SAINT-MICHEL-EN-GREVE, France — It should have been a perfect day for Vincent Petit, finishing up an afternoon gallop on a wide expanse of beach along a pastel-colored bay. Instead, he and his mount were sucked into a hole of noxious black sludge.
“The horse and I slid in,” said Petit, a 28-year-old researcher in a state-run virology lab who is trained in veterinary studies. “A horse in that situation is in an enormous panic, but he didn’t have time to struggle.”
Petit said he watched horrified as his horse stopped breathing and died within about 30 seconds, then he himself passed out. Petit was pulled from the mire by a bulldozer shovel after a man who witnessed the accident gave the alert.
The incident July 28 brought attention to a dirty secret on the Brittany coast — decaying green algae was fouling some of its best beaches.
A report ordered by the government after the accident found concentrations of hydrogen sulfide gas emitted by the rotting algae were as high as 1,000 parts per million on the beach where the horse died — an amount that “can be fatal in several minutes.”
There had been signs of a crisis for years in this idyllic corner of Brittany. But scaring away tourists was in the interest of no one, including the farming industry — the region’s economic backbone — whose nitrate-packed fertilizers power algae blooms.
In Brittany’s Cote d’Armor region, conditions are perfect for its spread — sunlight, shallow waters and flat beaches. Chemical and natural fertilizers such as pig excrement, loaded with nitrates and phosphorous, have saturated the land, spilling into rivers and the ocean, feeding the algae that then proliferate.
Harmless while in water, the algae form dangerous gases — notably hydrogen sulfide — when they wash up on land and decay. A white crust forms and traps the gases, which are released when stepped on or otherwise disturbed. Over time, putrefied algae turns sand into a black silt muck.
