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Algal Toxins, Food Safety, and Bioterrorism: A Food-and-Water Defense Perspective

Submitted:

25 June 2026

Posted:

26 June 2026

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Abstract
Food defense encompasses both the prevention of accidental contamination and the protection of food and water systems against deliberate adulteration. Within this framework, algal toxins deserve greater attention because they occupy a critical intersection of water security, seafood and drinking-water safety, environmental change, supply-chain continuity, and public health preparedness. The novelty of this review lies in reframing algal toxins from a primarily environmental, seafood-safety, or clinical-toxicology topic into an integrated food-and-water defense problem. This perspective brings together harmful algal bloom ecology, toxin toxicology, seafood safety, drinking-water protection, preparedness for intentional adulteration, climate-change risk, surveillance, and emergency response. Algal toxins can enter the human supply chain through multiple marine and freshwater pathways, are often undetectable by taste, odor, or appearance, may resist routine preparation measures, and can generate high-consequence disruptions even when contamination begins locally. The analysis further shows that prevention depends largely on upstream measures--including environmental surveillance, harvest-area restrictions, source-water protection, testing, supply-chain controls, and rapid public communication--rather than on consumer behavior. Framed in the context of the U.S. Food and Drug Administration’s Intentional Adulteration Rule under the Food Safety Modernization Act, this paper situates algal toxins within a preventive defense model that integrates monitoring, vulnerability reduction, and emergency preparedness. Although most harmful algal bloom events are naturally occurring, algal toxins warrant attention in food-defense planning because they can contaminate seafood and drinking-water systems, complicate detection and attribution, and expose vulnerabilities across interconnected food and water infrastructures.
Keywords: 
algal toxins
;  
harmful algal blooms
;  
food defense
;  
water security
;  
cyanotoxins
;  
seafood safety
;  
drinking water
;  
emergency preparedness
Subject: 
Public Health and Healthcare  -   Public, Environmental and Occupational Health

Introduction

The case for treating algal toxins as a food-and-water defense issue begins with their diverse routes of entry into the human food and water supply. In marine systems, filter-feeding shellfish—including oysters, clams, and mussels—bioaccumulate toxins produced by toxic phytoplankton, while certain finfish acquire these compounds through trophic transfer. These exposures are associated with recognized seafood poisoning syndromes, including paralytic shellfish poisoning caused by saxitoxins, amnesic shellfish poisoning caused by domoic acid, diarrhetic shellfish poisoning caused by okadaic acid and dinophysistoxins, neurotoxic shellfish poisoning caused by brevetoxins, azaspiracid shellfish poisoning, and ciguatera fish poisoning caused by ciguatoxins [1,2]. In freshwater systems, cyanotoxins such as microcystins, cylindrospermopsin, anatoxin-a, and saxitoxins may contaminate drinking-water sources, recreational waters, fish, irrigated crops, and blue-green algae dietary supplements [2,3]. Together, these pathways show that algal toxins are not confined to isolated ecological niches; they move through interconnected food, water, and consumer-product systems in ways that complicate prevention and response.
Their defense relevance is heightened by the fact that many algal toxins cannot be detected by consumers through taste, odor, or appearance. The Centers for Disease Control and Prevention notes that algal toxins in fish and shellfish may be organoleptically undetectable and that neither cooking nor food preservation reliably eliminates them [4]. Similarly, boiling water contaminated with cyanotoxins does not render it safe and may instead concentrate the toxin [5]. This combination of concealment and resistance shifts risk management away from end-user behavior and toward upstream controls such as environmental monitoring, harvest-area closures, product testing, source-water management, and rapid public notification. The central problem is therefore not simply exposure, but the failure of routine consumer safeguards to interrupt exposure once contamination has occurred.
This logic also explains why algal toxins remain relevant to bioterrorism and intentional-contamination planning, even though most harmful algal bloom events are naturally occurring rather than deliberate. Their importance lies not in evidence of common use in attacks, but in the convergence of features central to defense analysis: they are biologically derived toxins, can affect widely consumed foods and water supplies, may cause illness without obvious sensory warning, and can initially be difficult to distinguish from naturally occurring contamination events. Saxitoxin is particularly notable because it is both a naturally occurring algal toxin associated with paralytic shellfish poisoning and an HHS select toxin identified by the Federal Select Agent Program as capable of posing a severe threat to public health and safety [6,7]. This designation underscores a broader point: food-defense systems must be designed to detect and manage high-consequence toxin hazards regardless of whether an incident is ultimately judged accidental, environmental, or intentional (7a).
The contribution of this review is therefore not to suggest that algal toxins are commonly used as deliberate agents, but to show why they should be incorporated into the same preparedness architecture used for other high-consequence food-and-water hazards. Existing harmful algal bloom literature often treats bloom ecology, seafood poisoning, drinking-water management, and clinical toxicology as separate domains. A food-and-water defense perspective integrates these domains around the operational questions that matter during a serious incident: where contamination can enter or concentrate, how quickly it can be detected, which products or water systems may be affected, how exposure can be stopped, and how public health authorities can communicate credible risk information before preventable illness occurs.
Table 1 summarizes the principal algal toxin classes discussed above, highlighting their source organisms and dominant molecular targets (6b).
The broader significance of algal toxins becomes clearer when viewed against the scale and interconnectedness of contemporary food and water systems. The World Health Organization estimates that unsafe food causes approximately 600 million illnesses and 420,000 deaths globally each year and emphasizes that increasingly globalized food chains allow local contamination events to escalate rapidly into international concerns [8]. In the United States, commonly cited federal estimates attribute roughly 48 million foodborne illnesses, 128,000 hospitalizations, and 3,000 deaths annually to foodborne hazards overall [9]. Although these figures are not specific to algal toxins, they underscore the central point advanced here: hazards that begin as localized environmental events can become supply-chain and public-trust crises when they intersect with centralized processing, interstate commerce, and essential water infrastructure. For that reason, toxin-mediated hazards should be incorporated into preventive food-safety and defense systems rather than treated solely as episodic environmental anomalies.
Seafood safety programs are central to algal-toxin prevention. The National Shellfish Sanitation Program promotes public health protection for bivalve molluscan shellfish moving in interstate commerce through cooperation among state agencies, the FDA, the EPA, NOAA, and the shellfish industry [10,11]. This cooperative structure is important because shellfish can concentrate marine biotoxins even when the surrounding water appears safe to consumers. State officials may close harvest areas when monitoring shows unsafe levels of toxic algae or shellfish toxins, and consumers are advised to follow local shellfish, fishing, and swimming advisories [10,12].
Drinking-water systems require similar attention. Cyanobacterial toxins are among the most hazardous substances widely found in bodies of water, and the World Health Organization emphasizes that managing lakes, reservoirs, and rivers is critical to preventing cyanobacterial blooms and protecting public health [13]. EPA notes that harmful algal blooms that produce cyanotoxins can pose risks through drinking-water exposure and that severe blooms require proactive planning and active management to reduce risk in potable water supplies [14,15]. EPA has also issued drinking-water health advisories for microcystins and cylindrospermopsin; although these advisories are not legally enforceable federal standards, they provide technical guidance for protecting public health during contamination events [16]. The contrast between marine and freshwater toxin systems is summarized in Table 2, which shows how environmental setting, exposure pathway, and physicochemical behavior shape public health risk (16a).
Water-system preparedness is also a security issue. Under America’s Water Infrastructure Act, community drinking-water systems serving more than 3,300 people must develop or update risk and resilience assessments and emergency response plans [16]. These plans are directly relevant to algal toxins because cyanotoxin contamination can affect source-water quality, treatment decisions, public notification, alternative water supplies, healthcare preparedness, and public trust. Together with seafood controls, these water-system requirements clarify why algal toxins belong within a broader food-and-water defense framework, rather than solely within routine environmental or public health management.
From a food-defense perspective, algal toxins are concerning not only because they can contaminate seafood and other food inputs, but also because they challenge conventional assumptions about control. A vulnerability-based approach asks where an attacker—or a system failure—could introduce, concentrate, misclassify, or distribute toxin-contaminated material to achieve the greatest public health impact. In practice, that means focusing on high-risk points such as harvest-area verification, raw-material approval, receiving, bulk liquid handling, storage, blending, labeling, and distribution. Under the FDA’s food-defense framework, facilities are expected to identify significant vulnerabilities, establish mitigation strategies at actionable process steps, monitor those controls, and verify that they function as intended. For algal-toxin hazards, this perspective underscores the need for restricted access, chain-of-custody controls, supplier verification, product-hold procedures, and rapid traceback capability for seafood, algal ingredients, and water-dependent foods [3,17].
The main analytical and regulatory tools used to detect, evaluate, and manage algal-toxin risk are outlined in Table 3.
From a water-defense perspective, algal toxins demonstrate that source-water protection and treatment resilience are inseparable from security planning. America’s Water Infrastructure Act requires many community water systems to assess risks to source water, treatment processes, storage, distribution, monitoring practices, and emergency-response capacity. These requirements align closely with cyanotoxin preparedness. A defensible strategy includes source-water surveillance, clear trigger points for intensified sampling, treatment adjustments, redundancy for critical operations, alternative-water planning, and communication protocols that can be activated quickly if finished water is threatened. Because cyanotoxin incidents can resemble naturally occurring blooms yet still cause high-consequence disruptions, utilities also need detection, decision-making, and incident command systems that enable rapid coordination with public health agencies, laboratories, and emergency managers [4,5,12,16].

Food and Water Defense Implications

These considerations lead to a clear defense conclusion: algal toxins are not merely environmental contaminants or episodic public health curiosities, but operational hazards that expose vulnerabilities in both food and water systems. In food systems, this means protecting points at which contaminated seafood, algal ingredients, or process water could be introduced, concentrated, mislabeled, blended, or distributed at scale. In water systems, it means treating cyanotoxin events not only as water-quality incidents, but also as disruptions that can affect treatment performance, continuity of service, public communication, healthcare demand, and institutional trust. Across both domains, the same principle applies: effective prevention depends on identifying high-consequence failure points before exposure occurs and integrating monitoring, access control, traceback, emergency planning, and public health response within a single preparedness architecture.
Operationalizing that framework requires an integrated approach that combines food safety, water safety, environmental monitoring, and emergency planning. In practice, this includes monitoring harvest waters and source water, testing when indicated, optimizing treatment and control measures, maintaining traceback and communication systems, and applying food-defense safeguards at high-risk points such as sourcing, receiving, processing, storage, blending, and water inputs [3,17]. Recent international guidance reinforces this operational approach. The 2026 joint FAO/IOC-UNESCO/IAEA guidance on algal toxins in bivalve mollusks emphasizes harmful-algae monitoring, management of harvesting and production areas, pre-harvest monitoring, post-harvest batch testing, and microalgal monitoring as components of a risk-based system for preventing toxin-contaminated shellfish from entering commerce (38b).

Novelty and Significance of the Review

The significance of this review lies in explicitly reframing algal toxins as food-and-water defense hazards rather than treating them only as environmental contaminants, seafood syndromes, or drinking-water quality problems. This framing is novel because algal toxins occupy an unusual position among defense-relevant hazards: they are naturally occurring and biologically derived, yet their potency, concealment, resistance to routine consumer mitigation, uncertain attribution, and capacity to disrupt high-volume food and water systems create challenges similar to those considered in intentional-contamination planning. The defense question is therefore not limited to whether contamination is deliberate. It is whether the food and water system can rapidly detect, contain, trace, communicate, and recover from high-consequence toxin events before avoidable exposures occur.
This integrated framing also clarifies the practical value of the review. It brings together topics that are often managed separately--harmful algal bloom ecology, toxin mechanisms, seafood controls, drinking-water resilience, clinical recognition, laboratory testing, climate change, intentional-adulteration preparedness, and emergency communication--and organizes them around operational vulnerability. That approach supports a preparedness model in which seafood authorities, water utilities, laboratories, poison centers, clinicians, emergency managers, and food-sector operators can plan from a shared risk architecture rather than responding through disconnected programs.

Surveillance and Clinical Recognition

Harmful algal bloom-related illnesses may present with gastrointestinal, neurologic, respiratory, dermatologic, or hepatic effects, depending on the toxin and route of exposure. CDC notes that treatment for cyanotoxin-associated illnesses and foodborne illnesses caused by harmful algal bloom toxins is generally supportive and symptom-directed, and that no specific antidotes exist for many of these toxins [4]. This reality increases the importance of prevention, early reporting, poison-control consultation, public health notification, and laboratory coordination when contaminated seafood, drinking water, or algal products are suspected.
Recent U.S. outbreak surveillance reinforces the operational importance of this prevention-first approach. During 2011-2023, CDC identified 402 foodborne disease outbreaks associated with marine toxins, resulting in 1,280 illnesses, 96 hospitalizations, and one death; ciguatoxin alone caused 189 outbreaks, 619 illnesses, and 67 hospitalizations [41]. Although the CDC marine-toxin category also includes non-algal etiologies such as scombroid toxin, the report is directly relevant to algal-toxin preparedness because it emphasizes that ciguatoxin and shellfish-associated algal toxins are tasteless, odorless, and resistant to cooking or freezing once aquatic animals are contaminated [41]. These features reinforce the core defense argument of this review: consumer-level detection and routine preparation cannot be relied on as the final safety barrier. The range of human illnesses associated with these toxins is summarized in Table 4 to link exposure pathways to the syndromes most relevant to clinical and public health responses.

Climate Change and Emerging Risk

Climate change is not simply an environmental backdrop to harmful algal blooms; it is a force multiplier for food-and-water defense risk. Warmer surface waters, altered precipitation patterns, intensified stratification, nutrient runoff, eutrophication, drought-flood cycles, marine heatwaves, and changing circulation patterns can increase bloom frequency, extend bloom duration, expand geographic range, and shift species composition across freshwater, estuarine, and marine systems [31,32,33,34,35,38,39,40]. These changes matter operationally because the public health threat posed by harmful algal blooms depends not only on whether blooms occur, but also on which organisms dominate, what toxins they produce, how those toxins move through food and water systems, and whether surveillance systems can recognize changing exposure profiles.
Recent literature strengthens the evidence base for this risk. A 2024 review in Nature Reviews Earth & Environment reported that global inland harmful algal bloom occurrence has risen since the 1980s, including a 44% increase from the 2000s to the 2010s, and emphasized nutrient pollution, climate warming, legacy nutrients, integrated monitoring networks, and data-sharing frameworks as central to forecasting and mitigation [35]. In high-latitude coastal systems, modeling and observational work show that warming and freshening can change not only bloom frequency but also seasonality and toxin profiles. Along the Norwegian coast, a 3 °C warmer scenario was projected to increase Dinophysis acuta bloom frequency and reduce Alexandrium tamarense-complex blooms, implying a shift in relative exposure from paralytic to diarrhetic shellfish toxins in some settings [36].
Field evidence also links climate-related ocean change to food-web exposure. A 2025 Nature study quantified domoic acid and saxitoxin in bowhead whale samples collected over 19 years and found that algal-toxin prevalence and concentrations were correlated with ocean heat flux, open-water area, wind velocity, and atmospheric pressure, supporting a mechanistic link between warming conditions and increasing algal-toxin concentrations in Arctic food webs [37]. These findings are especially important for food-and-water defense because they connect environmental change to food security, subsistence harvesting, wildlife health, and the need for surveillance systems capable of detecting northward and seasonal shifts in toxin risk.
A One Health perspective further underscores the significance of algal toxins as sentinel hazards. A 2026 study of a harmful algal bloom in Golfo Nuevo, Argentina, documented phycotoxin transfer from phytoplankton to mesozooplankton, mussels, fish, whales, and sea lions; it also described sea-lion mortality, evidence of maternal toxin transfer, and gastrointestinal illness in approximately 10% of the local population during the bloom period [42]. In the Arctic, rapid detection and risk communication during a large Alexandrium catenella bloom demonstrated the value of near-real-time monitoring, interdisciplinary coordination, and stakeholder engagement in remote regions where routine laboratory capacity and public-health infrastructure may be limited [43]. Together, these studies show that climate-driven algal-toxin risks are not confined to environmental monitoring; they affect seafood safety, public communication, emergency preparedness, wildlife conservation, subsistence food security, and confidence in food and water systems.

Conclusion

In conclusion, algal toxins should be understood as a consequential component of modern food-and-water defense rather than as a marginal subset of environmental health. Their ability to contaminate seafood, drinking water, algal ingredients, and other water-dependent food pathways, to evade sensory detection, to resist routine preparation, and to disrupt interconnected supply systems makes them important hazards for preventive planning. The novelty of this review is its integration of algal-toxin toxicology, harmful algal bloom ecology, seafood safety, drinking-water protection, intentional-adulteration preparedness, climate change, and emergency response into a single defense-oriented framework. This perspective does not imply that most algal-toxin events are deliberate. Rather, it emphasizes that high-consequence toxin incidents require preparedness systems capable of functioning regardless of whether contamination is ultimately classified as natural, accidental, or intentional.
Credible preparedness, therefore, requires more than bloom awareness alone. It requires coordinated surveillance of source waters and harvest areas, risk-based testing, supplier and chain-of-custody controls, product-hold and traceback capacity, treatment resilience for drinking-water systems, clinical and poison-control recognition, public advisories, and emergency communication across the food and water continuum. As climate change, global seafood trade, expanding aquaculture, changing recreational and subsistence harvesting patterns, and water-system vulnerabilities alter exposure profiles, algal toxins provide a practical test case for whether contemporary food and water defense systems can manage biologically derived hazards that are environmentally driven, operationally complex, and socially disruptive.

Author Contributions

AN: writing-review and editing, reviewed all drafts, and approved the final manuscript. MTF-S: writing-review and editing, reviewed all drafts, and approved the final manuscript. AM: Conceptualization, worked on the original draft, writing-review and editing, reviewed all drafts and approved the final manuscript. PP: Conceptualization, enhanced original draft; writing-review and editing, reviewed all subsequent drafts and approved the final manuscript. AWH: Conceptualization, writing original draft, writing-review and editing, supervision, project administration, and approved the final manuscript. All authors have read and agreed to the published version of the paper.

Funding

This research received no funding (external or internal).

Institutional Review Board Statement

Not applicable.

Data Availability Statement

No new data were created or analyzed in this study. Data sharing is not applicable to this article.

Conflicts of Interest

None of the authors has a conflict of interest to declare.

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Table 1. Major Algal Toxin Classes, Representative Toxins, Source Organisms, and Primary Molecular Targets.
Table 1. Major Algal Toxin Classes, Representative Toxins, Source Organisms, and Primary Molecular Targets.
Toxin class Representative toxins Main source organisms Primary molecular target/action
Paralytic shellfish poisoning (PSP) Saxitoxin, neosaxitoxin, gonyautoxins Alexandrium, Gymnodinium, Pyrodinium, some cyanobacteria Blockade of voltage-gated sodium channels (7r-7u)
Amnesic shellfish poisoning (ASP) Domoic acid Pseudo-nitzschia Agonist at ionotropic glutamate receptors; excitotoxicity (7v,7w)
Diarrhetic shellfish poisoning (DSP) Okadaic acid, dinophysistoxins Dinophysis, Prorocentrum Inhibition of protein phosphatases 1 and 2A (16g,7x,7y)
Ciguatera fish poisoning (CFP) Ciguatoxins, maitotoxin, palytoxin-like compounds Gambierdiscus and related dinoflagellates Persistent activation of voltage-gated sodium channels; related membrane disruption (7g)
Neurotoxic shellfish poisoning (NSP) Brevetoxins Karenia brevis Persistent activation of voltage-gated sodium channels (7g)
Azaspiracid poisoning (AZP) Azaspiracids Azadinium and related dinoflagellates Multitarget cytotoxic effects; mechanism of action remains incompletely defined (7z,7aa)
Palytoxin poisoning Palytoxin and congeners Ostreopsis, zoanthids, and some marine organisms Disruption of Na+/K+-ATPase (16j,7bb)
Footnotes: PSP, ASP, DSP, CFP, NSP, and AZP are the principal human seafood poisoning syndromes caused by marine phycotoxins. The listed source organisms are representative and not exhaustive. Molecular targets summarize the dominant toxic mechanism most relevant to human disease.
Table 2. Freshwater and Marine Algal Toxins: Distribution, Physicochemical Tendencies, and Public Health Relevance.
Table 2. Freshwater and Marine Algal Toxins: Distribution, Physicochemical Tendencies, and Public Health Relevance.
Environmental setting Major toxin groups Dominant physicochemical tendency* Principal exposure pathway Public health relevance
Marine PSP, ASP, DSP, CFP, NSP, palytoxin-related toxins Mixed; hydrophilic toxins often produce rapid systemic effects; lipophilic toxins show broader tissue distribution (7b,7c,16c-16j) Seafood consumption; in some cases, aerosol inhalation Shellfish and fish safety; coastal respiratory events
Freshwater Microcystins, nodularin, cylindrospermopsin, saxitoxin, anatoxin-a, guanitoxin, dermatotoxins Many are hydrophilic (16k,16L); some are membrane-active irritants Drinking water, recreation, animal ingestion, skin contact Municipal water safety; livestock and wildlife mortality
Mixed coastal systems Brevetoxins, ciguatoxins, palytoxin-like compounds Often lipophilic and persistent (16c-16j,7f) Seafood, aerosols, marine contact Beach-related illness; seafood advisories; fishery impacts
*From PubChem, NIH, National Library of Medicine, National Center for Biotechnology Information. Footnotes: Physicochemical behavior influences tissue distribution, clearance, and persistence of toxicity. Hydrophilic toxins often act quickly and may be cleared faster, whereas lipophilic toxins may distribute more widely and persist longer. The route of exposure is a major determinant of the clinical syndrome.
Table 3. Analytical and Regulatory Approaches for Algal Toxins.
Table 3. Analytical and Regulatory Approaches for Algal Toxins.
Approach Use Strengths Limitations Representative application
Mouse bioassay [18,19] Historical regulatory screening Detects overall biological toxicity Ethical concerns, low specificity, variability Legacy screening for shellfish toxins
Chemical analysis [20,21,22,23,24] Toxin identification and quantitation High specificity, supports congener profiling Requires standards and instrumentation LC-MS/MS detection of marine and freshwater toxins
Immunoassays [18,25] Screening for selected toxins Rapid, relatively simple May miss analogs or structurally divergent toxins Shellfish monitoring
Receptor-binding assays [18,25] Functional detection of bioactive toxin classes Detects biologically active analogs Limited to toxins with known binding targets Saxitoxin and brevetoxin screening
Functional cell-based assays [26] Assessment of physiological toxicity Captures integrated cellular response Cell-line sensitivity varies; interpretation can be complex Neuronal or hepatocyte toxicity testing
Primary neuronal culture / MEA systems [27,28,29,30] Mechanistic neurotoxicity assessment Sensitive, dynamic, non-invasive electrophysiology Technically specialized Early detection of toxin effects on neuronal firing
Table 4. Human Syndromes Associated with Algal Toxins, Exposure Routes, and Hallmark Clinical Findings.
Table 4. Human Syndromes Associated with Algal Toxins, Exposure Routes, and Hallmark Clinical Findings.
Syndrome Typical toxins Common exposure route Hallmark clinical findings Typical clinical concern
PSP (7b,7c) Saxitoxins (4a) Contaminated shellfish Perioral numbness, paresthesia, weakness, paralysis Respiratory failure
ASP (16c-16g) Domoic acid Shellfish, occasionally other seafood Confusion, disorientation, amnesia, seizures Persistent neurologic injury
DSP (7x) Okadaic acid, dinophysistoxins Shellfish Diarrhea, abdominal cramps, nausea, vomiting Dehydration, transient illness
CFP (7d-7h,16i) Ciguatoxins Reef fish GI symptoms, paresthesia, temperature reversal, fatigue Prolonged neurologic symptoms
NSP (7g,16i) Brevetoxins Shellfish; aerosol near blooms Paresthesia, dizziness, bronchial irritation, respiratory complaints Neuro-respiratory toxicity
Cyanobacterial hepatotoxicity (7i-7L) Microcystins, nodularin, cylindrospermopsin Drinking water, recreation, food Nausea, vomiting, abdominal pain, liver dysfunction Hepatic injury
Cyanobacterial neurotoxicity (7m,7n) Saxitoxin, anatoxin-a, guanitoxin Drinking water, animal exposure, recreation Tremor, weakness, fasciculations, paralysis Respiratory compromise
Cyanobacterial dermatitis (7o-7q) Lyngbyatoxins, aplysiatoxins Skin contact, aerosols Rash, erythema, blistering, irritation Local tissue injury
Footnotes: Clinical manifestations vary with dose, route, toxin combination, and host factors. Some toxins produce overlapping syndromes, and sublethal exposures may still be clinically significant. Aerosol exposure is particularly relevant for brevetoxins and some cyanobacterial irritants.
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