Assessment of cyanobacteria toxins in freshwater fish: a case study of Murchison Bay (Lake Victoria) and Lake Mburo, Uganda

Cyanotoxins in food: Exposure assessment and health impact

The intricate nature of cyanotoxin exposure through food reveals a complex web of risks and uncertainties in our dietary choices. With the aim of starting to unravel this intricate nexus, a comprehensive review of 111 papers from the past two decades investigating cyanotoxin contamination in food was undertaken. It revealed a widespread occurrence of cyanotoxins in diverse food sources across 31 countries. Notably, 68% of the studies reported microcystin concentrations exceeding established Tolerable Daily Intake levels. Cyanotoxins were detected in muscles of many fish species, and while herbivorous fish exhibited the highest recorded concentration, omnivorous species displayed a higher propensity for cyanotoxin accumulation, exemplified by Oreochromis niloticus. Beyond fish, crustaceans and bivalves emerged as potent cyanotoxin accumulators. Gaps persist regarding contamination of terrestrial and exotic animals and their products, necessitating further exploration. Plant contamination under natural conditions remains underreported, yet evidence underscores irrigation-driven cyanotoxin accumulation, particularly affecting leafy vegetables. Finally, cyanobacterial-based food supplements often harbored cyanotoxins (57 % of samples were positive) warranting heightened scrutiny, especially for Aphanizomenon flos-aquae-based products. Uncertainties surround precise concentrations due to methodological variations (chemical and biochemical) and extraction limitations, along with the enigmatic fate of toxins during storage, processing, and digestion. Nonetheless, potential health consequences of cyanotoxin exposure via contaminated food include gastrointestinal and neurological disorders, organ damage (e.g. liver, kidneys, muscles), and even elevated cancer risks. While microcystins received significant attention, knowledge gaps persist regarding other cyanotoxins' accumulation, exposure, and effects, as well as combined exposure via multiple pathways. Intriguing and complex, cyanotoxin exposure through food beckons further research for our safer and healthier diets.

Assessment of cyanotoxins in water and fish in an African freshwater lagoon (Lagoon Aghien, Ivory Coast) and the application of WHO guidelines

In comparison with northern countries, limited data are available on the occurrence and potential toxicity of cyanobacterial blooms in lakes and ponds in sub-Saharan countries. With the aim of enhancing our knowledge on cyanobacteria and their toxins in Africa, we performed a 17-month monitoring of a freshwater ecosystem, Lagoon Aghien (Ivory Coast), which is used for multiple practices by riverine populations and for drinking water production in Abidjan city. The richness and diversity of the cyanobacterial community were high and displayed few variations during the entire survey. The monthly average abundances ranged from 4.1 × 104 to 1.8 × 105 cell mL-1, with higher abundances recorded during the dry seasons. Among the five cyanotoxin families analyzed (anatoxin-a, cylindrospermopsin, homoanatoxin, microcystins, saxitoxin), only microcystins (MC) were detected with concentrations ranging from 0 to 0.364 μg L-1 in phytoplankton cells, from 32 to 1092 μg fresh weight (FW) kg-1 in fish intestines, and from 33 to 383 μg FW kg-1 in fish livers. Even if the MC concentrations in water and fish are low, usually below the thresholds defined in WHO guidelines, these data raise the issue of the relevance of these WHO guidelines for sub-Saharan Africa, where local populations are exposed throughout the year to these toxins in multiple ways.

Transmission of Microcystins in Natural Systems and Resource Processes: A Review of Potential Risks to Humans Health

The rapid rise of microcystins (MCs) poses a serious threat to global freshwater ecosystems and has become an important issue of global public health. MCs have considerable stability and are the most widely distributed hepatotoxins. It cannot only accumulate in aquatic organisms and transfer to higher nutrients and levels, but also be degraded or transferred during the resource utilization of cyanobacteria. No matter which enrichment method, it will lead to the risk of human exposure. This review summarizes the research status of MCs, and introduces the distribution of MCs in different components of aquatic ecosystems. The distribution of MCs in different aquatic organisms was summarized, and the potential risks of MCs in the environment to human safety were summarized. MCs have polluted all areas of aquatic ecosystems. In order to protect human life from the health threats caused by MCs, this paper also proposes some future research directions to promote MCs control and reduce human exposure to MCs.

Cyanotoxins and Food Contamination in Developing Countries: Review of Their Types, Toxicity, Analysis, Occurrence and Mitigation Strategies

Cyanotoxins have gained global public interest due to their potential to bioaccumulate in food, which threatens human health. Bloom formation is usually enhanced under Mediterranean, subtropical and tropical climates which are the dominant climate types in developing countries. In this context, we present an up-to-date overview of cyanotoxins (types, toxic effects, analysis, occurrence, and mitigation) with a special focus on their contamination in (sea)food from all the developing countries in Africa, Asia, and Latin America as this has received less attention. A total of 65 publications have been found (from 2000 until October 2021) reporting the contamination by one or more cyanotoxins in seafood and edible plants (five papers). Only Brazil and China conducted more research on cyanotoxin contamination in food in comparison to other countries. The majority of research focused on the detection of microcystins using different analytical methods. The detected levels mostly surpassed the provisional tolerable daily intake limit set by the World Health Organization, indicating a real risk to the exposed population. Assessment of cyanotoxin contamination in foods from developing countries still requires further investigations by conducting more survey studies, especially the simultaneous detection of multiple categories of cyanotoxins in food.

Harmful Algal Blooms Threaten the Health of Peri-Urban Fisher Communities: A case study in Kisumu Bay, Lake Victoria, Kenya

Available guidance to mitigate health risks from exposure to freshwater harmful algal blooms (HABs) is largely derived from temperate ecosystems. Yet in tropical ecosystems, HABs can occur year-round, and resource-dependent populations face multiple routes of exposure to toxic components. Along Winam Gulf, Lake Victoria, Kenya, fisher communities rely on lake water contaminated with microcystins (MCs) from HABs. In these peri-urban communities near Kisumu, we tested hypotheses that MCs exceed exposure guidelines across seasons, and persistent HABs present a chronic risk to fisher communities through ingestion with minimal water treatment and frequent, direct contact. We tested source waters at eleven communities across dry and rainy seasons from September 2015 through May 2016. We measured MCs, other metabolites, physicochemical parameters, chlorophyll a, phytoplankton abundance and diversity, and fecal indicators. We then selected four communities for interviews about water sources, usage, and treatment. Greater than 30% of source water samples exceeded WHO drinking water guidelines for MCs (1μg/L), and over 60% of source water samples exceeded USEPA guidelines for children and immunocompromised individuals. 50% of households reported sole use of raw lake water for drinking and household use, with alternate sources including rain and boreholes. Household chlorination was the most widespread treatment utilized. At this tropical, eutrophic lake, HABs pose a year-round health risk for fisher communities in resource -limited settings. Community-based solutions and site-specific guidance for Kisumu Bay and similarly impacted regions is needed to address a chronic health exposure likely to increase in severity and duration with global climate change.

Impact of copper sulphate, potassium permanganate, and hydrogen peroxide on Pseudanabaena galeata cell integrity, release and degradation of 2-methylisoborneol

Frequent off-flavor events caused by geosmin and 2-methylisoborneol have caused concern among consumers about the quality of potable water. Pseudanabaena galeata, a filamentous cyanobacterium, is a known producer of 2-methylisoborneol in lakes and reservoirs. The use of algicides to control cyanobacteria must consider the potential release of contaminants into the water. This is the first study to systematically investigate the effectiveness of copper sulphate (CuSO₄), potassium permanganate (KMnO₄), and hydrogen peroxide (H₂O₂) on the cell viability and integrity of Pseudanabaena galeata. Following algicide or oxidant treatment, the release and degradation of 2-methylisoborneol was also examined. It is evident that all of these chemicals can decrease Pseudanabaena galeata viability and damage cell membranes and the filamentous Pseudanabaena galeata was more susceptible to treatment by these three algicides than unicellular colonial Microcystis aeruginosa. Of the three compounds used, KMnO₄ showed the stronger ability to compromise cell integrity and 5.0 mg/L KMnO₄ could induce 91 ± 1.5% lysis of Pseudanabaena galeata within 2 h. It was found that H₂O₂ had the potential to degrade 2-methylisoborneol with 16.0 ± 0.4% degraded by 20.0 mg/L H₂O₂ within 8 h. In contrast, 2-methylisoborneol could not be degraded by CuSO₄ (dosage: ≤ 1.5 mg/L; reaction time: ≤ 8 h) and KMnO₄ (dosage: ≤ 5.0 mg/L; reaction time: ≤ 3 h) basically. Results showed that the oxidation capacity of H₂O₂ against Pseudanabaena galeata was enhanced under sunlight. The results will help drinking water utilities to better understand the risk of Pseudanabaena galeata lysis and 2-methylisoborneol release during raw water treatment.

Detected cyanotoxins by UHPLC MS/MS technique in tropical reservoirs of northeastern Colombia

This study focused on the detection and quantification of eight cyanotoxins in water samples in three reservoirs located in the eastern department of Antioquia, Colombia. The reservoirs are a source of water supply and hydroelectricity, and also generate economic activities in fishing and recreation. Between May 2015 and October 2016, 8 samplings were carried out at times of high temperatures, which ranged from 20 to 29 °C. This period was selected because of a significant or strong El Niño phenomenon, according to the World Meteorological Organization. For the study, 270 integrated samples were taken from the photic zone (PZ) and the surface of the reservoirs, at each of the three sampling points. The samples were analyzed by the analytical technique of ultra-high-performance liquid chromatography coupled to triple quadrupole mass spectrometry (UHPLC MS/MS). The quantification performed for six microcystins (MCs), a nodularin (NOD) and a cylindrospermopsin (CYN), showed positive results well above 1 μg L^-1. In the water of the Abreo Malpaso and Peñol reservoirs, microcystin-LR (MC-LR), microcystin-YR (MC-YR) and [D-Asp³,(E)-Dhb⁷]- microcystin-RR toxins were detected at levels of considerable concentration, especially between May and September 2015, when there was no rainfall in this region. In the Playas reservoir, positive results for [D-Asp³,(E)-Dhb⁷]-MC-RR were detected from May to November 2015, with the highest concentrations being reached in dry season. The temperatures reached and the changes in climatic conditions witnessed during the monitoring period of this study were important factors in the production of cyanotoxins. This was evidenced in this work by the high concentrations of detected cyanotoxins and their absence in periods of rain, as happened from the second quarter of 2016 until the end of the study in October. This is the first study of the detection and quantification of cyanotoxins in tropical reservoirs of northeastern Colombia using the UHPLC MS/MS analytical technique, which allowed the toxins to be unequivocally detected and confirmed. A method was developed and validated, proving to be sensitive, reproducible and accurate. For each of the toxins (microcystin-LR (MC-LR), microcystin-RR (MC-RR), microcystin-YR (MC-YR), [D-Asp³,(E)-Dhb⁷]- microcystin-RR, microcystin-LW (MC-LW), microcystin-LF (MC-LF), nodularin (NOD) and cylindrospermopsina (CYN)) the correlation coefficients (R²) were in a range between 0.9907 and 0.9999. Verification of the accuracy of the method was performed through a calibration curve in solvent. The recovery percentages of the accuracy and precision tests of the method for low level, medium level and high level were in a range between 64% and 115% for all the cyanotoxins. The validation of the cyanotoxin method shows that it is possible to detect them individually in natural water with a quantification limit (LOQ) of approximately 0.05 μg L^-1.

Occurrence and toxicity of microcystin congeners other than MC-LR and MC-RR: A review

The occurrence of cyanobacterial toxins is being increasingly reported. This is a reason for concern as they can induce toxic effects both in humans and in the environment. Among them, microcystins (MCs) are the best described and most diverse group of cyanobacterial toxins, and MC-LR and MC-RR are the congeners most widely investigated. However, the number of MC variants has also increased in recent years. Some of these minority variants have been shown to have a different toxicokinetic and toxicodynamic profile, but research focused on them is still limited. Moreover, in some water bodies these minority variants can be the predominant toxins. Nonetheless, MC-LR is the only one used for risk evaluation purposes at present. In order to contribute to more realistic risk assessments in the future, the aim of this review was to compile the available information in the scientific literature regarding the occurrence and concentration of minority MCs in water and food samples, and their toxic effects. The data retrieved demonstrate the congener-specific toxicity of MCs, as well as many data gaps in relation to analytical or mechanistic aspects, among others. Therefore, further research is needed to improve the toxicological characterization of these toxins and the exposure scenarios.

Cyanobacterial Blooms and Microcystins in Southern Vietnam

Studies on cyanobacteria in Vietnam are limited and mainly restricted to large reservoirs. Cyanobacterial blooms in small water bodies may pose a health risk to local people. We sampled 17 water bodies in the vicinity of urban settlements throughout the Mekong basin and in southeast Vietnam. From these, 40 water samples were taken, 24 cyanobacterial strains were isolated and 129 fish, 68 snail, 7 shrimp, 4 clam, and 4 duck samples were analyzed for microcystins (MCs). MCs were detected up to 11,039 µg/L or to 4033 µg/g DW in water samples. MCs were detected in the viscera of the animals. MC-LR and MC-RR were most frequently detected, while MC-dmLR, MC-LW, and MC-LF were first recorded in Vietnam. Microcystis was the main potential toxin producer and the most common bloom-forming species. A potential health hazard was found in a duck⁻fish pond located in the catchment of DauTieng reservoir and in the DongNai river where raw water was collected for DongNai waterwork. The whole viscera of fish and snails must be completely removed during food processing. Cyanobacterial monitoring programs should be established to assess and minimize potential public health risks.

Microcystin Content in Phytoplankton and in Small Fish from Eutrophic Nyanza Gulf, Lake Victoria, Kenya

The human health risks posed by exposure to cyanobacterial toxins such as microcystin (MC) through water and fish consumption remain poorly described. During the last two decades, coastal regions of Lake Victoria such as Nyanza Gulf (Kisumu Bay) have shown severe signs of eutrophication with blooms formed by Microcystis producing MC. In this study, the spatial variability in MC concentration in Kisumu Bay was investigated which was mostly caused by Microcystis buoyancy and wind drifting. Small fish (<6 cm) mainly composed of Rastrineobola argentea were examined for MC content by means of biological methods such as ELISA and protein phosphatase inhibition assay (PPIA) and partly by chemical-analytical methods such as LC-MS/MS. Overall, the MC content in small fish was related to the MC content observed in the seston. When comparing the MC content in the seston in relation to dry weight with the MC content in small fish the latter was found three orders of magnitude decreased. On average, the ELISA-determined MC contents exceeded the PPIA-determined MC contents by a factor of 8.2 ± 0.5 (SE) while the MC contents as determined by LC-MS/MS were close to the detection limit. Using PPIA, the MC content varied from 25–109 (mean 62 ± 7) ng/g fish dry weight in Kisumu Bay vs. 14 ± 0.8 ng MC/g in the more open water of L. Victoria at Rusinga channel. Drying the fish under the sun showed little effect on MC content, although increased humidity might indirectly favor photocatalyzed MC degradation.

16S rRNA Gene Amplicon Sequencing Reveals Significant Changes in Microbial Compositions during Cyanobacteria-Laden Drinking Water Sludge Storage

This is the first study to systematically investigate the microbial community structure in cyanobacteria-laden drinking water sludge generated by different types of coagulants (including AlCl₃, FeCl₃, and polymeric aluminum ferric chloride (PAFC)) using Illumina 16S rRNA gene MiSeq sequencing. Results show that Cyanobacteria, Proteobacteria, Firmicutes, Bacteroidetes, Verrucomicrobia, and Planctomycetes were the most dominant phyla in sludge, and because of the toxicity of high Al and Fe level in AlCl₃ and FeCl₃ sludges, respectively, the PAFC sludge exhibited greater microbial richness than that in AlCl₃ and FeCl₃ sludges. Due to lack of light and oxygen in sludge, relative abundance of the dominant genera Microcystis, Rhodobacter, Phenylobacterium, and Hydrogenophaga clearly decreased, especially after 4 days storage, and the amounts of extracellular microcystin and organic matter rose. As a result, the relative abundance of microcystin and organic degradation bacteria increased significantly, including pathogens such as Bacillus cereus, in particular after 4 days storage. Hence, sludge should be disposed of within 4 days to prevent massive growth of pathogens. In addition, because the increase of extracellular microcystins, organic matter, and pathogens in AlCl₃ sludge was higher than that in FeCl₃ and PAFC sludges, FeCl₃ and PAFC may be ideal coagulants in drinking water treatment plants.

First report on free and covalently bound microcystins in fish and bivalves from Vietnam: Assessment of risks to humans

The free and covalently bound microcystins (MCs) in 3 fish and 2 bivalves from the Dau Tieng Reservoir in Vietnam were investigated for the first time in the present study. The results showed that all species were contaminated with MCs. Our findings indicate that eating the muscle of fish from the Dau Tieng Reservoir is safe but that eating the bivalves is not safe during toxic cyanobacterial bloom episodes. Environ Toxicol Chem 2017;36:2953-2957. © 2017 SETAC.

Characteristics of water obtained by dewatering cyanobacteria-containing sludge formed during drinking water treatment, including C-, N-disinfection byproduct formation

This is the first study to systematically investigate the characteristics of the water obtained by dewatering cyanobacteria-containing sludge generated in the drinking water treatment plant, including formation of C- and N-disinfection by-products (DBPs). Results showed that this 'dewatering water' (DW) had different properties when the sludge was stored at different times. The content of dissolved organic matter (DOM) and microcystins (MCs) in the DW were low when the sludge was treated or disposed of within 4 days; correspondingly, the C-, N-DBP production was also low. However, due to the damage of algal cells to some extent, the DOM and MC levels increased significantly for storage time longer than 4 days; the production of C-, N-DBPs also increased. There were also obvious differences in the characteristics of the DW from sludges generated with different coagulant species. Due to the better protective effect of FeCl₃ and polymeric aluminium ferric chloride (PAFC) flocs, the DOM and MC levels and the production of C-, N-DBPs in the DW with FeCl₃ and PAFC coagulation were lower than those with AlCl₃ coagulation, even though the sludges were stored for the same amount of time. Furthermore, because of the formation of Al and Fe hydroxides, precipitated onto the surface of flocs, the soluble Al and Fe in the DW decreased with increased storage time, especially in the first four days. Overall, this study revealed the trends in variation of DW quality for cyanobacteria-containing sludges formed with different coagulants, then FeCl₃ and PAFC coagulants are recommended and sludge should be treated or disposed of within 4 days.

Transfer, tissue distribution and bioaccumulation of microcystin LR in the phytoplanktivorous and carnivorous fish in Anzali wetland, with potential health risks to humans

This study was conducted to determine Microcystin LR concentration in the aquatic ecosystem of the Anzali wetland in Iran. Extraction and detection of MC-LR from the water and fish samples was conducted by the SPE and HPLC-UV apparatus. Our results showed that among toxic cyanobacteria, Anabaena was the dominant genera during the study period. The results indicated that MC-LR content in water ranged from 0.18 to 3.02μg/L in dissolved fraction and undetectable level to 1.13μg/L in cellular fraction, in all three seasons. The results of PCA revealed that the environmental parameters including EC, Chl-a, PO₄^3-, pH and temperature were the most effective factors influencing the MC-LR production. Results further showed the mean concentration of MC-LR in muscle and liver of silver carp ranged from 10.12 to 40.98 and from undetectable to 44.34μg/kg w.w, respectively. The mean concentration of MC-LR in northern pike was 15.18 to 35.1μg/kg w.w in muscle and undetectable to 51.91μg/kg w.w in liver samples. Our results suggest that consumption of fish harvested from the Anzali wetland seems to be unsafe for humans, based on obtained estimated daily intake values which were higher than the tolerable daily intake value recommended by WHO. In addition, bioaccumulation factor of MC-LR in edible tissues of fish was estimated based on lipid normalization. The results showed that the BAF of MC-LR in silver carp (1047±185L/kg of lipid) was lower than the northern pike (1272±185L/kg of lipid), although the difference was not significant.

Behaviors of Microcystis aeruginosa cells during floc storage in drinking water treatment process

This is the first study to systematically investigate the different behaviors of Microcystis aeruginosa in the sludges formed by AlCl₃, FeCl₃, and polymeric aluminium ferric chloride (PAFC) coagulants during storage. Results show that the viability of Microcystis aeruginosa in PAFC sludge was stronger than that of cells in either AlCl₃ or FeCl₃ sludge after the same storage time, while the cells’ viability in the latter two systems stayed at almost the same level. In AlCl₃ and FeCl₃ sludges high concentrations of Al and Fe were toxic to Microcystis aeruginosa, whereas in PAFC sludge low levels of Al showed little toxic effect on Microcystis aeruginosa growth and moderate amounts of Fe were beneficial to growth. The lysis of Microcystis aeruginosa in AlCl₃ sludge was more serious than that in PAFC sludge, for the same storage time. Although the cell viability in FeCl₃ sludge was low (similar to AlCl₃ sludge), the Microcystis aeruginosa cells remained basically intact after 10 d storage (similar to PAFC sludge). The maintenance of cellular integrity in FeCl₃ sludge might be due to the large floc size and high density, which had a protective effect for Microcystis aeruginosa.

Two homologs of rho-class and polymorphism in alpha-class glutathione S-transferase genes in the liver of three tilapias

To clarify detoxification metabolism of tilapia, a natural and biological control for removing the leftover toxicants in fresh water, sequence structure, expression profile and polymorphisms of members of glutathione S-transferase (GST) genes were analyzed in Nile tilapia, blue tilapia and their hybrid. Full-length mRNA sequences of alpha-class GST (GSTA) and two homologs of rho-class GST (GSTR) were identified. Sequence analysis confirmed the similarity in conserved domain regions and their phylogenetic relationships with GST genes in other fishes. In addition, three single nucleotide polymorphisms of GSTA genes were identified in the three populations, two (C266T and G525A) of which showed significant association. The relative mRNA expression of GSTA gene was significantly (P<0.05) increased in the liver of Nile tilapia at 24h post-injection of MC-LR, significantly (P<0.05) decreased in blue tilapia whereas slightly decreased (P>0.05) in hybrid tilapia.

Evidence of trophic transfer of microcystins from the gastropod Lymnaea stagnalis to the fish Gasterosteus aculeatus

According to our previous results the gastropod Lymnaea stagnalis exposed to MC-producing cyanobacteria accumulates microcystins (MCs) both as free and covalently bound forms in its tissues, therefore representing a potential risk of MC transfer through the food web. This study demonstrates in a laboratory experiment the transfer of free and bound MCs from L. stagnalis intoxicated by MC-producing Planktothrix agardhii ingestion to the fish Gasterosteus aculeatus. Fish were fed during five days with digestive glands of L. stagnalis containing various concentrations of free and bound MCs, then with toxin-free digestive glands during a 5-day depuration period. MC accumulation was measured in gastropod digestive gland and in various fish organs (liver, muscle, kidney, and gills). The impact on fish was evaluated through detoxification enzyme (glutathion-S-transferase, glutathion peroxydase and superoxyde dismutase) activities, hepatic histopathology, and modifications in gill ventilation, feeding and locomotion. G. aculeatus ingestion rate was similar with intoxicated and toxin-free diet. Fish accumulated MCs (up to 3.96±0.14μgg^-1DW) in all organs and in decreasing order in liver, muscle, kidney and gills. Hepatic histopathology was moderate. Glutathion peroxydase was activated in gills during intoxication suggesting a slight reactive oxygen species production, but without any impact on gill ventilation. Intoxication via ingestion of MC-intoxicated snails impacted fish locomotion. Intoxicated fish remained significantly less mobile than controls during the intoxication period possibly due to a lower health condition, whereas they showed a greater mobility during the depuration period that might be related to an acute foraging for food. During depuration, MC elimination was total in gills and kidney, but partial in liver and muscle. Our results assess the MC transfer from gastropods to fish and the potential risk induced by bound MCs in the food web.

Estimation of ion competition via correlated responsivity offset in linear ion trap mass spectrometry analysis: theory and practical use in the analysis of cyanobacterial hepatotoxin microcystin-LR in extracts of food additives

Responsivity is a conversion qualification of a measurement device given by the functional dependence between the input and output quantities. A concentration-response-dependent calibration curve represents the most simple experiment for the measurement of responsivity in mass spectrometry. The cyanobacterial hepatotoxin microcystin-LR content in complex biological matrices of food additives was chosen as a model example of a typical problem. The calibration curves for pure microcystin and its mixtures with extracts of green alga and fish meat were reconstructed from the series of measurement. A novel approach for the quantitative estimation of ion competition in ESI is proposed in this paper. We define the correlated responsivity offset in the intensity values using the approximation of minimal correlation given by the matrix to the target mass values of the analyte. The estimation of the matrix influence enables the approximation of the position of a priori unknown responsivity and was easily evaluated using a simple algorithm. The method itself is directly derived from the basic attributes of the theory of measurements. There is sufficient agreement between the theoretical and experimental values. However, some theoretical issues are discussed to avoid misinterpretations and excessive expectations.

Is exposure to cyanobacteria an environmental risk factor for amyotrophic lateral sclerosis and other neurodegenerative diseases?

There is a broad scientific consensus that amyotrophic lateral sclerosis (ALS) is caused by gene-environment interactions. Mutations in genes underlying familial ALS (fALS) have been discovered in only 5-10% of the total population of ALS patients. Relatively little attention has been paid to environmental and lifestyle factors that may trigger the cascade of motor neuron death leading to the syndrome of ALS, although exposure to chemicals including lead and pesticides, and to agricultural environments, smoking, certain sports, and trauma have all been identified with an increased risk of ALS. There is a need for research to quantify the relative roles of each of the identified risk factors for ALS. Recent evidence has strengthened the theory that chronic environmental exposure to the neurotoxic amino acid β-N-methylamino-L-alanine (BMAA) produced by cyanobacteria may be an environmental risk factor for ALS. Here we describe methods that may be used to assess exposure to cyanobacteria, and hence potentially to BMAA, namely an epidemiologic questionnaire and direct and indirect methods for estimating the cyanobacterial load in ecosystems. Rigorous epidemiologic studies could determine the risks associated with exposure to cyanobacteria, and if combined with genetic analysis of ALS cases and controls could reveal etiologically important gene-environment interactions in genetically vulnerable individuals.

First report of a toxic Nodularia spumigena (Nostocales/ Cyanobacteria) bloom in sub-tropical Australia. II. Bioaccumulation of nodularin in isolated populations of mullet (Mugilidae)

Fish collected after a mass mortality at an artificial lake in south-east Queensland, Australia, were examined for the presence of nodularin as the lake had earlier been affected by a Nodularia bloom. Methanol extracts of muscle, liver, peritoneal and stomach contents were analysed by HPLC and tandem mass spectrometry; histological examination was conducted on livers from captured mullet. Livers of sea mullet (Mugil cephalus) involved in the fish kill contained high concentrations of nodularin (median 43.6 mg/kg, range 40.8-47.8 mg/kg dry weight; n = 3) and the toxin was also present in muscle tissue (median 44.0 μg/kg, range 32.3-56.8 μg/kg dry weight). Livers of fish occupying higher trophic levels accumulated much lower concentrations. Mullet captured from the lake 10 months later were also found to have high hepatic nodularin levels. DNA sequencing of mullet specimens revealed two species inhabiting the study lake: M. cephalus and an unidentified mugilid. The two mullet species appear to differ in their exposure and/or uptake of nodularin, with M. cephalus demonstrating higher tissue concentrations. The feeding ecology of mullet would appear to explain the unusual capacity of these fish to concentrate nodularin in their livers; these findings may have public health implications for mullet fisheries and aquaculture production where toxic cyanobacteria blooms affect source waters. This report incorporates a systematic review of the literature on nodularin measured in edible fish, shellfish and crustaceans.

Organochlorine pesticide residues in sediments from the Uganda side of Lake Victoria

Organochlorine (OC) residues were analysed in 117 sediment samples collected from four bays of the Uganda side of Lake Victoria. The sediments were collected with a corer at a depth of 0-20 cm, and extracted for OC residues using a solid dispersion method. The extracts were cleaned using gel permeation chromatography and analysed for pesticide residues using a gas chromatograph (GC) equipped with an electron capture detector. The results were confirmed using a GC equipped with a mass spectrometer (MS). A total of 16 OC residues, most of them persistent organic pollutants (POPs) were identified and quantified. The OC residue levels were expressed on an oven dry weight (d.w.) basis. Endosulphan sulphate, in the range of 0.82-5.62 μg kg⁻¹ d.w., was the most frequently detected residue. Aldrin and dieldrin were in the ranges of 0.22-15.96 and 0.94-7.18 μg kg⁻¹ d.w., respectively. DDT and its metabolites lay between 0.11-3.59 for p,p'-DDE, 0.38-4.02 for p,p'-DDD, 0.04-1.46 for p,p'-DDT, 0.07-2.72 for o,p'-DDE and 0.01-1.63 μg kg⁻¹ d.w. for o,p'-DDT. The levels of γ-HCH varied from 0.05 to 5.48 μg kg⁻¹ d.w. Heptachlor was detected only once at a level of 0.81 μg kg⁻¹ d.w., while its photo-oxidation product, heptachlor epoxide, ranged between non-detectable (ND) to 3.19 μg kg⁻¹ d.w. Chlordane ranged from ND to 0.76 μg kg⁻¹ d.w. Based on the threshold effect concentration (TEC) for fresh water ecosystems, aldrin and dieldrin were the only OCs that seemed to be a threat to the lake environment.