Haem Peroxidase Activity in Daphnia magna: A Biomarker for Sub-lethal Toxicity Assessments of Kerosene-contaminated Groundwater

A novel biomarker was developed in Daphnia magna to detect organic pollution in groundwater. The haem peroxidase assay, which is an indirect means of measuring oxidase activity, was particularly sensitive to kerosene contamination. Exposure to sub-lethal concentrations of kerosene-contaminated groundwater resulted in a haem peroxidase activity increase by dose with a two-fold activity peak at 25%. Reproduction in D. magna remained unimpaired when exposed to concentrations below 25% for 21 days, and a decline in fecundity was only observed at concentrations above the peak in enzyme activity. The measurement of haem peroxidase activity in D. magna detected sublethal effects of kerosene in just 24h, whilst offering information on the health status of the organisms. The biomarker may be useful in determining concentrations above which detrimental effects would occur from long-term exposure for fuel hydrocarbons. Moreover, this novel assay detects exposure to chemicals in samples that would normally be classified as non-toxic by acute toxicity tests.     

Environmental levels of ultraviolet light potentiate the toxicity of sulfonamide antibiotics in Daphnia magna

We assessed the phototoxicity of several major sulfonamide antibiotics, i.e., sulfathiazole, sulfamethazine, and sulfamethoxazole, using acute 48 and 96 h Daphnia magna immobilization toxicity test under several indoor and outdoor lighting conditions. The lighting conditions were as follows: (1) fluorescent light only, (2) continuous irradiation with 15 μW/cm² UVB, (3) pulsed irradiation with 90 μW/cm² UVB for 4 h/d, and (4) natural sunlight (outdoors). Laboratory tests showed that phototoxicity resulting from exposure to continuous UVB light generally increased the acute toxicity of the sulfonamides in D. magna by up to 2.3-fold. However, pulsed UVB exposure resulted in a greater increase in phototoxicity. Compared to fluorescent light only (no UVB), pulsed UVB irradiation (96 h) resulted in 12.0-, 5.8-, and 4.4-fold increases in toxicity for sulfamethazine, sulfathiazole, and sulfamethoxazole, respectively. This suggests that the mode of UV irradiation is more important than the dose (UV-intensity × exposure time) for the photo-enhancement of sulfonamide toxicity. Natural sunlight enhanced the toxicity of the sulfonamides to an even greater degree, likely because of the contribution of UVA light. This study suggests that without taking into account the effects of UV irradiation, it is possible to underestimate the actual consequences of phototoxic sulfonamide antibiotics in the aquatic environment.     

Chronic toxicity of Great Lakes sediments to Daphnia magna: elutriate effects on survival, reproduction and population growth

Seventeen Great Lakes sediments ranging in degree of expected toxicity were evaluated using a 21 day sediment elutriate bioassay with Daphnia magna. Sediments differed in their effects on survival, age at first reproduction, the number of broods produced and the total number of young produced per adult. Sediments producing low survivorship (50–60%) also had negative effects on reproduction. However, both positive and negative effects on reproduction were found among sediments producing high survivorship. To integrate all test end-points, a stochastic matrix population model was constructed and parameterized with survival and reproduction data from each sediment. By including estimates of variability in vital rates, the model output provided quantitative estimates of uncertainty in projected population size. Sediment effects on survival and reproduction translated into large differences in projected population growth; mean estimates of projected population size at day 28 of the simulations ranged over two orders of magnitude among the 17 sediments. Reproductive timing (e.g. age at first reproduction), followed by fecundity and survivorship, had the largest effect on population growth. Results of this study also indicate that the presence of suspended sediment in elutriates may confound toxicity evaluations using cladocerans. The concentration of total suspended solids was negatively correlated with age at first reproduction and positively correlated with measures of fecundity and population growth. In order to realize the potential benefits of chronic testing we must develop ecologically relevant ways of interpreting sediment bioassay results and expressing the uncertainty associated with our estimates of ecological risk.     

Toxicological effects of military fog oil obscurant on Daphnia magna and Ceriodaphnia dubia in field and laboratory exposures

Our purpose was to determine if the acute and sub-lethal effects of fog oil, an obscurant used for military training, could be observed in realistic field exposures. To this end, we exposed Daphnia magna to oil fogs under actual release conditions at a U.S. Army training site. Guided by field investigations, acute toxicity experiments were conducted in the laboratory with the more sensitive species Ceriodaphnia dubia to test the hypothesis that dissolution of fog oil constituents into water is minimal and actual contact by organisms with the water surface is required to cause toxicity. We conducted further experiments to test the hypothesis that vaporization of fog oil alters its chemical composition and toxicity to freshwater invertebrates. In the field, daphnid mortality was minimal more than 5 m from the point of fog generation, but sub-lethal effects were more extensive. Both field and laboratory experiments suggested that physical contact with oils on the water surface was the most important factor driving toxicity. To our knowledge, this is the first attempt to evaluate toxicological endpoints with freshwater invertebrates in field exposures with fog oil.     

Ecotoxicological assessment of effluents in the Basque country (Northern Spain) by acute and chronic toxicity tests using Daphnia magna straus

Acute pass/fail, multi-concentration tests, and 3-brood chronic toxicity tests with Daphnia magna Straus (Cladocera, Crustacea) were used to characterise industrial and municipal effluents from various sources. The effluents that “passed” the pass/fail tests had 48-h EC₅₀ values >100% and reproduction No Observed Effect Concentration (NOECs) ≥100%, except for one effluent that had a reproduction NOEC of 31.6%. The acute multi-concentration toxicity tests allowed a rapid classification of effluents from Very Toxic (48-h EC₅₀<25%), to Non-Toxic (48-h EC₅₀ >100%). The acute-to-chronic ratio (ACR: 48-h EC₅₀ divided by the NOEC for reproduction) in the studied effluents ranged from 5 to about 100. From these results, we propose a step-wise protocol for assessing effluent toxicity. First, effluent is evaluated by means of simple and rapid pass/fail acute toxicity tests, to discriminate Non-Toxic from potentially Toxic effluents, thus facilitating the establishment of priority actions. Second, 48-h EC _x is estimated to classify effluents on a toxicity scale from Non-Toxic to Very Toxic. Third, chronic multi-concentration tests are used to calculate reproduction NOECs. These parameters combined with data on effluent chemical composition, chemical and hydrological characteristics of receiving waters, and biological quality criteria can be jointly used for more rational regulatory practices and risk assessment of effluents.     

Toxicity of the cyanobacterium Cylindrospermopsis raciborskii to Daphnia magna

The effect of two strains of Cylindrospermopsis raciborskii on the survivorship, somatic growth, and detoxification processes of juvenile Daphnia magna were investigated. Both strains of C. raciborskii (and also Ankistrodesmus falcatus, used as the control) were given to newborn D. magna at equivalent biovolumes. The survival curves for D. magna subjected to the two C. raciborskii treatments differed from those of the starved and fed treatments. After 48 h of exposure, the percentage of D. magna surviving after exposure to Cylin-A (a cylindrospermopsin-producing strain isolated from Australia) and Cylin-P (a non-cylindrospermopsin-producing strain isolated from Portugal) was 10.00% and 93.33%, respectively. The strain that produces cylindrospermopsin caused the greatest toxic effect in juvenile D. magna. Statistically significant differences in D. magna body size between the four treatments (Cylin-A, Cylin-P, A. falcatus, and starved) were detected after 48 h of exposure. The juvenile D. magna that received the two C. raciborskii treatments showed an increase in size (relative to their size at T(0)) of 2.54% and 38.14%, respectively. These values were statistically significantly different than those of the A. falcatus-fed control (55.54%) and the starved control (11.47%). In both C. raciborskii treatments there was a tendency for increased GST enzyme activities after 24 h of exposure. Cylindrospermopsin was detected (HPLC-MS/MS) in D. magna tissues after 24 and 48 h (0.025 and 0.02 ng animal(-)1, respectively). The results of this study indicate that C. raciborskii can affect the fitness and growth potential of juvenile D. magna.     

Toxicity prediction of binary combinations of cadmium, carbendazim and low dissolved oxygen on Daphnia magna

Environmental contamination is often characterised by a combination of stress factors of various sources (biological, physical and chemical). The predictability of their joint effects is an important stage in environmental risk assessment procedures. In this study, the two main conceptual models for mixture evaluation based on the effect of individual compounds, concentration addition (CA) and independent action (IA) and deviations to synergism/antagonism, "dose ratio" and "dose level" dependency were used. The single and combined effects of cadmium, carbendazim and low dissolved oxygen levels were assayed for life-cycle parameters (survival and feeding) of the water flea Daphnia magna Straus. The results of single exposures revealed an increase of acute and chronic toxicity as concentrations of cadmium and carbendazim increases. At low dissolved oxygen levels both survival and feeding parameters were significantly affected (P< or =0.05). In the acute mixture exposure of cadmium and carbendazim a "dose ratio" dependency was observed with a higher toxicity when cadmium was dominant whereas at high concentrations of carbendazim a lower effect on survival was observed. At chronic exposures an antagonistic deviation from IA model was observed for this mixture. The IA model showed to be adequate for toxicity prediction on acute exposure combinations with low DO levels where a synergistic behaviour was observed. However, at sublethal exposures IA and CA models failed by underestimation. Validation from toxicokinetic and toxicodynamic modelling studies should be made in the future as a way to understand toxicological pathways involved in complex mixture/combination exposures.     

Sub-lethal effects of acetone on <Emphasis Type="Italic">Daphnia magna</Emphasis>

There is increasing concern about the sub-lethal effect of hydrophobic chemicals in the water medium. Even though acetone is a commonly used solvent in toxicity testing, few studies have focussed on its chronic toxicity to Daphnia magna and the available results are often contradictory. In this study, acetone was tested on D. magna in a 21-day exposure experiment and the effects on mortality, fertility and morphology of exposed organisms (F₀) and offspring (F₁–F₂, reared without acetone) were evaluated. No significant reduction of survival was observed with increasing concentrations, and no significant reduction in fecundity in any treatment group in terms of average number of daphnids per mother was observed. Abnormal development of second antennae was observed on F₁ from F₀ exposed to 79 mg l⁻¹ solvent. The ET50 of acetone on the number of mothers that produced deformed offspring over time was 12.5 days. Our results suggest that the acetone concentration should not exceed 7.9 mg l⁻¹, which is 10 times less than the allowed concentration as determined by OECD chronic assays on D. magna. More attention should be paid to small, water-soluble molecules usually considered of low concern for chronic toxicity because they might affect other metabolic pathways.     

Responses of Daphnia magna to pulsed exposures of arsenic

Research on the toxicity of arsenic has focused on sublethal effects that do not provide sufficient information for risk estimation. While most studies have focused on organism response to constant arsenic exposures, organisms in nature are exposed to fluctuating As concentrations. Consequently, results obtained from standardized bioassays with constant exposures may not adequately characterize risk to indigenous biota. This research was designed to characterize the response of Daphnia magna to fluctuating arsenic exposures during 21-day experiments. At concentrations > or =3000 microg/L As, 21-day pulsed exposure mortality increased as a function of exposure concentration and duration. In addition, 21-day pulsed exposure mortality increased with increasing recovery time. Pulsed As exposure did not affect the growth of D. magna over 21 days. Twenty-one day accumulative reproduction of D. magna was only affected by pulsed exposures of high As concentration and long durations.     

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.     

Bioaccumulation of silver nanoparticles into Daphnia magna from a freshwater algal diet and the impact of phosphate availability

This study assessed the bioavailability, toxicity, and transfer of silver nanoparticles (AgNPs) in comparison with AgNO₃ in two model food chain organisms: the alga Chlamydomonas reinhardtii and the grazing crustacean Daphnia magna. The effects of phosphate, a potential Ag⁺-binding ligand and a determinant of phytoplankton productivity, were evaluated. Nano Ag derived from coated AgNPs and AgNO₃ was accumulated at similar concentrations into microalgae during high phosphate treatment, but AgNO₃ accumulation was increased by low phosphate availability. After feeding on Ag-containing algae, D. magna equally accumulated AgNO₃ and nano-derived Ag. There were significant reductions in feeding when D. magna were fed Ag-contaminated algae, with the AgNO₃, low phosphate-exposed cells being ingested the least. Nutritional quality characteristics including fatty acid and trace nutrient content were similar in all algal samples, indicating that feeding reduction is specifically due to the presence of Ag, with AgNO₃ being more toxic than nano Ag.     

Study of the combined effects of a peracetic acid-based disinfectant and surfactants contained in hospital effluents on <Emphasis Type="Italic">Daphnia magna</Emphasis>

Hospital effluents cause environmental problems since they are 5–15 more toxic than urban effluents and they are not subjected to any pre-treatment before being discharged into urban sewage networks. The hypothesis used to explain this toxicity is the presence of disinfectants and detergents. This study is aimed at highlighting the ecotoxicity of a peracetic acid-based disinfectant to Daphnia magna, as well as the combined effects of this disinfectant in binary mixtures with three types of detergent. The detergents used here are: cetyltrimethylammonium bromide (CTAB, cationic), sodium dodecylsulfate (SDS, anionic) and Triton X-100 (TX, non-ionic). The toxicity of the mixtures is studied as a function of five predefined ratios. At the end of the study, we conclude that peracetic acid seems to be slightly toxic to Daphnia magna. Indeed, the efficient concentration inhibiting the mobility of 50% of the population of Daphnia at 24 h (EC50) is 116.6 mg/l. Globally, additive effects are observed for all the binary peracetic acid-detergent mixtures. However, for the peracetic acid–TX mixture, its effects have antagonistic tendencies whereas the peracetic acid–CTAB mixture has slight synergic tendencies. The mixture containing peracetic acid and SDS is slightly antagonistic for ratios containing more than 50% peracetic acid.     

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 toxicities of a polyunsaturated fatty acid and a microcystin to Daphnia magna

Polyunsaturated fatty acids (PUFAs) are essential components of zooplankton diets. However, studies with PUFAs from cyanobacteria indicate toxic properties. We investigated the toxicity of the PUFA gamma-linolenic acid and the cyanobacterial peptide toxin microcystin-LR to Daphnia. The PUFA was acutely toxic at a concentration of 9 micrograms ml-1. The effect of microcystin-LR was not statistically significant at the concentration used (3 micrograms ml-1), but an additive effect with the PUFA was observed. Relative to LC50-values of well-known pollutants, the PUFA was intermediately toxic. The activity equaled that of microcystin-LR, which is commonly treated as one of the most potent cyanobacterial toxins. Our results suggest that the toxic properties of PUFAs deserve more attention.     

The chronic toxicity of ZnO nanoparticles and ZnCl2 to Daphnia magna and the use of different methods to assess nanoparticle aggregation and dissolution

In this study, the effect of ZnO nanoparticles and ZnCl₂ on growth, reproduction and accumulation of zinc in Daphnia magna was determined in a 21-day chronic toxicity test. A variety of techniques were used to distinguish the free zinc ion, dissolved, nanoparticle and aggregated zinc fraction in the Daphnia test medium. The results showed similar chronic effects on growth, reproduction and accumulation for the ZnO nanoparticles (EC₁₀, ₂₀, ₅₀ reproduction: 0.030, 0.049, 0.112 mg Zn/l) and the ZnCl₂ (EC₁₀, ₂₀, ₅₀ reproduction: 0.014, 0.027, 0.082 mg Zn/l). A large fraction of the nanoparticles rapidly dissolved after introduction in the exposure medium. Aggregation of nanoparticles was also observed but within 48 h of exposure most of these ZnO aggregates were dissolved. Based on the combined dissolution kinetics and toxicity results, it can be concluded that the toxicological effects of ZnO nanoparticles at the chronic level can be largely attributed to the dissolved fraction rather than the nanoparticles or initially formed aggregates.     

Oxidative and osmoregulatory effects of imidacloprid,cadmium, and their combinations on Daphnia magna

Oxidative stress and osmoregulatory system damage-inducing potential of binary mixtures of neonicotinoid insecticide imidacloprid (IMI) and Cd²⁺ in Daphnia magna were evaluated. Animals were subjected to subchronic (7 days) and acute (48 h) of IMI and Cd²⁺ effects with single and binary mixtures. ATPase and antioxidant enzyme activities with lipid peroxidation were measured. Morphometric characteristics were also evaluated. Response patterns showed variability due to the duration, concentration, and toxicant type. While the enzyme activities mostly showed a decreasing trend upon the subchronic IMI effect, there was an increasing trend after the Cd²⁺. Declined enzyme activities were more pronounced with the acute higher IMI+Cd²⁺ exposure. Ca²⁺-ATPase and CAT were the most sensitive biomarkers in the toxicity response. IMI+Cd²⁺ exposures are appeared to increase their toxic effects due to their oxidative potential. ATPase inhibition and antioxidant enzyme alterations with a decrease in morphometric characteristics in Daphnia even at their low concentrations of IMI and Cd²⁺ show evidence of their toxicities on aquatic life. It was emphasized that investigating the combined effects of toxicants at their environmental level based on the multi-biomarker approach is essential in toxicity evaluation.     

pH‐Dependence and QSAR analysis of the toxicity of phenols and anilines to Daphnia magna

The toxicity of 13 anilines and 11 phenols to Daphnia magna has been assessed at pH values of 6.0, 7.8, and 9.0. Toxicity of anilines decreases with decreasing pH, whereas the toxicity of phenols decreases with increasing pH. These variations in toxicity, are clearly brought about by the effect of ionization, especially for the phenols. Toxicity decreased with an increasing proportion of ionized molecules. The relative contribution of the ionized and unionized molecules was assessed. It is believed that, at least for the phenols, the ionized form of the compounds does contribute to the toxicity of the molecules. However, the decreased overall toxicity suggests that a lower relative toxicity is attributable to the ionized form. Attempts were also made to develop quantitative structure‐activity relationship (QSAR) models for these toxicity data. Reasonable QSARs were produced for the anilines and phenols, acting as polar narcotics, considered together; these QSARs included a measure of hydrophobicity, pK_a, and hydrogen bonding. When the phenols and anilines were considered separately, better, hydrophobicity‐based, QSARs were obtained. Most compounds, with the exception of 2,4‐dinitrophenol, resorcinol, and pentachlorophenol, were thought to be acting by a polar narcosis mechanism of toxic action. There was some evidence that 2,4‐dichlorophenol and 2,4,6‐trichlorophenol may be acting as weak acid respiratory uncouplers, despite earlier suggestions that they act as polar narcotics. © 2000 John Wiley & Sons, Inc. Environ Toxicol 15: 140–148, 2000