Enantiospecific toxicity of the beta-blocker propranolol to Daphnia magna and Pimephales promelas

Propranolol is a widely prescribed, nonselective beta-adrenergic receptor-blocking agent. Propranolol has been detected in municipal effluents from the ng/L to the low-microg/L range. Like many therapeutics and other aquatic contaminants, propranolol is distributed as a racemic mixture ((R,S)-propranolol hydrochloride). Although the (S)-enantiomer is the most active form in mammals (up to 100-fold difference), no information is available regarding the enantiospecific toxicity of propranolol to aquatic organisms. Acute and chronic studies were conducted with Daphnia magna and Pimephales promelas to determine enantiospecific toxicity of propranolol to a model aquatic invertebrate and vertebrate, respectively. Also, enantiospecific effects of propranolol on D. magna heart rate were examined. Propranolol treatment levels were verified using high-performance liquid chromatography/mass spectrometry. Acute (48-h) responses of both organisms were similar for all enantiomer treatments. Chronic P. promelas responses to propranolol enantiomers followed the hypothesized relationship of (S)-propranolol being more toxic than (R)-propranolol, but chronic D. magna responses did not. This is potentially the result of a lack of beta-type receptors in cladocerans. No enantiospecific effects on daphnid heart rate were observed in acute exposures. Interestingly, some propranolol enantiomer treatments produced significant increases in reproduction before causing reproduction to decrease at higher treatment levels. To our knowledge, this research represents the first study of enantiospecific toxicity of chiral pharmaceutical pollutants.     

Toxicity models of pulsed copper exposure to Pimephales promelas and Daphnia magna

Semiempirical models are useful for interpreting the response of aquatic organisms to toxicants as a function of exposure concentration and duration. Most applications predict cumulative mortality at the end of the test for constant exposure concentrations. Summary measures, such as the median lethal concentration, are then estimated as a function of concentration. Real-world exposures are not constant. Effects may depend on pulse timing, and cumulative analysis based only on integrated exposure concentration is not sufficient to interpret results. We undertook a series of pulsed-exposure experiments using standard toxicological protocols and interpreted the results (mortality, biomass, and reproduction) using a dynamic generalization of a Mancini/Breck--type model that includes two compartments, one for internal concentration as a function of exposure and one for site-of-action concentration or accumulated damage as a function of the internal dose. At exposure concentrations near the effects level, the model explained approximately 50% of the variability in the observed time history of survival, 43% of the change in biomass, and 83% of the variability in net reproduction. Unexplained variability may result from differences in organism susceptibility, amplified by the effects of small sample sizes in standard tests. The results suggest that response is sensitive to prior conditions and that constant-exposure experiments can underestimate the risk from intermittent exposures to the same concentration. For pulsed exposures, neither the average nor the maximum concentration alone is an adequate index of risk, which depends on both the magnitude, duration, and timing of exposure pulses. Better understanding about the impacts of pulsed exposures will require use of experimental protocols with significantly greater numbers of replicates.     

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.     

Acute Toxicity of Thallium to Daphnia magna and Ceriodaphnia dubia

No abstract available.     

Mixture toxicity of flubendazole and fenbendazole to Daphnia magna

Nowadays, residual amounts of many pharmaceuticals can be found in various environmental compartments including surface and ground waters, soils and sediments as well as biota. Even though they undergo degradability, their environmental discharge is relatively continuous, thus they may be regarded as quasi-persistent contaminants, and are also frequently regarded as emerging organic pollutants. Benzimidazoles, especially flubendazole (FLU) and fenbendazole (FEN), represent two anthelmintic drugs belonging to this group. Although their presence in environmental matrices has been reported, there is relatively little data concerning their (eco)toxicological impact. Furthermore, no data is available on their mixture toxicity. FLU and FEN have been found to have a strong impact on an environmentally important non-target organism – Daphnia magna. Moreover, these compounds are usually present in the environment as a part of pharmaceutical mixtures. Therefore, there is a need to evaluate their mixture toxicity, which was the main aim of this study. Single substance toxicity tests were carried out in parallel with mixture studies of FLU and FEN, with the application of two well established concepts of Concentration Addition (CA) and Independent Action (IA). As a result, both models (CA and IA) were found to underestimate the toxicity of mixtures, however CA yielded more accurate predictions.     

Influence of dissolved organic matter source on silver toxicity to Pimephales promelas

In the environment, the formation of organic and inorganic silver complexes can decrease Ag bioavailability (toxicity) to aquatic organisms. However, current water quality regulations do not consider the protective effects of water quality parameters such as dissolved organic carbon (DOC) concentration. To determine the effect of DOC concentration and source on silver toxicity, nine different natural organic matter isolates were used in 96-h static-renewal toxicity tests with fathead minnow (Pimephales promelas). The 96-h dissolved silver median lethal concentrations (LC50) among different sources of dissolved organic matter varied by up to fivefold (4.5-23.3 microg/L). Further, toxicity tests with organic matter from the site with the lowest 96-h LC50 value suggested only limited additional attenuation of silver toxicity when DOC concentration was increased from 5.1 to 14.0 mg/L. With this site excluded, we found little more than a twofold difference among 96-h dissolved Ag LC50s for the remaining sources (10.1-23.3 microg/L). However, significant toxicological differences among sites remained. It was apparent that organic matter from different sources varied both chemically and toxicologically, but no conclusions could be drawn that related compositional variation to observed Ag toxicity for these isolates.     

Acute toxicity of the natural algicide, cyanobacterin, to Daphnia magna

Cyanobacterin is a potent, photosynthetic inhibitor produced as a secondary metabolite by the filamentous, freshwater cyanobacterium Scytonema hofmanni. With a spectrum of activity encompassing species of cyanobacteria and eucaryotic algae as well as higher plants, cyanobacterin might be utilized as a commercial algicide for algae waterbloom control. As a component of the preliminary environmental risk/hazard evaluation of this proposed application, the acute toxicity of cyanobacterin to the planktonic crustacean, Daphnia magna, was assessed. Based on five trials, the 48-hr LC50 for D. magna was determined to be approximately 1.37 micrograms/ml (range: 0.78-2.58 micrograms/ml). In addition, a significant percentage of the surviving daphnids were completely immobile at the end of the 48-hr exposure period. These results give strong indication that cyanobacterin and/or its residues exhibit some nontarget organism lethality at projected use-concentration level. Furthermore, estimates of partition coefficients and bioconcentration factor, generated through quantitative structure-activity relationships, suggest that sediment, suspended particulates, and biota may serve as major compartments of cyanobacterin partitioning in an aquatic ecosystem. Before cyanobacterin should be further considered for application as a commercial algicide, a rigorous evaluation of nontarget organism lethality and environmental fate is required.     

Acute toxicity of trivalent thallium compounds to Daphnia magna

Daphnia magna was used to evaluate the aquatic toxicity of Tl(III) compounds including Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate. The results clearly show that Tl(III) is extremely toxic to daphnids. The 48-h LC50 values for Tl(III) nitrate, Tl(III) chloride, and Tl(III) acetate are 24, 61, and 203 microg/L, respectively. Tl(III) is much more toxic than Tl(I) and many other metals such as Cd(II), Cu(II), and Ni(II); it is similar to the toxicity that of Hg(II). The formation of Tl(III)-complexes would significantly reduce Tl(III) toxicity.     

Chronic toxicity of hexavalent chromium to the fathead minnow (Pimephales promelas)

The chronic effects of hexavalent chromium on the fathead minnow (Pimephales promelas) were investigated. Survival was affected only at the high test concentration of 3.95 mg Cr/L. All chromium concentrations, including 0.018 mg/L, the lowest tested, retarded the early growth of first-generation fish, but this effect was only temporary. Growth of second-generation fish was not affected at concentrations of 1.0 mg/L or lower. Reproduction and hatchability of eggs were not affected at any chromium concentration tested.The maximum acceptable toxicant concentration (MATC) for fathead minnows in hard water (209 mg/L as CaCO₃ at pH 7.7) was based on survival and lies between 1.0 and 3.95 mg Cr/L, respectively. The application factor (MATC/96-hr LC50) is between 0.03 and 0.11.     

Influence of organism age on metal toxicity to Daphnia magna

Aquatic organisms living in surface water experience contaminant exposure at different life stages. While some investigators have examined the influence of organism age on the toxicity of pollutants, the general assumption in toxicology has been that young organisms were more sensitive than older organisms. In fact, some standardized toxicity tests call for the use of organisms less than 24 h old. This research characterized the age sensitivity of the water flea Daphnia magna to copper, zinc, selenium, and arsenic. During 21-d toxicity tests, organisms were exposed to a single 12-h pulse of either 70 microg/L Cu, 750 microg/L Zn, 1000 microg/L Se, or 5000 microg/L As at different ages ranging from 3 h to 10 d old. Mortality and reproduction were compiled over 21 d. During the juvenile stage, mortality increased and cumulative reproduction decreased with age, respectively. However, mortality decreased and cumulative reproduction increased with age when organisms became adult. Peak sensitivity occurred in 4-d-old organisms exposed to Cu and Zn, while 2- to 3-d-old organisms were most sensitive to As and Se. Growth of D. magna over 21 d was not affected by the 12-h pulse of Cu, Zn, Se, or As given at any organism age. This indicates the recovery of the organisms after exposure termination.     

Toxicity of Silver and Titanium Dioxide Nanoparticle Suspensions to the Aquatic Invertebrate, Daphnia magna

The purpose of this study was to investigate the 48 h acute toxicity of capped silver nanoparticles (AgNPs), and capped and uncapped titanium dioxide (nTiO₂) to Daphnia magna neonates. In addition, a 24 days chronic toxicity study was performed for D. magna exposed to uncapped nTiO₂ to evaluate effects on growth, reproduction and survival. The 48 h median lethal concentrations (LC₅₀) for carboxy-functionalized capped AgNPs and uncapped nTiO₂ were 2.75 μg/L and 7.75 mg/L, respectively. In contrast, no mortalities were observed for Daphnia exposed to carboxy-functionalized capped nTiO₂ at concentrations up to 30 mg/L. In the chronic toxicity experiment with uncapped nTiO₂, the growth, reproduction and survival of D. magna were significantly (p < 0.05) reduced at concentrations ranging from 4.5 to 7.5 mg/L. Growth and reproduction were reduced by 35 % and 93 %, respectively in the treatments at the highest uncapped nTiO₂ concentration (7.5 mg/L). Time to first reproduction was delayed by 2–3 days in D. magna and the test organisms produced only 1–2 broods over 24 days exposure to the highest concentration of uncapped nTiO₂. Overall, the results from the present study indicate that exposures of aquatic invertebrates to nanoparticles could have important ecological effects on lower trophic levels in aquatic ecosystems.     

Aquatic toxicity of ethoxylated and propoxylated alcohols to daphnia magna

Ethoxylated alcohols, which are used as nonionic surfactants, are known to act as general narcotics in acute aquatic toxicity; that is, they behave in the same way as nonsurfactant unreactive organic chemicals. The toxicity of such chemicals is well predicted by quantitative structure-activity relationships based solely on the logarithm of the octanol/water partition coefficient (log P), which can be calculated from structure. In the present study, we have shown, using experimental results, that a similar approach can be used to determine the toxicity of ethoxylate/propoxylate alcohols (i.e., containing propoxy [PO] and ethoxy [EO] units). Our calculations indicate that use of the Roberts position-dependent branching factor in calculating the PO group contribution is more appropriate than the Leo and Hansch branch factor. The resulting log P value for a PO group is 0.01; that is, the overall contribution to the final log P value is close to zero. On this basis, it is predicted that nonionic surfactants containing both EO and PO groups should have the same molar toxicity as surfactants based on the same parent alcohol and with the same number of EO groups but with no PO groups. This prediction has been confirmed in Daphnia acute toxicity tests. Furthermore, both EO/PO and EO-only nonionics are found to fit the same linear relationship between log P and toxicity.     

A comparative study of rac- and S-metolachlor toxicity to Daphnia magna

Racemic product of metolachlor contains two R enantiomers and two S enantiomers. S-metolachlor is now widely used instead of rac-metolachlor because the former is more effective in herbicidal activity than the latter. The acute and chronic toxicities of rac- and S-metolachlor to Daphnia magna were determined and compared in this study. The acute 24-h LC50s for rac- and S-metolachlor to D. magna were 69.4 and 51.2 mgL(-1), respectively, indicating that the acute toxicity of S-metolachlor is slightly higher than that of rac-metolachlor. In chronic test, lowest-observed-effect concentration (LOEC), no-observed-effect concentration (NOEC), days to first brood, length, longevity, number of broods per female, number of young per female, and the intrinsic rate of natural increase (r) were determined. The results showed that the LOEC and NOEC of rac-metolachlor were 0.01 and 0.001 mgL(-1), while those of S-metolachlor were 0.5 and 0.1 mgL(-1), respectively. The first brood day of D. magna was not affected by rac- or S-metolachlor. Longevity and the number of broods per female were significantly (P<0.05) affected when rac-metolachlor concentration was higher than 1.0 mgL(-1) but were not significantly affected until S-metolachlor concentration was higher than 10 mgL(-1). The length was affected at the same concentration of rac- and S-metolachlor. Number of brood per female was significantly reduced when rac-metolachlor concentration was higher than 0.01 mgL(-1) but not significantly reduced until S-metolachlor concentration was higher than 0.5 mgL(-1). The r values were significantly reduced when the rac-metolachlor concentrations were above 0.01 mgL(-1) but not reduced only when S-metolachlor concentration was higher than 0.5 mgL(-1). The results of chronic toxicity indicated that rac-metolachlor was significantly (P<0.05) more toxic than S-metolachlor to D. magna.