A Daphnia magna first-brood chronic test: An alternative to the conventional 21-Day chronic bioassay?

Effects of microplastics on key reproductive and biochemical endpoints of the freshwater microcrustacean Daphnia magna

Human activities have directly impacted the environment, causing significant ecological imbalances. From the different contaminants resulting from human activities, plastics are of major environmental concern. Due to their high use and consequent discharge, plastics tend to accumulate in aquatic environments. There, plastics can form smaller particles (microplastics, MPs), due to fragmentation and weathering, which are more prone to interact with aquatic organisms and cause deleterious effects, including at the basis of different food webs. This study assessed the effects of two microplastics (polyethylene terephthalate, PET; and polypropylene, PP; both of common domestic use) in the freshwater cladoceran species Daphnia magna. Toxic effects were assessed by measuring reproductive traits (first brood and total number of offspring), and activities of biomarkers involved in xenobiotic metabolism (phase I: cytochrome P-450 isoenzymes CYP1A1, 1A2 and 3A4; phase II/conjugation: glutathione S-transferases; and antioxidant defense (catalase)). Both MPs showed a potential to significantly reduce reproductive parameters in D. magna. Furthermore, PET caused a significant increase in some isoenzymes of CYP450 in acutely exposed organisms, but this effect was not observed in chronically exposed animals. Similarly, the activity of the antioxidant defense (CAT) was significantly increased in acutely exposed animals, but not in chronically exposed organisms. This pattern of effects suggests a possible mechanism of long-term adaptation to the presence of the tested MPs. In conclusion, the herein tested MPs have shown the potential to induce deleterious effects on D. magna mainly observed in terms of the reproductive outcomes. Changes at the biochemical level seems transient and are not likely to occur in long term, environmentally exposed crustaceans.

Are biopesticides safe for the environment? Effects of pyrethrum extract on the non-target species Daphnia magna

Biopesticides are natural compounds considered more safe and sustainable for the environment. However, it is also important to evaluate the potential risk in non-target organisms. Pyrethrum extract (PE) is a biopesticide, widely used for agriculture, veterinary, and aquaculture. This work aimed to evaluate acute (0.6 - 40.0 µg/L; 96 h; E(L)C₅₀ toxicity) and sub-chronic (0.7 - 1.1 µg/L; 10 d; life-history parameters) effects of PE on Daphnia magna. Moreover, a biomarkers approach using antioxidant and biotransformation capacity, lipid peroxidation (LPO), neurotoxicity, and energy reserves content were evaluated. Acute effects (mortality, changes in swimming behavior, oxidative stress, lipid peroxidation, neurotoxicity) were recorded with the increase in PE concentration. Sub-chronic assay showed an increase in energy reserves content, antioxidant parameters, and LPO demonstrating that PE unbalances oxidative metabolism. This study can conclude that PE potentiates toxic effects in D. magna and demonstrates the vulnerability of a non-target organism to PE that is considered environmentally safe.

Warmer water, high light intensity, lithium and microplastics: Dangerous environmental combinations to zooplankton and Global Health?

Nowadays there is a high concern about the combined effects of global warming and emerging environmental contaminants with significant increasing trends of use, such as lithium (Li) and microplastics (MPs), both on wildlife and human health. Therefore, the effects of high light intensity (26,000 lx) or warmer water temperature (25 °C) on the long-term toxicity of Li and mixtures of Li and MPs (Li-MPs mixtures) were investigated using model populations of the freshwater zooplankton species Daphnia magna. Three 21-day bioassays were done in the laboratory at the following water temperatures and light intensities: (i) 20 °C/10830 lx; (ii) 20 °C/26000 lx (high light intensity); (iii) 25 °C/10830 lx (warmer temperature). Based on the 21-day EC50s on reproduction, high light intensity increased the reproductive toxicity of Li and Li-MPs mixtures by ~1.3 fold; warmer temperature increased the toxicity of Li by ~1.2 fold, and the toxicity of Li-MPs mixtures by ~1.4 fold based on the concentration of Li, and by ~2 fold based on the concentrations of MPs. At high light intensity, Li (0.04 mg/L) and Li-MPs mixtures (0.04 Li + 0.09 MPs mg/L) reduced the population fitness by 32 % and 41 %, respectively. Warmer temperature, Li (0.05 mg/L) and Li-MPs mixtures (0.05 Li + 0.09 MPs mg/L) reduced it by 63 % and 71 %, respectively. At warmer temperature or high light intensity, higher concentrations of Li and Li-MPs mixtures lead to population extinction. Based on the population growth rate and using data of bioassays with MPs alone done simultaneously, Li and MPs interactions were antagonistic or synergistic depending on the scenario. High light intensity and chemical stress generally acted synergistically. Warmer temperature and chemical stress always acted synergistically. These findings highlight the threats of long-term exposure to Li and Li-MPs mixtures to freshwater zooplankton and Global Health in a warmer world.

Endocrine-disrupting potential and toxicological effect of para-phenylphenol on Daphnia magna

Several phenol derivatives are suspected endocrine disruptors and have received attention in risk assessment studies for several decades owing to the structural similarity between estrogens and phenolic compounds. We assessed the endocrine disrupting effect of the phenolic compound para-phenylphenol (PPP) through acute tests and evaluating chronic endpoints in an invertebrate model, Daphnia magna. Exposure of D. magna to PPP induced substantial adverse effects, namely, reduced fecundity, slowed growth rate, delayed first brood, and a reduction in neonate size. Furthermore, we investigated the mRNA expression of relevant genes to elucidate the mechanism of endocrine disruption by PPP. Exposure of D. magna to PPP induced the substantial downregulation of genes and markers related to reproduction and development, such as EcR-A, EcR-B, Jhe, and Vtg. Consequently, we demonstrated that PPP has an endocrine disrupting effect on reproduction and development in D. magna.

Long-term effects of lithium and lithium-microplastic mixtures on the model species Daphnia magna: Toxicological interactions and implications to 'One Health'

Environmental contamination with lithium (Li) and microplastics (MP) has been steadily increasing and this trend is expected to continue in the future. Many freshwater ecosystems, which are crucial to reach the United Nations Sustainable Development Goals, are particularly vulnerable to Li and MP contamination, and other pressures. The long-term effects of Li, either alone or combined with MP (Li-MP mixtures), were investigated using the freshwater zooplankton micro-crustacean Daphnia magna as model species. In the laboratory, D. magna females were exposed for 21 days to water concentrations of Li (0.02, 0.04, 0.08 mg/L) or Li-MP mixtures (0.02 Li + 0.04 MP, 0.04 Li + 0.09 MP mg/L, 0.08 Li + 0.19 MP mg/L). In the range of concentrations tested, Li and Li-MP mixtures caused parental mortality, and decreased the somatic growth (up to 20% and 40% reduction, respectively) and the reproductive success (up to 93% and 90% reduction, respectively). The 21-day EC₅₀s of Li and Li-MP mixtures on D. magna reproduction were 0.039 mg/L and 0.039 Li + 0.086 MP mg/L, respectively. Under exposure to the highest concentration of Li (0.08 mg/L) and Li-MP mixtures (0.08 Li + 0.19 MP mg/L), the mean of D. magna population growth rate was reduced by 67% and 58%, respectively. Based on the population growth rate and using data from a bioassay testing the same concentrations of MP alone and carried simultaneously, the toxicological interaction between Li and MP was antagonism under exposure to the lowest and the highest concentrations of Li-MP mixtures, and synergism under exposure to the medium concentration of Li-MP mixtures. These findings highlight the need of further investigating the combined effects of contaminants, and the threat of long-term environmental contamination with Li and MP to freshwater zooplankton, biodiversity, ecosystem services and 'One Health'.

Long-term adverse effects of microplastics on Daphnia magna reproduction and population growth rate at increased water temperature and light intensity: Combined effects of stressors and interactions

In many ecosystems, the zooplankton community has been pressured simultaneously by microplastic pollution and alterations resulting from global climate changes. The potential influence of light intensity rise (from 10,830 lx to 26,000 lx) and water temperature rise (from 20 °C to 25 °C) on the long term-toxicity of microplastics (MPs) to Daphnia magna were investigated. Three 21-day laboratory bioassays with model MPs (1-5 μm diameter) were carried out at (i) 20 °C/10830 lx, (ii) 20 °C/26000 lx, and (iii) 25 °C/10830 lx. In each bioassay, one control (no MPs) and three MP concentrations (0.04, 0.09, 0.19 mg/L) were tested. In all the bioassays, MPs caused parental and juvenile mortality, and reduced the somatic growth, reproduction and population growth rate. The MP EC₅₀s on living offspring (95% confidence interval within brackets) were 0.146 mg/L (0.142-0.151 mg/L) at 20 °C/10830 lx, 0.102 mg/L (0.099-0.105 mg/L) at 20 °C/26000 lx, and 0.101 mg/L (0.098-0.104 mg/L) at 25 °C/10830 lx. Relatively to the respective control group, 0.19 mg/L of MPs decreased the mean of the population growth rate by 27% at 20 °C/10830 lx, 38% at 20 °C/26000 lx and 59% at 25 °C/10830 lx. Based on the population growth rate and in relation to 20 °C/10830 lx (control, no MPs), the interaction between increased light intensity (26,000 lx) and MPs was synergism (at all the MP concentrations tested). The interaction between water temperature rise (25 °C) and MPs was antagonism at 0.04 mg/L of MPs and synergism at 0.09 and 0.19 mg/L of MPs. In the present scenario of climate changes and global MP pollution such findings raise high concern because zooplankton communities are crucial for aquatic biodiversity conservation, ecosystem functioning and services provided to humans. Further studies on the combined effects of MPs, other common pollutants, and alterations due to climate changes are needed.

Transcriptional response provides insights into the effect of chronic polystyrene nanoplastic exposure on Daphnia pulex

Nanoplastic pollution is widespread and persistent across global water systems and can cause a negative effect on aquatic organisms, especially the zooplankter which is the keystone of the food chain. The present study uses RNA sequencing to assess the global change in gene expression caused by 21 days of exposure to 75 nm polystyrene (PS) nanoplastics on Daphnia pulex, a model organism for ecotoxicity. With the threshold value at P value < 0.05 and fold change >2, 244 differentially expressed genes were obtained. Combined with real-time PCR validation of several selected genes, our results indicated that a distinct expression profile of key genes, including downregulated trehalose transporter, trehalose 6-phosphate synthase/phosphatase, chitinase and cathepsin-L as well as upregulated doublesex 1 and doublesex and mab-3 related transcription factor-like protein, contributed to the toxic effects of chronic nanoplastic exposure on Daphnia, such as slowed growth, subdued reproductive ability and reproductive pattern shifting. Our study also showed that chronic exposure to nanoplastic changed the sex ratio of D. pulex neonates. By integrating the gene expression pattern in an important model organism, this study gained insight into the molecular mechanisms of the toxic effect of chronic PS nanoplastic exposure on D. pulex, which may also extend to other nanoplastics or aquatic animals.

Age-dependent survival, stress defense, and AMPK in Daphnia pulex after short-term exposure to a polystyrene nanoplastic

The widespread occurrence and accumulation of micro- and nanoplastics in aquatic environments has become a growing global concern. Generally, natural aquatic populations are characterized by a variety of multi-structured age groups, for which physiological and biochemical responses typically differ. The freshwater cladoceran, Daphnia pulex, is a model species used extensively in environmental monitoring studies and ecotoxicology testing. Here, the effects of a polystyrene nanoplastic on the physiological changes (i.e., survival) and expression levels of stress defense genes (i.e., those encoding antioxidant-mediated and heat shock proteins) in this freshwater flea were measured. Results from acute bioassays were used to determine the respective nanoplastic LC50 values for five age groups (1-, 4-, 7-, 14- and 21-day-old individuals): the obtained values for the 1- and 21-day-old D. pulex groups were similar (i.e., not significantly different). The expression levels of genes encoding key stress defense enzymes and proteins-SOD, CAT, GST, GPx, HSP70, and HSP90-were influenced by the nanoplastic in all the age groups, but not in the same way for each. Significant differences were observed among all age groups in their expression of the gene encoding the energy-sensing enzyme AMPK (adenosine monophosphate-activated protein kinase) α, β, and γ following exposure to the nanoplastic. Moreover, the expression of AMPK α was significantly increased in the 1-, 7-, and 21-day-old individuals exposed to nanoplastic relative to the control group. Together, these results indicate that age in D. pulex affects the sensitivity of its individuals to pollution from this nanoplastic, primarily via alterations to vital physiological and biochemical processes, such as cellular energy homeostasis and oxidation, which were demonstrated in vivo. We speculate that such age-related effects may extend to other nanoplastics and forms of pollution in D. pulex and perhaps similar marine organisms.

Transgenerational effects and recovery of microplastics exposure in model populations of the freshwater cladoceran Daphnia magna Straus

The environmental contamination by microplastics is a global challenge to ecosystem and human health, and the knowledge on the long-term effects of such particles is limited. Thus, the effects of microplastics and post-exposure recovery were investigated over 4 generations (F₀, F₁, F₂, F₃) using Daphnia magna as model. Effect criteria were parental mortality, growth, several reproductive parameters, and population growth rate. Microplastics exposure (0.1mg/l of pristine polymer microspheres 1-5μm diameter) caused parental mortality (10-100%), and significantly (p≤0.05) decreased growth, reproduction, and population growth rate leading to the extinction of the microplastics-exposed model population in the F₁ generation. Females descending from those exposed to microplastics in F₀ and exposed to clean medium presented some recovery but up to the F₃ generation they still had significantly (p≤0.05) reduced growth, reproduction, and population growth rate. Overall, these results indicate that D. magna recovery from chronic exposure to microplastics may take several generations, and that the continuous exposure over generations to microplastics may cause population extinction. These findings have implications to aquatic ecosystem functioning and services, and raise concern on the long-term animal and human exposure to microplastics through diverse routes.

Toxicological interactions induced by chronic exposure to gold nanoparticles and microplastics mixtures in Daphnia magna

The effects of emerging environmental contaminants on human and environmental health is of high concern, especially those potentially induced by mixtures. The main goal of the present study was to assess the chronic effects of mixtures of citrate stabilized ≈5 nm gold nanoparticles (AuNP) and 1-5μm microplastics (MP) on Daphnia magna. A 21-day bioassay was carried out. The effect criteria were parental mortality, somatic growth and several reproductive parameters. AuNP induced parental mortality, reduced the total offspring and caused immobile juveniles and aborted eggs. MP induced parental mortality, delayed the first brood release, decreased the number of broods released, the total offspring, and caused immobile juveniles. All the mixtures caused higher toxicity than AuNP and MP alone. Based on parental mortality, evidences of antagonism between AuNP and MP were observed at low concentrations of both mixture components, whereas evidences of synergism at high concentrations were found. Chronic (21-day) exposure of D. magna to AuNPs, MP, and their mixtures can impair development, reproduction, ultimately leading to death.

Transgenerational Effects of Toxicants: An Extension of the Daphnia 21-day Chronic Assay?

The assessment of transgenerational effects should be incorporated in standard chronic toxicity protocols for the sake of a realistic extrapolation of contaminant effects to the population level. We propose a simple add-on to the standard 21-day chronic Daphnia magna assay, allowing the assessment of the reproductive performance of the offspring (F₁ generation) born from the first clutch of the parental (F₀) generation. The extended generational assay was performed simultaneously with the standard reproduction assay. With this design, we evaluated the lethal, reproductive, and transgenerational effects of four widespread and extensively used substances: a biocide/anti-fouling (copper sulphate), an industrial oxidizing agent (potassium dichromate), a pharmaceutical (paracetamol), and a quaternary ammonium compound (benzalkonium chloride). Benzalkonium chloride was the most toxic in terms of lethality, whereas paracetamol, copper sulphate, and potassium dichromate caused deleterious effects in the reproductive performance of exposed D. magna. Adverse effects in the fitness of the daughter (F₁) generation were observed in the case of maternal exposure to paracetamol and copper sulphate, although they were not very pronounced. These findings highlight the usefulness of our approach and reinforce the view-shared by other authors-of the need for a generalised formal assessment of the transgenerational effects of pollutants.

Whole-organism and biomarker endpoints in Daphnia magna show uncoupling of oxidative stress and endocrine disruption in phenolic derivatives

During the past century, the amount of chemicals released into water bodies has increased, with particular emphasis being attributed to xenobiotics with endocrine disruption properties and/or pro-oxidant effects. Among these, it is possible to identify a specific chemical class, alkylphenols, which are of widespread use, and include a variety of chemicals with multiple uses. Bisphenol A is an important chemical used in industrial production of plastics, and has been extensively described as an endocrine disruptor. Paracetamol is a pharmaceutical compound used in human medicine, known for its therapeutic action but also for its evident pro-oxidant features. Additionally, previous studies have suggested that paracetamol may also exert endocrine disruption. The main goal of this study was to assess the effects of both paracetamol and bisphenol A as endocrine disruptors, and as promoters of oxidative stress and damage, on the freshwater microcrustacean Daphnia magna. The obtained results showed that bisphenol A was capable of altering population traits of exposed organisms, by impairing molting. On the contrary, paracetamol was not causative of any significant change in this parameter, despite having caused extensive oxidative stress.

Reproductive and developmental toxicity of the herbicide Betanal® Expert and corresponding active ingredients to Daphnia spp

The commercial herbicide formulation Betanal® Expert and its active ingredients (a.i.s) ethofumesate, phenmedipham and desmedipham were focused in this study. Following questions yielding from a previous study, an in-depth analysis of the reproductive toxicity of the pesticide was made. Long-term exposures of Daphnia magna and Daphnia longispina to Betanal® Expert, to each a.i. and to a customised mixture matching the a.i.s ratio within the commercial formulation were carried out, and deleterious effects in the offspring were recorded. This intended to clarify whether (1) the tested compounds induce reproductive injury; (2) there is interspecific variation in daphnids tolerance to the compounds; (3) there is an interaction between chemicals in combined treatments; and (4) the so-called inert ingredients added to the commercial formulation contribute to the toxicity of the herbicide. Generally, developmental impair was observed in both species (egg abortion and release of undeveloped embryos or dead offspring) at concentrations of any of the a.i.s below 1 mg L(-1). Ethofumesate was invariably the least toxic pesticide, and D. magna tended to be of slightly higher sensitivity to the exposures compared to D. longispina. Joint exposures indicated that the a.i.s can interact, inducing more than and less than additive effects for Betanal® Expert and the customised a.i. mixture, respectively. This indicates that inert ingredients co-formulating the commercial pesticide (which are absent from the customised a.i. mixture) actually contribute to its overall toxicity. This study constitutes an add-on to the discussion on the ecotoxicological framework required for authorisation of pesticide trade and usage. The results support the need to consider test species, long-term hazardous potential and toxicity of commercial formulations rather than solely that of active ingredients, as relevant variables in pesticide regulation.

Assessment of chronic effects of tebuconazole on survival, reproduction and growth of Daphnia magna after different exposure times

The effect of the fungicide tebuconazole (0.41, 0.52, 0.71 and 1.14mg/L) on survival, reproduction and growth of Daphnia magna organisms was monitored using 14 and 21 days exposure tests. A third experiment was performed by exposing D. magna to the fungicide for 14 days followed by 7 days of recovery (14+7). In order to test fungicide effects on D. magna, parameters as survival, mean whole body length, mean total number of neonates per female, mean number of broods per female, mean brood size per female, time to first brood/reproduction and intrinsic rate of natural increase (r) were used. Reproduction was seriously affected by tebuconazole. All tebuconazole concentrations tested affected the number of broods per female and day to first brood. At 14-days test, number of neonates per female and body size decreased by concentrations of tebuconazole higher than 0.52mg/L, whereas at 21-days test both parameters were affected at all the concentrations tested. Survival of the daphnids after 14 days fungicide exposure did not exhibited differences among experimental and control groups. In this experiment r value was reduced (in a 22%) when animals were exposed to concentrations of 0.71mg/L and 1.14mg/L. Survival of daphnids exposed during 21 days to 1.14mg/L declined, and the intrinsic rate of natural increase (r) decreased in a 30 % for tebuconazole concentrations higher than 0.41mg/L. Longevity of daphnids pre-exposed to tebuconazole for 14 days and 7 days in clean water did not show differences from control values and all of them survived the 21 days of the test. However, after 7 days in fungicide free medium animals were unable to restore control values for reproductive parameters and length. The maximum acceptable toxicant concentration (MATC) was calculated using the r values as parameter of evaluation. MATC estimations were 0.61mg/L and 0.46mg/L for 14 and 21 days, respectively. Results showed that the number of neonates per female was the highest sensitive parameter to the effects of tebuconazole on D. magna. On the other hand, a recovery period of 7 days in a free toxicant medium would not be longer enough to reestablish normal reproduction parameters in pre-exposed tebuconazole daphnids.

Evaluation and comparison of the relationship between NOEC and EC10 or EC20 values in chronic Daphnia toxicity testing

Hypothesis-based no-effect-concentration (NOEC) and regression-based x% effect concentration (ECx) values are common statistical approaches used to summarize ecotoxicological effects. Controversy over the NOEC model has prompted a movement toward discontinuation of the NOEC in favor of ECx, but the best x% effect surrogate for NOEC has not yet been determined. Historically, 10% and 20% effect concentrations (EC10 and EC20) have been treated as NOEC analogs. Given these measurements' importance to ecotoxicology, further understanding of the relationships between NOEC and EC10 or EC20 is crucial. In the present study, a metadataset of daphnid chronic toxicity tests was compiled to analyze the strength and significance of NOEC:EC10 and NOEC:EC20 relationships. The impact of endpoint (e.g., mortality, reproduction) and test condition parameters (e.g., pH, temperature) on NOEC:EC10 and NOEC:EC20 was evaluated. Mortality endpoints were most sensitive 51% of the time, with growth and reproductive endpoints constituting the remainder, underscoring the value of using multiple endpoints to evaluate toxic effects rather than relying on reproduction as the a priori most sensitive endpoint. When test condition parameters were less restricted (e.g., pH, hardness), the NOEC:EC20 association was more robust, suggesting that variability introduced by test implementation increased variability in ECx calculation. The analysis revealed that, overall, EC10 was a more suitable analog than EC20 for NOEC. Recommendations include refinement and reporting of the test parameters pH and hardness to minimize variability in ECx calculation.

Acute and chronic toxicity of chromium and cadmium to the tropical cladoceran pseudosida ramosa and the implications for ecotoxicological studies

In this study, the acute and chronic toxicity of the metals chromium and cadmium were tested against the tropical freshwater cladoceran Pseudosida ramosa. Acute tests showed that the 48-h LC50 of chromium was 29 μg L(-1) , while that of cadmium was 12 μg L(-1) . P. ramosa had a similar sensitivity to those of other cladoceran species cultured in the same conditions as in this study, or a higher sensitivity when water hardness was raised. Long-term chronic exposure of P. ramosa to chromium decreased maternal survival, fecundity, and fertility at a concentration of 10 μg L(-1) . For cadmium, reductions in the same endpoints were observed at a concentration of 3 μg L(-1) . Moreover, the degree of toxicity of the chromium and cadmium to P. ramosa after release of the first brood was similar to the result obtained after 21 days, using reproduction as the endpoint. Brazilian water bodies located near industrial areas already show concentrations of chromium and cadmium higher than levels causing acute and chronic toxicity to P. ramosa in our study. Many water quality criteria in tropical regions are based on ecotoxicological tests with non-native species and, consequently, this may lead to errors of interpretation when the permitted maximum levels of for each toxic substance are established. Therefore, we reinforce the idea of using native species to establish the maximum concentrations of toxic substances in water quality criteria, especially for metals, since their effects are related to water hardness, pH, and temperature specific to each region.

Chronic toxicity of the veterinary antibiotic florfenicol to Daphnia magna assessed at two temperatures

The hypothesis that temperature variation is able to modify the chronic toxicity of the antibiotic florfenicol (FLO) to Daphnia magna was tested in the present study. Twenty-one day laboratory bioassays were carried out at 20 and 25 °C. FLO concentrations and its potential decay during the assays were checked by spectrophotometry. At 20 °C, FLO significantly reduced the D. magna somatic growth (≥1.6 mg/L) and impaired its reproduction (EC₂₀=6.9 mg/L; EC₅₀=7.6 mg/L), with the population growth rate becoming negative at 12.6 mg/L. At 25 °C, the EC values were lower (1.7 and 1.9 mg/L, respectively) than at 20 °C, as well as the lowest exposure concentration causing a negative population growth rate (3.1 mg/L). These results clearly indicate that temperature raise from 20 to 25 °C was able to modify the FLO toxicity. Therefore, more studies on the combined effects of temperature changes and environmental contaminants are needed to improve the basis for ecological risk assessment, environmental and human safety.

Biochemical and genotoxic response of naphthalene to fingerlings of milkfish Chanos chanos

The present study investigated the acute toxicity, sub-lethal toxicity and biochemical response of naphthalene in fingerlings of milkfish Chanos chanos. The 96 h acute toxicity LC50 values for C. chanos exposed to naphthalene was 5.18 μg l(-1). The estimated no observed effect concentration and lowest observed effect concentration values for naphthalene in C. chanos were 0.42 and 0.69 μg l(-1) respectively for 30 days. The estimated maximum allowable toxicant concentration for naphthalene was 0.53 μg l(-1). Biochemical enzyme markers such as lipid peroxidation, catalase, glutathione S transferase and reduced glutathione were measured in gills and liver tissues of C. chanos exposed to sub-lethal concentrations of naphthalene. Fluctuation in lipid peroxidation and catalase level suggests that naphthalene concentrations play a vital role in induction of oxidative stress in fish. Induction of reduced glutathione level and inhibition of glutathione S-transferase level was observed in naphthalene exposed C. chanos suggesting that there may be enhanced oxidative damage due to free radicals. Increasing concentration increases in number of nuclear abnormalities. The formation of micronuclei and binucleated micronuclei induction by naphthalene confirm its genotoxic potential. The highest levels of DNA damage (% tail length) were observed at 1.24 μg l(-1) of naphthalene. The study suggests that biochemical enzymes, nuclear abnormalities and DNA damage index can serve as a biological marker for naphthalene contamination.

Evaluation of the Daphnia magna reproduction test for detecting endocrine disruptors

The Daphnia 21 d reproduction test is considered as a comprehensive and decisive test in the OECD Conceptual Framework for testing and assessment of endocrine disrupting chemicals (EDCs). However, how to interpret results of the Daphnia 21 d reproduction test for identification, risk assessment and testing strategy of EDCs remains an unsolved issue. This study analysed a total number of 135 published studies encompassing 86 known EDCs and non-EDCs with different modes of action. Our results show that the majority of effects on apical endpoints (survival, molting, growth, time to reproductive maturity, brood size, the number of broods, and the total number of offspring) do not seem to be EDC-specific. In contrast, the endpoint sex ratio is likely specific to juvenile hormones and their mimics. Variability is quantified for three most reported endpoints survival, the total number of offspring and sex ratio. Quantification of the endpoint sensitivity shows that the sensitivity of the sex ratio is lower than that of the total number of offspring. The Daphnia 21 d reproduction test gives insufficient information to conclude if a substance is an EDC or not. EDCs that are potent in assays in vitro may not be potent in the Daphnia 21 d reproduction test. We conclude that the Daphnia 21 d reproduction test is important for deriving No Observed Effect Concentrations for risk assessment but may produce false negatives in identification of EDCs when used on its own. A targeted testing strategy for selection of species, tests, and endpoints is suggested for identifying EDCs.

Optimal conditions for three brood chronic toxicity test method using a freshwater macroinvertebrate Moina macrocopa

Freshwater cladocera such as Daphnia magna and Ceriodaphnia dubia have been used extensively for freshwater toxicity test worldwide. However, these species may not be indigenous in certain geographical regions, which restrict the utility of these organisms as test species. In the present study, we investigated optimal culture and test conditions for an indigenous freshwater macroinvertebrate of Korea, Moina macrocopa. The culture conditions that were evaluated included water temperature (20°C and 25°C), rearing media (moderately hard water or MHW, with or without selenium supplementation, or Elendt M4), and food density (2.5 × 10(7) and 5 × 10(7) cells/mL of Selenastrum capricornutum), and their effects on the life history characteristics of M. macrocopa were determined. Population growth rate of M. macrocopa was maximized at 25°C with 5 × 10(7) cells/mL of algal food density in MHW. A series of chronic three brood reference toxicant tests were conducted under the ideal culture conditions that were identified here, and the results of the tests indicated reliable reproducibility of the test protocol. Optimal culture and test conditions that were identified for M. macrocopa in the present study are suggested for evaluation of chronic toxicity of chemicals and industrial or municipal discharge.

Energy resource reallocation in Daphnia schodleri (Anomopoda: Daphniidae) reproduction induced by exposure to hexavalent chromium

Cladocerans are able to store energy in the form of macromolecules such as proteins, lipids and carbohydrates. However, their ability to do so depends to a large extent on their physiological and reproductive condition as well as their age. These macromolecules constitute the total caloric reserves of the body and may be modified as a result of environmental stress conditions by either physical or nutritional factors or by exposure to toxic compounds. Neonates of the freshwater cladoceran Daphnia schodleri were exposed to 0.0064, 0.032 and 0.064 mg L(-1) of hexavalent chromium - Cr(VI) - up to age 5, 7, 14, 21 or 28 d. Survival and fecundity of parthenogenetic females was evaluated for 28d (maximum exposure period). Body length and maximum width were determined in specimens of all ages. Caloric content was evaluated in progeny and females within each age group. Female survival was significantly lower with exposure to 0.064 mg L(-1) of Cr(VI) than with other treatments, and negative effects on reproduction were observed from the lowest concentration on. Largest adult size was attained by control specimens towards the end of the observation period, but no significant differences in neonate size occurred between concentrations. Energy content decreased in adults as toxicant concentration increased, but these females allocated a larger amount of energy reserves to their progeny as a possible compensation aimed at ensuring neonate survival in an adverse environment due to toxicant presence. Sublethal concentrations of Cr(VI) modified energy content in D. schodleri, affecting to varying degrees its survival, growth and reproduction.

Age-altered susceptibility in hexavalent chromium-exposed Daphnia schodleri (Anomopoda: Daphniidae): integrated biomarker response implementation

Daphnia schodleri is a naturally occurring cladoceran in Mexican freshwater bodies and its relative big size and short life cycle allow its use in toxicological bioassays. Generally, life stages at opposite sides of a normal distribution are considered to be the most susceptible and/or sensitive because of several sub-individual level processes, such as ageing, in which antioxidant activity decreases and reactive oxygen species (ROS) cannot be totally neutralized. Most aquatic populations are structured by organisms of different ages, in which physiological and biochemical responses differ (in magnitude) from each other. According to these statements, seven age groups of D. schodleri (0, 3, 5, 7, 14, 21, and 28 d) were exposed to Cr (VI) in both acute and non-lethal bioassays. Results from acute bioassays were used to estimate the chromium LC(50) values for every age group, which ranged from 0.12 to 0.61 mg L(-1), with a normal pattern distribution. Antioxidant enzymatic activity of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx), and glutathione reductase (GR) was assessed in organisms exposed to two sublethal Cr(VI) concentrations (0.032 and 0.0064 mg L(-1)). Results showed that neonates' antioxidant activity increased with respect to their controls; nevertheless, the same pattern was not seen in the other age groups. Moreover, GPx activities followed a decreasing pattern with respect to their control groups in organisms 3-d and older. In addition, GR activities were barely modified by chromium exposure of neonates, but not in the other age groups; CAT was only modified in younger daphnids. Once the biomarker responses were normalized, it was possible to observe that enzyme participation differed during the life cycle of this cladoceran and, as a result of their decreasing antioxidant activity, relatively old organisms could have lower capability to deal with pro-oxidant toxicants such as Cr(VI).

Acute and chronic effects of sodium and potassium on the tropical freshwater cladoceran Pseudosida ramosa

In this study, the toxicities of sodium and potassium to the tropical freshwater cladoceran Pseudosida ramosa were assessed. Acute toxicity tests on this species showed that the 48-h LC(50) of Na(+) was 556 mg l(-1), while that of K(+) was 17.7 mg l(-1). Long-term exposure of female P. ramosa to sodium reduced the total number of survivors from 10 to 6 at a concentration of 249 mg l(-1), 21-day fecundity from 20.4 to 14.3 eggs female(-1) at concentrations ranging from 72 to 249 mg l(-1), 21-day fertility from 20.1 to 6.5 neonates female(-1) at concentrations ranging from 25 to 249 mg l(-1). Furthermore, fecundity of each brood from the second to the fifth was significantly lower at 249 mg l(-1) and fertility of each brood from the first to the fifth at concentrations ranging from 25 to 249 mg l(-1). A significant decrease in fertility was associated with an increase in the number of aborted eggs. Long-term exposure to potassium decreased the 21-day fecundity of P. ramosa from 14.2 to 10.8 eggs female(-1) at a concentration of 11 mg l(-1) and fertility (fourth brood only) at 6.2 and 11 mg l(-1). Tropical reservoirs located near areas where the soil is overloaded with fertilizers and ferti-irrigation with vinasse already show concentrations of Na(+) and K(+) very close to those producing sub-lethal long-term effects on P. ramosa. A possible consequence is that organisms of the aquatic biota cannot adapt and freshwater taxa may become locally extinct, transferring dominance to salt-tolerant taxa.

Effects of electromagnetic fields on parthenogenic eggs of Daphnia magna Straus

Developing parthenogenetic eggs of Daphnia magna were used as a test-system to evaluate the effect of a number of low-frequency electromagnetic fields (EMF) of 75microT density. Two blocks of EMF acting frequencies were found in the studied series-45, 110, and 175Hz, and 435 and 500Hz. Developing parthenogenetic eggs of D. magna exposed to EMF with indicated parameters have shown accelerated rates of embryonic development. Females that developed from exposed eggs have shown deteriorated production characteristics in their first brood. Used test-system may be successfully utilized to detect weak effects directly during embryogenesis. However, results obtained only during daphnids' early developmental stages are incomplete without observations on their further development.

A Saccharomyces cerevisiae-based bioassay for assessing pesticide toxicity

This study evaluates the toxic effect of three pesticides (Azoxystrobin, Cymoxanil, and Diuron) on the yeast Saccharomyces cerevisiae for the development of a new bioassay based on inhibition of S. cerevisiae metabolic activity at the level of adenosine-5-triphosphate (ATP) synthesis, as compared with two different toxicity tests based on inhibition of Daphnia magna mobility (NF EN ISO 6341) and inhibition of Vibrio fisheri activity (NF EN ISO 11348). The S. cerevisiae bioassay is cheaper and 96 times faster than the D. magna toxicity bioassay, but has lower sensitivity. It is as fast as the V. fisheri bioassay and more sensitive. Thus, this new toxicity test can be proposed for rapid detection of pesticide residues in environmental samples as a complement to the more expensive and time-consuming D. magna toxicity test.

Acute and chronic effects of testosterone and 4-hydroxyandrostenedione to the crustacean Daphnia magna

Steroid compounds have been globally detected in surface waters. The ecological impacts of these biologically active chemicals are largely unknown. Toxicity of testosterone and 4-hydroxyandrostenedione was assessed for the freshwater cladoceran Daphnia magna. Acute toxicity tests showed that 6.20 mg L(-1) of testosterone, the highest concentration tested, did not have effect on the daphnids, whereas 4-hydroxyandrostenedione had an EC(50) of 4.26 mg L(-1). Chronic toxicity tests were carried out using survival, body length, fecundity, and fertility as endpoints. Long-term testosterone exposure reduced D. magna fecundity and fertility at concentrations ranging from 0.31 to 2.48 mg L(-1). The significant decrease in fecundity was associated with an increase in aborted eggs. Long-term 4-hydroxyandrostenedione exposure at 0.84 mg L(-1) increased the mortality of the neonates. The chronic toxicity effects were observed at concentrations higher than the measured environmental concentrations of these compounds. Nevertheless, the reproductive impairment of the daphnids is likely to occur at environmental levels as an ultimate response to long-term exposure.

Short- and long-term responses of Daphnia spp. to propanil exposures in distinct food supply scenarios

The widespread increase of pesticides application in crops frequently leads to the contamination of vicinal freshwater lentic ecosystems. Herbicides such as propanil may impair cladoceran fitness, which is per se strongly influenced by the food availability and/or its acquisition efficiency. This work intended to evaluate the responses of Daphnia magna and three clonal lineages belonging to the Daphnia longispina complex to acute and chronic exposures of the herbicide propanil, as well as to assess whether food availability features these responses. Results showed that the agrochemical was acutely and chronically toxic to both D. magna and the D. cf. longispina clones at the same range of low concentrations, while relevant differences were depicted between the three distinct genotypes belonging to the D. longispina complex. Food-level conditioned the general fitness of the daphnids in the tests but evidences suggest that it does not interfere specifically with the toxicant mode of action.

Effects of an organophosphate on Daphnia magna at suborganismal and organismal levels: implications for population dynamics

The effects and recovery of 24 h pulse exposure to paraoxon-methyl on Daphnia magna were recorded for various endpoints to study the propagation of effects through various biological levels of organization. Above a threshold concentration (2.2 microgL(-1)), all selected endpoints were affected. Thus, effects at the suborganismal level (e.g., the biomarker response: transient inhibition of cholinesterase (ChE) activity) were accompanied by effects at the organismal (survival, reduction in reproductive performance, decrease in body size) and population (reduced population growth rate) levels. At intermediate and sublethal concentrations, exposure induced a transient ChE inhibition that was also accompanied by effects at the organismal level and that exerted long-term effects on population dynamics. At lower concentrations, although ChE activity was affected, there was no propagation of effects to higher biological levels. This study shows that effects of pulse exposure to organophosphates propagate from the suborganismal level toward the population level and demonstrates the significance of transient ChE inhibition on population dynamics.

Review of recent ecotoxicological studies on cladocerans

Cladocerans have been widely used as the bioassay organisms in evaluating the impact of different toxic substances. Literature survey during the last 10 years revealed that cladoceran ecotoxicological research has been in an exponential phase constituting nearly 10% of publications on this group. Many studies have considered typically planktonic taxa such as Daphnia magna, D. pulex, Moina macrocopa, M. micrura and Ceriodaphania dubia. Experimental data on toxicity tests, to a lesser extent, are also available for littoral-benthic genera such as Simocephalus, Macrothrix and Alona. Most toxicity tests are limited to the derivation of median lethal concentrations of various durations but mostly at 24 or 48 h. Studies related to the evaluation of changes in the life history variables of cladocerans as a result of sublethal exposure to toxic substances are not many, but gaining importance. The common toxic substances used in the cladoceran toxicity tests appear to be heavy metals, pesticides and a few natural toxins such as cyanotoxins. We review here the effect of different toxic substances on cladocerans based on both the field and the laboratory studies from an ecotoxicology point of view. Suggestions for the future cladoceran ecotoxicology are also commented on.

Evaluation of the toxicity of two soils from Jales Mine (Portugal) using aquatic bioassays

Soil contamination can be one path for streams and groundwater contamination. As a complement of chemical analysis and total contaminants determination, bioassays can provide information on the bioavailable fraction of chemical compounds, focusing on the retention and habitat function of soils. In this study the evaluation of the toxicity of two soils from the abandoned Jales Mine (Portugal) regarded both functions. The buffer capacity of soils was tested with bioassays carried out using the cladoceran Daphnia magna and the marine bacteria Vibrio fischeri. The habitat function of soils was evaluated with the reproduction bioassay with the collembolan Folsomia candida. The Microtox solid-phase test was performed with V. fischeri using soil as test medium, and soil elutriates were extracted to perform the Microtox basic test, and an immobilization and reproduction bioassay with D. magna. The marine bacteria showed high sensitivity to the soil with low heavy metal content (JNC soil) and to JNC soil elutriates, while the soil with highest heavy metal content (JC soil) or soil elutriates exposure did not cause any toxic effect. In the bioassays with D. magna, organisms showed sensitivity to JNC and also to JC soil elutriates. Both mobilization and reproduction features were inhibited. The bioassay with F. candida did not reflect any influence of the contaminants on their reproduction. Although JNC soil presented lower heavy metal contents, elutriates showed different patterns of contamination when compared to JC soil and elutriates, which indicates different retention and buffer capacities between soils. Results obtained in this study underlined the sensitivity and importance of soil elutriate bioassays with aquatic organisms in the evaluation strategy in soil ERA processes.

Modeling the concentration-response function of the herbicide dinoseb on Daphnia magna (survival time, reproduction) and Pseudokirchneriella subcapitata (growth rate)

Models describing dose-response relationships are becoming increasingly popular in ecotoxicology. They allow simple and thorough evaluations of toxicity test results, including inter- and extrapolations to concentrations or exposure times other than those tested. Simple parametric regression models are of particular interest because their parameters may be attributed mechanistic meanings and they can be applied without sophisticated mathematical and computational support. We recently proposed a four-parameter logistic regression model to fit the survival data of Daphnia magna under dinoseb stress. The model parameters are the maximum survival time, the minimum time required for an individual to die, effect concentration, EC(50), and a curve shape parameter. This model has now been applied to compare the lethality and reproduction toxicity of D. magna and the growth inhibition of Pseudokirchneriella subcapitata under dinoseb stress. It can be fitted adequately to all the measured data and the parameters can be attributed biological meanings in any of the three endpoints. A comparison of the modeled concentration-response functions of all three endpoints for dinoseb toxicity shows that the range of ECs with respect to both D. magna and algae is steep (a decrease of between 0.1 and 0.6 mg/L). The survival and reproduction of D. magna exhibit similar characteristic concentration-response functions and toxicities. The statistical no-effect concentration (SNEC) is 0.14 (survival) and 0.11 (reproduction)mg/L, respectively. On the other hand, algae seem to be less sensitive to dinoseb than D. magna (SNEC: 0.48 mg/L). However, further investigations of individual algae may lead to a more suitable comparison. We speculate that the four parameters of the model function can be related to specific properties of chemicals and organisms. Characterization of these properties would allow simple and appropriate estimation of the toxic effects of these chemicals.

Life-history traits of standard and autochthonous cladocerans: II. Acute and chronic effects of acetylsalicylic acid metabolites

Metabolic products are often more toxic than their pharmacological parent compounds. Therefore, the acute and chronic effects of the main metabolites--salicylic acid (SAL), gentisic acid (GEN), and o-hydroxyhippuric acid (HDP)--of acetylsalicylic acid (ASA), the active ingredient in Aspirin and many other pharmaceuticals, were assessed using standard (Daphnia magna) and autochthonous (Daphnia longispina) cladocerans. The sequence of decreasing levels of acute and chronic toxicity of ASA metabolites to daphnids was GEN > SAL > HDP. HDP did not present acute toxicity, but chronic exposures enabled the production of abnormal neonates and, in particular, egg abortion. Thus, reproduction was the end point most susceptible to HDP. On the other hand, SAL and GEN induced changes in the normal patterns of reproduction and growth of both species. In general, D. longispina was more sensitive than was D. magna, although the population growth of the autochthonous species was superior under SAL exposures than that of the standard test species. Although the concentrations that were determined to have a toxic effect were above the levels detected in aquatic environmental samples, exposure to low levels of pharmacologically active substances for a duration longer than the test period may induce changes in nontarget organisms.

On line biomonitors used as a tool for toxicity reduction evaluation of in situ groundwater remediation techniques

Success of groundwater remediation is typically controlled via snapshot analysis of selected chemical substances or physical parameters. Biological parameters, i.e. ecotoxicological assays, are rarely employed. Hence the aim of the study was to develop a bioassay tool, which allows an on line monitoring of contaminated groundwater, as well as a toxicity reduction evaluation (TRE) of different remediation techniques in parallel and may furthermore be used as an additional tool for process control to supervise remediation techniques in a real time mode. Parallel testing of groundwater remediation techniques was accomplished for short and long time periods, by using the energy dependent luminescence of the bacterium Vibrio fischeri as biological monitoring parameter. One data point every hour for each remediation technique was generated by an automated biomonitor. The bacteria proved to be highly sensitive to the contaminated groundwater and the biomonitor showed a long standing time despite the highly corrosive groundwater present in Bitterfeld, Germany. The bacterial biomonitor is demonstrated to be a valuable tool for remediation success evaluation. Dose response relationships were generated for the six quantitatively dominant groundwater contaminants (2-chlortoluene, 1,2- and 1,4-dichlorobenzene, monochlorobenzene, ethylenbenzene and benzene). The concentrations of individual volatile organic chemicals (VOCs) could not explain the observed effects in the bacteria. An expected mixture toxicity was calculated for the six components using the concept of concentration addition. The calculated EC(50) for the mixture was still one order of magnitude lower than the observed EC(50) of the actual groundwater. The results pointed out that chemical analysis of the six most quantitative substances alone was not able to explain the effects observed with the bacteria. Thus chemical analysis alone may not be an adequate tool for remediation success evaluation in terms of toxicity reduction.

Comparison between two common methods for measuring Giardia lamblia susceptibility to antiparasitic drugs in vitro

In this study a comparison between two different methods for measuring the susceptibility of Giardia lamblia trophozoites to metronidazole and albendazole is performed. Modifications of Meloni's method, based on the loss of adherence of parasites to surfaces, and the Hill method, based on the loss of parasite division capacity, are compared. A logistic model was used to calculate the inhibitory concentrations IC(10), IC(50) and IC(90) that were further compared using the respective standard errors. The results obtained, after contact of parasites with the antiparasitic drugs for 24h, show that the adherence method is more sensitive than the multiplication method for low and moderate inhibitory concentrations of albendazole. Conversely for metronidazole the multiplication method seems to be more sensitive for high inhibitory concentrations of the drug. For screening the IC(50), both methods seem to be effective, however, the inhibition of adherence method have even better performance for the benzimidazole like drugs.

Toxicity of copper-spiked sediments to Tubifex tubifex (Oligochaeta, Tubificidae): a comparison of the 28-day reproductive bioassay with a 6-month cohort experiment

Results from a 28-day adult reproductive bioassay using the aquatic oligochaete Tubifex tubifex (Müller, 1774) are compared with life table statistics obtained from a 6-month experiment on cohorts of the same species. This was done by simultaneously performing the two tests on copper spiked sediments. Five concentrations and a control were tested. The 28-day bioassay was performed 3 times in succession. Several endpoints were considered for each test and LOEC, IC10 and IC50 were calculated. IC50 estimates for the number of young produced in the 28-day bioassay range from 81 to 107 mg/kg; IC50 estimates for different endpoints of the cohort experiment ranged from 88 to 106 mg/kg. The 28-day bioassay showed essentially the same sensitivity as the cohort experiment to copper. This suggests that the 28-day reproductive bioassay does provide information that is relevant in assessing long-term toxic effects at the population level.

Acetylcholinesterase inhibition and increased food consumption rate in the zebrafish, Danio rerio, after chronic exposure to parathion

Acetylcholinesterase (AChE) inhibition is widely regarded as a good biomarker of exposure to organophosphorus pesticides (OP). However, less is known about the relationship between AChE inhibition and consequences for growth, reproduction and survival on organisms. Acute toxicity tests with fish have shown that high percentages of AChE inhibition are needed to cause detrimental effects, but not much is known about the consequences of chronic exposure to this group of chemicals for both AChE activity and higher levels of biological organisation. In this study, zebrafish (Danio rerio) were exposed to sublethal concentrations of the OP parathion for 250 days in a flow-through system. Besides AChE activity, a variety of other parameters were measured: whole-body protein and lactate content, consumption rate, survival, growth and reproduction. AChE inhibition was correlated with exposure concentration, but not with exposure time, and was significant above 0.9 microg/l after 144 days and above 4.3 microg/l after 250 days of exposure. Both parathion and the cosolvent dimethylsulfoxide (DMSO) significantly increased food consumption rate of the fish. Survival, growth, reproduction and lactate content were not affected, while protein concentrations showed only minor effects. These findings support the hypothesis that AChE is a very sensitive biomarker for exposure, but not accurately predict higher level adverse effects following long-term exposure to OPs.

Toxicity of 4-nonylphenol to Tubifex tubifex and Chironomus riparius in 28-day whole-sediment tests

Concern has been growing recently over the toxicity and the mimicking properties of 4-nonylphenol (4NP), the most persistent breakdown product of the nonionic surfactant nonylphenol ethoxylates, broadly used in industrial cleaning processes. Twenty-eight-day tests were performed to evaluate the toxicity and the effects on reproduction of 4NP spiked sediment to the benthic invertebrates Tubifex tubifex and Chironomus riparius. 4NP was directly added to the wet sediment, avoiding any solvent. The EC50 value for the emergence of chironomids was 380 microg 4NP g(-1) dry weight (dw); the EC50 values for the deposition of cocoons and the development of young worms were very similar (428 and 420 microg g(-1) dw, respectively). Regarding NP estrogenic activity and its effects on reproduction and development, no significant differences were noted in the sex ratio of the emerged chironomids when exposed to 4NP compared to the controls, but the emerged chironomids did not lay eggs at concentrations higher than the EC10 (250 microg 4NP g(-1) dw). Furthermore, at concentration of 610 microg 4NP g(-1) dw an interference in the development of the gonads of adult worms was observed, but it was impossible to determine whether this effect was due to 4NP toxicity or to its hormone mimicking properties.

In vitro development of parthenogenetic eggs: a fast ecotoxicity test with Daphnia magna?

In the present study, the authors investigated and defined development stages of Daphnia magna eggs that could be potential endpoints for sublethal toxicity tests with in vitro parthenogenetic egg cultures. Such an "egg test" could be a cost-effective alternative to the classic 21-day test with D. magna. Three main stages of embryonic development were considered: release of the egg external membrane, release of the internal membrane, and separation of the caudal spine. The first embryonic stage was attained approximately 30 h after transfer of eggs from ovaries to the brood chamber (considered as time zero), the second stage at 48 h, and the third stage at 68 h. Embryonic development was considered completed with the caudal spine separation. Thereafter, juveniles were able to swim in the water column. Egg mortality, duration of each egg stage, egg diameter, and egg abnormalities were investigated as potential endpoints. In vitro tests were carried out with several toxicants (DBS, 3,4-DCA, cadmium, and copper) and with acid mine drainage, sensitivity generally being higher than with the accepted chronic 21-day test with D. magna.

Yeasts as a model for assessing the toxicity of the fungicides Penconazol, Cymoxanil and Dichlofluanid

In the present work the sensitivity of yeast strains of Kluyveromyces marxianus, Pichia anomala, Candida utilis, Schizosaccharomyces pombe and Saccharomyces cerevisiae, to the fungicides cymoxanil, penconazol, and dichlofluanid, was evaluated. Dichlofluanid induced the most negative effects, whereas penconazol in general was not very toxic. Overall, our results show that the parameters IC50 for specific respiration rates of C. utilis and S. cerevisiae and C(D) for cell viability of S. cerevisiae can be applied to quantify the toxicity level of the above compounds in yeast. Hence, could be explored as an alternative or at least as a complementary test in toxicity studies and, therefore, its potential for inclusion in a tier testing toxicity test battery merits further research.

Development of batch injection analysis for electrochemical measurements of trace metal ions in ecotoxicological test media

Batch injection analysis with square-wave anodic stripping voltammetry has been developed as a powerful and rapid technique for obtaining data on the concentration of the fraction of labile metal ions present in media used in ecotoxicological tests. Microlitre samples of solution, without pretreatment, are injected directly over a detector electrode, the surface of which is protected by a thin Nafion polymer coating against irreversible adsorption by organic components. Examples are given showing the effect of adding vitamins and organic extract, singly and together, to the ASTM medium employed for tests using Daphnia magna and with lead and cadmium test ions. Such a methodology can be extended to other electroactive species present in these and similar media.