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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;00:1-13. © 2024 Syngenta Crop Protection AG. ibacon GmbH and The Author(s). Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

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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.

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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.

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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.

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The toxicity of the insecticide chlorantraniliprole and its formulated product Altacor® was determined for the Cladoceran, Ceriodaphnia dubia Richard. Acute toxicity (48 h) and 21 d population studies were conducted. The hypothesis of this study was that these two compounds would have different toxicities. We conducted acute and chronic toxicity studies for each compound and compared the results to test this hypothesis. 48 h LC50s (95% CL) for chlorantraniliprole and Altacor® were 8.5 (6.6-11.5) and 6.0 (3.7-9.0) µg chlorantraniliprole/L water, respectively. Therefore, chlorantraniliprole and Altacor® were equitoxic to C. dubia at LC50 based on overlap of the 95% CL. In the population study, chlorantraniliprole and Altacor® concentrations equivalent to the acute LC5, 10, 25, and 50 for each product were evaluated on populations of C. dubia. Number of individuals after 21 d was the endpoint evaluated. T-tests conducted at each LC value indicated that there was no significant difference in population size between these two products at each LC value evaluated. Previous studies show that toxicity can vary greatly between formulated and technical grade pesticides. However, our results show that chlorantraniliprole and its formulated product, Altacor® were equally toxic to C. dubia. Therefore, making assumptions about the toxicity of formulated and unformulated products is ill advised.

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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.

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The chronic toxicity of an innovative Hg water treatment system using tin (Sn) (II) chloride (SnCl2) followed by air stripping was assessed through measurements of survival, growth, and reproduction rate in the freshwater cladoceran Ceriodaphnia dubia, a model species for toxicity testing. We first calculated the concentrations of Hg causing 25% reduction in survival and reproduction (Lethal or Inhibition Concentrations, or LC25 and IC25, for survival and reproduction, respectively) through exposure to aqueous Hg at concentrations ranging from 0 to 25,000 ng L-1. Then, we treated media (DMW and natural stream water) contaminated with Hg at LC25 and IC25 concentrations with SnCl2 at a Sn:Hg stoichiometric ratio of 8:1 and air stripping and exposed C. dubia to this Sn-amended media. Our results showed that Hg significantly affected survival, reproduction rates and impaired growth. SnCl2-treatment removed 100% of the Hg from the media at all concentrations tested with no deleterious effects on survival, growth and reproduction. Our results confirmed the efficacy of SnCl2 in removing aqueous Hg from stream water and showed that the added Sn did not impact C. dubia at the concentrations tested, supporting the suitability of SnCl2-based treatments in appropriate Hg-contaminated environments.

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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.

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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.

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We conducted the first complete toxicological study of six quinolones, including acute, chronic, and recovery assays on Daphnia magna and Ceriodaphnia dubia. The assayed quinolones were second-generation ciprofloxacin (CIP), norfloxacin (NOR), enrofloxacin (ENR), and marbofloxacin (MAR); third-generation levofloxacin (LEV), and fourth-generation moxifloxacin (MOX). The median lethal concentrations (LC50) obtained for both species by acute ecotoxicity assay ranged from 14 to 73 mg L-1 and from 3 to 23 mg L-1 at 48 and 72 h, respectively; while the median effective concentration (EC50) ranged from 4 to 28 mg L-1 in the chronic ecotoxicity assays. C. dubia surviving the chronic exposure assay was monitored in recovery assays free of quinolones. A fluorometric method was used to confirm that there was no significant loss of quinolone concentrations during the acute assays. We also used this method to show that quinolone concentrations fell below 80% of the nominal value after 9-11 d if exposure solutions were not renewed. This study on the ecotoxicological and chemical behavior of quinolones in two cladoceran species fills a data gap about how these emerging contaminants affect nontarget aquatic organisms and how long they persist in the environment.

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On 5 November 2015, the Samarco Fe ore mining operations released approximately 50 million cubic meters of mining waste into the environment, due to a dam collapse. Aiming at understanding the potential effects on the Doce River, different regions of the course of tailings were monitored using acute and chronic ecotoxicological tests with 4 species: Ceriodaphnia dubia, Daphnia similis, Danio rerio, and Vibrio fischeri. The results showed no acute toxicity for water column organisms. However, chronic toxicity was observed with the tests with the microcrustacean C. dubia, mainly related to the physical effects of the passage of flood wave and increased suspended solids, given that toxicity was reduced after filtering the samples. The results showed different magnitudes of impact among the upper, middle, and lower Doce River, with greater impact close to the dam failure area. Integr Environ Assess Manag 2020;16:608-614. © 2020 SETAC.

Em 5 de novembro de 2015, aproximadamente 50 milhões de m3 de resíduos provenientes da barragem de rejeitos das operações de mineração de minério de ferro da Samarco atingiram o meio ambiente decorrente do seu rompimento. Com o objetivo de compreender os potenciais efeitos sobre o rio Doce, o monitoramento foi realizado, através de testes ecotoxicológicos com quatro espécies de diferentes, das regiões atingidas pela pluma de turbidez. Os resultados demonstraram, de modo geral, ausência de ecotoxicidade aguda para organismos de coluna de água. Entretanto, foi evidenciada ecotoxicidade crônica com o microcrustáceo Ceriodaphnia dubia, que esteve relacionada principalmente aos efeitos físicos da passagem da onda de cheia e ao aumento de sólidos em suspensão na coluna d'água. Os resultados mostraram que a magnitude do impacto foi diferente nas três regiões do rio Doce (alta, média e baixa), com maior intensidade na região mais próxima da área do rompimento da barragem. Integr Environ Assess Manag 2020;16:608-614.

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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.

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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.

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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.

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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.

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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.

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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.

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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.

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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 for Ceriodaphnia dubia exposed 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 decreases C. dubia chronic 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.

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RESUMO Os metais frequentemente são avaliados em águas doces como soluções dissolvidas, assumindo que o efeito tóxico é causado unicamente por via aquática (respiração e contato). No entanto, estudos abrangendo concomitantemente a toxicidade na água e no alimento, como acontece no meio, são pouco discutidos na literatura. No presente estudo, a toxicidade de zinco e cádmio foi avaliada expondo-se Ceriodaphnia dubia simultaneamente ao alimento e ao meio aquoso. A espécie de alga verde Raphidocelis subcapitata foi exposta durante 96h a concentrações de Zn (0,18 e 0,27 mg.L-1) e Cd (0,001 e 0,0015 mg.L-1). Os resultados foram analisados estatisticamente por meio da Análise de Variância (Kruskal-Wallis). As algas foram usadas como fonte de alimento para C. dubia, durante exposição crônica (oito dias), nas mesmas concentrações. Posteriormente, os neonatos (geração F1) foram introduzidos em água e alimentação sem contaminantes, para averiguação da capacidade de recuperação biológica. Foram avaliados número de neonatos por indivíduos, morfologia dos neonatos e quantificação dos metais em tecido biológico. Os resultados demonstraram que nas concentrações testadas não houve inibição no crescimento de R. subcapitata, enquanto para C. dubia evidenciou-se toxicidade crônica pela redução na taxa reprodutiva nas duas gerações, para ambos metais. Concluiu-se que, mesmo em concentrações relativamente baixas, os metais zinco e cádmio podem alterar o padrão reprodutivo dos invertebrados de água doce, comprometendo o ecossistema aquático e sua capacidade de recuperação. Considerando os efeitos tóxicos desses metais e sua interferência no sistema biológico, novos ensaios ecotoxicológicos devem ser realizados para melhor compreensão do comportamento dessas substâncias nos organismos.

ABSTRACT Metals are often evaluated in fresh water as dissolved solutions, assuming that the toxic effect is caused only by water (respiration and contact). However, toxicity studies in food and water, in a concomitant way, as occurs in the environment, are less discussed. In this study, zinc and cadmium toxicity was evaluated through the exposure of Ceriodaphnia dubia to contaminated food and water. The species of green algae Raphidocelis subcapitata was exposed for 96h to concentrations of Zn (0,18 and 0,27 mg.L-1) and Cd (0,001 and 0,0015 mg.L-1). The results were statistically analyzed by means of Analysis of Variance (Kruskal-Wallis). Algae were used as food source for C. dubia, during chronic exposure (eight days) in the same concentrations described. Subsequently, neonates (F1 generation) were introduced in non-contaminated water and food in order to ascertain their biological recovery capacity. The number of newborns by individuals, morphology of newborns, and quantification of metals in biological tissue were evaluated. The results showed that the tested concentrations did not inhibit the growth of R. subcapitata, while C. dubia had chronic toxicity, with reduction in the reproductive rate in both generations, for both metals. The results allowed the conclusion that, even at relatively low concentrations, the metals zinc and cadmium can alter the reproductive patterns of freshwater invertebrates, compromising the aquatic ecosystem and its resilience. Thus, considering the toxic effects of these metals and their interference in the biological system, new ecotoxicological tests should be performed to allow a better understanding of the behavior of these substances in organisms.