Thomas W. La Point

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.

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.

Snail bioaccumulation of triclocarban, triclosan, and methyltriclosan in a north texas, usa, stream affected by wastewater treatment plant runoff

Grazing by freshwater snails promotes nutrient turnover in algal communities. Grazed algal compartments may include antimicrobial agents and metabolites, such as triclocarban (TCC), triclosan (TCS), and methyltriclosan (MTCS), which are incompletely removed by wastewater treatment plant (WWTP) processing. The present study quantifies snail bioaccumulation factors (BAFs) for TCC, TCS, and MTCS at the outfall of Pecan Creek (TX, USA), the receiving stream for the city of Denton (TX, USA) WWTP. Helisoma trivolvis (Say) is ubiquitous and thrives under standard laboratory conditions, leading to its choice for this bioaccumulation study in conjunction with Cladophora spp. Along with providing substrate for epiphytic growth, Cladophora spp. provide a source of food and shelter for H. trivolvis. After being caged for two weeks, algae and snails were collected from the WWTP outfall, along with water-column samples, and analyzed by isotope dilution gas chromatography-mass spectrometry for TCS and MTCS and by liquid chromatography-mass spectrometry for TCC. Algal and snail samples were analyzed before exposure and found to be below practical quantitation limits for all antimicrobial agents. Triclocarban, TCS, and MTCS in water samples were at low-ppt concentrations (40-200 ng/L). Triclocarban, TCS, and MTCS were elevated to low-ppb concentrations (50-300 ng/g fresh wt) in caged snail samples and elevated to low-ppb concentrations (50-400 ng/g fresh wt) in caged algal samples. Resulting snail and algal BAFs were approximately three orders of magnitude, which supports rapid bioaccumulation among algae and adult caged snails at this receiving stream outfall. The results further support TCC, TCS, and MTCS as good candidate marker compounds for evaluation of environmental distribution of trace WWTP contaminants.

Recommendations for the assessment of TNT toxicity in sediment

Previous investigations of the ecotoxicity of TNT in spiked sediments noted the rapid degradation and disappearance of the toxicant, yet little is understood regarding the effects of this process on toxicity and subsequent derivation of toxicity reference values. We conducted environmental fate studies and 28-d sediment toxicity tests with benthic oligochaete worms (Tubifex tubifex) with sediments spiked at three different TNT concentrations (440, 1,409, and 4,403 nmol/g dry wt) aged for 1, 8, and 29 d. Because of rapid degradation of TNT, disappearance of degradation products, and partitioning to overlying water, only 25 to 40% of the added nitroaromatic mass balance was associated with sediment immediately after spiking. Lethal toxicity decreased with aging time and was best described by measured sediment nitroaromatic concentrations (sum of TNT and degradation products) at the beginning of exposure, with a median lethal concentration of nitroaromatic compounds of 184 nmol/g dry weight. To accurately describe the ephemeral exposure doses of TNT and its degradation products during toxicity tests with spiked sediments, we suggest that sediments should be aged at least 8 to 14 d after spiking, exposure should be based on measured sediment concentrations or chemical measures of availability, exchange of overlying water should be avoided or minimized, and short-term toxicity tests should be considered.

Solid-phase microextraction for predicting the bioavailability of 2,4,6-trinitrotoluene and its primary transformation products in sediment and water.

Disposable solid-phase microextraction fibers (SPMEs) were used to measure the availability of 2,4,6-trinitrotoluene (TNT) and its two primary transformation products, 2-amino-4,6-dinitrotoluene (2ADNT) and 4-amino-2,6-dinitrotoluene (4ADNT). The SPMEs (85-microm polyacrylate) and sediment-dwelling oligochaetes (Tubifex tubifex) were exposed to TNT-spiked sediment, to TNT-spiked sediment amended with activated carbon, and to TNT-, 2ADNT-, and 4ADNT-spiked water. Sediment concentration was a poor predictor of bioavailability in unamended and carbon-amended sediments (r2 = 0.14-0.73) The activated carbon amendment reduced the bioavailability of compounds in carbon-amended sediment, causing the relationships between Tubifex concentrations and sediment concentrations to differ significantly between unamended and carbon-amended sediment for all compounds. In contrast, SPME TNT concentrations predicted Tubifex TNT concentrations (r2 = 0.54-0.79). and regression models did not differ significantly among the three TNT-spiked matrices. The SPME 2ADNT and 4ADNT concentrations also were predictive of Tubifex 2ADNT and 4ADNT concentrations (r2 = 0.44-0.90). Relationships between Tubifex concentrations and SPME concentrations were the same between unamended and carbon-amended TNT-spiked sediments for 2ADNT and 4ADNT; however, the relationship in sediment (pooled data) differed from the relationship found in 2ADNT- and 4-ADNT-spiked water. The SPMEs provided carbon amendment-independent measures of ADNT availability in sediment and matrix-independent measures of TNT availability among the three matrices. The SPMEs show promise for predicting bioavailable organic compounds in sediment and water.

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.

Response of Ceriodaphnia dubia to ionic silver: discrepancies among model predictions, measured concentrations and mortality

Silver thiosulfate, often a waste product of photoprocessing, is less bioavailable or toxic to aquatic organisms than is ionic silver. We conducted duplicate 48-h Ceriodaphnia dubia tests in reconstituted laboratory water using treatments of 92.7 nM Ag+ with various concentrations of thiosulfate. Expected Ag+ concentrations were generated for thiosulfate treatment levels using MINEQL + chemical equilibrium modeling. Ag+ concentrations in treatments were determined using a novel silicon-based sensor. Based on predicted Ag+ and published 48-h LC50 values for C. dubia, we did not expect to observe adverse effects. Yet, 100% mortality was observed at low thiosulfate treatments, whereas > 85% and > 95% survival was observed at higher thiosulfate treatment levels, respectively. Our results indicate that biotic responses match the sensor-based Ag+ concentrations. However, there is a discrepancy between these empirical results and responses expected to occur with Ag+ concentrations as predicted by MINEQL + chemical modeling. By correlating silicon sensor data with toxicity results obtained from our laboratory, our work clearly relates a specific chemical form (Ag+) to toxicity results.

The Terminal Pleistocene Extinctions in North America, Hypermorphic Evolution, and the Dynamic Equilibrium Model

Abstract The cause of megafaunal extinctions at the end of the last glaciation has been hotly debated during the last few decades, most recently at the global scale. In North America and elsewhere the debate centers on whether or not human hunters, who seemingly first entered the continent during the extinction period, caused the extinctions through over-hunting. An alternative explanation is that climate change during the terminal Pleistocene radically modified existing habitats and this caused the extinctions. Hustons (1979, 1994) dynamic equilibrium model (DEM) of community species richness provides a theoretical context for explanations of the extinctions in North America and highlights life history characteristics of extinct mammals. These life history traits and associated phenotypes are a seldom-explored line of evidence concerning the causes of the extinctions. In light of life history traits, environmental disturbance is implicated as the proximate cause of the extinctions, but the DEM does not preclude overkill as a contributing cause in North America.

A comparison of chronic cadmium effects on Hyalella azteca in effluent‐dominated stream mesocosms to similar laboratory exposures in effluent and reconstituted hard water

Laboratory single-species toxicity tests are used to assess the effects of contaminants on aquatic biota. Questions remain as to how accurately these toxicity tests predict site-specific bioavailability and chronic effects of metals, particularly in streams that are effluent-dominated or dependent on effluent discharge for flow. Concurrent 42-d Hyalella azteca exposures were performed with cadmium and final treated municipal effluent in the laboratory and at the University of North Texas Stream Research Facility (Denton, TX, USA), a series of outdoor lotic mesocosms. An additional 42-d laboratory test was conducted with H. azteca to evaluate Cd toxicity in reconstituted hard water (RHW). Endpoints included Cd body burden, survival, growth, and reproduction. Calculated average bioaccumulation factors were: 2,581 (stream mesocosm test) < 3,626 (laboratory effluent) < 7,382 (laboratory RHW). The 42-d survival lowest-observed-effect concentrations (LOECs) were 0.94, 4.53, and 22.97 microg/L for the laboratory RHW, laboratory effluent, and stream mesocosm exposures, respectively. Baseline growth (dry wt) and reproduction (young female(-1)) among the three exposures followed the relationship: Stream mesocosms > laboratory effluent > laboratory RHW. Differences among response variables in the three tests likely resulted from increased food sources and decreased Cd bioavailability in lotic mesocosms. Our results demonstrate that laboratory toxicity tests may overestimate chronic toxicity responses of H. azteca to Cd in effluent-dominated streams.

Fracking vs Faucets: Balancing Energy Needs and Water Sustainability at Urban Frontiers

ewly accessible shale deposits have dramatically increasedglobal gas reserves and are touted as a bridge to a cleanenergy future. For example, in the U.S., where shale gas isprojected to comprise 49% of national natural gas productionby 2035, proponents argue that shale gas production canprovide energy independence, create employment, andstimulate regional economies.