Article

In situ studies on the distribution patterns and dynamics of microcystins in a biomanipulation fish - bighead carp (Aristichthys nobilis)

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  • Institute of Hydrobiology Chinese Academy of Sciences
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Abstract

The distribution and dynamics of microcystins in various organs of the phytoplanktivorous bighead carp were studied monthly in Lake Taihu, which is dominated by toxic cyanobacteria. There was a good agreement between LC-MS and HPLC-UV determinations. Average recoveries of spiked fish samples were 63% for MC-RR and 71% for MC-LR. The highest MC contents in intestine, liver, kidney and spleen were 85.67, 2.83, 1.70 and 1.57 mg g À1 DW, respectively. MCs were much higher in mid-gut walls (1.22 mg g À1 DW) than in hind-and fore-gut walls (0.31 and 0.18 mg g À1 DW, respectively), suggesting the importance of mid-gut wall as major site for MC absorption. A cysteine conjugate of MC-LR was detected frequently in kidney. Among the muscle samples analyzed, 25% were above the provisional tolerable daily intake level by WHO. Big-head is strongly resistant to microcystins and can be used as biomanipulation fish to counteract cyanotoxin contamination in eutrophic waters.

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... Bighead carp (Hypophthalmichthys nobilis), which belongs to the order Cypriniformes, family Cyprinidae, subfamily Hypophthalmichthyinae, and genus Hypophthalmichthys [15], is referred to China as one of the "four major domesticated fish" [16]. It is an omnivorous filterfeeding fish [17] that is highly popular in China due to its affordability, delicious taste, and high nutritional value [18]. It is also one of the world's most important aquaculture species [19], with an output of 3.187 million tons, accounting for 6.5% of the world's inland finfish production [20]. ...
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... The intestine is an important target tissue of MA and MC-LR toxicity. The intestine is directly in contact with MCs, and the content of MCs in the intestine is considerably higher than that in other tissues (Chen et al., 2007). MC-LR can enter intestinal epithelial cells through organic anion transport peptides (OATPs) (Fischer et al., 2005), accumulate in the intestine, and even enter other organs through the circulatory system Falconer et al., 1992). ...
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Covered by submerged plants, many shallow lakes in China had good water quality in the past and were sources of tap water. But now they are faced with eutrophication problems. For purifying raw water for tap water treatment, a physico-ecological engineering (PEEN) experiment has been carried out in a hypertrophic bay of Taihu Lake, China since June 1994. Ten channels with widths of 5 m and lengths of 40 m (total area of 2000 m2) were constructed using bamboo stakes, water-isolated materials and filters. Water was pumped from one end of the PEEN to simulate the dynamics of different retention times. Six main principles for design and management were introduced in practice and dealt with in the paper. Some species of floating, leave-floating, and submerged plants, as well as attached algae, and malacozoan were inventoried and some physical and integrated measurements of management were tested. Water quality indices of turbidity, ammonia-nitrogen, nitrite, and color were especially improved during the study.
Article
A long-term (28-year) data set was used to investigate historical changes in concentrations of phosphorus (P), nitrogen (N), N:P ratios, and Secchi disk transparency in a shallow subtropical lake (Lake Okeechobee, Florida, USA). The aim was to evaluate changes in the risk of N2-fixing cyanobacterial blooms, which have infrequently occurred in the lake's pelagic zone. Predictions regarding bloom risk were based on previously published N:P ratio models. Temporal trends in the biomass of cyanobacteria were evaluated using phytoplankton data collected in 1974, 1989–1992, and 1997–2000. Concentrations of pelagic total P increased from near 50 μg l−1 in the mid-1970s to over 100 μg l−1 in the late 1990s. Coincidentally, the total N:P (mass) ratio decreased from 30:1 to below 15:1, and soluble N:P ratio decreased from 15:1 to near 6:1, in the lake water. Published empirical models predict that current conditions favor cyanobacteria. The observations confirm this prediction: cyanobacteria presently account for 50–80% of total phytoplankton biovolume. The historical decrease in TN:TP ratio in the lake can be attributed to a decreased TN:TP ratio in the inflow water and to a decline in the lake's assimilation of P, relative to N. Coincident with these declines in total and soluble N:P ratios, Secchi disk transparency declined from 0.6 m to near 0.3 m, possibly due to increased mineral turbidity in the lake water. Empirical models predict that under the turbid, low irradiance conditions that prevail in this lake, non-heterocystous cyanobacteria should dominate the phytoplankton. Our observations confirmed this prediction: non-N2-fixing taxa (primarily Oscillatoria and Lyngbya spp.) typically dominated the cyanobacteria community during the last decade. The only exception was a year with very low water levels, when heterocystous N2-fixing Anabaena became dominant. In the near-shore regions of this shallow lake, low N:P ratios potentially favor blooms of N2-fixing cyanobacteria, but their occurrence in the pelagic zone is restricted by low irradiance and lack of stable stratification.
Article
Chronic and subchronic toxicity from exposure to microcystins, cyclic peptide liver toxins from certain cyanobacteria, poses an important hazard, which has received little study. No in vivo information exists on accumulation and transfer of microcystin from the food chain to humans. This paper present results of a 3-year study that demonstrates bioaccumulation of microcystins by fish and potential rates of microcystin ingestion by humans. The study was carried out in a shallow coastal lagoon in the city of Rio de Janeiro (Jacarepaguá Lagoon). Fish (Tilapia rendalli) were collected every 2 weeks from August 1996 to November 1999. Microcystins were analyzed by HPLC in phytoplankton, fish liver and viscera while fish muscle tissue was analyzed by enzyme linked immunosorbant assay (ELISA). Phytoplankton samples, dominated by the genus Microcystis, were confirmed to contain microcystins as were fish livers, viscera and muscle tissue. During the entire study period, including times of low water bloom densities, fish muscle tissue contained concentrations of microcystins close to or above the recommended limit for human consumption (0.04 μg kg−1 day). Our findings demonstrate that microcystins can accumulate in fish tissue used for human consumption. Rates of ingestion routinely exceed the TDI guidelines as set by the WHO for drinking water. Appropriate epidemiology and risk assessment should be undertaken so that an acceptable TDI and appropriate risk management decisions can be made for human consumption of fish which are harvested from cyanobacterial blooms that contain cyanotoxins.
Article
Microcystins LR, YR, and RR, cyclic heptapeptide hepatotoxins produced by cyanobacteria, were synthetically converted into glutathione (GSH) and cysteine (Cys) conjugates. Fast atom bombardment mass spectra showed [M + H]+ ions corresponding to GSH and Cys conjugates of microcystins LR, YR, and RR for the obtained compounds. 1H NMR spectral analyses revealed that two singlet signals of olefinic protons of N-methyldehydroalanine (Mdha) in microcystins disappeared in the conjugates, confirming that thiols of GSH and Cys added nucleophilically to the alpha, beta-unsaturated carbonyl of the Mdha moiety. On examination of the 50% lethal dose (LD50) with intravenous injection using mice, both GSH and Cys conjugates showed reduction in toxicity compared with microcystins, but their toxicity still remained. Microcystin LR and its GSH conjugate were separated and identified in a standard mixture by using a frit-fast atom bombardment liquid chromatography/mass spectrometry (Frit-FAB LC/MS) method. Obtained conjugates in the present study would be important compounds as the standard samples for study of metabolism of microcystins, and the Frit-FAB LC/MS method would be applicable to mass spectrometric identification of metabolites of microcystins.
Article
Biliary excretion of xenobiotics is a complex process involving uptake into liver cells, intracellular sequestration and/or biotransformation, and transport into bile. A description of liver morphology and the possible mechanisms of bile formation is included to aid in the understanding of how chemical and physiological factors affect bile flow, hepatic uptake, and biliary excretion. Enterohepatic circulation interferes with the biliary elimination of xenobiotics from the body. The considerable volume of information that has accumulated in recent years on the mechanisms of bile formation, hepatic uptake, and biliary excretion is discussed in this comprehensive review.
Article
Previous reports demonstrated that microcystin and related cyanobacteria polypeptides are rapidly cleared from plasma and accumulate in liver tissue. In the present study, we have used their ability to inhibit protein phosphatases to show that these cyanobacteria hepatotoxins are excreted into the bile of experimentally poisoned rainbow trout. At various times after oral administration of hepatotoxic Microcystis aeruginosa, bile samples were analysed for microcystin content by methanol extraction and protein phosphatase assays. An inhibitory principle that specifically suppressed protein phosphatase activity was detected in all bile samples removed between 1 and 72 h after oral exposure to toxic algae. These results indicate that biochemically active microcystin molecules are excreted into the biliary tract of poisoned fish.
Article
Over a period of 3 days saltwater mussels, Mytilus edulis, were fed a cyanobacteria, Microcystis aeruginosa, that contained a high concentration of microcystins. The mussels were killed on a periodic basis over the course of 2 months. Mussels were also collected at two sites were high levels of microcystins in tissues had been noted. A strategy based on the chemically unique nature of the C20 beta-amino acid, (2S,3S,8S,9S)-3-amino-9-methoxy-2,6,8-trimethyl-10-phenyldeca-4,6- dienoic acid (Adda), portion of the microcystins was used in conjunction with a protein phosphatase (PPase) assay to analyse for both covalently bound microcystins and free microcystins in the mussel tissues. The mussel PPase assay results were compared with the Lemieux oxidation gas chromatography-mass spectrometry (GCMS) analysis. Less than 0.1% of the total microcystin burden in the mussel tissue was found to be extractable with MeOH. Thus, direct evidence was provided for the existence of covalently bound microcystins in mussel tissues in vivo. The mussels rapidly cleared the covalently bound microcystins when transferred to untreated seawater. Within 4 days the total microcystin burden dropped from a high of 336.9 (+/- 45.8) micrograms/g wet tissue to 11.3 (+/- 2.6) micrograms/g. After 4 days postexposure until completion of the experiment the total levels remained below the detection limits of the GCMS method. The levels of free microcystins, extracted with MeOH and detected by the PPase assay, fell from 204 ng/g wet tissue to a residual 14 ng/g over a 53 day postexposure period. Presumably the bound microcystin present in the mussel tissue exists as a covalent complex with the PP-1 and PP-2A enzymes. We conclude that in any shellfish monitoring program it is the total tissue microcystin burden that needs to be considered.
Article
Cyanobacterial toxins have adverse effects on mammals, birds and fish and are being increasingly recognised as a potent stress factor and health hazard factor in aquatic ecosystems. Microcystins, cyclic heptapeptides and a main group of the cyanotoxins are mainly retained within the producer cells during cyanobacterial bloom development. However, these toxins are released into the surrounding medium by senescence and lysis of the blooms. Any toxin present could then come into contact with a wide range of aquatic organisms including phytoplankton grazers, invertebrates, fish and aquatic plants. Recent studies showed the conversion of microcystin in animal liver to a more polar compound in correlation with a depletion of the glutathione pool of the cell. The present study shows the existence of a microcystin-LR glutathione conjugate formed enzymatically via soluble glutathione S-transferase in various aquatic organisms ranging from plants (Ceratophyllum demersum), invertebrates (Dreissena polymorpha, Daphnia magna) up to fish eggs and fish (Danio rerio). The main derived conjugate was characterized by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry yielding a mass of m/z 1302, which is equivalent to the mass assumed for a glutathione microcystin-LR conjugate. This conjugate appears to be the first step in the detoxication of a cyanobacterial toxin in aquatic organisms.
Article
Anti-microcystin LR immunnoaffinity cartridges were evaluated for their ability to selectively remove microcystins from extracts of blue-green algae, fish and water samples for subsequent analysis by liquid chromatography with UV absorbance detection at 238 nm. Blue-green algae and fish samples were extracted with 75% methanol in water. A portion of the extract was diluted and passed through an immunoaffinity cartridge. Water samples were applied directly to the cartridge. The cartridge was rinsed with water and 25% methanol in water. The microcystins were eluted with 80% methanol in water containing 4% acetic acid. It was found that the cartridges were effective in isolating the microcystins from blue-green algae, fish and water samples, resulting in extracts that were clean enough to enable direct LC-UV detection down to approximately 0.03 microg/g in the blue-green algae and fish samples, and as low as 0.02 ng/ml for water samples. The cartridges were found to have a capacity of approximately 200 ng each for a mixture of microcystins RR, YR, LR and LA, or as much as 525-800 ng for individual compounds. Recoveries trough the complete analytical procedure ranged from 64 to 115% (all values) with an overall average of approximately 80% at spiking levels of 0.5-4.0 microg/g for the microcystins in blue-green algae. The average recoveries (n=8) from spiked (0.1-0.5 microg/g) fish samples were 73% for RR, 79% for YR, 81% for LR and 77% for LA, while from the spiked (2.0-0.04 ng/g) tap and river water samples (n=6), recoveries were 78% for RR, 86% for YR, 94% for LR and 89% for LA.
Article
Two metabolites of microcystin-LR glutathione conjugate and, microcystin-cysteine conjugate, as well as microcystin-RR (MCRR) are less toxic than microcystin-LR (MCLR). In the present study, we investigated why these compounds are weakly toxic in comparison with MCLR, as the reason is still unknown and no systematic study has so far been carried out for a clarification of this issue. Although they showed almost the same inhibitory activity against protein phosphatases 1 and 2A as MCLR in vitro, the apparent toxicity of these three compounds by intratracheal administration to mice decreased to about 1/12 the level of MCLR at 100microg/kg. An immunostaining study showed that these conjugates at a sublethal dose of 200microg/kg were prominently observed in the intestine and kidney, whereas effective accumulation and bleeding were not found in the liver in spite of the larger dosage. As an explanation for these results, there may be two possibilities. First, the transport system to the liver might not function well, and second, transported toxins may be effectively eliminated by an appropriate system such as the GS-X (ATP-dependent glutathione S-conjugate exported) pump. It was concluded that the inhibitory activity against protein phosphatases is not always related to the apparent LD(50) level, and that the appearance of toxicity by microcystins depends on the balance between accumulation and metabolism in the liver.
Article
The cyclic peptide toxins microcystins and nodularins are the most common and abundant cyanotoxins present in diverse water systems. They have been the cause of human and animal health hazards and even death. Over 60 microcystin variants have been reported so far. We report here the results of our study on comparative toxicity evaluation of three most predominant microcystins, MC-LR, MC-RR and MC-YR in mice. The mice were administered one LD(50) dose of MC-LR, RR and YR (43, 235.4 and 110.6 micro g/kg body weight, respectively), and biochemical and histological variables were determined at 30 min post-treatment and mean time to death (MTD). Significant increase in liver body weight index was induced by all three variants. There was marginal increase in serum levels of hepatic enzymes viz. AST, ALT and gamma-GT at 30 min post-treatment but 3-4 fold increase was observed at MTD. In contrast, enhanced LDH leakage, DNA fragmentation and depletion of hepatic glutathione was observed at 30 min post treatment in all three variants. There was no change in levels of serum protein, albumin and albumin/globulin ratio. Liver histology showed time dependent severe pathological lesions like congestion, haemorrhage, portal mononuclear cell infiltration and obliteration of chromatin material. Lung lesions were predominantly in bronchi and parenchyma. Though qualitatively lesions were identical in all three microcystin variants, degree of liver and lung lesions varied quantitatively with the toxin. The breathing pattern and respiratory frequency of the mice after i.p. administration of the toxin showed uniform pattern for 90 min followed by abrupt change in the respiratory pattern and instantaneous death. Based on biochemical and histological studies, MC-LR was found to be the most potent toxin followed by MC-YR and MC-RR.
Article
After intraperitoneal injection of microcystin-LR (MC-LR) (125 microg kg(-1) body wt.), the concentration of MC-LR in the liver of juvenile goldfish Carassius auratus (30 g body wt.) was assayed by a modified protein phosphatase inhibition method. A temporary accumulation occurred from 3 to 48 h post-injection, followed by a significant decrease between 48 and 96 h. Under our experimental conditions, contamination by MC-LR did not change ionic homeostasis, as attested by blood osmolality values and gill Na(+)/K(+) ATPase activity. Light microscopy observations revealed lesions and cellular necrosis progression, which was concomitant with an increase in enzyme activity of plasma aspartate aminotransferase (AspAT), alanine aminotransferase (AlaAT) and L-lactate dehydrogenase (LDH) and with a decrease of hepatic glutathione-S-transferase (GST) activity. Structural alterations and enzymatic activity modifications became significant within 24 h post-injection. Recovery of hepatocytes on day 21 after MC-LR injection was evident, together with a decrease in the MC-LR equivalent content of the liver.
Article
Blooms of cyanobacteria in water bodies cause serious environmental problems and the occurrence of toxic strains are also related with the human health. Aquatic animals could bioaccumulate microcystins (cyanobacteria hepatotoxins) and so, beyond water, the ingestion of contaminated food represents a human health risk. Recently, WHO recommended a maximum concentration of microcystins (MCYSTs) in drinking water and established the tolerable daily intake (TDI) for consumption of cyanobacteria products contends MCYSTs (0.04 microg(-1) kg(-1) day(-1)). Sepetiba Bay is located in the municipal districts of Rio de Janeiro, Mangaratiba and Itaguai; being an important place of fishing activity. Due to the industrial development in the area, this bay is submitted to different environmental impacts, increasing the organic and industrial pollution. A strain of the nanoplanktonic cyanobacteria Synechocystis aquatilis f. aquatilis that produce MCYSTs was already isolated. In this study, we verified MCYSTs presence in muscle tissue of fish and crustaceans, which were harvested monthly in Sepetiba Bay during 11 months, in order to evaluate the potential risk of their ingestion. MCYSTs were analyzed by immunoassay techniques using the ELISA Microcystin Plate Kit (ENVIROLOGIX INC) and the concentration were expressed as microcystin-LR equivalent. The analyses of seston samples, water, muscle tissues showed the presence of this cyanotoxin in all samples and it was verified that 19% of the animals' samples were above the limit recommended by WHO for human consumption. The maximum value found was of 103.3 microg kg(-1) (TDI 0.52 microg kg(-1) day(-1)) and the minimum, was 0.25 microg kg(-1) in crabs muscle tissue (TDI of 0.001 microg kg(-1) day(-1)). Such data demonstrate that, although in low concentrations, there is already a contamination of fish and crustaceans from Sepetiba Bay. We highlight that the recommended limit refers to healthy adult.
Article
A sub-chronic toxicity experiment was conducted to examine tissue distribution and depuration of two microcystins (microcystin-LR and microcystin -RR) in the phytoplanktivorous filter-feeding silver carp during a course of 80 days. Two large tanks (A, B) were used, and in Tank A, the fish were fed naturally with fresh Microcystis viridis cells (collected from a eutrophic pond) throughout the experiment, while in Tank B, the food of the fish were M. viridis cells for the first 40 days and then changed to artificial carp feed. High Performance Liquid Chromatography (HPLC) was used to measure MC-LR and MC-RR in the M. viridis cells, the seston, and the intestine, blood, liver and muscle tissue of silver carp at an interval of 20 days. MC-RR and MC-LR in the collected Microcystis cells varied between 268-580 and 110-292 microg g(-1) DW, respectively. In Tank A, MC-RR and MC-LR varied between 41.5-99.5 and 6.9-15.8 microg g(-1) DW in the seston, respectively. The maximum MC-RR in the blood, liver and muscle of the fish was 49.7, 17.8 and 1.77 microg g(-1) DW, respectively. No MC-LR was detectable in the muscle and blood samples of the silver carp in spite of the abundant presence of this toxin in the intestines (for the liver, there was only one case when a relatively minor quantity was detected). These findings contrast with previous experimental results on rainbow trout. Perhaps silver carp has a mechanism to degrade MC-LR actively and to inhibit MC-LR transportation across the intestines. The depuration of MC-RR concentrations occurred slowly than uptakes in blood, liver and muscle, and the depuration rate was in the order of blood>liver>muscle. The grazing ability of silver carp on toxic cyanobacteria suggests an applicability of using phytoplanktivorous fish to counteract cyanotoxin contamination in eutrophic waters.
Article
In order to understand accumulation and depuration of microcystins (MCYSTs) in Tilapia rendalli, three experiments with juveniles were done. The experiments simulated the fish diet during a Microcystis aeruginosa bloom in three different situations. In the first one each fish received daily, during 15 days, fish food plus toxic cells of M. aeruginosa (20.4 microg MCYSTs fish(-1) day(-1)). In the following 15 days they were fed without toxic cells. In the second experiment, fish were fed only with toxic cells during 28 days (14.6 microg MCYSTs fish(-1) day(-1)) and in the third experiment, during 42 days, fish were fed with fish food plus toxic cells (29.2 microg MCYSTs fish(-1) day(-1)) previously disrupted (to simulate a senescent bloom). MCYSTs analyses were done by enzyme-linked immunosorbent assay (ELISA) in liver and muscle samples in all experiments and in faeces in the first one (only in the depuration period). The results demonstrated different profiles of MCYSTs accumulation in liver and muscle of T. rendalli. Comparing the experiments, the highest MCYSTs accumulation in the liver (2.8 microg g(-1)) occurred in the second one, where fish had only toxic cells as feeding source. In the first experiment, the highest MCYSTs accumulation in liver (0.6 microg MCYSTs g(-1)) was observed during the accumulation period, while in muscle, interestingly, the highest concentration (0.05 microg MCYSTs g(-1)) occurred in the depuration period. In this same period, it was also observed elimination of toxins through faeces. The second and third experiments showed almost the same average concentrations in tissues although fish have received more MCYSTs in third one. With respect to implications of the fish comsumption, MCYSTs accumulation in muscle of T. rendalli in all three experiments reached concentrations that would represent an intake of these toxins above the tolerable limit for humans and these results confirmed our previous observations from a field study. In conclusion, in this study it was observed that T. rendalli is able to accumulate MCYSTs and the availability of other feeding sources, besides toxic cells, probably interferes with the accumulation rate. Therefore, the occurrence of toxic cyanobacterial blooms produncing MCYSTs in aquaculture ponds could represent a risk to the quality of fish to the consumers.
Article
Tissue distributions and seasonal dynamics of the hepatotoxic microcystins-LR and -RR in a freshwater snail (Bellamya aeruginosa) were studied monthly in a large shallow, eutrophic lake of the subtropical China during June-November, 2003. Microcystins (MCs) were quantitatively determined by High-Performance Liquid Chromatography (HPLC) with a qualitative analysis by a Finnigan LC-MS system. On the average of the study period, hepatopancreas was the highest in MC contents (mean 4.14 and range 1.06-7.42 microg g(-1)DW), followed by digestive tracts (mean 1.69 and range 0.8-4.54 microg g(-1)DW) and gonad (mean 0.715 and range 0-2.62 microg g(-1)DW), whereas foot was the least (mean 0.01 and range 0-0.06 microg g(-1)DW). There was a positive correlation in MC contents between digestive tracts and hepatopancreas. A constantly higher MC content in hepatopancreas than in digestive tracts indicates a substantial bioaccumulation of MCs in the hepatopancreas of the snail. The average ratio of MC-LR/MC-RR showed a steady increase from digestive tracts (0.44) to hepatopancreas (0.63) and to gonad (0.96), suggesting that MC-LR was more resistant to degradation in the snail. Since most MCs were present in the hepatopancreas, digestive tracts and gonad with only a very small amount in the edible foot, the risk to human health may not be significant if these toxic parts are removed prior to snail consumption. However, the possible transference of toxins along food chains should not be a negligible concern.
Article
So far no information is available on microcystin (MC) contents in shrimps, prawns or crayfish from natural freshwaters. Tissue distributions and seasonal dynamics of the hepatotoxic MC-LR and -RR in two freshwater shrimps, Palaemon modestus and Macrobrachium nipponensis were studied monthly (during June-November, 2003) in a Chinese lake containing toxic cyanobacterial blooms. The shrimps P. modestus and M. nipponensis accumulated high MCs not only in the hepatopancreas (mean 4.29 and 0.53 microg g(-1) DW, respectively) but also in the gonad (mean 1.17 and 0.48 microg g(-1) DW, respectively), and the crayfish Procambarus clarkii accumulated as much as 0.93 microg g(-1) DW in the gonad. This indicates that gonads of these invertebrates are the second important target organ of MCs. P. modestus apparently accumulated more MCs in their organs than M. nipponensis, which might be a reflection of their difference in trophic niche. Eggs of the shrimps accumulated 8.4% (M. nipponensis, 0.27 microg g(-1) DW) and 29.0% (P. modestus, 2.34 microg g(-1) DW) of total toxin burden, indicating that MCs had been transferred into offspring from their adults. Among the shrimp muscle samples analyzed, 31% were above the provisional WHO TDI level, suggesting the risk of consuming shrimps in Lake Chaohu.
Article
This article reports the organ distribution and bioaccumulation of hepatotoxic microcystins (MCs) in freshwater fishes at different trophic levels from the large, shallow, eutrophic Lake Chaohu in September 2003, when there were heavy surface blooms of toxic cyanobacteria. Among all fish, intestines and blood had the highest average content of MC-RR + MC-LR (22.0 and 14.5 microg g(-1) DW, respectively), followed by liver, bile, and kidney (7.77, 6.32, and 5.81 microg g(-1) DW, respectively), whereas muscle had the least (1.81 microg g(-1) DW). MC content in muscle was highest in carnivorous fish (Culter ilishaeformis, 2.22 microg g(-1) DW) and omnivorous fish (Carassius auratus, 1.96 microg g(-1) DW) and was lowest in phytoplanktivorous fish (Hypophthalmichthys molitrix, 1.65 microg g(-1) DW) and herbivorous fish (Parabramis pekinensis 0.660 microg g(-1) DW). However, the amount of MC in the gut of H. molitrix (137 microg g(-1) DW) was more than 20 times that in the other fish (<6.50 microg g(-1) DW). The MCs showed a tendency to accumulate up the food chain, and piscivorous fish at the top of the food chain were at high risk of exposure to MCs in Lake Chaohu. Our study is the first to report MC concentrations in the bile and blood of wild fish. One hundred grams of fish muscle would contain 2.64-49.7 microg of MC-LR equivalent, or about 1.3-25 times the recommended tolerable daily intake of MC-LR by humans, indicating that fish are already severely contaminated by MCs and that the local authorities should warn the public of the risk of poisoning by eating the contaminated fish.
Article
Phytoplanktivorous bighead carp were injected i.p. with extracted microcystins (mainly MC-RR and -LR) at two doses, 200 and 500 MC-LReq.microg kg(-1) bw, and the changes in extractable MCs in liver and in the ultrastructure of hepatocytes were studied at 1, 3, 12, 24 and 48 h after injection. Quantitative and qualitative determinations of MCs in the liver were conducted by HPLC and LC-MS, respectively. MC concentration in the liver reached the maxima at 12h (2.89 microg MCsg(-1) dry weight at the lower dose) or at 3h (5.43 microg MCsg(-1) dry weight at the higher dose) post-injection, followed by sharp declines afterwards, whereas the ultrastructural changes of hepatocytes in both dose groups suggest progressive increases in severity toward the directions of apoptosis and necrosis from 1 to 24h, respectively. There were two new findings in fish: widening of intercellular spaces was among the early ultrastructural changes induced by MCs and ultrastructural recovery of hepatocytes was evident at 48 h post-injection in both dose groups. Both the present and previous studies suggest that with in vivo or in vitro exposure to microcystins, hepatocyte damage in fish tends to proceed toward the direction of apoptosis at lower MC concentrations but toward the direction of necrosis at high MC concentrations. The temporal dynamics of MCs in the liver suggest that bighead carp may have a mechanism to degrade or bind MC-LR actively after it enters the blood system.
Article
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.
The toxicology of microcystins. Toxicon 36, 953e962. FAO, 1991. Fishery Statistics, Catches and Landing, FAO Yearbook
  • R M Dawson
Dawson, R.M., 1998. The toxicology of microcystins. Toxicon 36, 953e962. FAO, 1991. Fishery Statistics, Catches and Landing, FAO Yearbook. Food and Agriculture Organization of the United Nations, Rome.
The apparatus of filtering and feeding of silver carp and bighead carp
  • Y L Liang
Liang, Y.L., 1981. The apparatus of filtering and feeding of silver carp and bighead carp. Journal of Dalian Fisheries College 1, 13e33 (in Chinese).
Processes and Mechanisms of the Changes in Aquatic Environments in Lake Taihu
  • B Q Qin
  • W P Hu
  • W M Chen
Qin, B.Q., Hu, W.P., Chen, W.M., 2004a. Processes and Mechanisms of the Changes in Aquatic Environments in Lake Taihu. Science Press, Beijing (in Chinese).