Cyanobacteria in fresh water: ANSES makes proposals with a view to harmonising surveillance and control

Today, ANSES is publishing an opinion on the health risks associated with the presence of cyanobacteria and their toxins in recreational water, drinking water and water intended for fishing. This work has been used to update the list of toxin-producing cyanobacteria in fresh water that pose a threat to humans. To harmonise and improve water surveillance, quality monitoring and analysis activities, the Agency is offering fact sheets to aid management of the cyanotoxin risk for the various water uses. It is also providing useful guidance to managers on imposing or lifting bans on freshwater fish consumption in relation to the cyanobacterial blooms that can produce these toxins.

Cyanobacteria: micro-organisms whose spread is becoming a concern

Cyanobacteria are micro-organisms that thrive in terrestrial and aquatic environments, in both fresh and salt water. In favourable environmental conditions (i.e. with regard to temperature and nutrients), they can proliferate rapidly on a massive scale, sometimes in just a few days. This is known as an algal bloom. In some cases, these blooms lead to a change in the colour of the water (red, green, etc.), a foul odour and/or the accumulation of cyanobacteria on the water surface.

They are being seen more and more frequently on all continents. This is becoming a growing international concern because of the ecological, health and economic consequences of their proliferation.

In the aquatic environment, cyanobacteria can be divided into two groups according to how they live:

  • planktonic cyanobacteria remain suspended in the water column;
  • benthic cyanobacteria grow on the bottom of water courses, on mineral substrates (boulders, pebbles, sand, sediment, etc.) and even on the surface of aquatic plants.

In temperate climates, cyanobacterial blooms occur more often in the summer and early autumn, when there is abundant sunshine and water temperatures are above 20°C. In some cases, they may be observed as early as the spring. On rare occasions, longer lasting blooms are seen throughout the year, even in winter.

In tropical and subtropical climates, given the right conditions for their growth, blooms can be observed throughout the year.

Blooms are regularly accompanied by the production of cyanotoxins, of which the most monitored in fresh water are microcystins, a family of over 250 toxins. These can have consequences for health. In recent years, episodes of contamination by other cyanotoxins, in particular anatoxins and saxitoxins, have also been reported in metropolitan France. The toxicological data on cyanotoxins have been updated, enabling toxicity reference values for three of them (microcystin-LR (PDF), saxitoxin (PDF) and cylindrospermopsin (PDF) (in French)) to be determined.

Reduce nutrient inputs in water to protect ecosystems from cyanobacteria

When fresh water has been enriched by anthropogenic inputs of nitrogen and phosphorus, it becomes a particularly favourable breeding ground for planktonic cyanobacteria. Considering that the effects of climate change also play a role in the duration and intensity of their proliferation, human activity – both urban and rural – remains a major contributor to their development.

In order to limit surface water contamination and protect or even restore aquatic ecosystems, ANSES therefore stresses the need to control and reduce nutrient inputs (nitrogen and phosphorus) in water affected by human activities (for example, due to livestock manure, compost, sewage sludge, fertiliser applied to agricultural soil, insufficiently treated wastewater discharges, or leaching from soil during heavy rainfall).

Harmonise surveillance and monitoring of drinking water and recreational water

The data provided by local health authorities, operators of water supply facilities and managers of bathing and recreational waters show the lack of uniformity in current surveillance and control practices. The Agency emphasises the need to harmonise these surveillance and monitoring practices through the establishment of national standards. The surveillance strategy for resources used to produce drinking water should be based on routine monitoring by the water body manager. In the event of a suspected cyanobacterial bloom, this monitoring should be reinforced. If a bloom is actually observed, this monitoring should be accompanied by management measures to limit user exposure (improvement of the water treatment system, restriction of aquatic activities, ban on fishing). 

Freshwater fish consumption: acquire more data to assess dietary exposure of consumers to cyanotoxins

The Agency's 2016 (PDF) literature review on cyanotoxin contamination in freshwater fish has been updated (in French). There is still not enough knowledge about rates of cyanotoxin contamination and elimination by fish or the link between cyanobacterial blooms and the level of fish contamination. The Agency reiterates its recommendation on the need to acquire more data on the subject. In order to be able to assess the dietary exposure of consumers, the Agency also stresses the importance of obtaining data on contamination of freshwater fish by cyanotoxins in France.

Nevertheless, the Agency offers useful guidance to managers on imposing or lifting bans on freshwater fish consumption in relation to cyanobacterial blooms.

Lastly, the Agency points out that to limit consumer exposure to cyanotoxins, it is necessary to remove the head and guts of fish before consumption (or before freezing) and to avoid consuming small freshwater fish whole (fried).