High Microcystin Concentrations Research Articles

Drivers and mechanisms of harmful algal blooms across hydrologic extremes in hypereutrophic grand lake st marys (Ohio)

Grand Lake St. Marys (GLSM) is a large, shallow, hypereutrophic lake situated in an agricultural watershed with high-nutrient, non-point source runoff. The resulting harmful algal blooms (HABs) are typically dominated by Planktothrix, which can produce microcystin, a potent cyanobacterial toxin that has varied in concentration over the past decade. Some drivers of bloom biomass and toxicity in GLSM are described, but recent years (2019–2022) have exhibited anomalous combinations of winter ice cover and spring runoff, suggesting that additional factors contribute to variability in HAB severity and toxicity. 2020 and 2022 were typical water years, with normal tributary runoff volumes occurring primarily in late winter and spring after either little to no ice cover (2019–2020) or heavy/prolonged ice cover (2021–2022). However, 2021 exhibited prolonged winter ice and low winter/spring runoff. 2020 and 2022 were typical bloom years, with near monoculture, Planktothrix-dominated biomass (11 to 405 μg/L total chlorophyll) and high total concentrations of microcystins (<0.3 to 65 μg/L). However, the first half of 2021 exhibited lower biomass (18 to 65 μg/L chlorophyll a) and toxin concentrations (0.4 to 2.0 μg/L). While biomass returned to bloom levels when external tributary loading increased, ammonium uptake and regeneration rates and microcystin concentrations remained low throughout 2021 (in contrast to other years). Overall, potential ammonium uptake rates strongly correlated with chlorophyll and microcystin concentrations (Bayesian R2 = 0.59; 95% CI = 0.44 to 0.65). Phytoplankton diversity was higher in 2021 than other years, especially in spring/early summer, with increased dinoflagellates and diatoms in spring, followed by a mixed cyanobacterial assemblage in summer. These results suggest that lower external nutrient loads can drive immediate positive impacts on water quality, such as reduced HAB biomass and toxicity and higher phytoplankton diversity, even in hypereutrophic, shallow lakes.

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.

Eco-friendly management of harmful cyanobacterial blooms in eutrophic lakes through vertical flow multi-soil-layering technology

Eutrophication has led to the widespread occurrence of cyanobacterial blooms. Toxic cyanobacterial blooms with high concentrations of microcystins (MCs) have been identified in the Lalla Takerkoust reservoir in Morocco. The objective of this study was to evaluate the efficiency of the Multi-Soil-Layering (MSL) ecotechnology in removing natural cyanobacterial blooms from the lake. Two MSL pilots were used in rectangular glass tanks (60 × 10 × 70 cm). They consisted of permeable layers (PLs) made of pozzolan and a soil mixture layer (SML) containing local soil, ferrous metal, charcoal and sawdust. The main difference between the two systems was the type of local soil used: sandy soil for MSL1 and clayey soil for MSL2. Both MSL pilots effectively reduced cyanobacterial cell concentrations in the treated water to very low levels (0.09 and 0.001 cells/mL). MSL1 showed a gradual improvement in MC removal from 52 % to 99 %, while MSL2 started higher at 90 % but dropped to 54% before reaching 86%. Both MSL systems significantly reduced organic matter levels (97.2 % for MSL1 and 95.8 % for MSL2). Both MSLs were shown to be effective in removing cyanobacteria, MCs, and organic matter with comparable performance.

Cyanobacterial bloom monitoring and assessment in Latin America

Cyanobacterial blooms have serious adverse effects on human and environmental health. In Latin America, one of the main world's freshwater reserves, information on this phenomenon remains sparse. To assess the current situation, we gathered reports of cyanobacterial blooms and associated cyanotoxins in freshwater bodies from South America and the Caribbean (Latitude 22° N to 45° S) and compiled the regulation and monitoring procedures implemented in each country. As the operational definition of what is a cyanobacterial bloom remains controversial, we also analyzed the criteria used to determine the phenomena in the region. From 2000 to 2019, blooms were reported in 295 water bodies distributed in 14 countries, including shallow and deep lakes, reservoirs, and rivers. Cyanotoxins were found in nine countries and high concentrations of microcystins were reported in all types of water bodies. Blooms were defined according to different, and sometimes arbitrary criteria including qualitative (changes in water color, scum presence), quantitative (abundance), or both. We found 13 different cell abundance thresholds defining bloom events, from 2 × 103 to 1 × 107 cells mL−1. The use of different criteria hampers the estimation of bloom occurrence, and consequently the associated risks and economic impacts. The large differences between countries in terms of number of studies, monitoring efforts, public access to the data and regulations regarding cyanobacteria and cyanotoxins highlights the need to rethink cyanobacterial bloom monitoring, seeking common criteria. General policies leading to solid frameworks based on defined criteria are needed to improve the assessment of cyanobacterial blooms in Latin America. This review represents a starting point toward common approaches for cyanobacterial monitoring and risk assessment, needed to improve regional environmental policies.

Combination Effect of Microcystins and Arsenic Exposures on CKD: A Case-Control Study in China

Evidence has shown that exposure to environmental pollutants such as microcystins (MCs), arsenic (As), and cadmium (Cd) can lead to the occurrence and development of chronic kidney disease (CKD). There is a synergistic effect between MCs and Cd. However, the combined effect of MCs and As exposures on CKD remains unclear. In Hunan province, China, 135 controls and 135 CKD cases were enrolled in a case-control study. Serum MCs, plasma As and Cd concentrations were measured for all participants. We investigated the association between MCs/As and CKD risk using conditional logistic regression. The additive model explored the interaction effect, and the Bayesian kernel machine regression (BKMR) models investigated the combined effects of MCs, As, and Cd on CKD. The results showed that MCs and As were significantly associated with CKD risk. Participants in the highest MCs concentration had a 4,81-fold increased risk of CKD compared to those in the lowest quartile (95% confidence interval [CI]: 1,96 to 11,81). The highest quartile of As concentrations corresponded to an adjusted odds ratio of 3.40 (95% CI: 1.51, 7.65) relative to the lowest quartile. MCs/As and CKD risk exhibited significant dose-response correlations (all p for trend < 0.01). In addition, a positive interaction effect of MCs and As on CKD was also reported. The CKD risk due to interaction was 2.34 times (95% CI: 0.14, 4.54) relative to the CKD risk without interaction, and the attributable proportion of CKD due to interaction among individuals with both exposures was 56% (95% CI: 0.22, 0.91). In the BKMR, the combined effect of MCs, As, and Cd was positively associated with CKD. In conclusion, both MCs and As are independent risk factors for CKD, exerting a synergistic effect between them. Combined exposure to MCs, As, and Cd can increase the risk of CKD.

Characterization of Potential Threats from Cyanobacterial Toxins in Lake Victoria Embayments and during Water Treatment.

Africa’s water needs are often supported by eutrophic water bodies dominated by cyanobacteria posing health threats to riparian populations from cyanotoxins, and Lake Victoria is no exception. In two embayments of the lake (Murchison Bay and Napoleon Gulf), cyanobacterial surveys were conducted to characterize the dynamics of cyanotoxins in lake water and water treatment plants. Forty-six cyanobacterial taxa were recorded, and out of these, fourteen were considered potentially toxigenic (i.e., from the genera Dolichospermum, Microcystis, Oscillatoria, Pseudanabaena and Raphidiopsis). A higher concentration (ranging from 5 to 10 µg MC-LR equiv. L−1) of microcystins (MC) was detected in Murchison Bay compared to Napoleon Gulf, with a declining gradient from the inshore (max. 15 µg MC-LR equiv. L−1) to the open lake. In Murchison Bay, an increase in Microcystis sp. biovolume and MC was observed over the last two decades. Despite high cell densities of toxigenic Microcystis and high MC concentrations, the water treatment plant in Murchison Bay efficiently removed the cyanobacterial biomass, intracellular and dissolved MC to below the lifetime guideline value for exposure via drinking water (<1.0 µg MC-LR equiv. L−1). Thus, the potential health threats stem from the consumption of untreated water and recreational activities along the shores of the lake embayments. MC concentrations were predicted from Microcystis cell numbers regulated by environmental factors, such as solar radiation, wind speed in the N–S direction and turbidity. Thus, an early warning through microscopical counting of Microcystis cell numbers is proposed to better manage health risks from toxigenic cyanobacteria in Lake Victoria.

Co-occurrence of microcystin and cylindrospermopsin in hypereutrophic Mahakanadarawa and Nachchaduwa reservoirs

Microcystins (MCs) and cylindrospermopsin (CYN) are the most abundant toxins produced by cyanobacteria in tropical freshwaters. We studied the spatial distribution of MC and CYN in two multipurpose reservoirs, Mahakanadarawa and Nachchaduwa in Anuradhapura district in Sri Lanka in September 2020. Fourteen water quality parameters, phytoplankton composition, chlorophyll-a, MC and CYN concentrations were analyzed in triplicate in 25 sampling sites from each reservoir. Both reservoirs were at hypereutrophic status. Microcystis was the dominant cyanobacteria with 0-3.75 x 103 cell/mL in Mahakanadarawa and 1-7 x 103 cell/mL in Nachchaduwa. Besides Microcystis, no other potential MC-producing cyanobacteria were observed. In Mahakanadarawa, MC was detected in the range of 0.11-1.63 µg/L which was above the WHO permissible level (1.0 µg/L) for drinking water. Although comparatively high Microcystis cell density was present in Nachchaduwa, its MC concentration was low (0.06-0.17 µg/L). The CYN concentration in Nachchaduwa was above the WHO permissible level (0.7 µg/L) for drinking water. It was 0.20-1.02 µg/L in Nachchaduwa and 0.03-0.08 µg/L in Mahakanadarawa. We did not observe any potential CYN-producing cyanobacteria in either of the reservoirs. There was no relationship between the spatial distribution pattern of MC and Microcystis cell density in both reservoirs. Although the majority of physico-chemical properties of water indicated suitability for drinking, co-occurrence of high concentrations of MC and CYN indicated their unsuitability for drinking. Hence, this study highlights the necessity for routing detection of cyanotoxins in both reservoirs. Further, our findings alarm potential health risks for the local community that relies on Mahakanadarawa and Nachchaduwa reservoirs for drinking, irrigation and fisheries.

Massive fish death associated with the toxic cyanobacterial Planktothrix sp. bloom in the Béni-Haroun Reservoir (Algeria).

In July 2017, a massive bloom of the potentially toxic cyanobacterial species Planktothrix sp. was observed in the Béni-Haroun Reservoir (Algeria), which was followed by a massive fish death. Many questions were raised in association with the role of cyanotoxins and the fish massive mortality. The objective of this paper is twofold: (1) to investigate the variability of physicochemical and cyanobacterial parameters (chlorophyll-a, phycocyanin, allophycocyanin, and microcystins) throughout the period of July 2017 to June 2018; and (2) to determine the free and total MC levels in viscera and muscle tissues of the common carp (Cyprinus carpio), which are found dead in the considered reservoir in October 2017. Our results showed microcystin (MC) concentrations in water samples (by the protein phosphatase PP2A assay) had reached 651.2ng MC-LR equiv./L. Total MC levels (free + bound) in the viscera and muscle tissues of sampled dead fish were at 960.24 and 438.54µg MC-LR equiv./kg dw, respectively. It is assumed that high concentrations of MC observed in the tissues of common carp induced a strong degradation of the visceral contents resulting in the complete lysis of the hepatopancreas, and presumably the massive fish death.

Cyanobacterial Diversity and the Presence of Microcystins in the Küçük Menderes River Basin, Turkey

Although cyanobacteria are commonly associated with eutrophic lakes, they are the basic components of phytoplankton communities in lakes that have different trophic statuses. In inland waters, both nutrient loading from watersheds and warmer conditions promote phytoplankton growth and cause extensive cyanobacterial blooms. Certain bloom-forming cyanobacterial species can pose a health risk to humans and aquatic ecosystems through cyanotoxin production. The aim of this study was to evaluate the cyanobacterial composition and toxins in five reservoirs and two natural lakes in the Küçük Menderes River Basin, all with varying trophic statuses. Within this scope, samples were collected in autumn 2017 and spring 2018. Cyanobacterial species were enumerated according to the Utermöhl method. Cyanotoxin samples were analyzed using HPLC. To find the trophic status of the water bodies, the Trophic State Index (TSI) developed by Carlson (1977) was used and Total Phosphorus (TP), Secchi Depth (SD), and Chlorophyll-ɑ (chl-ɑ) measurements were performed. Cyanobacterial abundance, species composition, and cyanotoxin production differed significantly between the lakes and reservoirs. A total of 13 cyanobacteria species were identified including potential cyanotoxin producers such as Microcystis, Aphanizomenon, and Dolichospermum. According to the TSI, three reservoirs were mesotrophic and the other four waterbodies had eutrophic-hypereutrophic conditions. Microcystis is the most common bloom-forming freshwater cyanobacteria in the Küçük Menderes River Basin. However, microcystin concentrations were relatively low and the highest microcystin concentration was detected in the Tahtalı Reservoir at 9 µg/L. The Küçük Menderes River Basin is under water-stressed conditions and the cyanobacteria blooms in the region might pose another threat for wildlife and humans.&nbsp;

Risk assessment and identification of factors influencing the historical concentrations of microcystin in Lake Taihu, China

Understanding the history of microcystins (MCs) pollution in large lakes can help inform future lake management. We collected sediment cores from Lake Taihu to: investigate the long-term record of MCs (MC-LR, MC-YR, and MC-RR), explore the main environmental drivers of MCs, and assess their public health and ecological risks. Results showed that MCs content in all cores increased over time. The core from north Taihu had the highest MC concentrations, with an average total MCs (sum of MC-LR, MC-YR, and MC-RR = TMCs) content of (74.31±328.55) ng/g. The core from eastern Taihu showed the lowest average TMCs content of (2.91±3.95) ng/g. PCA showed that sediment MCs at the three sites were positively correlated with sediment chlorophyll-a. MC-LR and MC-YR in northern and western Taihu negatively correlated with both the sediment total organic carbon/sediment total nitrogen ratio (STOC/STN) and water nitrate (NO3−-N) concentration, but three MC congeners at eastern Taihu showed positive correlations with water orthophosphate (PO43−-P), NO3−-N, and STOC/STN. Generalized additive model analysis at each site revealed that NO3−-N was the main TMCs driver in northern and western Taihu where phytoplankton dominated, whereas PO43−-P was the main TMCs driver in eastern Taihu where macrophytes dominated. At the whole lake scale, total phosphorus (TP) and PO43−-P were the most important environmental drivers influencing MCs; TP explained 47.4%, 44.2%, and 47.6% while orthophosphate explained 34.8%, 31.2%, and 34.7% of the deviance on TMCs, MC-LR, and MC-YR, respectively. NO3−-N also showed a strong effect on MCs variation, especially on MC-YR. Risk assessment showed that both ecological and public health risk has increased in recent years. We conclude that while control of phosphorus and nitrogen input should be a major focus for future lake management, lake zone-specific management strategies may also be important.

Dynamics of the prokaryotic and eukaryotic microbial community during a cyanobacterial bloom.

Toxic cyanobacterial blooms frequently develop in eutrophic freshwater bodies worldwide. Microcystis species produce microcystins (MCs) as a cyanotoxin. Certain bacteria that harbor the mlr gene cluster, especially mlrA, are capable of degrading MCs. However, MC-degrading bacteria may possess or lack mlr genes (mlr+ and mlr- genotypes, respectively). In this study, we investigated the genotype that predominantly contributes to biodegradation and cyanobacterial predator community structure with change in total MC concentration in an aquatic environment. The 2 genotypes coexisted but mlr+ predominated, as indicated by the negative correlation between mlrA gene copy abundance and total MC concentration. At the highest MC concentrations, predation pressure by Phyllopoda, Copepoda, and Monogononta (rotifers) was reduced; thus, MCs may be toxic to cyanobacterial predators. The results suggest that cooperation between MC-degrading bacteria and predators may reduce Microcystis abundance and MC concentration.

Physiological and metabolic responses of Microcystis aeruginosa to a salinity gradient

Microcystis is a well-known toxic cyanobacterium in eutrophic environments, and an increasing number of Microcystis blooms have emerged in salty reservoirs and coastal rivers. This study observed that many Microcystis were identified in a coastal river in June 2020. The relative abundance of Microcystis decreased from 81.2 to 10.2% in the sampling sites from a salinity of 0 (Sal. 0) to a salinity of 12 (Sal. 12). Hepatotoxic microcystins (MCs) were identified in the coastal river and its estuary. Of the samples, those with a salinity of 5 (Sal. 5) had the highest concentration of MCs at 7.81 ± 0.67 μg L-1. In a saline water simulation experiment, the results showed that salt inhibited Microcystis (M.) aeruginosa growth, enhanced the activity levels of superoxide dismutase (SOD) and catalase (CAT) and stimulated microcystin production. Transcription analysis showed that the expression levels of the psaB and rbcL genes controlling photosymbiotic processes were downregulated, and capD and csaBgene-related polysaccharide productions were upregulated by salt incubation. Notably, metabolism analysis showed that the total polysaccharides, proteins and small molecular matter, such as sucrose, methionine and N-acetyl-D-glucosamine, in the Microcystis cells increased substantially to resist the extracellular hyperosmotic pressure caused by the high salinity levels in culture. These findings indicate that increased salt in a natural aquatic body shifts the phytoplankton community by influencing the physiological metabolism of cyanobacteria and poses a high risk of microcystin exposure during cyanobacterial blooms in coastal rivers.

The dynamics and release characteristics of microcystins in the plateau Lake Erhai, Southwest China.

Microcystins (MCs) have seriously polluted drinking water supplies and have caused great harm to aquatic organisms and humans. Understanding the dynamics of MC concentrations and its influencing factors is necessary for drinking water safety. Many previous studies on MC pollution focused on intracellular MCs rather than on extracellular MCs, which are more difficult to remove by water treatment. So far, the release characteristics of MCs and the relationships between intracellular and extracellular MCs are still unclear. To explore these questions, a survey was conducted at 18 sites across Lake Erhai from May 2014 to April 2015 as in Lake Erhai the frequency and coverage area of cyanobacterial blooms have been increasing. Variation of extracellular MCs lagged behind that of intracellular MCs. The highest value of intracellular MCs was 1.07μgL-1 in October 2014 and the highest extracellular MC concentration was 0.035μgL-1 in November 2014. Intracellular MCs were positively influenced by MC-producing cyanobacterial biomass, water temperature (WT), pH, and conductivity (Cond). The extracellular MCs showed little correlation with cyanobacterial abundances and intracellular MC concentrations, but showed significant negative correlations with WT, pH, and Cond. These results indicated that high biomass and high intracellular MC concentrations did not quickly lead to large releases of MCs, and that when cyanobacterial cells died and blooms disappeared, MCs were intensively released into the water, posing the greatest threat to drinking water supply.

Prevalence and persistence of microcystin in shoreline lake sediments and porewater, and associated potential for human health risk

Midlatitude waterbodies are experiencing increased cyanobacteria blooms that necessitate health advisories to protect waterbody users. Although surface waters may contain cyanotoxins such as microcystin (MC), at concentrations that pose potential public health risks, little is known about MC contamination of shoreline sediments. Based on growing evidence that lake and reservoir sediments can accumulate MCs, we hypothesized that shoreline sediments (i.e., recreational beaches) may accumulate MCs and thereby pose a potential health risk to recreational users even if people stay out of contaminated water. We sampled nearshore surface water, shoreline sediment, and porewater from seven Washington State, USA, lakes/reservoirs recreational beaches to determine MC presence/absence during or immediately following cyanobacteria blooms. We found MCs in shoreline sediments at all waterbodies using ELISA and LC-MS/MS. MC concentrations in shoreline sediments and porewaters persisted for 20 days following dissipation of cyanobacteria blooms when MC concentrations were near analytical reporting limits in corresponding surface waters. A human health risk assessment based on potential MC exposure through incidental ingestion of porewaters and sediments found, even when very high MC concentrations occur in surface waters (i.e., >11,000 μg/L), estimated ingestion doses are below MC World Health Organization tolerable daily intake and U.S. Environmental Protection Agency’s risk reference dose. While our findings suggest MCs in Washington State recreational beaches in 2018 did not present a significant human health risk, future blooms with higher MC concentrations could pose human health risks via the shoreline sediment/porewater exposure pathway.

Identification and quantification of microcystins in western Lake Erie during 2016 and 2017 harmful algal blooms

Liquid chromatography-mass spectrometry (LC-MS) and tandem mass spectrometry (MS/MS) were used to provide qualitative and quantitative information about microcystin (MC) congeners in western Lake Erie. Samples were collected at eight open-water locations on selected days during harmful algal blooms (HABs) in 2016 and 2017. Seven MCs were identified and 20 MCs were tentatively identified using high-resolution mass accuracies and a unique fragment (Adda m/z 135). The most abundant MC was MC-LR, followed by MC-RR, MC-YR, and MC-LA, and these congeners were quantified. Total (extracellular and intracellular) MC concentrations ranged from 0.068 to 14.88 µg/L in 2016, and from 0.050 to 10.15 µg/L in 2017, with averages of 2.71 and 1.86 µg/L, respectively. Near-shore sites in Lake Erie had higher MC concentrations and Microcystis biovolumes than off-shore sites. This implies that nutrient loading from the Maumee River greatly influences Maumee Bay, and this influence decreases with distance from the river. Consequently, six MCs (MC-LR, MC-RR, MC-LA, MC-YR, MC-LW, and MC-LF) were quantified in water samples collected from the Maumee River and the Maumee Bay shore of Lake Erie in 2017, and MC-RR was the most abundant. The total MC concentrations in river samples ranged from 0.17 to 305.03 µg/L. Additionally, an MC degradation product (linear MC-LR) was detected at all open-water locations, and data indicated an increase in its concentration towards the end of the bloom. The trends for 2016 and 2017 HABs are comparable in terms of spatial distribution and MC congeners produced, though the intensity and peak dates change.

Seasonal variation and potential risk assessment of microcystins in the sediments of Lake Taihu, China

High concentrations of microcystins (MCs) in sediment pose a serious hazard to aquatic and terrestrial organisms. Hence, we investigated the seasonal variation of dominant MCs (MC-LR, MC-RR and MC-YR) in sediments of Lake Taihu over four seasons for the first time. Sediment MCs varied seasonally (p < 0.01) with concentrations highest in August and lowest in February. The MCs were dominated by MC-LR (61.47%) with the content ranging from 0.02 to 2.37 μg/g dry weight in sediment. The three MC congeners and their proportions were significantly correlated with latitude and longitude. Meiliang Bay in the north had the highest MCs of all sites, while the eastern part of the lake had a high level especially in August. Variation of MC-LR and MC-RR concentrations was significantly correlated (p < 0.05) with water temperature, dissolved total organic carbon, cyanobacteria density, total suspended solid particles, and total organic carbon and total nitrogen in sediment, while MC-YR was negatively correlated (p < 0.01) with nutrients in the water column and heavy metals in sediments. An ecological risk assessment suggested the MCs already pose significant adverse effects on Potamopyrgus antipodarum; although the adverse effects on humans were weak, children were at greater risk than adults.

Detection of free and bound microcystins in tilapia fish from Egyptian fishpond farms and its related public health risk assessment

Microcystins (MCs), the most common cyanobacterial toxins in freshwaters, can accumulate in aquatic animals in free and bound forms. MCs therefore pose a risk to human health upon consumption of contaminated fish tissues, as they cause severe liver damage and death with potential carcinogenic effects. While there have been extensive studies on free MC contents in fish tissues, the detection of bound MCs in fish is largely unexplored. In the present study, both free and bound MCs were monthly monitored in tilapia fish from three tropical fishponds in Egypt for one year. Fishpond waters contained high concentrations of MCs (18–44 µg/l). Free MCs were estimated in tilapia fish organs at levels up to 11.8 ng/g in intestines, 8.3 ng/g in livers and 0.38 ng/g in edible tissues. Concentrations of bound MCs in edible tissues as determined by Lemieux oxidation technique (15,000–19,000 ng/g fresh weight, FW) were several-folds higher than free MCs. The estimated daily intake (EDI) for free MCs (0.0006–0.002 μg/kg/day MCs) in edible tissues was lower than the WHO limit (0.04 µg/kg/day), while EDI of bound MCs exceeded this limit by a factor of 77–2396. Therefore, both free and bound MCs in fish tissues should be considered when fish are monitored for human consumption.

Assessment of microcystin contamination of Amaranthus hybridus, Brassica oleracea, and Lactuca sativa sold in markets: a case study of Zaria, Nigeria.

Microcystins (MCs) are toxic secondary metabolites produced by several cyanobacteria genera that have been implicated in human cancer cases and deaths. Human exposure routes include direct contact with contaminated water and the consumption of contaminated food. The present study investigated the presence of MCs in three commonly consumed vegetables at the point of sale in market places as a means of assessing the direct human health risk of buying vegetables. Overall, 53% of the vegetables obtained from different markets had levels of MCs that were higher than 1.00 μg/g. Amaranthus hybridus L. (smooth amaranth) had the highest MC concentration (4.79 μg/g) in samples obtained from Sabon Gari Market, while Lactuca sativa L. (garden lettuce) had the lowest concentration (0.17 μg/g) in samples obtained from Dan-Magaji Market. The highest total daily intake (TDI) of MCs by an adult weighing 60 kg was 3.19 μg/kg for A. hybridus, 1.41 μg/kg for Brassica oleracea L. (cabbage), and 2.94 μg/kg for L. sativa. The highest TDI of MCs for a child weighing 25 kg was highest in A. hybridus (1.91 μg/kg), followed by L. sativa (1.77 μg/kg). These results revealed that the consumption of vegetables sold in markets in Zaria, Nigeria, during the dry season represents a major exposure route to MCs. There is, therefore, an urgent need to develop policies and monitoring strategies to tackle this problem in developing countries.

Floración excepcional de cianobacterias tóxicas en la costa de Uruguay, verano 2019

Cyanobacterial toxic blooms are a worldwide problem. In Rio de la Plata basin, anthropic eutrophication and dam construction have promoted an increase in cyanobacteria blooms, especially those of the Microcystis aeruginosa complex (CMA). Here, we describe the exceptional blooms observed in the summer of 2019 on the coast of Rio de la Plata and Atlantic coast of Uruguay. We discuss the main driving mechanisms using biological, meteorological and oceanographic sampling data, satellite images and reanalysis. The blooms covered a wide surface (Carmelo to Rocha; 500 km) and were persistent in time (ca. 4 months). Blooms were generated by CMA organisms having similar genetic structure and were associated to quantifiable and high microcystin concentrations. Given the observed oceanographic conditions and the similarity in organisms traits, we hypothesized that blooms had a common origin, probably associated with zones with high nutrient concentrations and high water residence time in the lower Rio de la Plata basin. Extreme precipitations induced high water flows that transported cyanobacteria blooms downstream. In addition, anomalous wind and temperature conditions facilitated their arrival to the Atlantic coast along Rocha, to environments with particular relevance for biodiversity and conservation (e.g. Rocha coastal lagoon).

The influence of nutrients limitation on phytoplankton growth and microcystins production in Spring Lake, USA

Due to excessive loadings of nitrogen (N) and phosphorus (P), frequent blooms of harmful cyanobacteria and their associated cyanotoxins pose serious threats to recreational usage and human health. However, whether cyanobacteria growth and toxin production are limited by N, P, or both N + P is still not clear. Thus, we conducted a nutrient enrichment bioassay in situ in Spring Lake, a eutrophic lake in west Michigan, USA, to examine the influence of nutrient limitation on the proliferation of algal blooms and the production of microcystins (MC). N or P addition alone resulted in a slight increase in the concentration of chlorophyll-a (Chl-a), suggesting a positive effect on phytoplankton growth, but alone, neither were sufficient to induce algal blooms. In contrast, the combination of N and P had a significant and positive influence on phytoplankton growth and MC production. Compared to controls, the N + P treatment resulted in high concentrations of Chl-a and MC, as well as high pH and dissolved oxygen. In addition, significant increases were observed in different MC analogues for each treatment; the highest concentrations of intracellular MC-LR, -RR, -YR, and TMC (total MC) were found in the N + P treatment with values of 9.16, 6.10, 2.57, and 17.82 μg/L, respectively. This study suggests that at least in this temperate coastal lake, cyanobacterial blooms and associated MC are influenced more by combined N and P enrichment than by N or P alone, indicating that managing both nutrients is important for effectively reducing algal blooms and MC production.