Fresh produce and their soils accumulate cyanotoxins from irrigation water: Implications for public health and food security

Toxic and non-toxic cyanobacterial biomass as a resource for sustainable agriculture: A lettuce cultivation experiment

Cyanobacteria represent a promising resource for sustainable agriculture, as they have demonstrated the ability to restore soil fertility even after death and decay. However, several cyanobacteria can also release secondary metabolites, such as cyanotoxins, which may compromise the quality of agricultural products and pose a potential risk to human health. Depending on the concentration of exposure, few studies reported deleterious effects on plant species when irrigated with cylindrospermopsin (CYN) contaminated water, impairing plant growth and leading to food product contamination, while other studies show promoting effects on plant yield. To evaluate the potential of cyanobacterial biomass (cyanotoxin-containing or not) as a sustainable resource for soil amendment, biostimulants or fertilizers for lettuce cultivation, a study was carried out that consisted of the culture of lettuce plants under controlled conditions, in soil: (1) with no extra nutrient addition (control) and supplemented with 0.6 g of freeze-dried Raphidiopsis raciborskii biomass of (2) a non-CYN-producing strain, (3) a CYN-producing strain, and (4) the same CYN-producing strain pasteurized. Results showed no significant differences in photosystem II efficiency with the amendment addition. On the contrary, shoot fresh weight significantly increased in lettuce plants grown with the cyanobacterial biomass addition, especially in condition (3). In addition, there were significant differences in mineral concentrations in lettuce leaves after the cyanobacterial biomass addition, such as K, Na, Ca, P, Mg, Mn, Zn, Cu, Mo, and Co. CYN accumulation was detected under conditions (3) and (4), with concentrations observed in descending order from roots > soil > shoot. Nevertheless, the CYN concentration in edible tissues did not exceed the WHO-proposed tolerable daily intake of 0.03 μg/kg/day. These findings suggest that incorporating cyanobacterial biomass as a soil amendment, biostimulant or fertilizer for lettuce cultivation, even with trace amounts of CYN (1-40 μg/g), may enhance plant yield without leading to cyanotoxin accumulation in edible tissues above the WHO-recommended tolerable daily intake.

Cyanobacterial Cultures, Cell Extracts, and Individual Toxins Decrease Photosynthesis in the Terrestrial Plants Lactuca sativa and Zea mays

Cyanobacterial harmful algal blooms (cHABs) are increasing due to eutrophication and climate change, as is irrigation of crops with freshwater contaminated with cHAB toxins. A few studies, mostly in aquatic protists and plants, have investigated the effects of cHAB toxins or cell extracts on various aspects of photosynthesis, with variable effects reported (negative to neutral to positive). We examined the effects of cyanobacterial live cultures and cell extracts (Microcystis aeruginosa or Anabaena flos-aquae) and individual cHAB toxins (anatoxin-a, ANA; beta-methyl-amino-L-alanine, BMAA; lipopolysaccharide, LPS; microcystin-LR, MC-LR) on photosynthesis in intact plants and leaf pieces in corn (Zea mays) and lettuce (Lactuca sativa). In intact plants grown in soil or hydroponically, overall net photosynthesis (Pn), but not Photosystem-II (PSII) electron-transport yield (ΦPSII), decreased when roots were exposed to cyanobacterial culture (whether with intact cells, cells removed, or cells lysed and removed) or individual toxins in solution (especially ANA, which also decreased rubisco activity); cyanobacterial culture also decreased leaf chlorophyll concentration. In contrast, ΦPSII decreased in leaf tissue vacuum-infiltrated with cyanobacterial culture or the individual toxins, LPS and MC-LR, though only in illuminated (vs. dark-adapted) leaves, and none of the toxins caused significant decreases in in vitro photosynthesis in thylakoids. Principal component analysis indicated unique overall effects of cyanobacterial culture and each toxin on photosynthesis. Hence, while cHAB toxins consistently impacted plant photosynthesis at ecologically relevant concentrations, the effects varied depending on the toxins and the mode of exposure.

Using dredged sediments from Lake Taihu as a plant-growing substrate: Focusing on the impact of microcystins

Using dredged sediment as plant growth substrates is a promising way to deal with large amounts of excavated sediments. However, it is a big challenge to deal with various pollutants in sediments, among which microcystins (MCs) gained limited attention. In this study, sediments collected from Lake Taihu were mixed with agricultural soil at a 1:1 ratio to create various growing substrates for lettuce (Lactuca sativa L. var. ramosa Hort.). Results indicated that fresh weight and leaf area of lettuce increased in some sediment-amended treatments due to additional nutrients, but food quality was negatively affected by sediment amendment as suggested by the soluble sugar and Vitamin C levels. MCs were detected in all lettuce grown in sediment-amended substrates, particularly in treatments with sediments collected during the bloom. The highest MC contents were found in treatment amended with sediments collected from Meiliang Bay in August (88.6 μg kg-1 for MC-LR and 65.6 μg kg-1 for MC-RR). MC accumulation in lettuce and the associated human health risks were significant, especially in treatments with sediments from the bloom period. Ecological risk assessments revealed high RQ values, indicating potential harm to the soil ecosystem. This study underscores the importance of considering MC content in sediments when evaluating their use as growing substrates. The findings contribute to understanding the environmental and health implications of sediment reuse, offering insights for safer agricultural practices and sediment management.

Accumulation of microcystin toxin in irrigation water and alfalfa (Medicago sativa) forage plant, and assessing the potential risk to animal health

Microcystin (MC) toxin produced by cyanobacteria has become a significant concern for societies worldwide. The risk of MC in drinking water has been assessed to human health. Nonetheless, its risk to animal health has not been thoroughly evaluated. This study investigated MCs in irrigation water and alfalfa plant from nearby farmlands. Both irrigation water and alfalfa shoots contained greater MC concentrations (1.8-17.4 μg L-1 and 0.053-0.128 μg g-1) during summer than winter (2.4 μg L-1 and 0.017 μg g-1). These MC concentrations showed a correlation with the predominance of cyanobacteria in the sites, triggering the potential risk of these microorganisms in irrigation waters. Accordingly, there would be a high risk (risk quotient, RQ > 1) during summer and a moderate risk (0.1 Collapse

Key Words

• Animal feed
• Cyanotoxins
• Freshwaters
• Livestock
• cyanobacteria

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MESH Headings

• Microcystins/metabolism
• Microcystins/analysis
• Medicago sativa/metabolism
• Animals
• Agricultural Irrigation
• Risk Assessment
• Environmental Monitoring
• Seasons
• Cyanobacteria/metabolism
• Water Pollutants, Chemical/metabolism
• Water Pollutants, Chemical/analysis
• Cattle
• Sheep

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Grants Collapse

Affiliation(s)

Zakaria A Mohamed Department of Botany and Microbiology, Faculty of Science, Sohag University, Sohag, 82524, Egypt.
Yasser Mostafa King Khalid University, College of Science, Department of Biology, Abha, P.O. Box 9004, Saudi Arabia
Saad Alamri King Khalid University, College of Science, Department of Biology, Abha, P.O. Box 9004, Saudi Arabia
Mohamed Hashem Assiut University, Faculty of Science, Botany and Microbiology Department, Assiut 71516, Egypt

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Microcystin levels in irrigation water and field-vegetable plants, and food safety risk assessment: A case study from Egypt

Microcystin (MC), a hepatotoxin that is harmful to human health, has frequently increased in freshwaters worldwide due to the increase in toxic cyanobacterial blooms. Despite many studies reported the human exposure to MC through drinking water, the potential transfer of this toxin to human via consumption of vegetables grown on farmlands that are naturally irrigated with contaminated water has not been largely investigated. Therefore, this study investigates the presence of MC in irrigation water and its potential accumulation in commonly consumed vegetables from Egyptian farmlands. The results of toxin analysis revealed that all irrigation water sites contained high MC concentrations (1.3-93.7 μg L-1) along the study period, in association with the abundance of dominant cyanobacteria in these sites. Meanwhile, MCs were detected in most vegetable plants surveyed, with highest levels in potato tubers (1100 μg kg-1 fresh weight, FW) followed by spinach (180 μg kg-1 FW), onion (170 μg g-1 FW), Swiss chard (160 μg kg-1 FW) and fava bean (46 μg kg-1 FW). These MC concentrations in vegetables led to estimated daily intake (EDI) values (0.08-1.13 μg kg bw-1 d-1 for adults and 0.11-1.5 μg kg bw-1 d-1 for children), through food consumption, exceeding the WHO recommended TDI (0.04 μg kg bw-1 d-1) for this toxin. As eutrophic water is widely used for irrigation in many parts of the world, our study suggests that cyanotoxins in irrigation waters and agricultural plants should be regularly monitored to safeguard the general public from inadvertent exposure to harmful toxins via food consumption.

Fungal removal of cyanotoxins in constructed wetlands: The forgotten degraders

Harmful cyanobacterial blooms have increased globally, releasing hazardous cyanotoxins that threaten the safety of water resources. Constructed wetlands (CWs) are a nature-based and low-cost solution to purify and remove cyanotoxins from water. However, bio-mechanistic understanding of the biotransformation processes expected to drive cyanotoxin removal in such systems is poor, and primarily focused on bacteria. Thus, the present study aimed at exploring the fungal contribution to microcystin-LR and cylindrospermopsin biodegradation in CWs. Based on CW mesocosms, two experimental approaches were taken: a) amplicon sequencing studies were conducted to investigate the involvement of the fungal community; and b) CW fungal isolates were tested for their microcystin-LR and cylindrospermopsin degradation capabilities. The data uncovered effects of seasonality (spring or summer), cyanotoxin exposure, vegetation (unplanted, Juncus effusus or Phragmites australis) and substratum (sand or gravel) on the fungal community structure. Additionally, the arbuscular mycorrhizal fungus Rhizophagus and the endophyte Myrmecridium showed positive correlations with cyanotoxin removal. Fungal isolates revealed microcystin-LR-removal potentials of approximately 25 % in in vitro biodegradation experiments, while the extracellular chemical fingerprint of the cultures suggested a potential intracellular metabolization. The results from this study may help us understand the fungal contribution to cyanotoxin removal, as well as their ecology in CWs.

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.

Microcystin Contamination in Irrigation Water and Health Risk

Microcystins (MCs), natural hepatotoxic compounds produced by cyanobacteria, pose significant risks to water quality, ecosystem stability, and the well-being of animals, plants, and humans when present in elevated concentrations. The escalating contamination of irrigation water with MCs presents a growing threat to terrestrial plants. The customary practice of irrigating crops from local water sources, including lakes and ponds hosting cyanobacterial blooms, serves as a primary conduit for transferring these toxins. Due to their high chemical stability and low molecular weight, MCs have the potential to accumulate in various parts of plants, thereby increasing health hazards for consumers of agricultural products, which serve as the foundation of the Earth's food chain. MCs can bioaccumulate, migrate, potentially biodegrade, and pose health hazards to humans within terrestrial food systems. This study highlights that MCs from irrigation water reservoirs can bioaccumulate and come into contact with plants, transferring into the food chain. Additionally, it investigates the natural mechanisms that organisms employ for conjugation and the microbial processes involved in MC degradation. To gain a comprehensive understanding of the role of MCs in the terrestrial food chain and to elucidate the specific health risks associated with consuming crops irrigated with water contaminated with these toxins, further research is necessary.

Microcystin influence on soil-plant microbiota: Unraveling microbiota modulations and assembly processes in the rhizosphere of Vicia faba

Microcystins (MCs) are frequently detected in cyanobacterial bloom-impacted waterbodies and introduced into agroecosystems via irrigation water. They are widely known as phytotoxic cyanotoxins, which impair the growth and physiological functions of crop plants. However, their impact on the plant-associated microbiota is scarcely tackled and poorly understood. Therefore, we aimed to investigate the effect of MCs on microbiota-inhabiting bulk soil (BS), root adhering soil (RAS), and root tissue (RT) of Vicia faba when exposed to 100 μg L-1 MCs in a greenhouse pot experiment. Under MC exposure, the structure, co-occurrence network, and assembly processes of the bacterial microbiota were modulated with the greatest impact on RT-inhabiting bacteria, followed by BS and, to a lesser extent, RAS. The analyses revealed a significant decrease in the abundances of several Actinobacteriota-related taxa within the RT microbiota, including the most abundant and known genus of Streptomyces. Furthermore, MCs significantly increased the abundance of methylotrophic bacteria (Methylobacillus, Methylotenera) and other Proteobacteria-affiliated genera (e.g., Paucibacter), which are supposed to degrade MCs. The co-occurrence network of the bacterial community in the presence of MCs was less complex than the control network. In MC-exposed RT, the turnover in community composition was more strongly driven by deterministic processes, as proven by the beta-nearest taxon index. Whereas in MC-treated BS and RAS, both deterministic and stochastic processes can influence community assembly to some extent, with a relative dominance of deterministic processes. Altogether, these results suggest that MCs may reshape the structure of the microbiota in the soil-plant system by reducing bacterial taxa with potential phytobeneficial traits and increasing other taxa with the potential capacity to degrade MCs.

Biological and Chemical Approaches for Controlling Harmful Microcystis Blooms

The proliferation of harmful cyanobacterial blooms dominated by Microcystis aeruginosa has become an increasingly serious problem in freshwater ecosystems due to climate change and eutrophication. Microcystis-blooms in freshwater generate compounds with unpleasant odors, reduce the levels of dissolved O2, and excrete microcystins into aquatic ecosystems, potentially harming various organisms, including humans. Various chemical and biological approaches have thus been developed to mitigate the impact of the blooms, though issues such as secondary pollution and high economic costs have not been adequately addressed. Red clays and H2O2 are conventional treatment methods that have been employed worldwide for the mitigation of the blooms, while novel approaches, such as the use of plant or microbial metabolites and antagonistic bacteria, have also recently been proposed. Many of these methods rely on the generation of reactive oxygen species, the inhibition of photosynthesis, and/or the disruption of cellular membranes as their mechanisms of action, which may also negatively impact other freshwater microbiota. Nevertheless, the underlying molecular mechanisms of anticyanobacterial chemicals and antagonistic bacteria remain unclear. This review thus discusses both conventional and innovative approaches for the management of M. aeruginosa in freshwater bodies.

Constructed wetland mesocosms improve the biodegradation of microcystin-LR and cylindrospermopsin by indigenous bacterial consortia

Cyanobacterial blooms releasing harmful cyanotoxins, such as microcystin (MC) and cylindrospermopsin (CYN), are prominent threats to human and animal health. Constructed wetlands (CW) may be a nature-based solution for bioremediation of lake surface water containing cyanotoxins, due to its low-cost requirement of infrastructure and environmentally friendly operation. There is recent evidence that microcystin-LR (MC-LR) can efficiently be removed in CW microcosms where CYN degradation in CW is unknown. Likewise, the mechanistic background regarding cyanotoxins transformation in CW is not yet elucidated. In the present study, the objective was to compare MC-LR and CYN degradation efficiencies by two similar microbial communities obtained from CW mesocosms, by two different experiments setup: 1) in vitro batch experiment in serum bottles with an introduced CW community, and 2) degradation in CW mesocosms. In experiment 1) MC-LR and CYN were spiked at 100 µg L-1 and in experiment 2) 200 µg L-1 were spiked. Results showed that MC-LR was degraded to ≤1 µg L-1 within seven days in both experiments. However, with a markedly higher degradation rate constant in the CW mesocosms (0.18 day-1 and 0.75 day-1, respectively). No CYN removal was detected in the in vitro incubations, whereas around 50 % of the spiked CYN was removed in the CW mesocosms. The microbial community responded markedly to the cyanotoxin treatment, with the most prominent increase of bacteria affiliated with Methylophilaceae (order: Methylophilales, phylum: Proteobacteria). The results strongly indicate that CWs can develop an active microbial community capable of efficient removal of MC-LR and CYN. However, the CW operational conditions need to be optimized to achieve a full CYN degradation. To the best of our knowledge, this study is the first to report the ability of CW mesocosms to degrade CYN.

Tracing the fate of microcystins from irrigation water to food chains: Studies with Fragaria vulgaris and Meriones shawi

Microcystins (MCs) are cyanobacterial toxins that can negatively impact human and animal health. This study investigated the bioaccumulation, transfer, depuration, and health risks of MCs in strawberry plants (Fragaria vulgaris) and Meriones shawi animals. The plants were irrigated with 1, 5, 10, and 20 μg/L MCs for 60 days (bioaccumulation phase) and then with clean water for 30 days (depuration phase). The harvested plants (roots and leaves) were then prepared in an aliquot form and used as feed for Meriones shawi. Liquid chromatography-mass spectrometry (LC/MS/MS) was used to measure MC concentrations in plant and animal tissues. The bioaccumulation of MCs was found to be highest in the roots, followed by leaves, fruits, liver, stomach, and fecal matter. The bioaccumulation factor (BAF) was highest in perlite (8.48), followed by roots (5.01), leaves (1.55), stomach (0.87), and fecal matter (1.18), indicating that the parts with high bioaccumulation factor had high translocation of MCs. The transfer of MCs to animal organs was low, and the daily toxin intake of adult consumers of strawberry fruit irrigated with 1, 5, 10, and 20 μg/L MC did not exceed the WHO-recommended limit of 0.04 μg MC-LR/Kg of bw/day. However, fruits from plants irrigated with 10 and 20 μg/L may pose a moderate health risk to children (25 Kg bw), and Meriones' consumption of leaves may pose a significant health risk. After the depuration phase, MC concentration in perlite, roots, leaves, and fruits decreased, indicating that depuration reduced the danger of MC transmission and bioaccumulation. The study also found that glutathione reductase and glutathione S-transferase activity were essential in the depuration of MCs in the tested plants. The findings suggest that legislation regulating the quality of irrigation water in terms of MC concentrations is necessary to prevent detrimental consequences to crops and human exposure.

The volatilome reveals microcystin concentration, microbial composition, and oxidative stress in a critical Oregon freshwater lake

IMPORTANCE

Harmful algal blooms are among the most significant threats to drinking water safety. Blooms dominated by cyanobacteria can produce potentially harmful toxins and, despite intensive research, toxin production remains unpredictable. We measured gaseous molecules in Upper Klamath Lake, Oregon, over 2 years and used them to predict the presence and concentration of the cyanotoxin, microcystin, and microbial community composition. Subsets of gaseous compounds were identified that are associated with microcystin production during oxidative stress, pointing to ecosystem-level interactions leading to microcystin contamination. Our approach shows potential for gaseous molecules to be harnessed in monitoring critical waterways.

Effect of different irrigation methods on the toxicity and bioavailability of microcystin-LR to lettuce and carrot

The use of cyanobacteria-polluted water for irrigation has become an increasing concern due to the potential contamination of microcystins (MCs). However, the effects of MCs on plant performance and food safety under different irrigation methods are not well understood. In this study, we investigated the effects of microcystin-LR (MC-LR) on the growth, food quality, and safety of lettuce and carrot using four irrigation methods (spray irrigation and three types of drip irrigation with different distances from the plant stem). Our results showed that exposure to 10 μg L-1 MC-LR negatively affected plant growth and food quality in treatments with spray irrigation (TS) and drip irrigation directly to the stem (TD0), but not in treatments with drip irrigation away from the plant stem (TD10 and TD20). Using soil as a filtration system, the bioavailability of MC-LR in soil was reduced in TD10 and TD20, resulting in less bioaccumulation in plant edible tissues. The estimated daily intake (EDI) values of TS and TD0 in both lettuce and carrot cultivation exceeded the tolerable daily intake (TDI) limit proposed by WHO, whereas the EDI values of TD10 and TD20 could be effectively reduced below the TDI limit. This study highlights the importance of drip irrigation away from the plant stem as a practical measure to mitigate the effects of cyanobacteria-polluted water in agricultural production.

Beyond cyanotoxins: increased Legionella, antibiotic resistance genes in western Lake Erie water and disinfection-byproducts in their finished water

Background

Western Lake Erie is suffering from harmful cyanobacterial blooms, primarily toxic Microcystis spp., affecting the ecosystem, water safety, and the regional economy. Continued bloom occurrence has raised concerns about public health implications. However, there has been no investigation regarding the potential increase of Legionella and antibiotic resistance genes in source water, and disinfection byproducts in municipal treated drinking water caused by these bloom events.

Methods

Over 2 years, source water (total n = 118) and finished water (total n = 118) samples were collected from drinking water plants situated in western Lake Erie (bloom site) and central Lake Erie (control site). Bloom-related parameters were determined, such as microcystin (MC), toxic Microcystis, total organic carbon, N, and P. Disinfection byproducts (DBPs) [total trihalomethanes (THMs) and haloacetic acids (HAAs)] were assessed in finished water. Genetic markers for Legionella, antibiotic resistance genes, and mobile genetic elements were quantified in source and finished waters.

Results

Significantly higher levels of MC-producing Microcystis were observed in the western Lake Erie site compared to the control site. Analysis of DBPs revealed significantly elevated THMs concentrations at the bloom site, while HAAs concentrations remained similar between the two sites. Legionella spp. levels were significantly higher in the bloom site, showing a significant relationship with total cyanobacteria. Abundance of ARGs (tetQ and sul1) and mobile genetic elements (MGEs) were also significantly higher at the bloom site.

Discussion

Although overall abundance decreased in finished water, relative abundance of ARGs and MGE among total bacteria increased after treatment, particularly at the bloom site. The findings underscore the need for ongoing efforts to mitigate bloom frequency and intensity in the lake. Moreover, optimizing water treatment processes during bloom episodes is crucial to maintain water quality. The associations observed between bloom conditions, ARGs, and Legionella, necessitate future investigations into the potential enhancement of antibiotic-resistant bacteria and Legionella spp. due to blooms, both in lake environments and drinking water distribution systems.

Health risk assessment of lake water contaminated with microcystins for fruit crop irrigation and farm animal drinking

The health risks linked to the consumption of microcystin-accumulating crops have been increasing worldwide in toxic cyanobloom-occurring regions. The bioaccumulation of microcystins (MCs) in agricultural produce at environmentally realistic concentrations is poorly investigated. In this field study, we assessed the health risks of MCs in raw water used for irrigating fruit crops (bioaccumulation) and watering farm animals in the Lalla Takerkoust agricultural region (Marrakesh, Morocco). Thus, MCs were extracted from water and fruit samples and quantified by enzyme-linked immunosorbent assay in order to calculate the health risk indicators. MCs posed a high health-risk level to poultry and horses, with estimated daily intakes (EDI) being 14- and 19-fold higher than the recommended limits (3.1 and 2.3 μg MC-LR L-1), respectively. Furthermore, pomegranate posed the same level of risk, with EDI being 22- and 53-fold higher than the limit dose (0.04 μg MC-LR kg-1) for adults and children, respectively. There was an urgent need for guidelines regarding water use and management in MC-polluted areas, besides the setup of nature-based tools for toxin removal from raw water used in farming practices. Moreover, MCs could contaminate the human food chain, which implies further investigations of their potential accumulation in livestock- and poultry-based food.

Satellite and in situ cyanobacteria monitoring: Understanding the impact of monitoring frequency on management decisions

Cyanobacterial harmful algal blooms (cyanoHABs) in reservoirs can be transported to downstream waters via scheduled discharges. Transport dynamics are difficult to capture in traditional cyanoHAB monitoring, which can be spatially disparate and temporally discontinuous. The introduction of satellite remote sensing for cyanoHAB monitoring provides opportunities to detect where cyanoHABs occur in relation to reservoir release locations, like canal inlets. The study objectives were to assess (1) differences in reservoir cyanoHAB frequencies as determined by in situ and remotely sensed data and (2) the feasibility of using satellite imagery to identify conditions associated with release-driven cyanoHAB export. As a representative case, Lake Okeechobee and the St. Lucie Estuary (Florida, USA), which receives controlled releases from Lake Okeechobee, were examined. Both systems are impacted by cyanoHABs, and the St. Lucie Estuary experienced states of emergency for extreme cyanoHABs in 2016 and 2018. Using the European Space Agency's Sentinel-3 OLCI imagery processed with the Cyanobacteria Index (CI cyano ), cyanoHAB frequencies across Lake Okeechobee from May 2016-April 2021 were compared to frequencies from in situ data. Strong agreement was observed in frequency rankings between the in situ and remotely sensed data in capturing intra-annual variability in bloom frequencies across Lake Okeechobee (Kendall's tau = 0.85, p-value = 0.0002), whereas no alignment was observed when evaluating inter-annual variation (Kendall's tau = 0, p-value = 1). Further, remotely sensed observations revealed that cyanoHABs were highly frequent near the inlet to the canal connecting Lake Okeechobee to the St. Lucie Estuary in state-of-emergency years, a pattern not evident from in situ data alone. This study demonstrates how remote sensing can complement traditional cyanoHAB monitoring to inform reservoir release decision making.

Towards a Better Quantification of Cyanotoxins in Fruits and Vegetables: Validation and Application of an UHPLC-MS/MS-Based Method on Belgian Products

Vegetables and fruits can potentially accumulate cyanotoxins after water contaminated with cyanobacteria is used for irrigation. We developed and validated an analytical method to quantify eight microcystin congeners (MCs) and nodularin (NOD) using ultra high-performance liquid chromatography coupled with tandem mass spectrometry (UHPLC-MS/MS) in three different matrices. Strawberries, carrots and lettuce are selected as model matrices to represent the fruits/berries, leafy and root vegetables, sequentially. The validation of a UHPLC-MS/MS method in the strawberry matrix is novel. Matrix effects are observed in all three matrices. Our methodology uses matrix-matched calibration curves to compensate for the matrix effect. The implementation of our method on 103 samples, containing nine different sorts of fruits and vegetables from the Belgian market, showed no presence of MCs or NOD. However, the recoveries of our quality controls showed the effectiveness of our method, illustrating that the use of this method in future research or monitoring as well as in official food controls in fruit and vegetable matrices is valid.

Accumulation of Microcystin from Oscillatoria limnetica Lemmermann and Microcystis aeruginosa (Kützing) in Two Leafy Green Vegetable Crop Plants Lactuca sativa L. and Eruca sativa

The use of contaminated water to irrigate crop plants poses a risk to human health from the bioaccumulation potential of microcystins (MCs) in the edible tissues of vegetable plants. The main objective of this study is to determine the concentration of total microcystins (MC-LR and MC-RR) in leafy green plants (Lactuca sativa L. var. longifolia and Eruca sativa) that have previously been irrigated with polluted water. Integrated water samples were collected by cleaned plastic bottles at a depth of about 30 cm from one of the sources of water used to irrigate agricultural lands for crop plants. At the same time, samples from plants were also collected because this water from the lake farm is used for the irrigation of surrounding vegetable plants such as Lactuca sativa L. var. longifolia and Eruca sativa. The dominant species of cyanobacteria in water samples are Microcystis aeruginosa (Kützing) and Oscillatoria limnetica Lemmermann, which were detected with an average cell count 2,300,000 and 450,000 cells/mL, respectively. These two dominant species in water produced two MCs variants (MC-LR, -RR) that were quantified by high-performance liquid chromatography (HPLC). Dissolve and particulate MCs were detected in the irrigation waters by HPLC with concentrations of 45.04–600 μg/L. MCs in the water samples exceeded the WHO safety limit (1 μg/L) of MC in drinking water. In addition, the total concentration of Microcystin in Lactuca sativa L. var. longifolia and Eruca sativa were 1044 and 1089 ng/g tissues, respectively. The estimated daily intake (EDI) of microcystins by a person (60 kg) consuming 300 g of fresh plants exceeded the total daily intake guidelines (0.04 μg kg⁻¹ body weight) for human food consumption. According to the findings of this study, irrigation water and plants used for human consumption should be tested for the presence of MCs regularly through critical and regularly monitored programs to prevent the accumulation and transfer of such toxins through the food web.

Microcystin Contamination and Toxicity: Implications for Agriculture and Public Health

Microcystins are natural hepatotoxic metabolites secreted by cyanobacteria in aquatic ecosystems. When present at elevated concentrations, microcystins can affect water quality aesthetics; contaminate drinking water reservoirs and recreational waters; disrupt normal ecosystem functioning; and cause health hazards to animals, plants, and humans. Animal and human exposures to microcystins generally result from ingesting contaminated drinking water or physically contacting tainted water. Much research has identified a multitude of liver problems from oral exposure to microcystins, varying from hepatocellular damage to primary liver cancer. Provisional guidelines for microcystins in drinking and recreational water have been established to prevent toxic exposures and protect public health. With increasing occurrences of eutrophication in freshwater systems, microcystin contamination in groundwater and surface waters is growing, posing threats to aquatic and terrestrial plants and agricultural soils used for crop production. These microcystins are often transferred to crops via irrigation with local sources of water, such as bloom-forming lakes and ponds. Microcystins can survive in high quantities in various parts of plants (roots, stems, and leaves) due to their high chemical stability and low molecular weight, increasing health risks for consumers of agricultural products. Studies have indicated potential health risks associated with contaminated fruits and vegetables sourced from irrigated water containing microcystins. This review considers the exposure risk to humans, plants, and the environment due to the presence of microcystins in local water reservoirs used for drinking and irrigation. Additional studies are needed to understand the specific health impacts associated with the consumption of microcystin-contaminated agricultural plants.

Multi-Soil-Layering Technology: A New Approach to Remove Microcystis aeruginosa and Microcystins from Water

Eutrophication of surface waters caused by toxic cyanobacteria such as Microcystis aeruginosa leads to the release of secondary metabolites called Microcystins (MCs), which are heptapeptides with adverse effects on soil microbiota, plants, animals, and human health. Therefore, to avoid succumbing to the negative effects of these cyanotoxins, various remediation approaches have been considered. These techniques involve expensive physico-chemical processes because of the specialized equipment and facilities required. Thus, implementing eco-technologies capable of handling this problem has become necessary. Indeed, multi-soil-layering (MSL) technology can essentially meet this requirement. This system requires little space, needs simple maintenance, and has energy-free operation and high durability (20 years). The performance of the system is such that it can remove 1.16 to 4.47 log10 units of fecal contamination from the water, 98% of suspended solids (SS), 92% of biological oxygen demand (BOD), 98% of chemical oxygen demand (COD), 92% of total nitrogen (TN), and 100% of total phosphorus (TP). The only reported use of the system to remove cyanotoxins has shown a 99% removal rate of MC-LR. However, the mechanisms involved in removing this toxin from the water are not fully understood. This paper proposes reviewing the principal methods employed in conventional water treatment and other technologies to eliminate MCs from the water. We also describe the principles of operation of MSL systems and compare the performance of this technology with others, highlighting some advantages of this technology in removing MCs. Overall, the combination of multiple processes (physico-chemical and biological) makes MSL technology a good choice of cyanobacterial contamination treatment system that is applicable in real-life conditions, especially in rural areas.

Using soil amendments to reduce microcystin-LR bioaccumulation in lettuce

Contamination of microcystins (MCs) in plant-soil system have become a serious problem worldwide, however, it remains largely unknown how to alleviate the potential risk of consuming MCs-contaminated plants. In the present study, attapulgite, biochar and peat were used as soil amendments to reduce MCs bioaccumulation in lettuce. Lettuce irrigated with 10 μg L-1 microcystin-LR (MC-LR) were growing in two different kinds of soils with or without soil amendments. Results showed that all soil amendments effectively reduced MC-LR bioaccumulation in lettuce roots and leaves. Compared with the control treatment, the MC-LR concentrations in leaves in treatments with attapulgite, biochar and peat decreased by 41.5%, 30.6%, 57.0% in soil A and 38.9%, 43.2%, 54.7% in soil B, respectively. Peat application was most effective in reducing MC-LR bioaccumulation. The decreased soil free MC-LR concentrations were positively correlated with MC-LR concentrations in lettuce, indicating decreased bioavailability of MC-LR by soil amendments. It is noteworthy that soil total MC-LR concentration in peat treatment significantly decreased by 33.3% and 29.4% in soil A and soil B, respectively, compared with the controls. According to the results from high-throughput sequencing, peat amendment increased the α-diversity of soil bacterial community and boosted the abundance of Sphingomonas and Methylobacillus (dozens of MC-degrading bacteria belong to these genera). This was in line with the results of soil total MC-LR concentration. It can be speculated that peat application directly and/or indirectly promoted microbial degradation of MC-LR in soils. This work proposed an effective way to alleviate the potential risks of MCs contamination in plant-soil system.

Co-occurrence of co-contaminants: Cyanotoxins and microplastics, in soil system and their health impacts on plant - A comprehensive review

Cyanotoxins (CTX) and micro/nanoplastics (M/NP) are ubiquitously distributed in every environmental compartment. But the distribution, abundance and associated ecological risks of CTX are still poorly understood in soil system. On the other hand, M/NP could serve as vectors for persistent organic/inorganic pollutants in the natural environment through the sorption of pollutants onto them. Thus, co-occurrence of CTX and M/NP in soils suggests the sorption of CTX onto M/NP. So, major aim of this review is to understand the relevance of CTX and M/NP in soils as co-contaminants, possible interactions between them and ecological risks of CTX in terms of phytotoxicity. In this study, we comprehensively discuss different sources and fate of CTX and the sorption of CTX onto M/NP in soil system, considering the partition coefficient of different phases of soil and mass balance. Phytotoxicity of CTX, CTX mixture and co-contaminants has also been discussed with insights on the mechanism of action. This study indicates the need for the evaluation of sorption between co-contaminants, especially CTX and M/NP, and their phytotoxicity assessment using environmentally relevant concentrations.

Spray irrigation with microcystins-rich water affects plant performance from the microscopic to the functional level and food safety of spinach (Spinacia oleracea L.)

Irrigation water coming from freshwater bodies that suffer toxic cyanobacterial blooms causes adverse effects on crop productivity and quality and raises concerns regarding food contamination and human exposure to toxins. The common agricultural practice of spray irrigation is an important exposure route to cyanotoxins, yet its impact on crops has received little attention. In the present study we attempted an integrated approach at the macro- and microscopic level to investigate whether spray or drip irrigation with microcystins (MCs)-rich water differently affect spinach performance. Growth and functional features, structural characteristics of stomata, and toxin bioaccumulation were determined. Additionally, the impact of irrigation method and water type on the abundance of leaf-attached microorganisms was assessed. Drip irrigation with MCs-rich water had detrimental effects on growth and photosynthetic characteristics of spinach, while spray irrigation ameliorated to various extents the observed impairments. The stomatal characteristics were differently affected by the irrigation method. Drip-irrigated spinach leaves showed significantly lower stomatal density in the abaxial epidermis and smaller stomatal size in the adaxial side compared to spray-irrigation treatment. Nevertheless, the latter deteriorated traits related to fresh produce quality and safety for human consumption; both the abundance of leaf-attached microorganisms and the MCs bioaccumulation in edible tissues well exceeded the corresponding values of drip-irrigated spinach with MC-rich water. The results highlight the significance of both the use of MCs-contaminated water in vegetable production and the irrigation method in shaping plant responses as well as health risk due to human and livestock exposure to MCs.

Role of Rhizospheric Microbiota as a Bioremediation Tool for the Protection of Soil-Plant Systems from Microcystins Phytotoxicity and Mitigating Toxin-Related Health Risk

Frequent toxic cyanoblooms in eutrophic freshwaters produce various cyanotoxins such as the monocyclic heptapeptides microcystins (MCs), known as deleterious compounds to plant growth and human health. Recently, MCs are a recurrent worldwide sanitary problem in irrigation waters and farmland soils due to their transfer and accumulation in the edible tissues of vegetable produce. In such cases, studies about the persistence and removal of MCs in soil are scarce and not fully investigated. In this study, we carried out a greenhouse trial on two crop species: faba bean (Vicia faba var. Alfia 321) and common wheat (Triticum aestivum var. Achtar) that were grown in sterile (microorganism-free soil) and non-sterile (microorganism-rich soil) soils and subjected to MC-induced stress at 100 µg equivalent MC-LR L⁻¹. The experimentation aimed to assess the prominent role of native rhizospheric microbiota in mitigating the phytotoxic impact of MCs on plant growth and reducing their accumulation in both soils and plant tissues. Moreover, we attempted to evaluate the health risk related to the consumption of MC-polluted plants for humans and cattle by determining the estimated daily intake (EDI) and health risk quotient (RQ) of MCs in these plants. Biodegradation was liable to be the main removal pathway of the toxin in the soil; and therefore, bulk soil (unplanted soil), as well as rhizospheric soil (planted soil), were used in this experiment to evaluate the accumulation of MCs in the presence and absence of microorganisms (sterile and non-sterile soils). The data obtained in this study showed that MCs had no significant effects on growth indicators of faba bean and common wheat plants in non-sterile soil as compared to the control group. In contrast, plants grown in sterile soil showed a significant decrease in growth parameters as compared to the control. These results suggest that MCs were highly bioavailable to the plants, resulting in severe growth impairments in the absence of native rhizospheric microbiota. Likewise, MCs were more accumulated in sterile soil and more bioconcentrated in root and shoot tissues of plants grown within when compared to non-sterile soil. Thereby, the EDI of MCs in plants grown in sterile soil was more beyond the tolerable daily intake recommended for both humans and cattle. The risk level was more pronounced in plants from the sterile soil than those from the non-sterile one. These findings suggest that microbial activity, eventually MC-biodegradation, is a crucial bioremediation tool to remove and prevent MCs from entering the agricultural food chain.

Histological and chemical damage induced by microcystin-LR and microcystin-RR on land snail Helix aspersa tissues after acute exposure

Microcystins (MCs) are the most common cyanotoxins with more than 200 variants. Among these cyanotoxins, microcystin-LR (MC-LR) and microcystin-RR (MC-RR) are the most studied congeners due to their high toxicity and frequent occurrence in surface waters. MC-LR has been detected in more than 75% of natural cyanobacteria bloom, along with other toxic and less toxic congeners. Accumulation of several microcystins variants (MC-LR and MC-RR) has been confirmed in aquatic snails exposed naturally or in the laboratory to toxic blooms. Thus, this paper aims to compare the biochemical and histological impact of both toxic variants (microcystin-LR and microcystin-RR) and their mixed form on a bioindicator, the land snail Helix aspersa. During experiments, snails were gavaged with a single acute dose (0.5 μg/g) of purified MC-LR, MC-RR, or mixed MC-LR + MC-RR (0.25 + 0.25 μg/g). After 96 h of exposure, effects on the hepatopancreas, kidney, intestine and lungs were assessed by histological observations and analysis of oxidative stress biomarkers. The results show that a small dose of MCs variants can increase the non-enzymatic antioxidant glutathione (GSH), inhibit glutathione-s-transferase (GST) level and trigger a defense system by activating glutathione peroxidase (GPx), catalase (CAT) and superoxide dismutase (SOD). Microcystin-RR causes serious anomalies in the hepatopancreas and kidney than Microcystin-LR. The organ most affected is the kidney. The damage caused by MC-LR + MC-RR is greater than that caused by single variants.

Mechanisms of parental co-exposure to polystyrene nanoplastics and microcystin-LR aggravated hatching inhibition of zebrafish offspring

The combined toxicity effects of microcystins-LR (MCLR) and polystyrene nanoplastics (PSNPs) on the hatching of F1 zebrafish (Danio rerio) embryos were investigated in this study due to the increasing concerns of both plastic pollution and eutrophication in aquatic environments. Three-month-old zebrafish were used to explore the molecular mechanisms underlying the combined effect of MCLR (0, 0.9, 4.5, and 22.5 μg/L) on egg hatching in the existence of PSNPs (100 μg/L). The results demonstrated the existence of PSNPs further increased the accumulation of MCLR in F1 embryos. The hatching rates of F1 embryos were inhibited after exposure to 22.5 μg/L MCLR, and the presence of PSNPs aggravated the hatching inhibition induced by MCLR. The decrease of hatching enzyme activity and the abnormality of spontaneous movement were observed. We examined the altered expression levels of the genes associated with the hatching enzyme (tox16, foxp1, ctslb, xpb1, klf4, cap1, bmp4, cd63, He1.2, zhe1, and prl), cholinergic system (ache and chrnα7), and muscle development (Wnt, MyoD, Myf5, Myogenin, and MRF4). The results suggested the existence of PSNPs exacerbated the hatching inhibition of F1 embryos through decreasing the activity of enzyme, interfering with the cholinergic system, and affecting the muscle development.

Algal Toxic Compounds and Their Aeroterrestrial, Airborne and other Extremophilic Producers with Attention to Soil and Plant Contamination: A Review

The review summarizes the available knowledge on toxins and their producers from rather disparate algal assemblages of aeroterrestrial, airborne and other versatile extreme environments (hot springs, deserts, ice, snow, caves, etc.) and on phycotoxins as contaminants of emergent concern in soil and plants. There is a growing body of evidence that algal toxins and their producers occur in all general types of extreme habitats, and cyanobacteria/cyanoprokaryotes dominate in most of them. Altogether, 55 toxigenic algal genera (47 cyanoprokaryotes) were enlisted, and our analysis showed that besides the “standard” toxins, routinely known from different waterbodies (microcystins, nodularins, anatoxins, saxitoxins, cylindrospermopsins, BMAA, etc.), they can produce some specific toxic compounds. Whether the toxic biomolecules are related with the harsh conditions on which algae have to thrive and what is their functional role may be answered by future studies. Therefore, we outline the gaps in knowledge and provide ideas for further research, considering, from one side, the health risk from phycotoxins on the background of the global warming and eutrophication and, from the other side, the current surge of interest which phycotoxins provoke due to their potential as novel compounds in medicine, pharmacy, cosmetics, bioremediation, agriculture and all aspects of biotechnological implications in human life.

Colonization of toxic cyanobacteria on the surface and inside of leafy green: A hidden source of cyanotoxin production and exposure

Cyanobacteria are a threat to the safety of water sources for drinking, recreation, and food production, because some cyanobacteria, such as Microcystis, produce cyanotoxins. However, the colonization of plants by Microcystis and the fate of their toxin, microcystins (MCs), in agricultural environments have not been thoroughly studied. This study examined the colonization of lettuce, as a representative of leafy greens, by Microcystis and its potential impact on food safety and crop health. The surfaces of lettuce leaves were exposed to environmentally relevant concentrations of M. aeruginosa (104, 106, and 108mcyE gene copies/mL) by mimicking contamination scenarios during cultivation, such as spraying irrigation with contaminated water or deposits of airborne Microcystis. Scanning electron microscope (SEM) and droplet digital PCR were used. The results showed that M. aeruginosa colonized the surface of leaves and MCs accumulated in the edible part of the lettuce (>20 μg/kg of lettuce). Crop productivity (length, weight, and number of leaves) was negatively affected. The SEM images provide evidence that M. aeruginosa deposited on the lettuce surface can be internalized via natural opening sites of the leaves and then proliferate within the plants. Our findings imply that toxic cyanobacteria contamination in agricultural environments can be a significant cyanotoxin exposure pathway.

Impacts of Microcystins on Morphological and Physiological Parameters of Agricultural Plants: A Review

Cyanobacteria are a group of photosynthetic prokaryotes that pose a great concern in the aquatic environments related to contamination and poisoning of wild life and humans. Some species of cyanobacteria produce potent toxins such as microcystins (MCs), which are extremely aggressive to several organisms, including animals and humans. In order to protect human health and prevent human exposure to this type of organisms and toxins, regulatory limits for MCs in drinking water have been established in most countries. In this regard, the World Health Organization (WHO) proposed 1 µg MCs/L as the highest acceptable concentration in drinking water. However, regulatory limits were not defined in waters used in other applications/activities, constituting a potential threat to the environment and to human health. Indeed, water contaminated with MCs or other cyanotoxins is recurrently used in agriculture and for crop and food production. Several deleterious effects of MCs including a decrease in growth, tissue necrosis, inhibition of photosynthesis and metabolic changes have been reported in plants leading to the impairment of crop productivity and economic loss. Studies have also revealed significant accumulation of MCs in edible tissues and plant organs, which raise concerns related to food safety. This work aims to systematize and analyze the information generated by previous scientific studies, namely on the phytotoxicity and the impact of MCs especially on growth, photosynthesis and productivity of agricultural plants. Morphological and physiological parameters of agronomic interest are overviewed in detail in this work, with the aim to evaluate the putative impact of MCs under field conditions. Finally, concentration-dependent effects are highlighted, as these can assist in future guidelines for irrigation waters and establish regulatory limits for MCs.

Protective Role of Native Rhizospheric Soil Microbiota Against the Exposure to Microcystins Introduced into Soil-Plant System via Contaminated Irrigation Water and Health Risk Assessment

Microcystins (MCs) produced in eutrophic waters may decrease crop yield, enter food chains and threaten human and animal health. The main objective of this research was to highlight the role of rhizospheric soil microbiota to protect faba bean plants from MCs toxicity after chronic exposure. Faba bean seedlings were grown in pots containing agricultural soil, during 1 month under natural environmental conditions of Marrakech city in Morocco (March–April 2018) and exposed to cyanobacterial extracts containing up to 2.5 mg·L⁻¹ of total MCs. Three independent exposure experiments were performed (a) agricultural soil was maintained intact “exposure experiment 1”; (b) agricultural soil was sterilized “exposure experiment 2”; (c) agricultural soil was sterilized and inoculated with the rhizobia strain Rhizobium leguminosarum RhOF34 “exposure experiment 3”. Overall, data showed evidence of an increased sensitivity of faba bean plants, grown in sterilized soil, to MCs in comparison to those grown in intact and inoculated soils. The study revealed the growth inhibition of plant shoots in both exposure experiments 2 and 3 when treated with 2.5 mg·L⁻¹ of MCs. The results also showed that the estimated daily intake (EDI) of MCs, in sterilized soil, exceeded 2.18 and 1.16 times the reference concentrations (0.04 and 0.45 µg of microcysin-leucine arginine (MC-LR). Kg⁻¹ DW) established for humans and cattle respectively, which raises concerns about human food chain contamination.

Microcystis toxin-mediated tumor promotion and toxicity lead to shifts in mouse gut microbiome

Microcystins (MCs) are the most prevalent cyanotoxins reported in freshwater. While numerous studies have examined the toxicological impacts of MCs on mammalian systems, very few have examined the chronic impacts of MCs on the gut microbiome of exposed organisms. Our understanding of the relationship of MCs, especially lysed toxic cyanobacteria, and the gut microbiota is very limited. The objective of this study was to determine the impacts of MC-LR and Microcystis lysate ingestion on the gut microbiome in a hepatocellular carcinoma mouse model, simulating a high-risk population and exposure at an environmentally relevant MC level. Mice were assigned to 4 groups (MC-LR; Microcystis lysate; Negative control; Positive (liver carcinogen) control). Fecal samples were collected every 8 weeks. Bacterial community and colony counts were analyzed. The abundance of Firmicutes in the positive control and lysate group was higher than the negative control and MC group. Exposure to MC-LR or lysate was associated with significantly decreased bacterial diversity. A distinct separation of the three groups (MC-LR/lysate/carcinogen) from the negative was much more apparent in their gut microbiome as the exposure time increased. The MC-LR and lysate groups showed gut microbiome structure responding to lipid metabolism disturbance and high stress. Bacterial colony count was significantly lower in all the treated groups than the negative control. Our study highlights that chronic exposure to MC-LR and Microcystis lysate negatively impacts gut microbiome succession and altered the bacterial community structure into the one similar to the carcinogen group, which may indicate that the change favors progression of hepatocellular carcinoma. In a future study, more in-depth investigation is warranted to better understand the liver-gut nexus in promoting liver cancer among those exposed to MC and toxic cyanobacteria.

Irrigation of radish (Raphanus sativus L.) with microcystin-enriched water holds low risk for plants and their associated rhizopheric and epiphytic microbiome

Microcystins (MCs) are toxins produced during cyanobacterial blooms. They reach soil and translocated to plants through irrigation of agricultural land with water from MC-impacted freshwater systems. To date we have good understanding of MC effects on plants, but not for their effects on plant-associated microbiota. We tested the hypothesis that MC-LR, either alone or with other stressors present in the water of the Karla reservoir (a low ecological quality and MC-impacted freshwater system), would affect radish plants and their rhizospheric and phyllospheric microbiome. In this context a pot experiment was employed where radish plants were irrigated with tap water without MC-LR (control) or with 2 or 12 μg L^-1 of pure MC-LR (MC2 and MC12), or water from the Karla reservoir amended (12 μg L^-1) or not with MC-LR. We measured MC levels in plants and rhizospheric soil and we determined effects on (i) plant growth and physiology (ii) the nitrifying microorganisms via q-PCR, (ii) the diversity of bacterial and fungal rhizospheric and epiphytic communities via amplicon sequencing. MC-LR and/or Karla water treatments resulted in the accumulation of MC in taproot at levels (480-700 ng g^-1) entailing possible health risks. MC did not affect plant growth or physiology and it did not impose a consistent inhibitory effect on soil nitrifiers. Karla water rather than MC-LR was the stronger determinant of the rhizospheric and epiphytic microbial communities, suggesting the presence of biotic or abiotic stressors, other than MC-LR, in the water of the Karla reservoir which affect microorganisms with a potential role (i.e. pathogens inhibition, methylotrophy) in the homeostasis of the plant-soil system. Overall, our findings suggest that MC-LR, when applied at environmentally relevant concentrations, is not expected to adversely affect the radish-microbiota system but might still pose risk for consumers' health.

Cyanotoxin impact on microbial-mediated nitrogen transformations at the interface of sediment-water column in surface water bodies

Harmful cyanobacterial blooms produce lethal toxins in many aquatic ecosystems experiencing eutrophication. This manuscript presents results on the effects of cyanotoxins on the aerobic microbial communities residing at the interface of sediments and water columns with the ammonia-oxidizing bacteria (AOB) as the model microbial community. Microcystin-LR (MC-LR), a heavily researched cyanotoxin variant, was used as the model cyanotoxin. To measure cyanotoxin influence on the activity of nitrifying microbial communities, an enriched culture of AOBs collected from an ongoing partial nitrification-nitritation reactor was examined for its exposure to 1, 5 and 10 μg/L of MC-LR. The nitritation kinetics experiment demonstrated MC-LR's ability at 1, 5, and 10 μg/L concentrations to prevent ammonium oxidation with statistically significant differences in nitritation rates between the blanks and spiked samples (One-way ANOVA, p < 0.05). Significantly decreased dissolved oxygen (DO) consumption during oxygen update batch tests demonstrated toxin's influence on AOB's oxidizing capabilities when exposed to even lower concentrations of 0.75, 0.5, and 0.25 μg/L of MC-LR in a separate set of experiments. Based on competitive kinetics, the MC-LR inhibition coefficient-the concentration needed to produce half-maximum inhibition of the mixed community AOBs was determined to be 0.083 μg/L. The stress tests proved the recovery of nitritation to some extent at lower MC-LR concentrations (1 and 5 μg/L), but significant irreversible inhibition was recorded when the AOB population was exposed to 10 μg/L MC-LR. The comparisons of amoA gene expressions corresponded well with nitrifying kinetics. All concentrations of MC-LR spiking were determined to produce a discernible impact on the AOB nitritation rate by either destroying the bacterial cell or immediately inhibiting the amoA gene expression.

Intraseasonal variation of phycocyanin concentrations and environmental covariates in two agricultural irrigation ponds in Maryland, USA

Recently, cyanobacteria blooms have become a concern for agricultural irrigation water quality. Numerous studies have shown that cyanotoxins from these harmful algal blooms (HABs) can be transported to and assimilated into crops when present in irrigation waters. Phycocyanin is a pigment known only to occur in cyanobacteria and is often used to indicate cyanobacteria presence in waters. The objective of this work was to identify the most influential environmental covariates affecting the phycocyanin concentrations in agricultural irrigation ponds that experience cyanobacteria blooms of the potentially toxigenic species Microcystis and Aphanizomenon using machine learning methodology. The study was performed at two agricultural irrigation ponds over a 5-month period in the summer of 2018. Phycocyanin concentrations, along with sensor-based and fluorometer-based water quality parameters including turbidity (NTU), pH, dissolved oxygen (DO), fluorescent dissolved organic matter (fDOM), conductivity, chlorophyll, color dissolved organic matter (CDOM), and extracted chlorophyll were measured. Regression tree analyses were used to determine the most influential water quality parameters on phycocyanin concentrations. Nearshore sampling locations had higher phycocyanin concentrations than interior sampling locations and "zones" of consistently higher concentrations of phycocyanin were found in both ponds. The regression tree analyses indicated extracted chlorophyll, CDOM, and NTU were the three most influential parameters on phycocyanin concentrations. This study indicates that sensor-based and fluorometer-based water quality parameters could be useful to identify spatial patterns of phycocyanin concentrations and therefore, cyanobacteria blooms, in agricultural irrigation ponds and potentially other water bodies.

Vitamin C Protects Porcine Oocytes From Microcystin-LR Toxicity During Maturation

Microcystin-leucine arginine (MC-LR) is the most toxic cyanotoxin found in water bodies. Microcystins are produced as secondary products of cyanobacteria metabolism. They have a stable structure, and can bioaccumulate in living organisms. Humans and livestock who drink fresh water containing MC-LR can be poisoned. However, few studies have reported the effects of MC-LR exposure on livestock or human reproduction. In this study, we used porcine oocytes as a model to explore the effects of MC-LR on oocyte maturation, and studied the impact of vitamin C (VC) administration on MC-LR-induced meiosis defects. Exposure to MC-LR significantly restricted cumulus cell expansion and decreased first polar body extrusion. Further studies showed that MC-LR exposure led to meiosis arrest by disturbing cytoskeleton dynamics with MC-LR exposed oocytes displaying aberrant spindle organization, low levels of acetylate α-tubulin, and disturbed actin polymerization. Additionally, MC-LR exposure impaired cytoplasmic maturation by inducing mitochondria dysfunction. Moreover, MC-LR also produced abnormal epigenetic modifications, and induced high levels of oxidative stress, caused DNA damage and early apoptosis. The administration of VC provided partial protection from all of the defects observed in oocytes exposed to MC-LR. These results demonstrate that MC-LR has a toxic effect on oocyte meiosis through mitochondrial dysfunction-induced ROS, DNA damage and early apoptosis. Supplementation of VC is able to protect against MC-LR-induced oocyte damage and represents a potential therapeutic strategy to improve the quality of MC-LR-exposed oocytes.

Quantifying the Human Health Benefits of Using Satellite Information to Detect Cyanobacterial Harmful Algal Blooms and Manage Recreational Advisories in U.S. Lakes

Significant recent advances in satellite remote sensing allow environmental managers to detect and monitor cyanobacterial harmful algal blooms (cyanoHAB), and these capabilities are being used more frequently in water quality management. A quantitative estimate of the socioeconomic benefits generated from these new capabilities, known as an impact assessment, was missing from the growing literature on cyanoHABs and remote sensing. In this paper, we present an impact assessment framework to characterize the socioeconomic benefits of satellite remote sensing for detecting cyanoHABs and managing recreational advisories at freshwater lakes. We then apply this framework to estimate the socioeconomic benefits of satellite data that were used to manage a 2017 cyanoHAB event in Utah Lake. CyanoHAB events on Utah Lake can pose health risks to people who interact with the blooms through recreation. We find that the availability of satellite data yielded socioeconomic benefits by improving human health outcomes valued at approximately $370,000, though a sensitivity analysis reveals that this central estimate can vary significantly ($55,000-$1,057,000 in benefits) as a result of different assumptions regarding the time delay in posting a recreational advisory, the number of people exposed to the cyanoHAB, the number of people who experience gastrointestinal symptoms, and the cost per case of illness.

Bioaccumulation and Phytotoxicity and Human Health Risk from Microcystin-LR under Various Treatments: A Pot Study

Microcystin-LR (MC-LR) is prevalent in water and can be translocated into soil-crop ecosystem via irrigation, overflow (pollution accident), and cyanobacterial manure applications, threatening agricultural production and human health. However, the effects of various input pathways on the bioaccumulation and toxicity of MCs in terrestrial plants have been hardly reported so far. In the present study, pot experiments were performed to compare the bioaccumulation, toxicity, and health risk of MC-LR as well as its degradation in soils among various treatments with the same total amount of added MC-LR (150 μg/kg). The treatments included irrigation with polluted water (IPW), cultivation with polluted soil (CPS), and application of cyanobacterial manure (ACM). Three common leaf-vegetables in southern China were used in the pot experiments, including Ipomoea batatas L., Brassica juncea L., and Brassica alboglabra L. All leaf vegetables could bioaccumulate MC-LR under the three treatments, with much higher MC-LR bioaccumulation, especially root bioconcentration observed in ACM treatment than IPW and CPS treatments. An opposite trend in MC-LR degradation in soils of these treatments indicated that ACM could limit MC-LR degradation in soils and thus promote its bioaccumulation in the vegetables. MC-LR bioaccumulation could cause toxicity to the vegetables, with the highest toxic effects observed in ACM treatment. Similarly, bioaccumulation of MC-LR in the edible parts of the leaf-vegetables posed 1.1~4.8 fold higher human health risks in ACM treatment than in IPW and CPS treatments. The findings of this study highlighted a great concern on applications of cyanobacterial manure.

Role of microRNA-122 in microcystin-leucine arginine-induced dysregulation of hepatic iron homeostasis in mice

Microcystin-leucine arginine (MC-LR) is a cyclic heptapeptide hepatotoxin produced by cyanobacteria. MicroRNA-122 (miR-122) is specifically expressed in the liver. This study focuses on the role of miR-122 in MC-LR-induced dysregulation of hepatic iron homeostasis in C57BL/6 mice. The thirty mice were randomly divided into five groups (Control, 12.5 μg/kg·BW MC-LR, 25 μg/kg·BW MC-LR, Negative control agomir and 25 μg/kg·BW MC-LR + miR-122 agomir). The results show that MC-LR decreases the expressions of miR-122, Hamp, and its related regulators, while increasing the content of hepatic iron and the expressions of FPN1 and Tmprss6. Furthermore, miR-122 agomir pretreatment improves MC-LR induced dysregulation of hepatic iron homeostasis by arousing the related regulators and reducing the expression of Tmprss6. These results suggest that miR-122 agomir can prevent the accumulation of hepatic iron induced by MC-LR, which may be related to the regulation of hepcidin by BMP/SMAD and IL-6/STAT signaling pathways.

Drinking water treatment residuals from cyanobacteria bloom-affected areas: Investigation of potential impact on agricultural land application

In cyanobacteria bloom-affected areas, drinking water treatment processes are optimized to ensure the absence of cyanotoxins in their finished water. A concern about the sludge generated from water treatment has emerged because the removed cyanotoxins and cyanobacteria can get concentrated in the sludge, called water treatment residuals (WTR), and these WTR are often applied on land for beneficial purposes. However, the impact of WTR from bloom-affected areas on the agricultural application and public health is hardly reported. The objective of this study was to characterize bloom-affected WTR by focusing on cyanotoxins, toxin-producing cyanobacteria, microbiomes, and resistome profiles. In addition, the fate of WTR-originated microcystin in crops and soil was examined. WTR samples were obtained from a bloom-affected area in Ohio, USA in November 2017. Cyanotoxins and toxin-producing cyanobacteria were quantified with the enzyme-linked immunosorbent assay and droplet digital PCR, respectively. Microbiome and resistome were determined with Nanopore sequencing. Cyanotoxin concentrations were measured: microcystin (259 μg/kg), saxitoxin (0.16 μg/kg), anatoxin-a (not detected), and β-Methylamino-L-alanine (BMAA) (575 μg/kg). MC-producing cyanobacteria concentrations were determined: Planktothrix (5.3 × 10⁷ gene copies/g) and Microcystis (3.3 × 10³ gene copies/g). Proteobacteria was the most predominant and Planktothrix phage was a remarkably dominant virus in the WTR microbiome. Aminoglycoside resistance was the most abundant class, and antibiotic resistance was found in multiple pathogens (e.g. Mycobacterium). WTR land application was simulated by growing carrots with a mixture of WTR and soil in a greenhouse. At harvest, ~80% of WTR-originated microcystin was found in the soil (83-96 μg/kg) and 5% accumulated in carrots (19-28 μg/kg). This study provides the first insight into the cyanotoxin, microbiome, and resistome profile of bloom-affected WTR. Our finding suggests that careful WTR management is needed for the beneficial use of WTR for protecting agricultural environments, especially soil and groundwater, and food safety.

High ecological and human health risks from microcystins in vegetable fields in southern China

Frequent cyanobacterial blooms in the eutrophic waters produce a variety of toxins such as the monocyclic heptapeptide microcystins, greatly harming aquatic ecosystems and human health. However, little information of microcystins in agricultural fields is known. This field study of three common microcystin variants (MC-LR, MC-RR, and MC-YR) in vegetables (n = 161), soils (n = 161) and irrigation water samples (n = 23) collected from southern China regions affected by cyanobacteria blooms, shows their prevalence with total concentrations up to 514 μg/L water, 187 μg/kg soil (dry weight) and 382 μg/kg vegetable (fresh weight). MC-RR was the primary variant in all types of samples, accounting for 51.3-100% of total microcystin concentrations. Significant concentration-dependent correlations (p < 0.05) demonstrated that microcystin-contained irrigation waters were the major source of microcystin accumulation in both vegetables and soils. Meanwhile, intracellular-microcystins in irrigation water was found to play an important role in microcystins bioaccumulation in vegetables for the first time. Most vegetable samples (≥60%), particularly celery posed moderate or high human health risk via diet based on toxicity equivalents of the microcystins and reference dose for MC-LR (0.04 μg/kg/d), showing high food safety hidden dangers. Soil microcystins, especially MC-RR in 46.4-88.3% of soils could pose high ecological risks. This study highlights the potential high ecological and human health risks of microcystins in the real soil-vegetable systems of areas affected by cyanobacteria blooms, implying the profound significance and urgent need of investigation on microcystins in terrestrial ecosystems.

Proteomic analysis of the hepatotoxicity of Microcystis aeruginosa in adult zebrafish (Danio rerio) and its potential mechanisms

Microcystis aeruginosa is one of the main species of cyanobacteria that causes water blooms. M. aeruginosa can release into the water several types of microcystins (MCs), which are harmful to aquatic organisms and even humans. However, few studies have investigated the hepatotoxicity of M. aeruginosa itself in zebrafish in environments that simulate natural aquatic systems. The objective of this study was to evaluate the hepatotoxicity of M. aeruginosa in adult zebrafish (Danio rerio) after short-term (96 h) exposure and to elucidate the potential underlying mechanisms. Distinct histological changes in the liver, such as enlargement of the peripheral nuclei and sinusoids and the appearance of fibroblasts, were observed in zebrafish grown in M. aeruginosa culture. In addition, antioxidant enzyme activity was activated and protein phosphatase (PP) activity was significantly decreased with increasing microalgal density. A proteomic analysis revealed alterations in a number of protein pathways, including ribosome translation, immune response, energy metabolism and oxidative phosphorylation pathways. Western blot and real-time PCR analyses confirmed the results of the proteomic analysis. All results indicated that M. aeruginosa could disrupt hepatic functions in adult zebrafish, thus highlighting the necessity of ecotoxicity assessments for M. aeruginosa at environmentally relevant densities.

Analysis of the Use of Cylindrospermopsin and/or Microcystin-Contaminated Water in the Growth, Mineral Content, and Contamination of Spinacia oleracea and Lactuca sativa

Cyanobacteria and cyanotoxins constitute a serious environmental and human health problem. Moreover, concerns are raised with the use of contaminated water in agriculture and vegetable production as this can lead to food contamination and human exposure to toxins as well as impairment in crop development and productivity. The objective of this work was to assess the susceptibility of two green vegetables, spinach and lettuce, to the cyanotoxins microcystin (MC) and cylindrospermopsin (CYN), individually and in mixture. The study consisted of growing both vegetables in hydroponics, under controlled conditions, for 21 days in nutrient medium doped with MC or CYN at 10 μg/L and 50 μg/L, or CYN/MC mixture at 5 + 5 μg/L and 25 + 25 μg/L. Extracts from M. aeruginosa and C. ovalisporum were used as sources of toxins. The study revealed growth inhibition of the aerial part (Leaves) in both species when treated with 50µg/L of MC, CYN and CYN/MC mixture. MC showed to be more harmful to plant growth than CYN. Moreover spinach leaves growth was inhibited by both 5 + 5 and 25 + 25 µg/L CYN/MC mixtures, whereas lettuce leaves growth was inhibited only by 25 + 25 µg/L CYN/MC mixture. Overall, growth data evidence increased sensitivity of spinach to cyanotoxins in comparison to lettuce. On the other hand, plants exposed to CYN/MC mixture showed differential accumulation of CYN and MC. In addition, CYN, but not MC, was translocated from the roots to the leaves. CYN and MC affected the levels of minerals particularly in plant roots. The elements most affected were Ca, K and Mg. However, in leaves K was the mineral that was affected by exposure to cyanotoxins.

Glutathione biosynthesis plays an important role in microcystin-LR depuration in lettuce and spinach

Irrigation of crop plants with microcystins (MCs) contaminated water could be a threat to human health via bioaccumulation. Despite the fact MCs bioaccumulation in crop plants is well documented, MCs depuration, as well as the mechanism involved remains unclear. The objectives of the present study were to investigate the bioaccumulation and depuration of microcystin-LR (MC-LR) in lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.), as well as to explore the role of glutathione (GSH) biosynthesis in MC-LR depuration. The tested plants were irrigated with deionized water containing 10 μg L-1 MC-LR for 12 days (bioaccumulation), and subsequently, with either deionized water only or deionized water containing 0.5 mM buthionine sulfoximine (BSO, a specific inhibitor of GSH biosynthesis) for 12 days (depuration). After bioaccumulation period, highest concentrations of MC-LR found in lettuce and spinach were 114.4 and 138.5 μg kg-1 dry weight (DW) respectively. Depuration rates of MC-LR in lettuce and spinach were 9.5 and 8.1 μg kg-1 DW d-1, which deceased to 3.7 and 4.6 μg kg-1 DW d-1 in treatments with BSO application. GSH content in both lettuce and spinach were not significantly affected during depuration without BSO; whereas after treatment with BSO, GSH content significantly decreased by 36.0% and 24.7% in lettuce and spinach on 15 d, and the decrease remained on 18 d and 21 d in lettuce. Moreover, during the bioaccumulation period, activities of glutathione reductase (GR) and glutathione S-transferase (GST) were enhanced in both plants. Our results suggested that GSH biosynthesis played an important role in MC-LR depuration in the tested plants. Concerning human health risk, most of the estimated daily intake (EDI) values during the bioaccumulation period exceeded the tolerable daily intake (TDI) guideline. However, the risk could be alleviated by irrigating with MCs-free water for a certain amount of time before harvest.

Economic impact of harmful algal blooms on human health: a systematic review

Harmful algal blooms (HABs) damage human activities and health. While there is wide literature on economic losses, little is known about the economic impact on human health. In this review, we systematically retrieved papers which presented health costs following exposure to HABs. A systematic review was conducted up to January 2019 in databases such as ScienceDirect and PubMed, and 16 studies were selected. Health costs included healthcare and medication expenses, loss of income due to illness, cost of pain and suffering, and cost of death. Two categories of illness (digestive and respiratory) were considered for health costs. For digestive illness cost, we found $86, $1,015 and $12,605, respectively, for mild, moderate and severe cases. For respiratory illness, costs were $86, $1,235 and $14,600, respectively, for mild, moderate and severe cases. We used Quality-Adjusted Life Years (QALYs) to access the loss of well-being due to illness caused by HABs. We found that breathing difficulty causes the most loss of QALYs, especially in children, with a loss of between 0.16 and 0.771 per child. Having gastroenteritis could cause a loss of between 2.2 and 7.1 QALYs per 1,000 children. Misleading symptoms of illness following exposure to HABs could cause bias in health costs estimations.

Mode of action and fate of microcystins in the complex soil-plant ecosystems

Over the last decades, global warming has increasingly stimulated the expansion of cyanobacterial blooms in freshwater ecosystems worldwide, in which toxic cyanobacteria produce various congeners of cyanotoxins, mainly dominated by microcystins (MCs). MCs introduced into agricultural soils have deleterious effects on the germination, growth and development of plants and their associated microbiota, leading to remarkable yield losses. Phytotoxicity of MCs may refer to the inhibition of phosphatases activity, generating deleterious reactive oxygen species, altering gene functioning and phytohormones translocation within the plant. It is also known that MCs can pass through the root membrane barrier, translocate within plant tissues and accumulate into different organs, including edible ones. Also, MCs impact the microbial activity in soil via altering plant-bacterial symbioses and decreasing bacterial growth rate of rhizospheric microbiota. Moreover, MCs can persist in agricultural soils through adsorption to clay-humic acid particles and results in a long-term contact with the plant-microflora complex. However, their bioavailability to plants and half-life in soil seem to be influenced by biodegradation process and soil physicochemical properties. This review reports the latest and most relevant information regarding MCs-phytotoxicity and impact on soil microbiota, the persistence in soil, the degradation by native microflora and the bioaccumulation within plant tissues.

An algicidal Streptomyces amritsarensis strain against Microcystis aeruginosa strongly inhibits microcystin synthesis simultaneously

Microcystis aeruginosa and hepatotoxic microcystins produced by it have posed a severe threat to aquatic ecological security and human health. In this study a Streptomyces amritsarensis HG-16, showing high algicidal activity against M. aeruginosa and strong inhibitory effect on microcystin synthesis, was obtained by screening some anti-Fusarium sp. microbial strains isolated before in our laboratory. HG-16 bound cyanobacterial cells by mycelia to form flocs and killed M. aeruginosa by secreting active substances, which were proteinase K resistant and stable in the temperature range of 35-75 °C and pH range of 3-11. HG-16 removed M. aeruginosa of 10⁵ and 10⁶ cell mL^-1 cell densities in similar rate and was active against all the tested harmful unicellular and filamentous cyanobacteria. Results of differential gene expression analysis indicated that HG-16 affected the photosynthesis system and microcystin synthesis of M. aeruginosa. Accordingly, the algicidal activity of HG-16 was light-dependent, and microcystin synthesis of M. aeruginosa decreased by 91.2% with HG-16 treatment. Thus, it is promising to utilize HG-16 to mitigate harmful cyanobacterial blooms, inhibit microcystin synthesis and control plant disease caused by Fusarium.spp. through irrigating farmland with eutrophic water applied HG-16.

MC-LR induces dysregulation of iron homeostasis by inhibiting hepcidin expression: A preliminary study

The liver is an important iron storage site and a primary MC-LR target. C57BL/6 and Hfe^-/- mice were used to investigate effects and mechanisms of MC-LR on systematic iron homeostasis. Body weight, tissue iron content, hematological and serological indexes, and histopathological were evaluated. Ultrastructure and iron metabolism-related genes and proteins were analyzed. MC-LR induced dose-dependent increases in red blood cells, hemoglobin, and hematocrit. In contrast MC-LR-induced dose-dependent decreases in mean corpuscular volume, hemoglobin, and hemoglobin concentration were observed both C57BL/6 and Hfe^-/- mice. In both mouse species, serological indexes increased. Aggravated liver and spleen iron were observed in C57BL/6 mice, consistent with Perls' Prussian blue staining. However, an opposite trend was observed in Hfe^-/- mice. C57BL/6 mice had lower Hamp1 (Hepcidn), Bmp6, Il-6, and Tmprss6. Significant increased Hjv, Hif-1α and Hif-2α were observed in both C57BL/6 and Hfe^-/- mice. MC-LR-induced pathological lesions were dose-dependent increase in C57BL/6 mice. More severe pathological injuries in MC-LR groups (25 μg/kg) were observed in Hfe^-/- mice than in C57BL/6 mice. In Hfe^-/- mice, upon exposure to 25 μg/kg MC-LR, mitochondrial membranes were damaged and mitochondrial counts increased with significant swelling. These results indicated that MC-LR can induce the accumulation of iron in C57BL/6 mice with the occurrence of anemia, similar to thalassemia. Moreover, dysregulation of iron homeostasis may be due to MC-LR-induced Hamp1 downregulation, possibly mediated by hypoxia or the IL6-STAT3 and BMP-SMAD signaling pathways.