Environmental factors modify silver nanoparticles ecotoxicity in Chydorus eurynotus (Cladocera).

Silver nanoparticles (AgNPs) are among the most produced nanomaterials in the world and are incorporated into several products due to their biocide and physicochemical properties. Since freshwater bodies are AgNPs main final sink, several consequences for biota are expected to occur. With the hypothesis that AgNPs can interact with environmental factors, we analyzed their ecotoxicity in combination with humic acids and algae. In addition to the specific AgNPs behavior in the media, we analyzed the mortality, growth, and phototactic behavior of Chydorus eurynotus (Cladocera) as response variables. While algae promoted Ag+ release, humic acids reduced it by adsorption, and their combination resulted in an intermediated Ag+ release. AgNPs affected C. eurynotus survival and growth, but algae and humic acids reduced AgNPs lethality, especially when combined. The humic acids mitigated AgNP effects in C. eurynotus growth, and both factors improved its phototactic behavior. It is essential to deepen the study of the isolated and combined influences of environmental factors on the ecotoxicity of nanoparticles to achieve accurate predictions under realistic exposure scenarios.

Sensitivity of Daphnia spinulata Birabén, 1917 to glyphosate at different salinity levels.

Daphnia spinulata Birabén, 1917 is an endemic cladoceran species, frequent in the zooplankton communities of the shallow lakes of the Pampean region of Argentina. These lakes have varying salinity levels and, being located in agricultural areas, are frequently subject to pesticide pollution. This study aimed to determine the effects of the herbicide glyphosate (Panzer Gold®) in combination with different salinity levels on the biological parameters of D. spinulata and its recovery ability after a short exposure. Three types of assays were performed: an acute toxicity test, a chronic assessment to determine survival, growth and reproduction, and recovery assays under optimal salinity conditions (1 g L-1). The LC50-48 h of glyphosate was 7.5 mg L-1 (CL 3.15 to 11.72). Longevity and the number of offspring and clutches were significantly reduced due to the combined exposure of glyphosate and increased salinity. The timing of the first offspring did not recover after glyphosate exposure. Our results reveal that D. spinulata is sensitive to the herbicide Panzer Gold® at concentrations well below those indicated in the safety data sheet of this commercial formulation, which causes stronger negative effects in conditions of higher salinity. Further research is needed to shed light on the sensitivity of this cladoceran to glyphosate and its variability under other interactive stress factors.

The relative importance of salinization in lowland stream zooplankton: Implications of the ecosystem nutrient status.

Salinization of aquatic systems is predicted to increase due to climate and land use changes. Nevertheless, community responses may be different according to the ecosystem characteristics and contextual scenarios. Small flowing waters are particularly vulnerable to salinization, which may impact on the biodiversity and ecosystem processes, but this remains unclear. We conducted a study in 42 lowland streams characterized by overall high nutrient levels along a salinity gradient between 2 and 160 g L-1 to analyze changes in zooplankton structural and functional metrics, and the grazing effects of zooplankton on phytoplankton affecting the energy transfer. Generalized additive models revealed that the analyzed metrics were relatively influenced by salinity, with factors related to trophic conditions playing an important role as well. Total abundance and biomass decreased along the salinity gradient while increasing at intermediate soluble reactive phosphorous concentrations (SRP) in the former and with a linear increase in the SRP in the latter case. Taxonomic richness decreased with salinity and dissolved inorganic nitrogen, with species replacement toward saline-tolerant ones according to the compositional and optimums analyses. In opposite, functional richness did not display any specific trend within the environmental gradients. This explains why zooplankton compositional changes were not reflected into shifts in the grazing pattern on phytoplankton, which was in turn driven by SRP and dissolved oxygen concentrations. Further research is a critical requirement in these poorly studied ecosystems for planning mitigation actions to the co-occurrence of eutrophication and salinization in a fast changing world.

Effects of bifenthrin on microcrustaceans grazing behavior on a phytoplankton assemblage dominated by Cyanobacteria.

Insecticides are widely used for pest control and frequently reach aquatic systems, imposing a risk to the biota. In this work, the effect of environmental concentrations of bifenthrin on the grazing capacity of Simocephalus vetulus (Cladocera) and Argyrodiaptomus falcifer (Copepoda) on phytoplankton was evaluated. Fifteen microcrustacean individuals and a natural phytoplankton assemblage dominated by Cyanobacteria were exposed during 46 h to three concentrations of bifenthrin (C0 0 µg L-1, C1 0.02 µg L-1, and C2 0.05 µg L-1). A significant decrease in both microcrustaceans grazing rates on total phytoplankton was observed in C2 compared to C0 and C1. The filtration rate (ml ind-1 h-1) of S. vetulus decreased significantly for the cyanobacteria Anabaenopsis arnoldii, Dolichospermum circinale, and Glaucospira sp. in C2 compared to C0 and C1. The ingestion rate (org ind-1 h-1) of A. falcifer decreased significantly in C1 and C2 compared to C0 only for A. arnoldii. Regarding phytoplankton morphological groups, the filtration rate of S. vetulus decreased in C1 and C2 compared to C0 for Colonies and Coenobiums in C2 concerning C0 and C1 for Filaments and in C2 compared to C0 for Silicified. For A. falcifer, the ingestion rate was reduced in C2 compared to C0 for Silicified, Flagellated, and Sessile. The results showed that bifenthrin affected both microcrustaceans grazing capacity on phytoplankton, especially at the highest insecticide concentration.

Nanosilica size-dependent toxicity in Ceriodaphnia reticulata (Cladocera).

Silica nanoparticles (SiNP) are the most produced nanomaterials due to their variety of applications. When released to environments, surface water bodies are their main final sink. SiNP toxicity is still inconclusive and may vary according to particle properties such as their size. We analyzed the size-related effects of SiNP (22 and 244 nm) on mortality, life history traits, and oxidative stress in the cladoceran Ceriodaphnia reticulata. The smaller SiNP (LC5072 h: 105.5 µg/ml) were more lethal than the larger ones (LC5072 h >500 µg/ml). The 22 nm-sized SiNP decreased the number of molts and neonates, increased superoxide dismutase and inhibited glutathione S-transferase activities, while larger SiNP did not exert substantial effects on the organisms at the tested concentrations. In conclusion, SiNP toxicity depended on their size, and this information should be considered for regulatory purposes and to the development of safe-by-design nanoproducts to ultimately guarantee the environment protection.

Ivermectin bioaccumulation and transfer through developmental stages in Culex pipiens (Diptera: Culicidae).

Ivermectin (IVM), one of the most widely used antiparasitics in livestock, could enters into the aquatic environment because the treated animal metabolizes only a small percentage of what is administered and the rest is eliminated through the feces, largely as a parent drug, imposing a risk to aquatic organisms. The aims of this study were to (1) assess the effect of IVM spiked in cattle dung on the survival and emergence of Culex pipiens (Diptera: Culicidae), and to (2) evaluate the accumulation of this drug in the different developmental stages of this taxon. Larvae were exposed to two IVM concentrations (T1: 1000 ng g-1 and T2: 500 ng g-1) for 9 days. At days 3, 6 and 9 survival and adult emergence were recorded and samples of larvae, pupae, pupal exuviae and adults were taken to analyze the IVM accumulation. At these concentrations, a reduction in survival and adult emergence of C. pipiens was recorded. In addition, the IVM accumulation was observed in all samples analyzed, decreasing it throughout the development of this taxon (larvae > pupae > adults). Although a large proportion of the drug was lost during the metamorphosis, being mainly eliminated through pupal exuviae during molting, this process is not enough to eliminate it completely. Thus, part of the drug was transferred to the adult stage and remains available to the aquatic and terrestrial food webs. These results show that IVM represents a risk to aquatic invertebrates and their predators, which deserves further studies, especially in the context of their bioaccumulation and biomagnification through the aquatic and terrestrial trophic webs.

Ecotoxicity of nanosilver on cladocerans and the role of algae provision.

Silver nanoparticles (AgNPs) are applied in diverse industries due to their biocide and physicochemical properties; therefore, they can be released into aquatic systems, interact with environmental factors, and ultimately exert adverse effects on the biota. We analyzed AgNPs effects on Ceriodaphnia reticulata (Cladocera) through mortality and life-history traits, considering the influence of food (Tetradesmus obliquus, Chlorophyceae) presence and concentration. C. reticulata was exposed to AgNPs in acute (absence and two algae concentrations plus five AgNPs treatments) and chronic assays (two algae concentrations plus three AgNPs treatments). AgNPs did not affect algae flocculation but increased Ag+ release, being these ions less toxic than AgNPs (as proved by the exposure to AgNO3). A reduction in AgNPs acute toxicity was observed when algae concentration increased. Acute AgNP exposure decreased C. reticulata body size and heart rate. The chronic AgNP exposure reduced C. reticulata molt number, growth, heart rate, and neonate size:number ratio, being these effects mitigated at the highest algae concentration. Increases in relative size and number of neonates were observed in AgNP treatments suggesting energy trade off. The increased Ag+ release with food presence suggests that the AgNP-algae interaction might be responsible of the decreased toxicity. Although algae reduced AgNP toxicity, they still exerted adverse effects on C. reticulata below predicted environmental concentrations. Since algae presence reduces AgNP effects but increases Ag+ release, studies should be continued to provide evidence on their toxicity to other organisms.

Effects of glyphosate on cladocera: A synthetic review.

Glyphosate [N-(phosphonomethyl) glycine] is currently the most widely used herbicide worldwide. Its application in agricultural and urban areas can lead to the dispersion and arrival to aquatic systems causing environmental deterioration with detrimental effects on the inhabiting biota. This is triggered not only by the herbicide per se but also its metabolite aminomethyl-phosphonic acid (AMPA), which can be highly toxic to many aquatic organisms. Water fleas are some of the key components in aquatic food webs, being one of the most sensitive groups to pollutants. Although being often used in standardized toxicity tests, they are comparatively less studied in relation to glyphosate exposition. Here we examine the current scientific literature regarding the acute and sublethal toxicity of glyphosate in the Cladocera taxonomic group, with special comparisons between the active ingredient (A.I) and formulations. Our results document a high variation in the lethal concentrations reported for different cladoceran species, due to the high diversity of products used in the toxicity tests. Most articles accounting for sublethal effects were performed on the standard Daphnia magna species. Reproduction, including decreased fecundity and delayed age of first reproduction, is usually one of the most severely affected individual traits. Although still scarce, studies documenting metabolic and genetic alterations might provide accurate information on the mechanisms of action of the herbicide.

Effect of rainfall runoff from agricultural areas and seasonal crop practices on zooplankton community in Pampean streams, Argentina.

Extreme climatic events are considered one of the main consequences of climate change. In the Pampas region, Argentina, an intensification of rainfall is expected during the periods of maximum agrochemical application. This study assesses the main factors determining the zooplankton community attributes in three streams belonging to the agricultural Pampas region, Argentina, and the effect of rainfall and seasonal crop practices on the zooplankton community composition. Sampling campaigns were performed before and after three rainfall events during two seasonal crop practices: (1) soybean chemical fallow-sowing and corn vegetative growth-flowering, (2) soybean vegetative growth-grain filling and corn sowing. The runoff in agricultural areas affected the zooplankton community attributes and composition. The biological oxygen demand, turbidity, and conductivity were the main water quality variables affecting the zooplankton community attributes. The increase of these variables after rainfall or during pre-emergence crop practices favoured the zooplankton groups most tolerant to eutrophication such as Bdelloidea, Chydoridae, Moinidae, and Sididae. Factors such as rainfall and seasonal crop practices must be considered in environmental monitoring design.

Metallic, metal oxide, and metalloid nanoparticles toxic effects on freshwater microcrustaceans: An update and basis for the use of new test species.

In this article, we performed a literature review on the metallic, metal oxide, and metalloid nanoparticles (NP) effects on freshwater microcrustaceans, specifically focusing on (i) the main factors influencing the NP toxicity and (ii) their main ecotoxicological effects. Also, given that most studies are currently developed on the standard test species Daphnia magna Straus, we analyzed (iii) the potential differences in the biological responses between D. magna and other freshwater microcrustacean, and (iv) the ecological implications of considering only D. magna as surrogate of other microcrustaceans. We found that NP effects on microcrustaceans depended on their intrinsic properties as well as the exposure conditions. Among the general responses to different NP, we identified body burial, feeding inhibition, biochemical effects, metabolic changes, and reproductive and behavioral alterations. The differences in the biological responses between D. magna and other freshwater microcrustacean rely on the morphology (size and shape), ecological traits (feeding mechanisms, life cycles), and intrinsic sensitivities. Thus, we strongly recommend the use of microcrustaceans species with different morphological, physiological, and ecological characteristics in future ecotoxicity tests with NP to provide relevant information with regulation purposes regarding the discharge of NP into aquatic environments. PRACTITIONER POINTS: Nanoparticles effects depend on intrinsic and external factors. Nanoparticles affect the morphology, physiology, and behavior. Effects on Daphnia differ from other microcrustaceans. The use of more diverse test species is suggested.

Influence of rainfall and seasonal crop practices on nutrient and pesticide runoff from soybean dominated agricultural areas in Pampean streams, Argentina.

An increase in the spatial variability of rainfall is expected due to climate change. This implies increasing rainfall rates during spring and summer in the Pampas region, Argentina, period of maximum application of agrochemicals, which might cause an increase in pesticides and nutrients carried to surface water systems, as runoff by rainfall is one of the main pathways for diffuse pollution. The crops phenological stage can also affect pesticide and nutrient runoff since the applied agrochemicals and soil cover differ in each stage. In this study, we assessed the influence of rainfall and seasonal crop practices on water quality (nutrient and pesticide concentrations) in three streams in the Pampas region, Argentina. Five sampling campaigns were performed before and after three rainfall events during two different seasons of crop practices (SCP1, SCP2) and the physicochemical characteristics of the stream and runoff water were analyzed. The pesticide concentrations in the streams presented a general increase immediately after the rainfall event. Water quality was also affected, as an increase in ammonium, soluble reactive phosphorus (SRP), biological oxygen demand (BOD), and turbidity was observed. The crops phenological stage influenced pesticide and nutrient types and concentrations detected in the streams. During SCP1, mainly characterized by chemical fallow and sowing of soybean and vegetative growth and flowering of corn, ammonium, SRP, BOD, turbidity, and some pesticides, such as metolachlor, showed significantly higher results than those found in SCP2 (grain filling and vegetative growth of soybean and corn sowing). The pesticide concentrations detected in runoff water depended mostly on the pesticide solubility, the lateral slope of the streams, and the percentage of woody riparian vegetation cover. The results obtained show the relevance of assessing the influence of rainfall and crops phenological stages on the dynamics of surface water and on pesticide and nutrient runoff for environmental monitoring.

Synergy between glyphosate and cypermethrin formulations on zooplankton: evidences from a single-specie test and a community mesocosm experiment.

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.

Responses of stream zooplankton diversity metrics to eutrophication and temporal environmental variability in agricultural catchments.

Eutrophication of rivers and streams in agricultural lands is one of the main threats for biodiversity and ecosystem functions. This study was focused on seven subtropical streams where agriculture is the predominant land use. We tested the hypothesis that (i) eutrophication causes a decrease in taxonomic and functional diversity of zooplankton, leading to potential consequences for the ecosystem integrity. Furthermore, given that the temporal variability in the environmental conditions of each stream may influence the species sorting mechanisms, we also hypothesized that (ii) streams with higher temporal environmental variability have greater taxonomic and functional alpha (α) and temporal beta (ßt) diversity measures regardless of the trophic state. Thus, we characterized the streams according to their trophic state and analyzed the zooplankton composition, α and ßt by using taxonomic and functional perspectives. We found differences in the zooplankton composition between mesotrophic and eutrophic streams. However, eutrophic streams supported similar taxonomic and functional α diversity and similar taxonomic ßt diversity to mesotrophic ones. These results were mainly explained by the occurrence of rare species occupying different temporal niches in eutrophic systems. On the contrary, functional ßt diversity was lower in the eutrophic streams, being nestedness the ecological mechanisms underlying the variability in the zooplankton functional groups. Streams with higher temporal environmental variability supported greater α taxonomic diversity. However, the ßt diversity metrics showed no correlation with the environmental variability, suggesting that the environmental filters of the studied systems were the overriding determinants of species turnover. Our study suggests that both taxonomic and functional perspectives should be considered to improve our knowledge on the biotic responses to environmental changes. Also, among all metrics analyzed on the zooplankton community, functional ßt diversity was the most sensitive indicator of the eutrophication impact.

Interactive effects of fish predation and sublethal insecticide concentrations on freshwater zooplankton communities.

Stresses imposed by insecticides and predators are possibly the most rigorous filters to which aquatic organisms are exposed in rivers and lakes associated with agricultural lands. However, their interactive effects on zooplankton communities are still unclear. This study elucidated the zooplankton community response to fish predation, the insecticide chlorpyrifos (CLP), and a combination of both factors, using a 30-day mesocosm experiment. The zooplankton assemblage was influenced by fish presence prior to CLP toxicity. Fish predation reduced microcrustacean density leading to a community dominated by microzooplankton (i.e.: rotifers and copepod nauplii). CLP decreased the species richness in treatments with and without fish, yielding an increase in the abundance of bdelloid rotifers, in the genera Lepadella and Trichocerca. The zooplankton:phytoplankton (<20 µm) ratio decreased substantially when the two stressors, fish predation and insecticide toxicity, were combined. Although CLP dissipated relatively rapidly in the aqueous phase and accumulated in sediment and fish tissue, zooplankton richness was unable to recover. A possible explanation for this could be the inhibitory effect of CLP on resting stage hatchings in the sediment. Therefore, the combined effects of fish predation and CLP might influence zooplankton richness, leading to an assemblage dominated by rotifers that appeared to be resistant to both factors, with a limited capability to control phytoplankton growth. Thus, the effects of natural and anthropogenic stressors should be considered together when assessing community dynamics in aquatic ecosystems.

Effects of a glyphosate-based herbicide on the development and biochemical biomarkers of the freshwater copepod Notodiaptomus carteri (Lowndes, 1934).

In this work we analyzed the effects of Sulfosato Touchdown®, a glyphosate-based herbicide, on the ontogenic development and biochemical markers of the freshwater copepod Notodiaptomus carteri. A 30-days life-cycle experiment was carried out with three different glyphosate concentrations (0, 0.38, and 0.81 mg L-1) to analyze the developmental time from nauplii to adult copepods and their individual growth. An additional 10-days experiment with the same glyphosate concentrations was designed to evaluate the energy reserves (glycogen, proteins and lipids) and the activity of three antioxidant enzymes, superoxide dismutase (SOD), catalase, and glutathione-S-transferase (GST) in adult copepods, separately for females and males. We found that the lowest glyphosate concentration increased the nauplii and total development time. The highest glyphosate concentration prevented copepods from reaching the adult stage, inhibited the growth of the first copepodite stage and increased the GST and SOD activity in adult females. According to our results, the presence of this herbicide in freshwater systems could impose a risk in the ecological role of copepods in nature. This study will contribute to propose the Notodiaptomus genus as model specie for monitoring purposes in the Neotropical aquatic systems.

Disruption of the hatching dynamics of zooplankton egg banks due to glyphosate application.

Hatching rhythms of eggs banks are important processes because they favor species co-existence and promote resilience of ecosystems after natural disturbances. Anthropogenic stressors can disrupt such natural hatching dynamics. This work examines the effects of concentrations ranging from 1 to 8 mg l-1 of a commercial glyphosate-based formulation (Sulfosato Touchdown®) on the hatching dynamics of zooplankton dormant stages, present in the sediment of a natural lake. Sediment samples were collected from the surface sediment (<10 cm deep) of an isolated shallow lake free from pesticide pollution. An ex situ emergence assessment method was carried out and four treatments plus one control (without pesticide) were performed with three replicate each. Zooplankton hatching from the resting stages was monitored during 30 days. In total, 30 zooplankton taxa were recognized. The species diversity decreased significantly at concentration above 2.7 mg l-1 glyphosate. The proportion of cladocerans within hatchling organisms decreased, while that of rotifers Bdelloidea increased in all treatments with glyphosate. Time of the first hatching (TFH), time of maximum hatching (TMH) and the frequency of hatchings (FH) of most zooplankton species were also altered. In conclusion, the application of a glyphosate-based pesticide selectively affected the hatching dynamic of zooplankton egg banks, which suggest that these resting structures are highly sensitive to the toxicity of the pesticide.

Predator-prey imbalances due to a pesticide: density and applicability timing as determining factors for experimental assessments.

Predator-prey relationships are determining factors in sustaining community structure but xenobiotics, including pesticides, have the potential to alter them, causing imbalances at the ecosystem level. Although invertebrate predation on zooplankton is of high importance in shallow lakes, there is still little information regarding disturbances on this trophic interaction. This work assessed the potential effects of a chlorpyrifos-based pesticide (CLP) on the interaction between prawns Macrobrachium borellii and cladocerans Ceriodaphnia dubia, taking into account prey densities, specific time of exposure and contamination level. The analysis was focused on the specific sensitivity of both species and, especially, on the predation rate of M. borellii on C. dubia. The latter was evaluated through different treatments that combined predator and/or prey exposure to the insecticide, before (lapse of 12 h) or during the interaction. Under low prey density, when prawns were previously exposed to the insecticide, their consumption rate was lower than that of controls. Conversely, when cladocerans or both species were previously exposed, the prawns' feeding rate was higher. Under high prey density, there were no substantial differences among treatments. Comparatively, cladocerans were significantly more consumed when the exposure of both species was performed before rather than during the interaction. From the results obtained, it can be assumed that the trophic interaction under study is sensitive to CLP and that individual density and specific time of exposure are important variables to be considered in similar studies in order to obtain realistic results.

Infodisruptions in predator-prey interactions: xenobiotics alter microcrustaceans responses to fish infochemicals.

Chemical communication is one of the most important ecological phenomena promoting the maintenance of ecosystem dynamics. In predator-prey interactions, mediation signals allow prey to detect their predators and can be crucial in the process of avoiding them. Since organisms in many natural waterbodies are often subjected to anthropogenic stressors, it is hypothesised that low concentrations of xenobiotic compounds can disturb this chemical communication, acting as infodisruptors. This study analyzes whether two anthropogenic pollutants (chromium and an insecticide) interfere in two freshwater predator-prey interactions, by altering the behavioural responses of a cladoceran and a copepod species to a fish chemical cue. The concentrations tested were lower than those considered innocuous under international water quality guidelines, and two types of behaviour were analysed: escape ability and depth selection in an artificial water column. Both species tested demonstrated a higher escape ability when exposed to the cue than when they were not exposed. Xenobiotics modified the responses of the copepod in opposite ways: chromium inhibited this behaviour and the insecticide prompted a higher than expected level of escape ability. The depth selection patterns were different between N. conifer and C. dubia. Fish kairomones did not modify them, however chromium and the insecticide caused important alterations in both cases. Such disruptions would be detrimental to the organisms' life cycle trajectories, which, in natural systems, would cause longterm damage in trophic structure and in evolutionary processes.

Exposure to sublethal chromium and endosulfan alter the diel vertical migration (DVM) in freshwater zooplankton crustaceans.

Among zooplankton behaviors, diel migrations constitute one of the most effective predator avoidance strategy and confer metabolic and demographic advantages. We aim to examine whether sublethal concentrations of two widespread pollutants (a pesticide with endosulfan and chromium as potassium dichromate) alter the depth selection, vertical migration and grouping of five freshwater species: Argyrodiaptomus falcifer, Notodiaptomus conifer, Pseudosida variabilis, Ceriodaphnia dubia and Daphnia magna. In a series of experimental assays, performed with 150 cm length transparent tubes, we analyzed the ascents and descents movements through periods of 24 h. Among controls, the copepods showed a tendency to remain closest to the surface, however, N. conifer registered a downward movement of 18.14 cm between 06:00 and 12:00. The cladoceran P. variabilis occupied the deeper position (85 cm), C. dubia showed a tendency to hike to the surface at 06:00 (57.7 cm) descending to lower levels at 18:00. D. magna showed a constant movement of ascent between 00:00 and 18:00, making an average travel of 29.4 cm. When subjected to pollutants, these behaviors were altered. It is hypothesized that a reduction in swimming activity and disorientation would be the main cause of such alterations. The high sensitivity of this endpoint sugests it to be adecuate as a complement in future standard toxicity tests.

Microcrustaceans escape behavior as an early bioindicator of copper, chromium and endosulfan toxicity.

The purpose of this work was to experimentally analyze the impact of copper, chromium and a commercial pesticide with endosulfan on the escape behavior of two copepods (Notodiaptomus conifer, Argyrodiaptomus falcifer) and three cladocerans (Daphnia magna, Pseudosida variabilis and Ceriodaphnia dubia). The experimental assays were carried out using a novel hydraulic devise designed to mimic three-speed predator capture behavior. Two concentrations, one "high" and one "low", were employed and the exposure time was 15 (±5) minutes. With two exceptions, the species exposed to heavy metals manifested higher ability to escape than controls. Both concentrations of the pesticide reduced the escape ability of cladocerans but copepods responded, in general, in a similar manner as for heavy metals. The immediate apparent advantage of low and early toxic effects is discussed and the high sensitivity of the escape behavior suggests that it could be a complementary endpoint to be used in future ecotoxicological tests.