Interactive effects of xenobiotic, abiotic and biotic stressors on Daphnia pulex--results from a multiple stressor experiment with a fractional multifactorial design

First insight of the intergenerational effects of tri-n-butyl phosphate and polystyrene microplastics to Daphnia magna

As an emerging organic pollutant, tributyl phosphate (TnBP) can be easily adsorbed by microplastics, resulting in compound toxic effects. In the present work, the effects of polystyrene microplastics (PS-MPs) and TnBP on the survival, growth, reproduction and oxidative stress of Daphnia magna (D. magna) have been evaluated through multigenerational test. Compared with the alone exposure groups, the somatic growth rate and the expression values of growth related genes rpa1, mre11, rnha, and rfc3_5 in the F1 generation of the combined exposure groups were significantly lower (p < 0.05), indicating synergistic effect of PS-MPs and TnBP on the growth toxicity and transgenerational effects. In addition, compared with the PS-MPs groups, significantly lower average number of offspring and expression values of reproduction related genes ccnb, mcm2, sgrap, and ptch1 were observed in the combined exposure group and TnBP group (p < 0.05), indicating TnBP might be the major factor causing reproductive toxicity to D. magna. Although PS-MPs and TnBP alone or in combination also had toxic impacts on the growth, survival and reproduction of D. magna in generations F0 and F2, the effects were less than F1 generation. Regarding oxidative stress, the activity of SOD, CAT and GSH-Px and MDA content in the generations F0 and F1 of combined exposure groups were higher than the TnBP group but lower than the PS-MPs groups, suggesting that PS-MPs might be the dominant cause of the oxidative damage in D. magna and the presence of TnBP would alleviate oxidative stress by reducing the bioaccumulation of PS-MPs. The present work will provide a theoretical basis for further understanding of the toxic effects and ecological risks of combined TnBP and microplastic pollution on aquatic organisms.

Chronic toxicity of diclofenac, carbamazepine and their mixture to Daphnia magna: a comparative two-generational study

The chronic toxicity of diclofenac (DCF) and carbamazepine (CBZ) as separate substances and in conjunction with their mixture on Daphnia magna was assessed in the parental (F0) and first filial (F1) generations. The second (F1-B2) and fifth (F1-B5) broods of F1 offspring were investigated and compared. Both drugs and their mixture were exposed to each generation of Daphnia magna for 21 days with life history, behavioural and gene expressions as measured endpoints. After the parental exposure, offspring from these two broods were transferred to a clean medium for a 21-day recovery. Exposure to diclofenac, carbamazepine and their mixture significantly inhibited growth, reproduction, swimming activities, heart rate, thoracic limb activities, reproductive and antioxidant-related genes in the parental as well as the first filial generations. These effects were relatively greater in the F1 generation. This indicates that Daphnia magna's sensitivity improved while its fitness declined over the two generations, which is an indicator of greater energy requirements for maintenance. Besides, the significant inhibition in the antioxidant-related genes implies that oxidative stress occurred in Daphnia magna under the exposure to these drugs. The significant reduction in the reproductive output, moulting frequency and cyp314 gene expression as a result of exposure to CBZ simultaneously obtained herein may indicate that this drug could act as an endocrine disruptor. Most of these significant effects were not recoverable after the 21-day recovery period. The findings reported herein highlight the necessity to include maternal effects in environmental risk assessment processes, considering that pollutant effects are underestimated during single-generational exposure.

Beef cattle feedlot surface water containing multi-class agrochemicals elicits physiological and behavioral responses among Daphnia pulex

Despite increasing public concern about air and water pollution risks posed by concentrated animal feeding operation areas (CAFOs), there is little information about bioavailability and ecosystem impacts of agrochemicals used to increase productivity. In this study, we investigated the toxicity of wastewaters originating from beef cattle feeding operation on Daphnia pulex. Specifically, we assessed lethal and chronic sublethal exposure effects using various endpoints including survival, oxygen consumption, morphology, reproduction, and swimming behavior. Exposure assessments (acute and chronic) were performed with ten (10) surface water samples collected from on-site retention ponds designated as A, B, C, D, E, F, G, H, I, and R (reference site). Surface water samples were diluted to yield five concentrations (stock, 1 × , 2 × , 3 × , and 4 ×) as treatments and deionized water was used as control. Results showed site-specific and concentration-related effects on toxicity endpoints. Among treatments, significant (p < 0.05) increase in mortality rate (for A, E, F, and H) and decreasing total body length and width (for B, C, D, and G) of D. pulex were observed with increasing wastewater concentration. However, treatments did not have significant effect on swimming behavior (average speed) after exposure to the wastewater samples from all sites except for site E. Evidence from this study suggested that surface waters near beef cattle feed yards affected physiological responses in D. pulex and therefore may similarly affect organisms in the surrounding aquatic ecosystems.

Climate change impacts on pollutants mobilization and interactive effects of climate change and pollutants on toxicity and bioaccumulation of pollutants in estuarine and marine biota and linkage to seafood security

This article provides an overview of the impacts of climate change stressors (temperature, ocean acidification, sea-level rise, and hypoxia) on estuarine and marine biota (algae, crustaceans, molluscs, corals, and fish). It also assessed possible/likely interactive impacts (combined impacts of climate change stressors and pollutants) on pollutants mobilization, pollutants toxicity (effects on growth, reproduction, mortality) and pollutants bioaccumulation in estuarine and marine biota. An increase in temperature and extreme events may enhance the release, degradation, transportation, and mobilization of both hydrophobic and hydrophilic pollutants in the estuarine and marine environments. Based on the available pollutants' toxicity trend data and information it reveals that the toxicity of several high-risk pollutants may increase with increasing levels of climate change stressors. It is likely that the interactive effects of climate change and pollutants may enhance the bioaccumulation of pollutants in seafood organisms. There is a paucity of literature relating to realistic interactive effects of climate change and pollutants. Therefore, future research should be directed towards the combined effects of climate change stressors and pollutants on estuarine and marine bota. A sustainable solution for pollution control caused by both greenhouse gas emissions (that cause climate change) and chemical pollutants would be required to safeguard the estuarine and marine biota.

Changes in the Magnitude of the Individual and Combined Effects of Contaminants, Warming, and Predators on Tropical Cladocerans across 11 Generations

A massive challenge in ecotoxicology is assessing how the interaction of contaminants, climate change, and biotic stressors shapes the structure and functions of natural populations. Furthermore, it is not known whether contemporary evolutionary responses to multiple stressors across multigenerations may alter the interaction of these stressors. To address these issues, we exposed Moina dubia to lead (Pb, 50 μg/L) under two temperatures (25 and 28 °C) with/without predator cues from climbing perch (Anabas testudineus) for 11 generations (F1-F11). We assessed changes in M. dubia fitness, including development time, adult size, lifespan, fecundity, and neonate production. We found strong negative effects of Pb, elevated temperature, and predator cues on the fitness of M. dubia. Strikingly, Pb-induced reduction in the performance of M. dubia was stronger at 25 °C and in the absence of predator cues. The individual and interactive effects of Pb, temperature, and predator cues on M. dubia were stronger across F1-F9 and generally leveled off in F10-F11. Our results highlight the high vulnerability of M. dubia to multiple stressors, thus weakening top-down control on algal blooms in eutrophic lakes. Our study underscores the importance of integrating evolutionary responses in realistic ecotoxicological risk assessments of contaminants interacting with climatic and biotic stressors.

Laboratory-to-field extrapolation: Increase in carbamazepine toxicity in a higher tier, multiple-stress experiment

The toxicity and environmental risk of chemicals, such as the antiepileptic drug carbamazepine (CBZ), is commonly assessed using standardized laboratory tests and laboratory-to-field extrapolation. To investigate the toxicity of CBZ to aquatic key organisms in a more complex and environmentally relevant scenario, we conducted a 32-day multiple-stress experiment in artificial indoor streams. We exposed the non-biting midge Chironomus riparius, the blackworm Lumbriculus variegatus, and the New Zealand mud snail Potamopyrgus antipodarum to 80 and 400 μg CBZ/L in six artificial indoor streams. In addition to hydraulic stress, species' interaction, and low organic content in the sediment, organisms were co-exposed to the herbicide terbutryn (TBY) as a second chemical stressor at a concentration of 6 μg/L. The exposure to CBZ under multiple stress conditions resulted in a 10- to more than 25-fold higher toxicity in C. riparius and P. antipodarum when compared to a previous, standardized laboratory experiment. The co-exposure to TBY enhanced the adverse effects of CBZ on snails (reduced production of embryos). This effect was additive as the single exposure to TBY also reduced the reproduction of snails, most likely through the reduction of biofilm biomass. The emergence of C. riparius declined at a CBZ concentration of 400 μg/L (without the co-exposure to TBY) and at 80 μg/L in combination with TBY. The difference in sensitivity between laboratory and indoor stream experiments is indicative of a potential underestimation of risk when toxicity data are extrapolated to field conditions. The present results suggest the inclusion of non-chemical and chemical stressors in environmental hazard and risk assessments.

Aquatic mesocosms exposed to a fungicide in warm and cold temperate European climate zones: Long-term macroinvertebrate response

At present, the European Union legislation facilitates the use of similar pesticides among European Member States, thereby assuming that biodiversity and ecosystems have equal sensitivities to contaminants throughout the whole of Europe. However, with this assumption, fundamental environmental and biological differences between climatic zones are being ignored in Environmental Risk Assessment. Such differences may strongly influence the behaviour of contaminants, their effects on biodiversity and on the natural functioning of ecosystems. Furthermore, toxicity testing in European ecoregions other than cold-temperate has largely depended on standardized tests using cold-temperate species and conditions, which may lead to a false estimation of risks to organisms from other ecoregions. The present study aim was to determine the response of freshwater macroinvertebrate communities to the fungicide pyrimethanil by conducting aquatic mesocosm experiments in two different ecoregions with different climates: cold-temperate (Frankfurt, Germany) and warm-temperate (Coimbra, Portugal). The results indicate that the community in the cold-temperate climate was more sensitive to the fungicide in comparison to the warm-temperate community. This difference was most likely related to a different rate of fungicide disappearance, which was slower in the colder climate. Based upon our results we discuss important implications for improving Environmental Risk Assessment across climate zones and under present-day global climate change scenarios.

Toward Sustainable Environmental Quality: Priority Research Questions for North America

Anticipating, identifying, and prioritizing strategic needs represent essential activities by research organizations. Decided benefits emerge when these pursuits engage globally important environment and health goals, including the United Nations Sustainable Development Goals. To this end, horizon scanning efforts can facilitate identification of specific research needs to address grand challenges. We report and discuss 40 priority research questions following engagement of scientists and engineers in North America. These timely questions identify the importance of stimulating innovation and developing new methods, tools, and concepts in environmental chemistry and toxicology to improve assessment and management of chemical contaminants and other diverse environmental stressors. Grand challenges to achieving sustainable management of the environment are becoming increasingly complex and structured by global megatrends, which collectively challenge existing sustainable environmental quality efforts. Transdisciplinary, systems-based approaches will be required to define and avoid adverse biological effects across temporal and spatial gradients. Similarly, coordinated research activities among organizations within and among countries are necessary to address the priority research needs reported here. Acquiring answers to these 40 research questions will not be trivial, but doing so promises to advance sustainable environmental quality in the 21st century. Environ Toxicol Chem 2019;38:1606-1624. © 2019 The Authors. Environmental Toxicology and Chemistry published by Wiley Periodicals, Inc. on behalf of SETAC.

Long-term effects of the fungicide pyrimethanil on aquatic primary producers in macrophyte-dominated outdoor mesocosms in two European ecoregions

Even though empirical data supporting sound ecoregion-specific ecotoxicological evaluations are still scarce, the differences of environmental (including climatic) conditions in specific ecoregions are already currently being regulated for environmental risk assessment of pesticides in Europe. To shed new light on the ecotoxicological effects of pesticides on aquatic communities across ecoregions, the model pollutant pyrimethanil (fungicide) was tested in an outdoor mesocosm study with macrophyte-dominated communities in the European "South" (Portugal) and "Centre" (Germany) regulatory zones. Phytoplankton indicators monitored over 12 months indicated a low risk of the fungicide (0.73 or 0.77 mg pyrimethanil L^-1, single application) to phytoplankton functioning; as expected since exposure simulated worst-case scenarios. However, the growth of key structural macroalgae and macrophytes was affected by the fungicide and negative effects occurred, especially in the Central zone experiment. Such effects were not detected earlier than approximately nine months post single pyrimethanil application. The presence or absence of such extremely long-lasting/delayed pyrimethanil effects depended on species, competitive situation, and ecoregion-specific physico-chemical environment. The present findings suggest that a better understanding of both direct and indirect effects of fungicide pollution on aquatic flora in two European ecoregions helps to consolidate the environmental risk assessment of pesticides in specific regulatory zones.

Comparison of lipid peroxidation and catalase response in invasive dreissenid mussels exposed to single and multiple stressors

Dreissenid mussels Dreissena bugensis (quagga mussel) and Dreissena polymorpha (zebra mussel) are prolific invasive species to the freshwaters of the United States and Western Europe. In the Great Lakes, D. polymorpha has initially dominated the system since its invasion in the mid-1980s; however, recently D. bugensis has displaced D. polymorpha as the dominant species. Dreissena bugensis has several competitive advantages over D. polymorpha, including greater tolerances to deeper and colder waters and lower respiration rates. Nevertheless, physiological differences between the species remain largely unknown. The oxidative stress response is a mechanism used by all organisms to mitigate environmental stress by reducing oxygen radicals in the body, and comparing this mechanism between similar species can be useful for understanding how different species compete in aquatic environments. We compared oxidative stress biomarkers (lipid peroxidation [LPO] and catalase [CAT] activity) in mussels after exposure to 4 stressors (i.e., high densities, temperature, hypoxia, and polychlorinated biphenyls [PCBs]) independently and in combinations of 2 stressors. Overall, D. bugensis had lower LPO and CAT activity than D. polymorpha when exposed to single stressors; however, in multiple stressor treatments D. bugensis had increased LPO, especially with high temperatures and PCBs. The lower lipid damage in D. bugensis compared with D. polymorpha under single stressor conditions may come at the cost of the ability to respond to multiple stressors. Environ Toxicol Chem 2018;37:1643-1654. © 2018 SETAC.

Effects of Seasonal Changes on the Toxic Impacts of Oil Sands Process-Affected Water on Daphnia magna

Oil sands process-affected water (OSPW), which can be potentially toxic to aquatic biota, is a major by-product of bitumen mining in northern Alberta. The effects of environmental factors on the toxicity of OSPW are understudied. In the present study, the impacts of seasonal changes in water quality on the toxic effects of OSPW (1 and 10%) on Daphnia magna was examined. Animals were chronically exposed to OSPW under conditions that represented water quality of a cold or warm seasonal condition. At each seasonal scenario survival, growth (length and mass) and reproduction of exposed D. magna were investigated. Survival and length of D. magna were only affected by OSPW in the cold-season treatment. Exposure to OSPW reduced the mass of D. magna in both cold and warm season scenarios. Daphnia magna in the cold-season treatment did not reproduce or produce eggs during the course of the experiment. The results of the present study suggest that seasonal changes in water quality may alter the toxicity of OSPW on D. magna.

Temperature modulates the interaction between fungicide pollution and disease: evidence from a Daphnia-microparasitic yeast model

Temperature is expected to modulate the responses of organisms to stress. Here, we aimed to assess the influence of temperature on the interaction between parasitism and fungicide contamination. Specifically, using the cladoceran Daphnia as a model system, we explored the isolated and interactive effects of parasite challenge (yeast Metschnikowia bicuspidata) and exposure to fungicides (copper sulphate and tebuconazole) at two temperatures (17 and 20 °C), in a fully factorial design. Confirming a previous study, M. bicuspidata infection and copper exposure caused independent effects on Daphnia life history, whereas infection was permanently suppressed with tebuconazole exposure. Here, we show that higher temperature generally increased the virulence of the parasite, with the hosts developing signs of infection earlier, reproducing less and dying at an earlier age. These effects were consistent across copper concentrations, whereas the joint effects of temperature (which enhanced the difference between non-infected and infected hosts) and the anti-parasitic action of tebuconazole resulted in a more pronounced parasite × tebuconazole interaction at the higher temperature. Thus, besides independently influencing parasite and contaminant effects, the temperature can act as a modulator of interactions between pollution and disease.

Toxicity of two fungicides in Daphnia: is it always temperature-dependent?

The joint effect of increasing temperature and pollution on aquatic organisms is important to understand and predict, as a combination of stressors might be more noxious when compared to their individual effects. Our goal was to determine the sensitivity of a model organism (Daphnia spp.) to contaminants at increasing temperatures, allowing prior acclimation of the organisms to the different temperatures. Prior to exposure, two Daphnia genotypes (Daphnia longispina species complex) were acclimated to three temperatures (17, 20, and 23 °C). Afterwards, a crossed design was established using different exposure temperatures and a range of concentrations of two common fungicides (tebuconazole and copper). Daphnia life history parameters were analysed in each temperature × toxicant combination for 21 days. Temperature was the most influencing factor: Daphnia reproduced later and had lower fecundity at 17 °C than at 20 and 23 °C. Both copper and tebuconazole also significantly reduced the fecundity and survival of Daphnia at environmentally-relevant concentrations. Temperature-dependence was found for both toxicants, but the response pattern was endpoint- and genotype-specific. The combination of contaminant and high temperature often had severe effects on survival. However, unlike some literature on the subject, our results do not support the theory that increasing temperatures consistently foment increasing reproductive toxicity. The absence of a clear temperature-dependent toxicity pattern may result from the previous acclimation to the temperature regime. However, a proper framework is lacking to compare such studies and to avoid misleading conclusions for climate change scenarios.

Progressive acclimation alters interaction between salinity and temperature in experimental Daphnia populations

Environmental stressors rarely act in isolation, giving rise to interacting environmental change scenarios. However, the impacts of such interactions on natural populations must consider the ability of organisms to adapt to environmental changes. The phenotypic adaptability of a Daphnia galeata clone to temperature rise and salinisation was investigated in this study, by evaluating its halotolerance at two different temperatures, along a short multigenerational acclimation scenario. Daphniids were acclimated to different temperatures (20°C and 25°C) and salinities (0gL(-1) and 1gL(-1), using NaCl as a proxy) in a fully crossed design. The objective was to understand whether acclimation to environmental stress (combinations of temperature and salinity) influenced the response to the latter exposure to these stressors. We hypothesize that acclimation to different temperature×salinity regimes should elicit an acclimation response of daphniids to saline stress or its interaction with temperature. Acute (survival time) and chronic (juvenile growth) halotolerance measures were obtained at discrete timings along the acclimation period (generations F1, F3 and F9). Overall, exposure temperature was the main determinant of the acute and chronic toxicity of NaCl: daphniid sensitivity (measured as the decrease of survival time or juvenile growth) was consistently higher at the highest temperature, irrespective of background conditions. However, this temperature-dependent effect was nullified after nine generations, but only when animals had been acclimated to both stressors (high salinity and high temperature). Such complex interaction scenarios should be taken in consideration in risk assessment practices.

Effects of intra- and interspecific competition on the sensitivity of Daphnia magna populations to the fungicide carbendazim

The ecological risk assessment of pesticides is generally based on toxicity data obtained from single-species laboratory experiments and does not take into account ecological interactions such as competition or predation. Intraspecific and interspecific competition are expected to result in additional stress and might increase the sensitivity of aquatic populations to pesticide contamination. To test this hypothesis, the effects of the fungicide carbendazim were assessed on the population dynamics of the micro-crustacean Daphnia magna under different levels of intraspecific and interspecific competition for an algal food resource, using the rotifer Brachionus calyciflorus as competing species. The experiments were performed in glass jars with three different carbendazim concentrations (i.e., 50, 100 and 150 µg/L), and had a duration of 25 days, with a 4-day pre-treatment period in which competition was allowed to take place and a 21-day exposure period. The endpoints evaluated were D. magna total population abundance and population structure. Results of these experiments show that competition stress on its own had a significant influence on shaping D. magna population's structure, however, a different response was observed in the intraspecific and interspecific competition experiments. The use of a 4-day pre-treatment period in the intraspecific experiment already led to an absence of interactive effects due to the quick abundance confluence between the different intraspecific treatments, thus not allowing the observation of interactive effects between competition and carbendazim stress. Results of the interspecific competition experiment showed that rotifers were quickly outcompeted by D. magna and that D. magna even profited from the rotifer presence through exploitative competition, which alleviated the original stress caused by the algal resource limitation. These experiments suggest that competition interactions play an important role in defining population-level effects of pesticides in a more complex way than was hypothesized ("increasing competition leading to a sensitivity increase"), as the interspecific experiment showed. Therefore, these should be taken into account in the extrapolation of single-species toxicity data to protect higher levels of biological organization.

The use of growth and behavioral endpoints to assess the effects of pesticide mixtures upon aquatic organisms

Aquatic communities are often subject to complex contaminant mixtures, usually at sublethal concentrations, that can cause long-term detrimental effects. Chemicals within mixtures can effectively interact, resulting in synergism, antagonism or additivity. We investigated the tertiary mixture effects of two pyrethroids, lambda-cyhalothrin and permethrin, and the organophosphate chlorpyrifos, evaluating sublethal endpoints; immobility and growth, on Chironomus dilutus in 10-day exposures. We utilized a toxic units (TU) approach, based on median lethal concentrations (LC50) for each compound. The concepts of independent action and concentration addition were used to compare predicted mixture toxicity to observed mixture toxicity. Increased immobility resulted from mixture concentrations ≥1 TU (7.45 ng/L lambda-cyhalothrin × 24.90 ng/L permethrin × 129.70 ng/L chlorpyrifos), and single pesticides concentrations ≥0.25 TU (5.50 ng/L lambda-cyhalothrin, 24.23 ng/L permethrin, 90.92 ng/L chlorpyrifos, respectively). Growth was inhibited by pesticide mixtures ≥0.125 TU (1.04 ng/L lambda-cyhalothrin × 3.15 ng/L permethrin × 15.47 ng/L chlorpyrifos), and singly by lambda-cyhalothrin ≥0.25 TU (5.50 ng/L), and permethrin ≥0.167 TU (18.21 ng/L). The no observed effect concentrations (NOEC) for immobility and growth, for both mixture and single-pyrethroid exposure, were up to 8.0 and 12.0 times respectively lower than the corresponding NOEC for survival. The median effective concentrations (EC50) for growth (mixture and single-pyrethroid exposure) were up to 7.0 times lower than the respective LC50. This study reinforces that the integration of sublethal endpoints in monitoring efforts is powerful in discerning toxic effects that would otherwise be missed by solely utilizing traditional toxicity assessments.

Immediate and mid-term effects of pyrimethanil toxicity on microalgae by simulating an episodic contamination

Since pesticides can represent a threat for non-target aquatic communities, including microalgae, we looked at the effects of the fungicide pyrimethanil on the growth of the freshwater green microalgae Selenastrum capricornutum. Additionally, attenuation of the toxicity of pyrimethanil due to its dissipation in the water was assessed. Pyrimethanil-contaminated samples were taken from outdoor mesocosms one (1.4 mg L(-1) of pyrimethanil) and ten (0.78 mg L(-1) of pyrimethanil) days after pyrimethanil application. Different dilutions were prepared using both nutrient-rich culture medium (LC Oligo) and non-contaminated mesocosm samples, and cell growth inhibition was assessed. Reference mesocosm samples were also diluted with LC Oligo in order to verify how the nutrient concentration in the LC Oligo could improve cell growth. Comparing cell growth of population exposed to pyrimethanil-treated sample taken at day 1 with cells growing in reference sample and LC Oligo, the growth inhibition was 80% (± 6.5) and 95% (± 2.0), respectively. The toxicity of samples taken from contaminated mesocosms at day 10 was attenuated to 34% (± 15) (when compared with reference sample) and 88% (± 3.0) (when compared with LC Oligo), as pyrimethanil concentrations in the mesocosms decreased. In conclusion, (i) pyrimethanil can be an environmental disturber for the microalgae; (ii) the toxicity of pyrimethanil in water was reduced almost 2.4 times (when compared with the reference sample) at as short a period as 10d if assuming that pesticide entrance is not continuous; (iii) toxicity of an environmental sample could be underestimated if the sample/medium used in dilution presents different nutrient levels.

Transgenerational effects of two antidepressants (sertraline and venlafaxine) on Daphnia magna life history traits

The low levels of antidepressants detected in surface waters currently raise concern about their potential long-term risks to nontarget aquatic organisms. We investigated the transgenerational effects of sertraline, a selective serotonin reuptake inhibitor, and venlafaxine, a serotonin-norepinephrine reuptake inhibitor, on the life traits of Daphnia magna over two generations under environmentally realistic concentrations. We also studied the reversibility of the effect using recovery experiments. We assessed daphnid survival, growth, and reproduction over 21 days and evidenced detectable effects of the antidepressants. Sertraline increased the F0-daphnid fecundity whereas it decreased the offspring number of F1-daphnids. Transfer to clean medium caused negative effects on the offspring of daphnids exposed to 0.3 μg L(–1), but improved the fecundity of offspring of daphnids exposed to 100 μg L(–1). Venlafaxine exposure decreased the offspring number of F0-daphnids and resulted in drug tolerance in the F1 generation. Sertraline, unlike venlafaxine, may turn out to be a true environmental threat due to its accumulation in algae and the physiological weakness observed over generations. These effects across generations point out to the need to perform multigeneration tests to assess the environmental risk of pharmaceuticals in nontarget organisms.

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.

Comparative study of non-invasive methods for assessing Daphnia magna embryo toxicity

Embryos, unlike adults, are typically sessile, which allows for an increase in the available metrics that can be used to assess chemical toxicity. We investigate Daphnia magna development rate and oxygen consumption as toxicity metrics and compare them to arrested embryo development using four different techniques with potassium cyanide (KCN) as a common toxicant. The EC50 (95 % CI) for arrested development was 2,535 (1,747-3,677) μg/L KCN. Using pixel intensity changes, recorded with difference imaging, we semi-quantitatively assessed a decrease in development rate at 200 μg/L KCN, threefold lower than the arrested development lowest observed effect concentration (LOEC). Respirometry and self-referencing (SR) microsensors were two unique techniques used to assess oxygen consumption. Using respirometry, an increase in oxygen consumption was found in the 5 μg/L KCN treatment and a decrease for 148 μg/L, but no change was found for the 78 μg/L KCN treatment. Whereas, with SR microsensors, we were able to detect significant changes in oxygen consumption for all three treatments: 5, 78, and 148 μg/L KCN. While SR offered the highest sensitivity, the respirometry platform developed for this study was much easier to use to measure the same endpoint. Oxygen consumption may be subject to change during the development process, meaning consumption assessment techniques may only be useful only for short-term experiments. Development rate was a more sensitive endpoint though was only reliable four of the six embryonic developmental stages examined. Despite being the least sensitive endpoint, arrested embryo development was the only technique capable of assessing the embryos throughout all developmental stages. In conclusion, each metric has advantages and limitations, but because all are non-invasive, it is possible to use any combination of the three.