Age related acute effects of microcystin-LR on Daphnia magna biotransformation and oxidative stress

Harmful planktonic Microcystis and benthic Oscillatoria-induced toxicological effects on the Asian clam (Corbicula fluminea): A survey on histopathology, behavior, oxidative stress, apoptosis and inflammation

Cyanobacterial blooms are worldwide distributed and threaten aquatic ecosystems and public health. The current studies mainly focus on the adverse impacts of planktonic cyanobacteria or pure cyanotoxins, while the benthic cyanobacteria-induced ecotoxic effects are relatively lacking. The cyanobacterial cell-induced toxic effects on aquatic organisms might be more serious and complex than the pure cyanotoxins and crude extracts of cyanobacteria. This study explored the chronic effects of toxin-producing planktonic Microcystis aeruginosa (producing microcystin) and benthic Oscillatoria sp. (producing cylindrospermopsin) on the behaviors, tissue structures, oxidative stress, apoptosis, and inflammation of the Asian clams (Corbicula fluminea) under 28-d exposure. The data showed that both M. aeruginosa and Oscillatoria sp. can decrease the behaviors associated with the feeding activity and induce tissue damage (i.e. gill and digestive gland) in clams. Furthermore, two kinds of cyanobacteria can alter the antioxidant enzyme activities and increase antioxidant, lipid oxidation product, and neurotransmitter degrading enzyme levels in clams. Moreover, two kinds of cyanobacteria can activate apoptosis-related enzyme activities and enhance the proinflammatory cytokine levels of clams. In addition, two kinds of cyanobacteria can disturb the transcript levels of genes linked with oxidative stress, apoptosis, and inflammation. These results suggested harmful cyanobacteria can threaten the survival and health of clams, while the benthic cyanobacteria-induced adverse effects deserve more attention. Our finding also indicated that it is necessary to focus on the entire algal cell-induced ecotoxicity when concerning the ecological impacts of cyanobacterial blooms.

Effects of cyanobacterial metabolites: Aeruginosin 98A, microginin-FR1, anabaenopeptin-A, cylindrospermopsin in binary and quadruple mixtures on the survival and oxidative stress biomarkers of Daphnia magna

The aim of our study was to determine the effects of aeruginosin 98 A (ARE-A), microginin-FR1 (MG-FR1), anabaenopeptin-A (ANA-A) cylindrospermopsin (CYL) and their binary and quadruple mixtures on the survival and the levels of oxidative stress biomarkers in Daphnia magna: total glutathione (GSH), catalase (CAT), dismutase (SOD) and malondialdehyde (MDA). The biochemical indicators were measured with ELISA kits and the interactive effects were determined by isobole and polygonal analysis with Compusyn® computer software. The study revealed that oligopeptides did not decrease daphnid survival, only CYL inhibited this parameter, with synergistic effects when it was used as a component. The single metabolites at the two highest concentrations and all the binary and quadruple mixtures at all concentrations diminished GSH level, however both in the binary and in the quadruple mixtures most of the interactions between the metabolites were antagonistic. Nearly additive effects were found only in AER-A + CYL and MG-FR1+CYL. On the other hand, CAT activity was slightly increased in daphnids exposed to the binary mixtures with antagonistic interactions, however nearly addivive effects were found in animals exposed to the mixture of AER-A + ANA-A and synergistic in the quadruple mixture. SOD was elevated in daphnids exposed to single AER-A and MG-FR1, however it was diminished in the animals exposed to ANA-A and CYL. Binary mixtures in which CYL was present as a component decreased the level of this enzyme with nearly additive interactions in ANA-A + CYL. The quadruple mixture increased SOD level, with antagonistic interactions. Both single cyanobacterial metabolites, their binary and quadruple mixtures induced lipid peroxidation measured by MDA level and most of interactions in the binary mixtures were synergistic. The study suggested that antioxidative system of Daphnia magna responded to the tested metabolites and the real exposure to mixtures of these products may lead to various interactive effects with varied total toxicity.

Transcriptomic analysis and transgenerational effects of ZnO nanoparticles on Daphnia magna: Endocrine-disrupting potential and energy metabolism

The widespread application of zinc oxide nanoparticles (ZnO NPs) has raised concerns over the adverse effects on aquatic species. In this study, transcriptomic analysis was applied to evaluate the chronic toxicity of ZnO NPs on the freshwater invertebrate Daphnia magna and the intergenerational effects were then further investigated. Parent daphnia (F0) were exposed to ZnO NPs at 3, 60, and 300 μg L^-1 for 21 days. ZnO NPs significantly inhibited the reproduction (first pregnancy and spawning time, total number of offspring) and growth (molting frequency and body length) of F0. Here, differentially expressed genes (DEGs) involved in lysosomal and phagosome, energy metabolism and endocrine disruption pathways were significantly downregulated. Furthermore, disruption on the transport and catabolic processes probably resulted in the particle accumulation. The inhibited pathways related to energy metabolism may partially account for the body length, molting and reproductive restriction. The suppression of growth and reproduction may attribute to the down-regulation of insulin secretion and ovarian steroidogenesis pathways, respectively. Partial recovery of growth and reproductive inhibition in F1 - F3 descended from the F0 generation exposure did not support constant transgenerational effects. This study unravels the molecular mechanisms and transgenerational consequences of the toxicity of nanoparticles on Daphnia.

Cell free Microcystis aeruginosa spent medium affects Daphnia magna survival and stress response

Primary consumers in freshwater ecosystems, such as the zooplankton organism Daphnia magna, are highly affected by cyanobacteria, both as they may use it as a food source but also by cyanobacterial metabolites present in the water. Here, we investigate the impacts of cyanobacterial metabolites focussing on the environmental realistic scenario of the naturally released mixture without crushing cyanobacterial cells or their uptake as food. Therefore, D. magna were exposed to two concentrations of cell free cyanobacterial spent medium from Microcystis aeruginosa PCC 7806 to represent higher and lower ecologically-relevant concentrations of cyanobacterial metabolites. Including microcystin-LR, 11 metabolites have been detected of which 5 were quantified. Hypothesising concentration and time dependent negative impact, survival, gene expression marking digestion and metabolism, oxidative stress response, cell cycle and molting as well as activities of detoxification and antioxidant enzymes were followed for 7 days. D. magna suffered from oxidative stress as both catalase and glutathione S-transferase enzyme activities significantly decreased, suggesting enzyme exhaustibility after 3 and 7 days. Moreover, gene-expressions of the 4 stress markers (glutathione S-transferase, glutathione peroxidase, catalase and thioredoxin) were merely downregulated after 7 days of exposure. Energy allocation (expression of glyceraldehyde-3-phosphate dehydrogenase) was increased after 3 days but decreased as well after 7 days exposure. Cell cycle was impacted time dependently but differently by the two concentrations, along with an increasing downregulation of myosin heavy chain responsible for cell arrangement and muscular movements. Deregulation of nuclear hormone receptor genes indicate that D. magna hormonal steering including molting seemed impaired despite no detection of microviridin J in the extracts. As a consequence of all those responses and presumably of more than investigated molecular and physiological changes, D. magna survival was impaired over time, in a concentration dependent manner. Our results confirm that besides microcystin-LR, other secondary metabolites contribute to negative impact on D. magna survival and stress response.

Using flocculation and subsequent biomanipulation to control microcystis blooms: A laboratory study

The frequent occurrence and long-term duration of Microcystis harmful algal blooms (HABs) are of great concern. Chemical flocculation is thought to be an effective way to deal with the HABs, while the application of the flocculants at a high dosage pose potential adverse impacts to the aquatic ecosystems. In this study, an alternative approach is proposed that involves the employment of polyaluminum chloride (PAC) combined with the Daphnia magna (D. magna) to achieve sustainable HABs removal efficiency with an acceptable ecological risk. It was found that under a dense Microcystis HABs (algal density of 1.5 × 10⁷ cells/ml), a PAC dosage of 30 mg/l triggered >95% algae removal, but the released Al³⁺ caused 90% mortality of planktonic D. magna. Reducing the PAC dosage to 15 mg/l resulted in a slightly lower algal removal efficiency (>90%). In addition the reduced PAC dosage benefited the proliferation of the remaining unicellular algal cells, which tended to form a large colony during the 25-day experiment. Incubation of D. magna following flocculation with 15 mg/l PAC effectively grazed the remaining algal cells, meanwhile increasing the D. magna density by approximately 40-folds, and enlarging the body size by 1.37-1.50 times. This result implied that the released Al³⁺ was not detrimental to the D. magna. Flocculation with a reduced dosage is sufficient for colonial and large algal cells mitigation, which creates a window time for the biomanipulation of the residual tiny algae. Hence, the subsequent addition of D. magna triggered the sustainable removal of the HABs cells. The present study provides an environmentally friendly strategy for cleaning up the green tides without obvious detrimental effects on the aquatic ecosystem.

Adverse effects in Daphnia magna exposed to e-waste leachate: Assessment based on life trait changes and responses of detoxification-related genes

The sharp increase in e-waste derived from great consumption of electronic products has become a potential global environmental challenge. Limited information is available about the potential detrimental impact of e-waste on aquatic organisms. The present study investigated the expression of detoxification-related genes and life-history parameter changes in Daphnia magna exposed to e-waste leachate, simultaneously integrating with the chemical analysis of typical pollutants from e-waste leachate. The study aims at assessing impacts of e-waste to aquatic invertebrates and providing insights into its toxic mechanisms. The results showed high concentration of heavy metals like Cu (1657.14 ± 259.3 μg g^-1, DW) and persistent organic compounds like polybrominated diphenyl ethers (7831.32 ± 1273.86 ng g^-1, DW) in stream sediments near e-waste dismantling areas. Chronic exposure to these pollutants can affect the growth and reproduction of D. magna, resulting in significant development retardation, decreased total egg production per female, and even smaller body size. Expression of some detoxification and reproduction-related genes including DappuHR96, CYP360a, P-gp, EcR, CYP314 and Vtg exhibited different response patterns depending on the e-waste leachate concentration. E-waste leachate may affect the expression of detoxification-related and growth and reproduction-related genes and disrupt the growth and reproduction processes of D. magna.

Cross talk: Two way allelopathic interactions between toxic Microcystis and Daphnia

Due to eutrophication, freshwater ecosystems frequently experience cyanobacterial blooms, many of which produce bioactive metabolites that can affect vertebrates and invertebrates life traits. Zooplankton are able to develop tolerance as a physiological response to cyanobacteria and their bioactive compounds, however, this comes with energetic cost that in turn influence Daphnia life traits and may impair populations. Vice versa, it has been suggested that Daphnia are able to reduce cyanobacterial dominance until a certain cyanobacterial density; it remains unclear whether Daphnia metabolites alone influence the physiological state and bioactive metabolites production of cyanobacteria. Hence, this study investigates mutual physiological reactions of toxic Microcystis aeruginosa PCC7806 and Daphnia magna. We hypothesize that a) the presence of D. magna will negatively affect growth, increase stress response and metabolites production in M. aeruginosa PCC7806 and b) the presence of M. aeruginosa PCC7806 will negatively affect physiological responses and life traits in D. magna. In order to test these hypotheses experiments were conducted in a specially designed co-culture chamber that allows exchange of the metabolites without direct contact. A clear mutual impact was evidenced. Cyanobacterial metabolites reduced survival of D. magna and decreased oxidative stress enzyme activity. Simultaneously, presence of D. magna did not affect photosynthetic activity. However, ROS increase and tendencies in cell density decrease were observed on the same day, suggesting possible energy allocation towards anti-oxidative stress enzymes, or other protection mechanisms against Daphnia infochemicals, as the strain managed to recover. Elevated concentration of intracellular and overall extracellular microcystin MC-LR, as well as intracellular concentrations of aerucyclamide A and D in the presence of Daphnia, indicating a potential protective or anti-grazing function. However, more research is needed to confirm these findings.

Analysis of Covalently Bound Microcystins in Sediments and Clam Tissue in the Sacramento-San Joaquin River Delta, California, USA

Harmful cyanobacterial blooms compromise human and environmental health, mainly due to the cyanotoxins they often produce. Microcystins (MCs) are the most commonly measured group of cyanotoxins and are hepatotoxic, neurotoxic, and cytotoxic. Due to MCs ability to covalently bind to proteins, quantification in complex matrices is difficult. To analyze bound and unbound MCs, analytical methods were optimized for analysis in sediment and clam tissues. A clean up step was incorporated to remove lipids, improving percent yield. This method was then applied to sediment and clam samples collected from the Sacramento-San Joaquin River Delta (Delta) in the spring and fall of 2017. Water samples were also tested for intracellular and extracellular MCs. These analyses were used to quantify the partitioning of MCs among sediment, clams, and water, and to examine whether MCs persist during non-summer months. Toxin analysis revealed that multiple sediment samples collected in the Delta were positive for MCs, with a majority of the positive samples from sites in the San Joaquin River, even while water samples from the same location were below detection limit. These data highlight the importance of analyzing MCs in complex matrices to accurately evaluate environmental risk.

Saxitoxin-producing Raphidiopsis raciborskii (cyanobacteria) inhibits swimming and physiological parameters in Daphnia similis

In this study we tested the effects of a neurotoxic strain of the cyanobacterium Raphidiopsis raciborskii (CYRF-01) on the swimming activity and physiological parameters of Daphnia similis such as movements of the antennae, thoracic limbs, post-abdominal claw and heart rate. An acute assay was performed to test the effect on swimming activity, exposing newborns (<24 h) to different concentrations of live cells and observing the number of immobilized animals over a period of 48 h. For testing the effects on physiological parameters adult females (10-15 days) were exposed in a flow-through system and recorded with a digital camera. Results showed rapid effect of the strain CYRF on all parameters. Animals started to be immobilized in the first 30 min exposure and showed complete paralysis after 2 h in 500 μg L^-1 and after 24 h in the other concentrations. Physiological parameters accompanied the same response pattern with effects starting after 30 min and some recovery at the end of 6 h exposure. Antennae stopped moving after 2-3 h at 250-500 μg L^-1, explaining the paralysis of the swimming activity in Daphnia. Thoracic limbs movements were significantly inhibited after 30 min in all concentrations, staying at lower levels than control through the experiment. Post-abdominal claw movement were completely ceased after 30 min and remained stopped until the end of the trial. Heart rate showed a tendency to decrease abruptly in the first 30 min exposure in all concentrations, but showed significant lower values than control only at 500 μg L^-1, between 3 and 4 h exposure, and a recovery at the end of 6 h. In conclusion, results show that neurotoxic cyanobacteria can impose severe constrains on the physiology of daphniids, which can have consequences to the oxygen uptake, swimming and feeding behavior and to the overall fitness of those organisms.

Photocatalytic degradation of Microcystin-LR by visible light active and magnetic, ZnFe2O4-Ag/rGO nanocomposite and toxicity assessment of the intermediates

In this work, we aimed to study photocatalytic degradation of Microcystin-LR (MC-LR), a cyanotoxin known to cause acute as well as chronic toxicity and even mortality. The nanocomposite (NC) based on zinc ferrite (ZnFe₂O₄) was modified with graphene oxide (GO) and Ag nanoparticles (NPs) to enhance its photocatalytic properties under visible light. The so-formed ZnFe₂O₄-Ag/rGO NC exhibited superior performance in visible light allowing complete degradation of MC-LR within 120 min of treatment with pseudo rate constant, k = 0.0515 min^-1, several times greater than other photocatalysts, TiO₂ (k = 0.0009 min^-1), ZnFe₂O₄ (k = 0.0021 min^-1), ZnFe₂O₄-Ag (k = 0.0046 min^-1) and ZnFe₂O₄/rGO (k = 0.007 min^-1) respectively. The total organic carbon analysis revealed that only 22% of MC-LR was mineralized on 120 min of treatment time indicating presence of different intermediate by-products. The intermediates formed during photocatalytic treatment were identified using liquid chromatography-mass spectrometry (LCMS) based on which probable degradation pathways were proposed. The attack from OH radicals formed during the photocatalytic process resulted to hydroxylation and subsequent cleavage of diene bond. The toxicity assessment with Daphnia magna revealed that the degradation process has alleviated toxicity of the MC-LR and no toxic intermediates were formed during the treatment which is very important from eco-toxicological view point. Therefore, ZnFe₂O₄-Ag/rGO has a good potential in the field of environmental applications as visible light active and magnetic photocatalyst with enhanced performance.

μEvaluation of microcystin-LR absorption using an in vivo intestine model and its effect on zebrafish intestine

Microcystin-LR (MC-LR) is regarded as one of the most toxic microcystins (MCs) isoforms. Microcystins could cause multiple organs dysfunction, and more attention has been drawn to the toxic effects on the gastrointestinal disorder. By using ex vivo everted gut sac model in 6 fish (Carassius auratus, Megalobrama amblycephala, Hypophthalmichthys molitrix, Aristichthys nobilis, Ctenopharyngodon idellus and Cyprinus carpio) and determining the accumulation of MC-LR in zebrafish intestine, we found a dose-dependent manner in the absorption and accumulation of MC-LR. Until now, little studies have been reported concerning the gut microbiota composition caused by different MC-LR exposure. The present study is the first time characterized the phylogenetic composition and taxonomic of the bacterial communities growth in the intestines of zebrafish treated with MC-LR using 16S rRNA pyrosequencing. After 30 days of treatment with 0, 1, 5 or 20 μg/L MC-LR, the alpha and beta diversity did not generate significant differences, indicating the existence of a core microbiota. However, db-RDA analysis showed that treatment with 20 μg/L MC-LR changed the characteristics of high abundances microbiota. The expression of Oatp2b1, stress related enzyme activities in gut and their associations with gut microbiota were also determined. The identified phylotypes including Actinobacteria, Lactobacillus and some opportunistic pathogens highlight the increasing risks of pathogen invasion and recovery tendency via potential probiotics resistance in zebrafish exposed to MC-LR.

Age-dependent antioxidant responses to the bioconcentration of microcystin-LR in the mysid crustacean, Neomysis awatschensis

Microcystins (MCs) are naturally occurring algal toxins in the aquatic environment and pose a serious threat to the ecosystem. In general, aquatic populations are structured by organisms of different ages, with varying degrees of biochemical and physiological responses. In this study, juvenile and adult marine mysids (Neomysis awatschensis) were exposed to MC-Leucine Arginine (MC-LR) (0.1, 1, and 10 μg L^-1) for 7 days, and the bioconcentration dynamics and responses of antioxidant defense system were measured during the exposure and additional depuration periods (7 days). MC-LR bioconcentrated in a dose-dependent manner, from a threshold concentration of 1 μg L^-1 in both stages, and the levels reduced gradually during the depuration phase. Bioconcentration patterns of MC-LR were highly age-specific, as juvenile mysids showed peaks during the exposure period, whereas adults exhibited a peak on the first day of depuration. After exposure to 10 μg L^-1 concentration, elevated levels of malondialdehyde (MDA) and glutathione (GSH) were observed during the late (days 5 and 7) exposure and early (days 1 and 3) depuration periods in juvenile mysids, while adult mysids showed a peak on day 7 of the exposure period. Age-specific responses were also observed in the enzymatic activities of glutathione S-transferase (GST), catalase (CAT), superoxide dismutase (SOD), glutathione peroxidase (GPx), and glutathione reductase (GR). Juvenile mysids showed a significant elevation in all enzymatic activities during the exposure and/or depuration phase upon exposure to 10 μg L^-1 MC-LR, but only CAT and SOD enzymes showed significant changes during the exposure and/or depuration periods in adults. Overall, our results indicate the bioconcentration potential of MC-LR and its threshold in the marine mysid, in addition to age-specific MC-LR dynamics and subsequent biochemical responses.

Grazing of Nuclearia thermophila and Nuclearia delicatula (Nucleariidae, Opisthokonta) on the toxic cyanobacterium Planktothrix rubescens

During the last decades, the planktonic cyanobacterium Planktothrix rubescens became a dominant primary producer in many deep pre-alpine lakes. While altered physiochemical conditions due to lake warming seem to favour this cyanobacterial species, its dominance is partly attributed to factors conferring grazing resistance. The rigid structure of the cyanobacterial filaments and toxic secondary metabolites (e.g. microcystins) protect against diverse grazers. Nonetheless, species of the protistan genus Nuclearia (Nucleariidae, Opisthokonta) are able to overcome this grazing protection. Time lapse video documentation served as tool to record slow feeding processes of N. thermophila and N. delicatula. Three different feeding strategies could be distinguished: (i) Phagocytosis of small fragments, (ii) serial break-ups of cyanobacterial cells and (iii) bending and breaking of filaments. While observations revealed mechanical manipulation to be important for the efficient breakdown of P. rubescens filaments, the toxin microcystin had no pronounced negative effects on nucleariid cells. Growth experiments with N. thermophila/N. delicatula and different accompanying bacterial assemblages pointed to a pivotal role of distinct prokaryotic species for toxin degradation and for the growth success of the protists. Thus, the synergistic effect of nucleariids and specific bacteria favours an efficient degradation of P. rubescens along with its toxin.

Metabolomic responses to sublethal contaminant exposure in neonate and adult Daphnia magna

The use of consumer products and pharmaceuticals that act as contaminants entering waterways through runoff and wastewater effluents alters aquatic ecosystem health. Traditional toxicological endpoints may underestimate the toxicity of contaminants, as lethal concentrations are often orders of magnitude higher than those found within freshwater ecosystems. While newer techniques examine the metabolic responses of sublethal contaminant exposure, there has been no direct comparison with ontogeny in Daphnia. It was hypothesized that Daphnia magna would have distinct metabolic changes after 3 different sublethal contaminant exposures, because of differences in the toxic mode of action and ontogeny. To test this hypothesis, the proton nuclear magnetic resonance metabolomic profiles were measured in D. magna aged day 0 and 18 after exposure to 28% of the lethal concentration of 50% of organisms tested (LC50) of atrazine, propranolol, and perfluorooctanesulfonic acid (PFOS) for 48 h. Principal component analysis revealed significant separation of contaminants from the control daphnids in both neonates and adults exposed to propranolol and PFOS. In contrast, atrazine exposure caused separation from the controls in only the adult D. magna. Minimal ontogenetic changes in the targeted metabolites were seen after exposure to propranolol. For both atrazine and PFOS exposures ontogeny exhibited unique changes in the targeted metabolites. These results indicate that, depending on the contaminant studied, neonates and adults respond uniquely to sublethal contaminant exposure. Environ Toxicol Chem 2017;36:938-946. © 2016 SETAC.

Harmful algae: Effects of cyanobacterial cyclic peptides on aquatic invertebrates-a short review

Cyanotoxins are secondary metabolites produced by cyanobacteria. Cyclic peptides, microcystins and nodularin commonly detected in water reservoirs of different parts of the world may induce various detrimental effects in a wide range of organisms from bacteria to humans. This paper presents the current state of knowledge on the effects of microcystins and nodularin on aquatic invertebrates: zooplankton, decapods and mollusks. Accumulation of microcystins and nodularin in these organisms and possible transfer of the cyanotoxins through the food web and possible threat to humans as consumers are also discussed.

Oxidative stress responses in the animal model, Daphnia pulex exposed to a natural bloom extract versus artificial cyanotoxin mixtures

In the natural environment, Daphnia spp. are constantly exposed to a complex matrix of biomolecules, especially during cyanobacterial bloom events. When cyanobacterial cells decay, not only are toxic secondary metabolites known as cyanotoxins released, but also multiple other secondary metabolites, some of which act as enzyme inhibitors. The present study examined the effects of such a natural toxin matrix (crude extract from a bloom) versus artificial toxin mixtures in terms of oxidative stress in Daphnia pulex. The results indicate that there is no significant effect on the survival of D. pulex. However, exposure to the bloom extract resulted in increased lipid peroxidation over a shorter exposure period and reduced antioxidative enzyme activities when compared to the artificial mixtures. The daphnids also needed a longer recovery time to reduce the increased cellular hydrogen peroxide concentration associated with the exposure to the crude extract than with the artificial mixtures. The results indicate a significant difference between the bloom crude extract and the two synthetic mixtures for all stress markers tested, indicating enhanced toxicity of the bloom extract.

Accumulation and detoxification dynamics of microcystin-LR and antioxidant responses in male red swamp crayfish Procambarus clarkii

MC-LR is one of major microcystin isoforms with potent hepatotoxicity. In the present study, we aim to: 1) explore the dynamics of MC-LR accumulation and elimination in different tissues of male red swamp crayfish Procambarus clarkii; 2) reveal the mechanisms underlying hepatic antioxidation and detoxification. In the semi-static toxicity tests under the water temperature of 25±2°C, P. clarkii were exposed to 0.1, 1, 10 and 100μg/L MC-LR for 7days for accumulation and subsequently relocated to freshwater for another 7days to depurate MC-LR. MC-LR was measured in the hepatopancreas, intestine, abdominal muscle and gill by HPLC. The enzyme activities of superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione S-transferase (GST), content of glutathione (GSH), and transcripts of Mn-sod, cat, gpx1, Mu-gst, heat shock protein90 (hsp90), hsp70 and hsp60 in hepatopancreas were detected. The results showed that P. clarkii accumulated more MC-LR in intestine, and less in abdominal muscle and gill during accumulation period and eliminated the toxin more quickly in gill and abdominal muscle, and comparatively slowly in intestine during depuration period. The fast increase of SOD and CAT activities at early stage, subsequent decrease at later stage of accumulation period and then fast increase during depuration period were partially consistent with the transcriptional changes of their respective genes. GPx was activated by longer MC-LR exposure and gpx1 mRNA expression showed uncoordinated regulation pattern compared with its enzyme. Hsp genes were up-regulated when P. clarkii was exposed to MC-LR.

Mechanism and Reaction Pathways for Microcystin-LR Degradation through UV/H2O2 Treatment

Microcystin-LR (MCLR) is the most common cyanotoxin in contaminated aquatic systems. MCLR inhibits protein phosphatases 1 and 2A, leading to liver damage and tumor formation. MCLR is relatively stable owing to its cyclic structures. The combined UV/H₂O₂ technology can degrade MCLR efficiently. The second-order rate constant of the reaction between MCLR and hydroxyl radical (·OH) is 2.79(±0.23)×10¹⁰ M⁻¹ s⁻¹ based on the competition kinetics model using nitrobenzene as reference compound. The probable degradation pathway was analyzed through liquid chromatography mass spectrometry. Results suggested that the major destruction pathways of MCLR were initiated by ·OH attack on the benzene ring and diene of the Adda side chain. The corresponding aldehyde or ketone peptide residues were formed through further oxidation. Another minor destruction pathway involved ·OH attack on the methoxy group of the Adda side chain, followed by complete removal of the methoxy group. The combined UV/H₂O₂ system is a promising technology for MCLR removal in contaminated aquatic systems.

Stress-responsive expression of a glutathione S-transferase (delta) gene in waterflea Daphnia magna challenged by microcystin-producing and microcystin-free Microcystis aeruginosa

Harmful cyanobacterial blooms resulting from eutrophication and global warming have emerged as a worldwide environmental concern. Some zooplankton populations, including Daphnia, have been shown to adapt locally to microcystin-producing Microcystis. Previous in vitro experiments indicate that glutathione-S-transferase (GST) may act as the first step of detoxification in Daphnia by conjugating microcystins (MCs) with glutathione. The GST family is categorized into many classes, and different classes present distinct responses to MC detoxification. To date, however, the molecular mechanism of single class GST participation in buffering the toxic effects of MCs in Daphnia remains poorly known. In this study, a full-length delta-GST cDNA of Daphnia magna (Dm-dGST) was isolated and characterized through bioinformatics. Differential gene expression studies revealed that short-term exposure to microcystin-producing (MP) Microcystis aeruginosa increased Dm-dGST transcript levels. By contrast, long-term exposure to MP or microcystin-free (MF) M. aeruginosa decreased Dm-dGST transcript levels. Together with changes in three other antioxidation biomarkers (catalase, CuZn- and Mn-superoxide dismutase), it is concluded that Dm-dGST can potentially biotransform MCs to reduce their toxicity. The present study highlights the importance of Dm-dGST in response to MC toxicity and may thus facilitate future research on the molecular mechanisms of MC tolerance in zooplankton under an increasing eutrophic world.

Changes in iTRAQ-Based Proteomic Profiling of the Cladoceran Daphnia magna Exposed to Microcystin-Producing and Microcystin-Free Microcystis aeruginosa

Global warming and increased nutrient fluxes cause cyanobacterial blooms in freshwater ecosystems. These phenomena have increased the concern for human health and ecosystem services. The mass occurrences of toxic cyanobacteria strongly affect freshwater zooplankton communities, especially the unselective filter feeder Daphnia. However, the molecular mechanisms of cyanobacterial toxicity remain poorly understood. This study is the first to combine the established body growth rate (BGR), which is an indicator of life-history fitness, with differential peptide labeling (iTRAQ)-based proteomics in Daphnia magna influenced by microcystin-producing (MP) and microcystin-free (MF) Microcystis aeruginosa. A significant decrease in BGR was detected when D. magna was exposed to MP or MF M. aeruginosa. Conducting iTRAQ proteomic analyses, we successfully identified and quantified 211 proteins with significant changes in expression. A cluster of orthologous groups revealed that M. aeruginosa-affected differential proteins were strongly associated with lipid, carbohydrate, amino acid, and energy metabolism. These parameters could potentially explain the reduced fitness based on the cost of the substance metabolism.

Use of cholinesterase activity as an ecotoxicological marker to assess anatoxin-a(s) exposure: Responses of two cladoceran species belonging to contrasting geographical regions

The specificity of cholinesterase (ChE) activity to detect the presence of anatoxin-a(s) and sublethal effects of a 7-day exposure to Anabaena spiroides extract containing anatoxin-a(s) were assessed in two freshwater cladoceran species. Activities of ChE of both Pseudosida ramosa and Daphnia magna can be used to indicate the presence of the neurotoxin anatoxin-a(s), but not for the hepatotoxic microcystin. Activity of ChE of P. ramosa, however, performed better as a biomarker of exposure to A. spiroides than that of D. magna. Furthermore, sublethal exposure to A. spiroides extract significantly inhibited the ChE activity in P. ramosa and negatively affected both individual and population endpoints. For D. magna, the inhibition of ChE activity was not related to effects at higher levels of biological organization, since no direct effect was recorded on the individual and population endpoints. The activity of ChE in P. ramosa also proved to be a good predictor of chronic effects of the A. spiroides extract at higher levels of biological organization, since 48-h ChE inhibition was linked to the sublethal effects on the individual and population. These relationships could not be established for D. magna. Since relationships between the effects of A. spiroides extract at different levels of biological organization were species-specific, it can be concluded that the choice of test organism interferes with the accuracy of the environment risk assessment of this neurotoxin and, hence, the use of native species is recommended for its assessment.

β-N-methylamino-L-alanine (BMAA) uptake by the animal model, Daphnia magna and subsequent oxidative stress

β-N-methylamino-l-alanine (BMAA), produced by cyanobacteria, is a neurotoxin implicated in Amyotrophic lateral sclerosis/Parkinsonism dementia complex (ALS/PDC). BMAA concentrations in cyanobacteria are lower than those thought to be necessary to result in neurological damage thus bioaccumulation or biomagnification is required to achieve concentrations able to cause neurodegeneration. Many cyanobacteria produce BMAA and uptake routes into the food web require examination. In this study we investigate the uptake of BMAA by adult phytoplanktivorus Daphnia magna via exposure to dissolved pure BMAA and BMAA containing cyanobacteria, as well as the subsequent oxidative stress response in the daphnia. Free BMAA and protein-associated BMAA were quantified by LC-MS/MS. Dissolved BMAA was taken up and was found as free BMAA in D. magna. No protein-associated BMAA was detected in D. magna after a 24-h exposure period. No BMAA was detectable in D. magna after exposure to BMAA containing cyanobacteria. BMAA inhibited the oxidative stress defence and biotransformation enzymes within 24-h exposure in the tested Daphnia and could therefore impair the oxidant status and the capability of detoxifying other substances in D. magna.

Arginine kinase in the cladoceran Daphnia magna: cDNA sequencing and expression is associated with resistance to toxic Microcystis

Nutrient loading derived from anthropogenic activities into lakes have increased the frequency, severity and duration of toxic cyanobacterial blooms around the world. Although herbivorous zooplankton are generally considered to be unable to control toxic cyanobacteria, populations of some zooplankton, including Daphnia, have been shown to locally adapt to toxic cyanobacteria and suppress cyanobacterial bloom formation. However, little is known about the physiology of zooplankton behind this phenomenon. One possible explanation is that some zooplankton may induce more tolerance by elevating energy production, thereby adding more energy allocation to detoxification expenditure. It is assumed that arginine kinase (AK) serves as a core in temporal and spatial adenosine triphosphate (ATP) buffering in cells with high fluctuating energy requirements. To test this hypothesis, we studied the energetic response of a single Daphnia magna clone exposed to a toxic strain of Microcystis aeruginosa, PCC7806. Arginine kinase of D. magna (Dm-AK) was successfully cloned. An ATP-gua PtransN domain which was described as a guanidine substrate specificity domain and an ATP-gua Ptrans domain which was responsible for binding ATP were both identified in the Dm-AK. Phylogenetic analysis of AKs in a range of arthropod taxa suggested that Dm-AK was as dissimilar to other crustaceans as it was to insects. Dm-AK transcript level and ATP content in the presence of M. aeruginosa were significantly lower than those in the control diet containing only the nutritious chlorophyte, Scenedesmus obliquus, whereas the two parameters in the neonates whose mothers had been previously exposed to M. aeruginosa were significantly higher than those of mothers fed with pure S. obliquus. These findings suggest that Dm-AK might play an essential role in the coupling of energy production and utilization and the tolerance of D. magna to toxic cyanobacteria.

Offspring performance of Daphnia magna after short-term maternal exposure to mixtures of microcystin and ammonia

During degradation of cyanobacterial blooms, some derived pollutants are released to the waters and last for a while before returning to normal levels. To assess whether the offspring of exposed Daphnia was affected by their maternal experience, we exposed mother Daphnia magna to mixtures of unionized ammonia (0, 0.30, and 0.48 mg L(-1)) and microcystin-LR (0, 10, 30, and 100 μg L(-1)) for 10 days and then immediately moved their offspring to a toxicant-free environment. The offspring were cultured for 21 days to record their survival, development, and reproduction. Results showed that the survival of the offspring of D. magna that experienced high doses of mixed toxicants decreased significantly, but there was no significant difference in development among the survivors of the offspring from different maternal treatments. However, reproductive performances significantly differed among the offspring from different maternal treatments, indicating that there existed a maternal effect in the offspring of D. magna that experienced high levels of mixed toxicants.

CYP-dependent induction of glutathione S-transferase in Daphnia similis exposed to a disperse azo dye

Disperse Red 1 (DR1) is an azo dye that can reach the aquatic environment through the discharge of textile industrial wastewaters. It has been tested in Daphnia similis and shown to be highly toxic. Cytochrome P450 (CYP) is a class of enzymes involved in phase I of detoxification, while glutathione S-transferase (GST) are a class of phase II enzymes. No information about phase I or II dye metabolism in microcrustacea were found in the literature. In this study we identified CYP and GST enzymes involved in the metabolism of DR1 in juveniles of D. similis. Using spectrophotometric analysis we showed that 50 % of the dye was absorbed by the organisms, which could be confirmed by the reddish color of animals exposed to DR1, however adsorption cannot be ruled out. GST activity increased from 280 to 615 nmol(-1 )min(-1 )mg when D. similis were exposed for 48 h to 0.2 mg L(-1) DR1 and from 274 to 815 nmol(-1) min(-1 )mg when exposed to 5 mg L(-1). Data clearly demonstrate that exposure to DR1 can stimulate a strong induction of GST activity, whose participation in DR1 metabolism needs to be confirmed. The induction of GST activity seems to be dependent on CYP activity, since treatment with SKF535A, a CYP inhibitor, blocked the DR1-dependent GST induction. We speculate that GST is involved in DR1 metabolism in Daphnia and that CYP activity is necessary to induce GST-activity, which is an indirect evidence of its role in the biotransformation of DR1.

The fate of microcystins in the environment and challenges for monitoring

Microcystins are secondary metabolites produced by cyanobacteria that act as hepatotoxins in higher organisms. These toxins can be altered through abiotic processes, such as photodegradation and adsorption, as well as through biological processes via metabolism and bacterial degradation. Some species of bacteria can degrade microcystins, and many other organisms metabolize microcystins into a series of conjugated products. There are toxicokinetic models used to examine microcystin uptake and elimination, which can be difficult to compare due to differences in compartmentalization and speciation. Metabolites of microcystins are formed as a detoxification mechanism, and little is known about how quickly these metabolites are formed. In summary, microcystins can undergo abiotic and biotic processes that alter the toxicity and structure of the microcystin molecule. The environmental impact and toxicity of these alterations and the metabolism of microcystins remains uncertain, making it difficult to establish guidelines for human health. Here, we present the current state of knowledge regarding the alterations microcystins can undergo in the environment.

Life history responses of Daphnia similoides simultaneously exposed to microcystin-LR and ammonia and their postexposure recovery

Aquatic organisms often suffer episodic stress from cyanobacterial bloom-derived concomitants and sometimes interactive stressors, and they may recover when stressors terminate. To assess whether exposed Daphnia can quickly recover from combined toxicity of bloom-derived stressors, Daphnia similoides were exposed to mixtures of ammonia (0 mg L(-1) , 0.37 mg L(-1) , and 0.58 mg L(-1) ) and dissolved microcystin-LR (0 µg L(-1) , 10 µg L(-1) , 30 µg L(-1) , and 100 µg L(-1) ) in a full factorial design for 14 d and subsequently allowed to recover for 7 d. During the exposure, the mixtures of ammonia and microcystin-LR showed different effects on the selected variables. Ammonia delayed the time to maturation, but microcystin-LR was not negative to the development of the tested daphnids. Furthermore, microcystin-LR reduced the prolonged developmental time to first eggs and first clutch caused by high ammonia. The total reproduction of D. similoides was dramatically reduced by 64% to 79% by both toxicants and their combinations, but there were no interactive effects. After the recovery period, organisms under most treatments did not recover completely from the combined stress but showed positive signs of recovery, based on the size of the last clutch and the mean number of clutches during recovery; thus the affected D. similoides have the potential to quickly recover from the combined toxic stressors.

Combined effects of the cyanobacterial toxin microcystin-LR and environmental factors on life-history traits of indigenous cladoceran Moina macrocopa

Environmental factors are important in that they might interact with toxicants and could affect the concentration-response relationship of the toxicants in the water environment. Microcystins (MCs) produced by algal blooming are natural toxins that exert severe impacts on aquatic organisms. Despite the possibility of interaction effects between environmental factors and MCs, very few studies have been carried out to date. In the present study, the authors evaluated the effect of 3 environmental factors on chronic toxicity of MC-leucine-arginine (MC-LR; 0 µg/L, 0.8 µg/L, 4 µg/L, 20 µg/L, 100 µg/L, 500 µg/L) to the freshwater invertebrate Moina macrocopa. Three environmental factors were determined to reflect the reasonable worst conditions of the water body in South Korea: high water temperature (25 °C), the highest concentration of nutrients (ammonia-nitrogen [NH3 -N] = 3.8 mg/L; nitrate-nitrogen [NO3 -N] = 8.5 mg/L) during the occurrence of algal bloom, and 2 pH conditions of 7.0 and 9.0, which satisfy the test acceptance criteria for the Daphnia test. Among the various environmental factors being tested, high water temperature and NO3 -N elevated chronic toxicity of MC-LR, whereas NH3 -N reduced toxicity. Water pH did not influence chronic toxicity of MC-LR to M. macrocopa. This observation suggests that those environmental factors are responsible for changing the trend of MC-LR toxicity.

Dietary exposure of Daphnia to microcystins: no in vivo relevance of biotransformation

Anthropogenic nutrient input into lakes has contributed to the increased frequency of toxic cyanobacterial blooms. Daphnia populations have been shown to be locally adapted to toxic cyanobacteria and are able to suppress bloom formation; little is known about the physiology behind this phenomenon. Microcystin-LR (MCLR) is the most widespread cyanobacterial toxin, and, based on in vitro experiments, it is assumed that the enzyme glutathione-S-transferase (GST) might act as the first step of detoxification in Daphnia by conjugating MCLR with glutathione. In the present study Daphnia magna was fed a diet of 100% Microcystis aeruginosa PCC7806, a cyanobacterial strain that contains MCLR in high amounts (4.8-5.6 fg cell(-1)), in order to test for a possible conjugation of MCLR with GST in Daphnia in vivo. We used high-resolution LCMS to analyze incubation water, cyanobacterial cells and Daphnia tissue for the presence of MCLR conjugation products as well as unconjugated MCLR. Newly formed conjugation products were detected neither in Daphnia tissue nor in the incubation water. Moreover, the presence of Daphnia led to a decrease in unconjugated MCLR in the cyanobacterial cell fraction due to grazing, in comparison to a control without daphnids, which was well reflected by a similar increase of MCLR in the respective incubation water. As a consequence, the MCLR content did not change due to Daphnia presence within the entire experimental setup. In summary, MCLR ingestion by Daphnia led neither to the formation of conjugation products, nor to a decrease of unconjugated MCLR. GST-mediated conjugation thus seems to be of minor relevance for microcystin (MC) tolerance in Daphnia in vivo. This finding is supported by the fact that GST activity in Daphnia feeding on the MC-containing wildtype or a MC-free mutant of M. aeruginosa PCC7806 revealed an identical increase of specific activity in comparison to a cyanobacteria-free diet. Therefore, the frequently observed induction of GST activity upon exposure to toxic cyanobacteria is not a specific MC effect but a general cyanobacterial effect. This suggests that GST in Daphnia is involved in an oxidative stress response rather than in the specific detoxification of MCs. Furthermore, our results indicate the presence of an efficient transport mechanism which efficiently removes unconjugated MCLR from the Daphnia tissue. Further studies are needed to elucidate the nature of this transport mechanism.

Molecular cloning of manganese superoxide dismutase gene in the cladoceran Daphnia magna: effects of microcystin, nitrite, and cadmium on gene expression profiles

Superoxide dismutases (SODs) are metalloenzymes that represent one important line of defense against oxidative stress produced by reactive oxygen species in aerobic organisms. Generally, waterborne pollutants caused by irregular anthropogenic activities often result in oxidative damage in aquatic organisms. The aim of this study was to molecularly characterize the manganese superoxide dismutase gene (Dm-MnSOD) in the waterflea, Daphnia magna, and evaluate the mRNA expression patterns quantified by real-time PCR after exposure to three common waterborne pollutants (microcystin-LR, nitrite, and cadmium). The results showed that the full-length Dm-MnSOD sequence consists of 954 bp nucleotides, encoding 215 amino acids, showing well-conserved domains that are required for metal binding and several common characteristics, such as two MnSOD domains. The deduced amino acid sequence of Dm-MnSOD shared over 70% similarity with homologues from Bythograea thermydron, Dromia personata, Cancer pagurus, and Scylla paramamosain. Dm-MnSOD gene expression was up-regulated in response to exposure to the three chemicals tested. The overall results indicated that Dm-MnSOD gene is an inducible gene and potential biomarker indicating these pollutants in the environment.

Maternal effects of inducible tolerance against the toxic cyanobacterium Microcystis aeruginosa in the grazer Daphnia carinata

Cyanobacterial blooms are becoming potent agents of natural selection in aquatic ecosystems because of their high production of some toxins and increased frequency in recent decades with eutrophication and climate change. Maternal exposure to the toxic Microcystis aeruginosa significantly increased the intrinsic rates of population increase, average life span, and net reproductive rates of a clone of the planktonic grazer Daphnia carinata in an offspring environment where cyanobacteria were present, but not for two additional clones. Offspring from mothers exposed to M. aeruginosa had lower intrinsic rates of population increase, average life span, and net reproductive rates than individuals from unexposed mothers when fed exclusively a green alga. These results suggest that benefits, costs, and clonal variations of maternal effects of inducible tolerance should be considered when trying to understand ecological consequences of cyanobacterial blooms since they can shape the trophic interactions between cyanobacteria and daphnids.

Effects of harmful cyanobacteria on the freshwater pathogenic free-living amoeba Acanthamoeba castellanii

Grazing is a major regulating factor in cyanobacterial population dynamics and, subsequently, considerable effort has been spent on investigating the effects of cyanotoxins on major metazoan grazers. However, protozoan grazers such as free-living amoebae can also feed efficiently on cyanobacteria, while simultaneously posing a major threat for public health as parasites of humans and potential reservoirs of opportunistic pathogens. In this study, we conducted several experiments in which the freshwater amoeba Acanthamoeba castellanii was exposed to pure microcystin-LR (MC-LR) and six cyanobacterial strains, three MC-producing strains (MC-LR, MC-RR, MC-YR, MC-WR, [Dha7] MC-RR) and three strains containing other oligopeptides such as anabaenopeptins and cyanopeptolins. Although the exposure to high concentrations of pure MC-LR yielded no effects on amoeba, all MC-producing strains inflicted high mortality rates on amoeba populations, suggesting that toxic effects must be mediated through the ingestion of toxic cells. Interestingly, an anabaenopeptin-producing strain caused the greatest inhibition of amoeba growth, indicating that toxic bioactive compounds other than MCs are of great importance for amoebae grazers. Confocal scanning microscopy revealed different alterations in amoeba cytoskeleton integrity and as such, the observed declines in amoeba densities could have indeed been caused via a cascade of cellular events primarily triggered by oligopeptides with protein-phosphatase inhibition capabilities such as MCs or anabaenopeptins. Moreover, inducible-defense mechanisms such as the egestion of toxic, MC-producing cyanobacterial cells and the increase of resting stages (encystation) in amoebae co-cultivated with all cyanobacterial strains were observed in our experiments. Consequently, cyanobacterial strains showed different susceptibilities to amoeba grazing which were possibly influenced by the potentiality of their toxic secondary metabolites. Hence, this study shows the importance of cyanobacterial toxicity against amoeba grazing and, that cyanobacteria may contain a wide range of chemical compounds capable of negatively affect free-living, herbivorous amoebae. Moreover, this is of high importance for understanding the interactions and population dynamics of such organisms in aquatic ecosystems.

Transgenerational effects of microcystin-LR on Daphnia magna

Anthropogenic and climate factors increase the frequency of problematic cyanobacterial blooms in freshwater. Among other toxins, some cyanobacteria produce microcystins (MCs), which inhibit phosphatases type 1 and type 2A and provokes oxidative stress. Toxic cyanobacteria affect the growth, survival and reproduction of zooplankton, particularly those from the genus Daphnia, which have a central position in pelagic food webs. However, one possibility to ameliorate effects is to biotransform MC via glutathione S transferase (GST) to a less toxic glutathione conjugate. This process was hypothesised to underlie the ability of Daphnia to withstand MC and to explain the enhanced tolerance of the offspring from mothers exposed to toxic cyanobacteria. Thus we conducted multigenerational experiments with D. magna, exposing the parental generation to MC for 1 or 7 days and determining the enzyme-mediated tolerance to MC in their offspring by assessing the acute effect of MC on biotransformation and antioxidant and metabolism enzymes, and through 21 day chronic tests on toxicity and growth. Seven days of exposure of the parental generation to MC induced higher activity of GST and malate dehydrogenase in the offspring and enabled them to increment the catalase activity when challenged with MC, whereas 1 day of exposure of the parental generation did not. Offspring from non-exposed and 1-day-exposed mothers suffered decreased survival when exposed to MC compared with offspring from 7-day-exposed mothers; survival was correlated with the elevated activity of GST, malate dehydrogenase and catalase, suggesting maternal transfer of activation factors. However, increased survival occurred at the expense of individual growth. These results suggest that transgenerational effects are provoked by MC in D. magna, which may explain the observed acquirement of enhanced tolerance over generations.

Time-dependent oxidative stress responses of submerged macrophyte Vallisneria natans seedlings exposed to ammonia in combination with microcystin under laboratory conditions

We studied the antioxidant responses of macrophyte Vallisnerria natans seedlings to combined ammonia (0, 0.21, and 0.85 mg L(-1)) and microcystin-LR (MC-LR) (0, 10, and 50 μg L(-1)) for 7 days. Results showed that superoxide dismutase, catalase (CAT), peroxidase, and glutathione were significantly induced by the mixtures of ammonia and MC-LR, and there were significant interactions between ammonia and MC-LR. Specially, CAT increased about fivefold at ammonia 0.85 mg L(-1) and MC-LR 50 μg L(-1) on day 3. Malondialdehyde fluctuated with both ammonia and MC-LR, and significant interactions were detected between the two stressors. Changes in all the measured variables were time-dependent.

Efficient removal of microcystin-LR by UV-C/H₂O₂ in synthetic and natural water samples

The destruction of the commonly found cyanobacterial toxin, microcystin-LR (MC-LR), in surface waters by UV-C/H(2)O(2) advanced oxidation process (AOP) was studied. Experiments were carried out in a bench scale photochemical apparatus with low pressure mercury vapor germicidal lamps emitting at 253.7 nm. The degradation of MC-LR was a function of UV fluence. A 93.9% removal with an initial MC-LR concentration of 1 μM was achieved with a UV fluence of 80 mJ/cm(2) and an initial H(2)O(2) concentration of 882 μM. When increasing the concentration of MC-LR only, the UV fluence-based pseudo-first order reaction rate constant generally decreased, which was probably due to the competition between by-products and MC-LR for hydroxyl radicals. An increase in H(2)O(2) concentration led to higher removal efficiency; however, the effect of HO scavenging by H(2)O(2) became significant for high H(2)O(2) concentrations. The impact of water quality parameters, such as pH, alkalinity and the presence of natural organic matter (NOM), was also studied. Field water samples from Lake Erie, Michigan and St. Johns River, Florida were employed to evaluate the potential application of this process for the degradation of MC-LR. Results showed that the presence of both alkalinity (as 89.6-117.8 mg CaCO(3)/L) and NOM (as ∼2 to ∼9.5 mg/L TOC) contributed to a significant decrease in the destruction rate of MC-LR. However, a final concentration of MC-LR bellow the guideline value of 1 μg/L was still achievable under current experimental conditions when an initial MC-LR concentration of 2.5 μg/L was spiked into those real water samples.

The interactive effects of ammonia and microcystin on life-history traits of the cladoceran Daphnia magna: synergistic or antagonistic?

The occurrence of Microcystis blooms is a worldwide concern that has caused numerous adverse effects on water quality and lake ecology. Elevated ammonia and microcystin concentrations co-occur during the degradation of Microcystis blooms and are toxic to aquatic organisms; we studied the relative and combined effects of these on the life history of the model organism Daphnia magna. Ammonia and microcystin-LR treatments were: 0, 0.366, 0.581 mg L⁻¹ and 0, 10, 30, 100 µg L⁻¹, respectively. Experiments followed a fully factorial design. Incubations were 14 d and recorded the following life-history traits: number of moults, time to first batch of eggs, time to first clutch, size at first batch of eggs, size at first clutch, number of clutches per female, number of offspring per clutch, and total offspring per female. Both ammonia and microcystin were detrimental to most life-history traits. Interactive effects of the toxins occurred for five traits: the time to first batch of eggs appearing in the brood pouch, time to first clutch, size at first clutch, number of clutches, and total offspring per female. The interactive effects of ammonia and microcystin appeared to be synergistic on some parameters (e.g., time to first eggs) and antagonistic on others (e.g., total offspring per female). In conclusion, the released toxins during the degradation of Microcystis blooms would result, according to our data, in substantially negative effect on D. magna.

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).