Harmful Algal Blooms Research Articles

Enhanced phosphorus removal from anoxic water using oxygen-carrying iron-rich biochar: Combined roles of adsorption and keystone taxa

Anthropogenic enrichment of phosphorus (P) in water environment can cause eutrophication, harmful algal blooms, and water quality deterioration. Adsorbents are often used for the removal and recovery of P from water, however, P is highly susceptible to re-release in anoxic benthic environments. As a response, this study prepared oxygen-carrying iron-rich biochar (O-Fe-BC) as an effective oxygen micro-nanobubble carrier (Q = 8.7024 cm³/g STP at 1.5 MPa) and P adsorbent (qm = 16.7097 mg P/g, q0.1 = 3.1974 mg P/g). Over the 90-day experimental period with O-Fe-BC, dissolved oxygen (DO) levels in the overlying water could maintain at ∼4 mg/L (peaking at ∼9.5 mg/L), and total phosphorus (TP) and soluble reactive phosphorus (SRP) levels decreased by over 96 %. The higher inorganic phosphorus content in the surface sediment-biochar mixture, along with the lower labile P and Fe concentration in the sediment pore water in the O-Fe-BC group compared to other groups, suggested the enhanced P immobilization. Further mechanism exploration revealed the combined roles of adsorption and microbial response, in which O-Fe-BC achieved efficient phosphate adsorption primarily through inner-sphere complexation via ligand exchange and keystone taxa (particularly Candidatus Electronema) played a crucial role in driving water chemistry divergence. Specially, these cable bacteria could provide large pools of Fe oxides in the surface sediment, binding with P to prevent its release, as supported by significant correlations between Ca. Electronema abundance and oxidation–reduction potential (ORP), TP, SRP, and sediment Fe-P variations. Additionally, a pot experiment with mung bean seedlings showed that the recovered O-Fe-BC significantly promoted the seed germination and growth, indicating its potential as a novel material for removing and recovering P from eutrophic waters. Taken together, our work provided a promising strategy for sustainable anoxia and P pollution mitigation, and also highlighted the indispensable roles of inner-sphere adsorption in P recovery and microbial keystone taxa in P cycling regulation.

The causal link between nitrogen structure and physiological processes of Ulva prolifera as the causative species of green tides

Harmful algal blooms (HABs) increase with eutrophication depending on the nutrient structure (availability and ratios), but an unequivocal causal link between these factors is rarely established. Here, we provide support for the causal link between the nitrogen structure and physiological processes of Ulva prolifera as the causative species of Yellow Sea green tides (YSGTs) using in situ and laboratory experiments. The results showed that the components of nitrogen nutrients in seawater exhibited significant spatiotemporal variation. The concentration of NO3−-N showed a notable decreasing trend from south to north. Sufficient dissolved inorganic nitrogen (DIN) induced increases in thalli nitrate reductase (NR) and glutamine synthetase (GS) activities. This could accelerate thalli uptake of nitrogen nutrients. The glutamate dehydrogenase (GDH) activity was significantly upregulated with the increasing proportion of dissolved organic nitrogen (DON) in seawater. The change in nitrogen structure regulated the activity of NR during the long-distance floating migration of the YSGTs. And the activity of NR could modulate the nitric oxide (NO) content in the thalli. NO was used as a signal molecule to enhance the antioxidant defense system of thalli. The efficient antioxidant system in the thalli could reduce oxidative stress and effectively maintain high photosynthetic activity. The findings deepen our understanding of the relationship between nitrogen structures and key biological processes in macroalgae. This study also suggest that NO can enhance key biological processes in U. prolifera under varying nitrogen structures.

Phytoplankton Structure in a Coastal Region of the Eastern Entrance of the Gulf of California during La Niña 2022

This paper assessed the phytoplankton structure and its relationship with the physical environment in the coastal region off Mazatlán, Mexico, in two seasons of 2022, a year in which a strong La Niña event took place: (1) the warmer (August) and (2) the transitional period to the cold phase (November), based on hydrographic data and samples collected in two systematic scientific expeditions. The results showed clear differences between both seasons. Regarding total abundance, August reached 125,200 cells L−1, while November amounted to 219,900 cells L−1. Regarding species composition, the diatoms Cylindrotheca closterium and Planktoniella sol were dominant in August, while Thalassionema nitzschioides and Tetramphora decussata dominated the assemblages in November. The dinoflagellate Protoperidinium punctulatum was dominant in both seasons. However, very marked differences in its abundance are reported. The differences observed in the species richness and abundance could be attributed to the physical configuration of the water column, particularly the surface temperature, which showed clear changes between both seasons. The results presented here confirmed the high phytoplankton richness (some of them with the potential to generate harmful algal blooms), abundance, and diversity values of the region, suggesting a strong relationship with the physical environment.

Quantile Regression Illuminates the Heterogeneous Effect of Water Quality on Phytoplankton in Lake Taihu, China

Lake Taihu, a subtropical shallow lake in the Yangtze River Basin, is the third-largest freshwater lake in China. It serves not only as a crucial source of drinking water and an ecological resource but also holds significant economic, tourism, and fisheries value. Phytoplankton, a vital component of aquatic ecosystems, plays a critical role in nutrient cycling and maintaining water structure. Its community composition and concentration reflect changes in the aquatic environment, making it an important biological indicator for monitoring ecological conditions. Understanding the impact of water quality on phytoplankton is essential for maintaining ecological balance and ensuring the sustainable use of water resources. This paper focuses on Lake Taihu, with water samples collected in February, May, August, and November from 2011 to 2019. Using quantile regression, a robust statistical analysis tool, the study investigates the heterogeneous effects of water quality on phytoplankton and seasonal variations. The results indicate significant seasonal differences in water quality in Lake Taihu, which substantially influence phytoplankton, showing weakly alkaline characteristics. When phytoplankton concentrations are low, pondus hydrogenii (pH), chemical oxygen demand (COD), total phosphorus (TP), total nitrogen (TN), water temperature (WT), and conductivity significantly affect them. At medium concentrations, COD, TP, TN, and WT have significant effects. At high concentrations, transparency and dissolved oxygen (DO) significantly impact phytoplankton, while TP no longer has a significant effect. These findings provide valuable insights for policymakers and environmental managers, supporting the prevention and control of harmful algal blooms in Lake Taihu and similar aquatic systems.

Annual cycle of phytoplankton in the Pacific ocean near Guatemala in relation to physicochemical parameters

Due to the lack of basic information on the behavior of the phytoplankton community of the Guatemalan Pacific, particularly of the factors that cause harmful algal blooms, monthly monitoring was performed during a year (January–December 2021), which included three hydrometeorological seasons at three sampling sites in Puerto Quetzal (Texaco Buoy, Recalada Buoy and Entre Morros Buoy) at two depths (1.5 m and 5.0 m). These sites are influenced by shipping and nearby human populations. The structure of the phytoplankton community (species composition, abundance, richness and diversity), with an emphasis on potentially toxic and non-toxic harmful species, were evaluated. A total of 53 diatom species from 26 genera and 13 orders and 42 dinoflagellate species from 14 genera and six orders were identified. No significant differences between the sampling depths and different quarters of the year were found. The comparison of the total cell abundance between the three sites showed no significant differences. The results obtained present novel information on the phytoplankton community of the Guatemalan Pacific, filling a gap in a region where algal blooms occur annually with consequent ecological impacts and human poisonings.

Perceived Effect of Shipborne Sewage Discharge on Water Quality of Apapa Sea Port

The Apapa Sea Port in Lagos, Nigeria, faces significant environmental concerns due to shipborne sewage discharge. Over 3 billion tons of sewage are discharged annually, posing health risks and causing disease outbreaks. Understanding this relationship is crucial for developing policies to protect marine environments and port operations. The study investigates the perceived effects of sewage wastewater pollution on the marine environment, focusing on Apapa Port, Nigeria’s largest and busiest port. The study used a sample of 475 individuals, with a stratified frame of 323 respondents, resulting in a sample size of 245 using Yaro Yamane’s formula. Descriptive statistical methods were used to summarize and interpret data, with a mean score of 2.5 as the threshold for classification. Inferential statistics, including ANOVA and regression analysis, were used to test the research hypotheses. The results shown that the perceived impact of sewage pollution on water quality, with findings showing a strong awareness and concern among port personnel regarding its deleterious effects, including eutrophication (mean rating: 3.825), harmful algal blooms (mean rating: 3.921), habitat degradation (mean rating: 3.868), and waterborne diseases (mean rating: 4.018). The Hypotheses testing confirmed that sewage discharge significantly impacts the study area (p-value = 0.048) and that the implementation of MARPOL Annex IV has a significant influence on pollution levels (p-value < 0.05). The study concludes with recommendations to improve treatment processes, enforcement mechanisms, infrastructure, and stakeholder collaboration to ensure compliance and protect the marine ecosystem at Lagos Port, among many others. Keywords: Apapa seaports, sewage, shipborne, pollution, waste management.

Analyzing the neurotoxic effects of anatoxin-a and saxitoxin in zebrafish larvae

Global warming due to climate change, as well as freshwater eutrophication caused by anthropogenic activities are responsible, among other factors, for an increasing occurrence of harmful algal blooms (HABs) in aquatic systems. These can lead to the generation of cyanotoxins, secondary metabolites coming from cyanobacteria, producing adverse effects in living organisms including death. This research aims to study the effects that two neurotoxins, anatoxin-a (ATX-a) and saxitoxin (STX), have on living organisms. Once the stability of both compounds in water was determined for a 24 h period using ultra-high-performance liquid chromatography coupled to a triple quadrupole mass spectrometer (UPLC-MS/MS), zebrafish larvae were exposed to different levels of toxins (1 ng L−1, 10 ng L−1, 100 ng L−1 and 1 μg L−1) during 24 h. Behavioral studies including vibrational startle response (VSR), habituation to vibrational stimuli, basal locomotor activity (BLM) and visual motor response (VMR) were performed using Danio Vision system, and neurotransmitters (NTs) from 15-head pools of control and exposed zebrafish larvae were extracted and analyzed by UPLC-MS/MS. Both compounds induced hypolocomotion in the individuals, while 10 and 100 ng L−1 of ATX-a significantly increased methionine (120 % and 126 %, respectively) and glutamate levels (118 % and 129 %, respectively). Saxitoxin enhanced 3-metoxytyramine (3-MT) levels at 1 ng L−1 by 185 %. The findings of this study show that both studied cyanotoxins influence the behavior of zebrafish larvae as well as their metabolism.

Composition and temporal dynamics of the phytoplankton community in Laizhou Bay revealed by microscopic observation and rbcL gene sequencing

Laizhou Bay, a major breeding ground for economic marine organisms in the northern waters of China, is facing rapid environmental degradation. In this study, field surveys in this area were conducted in the spring, summer, and autumn of 2020. Microscopic observation and RuBisCO large subunit (rbcL) gene analysis were employed to understand the community structure and temporal dynamics of phytoplankton. The phytoplankton community structures detected by the two methods showed significant differences. Microscopic observation revealed the dominance of dinoflagellates in spring that shifted to the dominance of diatoms in summer and autumn. However, rbcL gene sequencing consistently identified diatoms as dominant throughout all three seasons, with their relative abundance showing an increasing trend. Conversely, the relative abundance of the second- and third-most abundant taxa, namely, haptophytes and ochrophytes, decreased as the seasons transitioned. rbcL gene sequencing annotated more species than microscopy. It could detect haptophytes and cryptophytes, which were overlooked by microscopy. In addition, rbcL gene sequencing detected a remarkable amount of Thalassiosira profunda, which was previously unidentified in this sea area. However, it appeared to underestimate the contribution of dinoflagellates considerably, with most taxa being only identified through microscopic identification. The two methods jointly identified 28 harmful algal bloom taxa with similar detection quantities but substantial differences in species composition. Phytoplankton communities were influenced by temperature, salinity, and nutrients. The results of this work suggest that a combination of multiple techniques is necessary for a comprehensive understanding of phytoplankton.

Modification of the Trizol Method for the Extraction of RNA from Prorocentrum triestinum ACIZ_LEM2.

In samples of harmful algal blooms (HABs), seawater can contain a high abundance of microorganisms and elemental ions. Along with the hardness of the walls of key HAB dinoflagellates such as Prorocentrum triestinum, this makes RNA extraction very difficult. These components interfere with RNA isolation, causing its degradation, in addition to the complex seawater properties of HABs that could hinder RNA isolation for effective RNA sequencing and transcriptome profiling. In this study, an RNA isolation technique was established through the modification of the Trizol method by applying the Micropestle System on cell pellets of P. triestinum frozen at -20 °C, obtained from 400 mL of culture with a total of 107 cells/mL. The results of the modified Trizol protocol generated quality RNA samples for transcriptomics sequencing, as determined by their measurement in Analyzer Agilent 4150.

Isolation of ovatoxin-a from Ostreopsis cf. ovata cultures. A key step for hazard characterization and risk management of ovatoxins

Ostreopsis cf. ovata, a benthic/epiphytic marine dinoflagellate, is currently spreading in tropical, sub-tropical and temperate areas, causing periodic Harmful Algal Blooms (HABs). It produces a wide array of palytoxin-like compounds named ovatoxins (OVTXs), with OVTX-a generally the most abundant congener. Despite numerous cases of human poisonings and environmental damage associated with the presence of OVTXs and O. cf. ovata proliferations, a complete characterization of the toxicity of this class of molecules cannot be performed until Reference Material (RM) for individual congeners is available. This, in turn, requires the availability of sufficient amounts of toxin at a high purity grade. To achieve this goal, herein an analytical re-evaluation of critical-steps of OVTX-a isolation from O. cf. ovata cell pellets is reported. The overall procedure consists of four steps, namely an extraction, a Medium Pressure Liquid Chromatography (MPLC) separation, and two preparative High Performance Liquid Chromatography (HPLC) steps. Particular attention was paid to the extraction step to evaluate the repeatability in OVTX-a yields. For subsequent steps, loading sample preparation and chromatographic conditions were refined. As a result, a significant increase in recovery yields (from 12.5 to 20 ± 3%) and in purity grade (from 51% to 94%) of the isolated OVTX-a was achieved in comparison to previous studies. The improved procedure can easily be applied to isolate sufficient quantities of a good candidate RM for OVTX-a.

High-resolution temperature, salinity and depth data from southeastern Australian estuaries, 2018–2021

Estuaries are the important interface between the land and sea, providing significant environmental, economic, cultural and social values. However, they face unprecedented pressures including eutrophication, harmful algal blooms, habitat loss, and extreme weather due to climate change. Here we present an open access, quality-controlled water quality dataset collected from twelve diverse estuaries spanning 1000 km along the southeastern Australian coastline. Water depth, temperature and salinity data were collected across two years (2018–2021) capturing drought, wildfire and flood periods, using high accuracy Seabird MicroCAT field sensors located within oyster leases. These fully autonomous instruments collected and transmitted data every 10 minutes before downstream quality checking and uploading onto a public website. Simultaneous, high-resolution, longitudinal environmental data collected across multiple estuaries throughout a range of extreme weather events are exceptionally rare in the Southern Hemisphere, yet provide an invaluable resource for the aquaculture industry, researchers and environmental regulators alike.

A Tale of Two Tributaries: Source Delineation of Chloride in a Distressed Watershed (Grand Lake St. Marys, Ohio)

Various sources of pollution have been assigned as contributing to the Freshwater Salinization Syndrome (FSS), by which water bodies are undergoing concurrent salinization and alkalinization. In many urban areas that receive substantial snowfall, road salt application has been ascribed as the main source of chloride driving the FSS. In rural areas, however, inorganic (e.g. chemical) and organic (e.g. manure) fertilizer applications have been found to be the most important sources of chloride. Herein, we compared daily mean concentrations of chloride over the past decade of time between Coldwater Creek and Chickasaw Creek, two tributaries of Grand Lake St. Marys, the largest reservoir in Ohio. We also used Weighted Regressions on Time, Discharge, and Season (WRTDS) analyses to visualize trends in chloride data and compared chloride vs. nitrate levels to delineate likely sources of chloride for the two streams. We found that road salt application increased over time in both subwatersheds and that 37% and 25% of the chloride could be apportioned to road salt as a source in Coldwater Creek and Chickasaw Creek, respectively. Additionally, in Coldwater Creek, 37% of the chloride was apportioned to animal or septic sources, while 25% was apportioned to inorganic fertilizers, in comparison with 30% and 42% for Chickasaw Creek. Monitoring and assessing salinized streams for both chemical and biological water quality is important, particularly since the FSS has become increasingly linked to declines in water quality (e.g. harmful algal blooms, including recent upticks in Prymnesium parvum blooms) and is expected to be exacerbated with global climate change (e.g. increased precipitation causing increased runoff of chloride from the land).

The Role of Cyano-HAB (Cyanobacteria Harmful Algal Blooms) in the One Health Approach to Global Health

Harmful algal bloom events occur in salt, brackish, and fresh water. In bodies of water such as oceans and estuaries, diatoms or dinoflagellates form “tides” that produce toxins associated with seafood poisoning, including paralytic shellfish poisoning, or respiratory distress from inhalation of aerosolized toxins. Cyanobacteria predominantly bloom in fresh water; they can produce microcystins; cylindrospermopsin; and other toxins that humans or animals might be exposed to through water contact, inhalation, or ingestion. Animals that become ill or die can be sentinels for harmful algal bloom events. In a One Health approach, information about harmful algal bloom exposures and health effects support efforts to detect these events and mitigate and prevent associated illnesses. Human, animal, and environmental health partners can work together to document the occurrence and impacts of harmful algal bloom events and characterize associated illnesses.

Sensitivity analysis of a hydrodynamic and harmful algal model in a riverine system

Simulating algae blooms using a hydrodynamic-water quality model is challenging because it requires a thorough understanding of physical and biological processes and involves numerous parameters. This study conducted a sensitivity analysis of the EFDC+ hydrodynamic and water quality model for simulating cyanobacteria growth, an important Harmful Algal Bloom (HAB) species in the Ohio River, USA. The sensitivity analysis assessed 23 model input parameters, divided into nine functional groups according to their characteristics. This assessment analyzes the impact of changing these input parameters on four water quality model outputs including algae (i.e., cyanobacteria), dissolved oxygen, total nitrogen, and total phosphorus. Light extinction parameters, maximum algal growth rate, and algal base metabolism were identified as the most sensitive parameters for simulating algal growth. Solar radiation required for algal growth was moderately sensitive. Currently, there are only a few studies that simulate HAB dynamics in riverine systems. This study deepens our understanding of HAB development in rivers with lock and dam structures that create a series of pools along the river. Future work will involve focusing on the sensitive parameters in model calibration.

Scaling up the Natural Mode of Action of Macrophyte Allelochemicals and Their Effect on Toxic Cyanobacteria Using a Nitrogen-Limited Chemostat

This study investigates the inhibitory and hormetic effects of Myriophyllum spicatum extract on Microcystis aeruginosa in a controlled, continuous culture environment. To address the global challenge posed by harmful algal blooms, we used a range of extract concentrations to delineate the growth response patterns. At very low concentrations (6.25 and 12.5 mg/L), the addition of M. spicatum extract shows no discernible reduction in M. aeruginosa cell density or growth rate; instead, a slight increase is observed during exposure, suggesting a hormetic effect. However, at higher concentrations (75 and 100 mg/L), there is a drastic reduction of more than 50% in cell density and growth rate at 75 mg/L, with complete inhibition at 100 mg/L, leading to pronounced oxidative stress, damage to antioxidant defense systems, and increased cell mortality. Increased levels of malondialdehyde, catalase, and superoxide dismutase activities indicate the involvement of these enzymes in combating oxidative stress. Furthermore, intracellular and extracellular microcystins were significantly decreased at higher extract concentrations (50, 75, and 100 mg/L) in a dose-dependent manner. Our results indicate a dose-dependent response and provide insight into the potential application of natural water treatment solutions. Implications for ecological management and future research directions are discussed.

Harnessing green tide Ulva biomass for carbon dioxide sequestration

Harnessing green tide Ulva biomass for carbon dioxide sequestration

Deactivation of harmful green tide using Ag/SiO2 and Ag/Al2O3 coatings on low-density porous materials

Nowadays harmful bloom tides affect greatly the economy of coastal states. For this reason, the present communication reports on a practical method for synthesizing SiO2 and γ-alumina nanospheres, immobilized by sonochemistry on low-density porous foams and perlite granules, as a solution to this problem. A biostatic AgNP effect was incorporated into both materials, achieving AgSi and AgAl. The green-tide inactivation was performed by using Tetraselmis suecica under aqueous conditions. AgAl/FWGS displayed the best inactivation efficiency performance (94 %). Additionally, foams have significant buoyancy and are easy to handle, being an option for T. suecica inactivation for their easy recovering.

Effects of Harmful Algal Blooms on Amphibians and Reptiles are Under-Reported and Under-Represented.

Harmful algal blooms (HABs) are a persistent and increasing problem globally, yet we still have limited knowledge about how they affect wildlife. Although semi-aquatic and aquatic amphibians and reptiles have experienced large declines and occupy environments where HABs are increasingly problematic, their vulnerability to HABs remains unclear. To inform monitoring, management, and future research, we conducted a literature review, synthesized the studies, and report on the mortality events describing effects of cyanotoxins from HABs on freshwater herpetofauna. Our review identified 37 unique studies and 71 endpoints (no-observed-effect and lowest-observed-effect concentrations) involving 11 amphibian and 3 reptile species worldwide. Responses varied widely among studies, species, and exposure concentrations used in experiments. Concentrations causing lethal and sublethal effects in laboratory experiments were generally 1 to 100 µg/L, which contains the mean value of reported HAB events but is 70 times less than the maximum cyanotoxin concentrations reported in the environment. However, one species of amphibian was tolerant to concentrations of 10,000 µg/L, demonstrating potentially immense differences in sensitivities. Most studies focused on microcystin-LR (MC-LR), which can increase systemic inflammation and harm the digestive system, reproductive organs, liver, kidneys, and development. The few studies on other cyanotoxins illustrated that effects resembled those of MC-LR at similar concentrations, but more research is needed to describe effects of other cyanotoxins and mixtures of cyanotoxins that commonly occur in the environment. All experimental studies were on larval and adult amphibians; there were no such studies on reptiles. Experimental work with reptiles and adult amphibians is needed to clarify thresholds of tolerance. Only nine mortality events were reported, mostly for reptiles. Given that amphibians likely decay faster than reptiles, which have tissues that resist decomposition, mass amphibian mortality events from HABs have likely been under-reported. We propose that future efforts should be focused on seven major areas, to enhance our understanding of effects and monitoring of HABs on herpetofauna that fill important roles in freshwater and terrestrial environments. Environ Toxicol Chem 2024;43:1936-1949. Published 2024. This article is a U.S. Government work and is in the public domain in the USA. Environmental Toxicology and Chemistry published by Wiley Periodicals LLC on behalf of SETAC.

Microcystin-RR is a biliary toxin selective for neonatal extrahepatic cholangiocytes

BACKGROUND AND AIMSBiliary atresia is a fibrosing cholangiopathy affecting neonates that is thought to result from a prenatal environmental insult to the bile duct. Biliatresone, a plant toxin with an α-methylene ketone group, was previously implicated in biliary atresia in Australian livestock, but is found in a limited location and is highly unlikely to be a significant human toxin. We hypothesized that other unsaturated carbonyl compounds, some with the potential for significant human exposure, might also be biliary toxins. METHODSWe focused on the family of microcystins, cyclic peptide toxins from blue-green algae that are found worldwide, particularly during harmful algal blooms. We used primary extrahepatic cholangiocyte spheroids and extrahepatic bile duct explants from both neonatal (a total of 86 P2 mouse pups and 18 P2 rat pups (n=8-10 per condition for both species)) and adult rodents (a total of 31 P15-18 mice (n=10-11 per condition)) to study the biliary toxicity of microcystins and potential mechanisms RESULTSWe found that 400 nM microcystin-RR, but not six other microcystins or the related algal toxin nodularin, caused greater than 80% lumen closure in cell spheroids made from extrahepatic cholangiocytes isolated from 2-3-day-old mice (p<0.0001). In contrast, it resulted in less than an average of 5% lumen closure in spheroids derived from neonatal intrahepatic cholangiocytes or cells from adult mice (p=0.4366). We also found that microcystin-RR caused occlusion of extrahepatic bile duct explants from 2-day-old mice (p<0.0001), but not 18-day-old mice. Microcystin-RR caused a 2.3 times increase in reactive oxygen species in neonatal cholangiocytes (p<0.0001), and treatment with N-acetyl cysteine partially prevented microcystin-RR-induced lumen closure (p=0.0004), suggesting a role for redox homeostasis in its mechanism of action. CONCLUSIONSWe identify microcystin-RR as a selective neonatal extrahepatic cholangiocyte toxin and suggest that it acts by increasing redox stress.

Mixtures of organic micropollutants exacerbated in vitro neurotoxicity of prymnesins and contributed to aquatic toxicity during a toxic algal bloom

Prymnesins produced by an algal bloom of Prymnesium parvum led to the death of several hundred tons of freshwater fish in the Oder River in summer 2022. We investigated effects on aquatic life and human cell lines from exposure to extracts of contaminated water collected during the fish kill. We detected B-type prymnesins and >120 organic micropollutants. The micropollutants occurred at concentrations that would cause the predicted mixture risk quotient for aquatic life to exceed the acceptable threshold. Extracts of water and filters (biomass and particulates) induced moderate effects in vivo in algae, daphnids and zebrafish embryos but caused high effects in a human neuronal cell line indicating the presence of neurotoxicants. Mixture toxicity modelling demonstrated that the in vitro neurotoxic effects were mainly caused by the detected B-type prymnesins with minor contributions by organic micropollutants. Complex interactions between natural and anthropogenic toxicants may underestimate threats to aquatic ecosystems.