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Toxicokinetic–toxicodynamic (TKTD) modeling has received increasing attention in terms of the regulatory environmental risk assessment of chemicals. This type of mechanistic model can integrate all available data from individual‐level bioassays into a single framework and enable refined risk assessments by extrapolating from laboratory results to time‐variable exposure scenarios, based, for instance, on surface water exposure modeling (e.g., FOCUS). Dynamic energy budget (DEB) models coupled with TKTD modules (DEB–TKTD) constitute the leading approach to assess and predict sublethal effects of chemicals on individual organisms. However, thorough case studies are rare. We provide a state‐of‐the‐art example with the standard aquatic test species Ceriodaphnia dubia and the fungicide azoxystrobin, including all steps, from bespoke laboratory toxicity tests to model calibration and validation, through to environmental risk assessment. Following the framework proposed in the European Food Safety Authority Scientific Opinion from 2018, we designed bespoke good laboratory practice–compliant laboratory toxicity studies based on test guideline 211 of the Organisation for Economic Co‐operation and Development and then identified robust parameter values from those data for all relevant model parameters through model calibration. The DEB–TKTD model, DEBtox2019, then informed the design of the validation experiment. Once validated, the model was used to perform predictions for a time‐variable exposure scenario generated by FOCUS. A moving time‐window approach was used to perform the environmental risk assessment. This assessment method reduces uncertainty in the risk assessment while maintaining consistency with the traditional measures of risk. Environ Toxicol Chem 2024;43:2409–2421. © 2024 Syngenta Crop Protection AG. ibacon GmbH and The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC. [ABSTRACT FROM AUTHOR]

Amultigenerational study on Ceriodaphnia dubia was carried out by exposing three subsequent generations to pharmaceuticals chlorpromazine (CPZ) and diclofenac (DCF), and two lanthanide chlorides, gadolinium as GdCl3 and europium as EuCl3. As the treatments, environmentally relevant concentrations were chosen (0.001, 0.01 and 0.1 mg/L for CPZ; 0.1, 1 and 10 mg/L for DCF; 0.425, 4.25 and 42.5 µg/L for Gd and 0.41, 4.1 and 41 µg/L for Eu). Survival, population growth and reproduction success were evaluated at 21 and 30 days of exposure, and the whole observation period lasted 40 days. The least sensitive to all selected substances was the first daphnid generation (F1). Within 21-day exposure, no significant effects of the psychotropic drug CPZ on C. dubia survival were observed in generations F1–F3. The anti-inflammatory drug DCF did not affect survival in the F1 generation; however, it significantly reduced survival in the F3 generation at 1–10 mg/L. Both lanthanides did not affect survival in the F1 and F2 generations of C. dubia but considerably decreased survival in the F3 at 4–42 µg/L. Both pharmaceuticals stimulated the reproduction of C. dubia in the F1 generation, while inhibition occurred at the highest tested concentrations in generations F2 and F3. The inhibitory effect on the reproductive success of lanthanides in the F2 generation resembled that for CPZ but not for DCF. The dynamics of adverse effects during the 21–30-day period revealed that despite increased mortality in the controls (up to 30%), concentrations used in the study minified, in most instances, the survival and aggravated population growth and reproduction success of C. dubia. Our data suggest that C. dubia as a test organism can be used for 21 days in multigenerational investigations, especially when testing close to environmental concentrations. In this respect, the standard C. dubia chronic toxicity assay seems limited since prolonged observations and several generations of daphnids are required to obtain reliable information for the risk assessment of potentially aggressive chemicals.

The accessibility and popularity of additive manufacturing (AM) has increased over the past decade. Environmental hazard assessment and safety data sheets for 3D printer feedstocks has lagged technology development. Vat photopolymerization may have unique risks relative to other AM technologies due to mishandling of uncured monomers/oligomer feedstocks and its decreasing cost enabling uninformed residential use. The acute and chronic toxicity of six uncured resins to Ceriodaphnia dubia was explored. Two-day acute toxicity (LC50) ranged from 2.6 to 33 mg/L and inhibition concentrations (IC25) values for reproduction ranged from 0.33 to 16 mg/L. Cleaning and waste management procedures recommended in user guides could be the most hazardous handling scenario as use of isopropyl alcohol increases miscibility and thus the fate, transport and bioavailability of the uncured resins. Residential users may often be poorly informed about potential toxicity and the need for a plan for use, handling, and waste management of uncured resins. [ABSTRACT FROM AUTHOR]

Freshwater organisms are often exposed to contaminants such as heavy metals from stormwater discharges, which are dependent on rainfall duration and intensity. Therefore, standardized (48‐ or 96‐h) continuous exposure methods developed for whole effluent toxicity (WET) testing might not always accurately convey the effects of stormwater and runoff contaminants. The present study characterized the acute toxicity of copper (Cu), zinc (Zn), and cadmium (Cd) to freshwater amphipods (Hyalella azteca) and cadmium (Cd) to water fleas (Ceriodaphnia dubia) using a modified exposure design that integrated relevant pulsed durations and included post‐exposure monitoring. Less than 24‐h‐old C. dubia and 7 to 8‐day‐old H. azteca were exposed to water spiked with Cu, Zn, or Cd using 6‐, 12‐, 26‐, or 96‐h durations under standard laboratory conditions and monitored for cumulative mortality and reproduction (C. dubia only). Lethal effect (LC10s, LC25s, LC50s) and reproductive effect (EC25s, EC50s) were determined based on either mortality or reproduction of organisms at the end of each pulse (6, 12, or 26 h) and at the end of their respective tests (96 h). For all metals exposed to each organism, acute toxicity was found to be highest for the (96 h) continuous exposures. For pulsed exposures, mortality continued to increase following transfer to clean water for post‐exposure monitoring. These results indicate a latent effect of Cu, Zn, and Cd to H. azteca and Cd to C. dubia. The present study concluded that using the continuous (48‐ or 96‐h) WET exposure method overestimates the effects of stormwater and runoff contaminants. However, pulsed exposures without post‐exposure monitoring also underestimate the toxicity of contaminants. The proposed pulsed exposure design provides a compromise that is more realistic than current WET methods to assess impacts from episodic events and accounts for potential latent effects that may be overlooked without monitoring post‐exposure. Environ Toxicol Chem 2022;41:2488–2499. © 2022 SETAC [ABSTRACT FROM AUTHOR]

Antiviral drugs are a class of medications used for treating viral infections. Due to their widespread use, especially in cases of pandemics and limited human metabolism, antivirals have been detected in multiple environmental matrices. This study aims to evaluate the chronic effects of acyclovir, efavirenz, lamivudine and zidovudine using Ceriodaphnia dubia and Raphidocelis subcapitata. The results with R. subcapitata showed the following toxicities: zidovudine (IC50 = 5.442 mg L−1) < acyclovir (IC50 = 3.612 mg L−1) < lamivudine (IC50 = 3.013 mg L−1) < efavirenz (IC50 = 0.034 mg L−1). The results of the chronic bioassay with C. dubia demonstrated that zidovudine is the least toxic (EC50 = 5.671 mg L−1), followed by acyclovir (EC50 = 3.062 mg L−1), lamivudine (EC50 = 1.345 mg L−1) and efavirenz (EC50 = 0.026 mg L−1). Both species have been shown to be sensitive to efavirenz. A risk quotient (RQ) was calculated, and efavirenz had an RQ greater than 1 for both species, and lamivudine had an RQ greater than 1 for C. dubia, representing a high ecological risk for these organisms. Antivirals pose a significant environmental risk to aquatic organisms and should be taken into consideration in future monitoring of water sources. HIGHLIGHTS Evaluation of the ecotoxicity of acyclovir, efavirenz, lamivudine and zidovudine.; The most toxic antiviral for Ceriodaphnia dubia and Raphidocelis subcapitata was efavirenz.; Results suggest potential risk to environmental and public health.;

Perfluorooctane sulfonic acid (PFOS) is a ubiquitous and persistent contaminant in aquatic ecosystems. Chronic toxicity information for aquatic organisms is limited, therefore we conducted chronic PFOS toxicity tests for four model organisms commonly used for freshwater toxicology assays: Chironomus dilutus (midge), Ceriodaphnia dubia (water flea), Hyalella azteca (amphipod) and Danio rerio (zebrafish). The 16-day survival test with C. dilutus resulted in the lowest PFOS exposure concentrations to cause significant impacts, with reduced survival at 1 µg/L, a LC50 of 7.5 µg/L, and a growth EC10 of 1.5 µg/L. D. rerio was the next most sensitive species, with a 30-day LC50 of 490 µg/L and reduced growth at 260 µg/L. Effects for C. dubia and H. azteca occurred at concentrations a thousand-fold higher than for C. dilutus. H. azteca had a 42-day LC50 of 15 mg/L, an EC50 of 3.8 mg/L for reproduction (neonates per female) and an EC50 of 4.7 mg/L for growth. C. dubia was similarly tolerant of PFOS, with a 6-day LC50 of 20 mg/L for survival and an EC50 of 7 mg/L for reproduction (neonates per adult). H. azteca, C. dubia, and, to a lesser extent, D. rerio, appear tolerant of PFOS concentrations typically found in the environment. However, in agreement with previous studies, C. dilutus was particularly sensitive to PFOS exposure, with lethal and sublethal effects occurring at concentration levels present at highly contaminated sites.

We studied biotic ligand model (BLM) predictions of the toxicity of nickel (Ni) and zinc (Zn) in natural waters from Illinois and Minnesota, USA, which had combinations of pH, hardness, and dissolved organic carbon (DOC) more extreme than 99.7% of waters in a nationwide database. We conducted 7‐day chronic tests with Ceriodaphnia dubia and 96‐hour acute and 14‐day chronic tests with Neocloeon triangulifer and estimated median lethal concentrations and 20% effect concentrations for both species. Toxicity of Ni and Zn to both species differed among test waters by factors from 8 (Zn tests with C. dubia) to 35 (Zn tests with N. triangulifer). For both species and metals, tests with Minnesota waters (low pH and hardness, high DOC) showed lower toxicity than Illinois waters (high pH and high hardness, low DOC). Recalibration of the Ni BLM to be more responsive to pH‐related changes improved predictions of Ni toxicity, especially for C. dubia. For the Zn BLM, we compared several input data scenarios, which generally had minor effects on model performance scores (MPS). A scenario that included inputs of modeled dissolved inorganic carbon and measured Al and Fe(III) produced the highest MPS values for tests with both C. dubia and N. triangulifer. Overall, the BLM framework successfully modeled variation in toxicity for both Zn and Ni across wide ranges of water chemistry in tests with both standard and novel test organisms. Environ Toxicol Chem 2021;40:3049–3062. © 2021 SETAC. This article has been contributed to by US Government employees and their work is in the public domain in the USA. [ABSTRACT FROM AUTHOR]

Agrochemicals can reach freshwater bodies by drift, leaching, or runoff, where they constitute complex mixtures. Given that glyphosate and cypermethrin are within the most worldwide used pesticides, they are likely to co-occur in freshwater bodies. The aim of this study was to analyze the interaction between glyphosate and cypermethrin formulations on the cladoceran Ceriodaphnia dubia (Richard 1894) through an acute toxicity test and on a zooplankton assemblage through a mesocosm (30 L) experiment. The 24-h LC50 of both isolated pesticides and their equitoxic mixture was obtained for C. dubia. The mesocosm was performed by exposing a zooplankton assemblage to both pesticides isolated and in combination. The acute toxicity of the equitoxic mixture in C. dubia was 3 and 4 times higher than the isolated toxicity of glyphosate and cypermethrin, respectively. The total toxic units of the mixture were 0.53, indicating a synergistic interaction. In the mesocosm experiment, both pesticides also interacted causing a synergistic negative effect in Cladocera and Copepoda abundances. No interactions between pesticides were found for Rotifera; therefore, the mixture effect was considered additive. It is suggested to continue analyzing pesticide mixture effects on the basis of complementary scales of analysis to reach more environmentally relevant information. [ABSTRACT FROM AUTHOR]

This paper presents the results of a study of the effect of metabolic products of semiaquatic birds on planktonic crustaceans and fish in chronic laboratory experiments. The results of the studies showed that the waste pro ducts of birds in a concentration of from 0.5 to 2.5 g/l stimulate the fecundity of cladocerans, in the tissues of which the amount of lipids increases. The consumption of such cladocerans by fish causes a greater increase in their mass, and also contributes to an increase in their lipid content.

Seven-day sublethal toxicity tests were performed with the freshwater invertebrates Ceriodaphnia dubia, Hyalella azteca, and Chironomus dilutus to determine the effects of per- or polyfluorinated alkyl substances (PFAS) of varying chain length within four classes: perfluoroalkyl carboxylic acids (PFCAs), perfluoroalkyl sulfonic acids (PFSAs), perfluoroalkane sulfonamides, and fluorotelomer sulfonic acids. In general, toxicity increased with increasing chain length, but the slopes of these relationships varied markedly by species and chemical class. The toxicity of individual PFCAs was similar among species. The toxicity of PFSAs was similar to PFCAs for C. dubia and H. azteca, whereas PFSAs were much more toxic to C. dilutus, with median effect concentrations (EC50s) as low as 0.022 mg perfluorooctane sulfonate (PFOS)/L and 0.012 mg perfluorononane sulfonate (PFNS)/L. Despite the high sensitivity to PFOS and PFNS, C. dilutus was not very sensitive to structurally similar fluorotelomer sulfonates (6:2 and 8:2). Perfluoroalkane sulfonamides were the most toxic class tested among all species (e.g., EC50s of 0.011 and 0.017 mg perfluorooctane sulfonamide/L for C. dilutus and H. azteca, respectively). The differences in toxicity among species and chemical classes suggest that mechanisms of PFAS toxicity may differ as a function of both. Environ Toxicol Chem 2024;43:359-373. Published 2023. This article is a U.S. Government work and is in the public domain in the USA., (Published 2023. This article is a U.S. Government work and is in the public domain in the USA.)

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Cladocerans are constantly exposed to humic substances in nature, yet the effects of these substances on their survival and reproduction are not well known. Here, the effects of humic substances (20 and 40 mg L−1) (HS) on the life history variables of three common cladocerans, Ceriodaphnia dubia, Moina macrocopa, and Daphnia pulex were evaluated. The results showed that the effect of humic substances on the tested cladocerans is species-specific, affecting either survival, reproduction or both. For M. macrocopa, exposed to HS at a concentration of 40 mg L−1, the average lifespan and the life expectancy at birth were significantly reduced as compared to controls, but for C. dubia and D. pulex these parameters were increased. Gross reproductive rate was unaffected by the HS level for both D. pulex and M. macrocopa, but it was significantly higher for C. dubia. When compared to the corresponding controls, for HS-exposed cladocerans, the rate of population increase was significantly reduced in case of D. pulex while it was stimulated for both C. dubia and M. macrocopa. It appears that humic substances had a slightly stronger influence on survivorship than on reproduction of the tested cladocerans. [ABSTRACT FROM AUTHOR]

Ceriodaphnia dubia is a standardized test organism for regulatory toxicity testing of surface waters and commercial chemicals because of its simplicity to culture and responsiveness to toxicants. For testing convenience, C. dubia is often cultured for extended periods in the laboratory with little knowledge of the impact on subsequent generations. Extended laboratory rearing could impact how they respond to stressors and decrease the accuracy of test results. The present study investigated if C. dubia cultured for an extended period were representative of three recently collected field populations by comparing their culturing characteristics and sensitivities to toxicants. For culturing characteristics, the field cultures were more challenging because they had shorter body lengths, fewer neonates, and higher mortality rates than the laboratory culture. Comparative chronic toxicity tests with sodium chloride and the neonicotinoid insecticide thiamethoxam indicated that the laboratory and field organisms did not differ much in their toxicological responses but did differ in the variability of responses (percentage of coefficient of variation). The differences between the laboratory and field cultures found in the present study highlight the challenges of addressing discrepancies between laboratory and field applications in existing standardized methodologies. Environ Toxicol Chem 2024;43:159-169. © 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC., (© 2023 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.)

Amultigenerational study on Ceriodaphnia dubia was carried out by exposing three subsequent generations to pharmaceuticals chlorpromazine (CPZ) and diclofenac (DCF), and two lanthanide chlorides, gadolinium as GdCl 3 and europium as EuCl 3 . As the treatments, environmentally relevant concentrations were chosen (0.001, 0.01 and 0.1 mg/L for CPZ; 0.1, 1 and 10 mg/L for DCF; 0.425, 4.25 and 42.5 µg/L for Gd and 0.41, 4.1 and 41 µg/L for Eu). Survival, population growth and reproduction success were evaluated at 21 and 30 days of exposure, and the whole observation period lasted 40 days. The least sensitive to all selected substances was the first daphnid generation (F1). Within 21-day exposure, no significant effects of the psychotropic drug CPZ on C. dubia survival were observed in generations F1-F3. The anti-inflammatory drug DCF did not affect survival in the F1 generation; however, it significantly reduced survival in the F3 generation at 1-10 mg/L. Both lanthanides did not affect survival in the F1 and F2 generations of C. dubia but considerably decreased survival in the F3 at 4-42 µg/L. Both pharmaceuticals stimulated the reproduction of C. dubia in the F1 generation, while inhibition occurred at the highest tested concentrations in generations F2 and F3. The inhibitory effect on the reproductive success of lanthanides in the F2 generation resembled that for CPZ but not for DCF. The dynamics of adverse effects during the 21-30-day period revealed that despite increased mortality in the controls (up to 30%), concentrations used in the study minified, in most instances, the survival and aggravated population growth and reproduction success of C. dubia . Our data suggest that C. dubia as a test organism can be used for 21 days in multigenerational investigations, especially when testing close to environmental concentrations. In this respect, the standard C. dubia chronic toxicity assay seems limited since prolonged observations and several generations of daphnids are required to obtain reliable information for the risk assessment of potentially aggressive chemicals., Competing Interests: The authors declare there are no competing interests., (©2023 Gylytė et al.)

In this study, lethal concentration (LC) estimates for the semi-natural pesticide, spinetoram (Delegate?), were developed for three Cladoceran species: Ceriodaphnia dubia, Daphnia pulex, and Daphnia magna and compared to a previously published data set for these same species exposed to the related natural insecticide, spinosad. LC50's and 95% confidence limits (CL) were 12.47 (3.97-25.21), 3.44 (1.00-9.48), and 10.52 (2.52- 36.83) µg/L for C. dubia, D. pulex, and D. magna, respectively. Because the 95% CL for all the three species overlapped, spinetoram is equally susceptible to these species. However, spinetoram was found to be significantly less toxic than spinosad to C. dubia, significantly more toxic than spinosad to D. pulex, and equally toxic to D. magna. Therefore, even though spinetoram is derived from the same bacterial species as spinosad, there was no clear pattern of toxicity between these two related insecticides to the three species evaluated in this study. The results demonstrate the perils of inferring that the effects of one pesticide on indicator species will be similar to those of other chemicals despite similar modes of action and highlight the need to develop more nuanced risk assessment protocols. [ABSTRACT FROM AUTHOR]

Microplastics (<5 mm) are distributed ubiquitously in natural environments. The majority of microplastics in aquatic environments are shown to have rough surfaces due to various weathering processes (secondary microplastics; SMP), while laboratory studies predominantly utilise pristine microplastics (primary microplastics; PMP). Here we present the results from a study comparing the chronic effects of pristine PMP and artificially weathered SMP to three different Cladoceran species (Daphnia magna, Daphnia pulex, Ceriodaphnia dubia). We assessed the impact of PMP and SMP on reproductive output using various measured parameters, including time of first brood, size of first brood, size of first three broods, cumulative number of neonates, total number of broods and terminal length of test animals. Our results show that reproductive output of all species declined in a dose-dependent manner. The No Observed Effect Concentration (NOEC) was less than the lowest tested concentration (102 p/mL) for at least one measured endpoint for all species and both PMP and SMP. Further, it was inferred that species sensitivity varied inversely with body size for most endpoints, resulting in C. dubia being the most sensitive species; and D. magna being the least sensitive species under study. In addition, PMP appeared to have greater toxic potential as compared to SMP. This study is the first to directly compare the chronic toxicity of both pristine and weathered microplastic particles on three freshwater toxicological model organisms. Our results indicate that sensitivity in reproduction and growth to microplastics may differ between species and type of microplastic exposed; highlighting the importance of using multiple species and structural types of particles. Image 1 • Sensitivity of Cladoceran species to two types of microplastics (MPs) was compared. • Both primary (PMP) and secondary (SMP) particles elicited impacts on reproduction. • For most endpoints species sensitivity decreased with body size. • PMPs caused greater impact than SMPs to all three species studied. Capsule: Primary microplastics and artificially weathered secondary microplastics have species-specific effects on reproductive success in Cladoceran. [ABSTRACT FROM AUTHOR]

In the current study, the effect of different types of titanium dioxide (TiO2) nanoparticles (NPs) (rutile, anatase, and mixture) was analyzed on Ceriodaphnia dubia in the presence of algae under distinct irradiation conditions such as visible and UV-A. The toxicity experiments were performed in sterile freshwater to mimic the chemical composition of the freshwater system. In addition, the oxidative stress biomarkers such as MDA, catalase, and GSH were analyzed to elucidate the stress induced by the NPs on daphnids. Individually, both rutile and anatase NPs induced similar mortality under both visible and UV-A irradiations at all the test concentrations except 600 and 1200 μM where rutile induced higher mortality under UV-A. Upon visible irradiation, the binary mixture exhibited a synergistic effect at their lower concentration and an additive effect at higher concentrations. In contrast, UV-A irradiation demonstrated the additive effect of mixture except for 1200 μM which elucidated antagonistic effect. Mathematical model confirmed the effects of the binary mixture. The surface interaction between the individual NPs in the form of aggregation played a pivotal role in the induction of specific effects exhibited by the binary mixture. Oxidative stress biomarkers were highly increased upon NPs exposure especially under visible irradiation. These observations elucidated that the irradiation and crystallinity effect of TiO2 NPs were noted only on certain biomarkers and not on the mortality. [ABSTRACT FROM AUTHOR]

In previous work we intensively studied the acute responses of the cladoceran Ceriodaphnia dubia to major geochemical ions (Na+, K+, Ca2+, Mg2+, Cl–, SO42–, and HCO3–/CO32–), culminating in the development of models to predict acute toxicity from ionic composition. To quantitatively evaluate whether the toxicological behavior of major ions observed for C. dubia extends to chronic toxicity, we conducted 58 chronic toxicity tests with individual major salts and binary mixtures thereof. Chronic responses paralleled those demonstrated previously for acute exposure, specifically 1) similar relative toxicity of individual salts; 2) different Na salts showing similar potency when exposure is expressed as osmolarity; 3) toxicity of Mg, Ca, and K salts related to cation activity; 4) decreased toxicity of Na and Mg salts when Ca activity is increased at less than toxic concentrations; 5) additive behavior for salt mixtures sharing a common cation; and 6) independent behavior for salt mixtures with dissimilar cations, except Mg/Ca mixtures which appeared additive. Acute‐to‐chronic ratios were fairly consistent among salts, with values of approximately 1.8 for acute 50% lethal concentration (LC50) to chronic 50% effect concentration (EC50) and 2.8 for LC50/EC20 when expressed on an activity basis. Adjusting the previous acute toxicity model for acute‐to‐chronic ratios yielded chronic models that predict chronic toxicity within the range of intertest variability. Because these models are informed by a wide range of ion mixtures, they should provide robust assessment tools for natural waters enriched with major ions. Environ Toxicol Chem 2019;38:769–783. © Published 2018 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America [ABSTRACT FROM AUTHOR]

We compared 2 statistical hypothesis‐test approaches (no‐observed‐effect concentration [NOEC] and test of significant toxicity [TST]) to determine the influence of laboratory test performance on the false‐positive error rate using the US Environmental Protection Agency's Ceriodaphnia dubia reproduction whole‐effluent toxicity (WET) test endpoint. Simulation and power calculations were used to determine error rates based on observed control coefficients of variation (CV) for 8 laboratories over a range of effect levels. Average C. dubia control reproduction among laboratories was 20 to 40 offspring per female, and the 75th percentile CV was 0.10 to 0.31, reflecting a range in laboratory performance. The 2 approaches behave similarly for CVs of 0.2 to 0.3. At effects <10%, as CV decreases, TST is less likely to declare toxicity and NOEC is more likely to do so. Laboratory performance affects whether a sample is declared toxic and influences the probability of false‐positive (and −negative) error rates using either approach. At the 75th percentile control CV observed for each laboratory, 4 laboratories would achieve approximately a 5% false‐positive rate using 13 or fewer replicates for this test method. For the remaining 4 laboratories, more replicates would be needed to achieve a 5% false‐positive rate. The present analyses demonstrate how false‐positive rates are influenced by laboratory performance and WET test design. Environ Toxicol Chem 2019;38:511–523. Published 2019 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]

Neonicotinoid insecticides are a group of plant protectants frequently detected in surface waters at low concentrations. Aquatic invertebrates therefore have the potential to be exposed chronically to low concentrations of neonicotinoids. The cladocerans Daphnia magna and Ceriodaphnia dubia are among the most commonly used invertebrate test species in aquatic toxicology. Both species are known to be acutely insensitive to neonicotinoids, and while chronic toxicity has been characterized for D. magna , little research has been conducted with C. dubia. In the present study we conducted 7-d static-renewal life cycle tests for 6 neonicotinoids (acetamiprid, clothianidin, dinotefuran, imidacloprid, thiacloprid, and thiamethoxam) with C. dubia , and a 21-d test with imidacloprid with D. magna . 7-d LC50s for C. dubia ranged from 8.42 mg L −1 for imidacloprid to > 100 mg L −1 for clothianidin; 7-d reproduction EC50s were 2.98 for thiacloprid, to > 67 mg L −1 for dinotefuran. D. magna were less sensitive than C. dubia to imidacloprid, by 4-fold for lethality and 1.5-fold for reproduction; however, acute-to-chronic ratios (ACRs) were similar. ACRs, based on 48-h acute LC50s and 7- or 21-d chronic reproduction EC10s, ranged from 5.4 for acetamiprid to 53.0 for imidacloprid (mean 36.6, CV = 51%). Chronic toxicity values for both species were orders of magnitude greater than concentrations reported in the environment, and thus hazard to these cladocerans is negligible. [ABSTRACT FROM AUTHOR]

Degradation studies of the propylparaben (PrP), butylparaben (BuP) and of the propylparaben-butylparaben mixture (PrP-BuP) in deionized water and surface river water was investigated as a function of pH and initial concentration of the reactants using a medium-pressure mercury lamp. The photolysis of parabens (concentration ranging from 5 to 30 mg L −1 ) followed apparent pseudo-first-order kinetics, with rate constants ( k ) in deionized water and surface river water changed from 1.80 × 10 −1 to 3.68 × 10 −2 min −1 and 1.43 × 10 −1 to 1.45 × 10 −2 min −1 , respectively. Degradation reaction was faster at pH 5 in comparison with pH 7 or 11. The photolysis of parabens was greater than 91%, with low mineralization (26.15%) observed in acidic medium after 95 min. Analysis by chromatography coupled to mass spectrometry (LC-MS/MS) showed that only one product was generated during the degradation reaction and has UV bands similar to 3,4-dihydroxybenzoic acid. Estrogenic activity tests showed that non-degraded parabens stimulated the growth of breast adenocarcinoma (MCF-7) cells and this effect was evaluated after the photolysis. Cytotoxicity assays using fibroblasts cells (Balb/C 3T3 clone A31) indicated that the parental compounds and degradation products were not cytotoxic. On the contrary, non-degraded parabens were toxic to Ceriodaphnia dubia , but the product of photolysis was not. Overall, the photolytic method presented was able to degrade these parabens providing safe and non-estrogenic reaction product. [ABSTRACT FROM AUTHOR]

This work presents the development of a sensitive and friendly environment electrochemical methodology with high analytical performance for quinolone detection. The method is based on square-wave anodic stripping voltammetry which is simple and reliable for determination of quinolone family on the bismuth film electrode (BiFE). The deposition potential, deposition time, buffer solution pH, voltammetry detection technique and bismuth concentration at fixed quinolone concentration (1 μg L −1 ) were evaluated by fractionated factorial and central composite designs. The high cross-reactivity obtained in the evaluation of different quinolones showed that this methodology could be applied to quinolone family with limits of detection (LOD) close to 0.5 ng L −1 . Since is widely known that quinolones can reach aquatic ecosystems, the developed electroanalytical method was applied in the monitoring of moxifloxacin (MOXI) concentrations in ecotoxicity studies by means of acute toxicity test using two cladoceran species as biological models: Daphnia magna and Ceriodaphnia dubia . As a result of ecotoxicity, both species showed comparable sensitivities at MOXI. Toxicity studies of quinolones on aquatic organisms are very limited so the effects of MOXI to cladoceran species are highlighted. The interaction of both disciplines –Chemistry and Ecology- would allow knowing of global behavior of quinolones in natural environments, from an integrative perspective. [ABSTRACT FROM AUTHOR]

The general objective of this work is to experimentally assess the effects of acute glyphosate pollution on two freshwater cladoceran species (Daphnia magna and Ceriodaphnia dubia) and to use this information to predict the population dynamics and the potential for recovery of exposed organisms. Five to six concentrations of four formulations of glyphosate (4-Gly) (Eskoba®, Panzer Gold®, Roundup Ultramax® and Sulfosato Touchdown®) were evaluated in both cladoceran species through acute tests and 15-day recovery tests in order to estimate the population dynamics of microcrustaceans. The endpoints of the recovery test were: survival, growth (number of molts), fecundity, and the intrinsic population growth rate (r). A matrix population model (MPM) was applied to r of the survivor individuals of the acute tests, followed by a Monte Carlo simulation study. Among the 4-Gly tested, Sulfosato Touchdown® was the one that showed higher toxicity, and C. dubia was the most sensitive species. The Monte Carlo simulation study showed an average value of λ always <1 for D. magna, indicating that its populations would not be able to survive under natural environmental conditions after an acute Gly exposure between 0.25 and 35 a.e. mg L−1. The average value of λ for C. dubia was also <1 after exposure to Roundup Ultramax®: 1.30 and 1.20 for 1.21 and 2.5 mg a.e. L−1,respectively. The combined methodology—recovery tests and the later analysis through MPM with a Monte Carlo simulation study—is proposed to integrate key demographic parameters and predict the possible fate of microcrustacean populations after being exposed to acute 4-Gly contamination events. [ABSTRACT FROM AUTHOR]

Microplastics (<5 mm, MP) are ubiquitously distributed in the environment, causing increasing concern regarding their potential toxicity to organisms. To date, most research has focussed on the impacts of MPs on marine and estuarine organisms, with fewer studies focussing on the effects of microplastics on freshwater ecosystems, especially under different environmental conditions. In the present study, the sensitivity of two temperate Cladoceran species, Daphnia magna and Daphnia pulex, and a smaller tropical species Ceriodaphnia dubia , to primary microplastics (PMP) and secondary (weathered) microplastics (SMP) was assessed. A prolonged acute toxicity assay (up to 72 or 96 h) was performed at 18°, 22°, and 26 °C, to determine the influence of temperature as an additional stressor and survival data were analysed using toxicokinetic-toxicodynamic (TK-TD) model. Acute sensitivity of D. magna and D. pulex to both PMP and SMP increased sharply with temperature, whereas that of C. dubia remained relatively stable across temperatures. C. dubia was the most sensitive species at 18 °C, followed by D. pulex and D. magna, which were of comparable sensitivity. However, this ranking was reversed at 26 °C as could be seen from the No Effect Concentration (NEC) estimates of the TK-TD model. In addition, SMP and PMP had a similar effect on D. magna and D. pulex, but PMP was more toxic to C. dubia . Effects on survival were strongly time-dependent and became substantially more severe after the standard 48 h test period. Our results indicate that sensitivity to microplastics may differ between species for different types of microplastics, and could be drastically influenced by temperature albeit at high exposure concentrations. [ABSTRACT FROM AUTHOR]

A genetic variant of the entomopathogenic fungus Metarhizium anisopliae var anisopliae S54 (S54) was discovered and isolated from soil in Alberta, Canada and has been tested as a potential control agent for use against crop pest insects, principally grasshoppers (Orthoptera:Acrididae). The present study was conducted to evaluate the toxicity of this entomopathogenic fungus to a non-target cladoceran, Ceriodaphnia dubia Richard, a species commonly used in aquatic ecotoxicology tests. Acute mortality and population-level responses after chronic exposure were determined. Acute mortality of S54 (144 h exposure time) ranged from 5% in treatments of 1.33 x 104 spores/ml to 10% after exposure to 5.32 x 105 spores/ml. For the chronic population study, C. dubia populations were exposed to the expected environmental concentration (EEC) of the agricultural adjuvant R-11, the commonly used insecticide imidacloprid, the biopesticide, Azatin®, and S54. Imidacloprid had the greatest negative impact on C. dubia, reducing the number of founding individuals, offspring/female, final population size, and population growth rate compared to the control. Exposure to imidacloprid caused significantly greater reductions in the production of population parameters than the other compounds. R-11, Azatin®, and S54 were much less toxic to C. dubia than imidacloprid and these products are not expected to pose a significant risk to C. dubia after acute exposure to the EEC. Results of this study indicate that M. anisopliae var anisopliae S54 may be valuable as a natural insecticide applied in the context of integrated pest management of grasshoppers and other pest species with minimal impact on non-target aquatic organisms. [ABSTRACT FROM AUTHOR]

Abstract: Barium is present at elevated concentrations in oil and gas produced waters, and there is no international water quality guideline value to assess the potential risk of adverse effects to aquatic biota. Sulfate concentration largely controls the solubility of barium in aquatic systems, with insoluble barium sulfate (barite) assumed to be less bioavailable and less toxic than dissolved barium. We exposed aquatic biota to dissolved barium only and to a mixture of dissolved and precipitated barium. The chronic dissolved barium 48‐h growth rate inhibition effect concentrations, (EC10 and EC50) for the tropical freshwater alga Chlorella sp. 12 were 40 mg/L (27–54 mg/L 95% confidence limits [CL]), and 240 mg/L (200–280 mg/L 95% CL), respectively. The acute EC10 and EC50 values for 48‐h immobilization of the water flea (Ceriodaphnia dubia) by dissolved barium were 14 mg/L (13–15 mg/L 95% CL) and 17 mg/L (16–18 mg/L 95% CL), respectively. Chlorella sp. 12 was significantly more sensitive to precipitated barium than to dissolved barium, whereas the opposite seemed likely for C. dubia. Ceriodaphnia dubia was predicted to be chronically sensitive to dissolved barium at concentrations measured in produced waters and receiving waters, based on a predicted chronic EC10 of 1.7 mg/L derived from the acute EC50/10. Further chronic toxicity data that account for barium toxicity in dissolved and precipitated forms are required to derive a barium guideline for freshwater biota. Environ Toxicol Chem 2018;37:1632–1642. © 2018 SETAC [ABSTRACT FROM AUTHOR]

The sediment compartment stands out because it functions as both a temporary sink of pollutants and a potential source of these elements that may become available to the water column.This study aimed to correlate the concentrations of total metals in the crude sediment and in the interstitial water with the ecotoxicity in the water column using an a modified sediment ecotoxicity test with Ceriodaphnia dubia. The results indicate that the sediment may contribute to the toxicity in the water column and that such toxicity is possibly not related to the metals present. Based on the chemical analysis of the metals, the Canadian Sediment Quality Guidelines (SQGs) would frame the sediment as non-toxic to benthic organisms, but the SQGs have no reference standards for possible effects on nektonic organisms. Due to the complexity of this compartment, it is fundamental to evaluate the interactions of the different pollutants in the system and possible effects on the nektonic organisms. [ABSTRACT FROM AUTHOR]

Constructed wetland treatment systems (CWTSs) could provide a passive, low-energy strategy for mitigating risks associated with oil sands process-affected waters (OSPWs). Due to the large volumes (over 975 million m 3 ), heterogeneous composition, and acute and chronic toxicity of OSPW, passive and efficient treatment to decrease risks to biota will be necessary once operators obtain regulatory permission to discharge into aquatic receiving systems. The research objective was to design, assemble, and measure performance of a pilot-scale hybrid CWTS for treatment of OSPW. Constituents of concern (COCs) identified in OSPW included NAs, oil and grease, As, B, Cu, Pb, and Zn. Oxidizing conditions (net sediment redox > −50 mV) were promoted to allow aerobic degradation of organic constituents, and co-precipitation of arsenic with iron oxyhydroxides. Treatment of Cu, Pb, and Zn was targeted through precipitation with sulfides in reducing “micro-environments” in wetland sediments. Solar photocatalytic reactors (hybrid components) were used to remove recalcitrant organics. Performance was assessed using rates and extents of removal of COCs and changes in toxicity as indicated by Ceriodaphnia dubia . Mean total naphthenic acid fraction compound concentrations decreased from approximately 43 mg/L in untreated OSPW to 10 mg/L following a 16-d retention time in the hybrid CWTS. Mean As and Zn concentrations decreased from 0.026 mg/L and 0.129 mg/L in untreated OSPW to 0.011–0.014 mg/L and 0.052–0.062 mg/L in wetland outflows, respectively. Cu and Pb mass decreased by 13–26% in the CWTS; however, evaporative concentration masked removal (in terms of total metal concentrations). Toxicity (in terms of C. dubia survival and reproduction) of OSPW was eliminated following treatment. Results demonstrate that hybrid CWTSs can effectively degrade NAs and alleviate toxicity associated with metals and organics in OSPW. [ABSTRACT FROM AUTHOR]

Benzalkonium chloride (BAC) is a cationic surfactant commonly used as a disinfectant. Its ubiquitous nature is the result of high usage and frequent discharge into the environment and evidence of interaction with numerous contaminants, such as pharmaceutical active compound residues. Anticancer drugs, among these compounds, are able to exert eco-genotoxic effects at sub ng-µg/L. The purpose of this study was to assess the reproductive toxicity and the genotoxicity of 5-fluorouracil (5-FU), cisplatin (CDDP), etoposide (ET), and imatinib mesylate (IM)—binary mixtures combined with BAC in Ceriodaphnia dubia. The effects of the mixtures were assessed under the assumption of independent action in experiments that applied two effect levels. The type of interaction was not the same over the range of effect sizes. The combined action experiment on reproduction showed an antagonistic effect at higher effect levels for all binary combinations, except for BAC/IM, whereas independent action was observed in all mixtures at a low effect level. The results of binary combinations on genotoxicity showed antagonistic effects for BAC + ET and BAC + CDDP, whereas independence was expressed in BAC + IM and BAC + 5-FU. The antagonistic interactions still led to higher effects than those observed after single exposures at the same doses in most cases. The effects of mixtures of drugs should be taken into account for environmental risk assessment. [ABSTRACT FROM AUTHOR]

Owing to the increase in the usage of titanium dioxide nanoparticles (TiO 2 NPs), their release into the aquatic environment is inevitable. In the aquatic ecosystem, TiO 2 NPs can bio-magnify at various trophic levels in the food chain through dietary exposure. In the current study, the trophic transfer potential of two crystalline phases of TiO 2, anatase and rutile nanoparticles (individual as well as a binary mixture) has been evaluated in the lake water matrix using algae–daphnia system. Chlorella sp. and Ceriodaphnia dubia were used as test organisms to represent the algae–daphnia food chain of the freshwater ecosystem. Other than crystallinity, the effect of irradiation (visible and UV-A) was also investigated at the test concentrations, 75, 300, and 1200 μM. TiO 2 NPs treated algal diet produced significant mortality only at the test concentrations, 300 and 1200 μM. The type of irradiation and crystallinity doesn’t have any impact on the mortality of daphnids through the dietary exposure of TiO 2 NPs. Comparing the mixture with individual NPs, binary mixture induced less mortality on C. dubia which signifies the antagonistic effect of NPs when they coexist. Statistical modeling confirmed the antagonistic effect of the binary mixture on C. dubia . As individual NPs, anatase and rutile forms showed a maximum Ti accumulation under UV-A and visible irradiation, respectively. BMF of TiO 2 NPs has been in validation with the bioaccumulation noted in C. dubia . Individual NPs (75 μM) showed higher BMF value of ∼23 under both UV-A (anatase) and visible (rutile) irradiation. Individual NPs showing higher BMF confirmed their trophic transfer potential in the aquatic food chain, primarily through the diet. In contrast, the binary mixture obtained a higher BMF of 1.9 and 0.79 at 75 and 300 μM under visible and UV-A irradiation, respectively. The plausible reason behind this decrement was the antagonistic effect of the mixture which significantly reduced their Ti bioaccumulation on C. dubia . [ABSTRACT FROM AUTHOR]

Standardized ecotoxicity bioassays show some limits to assess properly long-term residual toxicity of complex mixture of pollutants often present at low concentration, such as stormwaters. Among invertebrate organisms used for ecotoxicity testing, the microcrustaceanCeriodaphnia dubia(C. dubia) is considered as one of the most sensitive, especially regarding reproduction impairment as a toxicity endpoint. Consequently, this work explores the interest to perform a multigenerational assay based on the study of the reproduction ofC. dubiato assess long-term ecotoxicity of complex mixture, using stormwater samples. With this in mind, a battery of standardized bioassays (Daphnia magnamobility,Pseudokirchneriella subcapitatapopulation growth,Heterocypris incongruensgrowth and one generationC. dubiareproduction inhibition assays) was performed in parallel to a three generationC. dubiareproduction inhibition assay on 2 stormwater samples. Results highlighted that while all standardized bioassays failed to reveal residual toxicity in the stormwater samples, theC. dubiamultigenerational assay exhibited an higher sensitivity than the previous ones. No adverse effect was observed for the first exposed generation, but an increase in mortality and a reproduction disturbance was obtained in the second and third exposed generation depending of the sample. Further experiments are now needed to optimize the exposure protocol of this multigenerational assay. [ABSTRACT FROM AUTHOR]

The top-down effects of consumers, such as predators, are known to affect abundances, size structure, and species composition in aquatic ecosystems. Parasites are also important in shaping the ecology of free-living species; however, their effects are often overlooked because parasites can be difficult to detect. Parasites can be particularly challenging to observe in zooplankton hosts because of their small size and ephemeral infection periods. To overcome these challenges, we used a quarantine approach combined with high-magnification microscopy to increase detection of parasites of the tropical Cladoceran, Ceriodaphnia cornuta, in Lake Gatun, Panamá. Using this approach, we were able to demonstrate that competing morphs of Ceriodaphnia experience differential rates of infection, where the subordinate competitor suffered higher parasite prevalence than did the dominant morph. Predation by fishes on the dominant morph is considered the principal mechanism for their coexistence, but we hypothesize that parasites may also play a role in maintaining morphotype diversity of Ceriodaphnia. [ABSTRACT FROM AUTHOR]

Dilbits are blends of bitumen and natural gas condensates or crude oils with only limited toxicity data. Two dilbits, Cold Lake Blend and Western Canadian Select, were tested as either unweathered or weathered oils for acute and chronic toxicity to standard freshwater and estuarine organisms. Water accommodated fractions of the dilbits were characterized for total petroleum hydrocarbons (TPH), polycyclic aromatic hydrocarbons (PAHs), and monoaromatics (BTEX). Acute toxicity of unweathered and weathered dilbits ranged from 4 to 16 mg/L TPH, 8 to 40 μg/L total PAHs, and 0.7 to 16 mg/L BTEX in Ceriodaphnia dubia , Pimephales promelas , Americamysis bahia , and Menidia beryllina . Concentrations of weathered dilbits causing impaired growth ( A. bahia ) and reproduction ( C. dubia ) ranged from 0.8 to 3.5 mg/L TPH and 6 to 16 μg/L PAHs. The two dilbits had generally similar acute and short term chronic toxicity expressed as TPH or total PAHs as other crude oils and other petroleum products. [ABSTRACT FROM AUTHOR]

The unique physico-chemical properties of nanomaterials have allowed their application in different areas including electronics, energy storage, nanomedicine, environmental remediation and biotechnology. Graphene and its derivatives, in particular, have been commercially available, with prediction for increasing their production in the next years, in a way that their release into aquatic environments is very likely to occur, and the impacts of such situation on organisms are still not completely understood. In this context, we evaluated graphene oxide (GO) effects on the freshwater cladoceran Ceriodaphnia dubia through acute and chronic toxicity, feeding rates, and reactive oxygen species (ROS) generation. The mean effective concentration (EC50) estimated during acute exposure was 1.25 mg L −1 of GO. The chronic exposure resulted in significant decrease in the number of neonates. The feeding rates were also decreased by GO exposure. Sub-lethal concentrations of GO caused an increase in ROS generation in the organisms. Our results indicated that GO cause acute and chronic effects to C. dubia . In the presence of GO there was a shift in the available energy for self-maintenance rather than feeding or reproduction activities. This study provides useful information on GO concentrations that might impair the aquatic biota, and supports regulatory efforts concerning the environmental safety of this product. [ABSTRACT FROM AUTHOR]

Based on previous research on the acute toxicity of major ions (Na+, K+, Ca2+, Mg2+, Cl-, SO42-, and HCO3-/CO32-) to Ceriodaphnia dubia, a mathematical model was developed for predicting the median lethal concentration (LC50) for any ion mixture, excepting those dominated by K-specific toxicity. One component of the model describes a mechanism of general ion toxicity to which all ions contribute and predicts LC50s as a function of osmolarity and Ca activity. The other component describes Mg/Ca-specific toxicity to apply when such toxicity exceeds the general ion toxicity and predicts LC50s as a function of Mg and Ca activities. This model not only tracks well the observed LC50s from past research used for model development but also successfully predicts LC50s from new toxicity tests on synthetic mixtures of ions emulating chemistries of various ion-enriched effluents and receiving waters. It also performs better than a previously published model for major ion toxicity. Because of the complexities of estimating chemical activities and osmolarity, a simplified model based directly on ion concentrations was also developed and found to provide useful predictions. Environ Toxicol Chem 2018;37:247-259. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]

The acute toxicity of silver to Ceriodaphnia dubia was investigated in laboratory reconstituted waters as well as in natural waters and reconstituted waters with natural organic matter. The water quality characteristics of the laboratory reconstituted waters were systematically varied. The parameters that demonstrated an ability to mitigate the acute toxic effects of silver were chloride, sodium, organic carbon, and chromium reducible sulfide. Factors that did not have a consistent effect on the acute toxicity of silver to C. dubia, at least over the range of conditions tested, included hardness, alkalinity, and pH. The biotic ligand model was calibrated to the observed test results and found to be of use in quantifying the effect of changing water quality characteristics on silver bioavailability and toxicity. The model generally predicted silver toxicity within a factor of two and should be useful in modifying water quality criteria. [ABSTRACT FROM AUTHOR]

There is limited knowledge regarding the adverse effects of wastewater-derived microplastics, particularly fibers, on aquatic biota. In this study, we examined the acute (48 h) and chronic (8 d) effects of microplastic polyester fibers and polyethylene (PE) beads on freshwater zooplankton Ceriodaphnia dubia. We also assessed the acute response of C. dubia to a binary mixture of microplastic beads and fibers for the first time. Acute exposure to fibers and PE beads both showed a dose-dependent effect on survival. An equitoxic binary mixture of beads and fibers resulted in a toxic unit of 1.85 indicating less than additive effects. Chronic exposure to lower concentrations did not significantly affect survival of C. dubia, but a dose-dependent effect on growth and reproduction was observed. Fibers showed greater adverse effects than PE beads. While ingestion of fibers was not observed, scanning electron microscopy showed carapace and antenna deformities after exposure to fibers, with no deformities observed after exposure to PE beads. While much of the current research has focused on microplastic beads, our study shows that microplastic fibers pose a greater risk to C. dubia, with reduced reproductive output observed at concentrations within an order of magnitude of reported environmental levels. [ABSTRACT FROM AUTHOR]

As integration of nanoparticles (NPs) into products becomes more common, the need to address the paucity of chronic hazard information for aquatic environments required to determine risk potential increases. This study generated acute and chronic toxicity reference values forCeriodaphnia dubiaexposed to 20 and 100 nm silver nanoparticles (AgNPs) and gold nanoparticles (AuNPs) to generate and evaluate potential differences in acute-to-chronic ratios (ACR) using two different feeding methods. A modified feeding procedure was employed alongside the standard procedures to investigate the influence of food on organism exposure. An 8-h period before food was added allowed direct organism exposure to NP dispersions (and associated ions) without food-to-NP interactions. The AgNPs [chronic lethal median concentrations (LC50) between 18.7 and 31.9 µg/L] were substantially more toxic than AuNPs (LC50 = 21 507 to >26 384 µg/L). The modified chronic testing method resulted in greater sensitivity in AgNPs exposures. However, the modified feeding ration had less of an effect in exposures to the larger (100 nm) AgNPs compared to smaller particles (20 nm). The ACRs for AgNPs using the standard feeding ration were 1.6 and 3.5 for 20 nm and 100 nm, respectively. The ACRs for AgNPs using the modified feeding ration were 3.4 and 7.6 for 20 nm and 100 nm NPs, respectively. This supports that the addition of the standard feeding ration decreasesC. dubiachronic sensitivity to AgNPs, although it must also be recognized organisms may be sensitized due to less access to food. The ACRs for 20 nm and 100 nm AuNPs (standard ration only) were 4.0 and 3.0, respectively. It is important to also consider that dissolved Ag+ions are more toxic than AgNPs, based on both acute toxicity values in the cited literature and chronic toxicity thresholds generated in this study that support existing thresholds that Ag+are likely protective of AgNPs effects. [ABSTRACT FROM AUTHOR]

Ivermectin (IVM) is a parasiticide widely used for livestock. It is a semisynthetic derivative of avermectin, a macrocyclic lactone produced by Streptomyces avermitilis . This drug is only partly metabolized by livestock; considerable amounts of parent drug are excreted mostly via feces. To simulate exposure of aquatic invertebrates and macrophytes to direct excretion of cattle dung into surface waters, a microcosm experiment with IVM spiked in cattle dung was conducted. The objectives of this study were to characterize accumulation of IVM in water, sediment+dung, roots of the floating fern Salvinia and the zooplankton Ceriodaphnia dubia , the amphipod Hyalella and the apple snail Pomacea ; to determine the effect of this drug spiked in cattle dung on life-history traits of these invertebrates; and to evaluate the influence of IVM on aquatic nutrient cycling. Dung was spiked with IVM to attain concentrations of 1150, 458, 50 and 22 µg kg −1 dung fresh weight, approximating those found in cattle dung at days 3, 7, 16 and 29 following subcutaneous injection. Concentrations found in dung during the first week of excretion were lethally toxic to Ceriodaphnia dubia and Hyalella , whereas no mortality was observed in Pomacea . Concentrations of IVM in roots, sediment + dung and Pomacea increased significantly from the lowest to the highest treatment level. The effect of this drug on decomposition and release of nutrients from dung would have negative consequences for nutrient cycling in water. Increasing concentrations in sediment + dung with days of the experiment suggested that toxic concentrations would persist for an extended period in the water–sediment system. IVM represents an ecological risk for aquatic ecosystems, underscoring the need for livestock management strategies to limit its entry into water bodies. [ABSTRACT FROM AUTHOR]

Understanding the effects of fungicides on nontarget organisms at realistic concentrations and exposure durations is vital for determining potential impacts on aquatic ecosystems. Environmental concentrations of the fungicide azoxystrobin have been reported up to 4.6 μg/L in the United States and 30 μg/L in Europe. The objective of the present study was to evaluate the chronic toxicity of azoxystrobin in water-only exposures with an amphipod ( Hyalella azteca; 42-d exposure), a midge ( Chironomus dilutus; 50-d exposure), a cladoceran ( Ceriodaphnia dubia; 7-d exposure), and a unionid mussel ( Lampsilis siliquoidea; 28-d exposure) at environmentally relevant concentrations. The potential photo-enhanced toxicity of azoxystrobin accumulated by C. dubia and L. siliquoidea following chronic exposures to azoxystrobin was also evaluated. The 20% effect concentrations (EC20s) based on the most sensitive endpoint were 4.2 μg/L for H. azteca reproduction, 12 μg/L for C. dubia reproduction and C. dilutus emergence, and >28 μg/L for L. siliquoidea. Hyalella azteca was more sensitive to azoxystrobin compared with the other 3 species in the chronic exposures. No photo-enhanced toxicity was observed for either C. dubia or L. siliquoidea exposed to ultraviolet light in control water following azoxystrobin tests. The results of the present study indicate chronic effects of azoxystrobin on 3 of 4 invertebrates tested at environmentally relevant concentrations. The changes noted in biomass and reproduction have the potential to alter the rate of ecological processes driven by aquatic invertebrates. Environ Toxicol Chem 2017;36:2308-2315. Published 2017 Wiley Periodicals Inc. on behalf of SETAC. This article is a US government work and, as such, is in the public domain in the United States of America. [ABSTRACT FROM AUTHOR]