Acute and chronic toxicity of five selective serotonin reuptake inhibitors in Ceriodaphnia dubia

Contamination of surface waters by pharmaceutical chemicals has raised concern among environmental scientists because of the potential for negative effects on aquatic organisms. Of particular importance are pharmaceutical compounds that affect the nervous or endocrine systems because effects on aquatic organisms are possible at low environmental concentrations. Selective serotonin reuptake inhibitors (SSRIs) are drugs used to treat clinical depression in humans, and have been detected in low concentrations in surface waters. In this investigation, the acute and chronic toxicity of five SSRIs (fluoxetine, Prozac; fluvoxamine, Luvox; paroxetine, Paxil; citalopram, Celexa; and sertraline, Zoloft) were evaluated in the daphnid Ceriodaphnia dubia. For each SSRI, the 48-h median lethal concentration (LC50) was determined in three static tests with neonate C. dubia, and chronic (8-d) tests were conducted to determine no-observable-effect concentrations (NOEC) and lowest-observable-effect concentrations (LOEC) for reproduction endpoints. The 48-h LC50 for the SSRIs ranged from 0.12 to 3.90 mg/L and the order of toxicity of the compounds was (lowest to highest): Citalopram, fluvoxamine, paroxetine, fluoxetine, sertraline. Mortality data for the 8-d chronic tests were similar to the 48-h acute data. The SSRIs negatively affected C. dubia reproduction by reducing the number of neonates per female, and for some SSRIs, by reducing the number of broods per female. For sertraline, the most toxic SSRI, the LOEC for the number of neonates per female was 0.045 mg/L and the NOEC was 0.009 mg/L. Results indicate that SSRIs can impact survival and reproduction of C. dubia; however, only at concentrations that are considerably higher than those expected in the environment.     

Acute Toxicity of Thallium to Daphnia magna and Ceriodaphnia dubia

No abstract available.     

Acute enantioselective toxicity of fipronil and its desulfinyl photoproduct to Ceriodaphnia dubia

Fipronil is a phenylpyrazole insecticide increasingly used in applications such as rice culture, turf grass management, and residential pest control, with a high probability to contaminate aquatic environments. As a chiral pesticide, fipronil is released to the environment as a racemic mixture (equal amounts of optical isomers called enantiomers). Enantiomers can have different toxicological and biological activity; however, information on these differences, which is necessary for accurate risk assessment of chiral pesticides, is limited. Here we examine the acute toxicity of fipronil enantiomers, the racemate, and its photoproduct (desulfinyl fipronil) to Ceriodaphnia dubia. The 48-h median lethal concentration (LC50) values based on measured concentrations of each compound indicate the (+) enantiomer (LC50 = 10.3 +/- 1.1 microg/L, mean +/- standard error [SE]) was significantly more toxic to C. dubia than either the (-) enantiomer (LC50 = 31.9 +/- 2.2 microg/L) or racemate (LC50 = 17.7 +/- 1.3 microg/L). To account for any potential loss of fipronil through photolysis, tests were performed under light (fluorescent) and dark exposure conditions, and no significant differences in toxicity were observed. Desulfinyl fipronil, the major photodegradation product, which is not chiral, was detected at < 1% of each parent compound in test solutions after 48 h. Separate toxicity tests with desulfinyl fipronil found a > 20-fold higher LC50 (355 +/- 9.3 microg/L) compared to the fipronil racemate, suggesting lower adverse effects to C. dubia as a result of fipronil photolysis. The present results suggest selection of the (-) enantiomer in fipronil production for lower impacts to C. dubia; however, the consistency and relevancy of fipronil's enantiomer-specific activity at both acute and chronic levels of concern to additional target and nontarget species needs further consideration.     

Effects of ligand-bound silver on Ceriodaphnia dubia

In aqueous media, ionic silver concentrations are low and transport occurs in the colloidal phase. In the aquatic environment, silver forms 1:1 complexes with thiol-containing compounds such as cysteine and glutathione. In order to quantitatively characterize the risk associated with silver in aquatic ecosystems, the bioavailabilities and toxicities of silver cysteinate and silver glutathionate were characterized. Static renewal bioassays were conducted with Ceriodaphnia dubia to estimate chronic toxicity, using mortality and reproduction as endpoints. Silver nitrate was the most lethal compound, with a median lethal concentration (8-d LC50) of 0.32 microg Ag/L (95% confidence interval [CI] = 0.19-0.54). The 48-h LC50 for AgNO3 was 0.5 microg/L and did not change significantly through 8 d. The presence of food in the bioassay did not change the 48-h LC50 for AgNO3. Silver glutathionate (AgGSH) and silver cysteinate (AgCys) induced less mortality during the 8-d bioassay. Silver cysteinate appeared to have the greatest effect on fecundity, with a no-observable-effect concentration (NOEC) less than 0.001 microg/L. Silver nitrate and AgGSH had lowest-observable-effect concentration (LOEC) values (nominal concentrations) of 0.01 and 0.6 microg/L, respectively. Results indicate that the ligand-bound silver in these laboratory studies is bioavailable and impairs reproduction of C. dubia at low aqueous concentrations.     

Acute toxicity of copper and silver to Ceriodaphnia dubia in the presence of food

Food is added to exposure solutions in cladoceran chronic toxicity tests and sometimes in acute toxicity tests, but its effects on the bioavailability of toxicants have not been studied extensively. We compared the toxicity of waterborne Ag and Cu to Ceriodaphnia dubia in the presence or absence of food (a mixture of a yeast--Cerophyll--trout chow slurry and a green alga) in two series of acute toxicity tests. In the first series, we added food to Ag or Cu exposure solutions 0, 30, 60, or 120 min before transferring C. dubia into the solutions. In the second series, we exposed C. dubia to waterborne Ag or Cu for 30, 60, and 120 min in the absence of food. Adding food before transferring C. dubia into the exposure solutions greatly decreased the toxicity of Ag, but had less effect on the toxicity of Cu. In contrast, adding food after transferring C. dubia into the exposure solutions did not alter the toxicity of Ag considerably and did not alter the toxicity of Cu as much as the reverse sequence. Median effects concentrations (EC50s) for 30-, 60-, and 120-min unfed Ag tests were within the range of EC50s for 48-h unfed Ag tests, suggesting most uptake that contributes to acute Ag toxicity to C. dubia occurs within the first 30 to 60 min. However, uptake that contributes to acute Cu toxicity to C. dubia appears to occur over more than 2 h. Therefore, standard food decreases the toxicity of waterborne Ag and Cu to C. dubia, and the timing of adding food to exposure solutions is especially important in Ag tests.     

Acute and chronic toxicity of nickel to a cladoceran (Ceriodaphnia dubia) and an amphipod (Hyalella azteca)

This study evaluated acute and chronic nickel (Ni) toxicity to Ceriodaphnia dubia and Hyalella azteca with the objective of generating information for the development of a biotic ligand model for Ni. Testing with C. dubia was used to evaluate the effect of ambient hardness on Ni toxicity, whereas the larger H. azteca was used to derive lethal body burden information for Ni toxicity. As was expected, acute C. dubia median lethal concentrations (LC50s) for Ni increased with increasing water hardness. The 48-h LC50s were 81, 148, 261, and 400 microg/L at hardnesses of 50, 113, 161, and 253 mg/L (as CaCO3), respectively. Ceriodaphnia dubia was found to be significantly more sensitive in chronic exposures than other species tested (including other daphnids such as Daphnia magna); chronic toxicity was less dependent on hardness than was acute toxicity. Chronic 20% effective concentrations (EC20s) were estimated at <3.8, 4.7, 4.0, and 6.9 microg/L at hardnesses of 50, 113, 161, and 253 mg/L, respectively. Testing with H. azteca resulted in a 96-h LC50 of 3,045 microg/L and a 14-d EC20 of 61 microg/L at a hardness of 98 mg/L (as CaCO3). Survival was more sensitive than was growth in the chronic study with H. azteca. The 20% lethal accumulation effect level based on measured Ni body burdens was 247 nmol/g wet weight.     

Toxicity of Manganese to Ceriodaphnia dubia and Hyalella azteca

Manganese is a toxic element frequently overlooked when assessing toxicity of effluents, sediments, and pore waters. Manganese can be present at toxic levels in anoxic solutions due to increased solubility under chemically reducing conditions, and it can remain at those levels for days in aerated test waters due to slow precipitation kinetics. Ceriodaphnia dubia and Hyalella azteca are freshwater organisms often used for toxicity testing and recommended for assessments of effluents and pore waters. Lethal and reproductive-inhibition concentrations of Mn were determined for C. dubia in acute 48-h tests and chronic three-brood tests using animals <24 h old and between 24 and 48 h old. Sensitivity of H. azteca to Mn was determined with 7-day-old animals in acute 96-h tests. Tests were run at three levels of water hardness to assess the amelioratory effect, which was often significant. Manganese concentrations were measured analytically at test initiation and after 96 h for calculation of toxicity and determination of Mn precipitation during the tests. Minimal amounts of Mn (≤3%) precipitated within 96 h. LC₅₀s determined for H. azteca progressively increased from 3.0 to 8.6 to 13.7 mg Mn/L in soft, moderately hard, and hard waters, respectively. The tolerance of C. dubia to Mn was not significantly different between moderately hard and hard waters, but was significantly lower in soft water. Manganese sensitivity of C. dubia was not significantly different between the ages tested. Acute LC₅₀ values for C. dubia averaged 6.2, 14.5 and 15.2 mg Mn/L and chronic IC₅₀ values averaged 3.9, 8.5 and 11.5 mg Mn/L for soft, moderately-hard and hard waters, respectively. Manganese toxicity should be considered when assessing solutions with concentrations approaching these levels. Received: 21 June 1999/Accepted: 5 October 1999     

Effects of dietborne copper and silver on reproduction by Ceriodaphnia dubia

Recent studies have indicated the potential for dietborne metals as an important exposure pathway for metal toxicity in freshwater organisms. We conducted a study in which freshwater cladocerans (Ceriodaphnia dubia) were fed green algae (either Pseudokirchneriella subcapitata or Chlorella vulgaris) that were grown in Ag- or Cu-contaminated media. In one series of toxicity tests patterned after the U.S. Environmental Protection Agency's three-brood C. dubia chronic toxicity test, we exposed C. dubia to waterborne Ag or Cu while feeding them normal amounts of uncontaminated yeast-Cerophyll-trout chow (YCT) slurry and either algae grown in standard media or algae grown in standard media supplemented with Ag or Cu (added as AgNO3 or CuSO4 x 5H2O). These parallel tests demonstrated that dietborne metal did not contribute to survival or reproduction effects beyond the effects caused by waterborne metal alone. We also conducted dietborne-only toxicity tests patterned after two other recently published experimental designs in which (1) C. dubia were fed only metal-contaminated algae for 4 h, transferred to fresh water, and fed uncontaminated algae and YCT slurry for the duration of the three-brood test or (2) C. dubia were fed standard amounts of metal-contaminated algae and uncontaminated YCT slurry for the entire three-brood test. In contrast to previous studies, we did not find consistent dietborne metal toxicity or standard concentration-response relationships in those two experiments. Instead, among-experiment variation in intracellular partitioning of metals in the algae fed to the C. dubia, among-laboratory differences in experimental procedures, selective feeding by C. dubia to avoid metal-contaminated algae, an interaction between reproductive status of the C. dubia and dietborne metal concentration, or a combination of these might help explain the apparently inconsistent results.     

Effects of metal and organophosphate mixtures on Ceriodaphnia dubia survival and reproduction

The toxicity of mixtures of copper, zinc, and diazinon were determined for Ceriodaphnia dubia using 7-d survival and reproduction tests. Fifteen treatments, including combinations of the chemicals at 0, 25, 50, 75, and 100% of their individual median lethal concentrations, adding up to one toxic unit (TU) were tested. The TU was then used to classify each mixture response as additive, greater than additive, or less than additive. For survival, additive responses occurred in the 75% zinc plus 25% diazinon and the 50% copper plus 25% zinc plus 25% diazinon treatments. For reproduction, additive responses occurred in the 75% copper plus 25% zinc, 75% copper plus 25% diazinon, and 75% zinc plus 25% diazinon treatments. Copper and zinc played a greater role in toxicity than diazinon did. Less-than-additive interactions were found in all remaining mixtures, perhaps because of differences in mode of action between diazinon and metals. Consideration of dose-response curves can help to explain inconsistencies regarding toxic response in treatments with different ratios of the same chemicals. As TU percentages changed, mixture components were taken from different locations on differently shaped dose-response curves. Because most responses were less than additive, however, water-quality criteria based on individual concentrations probably are protective for most metal-organophosphate mixtures.     

Effects of water chemistry on the chronic toxicity of lead to the cladoceran, Ceriodaphnia dubia

As the first step toward parameterization of a chronic lead (Pb) biotic ligand model (BLM) for Ceriodaphnia dubia, 7-d toxicity tests were performed in waters modified to evaluate the influences of hardness, DOM (as Suwannee River NOM and Aldrich humic acid (HA)), pH (buffered with 4 mM MOPS) and alkalinity on the chronic toxicity of Pb. Calculated EC₂₀s for the control base water test and each of the most extreme modified test waters were as follows in μg L⁻¹ Pb (95% confidence interval): base water control=45 (14-53), 5 mM CaSO₄=22 (12-30), 32 mg L⁻¹ DOM=523 (388-573), 2.5 mM NaHCO₃=73 (21-120) and pH 6.4 buffered with MOPS=3.9 μg L⁻¹ Pb (1-5). Results indicate that hardness does not protect against chronic toxicity of Pb to C. dubia, whereas HA does protect at the highest concentration tested (597 μM). Additionally, our findings suggest that low pH increases the chronic toxicity of Pb whereas increased alkalinity is protective. The findings reported herein support the need for a chronic Pb BLM as an alternative approach to hardness-based regulations.     

Joint acute toxicity of diazinon and copper to Ceriodaphnia dubia

Diazinon and copper are two contaminants that are widely found in urban streams and in municipal wastewater effluents. Because these contaminants may be found concurrently, the potential for their joint toxicity is of interest, particularly with regard to toxicity testing of wastewater effluents and the ecological implications of simultaneous exposures in urban streams. Although interactions between metals are well studied, relatively little is known about interactions between metals and organophosphate compounds such as diazinon. In this study, the interaction between copper and diazinon was evaluated using cladoceran (Ceriodaphnia dubia) in 48-h static tests within laboratory water. Using toxic units derived from concurrently established 48-h median lethal concentration values (LC50) of test organisms of each individual toxicant, the effects of the mixture of copper and diazinon on the survival of C. dubia were shown to be generally nonconcentration additive (LC50 significantly greater than one toxic unit). However, evaluation of the dose-response relationship across the entire range of effect levels revealed that the mortality induced by the mixture of copper and diazinon supported concentration additivity at higher effect levels.     

Comparative toxicity of chlorothalonil: Ceriodaphnia dubia and Pimephales promelas

Chlorothalonil is a commonly used fungicide in rural and urban environments and can be incidentally introduced into aquatic systems through rainfall runoff or direct overspray and drift from aerial applications. Few studies have been published regarding risks to aquatic organisms exposed to chlorothalonil, so this study was performed to provide a first-order risk characterization for receiving system biota. Definitive laboratory toxicity tests were conducted with aqueous solutions of chlorothalonil and sentinel aquatic organisms (Ceriodaphnia dubia Richard and Pimephales promelas Rafinesque). P. promelas was more sensitive (7-day potency=6.1% mortality/mug/L) than C. dubia (7-day potency=0.94% mortality/mug/L) to chlorothalonil exposures. All mortality of P. promelas and C. dubia resulting from these chlorothalonil exposures occurred within the first 96h and no sublethal effects (i.e., growth or reproduction) were detected under these experimental conditions following 7-day exposures.     

Prediction and experimental validation of acute toxicity of beta-blockers in Ceriodaphnia dubia

Acute toxicity of beta-adrenoceptor blockers (beta-blockers) was studied with beta-blockers as single compounds or in mixture using the standardized acute 2-d Ceriodaphnia dubia immobility test. The tested compounds were selected according to their selectivity for the beta1-adrenoceptor, with three beta1-selective blockers (acebutolol, atenolol, and metoprolol) and three non-beta1-selective blockers (nadolol, oxprenolol, and propranolol). The acute toxicity (median effective concentration) of the six single compounds ranged from 1.4 mg/L for propranolol to 163 mg/L for nadolol. According to European Union directive 93/67EEC, these values range from toxic for aquatic organisms to nonclassified. The more toxic compounds, propranolol and oxprenolol, are both characterized by a membrane-stabilizing activity, a strong affinity for the beta1-adrenoceptor, and a high octanol-water partition coefficient (log Kow). The property of beta-receptor selectivity seems not to be involved in the observed acute toxicity of the single compounds for C. dubia. Nevertheless, the toxicity of the selected compounds in mixture can be defined according to the beta1-selectivity. Two main joint effects have been detected: An independent action for the beta1-selective blockers, and an additive effect when either the nonselective beta1-selective blockers or the six compounds are tested together. The concentration addition model seems to be appropriate, providing a reasonable worst-case estimation of beta-blocker mixture toxicity for regulatory purposes.     

Effects of hardness and alkalinity in culture and test waters on reproduction of Ceriodaphnia dubia

Ceriodaphnia dubia were cultured in four reconstituted water formulations with hardness and alkalinity concentrations ranging from soft to the moderately hard water that is required by whole-effluent toxicity (WET) testing methods for culturing test organisms. The effects of these culture formulations alone and in combination with two levels of Cl-, SO4(2-), and HCO3- on reproduction of C. dubia were evaluated with the standard three-brood test. Reproduction was significantly reduced when test waters had lower hardness than culture waters. However, reproduction was not significantly different when animals cultured in low-hardness waters were exposed to moderately hard waters. The hardness of the culture water did not significantly affect the sensitivity of C. dubia to the three anions. Conversely, increased hardness in test waters significantly reduced the toxicities of Cl- and SO4(2-), with HCO3- toxicity following the same pattern. Alkalinity exhibited no consistent effect on Cl- and SO4(2-) toxicity. The physiological stress of placing animals cultured in moderately hard water into softer test waters might contribute to marginal failures of otherwise nontoxic effluents. The standard WET protocol should be revised to allow the culture of C. dubia under lower hardness conditions to better represent local surface water chemistries.     

Effects of depleted uranium on the health and survival of Ceriodaphnia dubia and Hyalella azteca

Depleted uranium (DU) has been used as a substitute for the fissionable enriched uranium component of atomic weapons tested at Los Alamos National Laboratory (LANL) (Los Alamos, NM, USA) since the early 1950s, resulting in considerable concentrations of DU in the soils within the test sites. Although the movement of DU into major aquatic systems has been shown to be minimal, there are many small-order ephemeral streams and areas of standing water in canyons throughout LANL that may be affected by inputs of DU via runoff, erosion, and leaching. Ninety-six-hour acute and 7-d chronic toxicity assays were conducted to measure the toxicity of DU on survival and reproduction of Ceriodaphnia dubia. A 14-d water-only assay was conducted to measure survival and growth of Hyalella azteca. The estimated median lethal concentration (LC50) to produce 50% mortality of the test population for the 96-h Ceriodaphnia dubia assay was 10.50 mg/L. Reproductive effects occurred at a lowest-observable-effect concentration > or = 3.91 mg/L with a no-observable-effect concentration of 1.97 mg/L. The estimated 14-d LC50 for the Hyalella azteca assay was 1.52 mg/L. No significant relationship was detected between growth and DU concentrations. Concentrations at which toxicity effects were observed in this study for both invertebrates exceeded concentrations of total uranium observed in runoff from LANL lands. Thus, it is likely that current runoff levels of uranium do not pose a threat to these types of aquatic invertebrates.