Chronic toxicity of dietary copper to Daphnia magna

There is a growing concern that dietborne metal toxicity might be important in aquatic ecosystems. However, the science behind this matter is insufficiently developed to explicitly and accurately account for this in metal regulation or risk assessment. We investigated the effects of a chronic exposure of Daphnia magna to an elevated level of Cu (3000 microg Cu/g dry wt) in their diet (the green alga Pseudokirchneriella subcapitata). Compared to daphnids fed with P. subcapitata containing a background of 10.6 microg Cu/g dry wt, daphnids fed for 21 days with this Cu-contaminated food accumulated a total copper body burden of 325 microg Cu/g dry wt, which is about 30-fold higher than the control body burden of 12.1 microg/g dry wt. The exposed daphnids experienced a 38% reduction of growth (measured as final dry body weight), a 50% reduction of reproduction (total number of juveniles produced per daphnid), and only produced three broods versus four broods by the control daphnids. Unlike most other studies, we were able to demonstrate that these effects were most likely not due to a reduced nutritional quality of the food, based on C:P ratios and fatty acid content and composition of the Cu-contaminated algae. Life-history analysis showed that time to first brood was not affected by dietary Cu, while the second and third broods were significantly delayed by 0.7 and 1.5 days, respectively. On the other hand, brood sizes of all three broods were significantly lower in Cu exposed daphnids, i.e. by 32-55%. The variety of effects observed suggest the possible, and perhaps simultaneous, involvement of several toxicity mechanisms such as increased metabolic cost, reduced energy acquisition (potentially via inhibition of digestive enzyme activity), targeted inhibition of reproduction (potentially via inhibition of vitellogenesis), and/or direct inhibition of molting. Further research is needed to differentiate between these postulated mechanisms of dietary Cu toxicity and to determine whether they act separately or in concert.     

Reproductive toxicity of dietary zinc to Daphnia magna

Regulatory assessments of metals in freshwaters are mostly based on dissolved metal concentrations, assuming that toxicity is caused by waterborne metal only. Little attention has been directed to the toxicity of dietary metals to freshwater invertebrates. In this study the chronic toxicity of dietary zinc to Daphnia magna was investigated. The green alga Pseudokirchneriella subcapitata was exposed for 64 h to a control and three dissolved zinc concentrations, i.e. 23, 28 and 61 microg L(-1), resulting in internal zinc burdens in the algae of 130, 200, 320 and 490 microg g(-1) dry weight, respectively. These algae were used as a food source in chronic, 21-day bioassays with D. magna in a test medium to which no dissolved zinc was added. None of the treatments resulted in effects on feeding rates or somatic growth of D. magna. In contrast, a significant 40% decrease of total reproduction (number of juveniles per adult) was observed in the 28 and 61 microg L(-1) treatments. Time to first brood was not affected, whereas the mean brood size and the fraction of reproducing parent daphnids were reduced from the second brood onwards and the magnitude of these reductions increased with each subsequent brood. The reduced reproduction was accompanied with an elevated zinc accumulation in the 61 microg L(-1) treatment only, suggesting that total body burden is no good indicator of dietary zinc toxicity. Overall our data suggest that dietary zinc specifically targets reproduction in D. magna through accumulation in particular target sites, possibly cells or tissues where vitellogenin synthesis or processing occur. Further, our data illustrate that the potential importance of the dietary exposure route should be carefully considered and interpreted in regulatory assessments of zinc.     

Acute toxicity of 50 metals to Daphnia magna

Metals are essential for human life and physiological functions but may sometimes cause disorders. Therefore, we conducted acute toxicity testing of 50 metals in Daphnia magna: EC50s of seven elements (Be, Cu, Ag, Cd, Os, Au and Hg) were < 100 µg l^?1; EC50s of 13 elements (Al, Sc, Cr, Co, Ni, Zn, Se, Rb, Y, Rh, Pt, Tl and Pb) were between 100 and 1000 µg l^?1; EC50s of 14 elements (Li, V, Mn, Fe, Ge, As, In, Sn, Sb, Te, Cs, Ba, W and Ir) were between 1,001 and 100,000 µg l^?1; EC50s of six elements (Na, Mg, K, Ca, Sr and Mo) were > 100,000 µg l^?1; and. 7 elements (Ti, Zr, Bi, Nb, Hf, Re and Ta) did not show EC50 at the upper limit of respective aqueous solubility, and EC50s were not obtained. Ga, Ru and Pd adhered to the body of D. magna and physically retarded the movement of D. magna. These metals formed hydroxides after adjusting the pH. Therefore, here, we distinguished this physical effect from the physiological toxic effect. The acute toxicity results of 40 elements obtained in this study were not correlated with electronegativity. Similarly, the acute toxicity results of metals including the rare metals were also not correlated with first ionization energy, atomic weight, atomic number, covalent radius, atomic radius or ionic radius. Copyright © 2014 John Wiley & Sons, Ltd.     

Acute toxicity of brass particles to Daphnia magna

The aquatic toxicity of brass particles was examined. Acute, 48 hour bioassays were performed using the water flea, Daphnia magna. Tests were conducted with uniform suspensions of uncoated brass particles, brass particles coated with a Teflon solution, silica particles, and titanium dioxide particles. The Teflon coating solution and the supernatant of the brass suspension (after settling of the brass) also were tested. All tests were conducted according to guidelines set forth by the US Environmental Protection Agency and the Organization for Economic Cooperation and Development. Mean EC50 determinations of 20.0 micrograms l-1 and 23.6 micrograms l-1 were calculated for uncoated brass particles and coated brass particles, respectively. The silica, titanium dioxide, and Teflon each had an EC50 greater than 1 g l-1. Chemical fate studies demonstrated that the brass dissociated to its ionic components of copper and zinc quickly at pH 2.0. At pH 5.0 and 6.5, the dissociation occurred too slowly to account for the observed toxicity. The data suggested that the toxicity is due to filtration by the daphnids and subsequent ingestion. EC50 determinations for the brass particles are nearly identical with published EC50 values for copper salts.     

Thiocyanate toxicity to Daphnia magna: modified by pH and temperature

The toxicity of thiocyanate to Daphnia magna was investigated under different conditions of pH (5, 6 and 7) and temperature (8, 12 and 16°C). Water hardness was kept constant at 75 mg/l. Results indicate that at all pH levels an increase in temperature from 8 to 16°C increased toxicity. A rise in temperature from 8 to 16°C at pH 7 showed the greatest increase in toxicity (10-fold); at pH 5, a similar increase in temperature resulted in a 5.5-fold increase in toxicity. At all temperatures tested, an increase in pH from 5 to 7 decreased toxicity. The most toxic combination was found at pH 5 at 16°C. There are two main conclusions to be found based on these data. (1) The currently proposed standard for thiocyanate in effluent is too high to safely maintain D. magna populations. (2) The parameters used, pH and temperature, are important modifying factors of thiocyanate toxicity.     

The possibility of using Daphnia magna as an alternative test object for evaluating the receptor selectivity of cholinotropic substances

The results of study of the selectivity of the effects of cholinonegative and cholinopositive agents obtained on Daphnia magna hydrobionts were compared with the results of investigations on rats. This allowed Daphnia to be recommended as an alternative test object for studying the selectivity of the effect of cholinotropic agents in relation to some subtypes of muscarine receptors in an intact organism.     

Prediction of the joint toxicity of five organophosphorus pesticides to Daphnia magna

The individual toxicities of five organophosphorus pesticides (dichlorvos, parathion, methyl parathion, malathion and dimethoate) to Daphnia magna were investigated in 24-h immobilization experiments. Using these toxicity data, their combined toxicities were measured in pesticide mixtures designed using either ‘equivalent-effect concentration ratios’ or ‘uniform-design concentration ratios’. The toxicities of mixtures of similarly or dissimilarly acting toxicants are often predicted from the individual toxicities of the component compounds, using one of two distinct biometric models: concentration addition (CA) or independent action (IA). The relative accuracies of the CA and IA models were assessed using the model deviation rate (MDR), which represents the difference between the effect predicted from the individual pesticide concentrations and the observed effect. The mean MDR value of CA was 0.93 (range 0.75–1.31) and the mean value obtained by IA was 3.13 (range 2.52–4.37). We conclude that the CA model is better able to predict the joint toxicities of mixtures of organophosphorus pesticides to D. magna.     

Study on acute toxicity and structure-activity relationship of Daphnia magna exposed to naphthoquinones

The acute toxicities of the six naphthoquinone compounds on Daphnia magna (D. magna) at 48 h were classified as harmful, toxic, and very toxic. The results indicated that logP played an important part in the toxicity of compounds to organism. And 1-carbonyl or the other hydrophobic substituents of the naphthoquinone compounds are likely to mediate the binding of the compound to the target via hydrogen bonding and hydrophobic interactions. Our results provided a foundation for further investigation using 3D-QSAR and HQSAR to evaluate the aquatic ecological risk and the mechanism of toxicity of naphthoquinones.     

Importance of surface coatings and soluble silver in silver nanoparticles toxicity to Daphnia magna

Silver nanoparticles (AgNPs) are now widely used in antibacterial and personal care products. However, the underlying physicochemical mechanisms leading to the toxicity of AgNPs are still under debate. The present study revealed the different effects of three surface coatings (including lactate, polyvinylpyrrolidone, and sodium dodecylbenzene sulfonate, as AgNPs-L, AgNPs-P and AgNPs-S, respectively) on the acute toxicity of AgNPs to a model freshwater cladoceran Daphnia magna. Significant difference in mortality was observed among these three surface coatings of AgNPs, with the 48-h 50% lethal concentrations (48-h LC50s) of AgNPs-L, AgNPs-P and AgNPs-S being 28.7, 2.0 and 1.1 μg/L, respectively. In contrast, when the daphnids were exposed to soluble Ag released from AgNPs-L and AgNPs-P, the difference in the 48-h LC50s between the two surface coatings (1.1 μg/L and 0.57 μg/L, respectively) decreased significantly. These 48-h LC50s were comparable to that of AgNO? (0.88 μg/L), indicating that soluble Ag was the primarily cause of the observed toxicity of AgNPs. Indeed, the surface coatings influenced the dissolution of AgNPs into soluble Ag, resulting in the different toxicities of AgNP to the daphnids. Additionally, the 48-h bioaccumulation of AgNPs in daphnids was also dependent on the characteristics of the nanoparticles, such as particle size and surface coating. Our results point to the need to consider the effects of surface coating on the toxicity of AgNPs in environmental risk assessments.     

Effects of water hardness and humic acid on zinc toxicity to Daphnia magna Straus

The effects of water hardness and humic acid (HA) on the acute and chronic toxicity of zinc to Daphnia magna were evaluated. Increases in either water hardness or HA concentration resulted in proportional decreases in both acute (3-day) and chronic (50-day) zinc toxicity. The effect of either of these variables (hardness or HA) was independent of the other in acute tests. In chronic tests, HA reduced the toxic effect of zinc on reproduction more in soft water than in hard water. In addition to reducing the chronic toxicity of zinc, our data suggest that an increase in water hardness also changes the mode of chronic toxic action of zinc. As previously shown for other metals, this study indicates that a reliance on only reproductive and survival endpoints in short-duration chronic tests may lead to an underestimation of the chronic toxicity of zinc.     

Chronic toxicity of chlordane to Daphnia magna and Ceriodaphnia dubia: A comparative study

Chronic toxicity of chlordane, an organochlorine insecticide, was assessed on Ceriodaphnia dubia under standardized conditions of testing. Results were compared to Daphnia magna to determine the sensitivity of the two freshwater cladoceran species to this persistent organic pollutant (POP) and to explore the possibility of using the 7‐day C. dubia test as an alternative to the 21‐day D. magna test in chronic toxicity assessment of POPs. The NOEC‐7d value of chlordane on reproduction of C. dubia (2.9 μg/L) was much higher than the NOEC‐21d value of D. magna (0.18 μg/L), attesting that the 7‐day test on C. dubia was less sensitive than the 21‐day reproduction test on D. magna to chlordane. However, extending the period of exposure of C. dubia to chlordane from 7 to 14 days led to a NOEC‐14d value similar to the NOEC‐21d value in D. magna (0.18 μg/L). This study highlights the usefulness of prolonging the exposure time of the reproduction test in C. dubia from 7 to 14 days to increase the performances of the reproduction test on C. dubia for assessing chronic toxicity of POPs. © 2010 Wiley Periodicals, Inc. Environ Toxicol, 2012.     

The joint acute toxicity to Daphnia magna of industrial organic chemicals at low concentrations

The joint acute toxicity of a mixture of 50 nonreactive organic chemicals towards Daphnia magna was investigated. It was found that the observed toxicity is accurately predicted by the model of concentration addition, even at very low concentrations of the individual compounds. The implications these findings may have on the prediction of the toxicity of mixtures of chemicals occurring in nature are briefly discussed.     

Biomarker-based assessment of the toxicity of the antifungal clotrimazol to the microcrustacean Daphnia magna

Among the vast list of xenobiotics that may promote harmful effects in aquatic ecosystems, pharmaceuticals are currently a prominent class due to their ability to persist in these environments and also due to the lack of information regarding their effects on the different components of the aquatic biota. Antifungals in particular, despite their massive use, are not extensively studied in environbmental terms. The main objective of this study was to characterize the toxicity of the antifungal clotrimazole to the aquatic organism Daphnia magna. To attain this purpose, the effects of this compound were measured, focusing on the determination of acute lethality, and quantification of biomarkers, such as neurotoxicity (soluble cholinesterases, ChEs); and oxidative stress and metabolism (such as catalase, CAT; and glutathione-S-transferases, GSTs). The toxicity assessment with biomarkers was based on animals exposed to concentrations similar to those already found in surface waters in order to increase the ecological relevance of the obtained data. The results showed that exposure to clotrimazole was able to induce significant increases in both CAT amd GSTs activities. ChE activity was not significantly altered after clotrimazol exposure. In view of the above, it is concluded that the drug studied caused adverse effects in terms of oxidative stress, at an ecological relevant levels, showing that the presence of clotrimazol in the wild is not innocuous.     

Liposomes as alternative vehicles for sun filter formulations

The aim of our study was to determine the influence of several types of liposomes with a different lipid composition on the percutaneous absorption of one conventional sun filter with a lipophilic character (ethyl hexyl methoxycinnamate) using both in vitro and in vivo methodologies. Three different liposomes were prepared with unsaturated and saturated phosphatidylcholine (PC, HPC) and with a wool lipid mixture (IWL) with a composition similar to that of the stratum corneum lipids. Results showed that the liquid crystalline state associated with PC liposomes plays a key role in enhancing skin penetration. When liposomes with a composition and structural organization similar to that of the stratum corneum lipids (HPC and IWL) are used, the skin penetration is retarded, suggesting a certain reinforcement of the stratum corneum barrier. These two types of liposomes could be regarded as alternatives to conventional oil/water emulsions in the formulations of lipidic sun filters. Finally, an acceptable correlation was obtained using both in vitro and in vivo methodologies to evaluate the corresponding skin absorption profile.     

Suitability of <Emphasis Type="Italic">Daphnia similis</Emphasis> as an alternative organism in ecotoxicological tests: implications for metal toxicity

The acute toxicity of metals to Daphnia similis was determined and compared to other daphnid species to evaluate the suitability of this organism in ecotoxicology bioassays. To verify the performance D. similis in toxicity tests, we also investigated the effect of Pseudokirchneriella subcapitata at 1 × 10⁵ and 1 × 10⁶ cells ml⁻¹ on Cd and Cr acute toxicity to the cladoceran. Daphnid neonates were exposed to a range of chromium and cadmium concentrations in the absence and presence of the algal cells. Metal speciation calculations using MINEQL⁺ showed that total dissolved metal concentrations in zooplankton culture corresponded to 96.2% free Cd and 100% free Cr concentrations. Initial total dissolved metal concentrations were used for 48 h-LC₅₀ determination. LC₅₀ for D. similis was 5.15 × 10⁻⁷ mol l⁻¹ dissolved Cd without algal cells, whereas with 1 × 10⁵ cells ml⁻¹, it was significantly higher (7.15 × 10⁻⁷ mol l⁻¹ dissolved Cd). For Cr, the 48 h-LC₅₀ value of 9.17 × 10⁻⁷ mol l⁻¹ obtained for the cladoceran in tests with 1 × 10⁶ cells ml⁻¹ of P. subcapitata was also significantly higher than that obtained in tests without algal cells (5.28 × 10⁻⁷ mol l⁻¹ dissolved Cr). The presence of algal cells reduced the toxicity of metals to D. similis, as observed in other studies that investigated the effects of food on metal toxicity to standard cladocerans. Comparing our results to those of literature, we observed that D. similis is as sensitive to metals as other standardized Daphnia species and may serve as a potential test species in ecotoxicological evaluations.     

Chronic toxicity of silver nitrate to Ceriodaphnia dubia and Daphnia magna, and potential mitigating factors

We investigated the chronic toxicity of Ag, as silver nitrate, using two freshwater aquatic cladoceran species, Ceriodaphnia dubia and Daphnia magna, to generate data for the development of a chronic ambient water quality criterion for Ag. Preliminary studies with C. dubia showed variable results which were related to the equilibration time between food and silver. Follow-up testing was conducted using a 3h equilibration time, which stabilized dissolved Ag concentrations and the toxicity of Ag(+). Results with C. dubia conducted individually (1 per cup, n=10) and in mass (30 per chamber, n=2) gave similar results once similar standardized equilibration times were used. The maximum acceptable toxicant concentration (MATC) of Ag to C. dubia and D. magna was 9.61 and 3.00microg dissolved Ag/L, respectively. The chronic toxicity of Ag(+) to C. dubia was also evaluated in the presence of: (1) dissolved organic carbon (DOC) and (2) sulfide. The addition of DOC (0.4mg/L) resulted in a approximately 50% decrease in toxicity while the addition of sulfide (75.4nM) deceased toxicity by 42%. Whole-body Ag concentration in D. magna was positively correlated with increased levels of Ag exposure, however; we observed a non-statistical decrease in whole-body Na levels, an estimator of sodium homeostasis.     

Chronic toxicity and responses of several important enzymes in Daphnia magna on exposure to sublethal microcystin-LR

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.