Physiological and reproductive effects of beta adrenergic receptor antagonists in Daphnia magna.

Although pharmaceuticals are increasingly found in surface waters, environmental levels of many of these compounds are not acutely toxic to model test organisms. Prior to conducting appropriate ecological risk assessments of pharmaceuticals, the mode of action-based biomarkers needs to be developed for non-target species. To evaluate toxicity of the beta-adrenergic blockers propranolol and metoprolol on non-target biota, we assessed standard ecotoxicological endpoints after 9 days of subchronic exposure in a transgenerational study with Daphnia magna. On day 9 of exposure, the lowest observed effects concentration (LOEC) for growth were 0.44 mg L(-1) for propranolol and 12 mg L(-1) for metoprolol. Total fecundity LOECs for the 9-day exposure were 0.11 mg L(-1) and 6 mg L(-1) for propranolol and metoprolol, respectively. In addition to typical ecotoxicological endpoints, we evaluated the utility of employing the physiological biomarkers of heart rate and metabolic rate following subchronic and acute exposures to propranolol and metoprolol. Propranolol and metoprolol LOECs for heart rate were 0.055 mg L(-1) and 3.1 mg L(-1), significantly lower than the LOECs for growth and reproduction. At these concentrations, heart rate was significantly lower than the control values for both compounds. Daphnia magna endpoint sensitivity to chronic propranolol and metoprolol exposure was mortality < growth < fecundity < heart rate. Second generation D. magna were less sensitive to both compounds. Responses of the physiological biomarkers heart rate and metabolic activity suggest that propranolol and metoprolol exerts sublethal toxicity to D. magna at lower concentrations than observed in the classical endpoints.

Increased toxicity to Ceriodaphnia dubia in mixtures of atrazine and diazinon at environmentally realistic concentrations.

The acute toxicity of diazinon in combination with atrazine concentrations of 5, 10, 20, and 40 microg/L was evaluated using Ceriodaphnia dubia. Atrazine concentrations as low as 5 microg/L in combination with diazinon significantly increased toxicity to C. dubia compared to diazinon alone. Atrazine and diazinon residues within water samples collected from 65 subbasins throughout Denton, Texas, USA were used to assess the environmental relevance of pesticide concentrations. A geographical information system was used to examine the relationship between subbasin land uses and pesticide concentrations. Significant correlations were observed between in situ atrazine and diazinon concentrations and some subbasin land uses. Atrazine was significantly (P < 0.05) correlated to diazinon during some months. Of the 276 samples collected, 39% exceeded our experimentally derived diazinon LC(50) value, and 39% exceeded our minimum atrazine concentration of 5.0 microg/L. Results indicate the potential for increased toxicity from mixtures of compounds at environmentally realistic concentrations.

Laboratory and field responses to cadmium: an experimental study in effluent-dominated stream mesocosms.

Although select stream flows in the southwestern United States are dominated by effluent discharges, metal hazards have not been experimentally evaluated in effluent-dominated streams. Lotic mesocosms were designed to assess cadmium effects on multiple levels of biological organization, to determine relevance to regulatory criteria of standard laboratory toxicity tests, and to link laboratory tests to stream responses. Replicate streams were treated with 15 or 143 microg/L Cd during a 10-d study. Streams were sampled on days 0 and 10 for benthic macroinvertebrates, periphyton, and ecosystem metabolism. Concurrent Ceriodaphnia dubia and Pimephales promelas laboratory tests were performed with water from streams. Individual organism, population, and community response variables were affected by 143 microg/L Cd but not by the I5-microg/L treatment level. A biotic ligand model for cadmium predicted a 48-h median effective concentration (EC50) value of 280 microg/L Cd for C. dubia in these effluent-dominated streams: an EC50 value of 38.3 microg/L Cd was estimated for C. dubia in tests performed with reconstituted hard water. Our findings generally support use of the biotic ligand model for establishing site-specific, acute water quality criteria for cadmium. However, future effluent-dominated stream research is required to evaluate relationships between chronic cadmium exposure and organismal and community responses.

Temporal and spatial variability in the estrogenicity of a municipal wastewater effluent.

The estrogenicity of a municipal wastewater effluent was monitored using the vitellogenin biomarker in adult male fathead minnows (Pimephales promelas). The variability in the expression of vitellogenin was evident among the monitoring periods. Significant (alpha< or =0.05) increases in plasma vitellogenin concentrations were detected in March and December, but not in August or June. Additionally, the magnitude of expression was variable. Variability in the spatial scale was also evident during the March and June exposure months. Concurrent exposures in both the creek receiving the effluent from a wastewater treatment plant and an experimental wetland showed estrogenicity to be different with distance from the respective effluent inflow sites. March exposures showed estrogenicity to be somewhat persistent in the receiving creek (>600 m), but to decrease rapidly within the experimental wetland (<40 m). Results are discussed relative to the monitoring season, to the spatial distribution of the response in both receiving systems, and to possible causative factors contributing to the effluent estrogenicity.

Waterborne and sediment toxicity of fluoxetine to select organisms.

Ecological risk assessments of pharmaceuticals are currently difficult because little-to-no aquatic hazard and exposure information exists in the peer-reviewed literature for most therapeutics. Recently several studies have identified fluoxetine, a widely prescribed antidepressant, in municipal effluents. To evaluate the potential aquatic toxicity of fluoxetine, single species laboratory toxicity tests were performed to assess hazard to aquatic biota. Average LC(50) values for Ceriodaphnia dubia, Daphnia magna, and Pimephales promelas were 0.756 (234 microg/l), 2.65 (820 microg/l), and 2.28 microM (705 microg/l), respectively. Pseudokirchneriella subcapitata growth and C. dubia fecundity were decreased by 0.044 (14 microg/l) and 0.72 microM (223 microg/l) fluoxetine treatments, respectively. Oryias latipes survival was not affected by fluoxteine exposure up to a concentration of 28.9 microM (8.9 mg/l). An LC(50) of 15.2 mg/kg was estimated for Chironomus tentans. Hyalella azteca survival was not affected up to 43 mg/kg fluoxetine sediment exposure. Growth lowest observed effect concentrations for C. tentans and H. azteca were 1.3 and 5.6 mg/kg, respectively. Our findings indicate that lowest measured fluoxetine effect levels are an order of magnitude higher than highest reported municipal effluent concentrations.

Aquatic ecotoxicology of fluoxetine.

Recent studies indicate that the pharmaceutical fluoxetine, a selective serotonin reuptake inhibitor, is discharged in municipal wastewater treatment plant effluents to surface waters. Few data on environmental fluoxetine exposure and hazard to aquatic life are currently available in the literature. Here, we summarize information on fluoxetine detection in surface waters and review research on single-species toxicity test, Japanese medaka (Oryzias latipes) reproduction and endocrine function, and freshwater mesocosm community responses to fluoxetine exposure. Based on results from our studies and calculations of expected introduction concentrations, we also provide a preliminary aquatic risk characterization for fluoxetine. If standard toxicity test responses and a hazard quotient risk characterization approach are solely considered, little risk of fluoxetine exposure may be expected to aquatic life. However, our findings indicate that: (1) the magnitude, duration and frequency of fluoxetine exposure in aquatic systems requires further investigation; (2) mechanistic toxicity of fluoxetine in non-target biota, including behavioral responses, are clearly not understood; and (3) an assessment of environmentally relevant fluoxetine concentrations is needed to characterize ecological community responses.