In the middle of the reeds, a piece of red plastic encysts in the earth around the roots of the plants. Upstream of the Tancarville bridge (Seine-Maritime), near the mouth of the Seine, the waste carried by the river has penetrated the thickness of the bank. This waste has a story. The label EF56308 that it bears attests to this: it “was thrown on September 26, 2018” in Rouen, 70 kilometers upstream from the river estuary.
Tossed around for years
Romain Tramoy is formal because it was he who “released” him more than four years ago. This geologist, a sediment specialist, has been conducting unprecedented experiments for years to study the crazy life of plastics in the Seine and understand not only how many end up there, but also where they come from and how they travel.
Its results are alarming: certainly, there are proportionally few large plastics (more than 5 mm) in the Seine, given the 16 million inhabitants of the basin. But these are tossed about by the currents, sometimes for years, without all reaching the English Channel, creating in the estuary “a machine for manufacturing microplastics”.
“In a country like France, where waste collection is organised, and where the sewage system works – except for overflows linked to storms, for example – there is much less plastic in the rivers than in countries without collection. , and with steep gorges, as in Southeast Asia for example, ”says Romain Tramoy, along a bank yet strewn with waste, in Yville-sur-Seine (Seine-Maritime).
But the waste “remains for years” going “from one bank to another”. “No waste goes to the sea in a linear way”, says the researcher in paleoclimatology at the University of Paris-Est-Créteil. “They go up and down several times with the tide. “Plastics, “you find them everywhere, macro, micro, even nano…”
100 to 200 tons per year arrive at the sea
The Seine has its source on the plateau of Langres in Côte-d’Or and flows into Le Havre after having watered the feet of the Eiffel Tower and Rouen. Romain Tramoy inventories the waste in several sites, whether on the bank of Yville, downstream from Rouen, in the bends of the Seine dear to the Impressionists, or along a Normandy bocage landscape.
There are so-called “accumulation” sites, “real waste collection centres”, and others, “dynamic”, where waste “leaves and arrives every day”.
Sometimes, he “tags” the plastics in fluorescent pink or yellow, to find them, perhaps, elsewhere, later. One day in February, on a stony bank, we can make out the different incoming waves. In the “leashes”, branches and driftwood abandoned by the tides mingle various pieces that Romain Tramoy has rightly labeled in the past.
Detergent bottles, cans, yoghurt pots, candy bags, lids, sandals… A Prévert-style inventory of modern consumption. The experiments of his team between 2017 and 2020 have established that, via the Seine, “100 to 200 tonnes of plastic per year arrive at the sea”, much less than his initial assumptions.
Floating booms against… wipes
The Seine is in fact cleaned, in particular, for 40 years, by Vinci Construction Maritime and Fluvial, whose boats take care of 66 km of banks. 26 floating dams are spread over the river as well as the Marne. And associations are collecting on the banks. However, there is still waste. To track them, Romain Tramoy has placed “nets” in Rouen, at the exit of “storm overflows” where the surplus sewer passes after the rains. The contents are washed, dried, weighed and listed in his laboratory.
“There are about twenty different plastics, and two types of waste: those from the road, such as plastic bottles or cigarette butts from the sewers, and those from the toilets,” he says. In the net placed near the Jeanne-d’Arc bridge, in Rouen, between April 14 and May 23, 2022, 44% of the mass of dried waste consisted of wipes, the scourge of wastewater treatment plants.
In Petitville, 20,000 pieces of plastic debris in a square meter
Like an Anthropocene archaeologist, the researcher uses recurring products to date flows. One of his favorite markers is “the tube of Microlax”, a laxative drug often flushed down the toilet, found in abundance. This allows dating, “almost like carbon 14”, thanks to the expiry dates of the tube.
At La Chapelle-Gravenchon (Seine-Maritime), at a place called Petitville, near the petrochemical plants, the road winds between flat fields and Norman farms. Reedbeds line the towpaths. There, the researcher discovered an astonishing area, regularly flooded in winter, where a very dense stock of corks, lighters, cotton swabs mixed with snail shells and small vegetable waste, all in the process of fragmentation. “In 2018, we took a square meter of soil in this area, there were 20,000 different pieces of debris weighing a total of 4 kg, including 10,000 new industrial plastic pellets”: the equivalent of “decades of accumulation”.
An earthworm pushes its way through a plastic cylinder. A “kiki” head, a famous doll from the 80s, sports a green moss hairstyle. Plastic is now part of nature.
letelegramme Fr Trans