four questions about the last “planetary limit” crossed by humanity

“We suffocate from our chemicals and plastics.” Here is the shock message written on Twitter by Olivier Fontan, former director of the High Council for the Climate, on January 18. He was reacting to the Stockholm Resilience Center announcement. The Swedish authority affirmed, on January 18, that we had officially crossed a fifth “planetary limit”. (document in English), that of “the introduction of new entities into the biosphere”. Franceinfo details the issues and consequences of this announcement.

1What is a “planetary boundary”?

This scientific notion was created in 2009, as explained Nature (article in English) and was supported by the Stockholm Resilience Center. It was then taken up by the UN and the European Commission. In total, nine “planetary boundaries” have been defined by the Swedish institution: climate change, erosion of biodiversity, disruption of biogeochemical cycles of nitrogen and phosphorus, changes in land use, ocean acidification, global water use, stratospheric ozone depletion, increased aerosols in the atmosphere and the introduction of new entities into the biosphere, as explained by franceinfo in this video.

“The concept of ‘planetary boundary’ is the idea that if the planet crosses a certain threshold in terms of pollution, we will have a change in the state of the planetary ecosystem”, explains to franceinfo Natacha Gondran, co-author of the book planetary boundaries (La Découverte editions, 2020). “This new state will probably be much less pleasant for humans than the state we know with the Holocene, the geological era that began 10,000 years ago”, continues the professor of environmental assessment at the School of Mines in Saint-Etienne (Loire).

Until now, four limits out of nine had been crossed: climate change, erosion of biodiversity, disruption of the biogeochemical cycles of nitrogen and phosphorus, changes in land use.

2What does the last “planetary limit” exceeded represent?

The last to be shattered is “the introduction of new entities into the biosphere”. More simply, we also speak of “chemical pollution” or even of “plastic pollution”. “These are elements introduced by man, which do not exist in the natural state”, summarizes Natacha Gondran. “The most serious is plastic packaging, hence the importance of reducing single-use plastic”, slips Pascale Fabre, research director at the CNRS and director of the Polymers and Oceans research group.

“In the plastic, there is the polymer, its main constituent, but also all the additives which are much more soluble and harmful chemicals.”

Pascale Fabre, director of the Polymers and oceans research group

at franceinfo

These additives can be anti-UV, so that the plastic does not deteriorate in the sun, or even “flame retardants”, which prevent the plastic from catching fire, specifies the physico-chemist to franceinfo. They constitute, according to the specialist, “a big problem because manufacturers do not necessarily give their exact composition”.

The crossing of this “planetary limit” is not surprising. “Given the increase rates of chemicals and plastics, this is not a surprise”, estimates with franceinfo Carlos Marques, researcher at the CNRS and the University of Strasbourg. In 2016, humans dumped 11 million tons of plastic into the oceans every year. A number that continues to rise. “With current policies, the amount of this urban solid plastic waste is set to double by 2040, the amount of plastic released into the oceans is expected to almost triple and the amount of plastic in the oceans is expected to quadruple”, writes the UN.

3What happens when a “planetary boundary” is crossed?

Passing a “planetary limit” does not translate into a sharp and clear swing. “It’s not changing overnight. There’s going to be a whole bunch of little signals, early warnings”, explains Natacha Gondran. Above all, crossing a “planetary limit” is considered irreversible, she insists.

“If we cross a ‘planetary limit’, we can’t go back. It’s too late. We’re going to have runaway phenomena, acceleration. That means we have to adapt.”

Natacha Gondran, engineer and professor of environmental assessment

at franceinfo

This phenomenon of runaway, the scientists note it with the global warming which accelerates, accentuates and worsens.

>> Climate change: what to remember from the sixth report of the IPCC experts

4What are the consequences of this chemical and plastic pollution?

on aquatic environments. According to the French Research Institute for the Exploitation of the Sea (Ifremer), 95% of plastic waste floating on the surface of the water ends up in the seabed. For the latter, it is already too late: it is no longer possible to collect them because it would be too expensive, said, in February 2021, researchers from the Polymers and Oceans research group, reported France 3 Bretagne. Plastic has even become a new type of sediment. Researchers from the Commonwealth Scientific and Industrial Research Organization (CSIRO), the Australian government agency for scientific research, estimate that the seabed of our planet is covered with 8 to 14 million tonnes of microplastic, reported the site Futura Sciences , in October 2020.

If images of plastic waste on the surface of the oceans have gone around the world, and sea turtles are known to choke on plastic bags that they confuse with jellyfish, a large part of the problem is indeed invisible to the naked eye. It comes from the degradation of plastic in water which therefore becomes microplastic then nanoplastic, pieces whose size is less than a thousandth of a millimetre.

In the Seine estuary, the first study on microplastic pollution, relayed by France 3 Normandie, found up to 45 particles per cubic meter of water, and 300 to 3000 microplastics per kilo of sediment in 2021 The researchers also found, on average, one microplastic fiber per gram of mussel flesh.

On the floors. The situation is also dramatic for soils. The plastic used for crops, like the use of a simple tarpaulin, has long-term consequences, notes Thierry Lebeau, professor at Nantes University, attached to the Laboratory of Planetology and Geosciences. In addition to market garden soils, he mentions landfills and urban soils, which are “mixtures of natural soils with fill and waste”.

As in the oceans, the countless pieces of plastic present in the soil are degrading into smaller and smaller elements. They can then be found in earthworms and other organisms, illustrates this specialist in soil pollution. There can also be an exchange of these degraded plastics between soils and water, from rivers to seas and oceans.

Regarding chemical pollution, Thierry Lebeau believes that “the pressure is important” on land used for cultivation. “Viticulture is 3% of French agricultural land, but it is 20% of sales of phytosanitary products in France”, illustrates the scientist. A concentration that weakens soil health.

On humans. This time, the effects of this pollution are still little known. “Research is just beginning in this area, explains Pascale Fabre, while recalling that microplastics have been discovered in human placenta.

Carlos Marques, researcher at the CNRS, worked on “the hidden threat of oligomers”, these elements chunits which consist of a small number of units. He showed, in 2021, that microscopic residues from polystyrene were capable of affecting the functioning of our cells by becoming lodged in the membrane layers. “It’s serious because it’s generic, insists the scientist, all cells have membrane walls. We are made of cells.” Potentially, it could disrupt neuronal or intestinal cells, or cells in any other part of the body. His next work should investigate the speed and ease with which oligomers enter cells. It would also be necessary, according to him, to carry out measurements in order to be able to quantify the oligomers in living beings.

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