustacea, with the exception of the order Isopoda, are much more sensitive. For metal compounds, approximately 30% of the investigated taxa were more sensitive than D. magna. Hence, D. magna is among the most sensitive taxa regarding both groups of toxicants. The sensitivities for several taxa are listed, and use of the relative sensitivity distribution to link toxicant effects in mesocosm studies and field investigations is discussed. [source] Intraclonal variability in Daphnia acetylcholinesterase activity: The implications for its applicability as a biomarkerENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2003Liane Biehl Printes Abstract The relationship between individual growth and acetylcholinesterase (AChE) activity was evaluated for Daphnia magna. Analysis on the influence of two different culture media on baseline AChE activity was performed with Daphnia similis. The results indicated an inverse relationship between D. magna body length and AChE activity. An increase in total protein, which was not proportional to an increase in the rate of the substrate hydrolysis (, absorbance/min), seems to be the reason for this inverse size versus AChE activity relationship. Therefore, toxicants such as phenobarbital, which affect protein and size but not AChE activity directly, have an overall affect on AChE activity. In contrast, the AChE inhibitor parathion altered AChE activity but not protein. Culture medium also had a significant affect on AChE activity in D. similis. Changes in total protein seem to be the main reason for the variations in baseline AChE activity in Daphnia observed in the different evaluations performed in this work. Therefore, AChE activity in Daphnia must be interpreted carefully, and variations related to changes in total protein must be taken into account when applying this enzyme as a biomarker in biological monitoring. [source] Toxicity and chemistry of aspen wood leachate to aquatic life: Field studyENVIRONMENTAL TOXICOLOGY & CHEMISTRY, Issue 9 2003Barry R. Taylor Abstract A dark, toxic leachate has been observed around woodpiles of trembling aspen (Populus tremuloides Michx.) cut in winter for pulp or structural lumber. We measured production of leachate from 18 m3 of harvestable aspen logs stacked in an open field near Dawson Creek, British Columbia, Canada. The logpile began producing leachate during the first winter thaw and continued to do so for the duration of the two-year study (mean, 250 L/collection). Aspen leachate was characterized by dark color, acidic pH (5.0-6.5), elevated conductivity (200-500 ,S/cm), high to very high biochemical oxygen demand (500-5,000 mg/L) and total organic carbon concentrations (500-2,000 mg/L), variable levels of phenolic compounds (2-27 mg/L), and low dissolved oxygen tensions (<2 mg/L). In tests with rainbow trout (Oncorhynchus mykiss), Daphnia magna, and luminescent bacteria, the leachate varied from weakly toxic (median lethal concentration, >10%) to very toxic (median lethal concentration, <1%). The volume of leachate generated by the logpile was correlated with total precipitation (rain or snow) since the last collection. Loads of chemical constituents or toxicity (lethal concentration × volume) in the leachate did not decline over the duration of the study. Less than 10% of the total mass of leachable material in the aspen logs was removed during two years of exposure. [source] | ||||||||||||||||||||||||||||||||||