Depuration kinetics and persistence of the cyanobacterial toxin microcystin-LR in the freshwater bivalve Unio douglasiae

Microcystins in the benthic food-web of the Sacramento-San Joaquin Delta, California

Harmful cyanobacteria blooms are a growing threat in estuarine waters as upstream blooms are exported into coastal environments. Cyanobacteria can produce potent toxins, one of which-hepatotoxic microcystins (MCs)-can persist and accumulate within the food web. Filter-feeding invertebrates may biomagnify toxins up to 100× ambient concentrations. As such, bivalves can be used as an environmentally relevant and highly sensitive sentinel for MC monitoring. To date there has been little research on cyanotoxin bioaccumulation in estuaries. The Sacramento-San Joaquin Delta (Delta) aquatic food web has undergone a profound change in response to widespread colonization of aquatic invasive species such as Asian clams (Corbicula fluminea) in the freshwater portion of the Delta. These clams are prolific-blanketing areas of the Delta at densities up to 1000 clams/m2 and are directly implicated in the pelagic organism decline of threatened and endangered fishes. We hypothesized that Asian clams accumulate MCs which may act as an additional stressor to the food web and MCs would seasonally be in exceedance of public health advisory levels. MCs accumulation in Delta Asian clams and signal crayfish (Pacifastacus leniusculus) were studied over a two-year period. ELISA and LC-MS analytical methods were used to measure free and protein-bound MCs in clam and crayfish tissues. We describe an improved MC extraction method for use when analyzing these taxa by LC-MS. MCs were found to accumulate in Asian clams across all months and at all study sites, with seasonal maxima occurring during the summer. Although MC concentrations rarely exceeded public health advisory levels, the persistence of MCs year-round still poses a chronic risk to consumers. Crayfish at times also accumulated high concentrations of MCs. Our results highlight the utility of shellfish as sentinel organisms for monitoring in estuarine areas.

Cyanobacteria and Macroinvertebrate Relationships in Freshwater Benthic Communities beyond Cytotoxicity

Cyanobacteria are harmful algae that are monitored worldwide to prevent the effects of the toxins that they can produce. Most research efforts have focused on direct or indirect effects on human populations, with a view to gain easy accurate detection and quantification methods, mainly in planktic communities, but with increasing interest shown in benthos. However, cyanobacteria have played a fundamental role from the very beginning in both the development of our planet's biodiversity and the construction of new habitats. These organisms have colonized almost every possible planktic or benthic environment on earth, including the most extreme ones, and display a vast number of adaptations. All this explains why they are the most important or the only phototrophs in some habitats. The negative effects of cyanotoxins on macroinvertebrates have been demonstrated, but usually under conditions that are far from natural, and on forms of exposure, toxin concentration, or composition. The cohabitation of cyanobacteria with most invertebrate groups is long-standing and has probably contributed to the development of detoxification means, which would explain the survival of some species inside cyanobacteria colonies. This review focuses on benthic cyanobacteria, their capacity to produce several types of toxins, and their relationships with benthic macroinvertebrates beyond toxicity.

Dual characteristics of Bellamya aeruginosa encountering Microcystis aeruginosa: Algal control and toxin depuration

The benthic gastropods Bellamya aeruginosa (B. aeruginosa) is ubiquitous in freshwater in China and neighboring countries with great edible value. It has been recognized as a potential manipulator to control harmful algal blooms due to its filtration on algal cells. In this study, the control effect of B. aeruginosa on toxic and non-toxic Microcystis aeruginosa (M. aeruginosa), and the accumulation and depuration of microcystins (MCs) in the snail were systematically explored. Results indicated that although toxic M. aeruginosa could protect itself via producing MCs, the introduction of B. aeruginosa could still effectively inhibit the algae with cell density below 1 × 10⁶ cells/mL. Hepatopancreas was the primary target of MCs in all tissues of B. aeruginosa, presenting a maximum of 3089.60 ng/g DW when exposed to toxic M. aeruginosa of 1.0 × 10⁷ cells/mL. The enrichment of MCs in other tissues following the order of digestive tract > gonad > mantle > muscle. Interestingly, snail could again excrete previously enriched MCs when transferred to non-toxic M. aeruginosa, giving rise to over 80% reduction of MCs in the body. After depuration, the estimated daily intake (EDI) of free MCs in intact individuals and the edible parts of B. aeruginosa were both lower than the tolerable daily intake (TDI). These results implicated that B. aeruginosa could control low density of M. aeruginosa in spring. Particularly, the snail could be perfectly safe to consume by purifying for a while after using as manipulator.

PI3K/AKT/mTOR pathway mediated-cell cycle dysregulation contribute to malignant proliferation of mouse spermatogonia induced by microcystin-leucine arginine

Environmental cyanotoxin exposure may be a trigger of testicular cancer. Activation of PI3K/AKT/mTOR signaling pathway is the critical molecular event in testicular carcinogenesis. As a widespread cyanotoxin, microcystin-leucine arginine (MC-LR) is known to induce cell malignant transformation and tumorigenesis. However, the effects of MC-LR on the regulatory mechanism of PI3K/AKT/mTOR pathway in seminoma, the most common testicular tumor, are unknown. In this study, mouse spermatogonia cell line (GC-1) and nude mice were used to investigate the effects and mechanisms of MC-LR on the malignant transformation of spermatogonia by nude mouse tumorigenesis assay, cell migration invasion assay, western blot, and cell cycle assay, and so forth. The results showed that, after continuous exposure to environmentally relevant concentrations of MC-LR (20 nM) for 35 generations, the proliferation, migration, and invasion abilities of GC-1 cells were increased by 120%, 340%, and 370%, respectively. In nude mice, MC-LR-treated GC-1 cells formed tumors with significantly greater volume (0.998 ± 0.768 cm³ ) and weight (0.637 ± 0.406 g) than the control group (0.067 ± 0.039 cm³ ; 0.094 ± 0.087 g) (P < .05). Furthermore, PI3K inhibitor Wortmannin inhibited the PI3K/AKT/mTOR pathway and its downstream proteins (c-MYC, CDK4, CCND1, and MMP14) activated by MC-LR. Blocking PI3K alleviated MC-LR-induced cell cycle disorder and malignant proliferation, migration and invasive of GC-1 cells. Altogether, our findings suggest that MC-LR can induce malignant transformation of mouse spermatogonia, and the PI3K/AKT/mTOR pathway-mediated cell cycle dysregulation may be an important target for malignant proliferation. This study provides clues to further reveal the etiology and pathogenesis of seminoma.

Research progress in relationships between freshwater bivalves and algae

Eutrophication in freshwater has become increasingly severe around the world, resulting in phytoplankton overgrowth and benthic algae reduction. Bivalves can change the density, dominant species and community structure of phytoplankton, increase available light levels, and provide physical habitats and growth conditions for benthic algae. The nutritional composition, density, community structure, and toxin of algae affect the growth, feeding, digestion, metabolism, immunity of bivalves in return. Interactions of bivalves and algae and effects of environmental factors on these interactions need a synthesis of studies, when using bivalves as a biomanipulation tool to control eutrophication. Whether bivalves can effectively suppress phytoplankton and promote benthic algae is related to the collective filtration and excretion capacity determined by size, species, population densities of bivalves, the quantity and quality of algae, and environmental factors such as temperature, dissolved oxygen, pH, and hydrodynamic. Small scale bivalve biomanipulation experiments are mostly conducted in lakes, urban ponds, and reservoirs with some success, applying in the whole ecosystem should consider more questions such as natural conditions, selection and death or reproduction of bivalves, and ecological disturbances. This review provides new considerations for technical issues such as the sustainable cultivation of bivalves and the implementation of biomanipulation in eutrophic waters.

Physiological Response of the Freshwater Mussel Unio douglasiae in Microcystis aeruginosa Bloom Waters

In the present study, we evaluated the effects of different environments on the filtering rate (FR), mortality, and biodeposition (BD) of the freshwater mussel Unio douglasiae in bloom waters containing the toxic cyanobacterium Microcystis aeruginosa. The mean FR of 19 selected individuals (shell length, 5.0–9.8 cm) was $0.30\pm 0.03\text{L}{\text{g}}^{-1}{\text{h}}^{-1}$ ( $\text{range}=0.24–0.35\text{L}{\text{g}}^{-1}{\text{h}}^{-1}$ ). Shell length was strongly correlated with both net and gross BD of mussels ( $P<0.0001$ ). The mean FR was higher in river water ( $0.405\pm 0.052\text{L}{\text{g}}^{-1}{\text{h}}^{-1}$ ) than in lake water ( $0.304\pm 0.051\text{L}{\text{g}}^{-1}{\text{h}}^{-1}$ ). In contrast, the BD of mussels was higher in RW ( $0.671\pm 0.609\text{mg}{\text{g}}^{-1}{\text{h}}^{-1}$ ) than in LW ( $0.275\pm 0.027\text{mg}{\text{g}}^{-1}{\text{h}}^{-1}$ ). For algal species, the FR of mussels ranged from $0.114\pm 0.024$ to $0.553\pm 0.019\text{L}{\text{g}}^{-1}{\text{h}}^{-1}$ . The FR of U. douglasiae was higher in river water (mainly diatoms), whereas BD was higher in lake water (mainly Microcystis). U. douglasiae did not prefer toxic M. aeruginosa, which was significantly accumulated in pseudofaeces and faeces. The maximum FR of U. douglasiae in algal bloom water was recorded at a water temperature of 25°C and water depth of 50 cm. Moreover, the in situ mortality of U. douglasiae was strongly affected by water temperature and nitrogen concentration. Overall, U. douglasiae can enhance water quality in eutrophic areas by removing dominant cyanobacteria, although its removal efficiency depends on environmental parameters and site of introduction.

Mussel Unio douglasiae MG from the Chihe River: mitogenome description and phylogenetic analysis

The genus Unio is one of the widespread freshwater bivalves. To date, its intra-generic phylogeny remains controversial and therefore the mitochondrial genome data is needed. Here, we report the complete mitogenome of Unio douglasiae MG that is distributed in the Chihe River, a branch of Huaihe River, East China. This mitochondrial genome is 15,764 base pair in total length. It consists of 37 genes: 13 protein-coding genes, 22 tRNA genes, and 2 rRNA genes (12S and 16S). The base composition was 38.38% for A, 26.48% for T, 23.17% for C, and 11.98% for G, showing an obvious bias of higher A + T content (64.86%) than the G + C content (35.14%). Phylogenetic analysis showed that U. douglasiae MG is clustered with other Unio and Nodularia mollusks in the family Unionidae. These results showed that combine with morphological techniques, the mitogenome can provide useful information to further understanding of the genetics, systematics, and conservation of this endangered species.

First report of detection of microcystins in farmed mediterranean mussels Mytilus galloprovincialis in Thermaikos gulf in Greece

BACKGROUND

Microcystins are emerging marine biotoxins, produced by potentially toxic cyanobacteria. Their presence has been reported in aquatic animals in Greek freshwater, while data are few in marine environments. Since the climate change induces eutrophication and harmful algal blooms in coastal marine ecosystems affecting the public health, further research on microcystins' presence in marine waters is required. The aim of this study was to examine the potential presence of microcystins in mussels Mytilus galloprovincialis in the largest farming areas in Thermaikos gulf, in Northern Greece, and to investigate their temporal and spatial distribution, adding to the knowledge of microcystins presence in Greek Mediterranean mussels.

RESULTS

A 4-year microcystins' assessment was conducted from 2013 to 2016, in farmed Mediterranean mussels M. galloprovincialis, in five sampling areas in Thermaikos gulf, in northern Greece, where the 90% of the Greek mussels' farming activities is located. The isolation of potentially toxic cyanobacteria was confirmed by molecular methods. An initial screening was performed with a qualitative and quantitative direct monoclonal (DM) ELISA and results above 1 ng g-1 were confirmed for the occurrence of the most common microcystins-RR, -LR and -YR, by Ultra High Performance Liquid Chromatography (UHPLC) coupled with a high- resolution mass spectrometer (HRMS) (Orbitrap analyzer). Microcystin-RR and microcystin-LR were detected, while the intensity of microcystin-YR was below the method detection limit. Most samples that exhibited concentrations above 1 ng g-1 were detected during the warm seasons of the year and especially in spring. Results indicated an overestimation of the ELISA method, since concentrations ranged between 0.70 ± 0.15 ng g-1 and 53.90 ± 3.18 ng g-1, while the confirmation denoted that the levels of microcystins were 6 to 22 times lower.

CONCLUSIONS

Microcystin-RR and microcystin-LR were detected for the first time in mussel M. galloprovincialis, harvested from farms in Thermaikos gulf, in Central Macedonia, Greece. Their presence was linked to potentially toxic cyanobacteria. Bioaccumulation was observed in digestive gland, while the concentrations in muscles were found extremely low. Samples with levels above 1 ng g-1 were observed mostly during spring, confirming the seasonal distribution of microcystins. The comparison of the results by the ELISA and the LC-Orbitrap MS method indicated an overestimation of concentration by the ELISA method.

Fatty acid response of the invasive bivalve Limnoperna fortunei fed with Microcystis aeruginosa exposed to high temperature

The success of Limnoperna fortunei as an invasive freshwater bivalve species is related to its physiological plasticity to endure changes in environmental conditions. The aim of this study was to investigate the physiological responses of L. fortunei after feeding on Microcystis aeruginosa grown at 26 °C (control) and 29 °C during 10 days. At the beginning, we measured biomass, fatty acids (FAs) composition on Cyanobacteria grown at both temperatures at different time intervals. Afterwards, mussels were fed with the thawed M. aeruginosa cells and their FA profile was measured after 15 days of feeding. M. aeruginosa exposed to 29 °C had the highest content of the FAs 18:2ω6 and cis-18:1ω9. The FA profile of the consumer L. fortunei fed with M. aeruginosa cultures grown at 29 °C was also significantly different to those fed with cultures grown at 26 °C, with a significant increased Eicosapentaenoic acid (EPA, 20:5ω3) and Arachidonic acid (ARA, 20:4ω6) concentrations. L. fortunei was already known to be physiologically adapted to live at 29 °C, but our results also shown a high biosynthesis of EPA and ARA (increase of 70 and 40% respectively, compared with 26 °C) and avoided the lipid peroxidation of both FAs. This increased EPA and ARA biosynthesis may be an important source of ω3 and ω6 polyunsaturated FAs (PUFAs) for higher trophic levels, such as the pelagic fishes or birds that mainly prey on these mussels. The transfer of the cyanobacterial response at higher temperature to higher trophic levels will influence the overall functioning of freshwater bodies.

Antioxidant responses of triangle sail mussel Hyriopsis cumingii exposed to toxic Microcystis aeruginosa and thermal stress

Harmful algal blooms (HABs) and thermal stress as climate changes become more common in global water ecosystem, especially under eutrophic habitats. Here our study examined the combined impacts of bloom forming cyanobacteria Microcystis aeruginosa and thermal stress on the antioxidant responses of the ecologically important species triangle sail mussel Hyriopsis cumingii. The differential responses of a series of enzymes, e.g. superoxide dismutase (SOD), catalase (CAT), glutathione peroxidase (GPx) and glutathione-S-transferase (GST), as well as signal metabolites including reactive oxygen species (ROS), malondialdehyde (MDA) and glutathione (GSH) involved in antioxidant defense mechanisms were analyzed during 14 d exposure to toxic cyanobacterium M. aeruginosa and 7 d depuration period. The activities of SOD and GPx as well as the content of ROS and MDA in H. cumingii increased, while CAT activity reduced due to M. aeruginosa exposure. Thermal stress resulted in decrease of CAT, the accumulation of GSH and the enhance of GST and SOD. Meanwhile, the interactive effects among M. aeruginosa, thermal stress and time were also observed on most parameters except for GST activity. The total amount of microcystins (MC) in sail mussels increased with concentrations of exposed M. aeruginosa, independently of the presence or absence of thermal stress. Although around 50% of MC in mussels dropped in the depuration period, most parameters showed alterations because of cyanobacteria exposure and thermal stress. Overall, these findings suggested that toxic cyanobacteria or thermal stress induces oxidative stress and severely affects the enzymes activities and intermediates level associated with antioxidant defense mechanisms in sail mussels respectively. More importantly, the toxic impacts on sail mussels could be intensified by their combination.

Biomarkers in bivalve mollusks and amphipods for assessment of effects linked to cyanobacteria and elodea: Mesocosm study

The effects of cyanobacteria (Aphanizomenon flos-aquae (90%), Microcystis aeruginosa) and dense Elodea canadensis beds on the health endpoints of the amphipod Gmelinoides fasciatus and bivalve mollusc Unio pictorum were examined in mesocosms with simulated summer conditions (July-August 2018) in the environment of the Rybinsk Reservoir (Volga River Basin, Russia). Four treatments were conducted, including one control and three treatments with influencing factors, cyanobacteria and dense elodea beds (separately and combined). After 20 days of exposure, we evaluated the frequency of malformed and dead embryos in amphipods, heart rate (HR) and its recovery (HRR) after stress tests in molluscs as well as heat tolerance (critical thermal maximum or CTMax) in both amphipods and molluscs. The significant effect, such as elevated number of malformed embryos, was recorded after exposure with cyanobacteria (separately and combined with elodea) and presence of microcystins (MC) in water (0.17 μg/l, 40% of the most toxic MC-LR contribution). This study provided evidence that an elevated number (>5% of the total number per female) of malformed embryos in amphipods showed noticeable toxicity effects in the presence of cyanobacteria. The decreased oxygen under the influence of dense elodea beds led to a decrease in HR (and an increase in HRR) in molluscs. The notable effects on all studied biomarkers, embryo malformation frequency and heat tolerance in the amphipod G. fasciatus, as well as the heat tolerance and heart rate in the mollusc U. pictorum, were found when both factors (elodea and cyanobacteria) were combined. The applied endpoints could be further developed for environmental monitoring, but the obtained results support the importance of the combined use of several biomarkers and species, especially in the case of multi-factor environmental stress.

Seasonal variation of microcystins and their accumulation in fish in two large shallow lakes of China

Bioaccumulation of microcystins (MCs) has been widely observed in aquatic vertebrates and invertebrates, but its seasonal and specific variations remain unclear. In the present study, dissolved MCs in water, algal cell-bound MCs and muscle tissue MCs of nine fish species were investigated monthly in two of the largest shallow lakes in China: Lake Taihu and Lake Chaohu. The fish species were grouped as carnivorous, planktivorous, and omnivorous fish. Seasonal variations in dissolved and algal cell-bound MCs in water and MCs contents of fish hepatopancreas and muscle were investigated in the two lakes from 2009 to 2010. Dissolved MCs in water ranged from 0.35 to 2.56 µg l^-1 in Lake Taihu and 0.16 to 2.45 µg l^-1 in Lake Chaohu, and showed seasonally a unimodal distribution. Algal cell-bound MCs also showed a similar seasonal variation in both lakes, but dissolved MCs in water peaked about one month later than algal cell-bound MCs. The MCs content in the Fish muscle was higher MCs from October to December than in the other months. For most of the fish species, it exceeded the tolerable daily intake value established by the WHO. The averaged MCs content in the muscle of carnivorous, planktivorous, omnivorous fish was 48.2, 28.7 and 37.8 μg kg^-1 in Lake Taihu, respectively, and 27.8, 18.6 and 20.4 μg kg^-1 in Lake Chaohu. It was significantly higher in carnivorous fish than in planktivorous and omnivorous fish, indicating that carnivorous fish has a higher exposure risk to the local people when consuming the harvested fish. The average ratio of hepatopancreas to muscle MCs contents was 13.0, 25.2, 13.8 for carnivorous, planktivorous, omnivorous fishes in Lake Taihu, respectively, and 18.0, 24.9, 14.8 in Lake Chaohu. These ratio for planktivorous fish almost doubled that for carnivorous and omnivorous fish. High correlation of MC content in carnivorous, omnivorous and planktivorous fish indicates that MCs can be delivered along trophic levels in the food chains.

Accumulation of Microcystin (LR, RR and YR) in Three Freshwater Bivalves in Microcystis aeruginosa Bloom Using Dual Isotope Tracer

Abstract: Stable isotope tracers were first applied to evaluate the Microcystis cell assimilation efficiency of Sinanodonta bivalves, since the past identification method has been limited to tracking the changes of each chl-a, clearity, and nutrient. The toxicity profile and accumulation of MC-LR, -RR and -YR in different organs (foot and digestive organs) from the three filter-feeders (Sinanodonta woodina, Sinanodonta arcaeformis, and Unio douglasiae) were assessed under the condition of toxigenic cyanobacteria (Microcystis aeruginosa) blooms through an in situ pond experiment using ¹³C and ¹⁵N dual isotope tracers. Chl-a concentration in the manipulated pond was dramatically decreased after the beginning of the second day, ranging from 217.5 to 15.6 μg·L^-1. The highest amount of MCs was incorporated into muscle and gland tissues in U. douglasiae during the study period, at nearly 2 or 3 times higher than in S.woodiana and S. arcaeformis. In addition, the incorporated ¹³C and ¹⁵N atom % in the U. douglasiae bivalve showed lower values than in other bivalves. The results demonstrate that U. douglasiae has less capacity to assimilate toxic cyanobacteria derived from diet. However, the incorporated ¹³C and ¹⁵N atom % of S. arcaeformis showed a larger feeding capacity than U. douglasiae and S. wodiana. Our results therefore also indicate that S. arcaeformis can eliminate the toxin more rapidly than U. douglasiae, having a larger detoxification capacity.

Effects of depuration on histopathological changes in tilapia (Oreochromis niloticus) after exposure to cylindrospermopsin

Cylindrospermopsin (CYN) is a highly water-soluble cytotoxin produced by several species of freshwater cyanobacteria and it is considered the second most studied cyanotoxin worldwide. CYN acts as a potent protein and glutathione synthesis inhibitor, as well as inducing genotoxicity, oxidative stress and histopathological alterations. Studies concerning the depuration of cyanobacterial toxins in aquatic organisms, especially in fish, are of great interest for fish economy and public health, but are scarce in the case of CYN. This is the first study reporting the ability of depuration (3 - 7 days) in reversing or ameliorating the histopathological lesions induced in liver, kidney, heart, intestines, and gills of tilapia (Oreochromis niloticus) due to exposure by immersion to repeated doses of a CYN-containing culture of A. ovalisporum for 14 days. The main histopathological changes induced by CYN were glucogenic degeneration and loss of the normal hepatic cord-structure (liver), hyperemia, dilated Bowman's capsule and cellular tumefaction (kidney), myofibrolysis, hemorrhages and edema (heart), necrosis and partial loss of microvilli (gastrointestinal tract), and hyperemia and inflammatory cells infiltrates (gills). After 3 days of depuration, gills were totally recovered, while the liver, kidney, and gastrointestinal tract required 7 days, and longer depuration periods may be needed for a full recovery of the heart. In addition, the morphometric study indicated that depuration managed to reverse the affectation in the hepatocytes nuclear diameters and cross sections of the proximal and distal convoluted tubules induced in CYN-exposed fish. In general, these results validate depuration as an effective practice for detoxification of fish contaminated with CYN. © 2016 Wiley Periodicals, Inc. Environ Toxicol 32: 1318-1332, 2017.

Evidence of freshwater algal toxins in marine shellfish: Implications for human and aquatic health

The occurrence of freshwater harmful algal bloom toxins impacting the coastal ocean is an emerging threat, and the potential for invertebrate prey items to concentrate toxin and cause harm to human and wildlife consumers is not yet fully recognized. We examined toxin uptake and release in marine mussels for both particulate and dissolved phases of the hepatotoxin microcystin, produced by the freshwater cyanobacterial genus Microcystis. We also extended our experimental investigation of particulate toxin to include oysters (Crassostrea sp.) grown commercially for aquaculture. California mussels (Mytilus californianus) and oysters were exposed to Microcystis and microcystin toxin for 24h at varying concentrations, and then were placed in constantly flowing seawater and sampled through time simulating riverine flushing events to the coastal ocean. Mussels exposed to particulate microcystin purged the toxin slowly, with toxin detectable for at least 8 weeks post-exposure and maximum toxin of 39.11ng/g after exposure to 26.65μg/L microcystins. Dissolved toxin was also taken up by California mussels, with maximum concentrations of 20.74ng/g after exposure to 7.74μg/L microcystin, but was purged more rapidly. Oysters also took up particulate toxin but purged it more quickly than mussels. Additionally, naturally occurring marine mussels collected from San Francisco Bay tested positive for high levels of microcystin toxin. These results suggest that ephemeral discharge of Microcystis or microcystin to estuaries and the coastal ocean accumulate in higher trophic levels for weeks to months following exposure.

Accumulation of microcystins in a dominant Chironomid Larvae (Tanypus chinensis) of a large, shallow and eutrophic Chinese lake, Lake Taihu

Although there have been numerous studies on microcystin (MC) accumulation in aquatic organisms recently, the bioaccumulation of MCs in relatively small sized organisms, as well as potential influencing factors, has been rarely studied. Thus, in this study, we investigated the bioaccumulation of three MC congeners (-LR, -RR and -YR) in the chironomid larvae of Tanypus chinensis (an excellent food source for certain fishes), the potential sources of these MCs, and potentially relevant environmental parameters over the course of one year in Lake Taihu, China. MC concentrations in T. chinensis varied temporally with highest concentrations during the warmest months (except August 2013) and very low concentrations during the remaining months. Among the three potential MC sources, only intracellular MCs were significantly and positively correlated with MCs in T. chinensis. Although MC concentrations in T. chinensis significantly correlated with a series of physicochemical parameters of water column, cyanobacteria species explained the most variability of MC accumulation, with the rest primarily explained by extraMC-LR. These results indicated that ingestion of MC-producing algae of cyanobacteria accounted for most of the MC that accumulated in T. chinensis. The high MC concentrations in T. chinensis may pose a potential health threat to humans through trophic transfer.

Microcystin accumulation and biochemical responses in the edible clam Corbiculaleana P. exposed to cyanobacterial crude extract

We investigated the accumulation and effects of cyanobacterial crude extract (CCE) containing microcystins (MCs) on the edible clam Corbiculaleana P. Toxic effects were evaluated through the activity of antioxidant and detoxification enzymes: catalase (CAT), superoxide dismutase (SOD), and glutathione-S-transferases (GSTs) from gills, foot, mantle and remaining soft tissues. Clams were exposed to CCE containing 400μg MC-LReq/L for 10days and were then kept in toxin-free water for 5days. Clam accumulated MCs (up to 3.41±0.63μg/g dry weight (DW) of unbound MC and 0.31±0.013μg/g DW of covalently bound MC). Detoxification and antioxidant enzymes in different organs responded differently to CCE during the experiment. The activity of SOD, CAT, and GST in the gills and mantle increased in MC-treated clams. In contrast, CAT and GST activity was significantly inhibited in the foot and mostly only slightly changed in the remaining tissues. The responses of biotransformation, antioxidant enzyme activity to CCE and the fast elimination of MCs during depuration help to explain how the clam can survive for long periods (over a week) during the decay of toxic cyanobacterial blooms in nature.

Temperature and food concentration have limited influence on the mixture toxicity of copper and Microcystis aeruginosa to Daphnia magna

Standard ecotoxicity tests are conducted under constant and favorable experimental conditions. In natural communities, however, the toxicity of chemicals may be influenced by abiotic and biotic environmental factors. Firstly, the authors examined the influence of temperature and total food concentration on the nature of the combined effects of copper (Cu) and the cyanobacterium Microcystis aeruginosa to Daphnia magna (i.e., whether the combined effects deviated from noninteraction). Secondly, the authors investigated the relative influence of the percentage of M. aeruginosa in the diet, temperature, and total food concentration on chronic Cu toxicity to D. magna. The nature of the combined effects between Cu and M. aeruginosa (i.e., synergism according to the independent action reference model and noninteraction according to concentration addition reference model) was not affected by temperature and total food concentration. In line with other studies, the concentration addition reference model gave rise to more protective predictions of mixture toxicity than the independent action reference model, thus confirming the former model's suitability as a conservative scenario for evaluating mixture toxicity of Cu and M. aeruginosa under the temperature and food concentrations tested. Further, the 21-d median effective concentration for Cu based on reproduction varied between 20 μg/L and 100 μg/L, and the results indicate that the percentage of M. aeruginosa explained 76% of the variance in the Cu median effective concentration for reproduction, whereas the effects of temperature and total food were limited (together explaining 11% of the variance). The present study suggests that environmental risk assessment of Cu should consider specific situations where harmful M. aeruginosa blooms can co-occur with elevated Cu exposure.

Microcystin release and Microcystis cell damage mechanism by alum treatment with long-term and large dose as in-lake treatment

Most of our previous studies reported aluminum causes no cell damage or lysis, and no subsequent toxin release in conventional treatment of drinking water or in the laboratory, on the contrary, we investigated the effect of long-term and large-dose alum treatment, because the environmental conditions in lakes and treatment plants are widely different. The microcosm experiments were designed to simulate the effect of adding alum under the similar conditions of common lakes and reservoirs, and the bottle experiments were conducted to examine the budget or dynamics of microcystin after adding alum. In precipitate analyses, we also confirm the release and dynamics of microcystin and the damage mechanisms of Microcystis cells under alum treatment. In microcosms treated with alum alone, the extracellular microcystin-LR (MC-LR) concentration increased to approximately 82% in 7 days. Similar results were obtained in bottle experiments. By plotting the concentration of released microcystin over time, we inferred that the extracellular MC-LR concentration exponentially rose toward an asymptotic maximum. Moreover, in scanning electron microscope images, some cells exhibited torn membranes with miniscule traces of aluminum hydroxide coating. We conclude that alum treatment, particularly at maximum dosage administered over long periods, seriously damages Microcystis cells and induces microcystin release. Therefore, long-term application of large alum doses is not recommended as an in-lake treatment.

Microcystin uptake and biochemical responses in the freshwater clam Corbicula leana P. exposed to toxic and non-toxic Microcystis aeruginosa: Evidence of tolerance to cyanotoxins

We investigated the accumulation and adverse effects of toxic and non-toxic Microcystis in the edible clam Corbicula leana. Treated clams were exposed to toxic Microcystis at 100 μg of MC (microcystin)-LR_eq L^-1 for 10 days. The experimental organism was then placed in toxin-free water and fed on non-toxic Microcystis for the following 10 days for depuration. Filtering rates (FRs) by C. leana of toxic and non-toxic Microcystis and of the green alga Chlorella vulgaris as a control were estimated. Adverse effects were evaluated though the activity of catalase (CAT), superoxide dismutase (SOD) and glutathione S-transferase (GST). Clam accumulated MCs (up to 12.7 ± 2.5 μg g^-1 dry weight (DW) of free MC and 4.2 ± 0.6 μg g^-1 DW of covalently bound MC). Our results suggest that although both toxic and non-toxic cyanobacteria caused adverse effects by inducing the detoxification and antioxidant defense system, the clam was quite resistant to cyanotoxins. The estimated MC concentration in C. leana was far beyond the World Health Organization's (WHO) provisional tolerable daily intake (0.04 μg kg^-1 day^-1), suggesting that consuming clams harvested during cyanobacterial blooms carries a high health risk.

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.

The effect of temperature on the sensitivity of Daphnia magna to cyanobacteria is genus dependent

In the present study, the authors investigated the effects of 6 different genera of cyanobacteria on multiple endpoints of Daphnia magna in a 21-d life table experiment conducted at 3 different temperatures (15 °C, 19 °C, and 23 °C). The specific aims were to test if the effect of temperature on Daphnia's sensitivity to cyanobacteria differed among different cyanobacteria and if the rank order from most to least harmful cyanobacteria to Daphnia reproduction changed or remained the same across the studied temperature range. Overall, the authors observed a decrease in harmful effects on reproduction with increasing temperature for Microcystis, Nodularia, and Aphanizomenon, and an increase in harmful effects with increasing temperature for Anabaena and Oscillatoria. No effect of temperature was observed on Daphnia sensitivity to Cylindrospermopsis. Harmful effects of Microcystis and Nodularia on reproduction appear to be mirrored by a decrease in length. On the other hand, harmful effects of Anabaena, Aphanizomenon, and Oscillatoria on reproduction were correlated with a decrease in intrinsic rate of natural increase, which was matched by a later onset of reproduction in exposures to Oscillatoria. In addition, the results suggest that the cyanobacteria rank order of harmfulness may change with temperature. Higher temperatures may increase the sensitivity of D. magna to the presence of some cyanobacteria (Anabaena and Oscillatoria) in their diet, whereas the harmful effects of others (Microcystis, Nodularia, and Aphanizomenon) may be reduced by higher temperatures.

Inhibitory effect of naringin on microcystin-LR uptake in the freshwater snail Sinotaia histrica

Gastropods are an important food source for aquatic animals, and have been demonstrated to transfer microcystin (MC) to higher trophic levels through the food web. In this study, we performed an oral administration experiment to evaluate whether naringin can inhibit MC-LR uptake in the freshwater snail Sinotaia histrica. We also observed the effect of MC-LR on the organizational pathology of the hepatopancreas in S. histrica. Following exposure to cells of Microcystis ichthyoblabe, S. histrica showed vacuolization and separation of the basal lamina from cells in the hepatopancreas. Initial treatment with 1mM naringin resulted in the prevention of MC-LR uptake rate by approximately 60% over 8days, whereas initial treatment with 10mM naringin suppressed microcystin uptake in 2days, despite an increase in MC-LR levels in the snail from days 5 to 8. With continuous treatment of 10mM naringin, the uptake prevention rate was 100%. Overall, we observed a strong inhibitory effect against MC-LR with naringin treatment. This study provides a potential mechanism to prevent the uptake of microcystin in the aquatic food web, thereby limiting its toxicity in cyanobacterial bloom-polluted areas where the environment can be controlled and may have further applications in the aquaculture of gastropods.

Toxicity thresholds for juvenile freshwater mussels Echyridella menziesii and crayfish Paranephrops planifrons, after acute or chronic exposure to Microcystis sp

Survival of juvenile freshwater mussels (Echyridella menziesii (Gray, 1843) formerly known as Hyridella menziesi) and crayfish (Paranephrops planifrons, White, 1842) decreased after four days exposure to microcystin-containing cell-free extracts (MCFE) of Microcystis sp. at concentrations typical of severe cyanobacterial blooms. Crayfish survival was 100, 80, and 50% in microcystin concentrations of 1339, 2426, and 11146 μg L(-1) respectively, and shade- and shelter-seeking behavior was negatively affected when concentrations were ≥2426 μg L(-1) . Mussel survival decreased to 92% and reburial rates decreased to 16% after exposure for 96 h to MCFE containing microcystins at concentrations of 5300 μg L(-1) . Crayfish survival was 100% when fed freeze-dried Microcystis sp. incorporated into an artificial diet (6-100 μg microcystin kg(-1) ww) at dietary doses from 0.03 to 0.55 μg g(-1) body weight d(-1) for 27 days. Specific growth rate was significantly lower in crayfish fed ≥0.15 μg g(-1) body weight day(-1) compared with controls, but not compared with a diet incorporating nontoxic cyanobacteria. Microcystins accumulated preferentially in crayfish hepatopancreas and mussel digesta as MCFE or dietary concentrations increased. These laboratory data indicate that, assuming dissolved oxygen concentrations remain adequate, and no simultaneous exposure to live Microcystis sp. cells, cell-free microcystins will only be a significant stressor to juvenile crayfish and mussels in severe Microcystis sp. blooms. In contrast, crayfish were negatively affected by relatively low concentrations of microcystins in artificial diets compared with those measured locally in benthic cyanobacterial mats.

Microcystin Contamination in Sea Mussel Farms from the Italian Southern Adriatic Coast following Cyanobacterial Blooms in an Artificial Reservoir

An experimental study was performed in 2009-2010 to investigate the polluting effect of eutrophic inland waters communicating with the sea coast. The study was planned after a heavy and long-lasting Planktothrix rubescens bloom occurred in the Lake Occhito, an artificial reservoir. The waters of the reservoir flow into the southern Adriatic Sea, near several marine breeding of Mytilus galloprovincialis mussels, a typical seafood from the Apulia region (Southern Italy). A monitoring study of water and mussels from the sea coast of northern Apulia region and on the Occhito reservoir was carried out over twelve months, to get more information regarding the contamination by cyanobacteria and related cyanotoxins. Elisa immunoassay analyses estimated total microcystin amounts from 1.73 to 256 ng/g in mussels, up to 0.61 μg/L in sea water and up to 298.7 μg/L in lake water. Analyses of some samples of free-living marine clams as well as of marine and freshwater fish proved microcystin contamination. Selective confirmatory analyses by LC/ESI-Q-ToF-MS/MS on some mussel samples identified the microcystin desMe-MC-RR as the major toxin; this compound has been reported in the literature as a specific marker toxin of Planktothrix rubescens blooms. Our study describes for the first time the direct relationship between environmental pollution and food safety, caused by seafood contamination from freshwater toxic blooms.

Specific proteomic response of Unio pictorum mussel to a mixture of glyphosate and microcystin-LR

Cyanobacterial toxins and pesticides regularly impact freshwaters. Microcystin-LR is one of the most toxic and common cyanobacterial toxins whereas glyphosate is the active ingredient of a widely use herbicide. As filter feeders, freshwater mussels are particularly exposed. Like many native bivalve species, Unio pictorum suffers from a continuous decline in Europe. In order to get a deeper insight of its response to contaminants, U. pictorum was exposed to either 10 μg L(-1) of microcystin-LR or 10 μg L(-1) of glyphosate or a mixture of both. Proteins of the digestive glands were extracted and analyzed by DIGE. Gel analysis revealed 103 spots with statistical variations, and the response seems to be less toward glyphosate than to microcystin-LR. Specific spots have variations only when exposed to the mixture, showing that there is an interaction of both contaminants in the responses triggered. The proteins of 30 spots have been identified. They belong mostly to the cytoskeleton family, but proteins of the oxidative pathway, detoxification, and energetic metabolism were affected either by glyphosate or microcystin-LR or by the mixture. These results demonstrate the importance to study contaminants at low concentrations representative of those found in the field and that multicontaminations can lead to different response pathways.

The effect of alum coagulation for in-lake treatment of toxic Microcystis and other cyanobacteria related organisms in microcosm experiments

Microcosm and bottle experiments were conducted to evaluate the effects of alum treatment on cyanobacteria-lysing organisms and microcystin-degrading bacteria as well as Microcystis cells, and to provide detailed evidence of Microcystis cell damage by investigating precipitated Microcystis cells. The alum concentration to be pH 6.0 is the maximum which does not cause toxicity by monomeric Al, therefore, this concentration was defined as maximum dose. Microcystis cells were considerably damaged by the alum treatment with maximum dose and long contact time. Seven days post-treatment, intracellular microcystin-LR was released into the extracellular environment in excess of 95 percent and chlorophyll a is not easily released from inside the cell, chl.a of precipitated Microcystis cells was also decreased to approximately 50 percent. Moreover, alum treatment caused damage to cyanobacteria-lysing organisms and microcystin-degrading bacteria, as well as to Microcystis cells. Therefore, it could be concluded that alum treatment with maximum dose (48 mg L(-1) as AI) is not suitable for removing cyanobacterial bloom without the release of cyanotoxin in reservoirs and ponds.

Assessment of microcystin distribution and biomagnification in tissues of aquatic food web compartments from a shallow lake and evaluation of potential risks to public health

The objectives of this study were: (1) to examine the distribution and bioaccumulation of microcystins in the main components of the food web (phytoplankton, zooplankton, crayfish, shrimp, mussel, snail, fish, frog) of Lake Pamvotis (NW Greece), (2) to investigate the possibility of microcystin biomagnification and (3) to evaluate the potential threat of the contaminated aquatic organisms to human health. Significant microcystin concentrations were detected in all the aquatic organisms during two different periods, with the higher concentrations observed in phytoplankton and the lower in fish species and frogs. This is the first study reporting microcystin accumulation in the body of the freshwater shrimp Atyaephyra desmsaresti, in the brain of the fish species common carp (Cyprinus carpio) and in the skin of the frog Rana epirotica. Although there was no evidence for microcystin biomagnification, the fact that microcystins were found in lake water and in the tissues of aquatic organisms, suggests that serious risks to animal and public health are possible to occur. In addition, it is likely to be unsafe to consume aquatic species harvested in Lake Pamvotis due to the high-concentrations of accumulated microcystins.

Adaptation of freshwater mussels to cyanobacterial toxins: response of the biotransformation and antioxidant enzymes

Freshwater mussels such as the invasive Dreissena polymorpha and the indigenous Unio tumidus nourish by high filtration rates and may accumulate cyanobacteria and their toxins during cyanobacterial blooms. Physiological adaptations to cyanotoxins enable organisms to endure cyanobacterial blooms but may differ between species. Biotransformation and excretion capacities for cyanobacteria and anthropogenic pollutants have been demonstrated for Dreissena polymorpha but less for unionid species. This study compares the activities of biotransformation (glutathione S-transferase, GST) and antioxidant enzymes (superoxide dismutase, SOD and catalase, CAT) in Dreissena polymorpha to Unio tumidus in response to cyanotoxin exposure (10 μg L(-1) and 50 μg L(-1) microcystin-LR, respectively, total microcystin from a cyanobacterial crude extract) for 24 h and 7d exposure duration. Enzyme activities in Dreissena polymorpha were measured in the whole mussel tissue, digestive gland and in gills and in Unio tumidus in the digestive gland, gills, mantle, foot as well as in the remaining tissue. The sGST was elevated for the entire exposure period in the whole mussel tissue of Dreissena polymorpha but despite higher basal activities in digestive gland and gills of Unio tumidus, it was rather inhibited or unaltered in most of their tissues. Elevated SOD activity indicated oxidative stress response in Dreissena polymorpha, but not in Unio tumidus. The CAT activity was barely affected in both species, rather inhibited in Unio tumidus, despite again higher basal activities in digestive gland and remaining tissue. Compared to the indigenous Unio tumidus, the investigated biotransformation and oxidative stress combating enzymes respond stronger in the invasive Dreissena polymorpha.

Cyanotoxins: bioaccumulation and effects on aquatic animals

Cyanobacteria are photosynthetic prokaryotes with wide geographic distribution that can produce secondary metabolites named cyanotoxins. These toxins can be classified into three main types according to their mechanism of action in vertebrates: hepatotoxins, dermatotoxins and neurotoxins. Many studies on the effects of cyanobacteria and their toxins over a wide range of aquatic organisms, including invertebrates and vertebrates, have reported acute effects (e.g., reduction in survivorship, feeding inhibition, paralysis), chronic effects (e.g., reduction in growth and fecundity), biochemical alterations (e.g., activity of phosphatases, GST, AChE, proteases), and behavioral alterations. Research has also focused on the potential for bioaccumulation and transferring of these toxins through the food chain. Although the herbivorous zooplankton is hypothesized as the main target of cyanotoxins, there is not unquestionable evidence of the deleterious effects of cyanobacteria and their toxins on these organisms. Also, the low toxin burden in secondary consumers points towards biodilution of microcystins in the food web as the predominant process. In this broad review we discuss important issues on bioaccumulation and the effects of cyanotoxins, with emphasis on microcystins, as well as drawbacks and future needs in this field of research.

Effect of different microcystin profiles on toxin bioaccumulation in common carp (Cyprinus carpio) larvae via Artemia nauplii

In this study, a 12-day growth trial was conducted to compare the effect of the variation in microcystin (MC) composition in two Microcystis aeruginosa bloom samples on the growth performance and MC accumulation/transfer in the common carp (Cyprinus carpio L.) larvae. Fish were fed Artemia salina nauplii that had been preexposed to extracts from two M. aeruginosa natural blooms with different microcystins (MCs) profiles. Bloom A had MC-LR as major toxin (74.05%) while bloom B had a diversity of MC (MC-RR; MC-(H4)YR; MC-YR; MC-LR; MC-FR; MC-WR) with no dominance of MC-LR. Newly-hatched Artemia nauplii were exposed separately to the two M. aeruginosa extracts A and B (100 microg L(-1)EqMC-LR) for 2h. The MC concentration in the nauplii was 73.60+/-7.88ngEqMC-LRg(-1)FW (n=4, mean+/-SE) for bloom A and 87.04+/-10.31ngEqMC-LRg(-1)FW for bloom B. These contaminated nauplii were given at the same ration to different groups (A and B) of fish larvae. Larval weight and length from day 9 were significantly different between groups A and B, and in both cases lower than that of a control group fed non-exposed nauplii. MCs accumulation by larvae, inversely correlated with the growth performance, was also significantly different between groups A and B (37.43+/-2.61 and 54.55+/-3.01ngEqMC-LRg(-1) FW, respectively, at the end of the experimental period). These results indicate that MC profile of a bloom may have differential effects on toxin accumulation/transfer and toxicity.

Changes in the GST activity of the mussel Mytilus galloprovincialis during exposure and depuration of microcystins

Mussels are quite resistant to cyanotoxins and their resistance may be because of an efficient metabolization of cyanotoxins by glutathione-S-transferases (GST) activity. Nevertheless, other secondary metabolites may interfere with the detoxication efficiency. The accumulation and depuration of hepatotoxins produced by the freshwater cyanobacterium Microcystis aeruginosa in the mussel Mytilus galloprovincialis were studied. Mussels were fed twice a day 1.5x10(5) cells/mL of the toxic cyanobacterium, which produces microcystins (MCs) -FR, -LR and -WR, for 4 days. After that period, the animals were placed in toxin-free water and were fed the green algae Ankistrodesmus sp. During 2 weeks, the concentration of the toxin in the mussels was monitored using an ELISA assay. Mussels showed a maximum detectable level of MCs of 0.38 microg/g mussels dry weight (DW) during the accumulation period and 0.37 microg MC/g mussel DW by day 4 of the depuration period. Then there was a decrease trend with peaks of toxin at days 8 and 12 of the depuration period. The activity of the detoxication enzymes GST was studied and the results showed that the peaks of toxin in the mussels coincide with an increase in the activity of GST. These results support the hypothesis that the rise of the toxin level on days 4, 8 and 12 of the depuration period in the mussels may be related to the renewal of protein phosphatases and subsequent release of unbound toxins.

Influence of toxic cyanobacteria on community structure and microcystin accumulation of freshwater molluscs

Community structure and microcystin accumulation of freshwater molluscs were studied before and after cyanobacterial proliferations, in order to assess the impact of toxic blooms on molluscs and the risk of microcystin transfer in food web. Observed decrease in mollusc abundance and changes in species richness in highly contaminated waters were not significant; however, relative abundances of taxa (prosobranchs, pulmonates, bivalves) were significantly different before and after cyanobacterial bloom. Pulmonates constituted the dominant taxon, and bivalves never occurred after bloom. Microcystin accumulation was significantly higher in molluscs from highly (versus lowly) contaminated waters, in adults (versus juveniles) and in pulmonates (versus prosobranchs and bivalves). Results are discussed according to the ecology of molluscs, their sensitivity and their ability to detoxify.

Spatial and temporal variations of microcystins in hepatopancreas of a freshwater snail from Lake Taihu

In this paper, spatial and temporal variations of three common microcystins (MC-RR, MC-YR, and MC-LR) in the hepatopancreas of a freshwater snail (Bellamya aeruginosa) were studied monthly in two bays of Lake Taihu. Microcystins (MCs) concentration in hepatopancreas was quantified by liquid chromatography-mass spectrometry (LC-MS). The MCs concentrations in hepatopancreas were higher at Site 1 than those at other sites, which was in agreement with the changes of intracellular MCs concentrations in the water column. There was a significant correlation between MCs concentrations in the hepatopancreas and that in the seston, suggesting that spatial variances of MCs concentrations in hepatopancreas among the five sites were due to spatial changes of toxic Microcystis cells in the water column. PCCA indicates that in addition to Microcystis, other factors (e.g., water temperature) also substantially affected the accumulation of MCs in hepatopancreas of the snail.

Microcystin dynamics in aquatic organisms

Eutrophication of surface water has increased significantly during the past decade, resulting in increased occurrences of toxic blooms. Cyanotoxins have become a global health threat to humans, wild animals, or domestic livestock. Hepatotoxic microcystins (MC) are the predominant cyanotoxins, which accumulate in aquatic organisms and are transferred to higher trophic levels. This is an issue of major concern in aquatic toxicology, as it involves the risk for human exposure through the consumption of contaminated fish and other aquatic organisms. The persistence and detoxification of MC in aquatic organisms are important issues for public health and fishery economics. Bioaccumulation of MC depends on the toxicity of the strains, mode of feeding, and detoxication mechanisms. Although mussels, as sessile filter feeders, seem to be organisms that ingest more MC, other molluscs like gastropods, as well as zooplankton and fish, may also retain average similar levels of toxins. Edible animals such as some species of molluscs, crustaceans, and fish present different risk because toxins accumulate in muscle at low levels. Carnivorous fish seem to accumulate high MC concentrations compared to phytophagous or omnivorous fish. This review summarizes the existing data on the distribution and dynamics of MC in contaminated aquatic organisms.

Uptake and depuration of anatoxin-a by the mussel Mytilus galloprovincialis (Lamarck, 1819) under laboratory conditions

Cyanobacterial blooms tend to be more common in warm and nutrient-enriched waters and are increasing in many aquatic water bodies due to eutrophication. The aim of this work is to study the accumulation and depuration of anatoxin-a by Mytilus galloprovincialis a widespread distributed mussel living in estuarine and coastal waters and recognized worldwide as a bioindicator (e.g. Mussel Watch programs). Research on the distribution and biological effects of anatoxin-a in M. galloprovincialis is important. Nevertheless, the risk of human intoxication due to the consumption of contaminated bivalves should also be considered. A toxic bloom was simulated in an aquarium with 5 x 10(5) cell ml(-1) of Anabaena sp. (ANA 37), an anatoxin-a producing strain. Mussels were exposed to Anabaena for 15 days and then 15 days of depuration followed. Three or more animals were sampled every 24h for total toxin quantification and distribution in soft tissues (edible parts). Water samples were also taken every 24h in order to calculate total dissolved and particulate anatoxin-a concentrations. Anatoxin-a was quantified by HPLC with fluorescence detection. No deaths occurred during accumulation and depuration periods. One day after the beginning of depuration, the toxin could not be detected in the animals. Anatoxin-a is distributed in the digestive tract, muscles and foot and is probably actively detoxified.

Cyanobacterial toxins: a qualitative meta-analysis of concentrations, dosage and effects in freshwater, estuarine and marine biota

This paper reviews the rapidly expanding literature on the ecological effects of cyanobacterial toxins. The study employs a qualitative meta-analysis from the literature examining results from a large number of independent studies and extracts general patterns from the literature or signals contradictions. The meta-analysis is set up by putting together two large tables--embodying a large and representative part of the literature (see Appendix A). The first table (Table A.1) reviews the presence (concentrations) of different cyanobacterial toxins in the tissues of various groups of aquatic biota after exposure via different routes, experimentally in the lab or via natural routes in the environment. The second table (Table A.2) reviews the dose dependent effect of toxins on biota. The great majority of studies deal with the presence and effects of microcystin, especially of the MC-LR congener. Although this may partly be justified--MC-LR is an abundant and highly toxic protein--our review also emphasizes what is known about (i) other MC congeners (a number of studies showed a preferred accumulation of the less toxic variant MC-RR in animal tissues), (ii) nodularin (data on a range of biota from studies on the Baltic Sea), (iii) neurotoxins like anatoxin-a(s), which are conspicuously often present at times when mass mortalities of birds occur, (iv) a few studies on the presence and effects of cylindrospermposin, as well as (v) the first examples of ecological effects of newly identified bioactive compounds, like microviridin-J. Data were reorganized to assess to what extent bioconcentration (uptake and concentration of toxins from the water) or biomagnification (uptake and concentration via the food) of cyanobacterial toxins occurs in ecosystems. There is little support for the occurrence of biomagnification, and this reduces the risk for biota at higher trophic levels. Rather than biomagnification biodilution seems to occur in the foodweb with toxins being subject to degradation and excretion at every level. Nevertheless toxins were present at all tropic levels, indicating that some vectorial transport must take place, and in sufficient quantities for effects to possibly occur. Feeding seemed to be the most important route for exposure of aquatic biota to cyanobacterial toxins. A fair number of studies focus on dissolved toxins, but in those studies purified toxin typically is used, and biota do not appear very sensitive to this form of exposure. More effects are found when crude cyanobacterial cell lysates are used, indicating that there may be synergistic effects between different bioactive compounds. Aquatic biota are by no means defenseless against toxic cyanobacteria. Several studies indicate that those species that are most frequently exposed to toxins in their natural environment are also the most tolerant. Protection includes behavioral mechanisms, detoxication of MC and NODLN by conjugation with glutathione, and fairly rapid depuration and excretion. A common theme in much of the ecological studies is that of modulating factors. Effects are seldom straightforward, but are dependent on factors like the (feeding) condition of the animals, environmental conditions and the history of exposure (acclimation and adaptation to toxic cyanobacteria). This makes it harder to generalize on what is known about ecological effects of cyanobacterial toxins. The paper concludes by summarizing the risks for birds, fish, macroinvertebrates and zooplankton. Although acute (lethal) effects are mentioned in the literature, mass mortalities of--especially--fish are more likely to be the result of multiple stress factors that co-occur during cyanobacterial blooms. Bivalves appear remarkably resistant, whilst the harmful effects of cyanobacteria on zooplankton vary widely and the specific contribution of toxins is hard to evaluate.

Accumulation of cyanobacterial toxins in freshwater "seafood" and its consequences for public health: a review

This review summarizes and discusses the current understanding of human exposure to cyanobacterial toxins in "seafood" collected from freshwater and coastal areas. The review consists of three parts: (a) the existing literature on concentrations of cyanobacterial toxins in seafood is reviewed, and the likelihood of bioaccumulation discussed; (b) we derive cyanotoxin doses likely to occur through seafood consumption and propose guideline values for seafood and compare these to guidelines for drinking water; and (c) we discuss means to assess, control or mitigate the risks of exposure to cyanotoxins through seafood consumption. This is discussed in the context of two specific procedures, the food specific HACCP-approach and the water-specific Water Safety Plan approach by the WHO. Risks of exposure to cyanotoxins in food are sometimes underestimated. Risk assessments should acknowledge this and investigate the partitioning of exposure between drinking-water and food, which may vary depending on local circumstances.

Toxins of cyanobacteria

Blue-green algae are found in lakes, ponds, rivers and brackish waters throughout the world. In case of excessive growth such as bloom formation, these bacteria can produce inherent toxins in quantities causing toxicity in mammals, including humans. These cyanotoxins include cyclic peptides and alkaloids. Among the cyclic peptides are the microcystins and the nodularins. The alkaloids include anatoxin-a, anatoxin-a(S), cylindrospermopsin, saxitoxins (STXs), aplysiatoxins and lyngbyatoxin. Both biological and chemical methods are used to determine cyanotoxins. Bioassays and biochemical assays are nonspecific, so they can only be used as screening methods. HPLC has some good prospects. For the subsequent detection of these toxins different detectors may be used, ranging from simple UV-spectrometry via fluorescence detection to various types of MS. The main problem in the determination of cyanobacterial toxins is the lack of reference materials of all relevant toxins. In general, toxicity data on cyanotoxins are rather scarce. A majority of toxicity data are known to be of microcystin-LR. For nodularins, data from a few animal studies are available. For the alkaloids, limited toxicity data exist for anatoxin-a, cylindrospermopsin and STX. Risk assessment for acute exposure could be relevant for some types of exposure. Nevertheless, no acute reference doses have formally been derived thus far. For STX(s), many countries have established tolerance levels in bivalves, but these limits were set in view of STX(s) as biotoxins, accumulating in marine shellfish. Official regulations for other cyanotoxins have not been established, although some (provisional) guideline values have been derived for microcystins in drinking water by WHO and several countries.

Accumulation of nodularin in sediments, mussels, and fish from the Gulf of Gdańsk, southern Baltic Sea

In the Gulf of Gdańsk, as in other parts of the Baltic Sea, toxic blooms of Nodularia spumigena are an annual phenomenon. In the present work, the accumulation of nodularin (NOD), a cyanobacterial pentapeptide hepatotoxin, in sediments, blue mussels, and flounders from the Gulf of Gdańsk was studied by enzyme-linked immunosorbent assay (ELISA). In the surface layers of the sediments NOD concentration ranged from 2.3 ng/g dry weight (dw) several months after cyanobacterial bloom to 75 ng/g dw during the bloom. The highest toxin content in mussels was 139 ng/g dw. In two sampling stations situated in the coastal waters of the Gulf of Gdańsk the concentrations of NOD in sediments and mussels were significantly lower than those measured in the Gulf of Finland. In sediments and mussels collected in the Gulf of Gdańsk, the toxin was also detected in March when N. spumigena did not occur. In flounder, NOD accumulated in the liver (489 ng/g dw), guts (21 ng/g dw), and gonads (21 ng/g dw). Hybride quadrupole-time-of-flight liquid chromatography/mass spectrometry/mass spectrometry (TOF-LC/MS/MS) confirmed the presence of NOD in sediment, mussel, and fish samples. Additionally, other NOD analogues, ([DMAdda(3)]NOD and [dhb(5)]NOD), were detected in sediments and mussel tissue. No NOD conjugates with reduced glutathione or cysteine were found in fish and mussels.

Foodweb transfer, accumulation, and depuration of microcystins, a cyanobacterial toxin, in pumpkinseed sunfish (Lepomis gibbosus)

Zooplankton accumulate microcystins (MC), a potent cyanobacteria toxin, and therefore may act as vectors of the toxin up the aquatic food web; however this transfer has not yet been quantified. In addition there is a lack of information regarding fish's ability to metabolize MC when administered a low dose over a longer period of time. We monitored MC concentrations in three levels of an aquatic food web: phytoplankton, zooplankton, and sunfish (Lepomis gibbosus). Bosmina appeared to be both a major accumulator of MC in zooplankton and the major vector of MC to sunfish. In an accumulation experiment, sunfish were brought into the laboratory and fed MC-rich zooplankton pellets (50 ng MC kg(-1)d(-1)) for 9 days. Zooplankton directly transferred MC to sunfish, resulting in liver and muscle tissue accumulation. However, after 6 days of accumulation fish significantly decreased concentrations in their liver and muscle tissue, indicating the induction of a detoxification and excretion pathway. Sunfish retained MC in their liver and muscle tissue, showing no significant changes in toxin concentration over 2 weeks of fasted depuration.

Changes in concentrations of microcystins in rainbow trout, freshwater mussels, and cyanobacteria in Lakes Rotoiti and Rotoehu

Microcystin concentrations in cyanobacteria and their accumulation in rainbow trout (Oncorhynchus mykiss) and freshwater mussels (Hyridella menziesi) in Lakes Rotoiti and Rotoehu (New Zealand) were investigated. Hatchery rainbow trout were added to an enclosure in Lake Rotoiti where concentrations of microcystins in the phytoplankton and cyanobacterial cell concentrations could be closely monitored. Rainbow trout that were free to roam in the entire area of each lake were also included in the study. Freshwater mussels were suspended subsurface in cages in the enclosure. Phytoplankton samples, rainbow trout liver and muscle tissue, and the tissues of mussels were analyzed for microcystins using the ADDA-ELISA method, and selected samples were analyzed using LC-MS. A maximum concentration of microcystins in the phytoplankton samples of 760 microg L(-1) was recorded in Te Weta Bay, Lake Rotoiti, in March 2004. ELISA results confirmed microcystin immunoreactivity in rainbow trout liver and muscle tissues and in freshwater mussels. The microcystin congeners LR, YR, RR, AR, FR, LA, and WR were detected by LC-MS in caged freshwater mussels in Lake Rotoiti but were not detected in either muscle or liver tissue of rainbow trout. The daily tolerable intake limit of microcystins for human consumption recommended by the World Health Organisation is 0.04 microg kg(-1) day(-1). Modeling was carried out for the human intake of microcystin compounds from rainbow trout muscle tissue, and the potential health risks were estimated, assuming the ADDA-ELISA was determining compounds of toxicity equivalent to microcystin-LR.

Influence of intracellular toxin concentrations on cylindrospermopsin bioaccumulation in a freshwater gastropod (Melanoides tuberculata)

Scant information is available regarding the bioaccumulation of cylindrospermopsin (CYN) in aquatic organisms, particularly in invertebrates. This study examined toxin bioconcentration and bioaccumulation in the aquatic snail, Melanoides tuberculata, following exposure to freeze-thawed whole cell extracts and a live Cylindrospermopsis raciborskii culture containing CYN. Both bioconcentration and bioaccumulation were evident, but exposure to toxin in the freeze-thawed solutions resulted in minor tissue contamination compared with that resulting from live C. raciborskii exposure. Thus, whilst CYN uptake resulted from both extracellular and intracellular exposures, the availability of intracellular toxin was critical in affecting tissue CYN values. M. tuberculata did not bioconcentrate CYN into the shell. Bioaccumulation of the analog deoxy-CYN was also recorded. Knowledge of intracellular toxin concentrations may be critical in evaluating the bioaccumulation, ecological and human health risks associated with contaminated systems.

Depuration of microcystins in tilapia fish exposed to natural populations of toxic cyanobacteria: a laboratory study

Previous studies demonstrated that microcystins (MCYSTs) can be accumulated in different organs, particularly the liver, of tilapia fish (Oreochromis niloticus) in an Egyptian fish farm containing toxic blooms of Microcystis aeruginosa. In the present study, a microcosm experiment was conducted to examine the depuration of MCYSTs in tilapia fish from this fish farm. Fish were grown in a 100-L aerated recirculation tank containing dechlorinated water at room temperature (25+/-2 degrees C) for 96 h. MCYST concentrations in livers, intestines, and gallbladders of each daily sacrificed fish were determined by both enzyme-linked immunosorbent assay (ELISA) and protein phosphatase inhibition assay (PPIA). MCYST concentrations in the surrounding water were also determined by the same methods. The results showed that MCYST concentrations in the liver and intestine decreased gradually throughout the experimental period. This decrease was accompanied by an increase in MCYST concentrations in the gallbladder and surrounding water. The maximum value of MCYST in the surrounding water was obtained after 96 h at a level of 1.2 microg/L by ELISA, while it was obtained after 24 h at a level of 0.5 microg/L by PPIA and remained stable until the end of the experiment. The present study revealed that tilapia fish can depurate and excrete MCYSTs into the bile and surrounding water as a way to avoid toxicity from such a potent hepatotoxin.

Seasonal dynamics of the hepatotoxic microcystins in various organs of four freshwater bivalves from the large eutrophic lake Taihu of subtropical China and the risk to human consumption

So far, little is known on the distribution of hepatotoxic microcystin (MC) in various organs of bivalves, and there is no study on MC accumulation in bivalves from Chinese waters. Distribution pattern and seasonal dynamics of MC-LR, -YR and -RR in various organs (hepatopancreas, intestine, visceral mass, gill, foot, and rest) of four edible freshwater mussels (Anodonta woodiana, Hyriopsis cumingii, Cristaria plicata, and Lamprotula leai) were studied monthly during Oct. 2003-Sep. 2004 in Lake Taihu with toxic cyanobacterial blooms in the summer. Qualitative and quantitative determinations of MCs in the organs were done by LC-MS and HPLC. The major toxins were present in the hepatopancreas (45.5-55.4%), followed by visceral mass with substantial amount of gonad (27.6-35.5%), whereas gill and foot were the least (1.8-5.1%). The maximum MC contents in the hepatopancreas, intestine, visceral mass, gill, foot, and rest were 38.48, 20.65, 1.70, 0.64, 0.58, and 0.61 microg/g DW, respectively. There were rather good positive correlation in MC contents between intestines and hepatopancreas of the four bivalves (r=0.75-0.97, p<0.05). There appeared to be positive correlations between the maximum MC content in the hepatopancreas and the delta13C (r=0.919) or delta15N (r=0.878) of the foot, indicating that the different MC content in the hepatopancreas might be due to different food ingestion. A glutathione (GSH) conjugate of MC-LR was also detected in the foot sample of C. plicata. Among the foot samples analyzed, 54% were above the provisional WHO tolerable daily intake (TDI) level, and the mean daily intakes from the four bivalves were 8-23.5 times the TDI value when the bivalves are eaten as a whole, suggesting the high risk of consuming bivalves in Lake Taihu.