The alert threshold for exposure to hydrogen sulphide, a potentially deadly gas emanating from the putrefaction of green algae, was exceeded early Wednesday July 20 on a beach in the bay of Saint-Brieuc, announced the prefecture of Cotes d'Armor.
“
As part of the monitoring of the health risk of exposure to hydrogen sulphide emanating from the putrefaction of green algae, it was detected in the commune of Hillion on the Saint-Guimond site that the alert threshold was exceeded
“, indicates the prefecture.
This is the first time that an alert of this type has been triggered, since the establishment of a network of sensors on several Breton beaches.
Measurement points in seven Breton bays
Present at sea in their natural state, green algae began to multiply more than 40 years ago on certain Breton beaches, where they are nourished by nitrates spread by farmers in the fields and whose surpluses are transported by coastal rivers.
The readings, carried out by the Air Breizh air quality observatory, "
reached 1.565 ppm
" (part per million) around 3:00 a.m. Wednesday and therefore exceeded the threshold set by the High Council for Public Health (HCSP). ), at 1 ppm.
Since this summer, Air Breizh has been carrying out hydrogen sulphide readings at 12 measurement points in seven Breton bays from Douarnenez (Finistère) to La Fresnaye (Côtes d'Armor).
An update on the prefecture's website reported a value lower (0.128) than the alert threshold noted at 4:00 p.m., but the sector remains on alert.
Read alsoToxic tropical algae in Europe
Contacted by AFP, the expert sub-prefect "
Water, green algae and agro-ecological transition
" Étienne Guillet confirmed that "
the entire beach
" of Saint-Guimond was "
closed to the public by order of the mayor until further notice
. and that a single peak (readings are taken every 15 minutes) had exceeded the alert threshold overnight from Tuesday to Wednesday.