• Recently installed, the hydrogen sulfide sensors exceeded the alert threshold in Hillion, in the Côtes-d'Armor.

  • This potentially deadly gas is generated by rotting green algae washing up on Brittany's beaches.

  • The network of sensors aims to protect populations but also to provide more transparency on the dangerousness of the most affected sites.

The sensors have already sounded.

Installed at the beginning of July on the coasts of northern Brittany, the devices for measuring hydrogen sulphide emanations issued their first alert.

This potentially deadly gas is generated by rotting green algae.

He has already killed several animals in Brittany, perhaps even men.

On Wednesday, the alert threshold was exceeded for the first time since the installation of the 12 sensors in early July.

On the beach of Saint-Guimond, in Hillion (Côtes-d'Armor), a reading showed a concentration of 1.565 ppm (part per million) overnight from Tuesday to Wednesday.

A figure that exceeds the threshold set at 1 ppm by the High Council for Public Health and which has led to the sector being placed on alert for at least two days.

The Côtes-d'Armor prefecture recalls that it is necessary to "stay away from green algae stranding areas" and to "respect the access bans" to the sites concerned.

Concentrations have since fallen.

The fear of massive strandings this summer

Reinforced at the beginning of the summer, the measurement network piloted by the Air Breizh association now has twelve sensors distributed in different sites regularly polluted by green algae.

After a calm winter and a very warm spring, the stocks of green algae present along the coast of Brittany were very high this year.

Specialists feared that the strandings would be substantial this summer, especially in the bay of Saint-Brieuc, which has been particularly affected in recent years.

Pinned by the Court of Auditors and then by the Senate, the plan to combat green algae was deemed "largely insufficient" by the supervisory authorities, who invited the State and the communities to put more resources into treating this scourge. which has been rotting on the beaches of Brittany for forty years.

A new plan has been launched for a period of five years.

In particular, it aims to reduce nitrate inputs into rivers, which cause nitrogen concentrations to explode in the shallow bays of the Brittany coast.

The spreading of slurry and the use of phytosanitary products by the agricultural sector are particularly targeted.

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  • Planet

  • reindeer

  • Saint Brieuc

  • green algae

  • Pollution

  • Air pollution

  • Agriculture

  • Brittany