In 2013, a schooner named Tara carrying a team of explorers and scientists completed a three-year odyssey across the world’s oceans. The expedition conducted the largest ever census of marine plankton: drifting micro-organisms that generate half of the oxygen in the Earth’s atmosphere.
But on that voyage, researchers found something more than plankton in their nets: they also caught microplastics, particles measuring under five millimeters in diameter that can disperse bacteria and even enter the food chain.
Lisa Weiss, researcher
“We know that in some parts of the Mediterranean, there are as many microplastics as there is plankton,” explains Lisa Weiss, a physicist who is one of the 40 scientists participating in the Tara’s new mission.
Researchers rotate periodically, so that there are only around 14 scientists on board the schooner at any one time. This year, the France-based vessel is traveling along Europe’s coasts to take samples at the mouths of 10 major rivers in order to find the source of the plastic waste that ends up in the sea.
The work is being done in the Thames (England); the Elbe and Rhine (Germany); the Seine, Loire, Garonne and Rhone (France); the Tagus (Portugal); the Ebro (Spain); and the Tiber (Italy). EL PAÍS was invited aboard the Tara during its time at the mouth of the Ebro, in the region of Catalonia.
Europe, say the scientists, is one of the three most polluting continents in the world. Like all garbage, microplastics accumulate in five major oceanic gyres where the sea currents converge: two in the Pacific, two in the Atlantic and one in the Indian Ocean. But these particles are everywhere: they have been found inside the Mariana Trench, 11 kilometers deep into the Earth, and on Mount Everest, at an altitude of 8,000 meters. And now it is thought that they might be in the air that we breathe and in some of the food that we eat.
Weiss is a PhD student at Cefrem, a French research center focusing on the Mediterranean. Her team is trying to put a number on the flow of microplastics that go from land to sea. Right now it is believed that 80% of microplastics in the oceans come directly from rivers, but this is a ballpark estimate, says Weiss.
The mission, named Tara Microplastics, is a joint project of the Tara Oceans Foundation, the CNRS (Centre National de la Recherche Scientifique) and the European Molecular Biology Laboratory (EMBL). Dozens of research centers and sponsoring institutions are taking part. Right now the 120-ton schooner is anchored off the port of L’Ampolla, just a few kilometers from the Delta del Ebro, the estuary where the Ebro River flows into the sea.
Leila Meistertzheim, researcher
At 8am, several researchers climb aboard a rigid inflatable boat armed with bottles, jars, salinity meters and sophisticated filtering nets that will help them collect samples in the estuary. During this part of the mission, Soline Alligant, who is getting a PhD in chemistry from the French center Leesu, is in charge of coordinating the field work.
“We are taking samples from the surface to catch the micro-organisms that live in these waters,” she explains, dipping an eight-liter cylinder inside the river. Then she deploys a funnel-shaped net that she drags behind her for a few minutes to filter large volumes of water and collect the kinds of organisms and plastics that are not in plain view.
All the samples end up inside a freezer bag to keep them cool, then get processed on the ship and sent to a lab in France. The information they provide will tell scientists whether the plastics have traveled a long way, based on the kind of living organisms found on their surface and whether these are naturally present in the Ebro mouth.
“Microplastics act like a raft for micro-organisms,” says Alligant. “This could have environmental consequences, because plastics sometimes carry invasive species or pathogens.” During a previous expedition in the Mediterranean, the Tara found the bacterium that causes cholera, Vibrio cholerae, in microplastics on the French coast.
This is particularly alarming for the toxicologist Leila Meistertzheim, founder of the sustainable development company Plastic@Sea, the only private sector entity to be collaborating on Tara’s mission. She takes samples of trash on the beaches: bottle caps, wrappers, doggie bags with the excrement still inside...
“This is pretty clean compared to the Seine,” she notes. Later she puts on her bathing suit and walks into the sea, feeling with her feet for something that she tied down there a month ago. It’s a small cage with five different types of plastic polymers, such as polyethylene and nylon. Meistertzheim has been planting identical cages in all the estuaries where the Tara makes a stop, always one month in advance.
When the ship arrives, she collects them to analyze the microorganisms that have colonized the surface of each sample. This seeks to find answers to a wealth of questions such as: is the growth of microbes capable of breaking down plastics? Is there a greater concentration of pathogens on the samples? Does each polymer have a specific set of settlers?
The cages also contain mussels, which act as natural water filters that involuntarily trap microplastics in their digestive tracts and can be dissected to find a good inventory of the pollutants in each river. Meistertzheim knows that her mussels suffer from changes to their immune and reproductive systems as a result of the exposure to plastics, although “we don’t know whether the microplastics have a direct effect on human health. We do know that they are a problem for marine ecosystems.”
In the rivers, scientists can observe which particles sink and which remain floating on the surface. Another question is where they originate: the idea would be to stop pollution at the source.
“We used to think that rivers only carried large plastics and that these broke down out at sea,” explains Meistertzheim. “Now we know that’s not true: the rivers are already carrying microplastics that are not caused by degradation. In the Thames, we found 66% of polymers that were only present in the shape of microplastics.” These primary microplastics, which are not the result of degradation and are found in textiles and cosmetics, for instance, are a major source of pollution in themselves.
Although the results of the mission will not be available before late 2019, scientists have already reached a preliminary conclusion: the solutions to sea pollution are to be found on land. Cleaning the oceans is an impossible task, so the most efficient solution is to go straight to the source and stop the flow of garbage into the sea.
English version by Susana Urra.