48-h EC50 Research Articles

Characterisation of artisanal mine waste on Buru Island, Indonesia and toxicity to the brittle star Amphipholis squamata

Artisanal small-scale gold mining (ASGM) using mercury (Hg) amalgamation commenced on Buru Island, Indonesia, in 2012, but was halted in 2015 due to concerns of widespread Hg contamination. Much of the Hg used in the mining process is lost to trommel waste which is disposed of in settlement ponds that drain into adjacent waterways and into Kayeli Bay. Several thousand unmanaged trommel sites and associated tailing ponds exist on Buru Island. This study shows that waste from the Marloso trommel at the Gogrea site contained 203 mg/kg total Hg (THg), with a negligible proportion present as bioavailable methyl Hg (MeHg) and a low total organic carbon content. There are currently very few tools available for ecotoxicological risk assessment of mine tailings for tropical marine ecosystems, and we support the development of Tailings Toxicity Tests (TTTs) and describe laboratory toxicity test methods using the cosmopolitan benthic echinoderm Amphipholis squamata. Undiluted trommel waste caused 100% mortality of A. squamata within 48 h, and a 96-h LC50 of 6.7% w/w trommel waste (4 mg/kg THg) was estimated. Sub-lethal effects on the water vascular system of the brittle star were assessed by quantification of the Ability to Right Itself (ARI), and a 48-h EC50 of 7.3% w/w trommel waste (14.4 mg/kg THg) was estimated. The results show that trommel waste produced on Buru Island is highly contaminated with THg and is acutely toxic, raising serious concern for receiving ecosystems where Hg methylation to more toxic and bioavailable forms is likely.

The oxidative stress response of oxytetracycline in the ciliate Pseudocohnilembus persalinus

Oxytetracycline (OTC) is commonly employed in fish farms to prevent bacterial infections in China, and because of their widely and intensive use, the potential harmful effects on organisms in aquatic environment are of great concern. Ciliates play an important role in aquatic food webs as secondary producers, and Pseudocohnilembus persalinus, is one kind of them which are easily found in fish farms, surviving in polluted water. Therefore, using P. persalinus as experimental models, this study investigated the effects of oxytetracycline (OTC) on the growth, antioxidant system and morphological damage in pollution-resistant ciliates species. Our results showed that the 96-h EC50 values for OTC of P. persalinus was 21.38mgL−1. The increased level of SOD and GSH during 96h OTC stress was related to an adaptive response under oxidative stress induced in ciliates. Additionally, sod1, sod2 and sod3 exhibited a significant increased expression level compared to control group at 24h treatment, indicating a promoting of dense system in ciliates at this exposure time. However, only sod1 and sod2 showed raised expression level at 48h stress, showing the different sensitive of gene isoforms to some extent. With OTC treatment, damage of regular wrinkles, shrunk, twisted on the cell surface, even forming cyst of scuticociliatid ciliate cells were firstly observed by SEM (scanning electron microscope) in this study. Overall, physiological, molecular and morphological information on the toxicological studies of ciliates and more information on possibility of ciliates as indicators of contamination were provided in this study.

Cell density dependence of Microcystis aeruginosa responses to copper algaecide concentrations: Implications for microcystin-LR release

Along with mechanistic models, predictions of exposure-response relationships for copper are often derived from laboratory toxicity experiments with standardized experimental exposures and conditions. For predictions of copper toxicity to algae, cell density is a critical factor often overlooked. For pulse exposures of copper-based algaecides in aquatic systems, cell density can significantly influence copper sorbed by the algal population, and consequent responses. A cyanobacterium, Microcystis aeruginosa, was exposed to a copper-based algaecide over a range of cell densities to model the density-dependence of exposures, and effects on microcystin-LR (MC-LR) release. Copper exposure concentrations were arrayed to result in a gradient of MC-LR release, and masses of copper sorbed to algal populations were measured following exposures. While copper exposure concentrations eliciting comparable MC-LR release ranged an order of magnitude (24-h EC50s 0.03–0.3mg Cu/L) among cell densities of 106 through 107 cells/mL, copper doses (mg Cu/mg algae) were similar (24-h EC50s 0.005–0.006mg Cu/mg algae). Comparisons of MC-LR release as a function of copper exposure concentrations and doses provided a metric of the density dependence of algal responses in the context of copper-based algaecide applications. Combined with estimates of other site-specific factors (e.g. water characteristics) and fate processes (e.g. dilution and dispersion, sorption to organic matter and sediments), measuring exposure-response relationships for specific cell densities can refine predictions for in situ exposures and algal responses. These measurements can in turn decrease the likelihood of amending unnecessary copper concentrations to aquatic systems, and minimize risks for non-target aquatic organisms.

Cytotoxicity and CYP1A inhibition in rainbow trout liver (RTL-W1) cell lines exposed to dispersant Corexit 9500 and its major surfactant components

As part of a large study examining the toxicity of the Corexit® family of oil spill dispersants on aquatic vertebrates, we examined effects on the liver in an in vitro study using the rainbow trout liver cell line (RTL-W1). We exposed RTL-W1 cells to the dispersant Corexit 9500 and its major surfactant components and measured their cytotoxic effects as well as modulation of activity of CYP1A, one of the major enzymes responsible for organic contaminant metabolism. The anionic surfactant DOSS was found to be the most cytotoxic with a 24h EC50 of 10mg/L, as compared to 45 to 91mg/L for the non-ionic surfactants, Tween 80 and 85 and Span 80. The EC50 for Corexit was intermediate between these compounds at 29mg/L. Corexit 9500 and the non-ionic surfactants Tween 80 and 85, but not DOSS or Span 80 knocked down CYP1A activity induced by benzo[a]pyrene, a model agonist, demonstrating the potential of these compounds to compromise the ability of exposed organisms to metabolize petroleum hydrocarbons or other CYP1A substrates.

Interaction patterns and toxicities of binary and ternary pesticide mixtures to Daphnia magna estimated by an accelerated failure time model

Organisms in natural environments are often exposed to a broad variety of chemicals, and the multi-chemical mixtures exposure may produce significant toxic effects, even though the individual chemicals are present at concentrations below their no-observed-effect concentrations. This study represents the first attempt that uses the accelerated failure time (AFT) model to quantify the interaction and toxicity of multi-chemical mixtures in environmental toxicology. We firstly conducted the acute immobilization tests with Daphnia magna exposed to mixtures of diazinon (DZN), fenitrothion (MEP); and thiobencarb (TB) in single, binary, and ternary formulations, and then fitted the results to the AFT model. The 48-h EC50 (concentration required to immobilize 50% of the daphnids at 48h) values for each pesticide obtained from the AFT model are within a factor of 2 of the corresponding values calculated from the single pesticide exposure tests, indicating the methodology is able to provide credible toxicity values. The AFT model revealed either significant synergistic (DZN and MEP; DZN and TB) or antagonistic (MEP and TB) interactions in binary mixtures, while the interaction pattern of ternary mixture depended on both the concentration levels and concentration ratios of pesticides. With a factor of 2, the AFT model accurately estimated the toxicities for 78% of binary mixture formulations that exhibited significant synergistic effects, and the toxicities for all the ternary formulations. Our results showed that the AFT model can provide a simple and efficient way to quantify the interactions between pesticides and to assess the toxicity of their mixtures. This ability may greatly facilitate the ecotoxicological risk assessment of exposure to multi-chemical mixtures.

Acute toxicity of chlorpyrifos and carbosulfan to glochidia of the freshwater mussel Hyriopsis bialata Simpson, 1900.

The acute toxicity of carbosulfan and chlorpyrifos in formulated pesticides to glochidia (larvae) of the freshwater mussel (Hyriopsis bialata Simpson, 1900) was evaluated under static conditions in moderately hard dechlorinated tap water. Measured pesticide concentrations were 26 to 34% lower than nominal concentrations; therefore, all results are expressed in terms of measured active ingredient. Carbosulfan was relatively non-toxic to the mussel larvae with median effective concentrations (EC50) of carbosulfan at 24 and 48h greater than 0.10mg/L. The EC50s of chlorpyrifos at 24 and 48h were 0.083 and 0.078mg/L, respectively (measured concentrations). The 48-h EC50 of a combined exposure to a mixture of chlorpyrifos and carbosulfan at a constant ratio of 2.9:1 was 0.0142:0.049mg CP:CB/L. In a separate experiment, the effect of water hardness on carbosulfan, chlorpyrifos, or a combined exposure was assessed using glochidia exposed to either soft, moderately hard, or hard reconstituted water. There was no effect of water hardness on the survival of glochidia after 24- or 48-h exposure to carbosulfan. The chlorpyrifos 48-h EC50s in soft water, moderately hard water, and hard water were 0.18, 0.11, and 0.16mg/L, respectively. The data indicate that the lowest water hardness resulted in the highest survival of glochidia, whereas an increase to moderate water hardness resulted in significantly decreased survival of glochidia (F=15.5, P<0.05). The EC50s of a combined exposure at 48h in soft water, moderately hard water, and hard water were 0.124:0.044, 0.132:0.047, and 0.064:0.022mg CP:CB/L, respectively. The data indicate that the combined toxicity was lowest at low and moderate water hardness, whereas an increase to high water hardness resulted in a significantly decreased survival of glochidia. After 48h, the toxicity of the combined chlorpyrifos and carbosulfan exposure in soft and hard water was greater than that of chlorpyrifos alone.

Assessing the toxicity and risk of salt-impacted winter road runoff to the early life stages of freshwater mussels in the Canadian province of Ontario

In temperate urbanized areas where road salting is used for winter road maintenance, the level of chloride in surface waters has been increasing. While a number of studies have shown that the early-life stages of freshwater mussels are particularly sensitive to salt; few studies have examined the toxicity of salt-impacted winter road runoff to the early-life stages of freshwater mussels to confirm that chloride is the driver of toxicity in this mixture. This study examines the acute toxicity of field-collected winter road runoff to the glochidia of wavy-rayed lampmussels (Lampsilis fasciola) (48 h exposure) and newly released juvenile fatmucket mussels (Lampsilis siliquoidea) (<1 week old; 96 h exposure) under different water hardness. The chronic toxicity (28 d) to older juvenile L. siliquoidea (7–12 months old) was also investigated. The 48-h EC50 and 96-h LC50 for L. fasciola glochidia and L. siliquoidea juveniles exposed to different dilutions of road run-off created with moderately hard synthetic water (∼80 mg CaCO3/L) were 1177 (95% confidence interval (CI): 1011–1344 mg Cl−/L) and 2276 mg Cl−/L (95% CI: 1698–2854 mg Cl−/L), respectively. These effect concentrations correspond with the toxicity of chloride reported in other studies, indicating that chloride is likely the driver of toxicity in salt-impacted road-runoff, with other contaminants (e.g., metals, polycyclic aromatic hydrocarbons) playing a de minimis role. Toxicity data from the current study and literature and concentrations of chloride in the surface waters of Ontario were used to conduct a probabilistic risk assessment of chloride to early-life stage freshwater mussels. The assessment indicated that chronic exposure to elevated chloride levels could pose a risk to freshwater mussels; further investigation is warranted to ensure that the most sensitive organisms are protected.

Effect of substituted phenylamine antioxidants on three life stages of the freshwater mussel Lampsilis siliquoidea

Substituted phenylamines (SPAs) are incorporated into a variety of consumer products (e.g., polymers, lubricants) in order to increase the lifespan of the products by acting as a primary antioxidant. Based on their physicochemical properties, if SPAs were to enter the aquatic environment, they would likely partition into sediment. No studies to date have investigated the effect of sediment-associated SPAs on aquatic organisms. The current study examined the effect of four SPAs (diphenylamine (DPA); N-phenyl-1-napthylamine (PNA); N-(1,3-dimethylbutyl)-N’-phenyl-1,4-phenylenediamine (DPPDA); 4,4’-methylene-bis[N-sec-butylaniline] (MBA)) on three different life stages of the freshwater mussel, Lampsilis siliquoidea. The viability of larvae (glochidia) of L. siliquoidea and Lampsilis fasciola was assessed after 48 h of exposure to SPAs in water. The 48-h EC50s for glochidia viability of L. siliquoidea were 5951, 606, 439, and 258 μg/L for DPA, PNA, DPPDA, and MBA, respectively, and 7946, 591, 137, and 47 μg/L, respectively, for L. fasciola. Juvenile (7–15 months) and adult L. siliquoidea were exposed to sediment-associated SPAs for 28 d. LC50s for juvenile mussels were 18, 55, 62, and 109 μg/g dry weight (dw) of sediment for DPA, PNA, DPPDA, and MBA, respectively. Adult mussels were exposed to sub-lethal concentrations of sediment-associated SPAs in order to investigate reactive oxygen species (ROS), lipid peroxidation and total glutathione in the gill, gonad, and digestive gland tissue, and viability and DNA damage in hemocytes. No significant concentration-dependent trend in any of these biochemical and cellular endpoints relative to the concentration of sediment-associated SPAs was observed in any tissues. Investigations into the concentration of SPAs in the aquatic environment are required before a conclusion can be made on whether these compounds pose a hazard to the different life stages of freshwater mussels.

Exposure to sublethal concentrations of Co3O4 and Mn2O3 nanoparticles induced elevated metal body burden in Daphnia magna

Despite the significant progress made in ecotoxicological research on nanoparticles (NPs), there is still very limited information available regarding the biological effects of certain types of NPs such as Co3O4 and Mn2O3. Only a couple of studies provide data on their impact on aquatic organisms whereas, alarmingly, these NPs have been proposed to have high toxicity potential. In addition, more data are needed to determine whether the adverse effects the metal NPs induce on aquatic organisms are rather due to their chemical or particulate nature. To address these open questions, the (sub)lethal effects of Co and Mn NPs in parallel with the respective soluble metal salts on Daphnia magna were studied.The aims of the current study were to i) assess the acute toxicity of Co3O4 and Mn2O3 NPs (primary size 10–30nm) to D. magna, ii) evaluate whether the acute NP exposure at sublethal concentrations influences D. magna post-exposure feeding behaviour and iii) quantify D. magna metal body burden after exposure and after the post-exposure feeding to estimate the potential of trophic transfer of metals. Flow cytometry and total reflection X-ray fluorescence spectroscopy were applied for feeding and metal body burden evaluations, respectively. CuO NPs (primary size 22–25nm) that are very toxic to D. magna were included in the study as a positive control. Since the release of metal ions is an important possibility for toxicity of metal NPs, soluble Co-, Mn- and Cu-salts were analysed in parallel.The solubilisation of Co3O4 NPs in the OECD202 assay conditions was 0.1% and Mn2O3 NPs 35%. Mn2O3 NPs also produced reactive oxygen species in abiotic conditions. However Co3O4 and Mn2O3 NPs were not acutely toxic to D. magna (48h EC50>100mg metal/L) at OECD202 assay conditions. The 48h EC50 values of soluble Co- and Mn-salts were 3.2mgCo/L and 41mgMn/L, respectively. Post-exposure feeding behaviour after 48h exposure to sublethal concentrations (≤10mg/L) of Co3O4 and Mn2O3 NPs differed from that of the unexposed (control) D. magna only at the highest exposure concentrations but was comparable to the feeding behaviour of the respective metal salt-exposed organisms. Upon 48h exposure, dose-dependent increase of D. magna total metal body burden in case of both the NPs and the soluble salts was observed. After 48h post-exposure feeding with algae C. reinhardtii (depuration): D. magna body burden remained elevated (up to 760-fold compared to the control organism) only in case of the NPs. This may indicate potential for trophic transfer of NPs/heavy metals and thus hazard for freshwater ecosystem.

Triclocarban: UV photolysis, wastewater disinfection, and ecotoxicity assessment using molecular biomarkers.

Triclocarban (TCC) is an antibacterial agent found in pharmaceuticals and personal care products (PPCP). It is potentially bioaccumulative and an endocrine disruptor, being classified as a contaminant of emerging concern (CEC). In normal uses, approximately 96% of the used TCC can be washed down the drain going into the sewer system and eventually enter in the aquatic environment. UV photolysis can be used to photodegrade TCC and ecotoxicity assays could indicate the photodegradation efficiency, since the enormous structural diversity of photoproducts and their low concentrations do not always allow to identify and quantify them. In this work, the TCC was efficiently degraded by UVC direct photolysis and the ecotoxicity of the UV-treated mixtures was investigated. Bioassays indicates that Daphnia similis (48h EC50=0.044μM) was more sensitive to TCC than Pseudokirchneriella subcapitata (72h IC50=1.01μM). TCC and its photoproducts caused significant effects on Eisenia andrei biochemical responses (catalase and glutathione-S-transferase); 48h was a critical exposure time, since GST reached the highest activity values. UVC reduced the TCC toxic effect after 120min. Furthermore, TCC was photodegraded in domestic wastewater which was simultaneously disinfected for total coliform bacterial (TCB) (360min) and Escherichia coli (60min). Graphical abstract TCC degradation and ecotoxicological assessment.

Toxicological effects of phenol on four marine microalgae

The toxic effects of phenol on four marine microalgae (Dunaliella salina, Platymonas subcordiformis, Phaeodactylum tricornutum Bohlin, and Skeletonema costatum) were evaluated. The 96h EC50 values were 72.29, 92.97, 27.32, and 27.32mgL−1, respectively, which were lower than those values of freshwater microalgae reported in the literature. During a 96-h exposure to a sub-lethal concentration of phenol (1/2 96h EC50) with green alga (D. salina) and diatom (S. costatum), reactive oxygen species (ROS) accumulation, and chlorophyll a (Chl a) content decrease were simultaneously observed in diatom cells after 48h treatment. On the contrary, other chlorophylls in both algae were unaffected. Under transmission electron microscopy (TEM), the phenol-induced ultrastructure alterations included disappearance, or shrinkage, of nucleolus and enlargement of vacuoles, which may result in programmed cell death (PCD). The increase in number of lipid droplets may be related to phenol detoxification. These results indicate that the sensitivity of marine microalgae to phenol was dependent on some biotic factors such as cell size, ROS production, and phenol degradation ability in algal cells.

Multigenerational effects of two glucocorticoids (prednisolone and dexamethasone) on life-history parameters of crustacean Ceriodaphnia dubia (Cladocera)

Synthetic glucocorticoids (GCs) such as dexamethasone (DEX) and prednisolone (PDS) have been used since the 1940s to cure inflammatory and auto-immune disorders. Their use has been linked to a host of deleterious effects in aquatic ecosystems such as osteoporosis in vertebrates, developmental impairments in molluscs and reduced fecundity and growth in cladocerans. Apart from these handful of studies, the effects of GCs on aquatic biota are largely unknown. The present study is a first of its kind aiming to assess the multi-generational exposure effects of DEX and PDS on the life history parameters of Ceriodaphnia dubia (C. dubia). Multigenerational studies have proved to be an advantage in assessing the cumulative damage caused by aquatic toxicants at the population level of the exposed organisms over a period of successive generations using multiple biological endpoints. Test results demonstrated that C. dubia exhibited varied sensitivities towards both the studied chemicals however were more sensitive to DEX with 48-h EC50 (95% confidence interval) of 0.75 mg/L (CI: 0.59–0.92) in comparison to PDS [19 mg/L (CI: 15–23)]. EC10 values for F0 in a multigenerational chronic bioassays were 48 μg/L (CI: 37.4–61) for DEX and 460 μg/L (CI: 341–606) for PDS and in F3 were 2.2 μg/L (CI: 1.6–3.1) for DEX and 31 μg/L (CI: 19.4–46) for PDS. There was a positive trend of increased toxicity followed by reduced life history traits such as fecundity, brood size and time to first brood and intrinsic rate of population increase and body growth (length and area) of C. dubia in the case of both studied chemicals. The results from the current work highlighted the importance of multigenerational studies in identifying the evolutionary responses of stressed non-target aquatic organisms, and data obtained can be further used in developing water quality guidelines.

Fast algal eco-toxicity assessment: Influence of light intensity and exposure time on Chlorella vulgaris inhibition by atrazine and DCMU

In order to develop a rapid assay suitable for algal eco-toxicity assessments under conditions representative of natural ecosystems, this study evaluated the short-term (<1h) response of algae exposed to atrazine and DCMU using oxygen productivity measurements. When Chlorella vulgaris was exposed to these herbicides under ‘standard’ low light intensity (as prescribed by OECD201 guideline), the 20min-EC50 values recorded via oxygen productivity (atrazine: 1.32±0.07μM; DCMU: 0.31±0.005μM) were similar the 96-h EC50 recorded via algal growth (atrazine: 0.56μM; DCMU: 0.41μM), and within the range of values reported in the literature. 20min-EC50 values increased by factors of 3.0 and 2.1 for atrazine and DCMU, respectively, when light intensity increased from 60 to 1400μmolm−2s−1 of photosynthetically active radiation, or PAR. Further investigation showed that exposure time significantly also impacted the sensitivity of C. vulgaris under high light intensity (>840μmolm−2s−1 as PAR) as the EC50 for atrazine and DCMU decreased by up to 6.2 and 2.1 folds, respectively, after 50min of exposure at a light irradiance of 1400μmolm−2s−1 as PAR. This decrease was particularly marked at high light intensities and low algae concentrations and is explained by the herbicide disruption of the electron transfer chain triggering photo-inhibition at high light intensities. Eco-toxicity assessments aiming to understand the potential impact of toxic compounds on natural ecosystems should therefore be performed over sufficient exposure times (>20min for C. vulgaris) and under light intensities relevant to these ecosystems.

Acute toxicity and antioxidant responses in the water flea Daphnia magna to xenobiotics (cadmium, lead, mercury, bisphenol A, and 4-nonylphenol)

Heavy metals have adverse effects to aquatic organisms, and endocrine-disrupting chemicals (EDCs) alter the normal functioning of hormones in living organisms. In the present study, an acute toxicity test was performed to determine the EC50 values in the water flea Daphnia magna exposed to Cd, Pb, Hg, 4-nonylphenol (NP) and bisphenol A (BPA) for 48 h, according to the OECD test guideline 202. The mRNA expression of Cu/Zn-SOD, Mn-SOD, and catalase (CAT) was analyzed using real time RT-PCR. The results indicate that all chemicals tested showed a negative effect on the mobility of D. magna. The 48-h EC50 values were 21.0 μg/L for Cd, 694.6 μg/L for Pb, 3.8 μg/L for Hg, 18.9 μg/L for 4-NP and 8.3 mg/L for BPA. The order of toxicity based on the EC50 values was as follows: Hg>4-NP>Cd>Pb>BPA. Gene expression patterns indicated that Cd and Pb increased the mRNA levels of the genes encoding three antioxidant enzymes upon exposure for 48 h. Mn-SOD and CAT mRNAs were sensitively modulated in response to Pb. In contrast, the expression of these genes was up-regulated at 24 h and then reduced at 48 h after exposure to Hg. These findings suggest that the heavy metals (Cd, Pb, and Hg) can induce oxidative stress in D. magna and that the antioxidant enzymes were sensitive to 24h-Hg and 48h-Pb exposure. A significant increase in the mRNA expression of three antioxidant enzymes was observed after exposure to 4-NP, whereas a slight modulation of Mn-SOD and CAT mRNA levels was detected in response to BPA, indicating that these genes are involved in a cellular defense system against EDCs-mediated oxidative stress.

Bioconversion of non-steroidal anti-inflammatory drugs diclofenac and naproxen by chloroperoxidase

Non-steroidal anti-inflammatory drugs diclofenac and naproxen are widely used for the treatment of arthritis, ankylosing spondylitis, and acute muscle pain. However, most of them are usually not metabolized and simply pass through human body. These drugs are difficult to be decomposed by general waste treatment strategies and have caused serious environmental concerns. We report a rapid and efficient conversion of diclofenac and naproxen by chloroperoxidase-catalyzed H2O2-oxidation, a heme protein isolated from Caldarimyces fumago. Complete conversion of diclofenac and naproxen was achieved in only 9 and 7min respectively with 0.1mmolL−1H2O2 and nanomolar enzyme concentration at pH 3.0. The converted products were identified by HPLC–MS and NMR, suggesting involvement of multiple steps in CPO catalyzed conversion. Our work demonstrated that CPO treatment (with COD removal of 4.9%, 9.1% for diclofenac and naproxen, respectively) followed by existing bioremediation technologies (activated sludge) greatly improved the decontaminating these two drugs from waste water (COD removal was enhanced to 85% and 86%, respectively). The eco-toxicity evaluation according to the 72-h EC50 value using the green algae Chlorella Pyrenoidos as ecological indicators showed that the converted products of diclofenac and naproxen had lower toxicity than the original drugs.

Changes in aquatic toxicity of potassium dichromate as a function of water quality parameters

Potassium dichromate (K2Cr2O7) is used as a general reference toxicant in aquatic toxicity testing, but relatively little is known regarding the effects of water quality parameters on K2Cr2O7 toxicity to Daphnia magna. The acute toxicity of K2Cr2O7 to D. magna was comparatively examined in one very hard (M4 medium for D. magna assay), four hard, one moderately hard and one soft dilution water samples. The 48-h EC50 (50% effective concentration) of K2Cr2O7 to D. magna was reproducible (coefficient of variation [CV]: 13%) in tests using the same dilution water sample, but reproducibility was poor (CV: 62%) in tests using seven different dilution water samples. The observed 48-h EC50 value increased with increasing water hardness (28–250 mg CaCO3/L) and Na+ concentration (4.3–19.7 mg Na/L). The effect of Ca2+ and Mg2+ on K2Cr2O7 toxicity was equivalent in terms of molar concentration. The 48-h EC50 for K2Cr2O7 was determined according to OECD TG 202 by six contract laboratories using M4 medium and were shown to be reproducible (CV: 15%), indicating that the toxicity level can be determined with high accuracy if holding and dilution water samples are standardized. Multiple regression analysis revealed that the 48-h EC50 was strongly correlated (r2 = 0.927) with the Ca2+, Mg2+, Na+ concentration, and alkalinity of the dilution water samples. Detailed monitoring of water quality characteristics thus facilitates intra- and inter-laboratory comparisons of toxicity data and enables predictions of changes in the susceptibility of test animals.

Effects of three diamides (chlorantraniliprole, cyantraniliprole and flubendiamide) on life history, embryonic development and oxidative stress biomarkers of Daphnia magna

The diamides have become one of the most promising new classes of insecticides. In this study, we evaluated the toxicity of three diamides (chlorantraniliprole, cyantraniliprole and flubendiamide) to Daphnia magna. The acute toxicity test showed that the 48-h EC50 of chlorantraniliprole, cyantraniliprole and flubendiamide were 8.5, 23.9 and 63.5 μg/L, respectively. Biochemical measurements revealed a significant increase in reactive oxygen species (ROS) in D. magna after acute exposure to the three diamides. A significant decrease in activities of antioxidant enzymes superoxide dismutase (SOD) and glutathione peroxidase (GPx) was observed, which was consistent with the down-regulated transcription of antioxidant genes sod and gpx. Catalase (CAT) activity exhibited a significant increase while the related gene cat showed no obvious change in daphnids acutely exposed to the three diamides. The chronic test revealed that the three diamides could cause lethal and sub-lethal effects on daphnids within constricted range of concentrations at μg/L level. The 21-d EC50 of chlorantraniliprole, cyantraniliprole and flubendiamide for mobility were 5.0, 13.6 and 36.8 μg/L, respectively. The chronic LOEC of chlorantraniliprole, cyantraniliprole and flubendiamide based on survival, growth and reproduction of D. magna were 4.05, 10.24 and 19.36 μg/L, respectively. Moreover, these three diamides can induce severe developmental abnormalities in D. magna embryos including underdeveloped second antennae, curved tail spine and abnormal body region after acute exposure and the 48-h EC50 were 6.2, 14.1 and 30.8 μg/L for chlorantraniliprole, cyantraniliprole and flubendiamide respectively. Our findings indicate that even low levels of diamides can pose ecological risks to aquatic ecosystems.

Effects of Ammonia and Density on Filtering of Commensal and Pathogenic Escherichia coli by the Cladoceran Daphnia magna.

Grazing by cladocerans can reduce the survival of enteric bacteria associated with fecal pollution. This study examined the potential of Daphnia magna to filter commensal and pathogenic Escherichia coli of human origin. Grazing on commensal and pathogenic bacteria was comparable, but slightly greater at 20 compared to 15 and 25°C. Filtering activity was strongly dependent on D. magna and E. coli densities at environmentally relevant bacterial concentrations. Maximum feeding rates were >107 cells h-1daphnid-1, clearance rates were 1-6mLh-1daphnid-1, and filtering was independent of bacterial cell sizes between 0.7 and 1.8µm. Filtering and ingestion of E. coli by D. magna was susceptible to acute inhibition by unionized ammonia with a 24h EC50 of 0.18mgL-1 NH3-N, and a LOEC of 0.09mgL-1 NH3-N. The study indicated that biological and chemical constraints should be considered when applying Daphnia for attenuation of fecal pollution.

Antimicrobial filtration with electrospun poly(vinyl alcohol) nanofibers containing benzyl triethylammonium chloride: Immersion, leaching, toxicity, and filtration tests

Antimicrobial electrospun poly(vinyl alcohol) (PVA) nanofibers were synthesized by impregnating benzyl triethylammonium chloride (BTEAC) as an antimicrobial agent into PVA nanofibers. The BTEAC-PVA nanofibers were heat-methanol treated during the preparation for various tests. The BTEAC-PVA nanofibers became more hydrophilic than the PVA nanofibers due to incorporation of BTEAC. Through heat-methanol treatment, thermal property, crystallinity, and water stability of BTEAC-PVA nanofibers were improved considerably. The immersion test shows that heat-methanol treatment has an advantage over heat treatment to maintain BTEAC content in BTEAC-PVA nanofibers. The acute toxicity test demonstrates that the 24-h EC50 and 48-h EC50 values (EC50 = median effective concentration) of BTEAC to Daphnia magna were 113 and 90 mg/L, respectively. The leaching test indicates that the BTEAC concentration leached from BTEAC-PVA nanofibers was far below the concentration affecting the immobilization of D. magna. For antimicrobial filtration tests, the BTEAC-PVA nanofibers were deposited onto glass fiber filter. The antimicrobial filtration test was conducted against bacteria (Escherichia coli, Staphylococcus aureus) and bacteriophages (MS2, PhiX174), demonstrating that the BTEAC-PVA nanofibers could enhance the removal of E. coli and S. aureus considerably but not the removal of MS2 and PhiX174 under dynamic flow conditions.

Intoxication and biochemical responses of freshwater snail Bellamya aeruginosa to ethylbenzene.

No acute toxic data of ethylbenzene on gastropod is available in literature. In the present study, the acute toxicity of ethylbenzene was assessed on a freshwater snail Bellamya aeruginosa, which was exposed to ethylbenzene concentration from 1 to 100mg/L for 96h. No mortality occurred, but a manifestation of intoxication (distress syndrome) was observed in part of exposed snails, and meanwhile, another part was moved normally. The distress syndrome showed clear dose- and time-dependent effects, and the 96-h EC50 value for distress syndrome was 13.3mg/L in snail. The biochemical responses induced by ethylbenzene to the snail, including acetylcholinesterase (AChE) in the whole body and superoxide dismutase (SOD), catalase (CAT), glutathione S-transferases (GST), and reduced glutathione (GSH) in the hepatopancreas, were evaluated both for distressed snail and moved snail. The AChE activity of distressed snail was all inhibited more than 45%, and the inhibition of AChE activity in the moved snail was all less than 30% and more than 20%, demonstrating that ethylbenzene exerted nervous toxicity to both distressed snail and moved snail. Meanwhile, the difference for AChE activity between the two different response snails was significant. Among the antioxidant biomarkers (SOD, CAT, GST, and GSH), only GST displayed significant difference between the distressed snail and moved snail. However, the activities of enzymes (SOD, CAT, and GST) in the moved snail were greater than those in the distressed snail, no matter significantly or insignificantly, which indicated that the ability of antioxidant defense in the distressed snail was weaker than that in the moved snail. The findings here reported manifest that ethylbenzene exerted nervous toxicity to snail, and the snail with intoxication response (distress syndrome) presented larger inhibition on AChE activity and weaker antioxidant ability in comparison with the moved snail.