Harmful algal blooms, a toxic threat.

In the water there are invisible algae to our eyes and under certain conditions are a deadly danger.

Cyanobacteria or blue-green algae are microorganisms with characteristics of both algae and bacteria. Under favorable environmental conditions such as temperature or nutrient availability, a phenomenon known as “algal blooms” or “bloom algae” occurs, which is the excessive growth of a microalgae, affecting the water quality and its use.

El Pañe reservoir Arequipa, Peru. Source: TOXICROP project.

The factors that favor the development of algal blooms are the following:

• Eutrophication of aquatic ecosystems, which consists of an increase in the concentration of nutrients, mainly nitrogen and phosphorus, which generally come from agricultural, industrial, and domestic activities.
• Long residence time of water within an ecosystem, favoring the dominance of cyanobacteria over other microalgae.
• Natural factors such as temperature increase, pH variations, light intensity and low water turbulence are very important.

Cyanobacterial blooms can cause problems in water quality due to their rapid growth and abundance. In addition, they generate excess biomass, causing physical, chemical, and biological changes in the ecosystem that can produce a large number of adverse effects on this resource. One of the most important aspects is their ability to produce toxins that have serious consequences for public health and animal health. It is estimated that more than 50% of algal blooms turn out to be toxic.

Algal bloom in El Pañe reservoir, Perú. Source: TOXICROP project

The toxins produced by cyanobacteria are known as cyanotoxins and can be classified according to the effects they produce:

• Dermatotoxins: they are not lethal to the organism, but cause skin irritation on contact.
• Neurotoxins: act on nerve impulse transmission and can cause death by respiratory failure, as a consequence of muscular paralysis.
• Hepatotoxins: cause the most common type of poisoning related to cyanobacteria and acute lethal poisoning. They produce liver damage that can even lead to death by bleeding. In concentrations non-lethal to these toxins have been attributed a carcinogenic effect.

In case of suspected cyanobacterial bloom, caution should be applied, assuming it is toxigenic until proven otherwise. The work protocol should be applied, it consists in periodic sampling, microscopic analysis, toxicity testing and if the toxic bloom is confirmed, a set of measures must be deployed to prevent access to people and animals, as well as limit its use.