Marine Toxins

Unique identifier / Notation

CH0605

Synonyms

Algal bloom toxins biotoxins ichthyotoxins phycotoxins seafood toxins shellfish toxins

Marine toxins (biotoxins) are naturally occurring, toxic substances, mostly caused by certain types of marine organisms such as toxic algae, but also by bacteria. These toxins can accumulate in fish and shellfish, causing significant public health concerns due to their potential to cause a wide range of adverse health effects.

Primary reference(s)

WHO, 2024. Natural Toxins in Food (2024). World Health Organisation (WHO). Accessed 16 June 2024.

Annotations

GHS Classification

GHS09 - Environment

Additional scientific description

Marine toxins are primarily produced by algae or bacteria and are concentrated in contaminated fishery and aquaculture products. When people consume these contaminated products, depending on the toxin, the symptoms can be diarrheic, paralytic, amnesic, or neurologic, some of which result in high mortality and long-term morbidity (Sobel and Painter, 2005).

Routine clinical diagnostic tests are not available for these toxins; diagnosis is based on clinical presentation and a history of eating fishery and aquaculture products in the preceding 24 hours (Sobel and Painter, 2005). There is no antidote for any of the marine toxins, and supportive care is the mainstay of treatment. Paralytic shellfish poisoning, and puffer fish poisoning can cause death within hours of consuming the toxins and may require immediate intensive care (Sobel and Painter, 2005).

A Joint FAO/IOC/WHO expert meeting classified the toxins into eight groups based on their chemical structure (FAO/WHO, 2016): the Azaspiracid (AZA) group, Brevetoxin group, Cyclic Imines group, Domoic Acid (DA) group, Okadaic Acid (OA) group, Pectenotoxin (PTX) group, Saxitoxin (STX) group, and Yessotoxin (YTX) group.

The Food and Agriculture Organization of the United Nations (FAO) reports that they can also be classified by the type of poisoning they cause (FAO, 2004):

Paralytic shellfish poisoning (PSP) (FAO, 2004): PSP poisoning in humans is caused by ingestion of shellfish containing PSP toxins, which accumulate by shellfish grazing on algae producing these toxins.

Symptoms: slight tingling or numbness to complete respiratory paralysis.
In fatal cases, respiratory paralysis occurs within 2 to 12 hours of consuming the PSP-contaminated food.

Diarrhoeic shellfish poisoning (DSP) (FAO, 2004): In humans, DSP poisoning is caused by the ingestion of contaminated bivalves such as mussels, scallops, oysters or clams. The fat-soluble DSP toxins accumulate in the fatty tissue of the bivalves.

Symptoms: diarrhoea, nausea, vomiting and abdominal pain starting 30 minutes to a few hours after ingestion and complete recovery occurs within three days.
DSP toxins can be divided into different groups depending on chemical structure - the first group, acidic toxins, includes okadaic acid and its derivatives named dynophysistoxins; the second group, neutral toxins, consists of polyether-lactones of the pectenotoxin group; the third group includes a sulphated polyether and its derivatives the yessotoxins .

Amnesic shellfish poisoning (ASP) (FAO, 2004): In humans, ASP is also known as domoic acid poisoning (DAP) because amnesia is not always present.

Symptoms: abdominal cramps, vomiting, disorientation and memory loss (amnesia).
The causative toxin (the excitatory amino acid domoic acid or DA) was produced by the diatom species Pseudo-nitzschia pungens f. multiseries (Nitzschia pungens f. multiseries).

Neurotoxic shellfish poisoning (NSP) (FAO, 2004): NSP is caused by polyether brevetoxins produced by the unarmoured dinoflagellate Gymnodinium breve (also called Ptychodiscus breve, since 2000 called Karenia brevis) are toxic to fish, marine mammals, birds and humans, but not to shellfish.

An unusual feature of G. breve is the formation by wave action of toxic aerosols which can lead to asthma-like symptoms in humans.

Azaspiracid shellfish poisoning (AZP) (FAO, 2004): In November 1995, at least eight people in the Netherlands became ill after eating mussels (Mytilus edulis) cultivated at Killary Harbour, Ireland. Although the symptoms resembled those of diarrhoeic shellfish poisoning (DSP), concentrations of the major DSP toxins were very low.

The known organisms producing DSP toxins were not observed in water samples collected at that time.
In addition, a slowly progressing paralysis was observed in the mouse assay using the mussel extracts. These neurotoxic symptoms were different from typical DSP toxicity.
It was then that azaspiracid (formerly called Killary Toxin-3 or KT3) was identified and the new toxic syndrome was called azaspiracid poisoning (AZP).

Ciguatoxins causing ciguatera poisoning (CP) (FAO, 2004): The name ciguatera was given by Don Antonio Parra in Cuba in 1787 to intoxication following ingestion of the 'cigua', the Spanish trivial name of a univalve mollusc, Turbo pica, reputed to cause indigestion.

The term cigua was somehow transferred to an intoxication caused by the ingestion of coral reef fish species.
The causative toxins, the ciguatoxins, accumulate through the food chain, from small herbivorous fish grazing on the coral reefs to organs of the bigger carnivorous fish that feed on them.

Metrics and numeric limits

The maximum level per kilogram of mollusc flesh for the different toxin groups are as follows:

Saxitoxin (STX) group: ≤ 0.8 mg of saxitoxin equivalent
Okadaic acid (OA) group: < 0.16 mg of okadaic acid equivalent
Domoic acid (DA) group: < 20 mg of domoic acid
Brevetoxin (BTX) group: < 200 mouse units or equivalent
Azaspiracid (AZA) group: < 0.16 mg

Key relevant UN convention / multilateral treaty

The Codex Alimentarius Commission (CAC) Food and Agricultural Organization of the United Nations (FAO) and World Health Organization (WHO), (FAO/WHO, 2024)

The Convention on Biological Diversity (CBD) (CBD, 2024)

International Maritime Organization, The International Convention for the Prevention of Pollution from Ships (MARPOL) (IMO, 1973)

Stockholm Convention on Persistent Organic Pollutants (POPs) (UNEP, 2019)

United Nations Oceans & Law of the Sea (UNOLS), The United Nations Convention on the Law of the Sea (UNCLOS) (UNOLS, 1982)

Drivers

The substantial increase in the consumption of the fishery and aquaculture products in recent years, together with globalisation of trade, has increased the potential for human exposure to these marine biotoxins. Monitoring programmes for the toxins and their source organisms, and rapid notification of food safety issues by the authorities is essential to avoid foodborne intoxications. Toxic cyanobacteria can also occur in freshwater, affecting water supplies (He 2016). Extensive environmental monitoring and sometimes seasonal quarantine of a harvest are used to reduce risk of exposure (Sobel and Painter, 2005).

It is difficult to predict when a bloom will develop. Climatic and environmental conditions such as changes in salinity, rising water temperature, and increased nutrient levels and sunlight can influence population growth. Other drivers of marine toxins include climate change and ballast water discharge. Rising sea temperatures and changes in ocean circulation patterns cause warmer temperatures and altered currents can enhance algal growth and toxin production (EPA, 2024). Ships discharging ballast water into oceans and seas introduces non-native, potentially toxic algal species into waters (IMO, 2019). Excessive nutrients can also lead to the proliferation of toxin-producing algae (NOS, 2023).

Impacts

Impacts of marine toxins include human health effects such as gastrointestinal, neurological, and cardiovascular issues and in severe cases, death. Marine and freshwater ecosystems are also affected, including disruption of food webs, fish kills, and loss of biodiversity. Economic impacts include loss of revenue from fisheries, tourism, and aquaculture, as well as increased public health costs (FAO, 1999).

Multi-hazard context

The figure below summarises common interactions between marine toxins and other hazards. This information should be used with caution and not be solely relied upon in Disaster Risk Management, particularly as some interactions may not have been included. Note that hazardous events occurring together or locally in space or time may not necessarily cause, amplify or be otherwise related to each other. Specific examples of multi-hazard context can be found in the ‘Hazard drivers’ and ‘Impacts’ sections above.

Multi-hazard diagram

Risk Management

Risk Management includes the establishment of national monitoring programmes for marine biotoxins and their source organisms, by methods such as regular sampling and testing of water and seafood for toxins, and their continuous update to include new and emerging toxins when necessary (WHO, 2017). Implementing regulatory limits and standards, as well as informing the public about risks and safe consumption practices, are risk management protocols that should be implemented. Other mitigation strategies include reducing nutrient runoff through best management practices (BMPs) in agriculture, and improving sewage treatment; also reducing greenhouse gas emissions, protecting marine environments (EPA, 2023; UNCC, 2024).

Monitoring

The section and the table below offer an overview of monitoring marine toxins. This information can be used for forecasting within a national early warning system (EWS). Since EWS capacities and processes differ across countries, the most current and specific information regarding EWS should be obtained from the appropriate national or regional agency/authority responsible for disaster management.

Which institution(s) produce(s) Disaster Risk Data/Information?	European Commission (EC); National Oceanic and Atmospheric Administration (NOAA); environmental agencies
How is the Hazard Observed/Monitored/Forecast?	Monitoring and remote sensing; prediction modelling; communication