Marsha C. Black

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.

Water quality guidance for protection of freshwater mussels (Unionidae) from ammonia exposure

Ammonia toxicity data for freshwater mussels (Unionidae), a significantly imperiled taxa, were used to derive estimates of concentrations that would not likely be harmful in acute and chronic exposures and to assess the protectiveness of current U.S. Environmental Protection Agency (U.S. EPA) water quality criteria to this family of organisms. Thirty acute (24-96-h) median lethal concentrations (LC50s), covering 10 species in eight unionid genera, were used to calculate genus mean acute values (GMAVs) ranging from 2.56 to 8.97 mg/L total ammonia as N at pH 8. Freshwater mussels are at the sensitive end of the range when added to the GMAVs from the database used to derive the U.S. EPA criteria maximum concentration (CMC). We derived two estimates of acute exposure water quality guidance for the protection of freshwater mussels (CMC(FM)) by a recalculation of the CMC after adding freshwater mussel GMAVs to the U.S. EPA data set. The CMC(FM)s of 1.75 and 2.50 mg/L total ammonia as N at pH 8 average 60% less than the U.S. EPA CMC of 5.62 mg/L total ammonia as N at pH 8 for application when salmonids are present. These values average about 75% less than the CMC for application when salmonids are absent. No chronic ammonia exposure data existed for unionids. Thus, we applied a range of estimated acute:chronic ratios to the acute toxicity data set, expanded with the freshwater mussel GMAVs. to estimate continuous ammonia concentrations that may be protective of freshwater mussels. These estimates ranged from 0.3 to 1.0 mg/L total ammonia as N at pH 8, about 20 to 75% less than the U.S. EPA criteria continuous concentration (CCC) of 1.24 mg/L total ammonia as N at pH 8 and 25 degrees C. The current numeric criteria for ammonia may not be protective of mussels, more than half of whose nearly 300 species are in decline in North America. While the CMC(FM) and CCC(FM) are not equivalent to revised U.S. EPA criteria, they are offered as interim guidance for the protection of freshwater mussels.

Toxicity of fipronil and its enantiomers to marine and freshwater non-targets

Fipronil is a phenylpyrazole insecticide used in agricultural and domestic settings for controlling various insect pests in crops, lawns, and residential structures. Fipronil is chiral; however, it is released into the environment as a racemic mixture of two enantiomers. In this study, the acute toxicity of the (S,+) and (R,−) enantiomers and the racemic mixture of fipronil were assessed using Simulium vittatum IS-7 (black fly), Xenopus laevis (African clawed frog), Procambarus clarkii (crayfish), Palaemonetes pugio (grass shrimp), Mercenaria mercenaria (hardshell clam), and Dunaliella tertiolecta (phytoplankton). Results showed that S. vittatum IS-7 was the most sensitive freshwater species to the racemic mixture of fipronil (LC50 = 0.65 μ g/L) while P. pugio was the most sensitive marine species (LC50 = 0.32 μ g/L). Procambarus clarkii were significantly more sensitive to the (S,+) enantiomer while larval P. pugio were significantly more sensitive to the (R,−) enantiomer. Enantioselective toxicity was not observed in the other organisms tested. Increased mortality and minimal recovery was observed in all species tested for recovery from fipronil exposure. These results indicate that the most toxic isomer of fipronil is organism-specific and that enantioselective toxicity may be more common in crustaceans than in other aquatic organisms.

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 fipronils enantiomer-specific activity at both acute and chronic levels of concern to additional target and nontarget species needs further consideration.

Growth and development of tadpoles (Xenopus laevis) exposed to selective serotonin reuptake inhibitors, fluoxetine and sertraline, throughout metamorphosis.

Selective serotonin reuptake inhibitors (SSRIs) are widely prescribed drugs that are present in sewage effluents and surface waters. The objective of the present study was to determine whether low environmentally relevant concentrations of the SSRIs fluoxetine and sertraline could impair growth and development in tadpoles of the African clawed frog (Xenopus laevis) and to evaluate if such effects may be caused by a disruption of the neuroendocrine system. Tadpoles were exposed to SSRIs at concentrations of 0.1, 1, and 10 microg/L for 70 d throughout metamorphosis. No effects on deformities were observed. Tadpoles exposed to fluoxetine (10 microg/L) and sertraline (0.1, 1, and 10 microg/L) exhibited reduced growth at metamorphosis. Tadpoles exposed to sertraline (0.1 and 1 microg/L) exhibited an acceleration of development as indicated by an increase in the time to tail resorption. The effects of SSRIs on growth and development in tadpoles were likely driven by reduced food intake. Reduced feeding rates were observed in SSRI-exposed tadpoles, and nutritional status can influence growth and development in amphibians via effects on the neuroendocrine system. Only sertraline was capable of causing developmental toxicity in tadpoles at environmentally relevant concentrations. These data warrant additional research to characterize the risks to human health and wildlife from pharmaceutical exposures.

Mixture and single‐substance acute toxicity of selective serotonin reuptake inhibitors in Ceriodaphnia dubia

Selective serotonin reuptake inhibitors (SSRIs) are neurologically active drugs that can contaminate surface waters and have the potential to negatively affect aquatic organisms. In this investigation, the 48-h acute toxicity of mixtures (binary and quaternary) of four common SSRIs (fluoxetine [Prozac], sertraline [Zoloft], paroxetine [Paxil], and citalopram [Celexa]) were determined in the daphnid Ceriodaphnia dubia. Logistic regression was used to model mortality data and to investigate the applicability of concentration addition and independent action models to explain observed mortality. The concentrations estimated to induce 50% mortality in 48 h for the individual SSRIs sertraline, fluoxetine, paroxetine, and citalopram were 0.48 to 0.66, 1.23 to 1.84, 2.23 to 3.57, and 10.47 to 14.53 microM, respectively. Concentration addition was a better predictor of mixture effects than independent action and suggested that the tested SSRIs have a similar mechanism of action. Results indicate that environmental hazard assessments should be conservative and consider that acutely toxic effects in aquatic organisms can be additive for each SSRI in a mixture.

Effects of Salinity, Temperature, and Weight on the Survival of Young-of-Year Shortnose Sturgeon

Abstract Anthropogenic modifications of rivers and estuarine habitats have reduced the growth and recruitment of shortnose sturgeon Acipenser brevirostrum throughout its native range. This study used data from laboratory experiments to examine the individual and interactive effects of salinity, temperature, and fish weight on the survival of young-of-year shortnose sturgeon. The shortnose sturgeon in these experiments ranged from 56 to 187 mm in total length, from 0.4 to 42.8 g in weight, and from 66 to 144 d posthatch in age. Survival in 23°C water declined as salinity increased, but salinity tolerance increased with body size. The salinity lethal to 50% of the test fish after 48 h ranged from 14.8‰ to 20.9‰. Survival in freshwater declined as temperature increased, but temperature tolerance increased with body size. The temperature lethal to 50% of the test fish after 48 h ranged from 28.2°C to 30.7°C. In factorial experiments, salinity and temperature interacted significantly to affect young-of-year su...

Enantioselective toxicity and bioaccumulation of fipronil in fathead minnows (Pimephales promelas) following water and sediment exposures

Fipronil is a widely used, broad-spectrum pesticide that is applied as an equal mixture of two enantiomers. As regulations on older pesticides become more stringent, production and application of fipronil is expected to grow, leading to increased inputs into aquatic environments and complex exposures to biota. To better understand the potential exposures introduced by fipronil contamination, we conducted subchronic toxicity tests with larval fathead minnows (Pimephales promelas) and waterborne fipronil and its enantiomers and exposed juvenile fathead minnows to fipronil-spiked sediment. Enantioselective toxicity was observed in fish after the 7-d subchronic exposure, with increased toxicity of the racemate and (+) enantiomer observed compared with the (-) enantiomer. Curiously, toxicities of the racemate and (+) enantiomer were not significantly different, even though the racemate contains 50% of the (+) enantiomer and 50% of the less toxic (-) enantiomer. During the sediment exposure, racemic fipronil in sediment was transformed primarily to fipronil sulfide, while exposed fish rapidly accumulated fipronil and/or fipronil sulfide and transformed the majority to fipronil sulfone. Using the results of the sediment-exposure experiment, the authors explored a mechanism that may contribute to the interesting trends in enantioselective toxicity observed during the waterborne exposures. In tandem, the aquatic toxicity experiment and the spiked sediment exposure demonstrate the potentially complex behavior of fipronil in sediment and fish.

Comparison of metal concentrations in Corbicula fluminea and Elliptio hopetonensis in the Altamaha River system, Georgia, USA

The present study evaluated the use of the invasive clam Corbicula fluminea as a surrogate for metal accumulation in native mussels. The tissue concentrations of As, Cd, Cu, Hg, Mn, Ni, Pb, and Zn were analyzed in Corbicula and a native Unionid mussel species (Elliptio hopetonensis) collected from 13 sites in the Altamaha River system (GA, USA). Corbicula accumulated greater concentrations of As, Cd, Cu, Hg, and Ni when compared to E. hopetonensis at the same sites. The reverse was true for the metals Mn and Zn, with E. hopetonensis accumulating greater concentrations than Corbicula. Concentrations of As, Cd, Cu, Hg, and Pb were found to be significantly (alpha = 0.05) positively correlated between the two species. Greater water alkalinity and hardness tended to negatively correlate with metal accumulation, while organism size tended to correlate positively with tissue concentrations. Tissue Cd, Cu, and Pb concentrations demonstrated a correlation between bivalve tissues and concentrations of those metals in fine sediments. These correlations were significant (alpha = 0.05) for Cd and Cu concentrations in Corbicula and Pb concentrations in E. hopetonensis. The present findings support the hypothesis that bioaccumulation of some metals by Corbicula can be used to approximate levels accumulated by co-occurring native mussel species.

The Asian clam Corbicula fluminea as a biomonitor of trace element contamination: Accounting for different sources of variation using an hierarchical linear model

In the present study, specimens of the invasive clam, Corbicula fluminea, were collected above and below possible sources of potentially toxic trace elements (As, Cd, Cr, Cu, Hg, Pb, and Zn) in the Altamaha River system (Georgia, U.S.A.). Bioaccumulation of these elements was quantified, along with environmental (water and sediment) concentrations. Hierarchical linear models were used to account for variability in tissue concentrations related to environmental (site water chemistry and sediment characteristics) and individual (growth metrics) variables while identifying the strongest relations between these variables and trace element accumulation. The present study found significantly elevated concentrations of Cd, Cu, and Hg downstream of the outfall of kaolin-processing facilities, Zn downstream of a tire cording facility, and Cr downstream of both a nuclear power plant and a paper pulp mill. Models of the present study indicated that variation in trace element accumulation was linked to distance upstream from the estuary, dissolved oxygen, percentage of silt and clay in the sediment, elemental concentrations in sediment, shell length, and bivalve condition index. By explicitly modeling environmental variability, the Hierarchical linear modeling procedure allowed the identification of sites showing increased accumulation of trace elements that may have been caused by human activity. Hierarchical linear modeling is a useful tool for accounting for environmental and individual sources of variation in bioaccumulation studies.