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The Algae´s Toxic Brews


The poisonous algae contaminate shellfish with toxins that rank among the most potent natural poisons in the world. (Photo credit: M. Caniggia) See photo gallery

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Harmful Algal Blooms, or "red tides" are a good thing gone bad. Most species of algae are not harmful but vital to the food chain, feeding a host of marine life such as oysters and clams. Sometimes, the algae grow extremely fast or "bloom" into thick reddish patches near the surface of the water. But a small number of species produce potent poisons called saxitoxins. When these species "bloom" the results can be deadly. Shellfish filter and absorb the toxic algae. If humans eat the contaminated seafood it blocks the flow of sodium through nerves. Symptoms range from mild discomfort and vomiting, affixation, paralysis, seizures and even death from cardiac and respiratory failure.

Paralytic Shellfish Poisoning (PSP) is the commonest threat to humans eating toxic shellfish. In worse cases, the toxins block nerves in the body that results in paralysis (although the heart and brain still function) before death comes via suffocation. There is no antidote for PSP.

Tierra del Fuego in Southern Chile is the world´s most toxic coastline, followed by British Columbia. Levels of PSP toxins recorded there show as little as 100 grams of meat could kill 16 people.

The HAB phenomenon has dramatically increased in the last 30 years. Scientists do not know for certain why the rash of blooms and poisoning is increasing. One theory is that it is a consequence of global warming.

In some cases HAB outbreaks might be triggered by environmental stresses including human pollution. Before the outbreak in Chile in January 2002, there was a storm followed by exceptionally hot summer days.

Although not well understood, possible explanations as to why HAB occurs relate to human activities and global change issues. For example:

  • Replacing natural wetlands, salt marshes and mangroves with aquacultural ponds (for large scale "fish farming");
  • Accidental introduction of toxic algae via ballast water discharges, as ships move from one country's coastline to the next; and
  • General alterations of costal water quality due to acid rain, deforestation or pollution.

Florence Boisson, Research Scientist at the IAEA´s Marine Environment Laboratory in Monaco says the expanding HAB problem goes hand-in-hand with increasing requests for assistance from countries.

"The IAEA has a clear leadership role in delivering the benefits of the Receptor Binding Assay (RBA) to its 137 Member States, assigning this effort the highest priority under the coastal zone management theme," she said.

IAEA technical assistance is helping China, Indonesia, Malaysia, Pakistan, Thailand, Vietnam, the Philippines, Angola, Namibia, South Africa and Chile to use the RBA as a monitoring system to detect any dangerous blooms. The end goal - to improve public safety worldwide, and give coastal communities the chance to take more control over their future by removing the uncertainty that red tides can bring. -- Kirstie Hansen, IAEA Division of Public Information

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