48-h EC50 Research Articles

Life Stage Sensitivity of a Freshwater Snail to Herbicides Used in Invasive Aquatic Weed Control

Invasive aquatic plants like hydrilla (Hydrilla verticillata) threaten native species in many ways, ultimately degrading overall habitat quality and quantity. Aquatic herbicides are often chosen as a control and management strategy, but few peer-reviewed studies address their effects on non-target organisms, especially native freshwater mussels and snails. The aim of this study was to assess the life stage sensitivity of a rare snail, Somatogyrus virginicus (Lithoglyphidae), to two aquatic herbicides (dipotassium salt of endothall and fluridone). We collected adult snails, cultured their eggs on a vinyl card substrate, exposed adults and eggs in 96-h static-renewal experiments, and monitored eggs through hatching. Because fluridone is typically applied for ≥ 60 d, an additional treatment was exposed in staticrenewal through hatching (30 d total) to improve environmental relevance. Eggs present on the shells of adult snails were also monitored. Endpoints were adult survival and egg hatching success. Fluridone did not affect adult snail survival at concentrations up to 1500 µg/L, and in the test with eggs on vinyl cards, fluridone did not significantly delay (p = 0.12) or influence overall hatching success (p = 0.22), including in the 30-d exposure (Dunnett's p = 0.09). However, fluridone significantly delayed hatching of eggs on adult shells (p < 0.01) and reduced their overall hatching success (p < 0.01). The 96-h median effect concentration (EC50) for fluridone on hatching success of eggs on adults was 1334 µg/L (95% CI, 1215 – 1466 µg/L). For endothall, the adult 96-h median lethal concentration (LC50) was 223 mg/L (157 – 318 mg/L). Endothall negatively affected hatching success in both egg tests by delaying hatching (p < 0.01 in both tests) and by reducing overall hatching success (p = 0.04 for eggs on cards, and p < 0.01 for eggs on adults). The endothall 96-h EC50s for egg hatching success were 54.1 mg/L (95% CI, 35.6 – 82.2 mg/L; eggs on adults) and 83.4 mg/L (95% CI, 60.4 – 115.2 mg/L; eggs on cards). Neither herbicide had toxic effects to either life stage at concentrations typically prescribed for control of hydrilla (5 – 15 µg/L fluridone and 1 – 5 mg/L endothall). However, applying the minimum amount of herbicide needed for effective weed control is recommended for ensuring safety of non-target organisms.

Behavioral responses of juvenile Daphnia magna after exposure to glyphosate and glyphosate-copper complexes

Glyphosate (N-(phosphonomethyl)glycine) is the active ingredient in a range of popular broad-spectrum herbicide formulations. Glyphosate is a chelating agent that can form stable complexes with divalent metal ions including Cu(II). Little is known about the bioavailability and ecotoxicity of glyphosate-Cu(II) complexes to aquatic organisms. In this study, we used video tracking and behavior analysis to investigate sublethal effects of binary mixtures of glyphosate and Cu(II) to juvenile D. magna. Behavioral responses were quantified for individual D. magna after 24h and 48h exposure to glyphosate and glyhosate-Cu(II) mixtures. Sublethal concentrations resulted in decreases in swimming velocity, acceleration speed, and distance moved whereas inactive time of D. magna increased. Distance moved and inactive time were the most responsive parameters to glyphosate and glyphosate-Cu(II) exposure. On a molar basis, glyphosate-Cu(II) complexes appeared more toxic to D. magna than glyphosate alone. The 48h EC50 for glyphosate and glyphosate-Cu(II) determined from swimming distance were 75.2μM and 8.4μM, respectively. In comparison, traditional visual observation of mobility resulted in 48h EC50 values of 52.8μM and 25.5μM for glyphosate and glyphosate-Cu(II), respectively. The behavioral responses indicated that exposure of D. magna to mixtures of glyphosate and Cu(II) attenuated acute metal toxicity but increased apparent glyphosate toxicity due to complexation with Cu(II). The study suggests that glyphosate is a likely mediator of aquatic metal toxicity, and that video tracking provides an opportunity for quantitative studies of sublethal effects of pesticide complexes.

Toxicity of three strobilurins (kresoxim-methyl, pyraclostrobin, and trifloxystrobin) on Daphnia magna.

Strobilurins constitute a new class of fungicides that is the most widely used in the world. The present study was conducted to investigate the aquatic toxicity of 3 common strobilurin fungicides (kresoxim-methyl, pyraclostrobin, and trifloxystrobin) to Daphnia magna. The neonate acute immobilization test showed that the 48-h 50% effective concentration (EC50) values of kresoxim-methyl, pyraclostrobin, and trifloxystrobin were 443.3 µg/L, 20.9 µg/L, and 23.0 µg/L, respectively. In addition, the 3 strobilurins significantly induced activity of the important detoxification enzyme glutathione S-transferase (GST) in D. magna, and there was a significant positive relationship between GST activity and immobility of D. magna after acute exposure. The 3 strobilurins showed higher toxicity to D. magna embryos, and the 48-h EC50 were 157.3 µg/L, 3.9 µg/L, and 1.7 µg/L for kresoxim-methyl, pyraclostrobin, and trifloxystrobin, respectively. The 21-d chronic test revealed that the strobilurins could also significantly affect the reproduction, development, and growth of D. magna at sublethal concentrations. The lowest-observed-effect concentrations of kresoxim-methyl, pyraclostrobin, and trifloxystrobin for reproduction were 20 µg/L, 0.15 µg/L, and 0.2 µg/L, respectively, which were close to environmental concentrations. The findings indicate that strobilurin fungicides are very toxic to D. magna and they are sufficient to cause harm to D. magna at environmentally relevant concentrations. Environ Toxicol Chem 2017;36:182-189. © 2016 SETAC.

Can⿿t take the heat: Temperature-enhanced toxicity in the mayfly Isonychia bicolor exposed to the neonicotinoid insecticide imidacloprid

Neonicotinoid insecticide usage has increased globally in recent decades. Neonicotinoids, such as imidacloprid, are potent insect neurotoxicants that may pose a threat to non-target aquatic organisms, such as aquatic insects. In nature, insects typically live in thermally fluctuating conditions, which may significantly alter both contaminant exposures and affects. Here we investigate the relationship between temperature and time-to-effect for imidacloprid toxicity with the aquatic insect Isonychia bicolor, a lotic mayfly. Additionally, we examined the mechanisms driving temperature-enhanced toxicity including metabolic rate, imidacloprid uptake rate, and tissue bioconcentration. Experiments included acute toxicity tests utilizing sublethal endpoints and mortality, as well as respirometry and radiotracer assays with [14C] imidacloprid. Further, we conducted additional uptake experiments with a suite of aquatic invertebrates (including I. bicolor, Neocloeon triangulifer, Macaffertium modestum, Pteronarcys proteus, Acroneuria carolinensis, and Pleuroceridae sp) to confirm and contextualize our findings from initial experiments. The 96h EC50 (immobility) for I. bicolor at 15°C was 5.81μg/L which was approximately 3.2 fold lower than concentrations associated with 50% mortality. Assays examining the impact of temperature were conducted at 15, 18, 21, and 24°C and demonstrated that time-to-effect for sublethal impairment and immobility was significantly decreased with increasing temperature. Uptake experiments with [14C] imidacloprid revealed that initial uptake rates were significantly increased with increasing temperature for I. bicolor, as were oxygen consumption rates. Further, in the separate experiment with multiple species across temperatures 15, 20, and 25°C, we found that all the aquatic insects tested had significantly increased imidacloprid uptake with increasing temperatures, with N. triangulifer accumulating the most imidacloprid on a mass-specific basis. Our acute toxicity results highlight the importance of evaluating sublethal endpoints, as profound impairments of motor function were evident far before mortality. Further, we demonstrate that temperature is a powerful modulator of sublethal toxicity within a range of environmentally relevant temperatures, impacting both uptake rates and metabolic rates of I. bicolor. Finally, we show that temperature alters imidacloprid uptake across a range of species, highlighting the physiological variation present within aquatic invertebrate communities and the challenge associated with relying solely on surrogate species. Taken together, this research points to the need to consider the role of temperature in toxicity assessments.

Effects of Calcium and Magnesium Ions on Acute Copper Toxicity to Glochidia and Early Juveniles of the Chinese Pond Mussel Anodonta woodiana.

We evaluated the effects of calcium (Ca(2+)) and magnesium (Mg(2+)) ions on copper (Cu) toxicity to glochidia and newly-transformed juvenile mussels (age 1-2days) of the Chinese pond mussel (Anodonta woodiana). Acute Cu toxicity tests were performed with glochidia for 24h and juveniles for 96h with measured Ca(2+) concentrations of 1.1, 14, 26, 51, and 99mgL(-1), or measured Mg(2+) concentrations of 2.6, 11, 21, and 39mgL(-1). The Ca(2+) and Mg(2+) cations provided no statistically significant protection against Cu toxicity to glochidia or juveniles. The 24-h EC50 value for glochidia was 82μgL(-1) Cu, and contrastly, 96-h EC50 value for newly-transformed juvenile mussels was as low as 12μgL(-1) Cu, implying that the juveniles of A. woodiana are more vulnerable to Cu contamination at concentrations close to currently-accepted levels.

Response of Microcystis aeruginosa Growth to Arsenate Under Different Phosphorus Regimes

To better understand and then to predict the ecological risk of arsenic influenced by phosphorus regimes in freshwater environment, the growth differences of Microcystis aeruginosa (M. aeruginosa) as well as its responses to the toxic stress of arsenate [As(Ⅴ)]were investigated under orthophosphate (DIP) and dissolved organic phosphorous (DOP) [adenosine triphosphate (ATP-P) and β-sodium glycerophosphate (β-P)] culture conditions. The results showed that M. aeruginosa grew and proliferated without any differences under DOP and DIP conditions during the first 5 days, while slower growth rates were observed in DOP conditions. Herein, the cell optical density (D) of M. aeruginosa in β-P and ATP-P conditions was 78.0% and 75.4% of that under DIP condition respectively on the 7th day. The negative correlations between actual quantum yield (Yield) and Chlorophyll a (Chl-a) and D indicated that Yield should not be used as a stable index to reflect the nutrition conditions of algae. However, Yield was a sensitive index to exactly represent the responses of M. aeruginosa to As(Ⅴ) toxicity, which showed significant differences under different phosphorus regimes. Obtained by D, Yield and Chl-a, the 96h EC50 was in the order of DIP > β-P > ATP-P. The similar toxic tolerant abilities to As(Ⅴ) of M. aeruginosa under β-P and ATP-P conditions were lower than that of EC50 under DIP conditions by one to five orders of magnitude.

Multilaboratory evaluation of 15 bioassays for (eco)toxicity screening and hazard ranking of engineered nanomaterials: FP7 project NANOVALID

Within EU FP7 project NANOVALID, the (eco)toxicity of 7 well-characterized engineered nanomaterials (NMs) was evaluated by 15 bioassays in 4 laboratories. The highest tested nominal concentration of NMs was 100 mg/l. The panel of the bioassays yielded the following toxicity order: Ag > ZnO > CuO > TiO2 > MWCNTs > SiO2 > Au. Ag, ZnO and CuO proved very toxic in the majority of assays, assumingly due to dissolution. The latter was supported by the parallel analysis of the toxicity of respective soluble metal salts. The most sensitive tests/species were Daphnia magna (towards Ag NMs, 24-h EC50 = 0.003 mg Ag/l), algae Raphidocelis subcapitata (ZnO and CuO, 72-h EC50 = 0.14 mg Zn/l and 0.7 mg Cu/l, respectively) and murine fibroblasts BALB/3T3 (CuO, 48-h EC50 = 0.7 mg Cu/l). MWCNTs showed toxicity only towards rat alveolar macrophages (EC50 = 15.3 mg/l) assumingly due to high aspect ratio and TiO2 towards R. subcapitata (EC50 = 6.8 mg Ti/l) due to agglomeration of TiO2 and entrapment of algal cells. Finally, we constructed a decision tree to select the bioassays for hazard ranking of NMs. For NM testing, we recommend a multitrophic suite of 4 in vitro (eco)toxicity assays: 48-h D. magna immobilization (OECD202), 72-h R. subcapitata growth inhibition (OECD201), 30-min Vibrio fischeri bioluminescence inhibition (ISO2010) and 48-h murine fibroblast BALB/3T3 neutral red uptake in vitro (OECD129) representing crustaceans, algae, bacteria and mammalian cells, respectively. Notably, our results showed that these assays, standardized for toxicity evaluation of “regular” chemicals, proved efficient also for shortlisting of hazardous NMs. Additional assays are recommended for immunotoxicity evaluation of high aspect ratio NMs (such as MWCNTs).

Influence of light, nutrients, and temperature on the toxicity of atrazine to the algal species Raphidocelis subcapitata: Implications for the risk assessment of herbicides

The acute toxicity of herbicides to algae is commonly assessed under conditions (e.g., light intensity, water temperature, concentration of nutrients, pH) prescribed by standard test protocols. However, the observed toxicity may vary with changes in one or more of these parameters. This study examined variation in toxicity of the herbicide atrazine to a representative green algal species Raphidocelis subcapitata (formerly Pseudokirchneriella subcapitata) with changes in light intensity, water temperature, concentrations of nutrients or combinations of these three parameters. Conditions were chosen that could be representative of the intensive corn growing Midwestern region of the United States of America where atrazine is used extensively. Varying light intensity (4–58µmol/m2s) resulted in no observable trend in 96-h EC50 values for growth rate. EC50 values for PSII yield generally increased with decreasing light intensity but not significantly in all cases. The 96-h EC50 values for growth rate decreased with decreases in temperature (20–5°C) from standard conditions (25°C), but EC50 values for PSII yield at lower temperatures were not significantly different from standard conditions. Finally, there was no clear trend in 96-h EC50 values for both endpoints with increases in nitrogen (4.1–20mg/L) and phosphorus (0.24–1.2mg/L). The 96-h EC50 values for both endpoints under combinations of conditions mimicking aquatic systems in the Midwestern U.S. were not significantly different from EC50 values generated under standard test conditions. This combination of decreased light intensity and temperature and increased nutrients relative to standard conditions does not appear to significantly affect the observed toxicity of atrazine to R. subcapitata. For atrazine specifically, and for perhaps other herbicides, this means current laboratory protocols are useful for extrapolating to effects on algae under realistic environmental conditions.

Management of Target Algae by Using Copper-Based Algaecides: Effects of Algal Cell Density and Sensitivity to Copper

Public concerns regarding the use of copper-based algaecide for controlling problematic algae may arise due to the risks it creates to non-target algae. To examine this concern, a series of comparative algal toxicity experiments were conducted to study effects of prokaryotic and eukaryotic algal cell densities on their responses to exposures of copper sulfate and copper-ethanolamine (Cu-EA). Microcystis aeruginosa and Pseudokirchneriella subcapitata were cultured separately in BG 11 medium to three initial cell densities (5 × 104, 5 × 105, and 5 × 106 cells/mL). The 96-h EC50 values of copper sulfate for M. aeruginosa at the three cell densities were 9, 63, and 112 μg Cu/L, respectively; and were 192, 1873, and 4619 μg Cu/L for P. subcapitata. The 96-h EC50 values of Cu-EA were 101 and 2579 μg Cu/L for M. aeruginosa and P. subcapitata at 106 cells/mL. The margin of safety (MOS) for P. subcapitata at 104 cells/mL was 1.3, 0.9, and 0.8 when M. aeruginosa cell density was 104, 105, and 106 cells/mL. This laboratory study suggests that applying copper-based algaecides to control problematic algae at a relatively low cell density would inhibit their growth with minimum impacts on non-target algae; risks to non-target algae would increase with increases of problematic algal cell density.

Acute toxicity and histopathological effects of naproxen in zebrafish (Danio rerio) early life stages.

Zebrafish (Danio rerio) embryos and larvae were selected to investigate the potential risk and aquatic toxicity of a widely used pharmaceutical, naproxen. The acute toxicity of naproxen to embryos and larvae was measured, respectively. The histopathology was investigated in the liver of zebrafish larvae after 8-day embryo-larvae exposure to naproxen. The values of 96-h LC50 were 115.2mg/L for embryos and 147.6mg/L for larvae, indicating that zebrafish embryos were more sensitive than larvae to naproxen exposure. Large suites of symptoms were induced in zebrafish (D. rerio) early life stages by different dosages of naproxen, including hatching inhibition, lower heart rate, and morphological abnormalities. The most sensitive sub-lethal effect caused by naproxen was pericardial edema, the 72-h EC50 values of which for embryos and larvae were 98.3 and 149.0mg/L, respectively. In addition, naproxen-treated zebrafish larvae exhibited histopathological liver damage, including swollen hepatocytes, vacuolar degeneration, and nuclei pycnosis. The results indicated that naproxen is a potential threat to aquatic organisms.

Comparative toxicity of sodium carbonate peroxyhydrate to freshwater organisms

Sodium carbonate peroxyhydrate (SCP) is a granular algaecide containing H2O2 as an active ingredient to control growth of noxious algae. Measurements of sensitivities of target and non-target species to hydrogen peroxide are necessary for water resource managers to make informed decisions and minimize risks for non-target species when treating noxious algae. The objective of this study was to measure and compare responses among a target noxious alga (cyanobacterium Microcystis aeruginosa) and non-target organisms including a eukaryotic alga (chlorophyte Pseudokirchneriella subcapitata), microcrustacean (Ceriodaphnia dubia), benthic amphipod (Hyalella azteca), and fathead minnow (Pimephales promelas) to exposures of hydrogen peroxide as SCP. Hydrogen peroxide exposures were confirmed using the I3− method. SCP margins of safety for these organisms were compared with published toxicity data to provide context for other commonly used algaecides and herbicides (e.g. copper formulations, endothall, and diquat dibromide). Algal responses (cell density and chlorophyll a concentrations) and animal mortality were measured after 96h aqueous exposures to SCP in laboratory-formulated water to estimate EC50 and LC50 values, as well as potency slopes. Despite a shorter test duration, M. aeruginosa was more sensitive to hydrogen peroxide as SCP (96h EC50:0.9–1.0mgL−1 H2O2) than the eukaryotic alga P. subcapitata (7-d EC50:5.2–9.2mgL−1 H2O2), indicating potential for selective control of prokaryotic algae. For the three non-target animals evaluated, measured 96-h LC50 values ranged from 1.0 to 19.7mgL−1 H2O2. C. dubia was the most sensitive species, and the least sensitive species was P. promelas, which is not likely to be affected by concentrations of hydrogen peroxide as SCP that would be used to control noxious algae (e.g. M. aeruginosa). Based on information from peer-reviewed literature, other algaecides could be similarly selective for cyanobacteria. Of the algaecides compared, SCP can selectively mitigate risks associated with noxious cyanobacterial growths (e.g. M. aeruginosa), with an enhanced margin of safety for non-target species (e.g. P. promelas).

The unicellular fungal tool RhoTox for risk assessments in groundwater systems

The recent inclusion of yeasts in environmental monitoring recognizes their ecological significance and sensitivity to toxicants. Here we present a robust and simple two-step toxicity assay and demonstrate the sensitivity of an ubiquitous groundwater yeast, Rhodotorula minuta, to a range of metals and metalloids. The test species was sensitive to copper with a 24h EC50 of 35µg Cu/L, followed in order of decreasing sensitivity by zinc, chromium (VI) and arsenic (EC50 4.40mg As (III)/L). The strain demonstrated an unexpected tolerance to chromium (VI), having an EC50 value (3.45mg Cr (VI)/L) similar to that of arsenic. The inclusion of a unicellular, microbial test-species into the suite of existing multicellular test species for toxicity evaluation is a key step towards strengthening the assessment of risk for groundwater ecosystems.

Predicting changes in aquatic toxicity of chemicals resulting from solvent or dispersant use as vehicle

The influence of two vehicles (N,N-dimethylformamide [DMF] as solvent and polyoxyethylene hydrogenated castor oil [HCO-40] as a dispersant) on the acute toxicity of eight hydrophobic chemicals with a non-specific mode of action to Daphnia magna was investigated according to the OECD Guidelines for the Testing of Chemicals, No. 202. An increased 48-h EC50 value for D. magna or reduced toxicity resulting from the addition of HCO-40 to the test medium was observed for five of the eight chemicals examined.Each of eight chemicals was dissolved in water at a concentration of either 10 mg/L or 1.0 mg/L, with or without DMF or HCO-40. Silicone film as a model of a biological membrane was then immersed in each solution, and the concentration of each chemical in the water was monitored until equilibrium was reached for each test substance, after which the adsorbed amount of each chemical was determined. The amounts of p-pentylphenol and four other substances with log Pow (1-octanol/water partition coefficient) values greater than 3.4 adsorbed onto the silicone film decreased with increasing concentrations of HCO-40. However, 3-chloro-4-fluoronitrobenzene and two other substances with log Pow values less than 2.6 demonstrated no changes in adsorption with either increasing HCO-40 concentration or the addition of DMF.The reduced adsorption in the presence of a vehicle on the silicone film correlated closely with changes in toxicity. These results indicate that the methodology developed in this study enables the prediction of changes in toxicity resulting from the addition of vehicles to a test system.

Influence of pH and media composition on suspension stability of silver, zinc oxide, and titanium dioxide nanoparticles and immobilization of Daphnia magna under guideline testing conditions

In aquatic toxicity testing of engineered nanoparticles (ENPs) the process of agglomeration is very important as it may alter bioavailability and toxicity. In the present study, we aimed to identify test conditions that are favorable for maintaining stable ENP suspensions. We evaluated the influence of key environmental parameters: pH (2–12) and ionic strength using M7, Soft EPA (S EPA) medium, and Very Soft EPA (VS EPA) medium; and observed the influence of these parameters on zeta potential, zeta average, and acute immobilization of Daphnia magna for three different ENPs. Despite being sterically stabilized, test suspensions of silver (Ag) ENPs formed large agglomerates in both VS EPA and M7 media; and toxicity was found to be higher in VS EPA medium due to increased dissolution. Low-agglomerate suspensions for zinc oxide (ZnO) could be obtained at pH 7 in VS EPA medium, but the increase in dissolution caused higher toxicity than in M7 medium. Titanium dioxide (TiO2) ENPs had a point of zero charge in the range of pH 7–8. At pH 7 in VS EPA, agglomerates with smaller hydrodynamic diameters (~200nm) were present compared to the high ionic strength M7 medium where hydrodynamic diameters reached micrometer range. The stable suspensions of TiO2 ENPs caused immobilization of D. magna, 48-h EC50 value of 13.7mgL−1 (95% CI, 2.4mg–79.1mgL−1); whereas no toxicity was seen in the unstable, highly agglomerated M7 medium suspensions, 48-h EC50 >100mgL−1. The current study provides a preliminary approach for methodology in testing and assessing stability and toxicity of ENPs in aquatic toxicity tests of regulatory relevance.

The oxidative stress response of myclobutanil and cyproconazole on Tetrahymena thermophila

Using Tetrahymena thermophila as experimental models, the oxidative stress of triazole fungicides myclobutanil (MYC) and cyproconazole (CYP) was investigated. Results showed that 24-h EC50 values for MYC and CYP were 16.67 (13.37-19.65) and 20.44 (18.85-21.96) mg/L, respectively; 48-h EC50 values for MYC and CYP were 14.31 (13.13-15.42) and 18.76 (17.09-20.31) mg/L, respectively. Reactive oxygen species was significantly induced and cytotoxicity was caused by MYC and CYP by increasing propidium iodide (PI) fluorescence. Damage of regular wrinkles and appearing of small holes on the cell surface were observed by SEM. Furthermore, MYC and CYP also caused notable changes in enzyme activities and mRNA levels. Overall, the present study points out that MYC and CYP lead to oxidative stress on T. thermophila. The information presented in this study will provide insights into the mechanism of triazoles-induced oxidative stress on T. thermophila.

Acute and chronic toxicity of neonicotinoids to nymphs of a mayfly species and some notes on seasonal differences.

Mayfly nymphs are among the most sensitive taxa to neonicotinoids. The present study presents the acute and chronic toxicity of 3 neonicotinoids (imidacloprid, thiacloprid, and thiamethoxam) to a mayfly species (Cloeon dipterum) and some notes on the seasonality of the toxicity of imidacloprid to C. dipterum and 5 other invertebrate species. Imidacloprid and thiamethoxam showed equal acute and chronic toxicity to a winter generation of C. dipterum, whereas thiacloprid was approximately twice as toxic. The acute and chronic toxicity of imidacloprid was much higher for the C. dipterum summer generation than for the winter one. The acute toxicity differs by a factor of 20 for the 96-h 50% effective concentration (EC50) and by a factor of 5.4 for the chronic 28-d EC50. Temperature had only a slight effect on the sensitivity of C. dipterum to imidacloprid because we only found a factor of 1.7 difference in the 96-h EC50 between tests performed at 10 °C and 18 °C. The difference in sensitivity between summer and overwintering generations was also found for 3 other insect species. The results indicate that if the use and environmental fate of the 3 neonicotinoids are comparable, replacing imidacloprid by another neonicotinoid might not reduce the environmental impact on the mayfly nymph C. dipterum. The results also show the importance of reporting which generation is tested because sensitivity values of insects in the summer might be underestimated by the experiments performed with neonicotinoids and an overwintering population.

Acute Toxicity of Water-Accommodated Fraction and Chemically Enhanced WAF of Bunker C Oil and Dispersant to a Microalga Tetraselmis tetrathele.

This study assessed the toxicity of water-accommodated fraction (WAF) and chemically enhanced WAF (CEWAF) of bunker C oil and dispersant (DISP) to a microalga, Tetraselmis tetrathele. The 72-h median effective concentration (72-h EC50) of CEWAF and DISP were determined at 3.30% and 2.40%, respectively. The no observed effect concentration (NOEC) of CEWAF to T. tetrathele was at 2.0% and lowest observed effect concentration (LOEC) was at 3.0% while NOEC and LOEC of DISP to T. tetrathele were determined at 1.0% and 2.0%, respectively. The addition of dispersant to oil increased the amount of total PAH present in the CEWAF test solutions. DISP alone was highly toxic, and the toxicity of CEWAF was primarily caused by the presence of dispersant.

Toxic effects of magnesium oxide nanoparticles on early developmental and larval stages of zebrafish (Danio rerio)

Magnesium oxide nanoparticles (MgONPs) are used in medicine, manufacturing and food industries. Because of their extensive application in our daily lives, environmental exposure to these nanoparticles is inevitable. The present study examined the effects of MgONPs on zebrafish (Danio rerio) early developmental stages. The results showed that, at different concentrations, MgONPs induced cellular apoptosis and intracellular reactive oxygen species. The hatching rate and survival of embryos decreased in a dose dependent manner. The 96-h LC50 value of MgONPs on zebrafish survival was 428mg/l and the 48-h EC50 value of MgONPs on zebrafish embryo hatching rate was 175mg/l. Moreover different types of malformation were observed in exposed embryos. The results demonstrate the toxic effects of MgONPs on zebrafish embryos and emphasize the need for further studies.

Effects of triclosan and triclocarban on the growth inhibition, cell viability, genotoxicity and multixenobiotic resistance responses of Tetrahymena thermophila

The information about adverse effects of emerging contaminants on aquatic protozoa is very scarce. The growth inhibition effect, cell viability, genotoxicity and multixenobiotic resistance (MXR) responses of two commonly used antimicrobial agents, triclosan (TCS) and triclocarban (TCC) to protozoan Tetrahymena thermophila were investigated in this study. The results revealed that TCS and TCC can inhibit the growth of T. thermophila with 24h EC50 values of 1063 and 295μgL−1, respectively. The impairment of plasma membrane was observed after 2h exposure of TCS or TCC at the level of mg/L. Furthermore, it is noticeable that at environmentally relevant concentration (1.0μgL−1), both TCS and TCC can lead to statistically significant DNA damage in T. thermophila, while the inhibition of growth and change of cell viability cannot be observed. Our results firstly provide the evidence for genotoxic effects of TCS and TCC on the freshwater protozoan. Additionally, both TCS and TCC were found to inhibit the efflux transporter activities, with the inhibitory potencies of 39% and 40% (using verapamil as a model inhibitor), respectively. Particularly, TCC could significantly down-regulate the expression of MXR related gene Abcb15, which encodes the membrane efflux protein that acting as P-gp in T. thermophila. The results raise the awareness of potential aquatic ecological and human health risks from the exposure of TCS and TCC, as they might potentiate the toxic effects by chemosensitizing with co-existing toxicants.

The acute toxicity of thallium to freshwater organisms: Implications for risk assessment

The acute toxicity of Tl(I) to the microalga, Pseudokirchneriella subcapitata, the planktonic crustaceans, Daphnia magna and Daphnia pulex, and early-life stage of the zebrafish, Danio rerio, has been studied according to OECD protocols. Toxicological end-point concentrations for the microalga ranged from 17μgl−1 for a 72h EyC25 (yield inhibition) to 80μgl−1 for a 72h ErC50 (growth inhibition). Daphnia were less sensitive to Tl, with 48h EC50s of about 1000μgl−1 and 1200μgl−1 for D. magna and D. pulex, respectively; however, end-point concentrations were reduced considerably (to about 510μgl−1 and 730μgl−1, respectively) when experiments were repeated in dechlorinated Plymouth tap water (rather than OECD medium). The 96h LC50 for D. rerio was 870μgl−1 but a variety of sub-lethal effects, including enlargement of yolk sac and reduction in heart beat rate, were observed when larvae were exposed to lower concentrations. Based on these results, a predicted no effect concentration (PNEC) for Tl in freshwaters of 0.087μgl−1 is proposed. The PNEC is an order of magnitude lower than the only (Canadian) water quality guideline for Tl that appears to exist, and is lower than Tl concentrations reported in freshwaters impacted by historical or contemporary metal mining. Our results are also consistent with previous studies that employ different organisms and end-points in that Tl toxicity is dependent on the concentration of K+, the biogeochemical analogue of Tl+. Accordingly, regulation of Tl in the freshwater environment should factor in the relative abundance of K.