The oceans are struggling with plastics

*Ifremer : French national institute for ocean science and technology

Everywhere in the ocean 

Today, this reality is not immediately obvious: we often only worry about the macro plastics visible to the naked eye, which in the end represent "only" 10% of the plastic waste found in the oceans. The rest is made up of microplastics, i.e. fragments of less than 5 millimetres, equivalent to the size of a round grain of rice, or even nanoplastics with a diameter of no more than 1 micrometre, i.e. 10 times smaller than the diameter of a human hair, to give an order of scale. At this infinitesimal size, "these particles are even present in the air and sent back into the atmosphere by sea spray". 

Most plastic washed is washed from land to sea  

If we want to trace the origins of this plastic, we need to look to the land, where most of the plastic waste originates, carried by the rain into rivers. Once in the water, some macro-waste is deposited on sediments. Some underwater canyons are literally covered in plastic bottles, as shown by the first video images of this pollution analysed in 2021. Others set off on a long journey of several months around the globe and gather in gyres, the gigantic oceanic eddies created when currents converge, at the intersection of which the famous plastic 'continents' are formed. It is the fragmentation of this macro-waste, particularly under the influence of water and UV radiation, that gives rise to micro- and nanoplastics. However, some of this waste ends up directly in the environment in the form of microplastics, such as textile fibres from washing machines, plastic microspheres, a raw material for the plastics industry, tyre fragments and so on. 

The Mediterranean holds one of the records for the highest microplastic contamination, while Asian areas such as the Bay of Bengal are the most affected by macro-waste. 

Highly toxic for the ecosystem 

This plastic 'soup' is not only indigestible, it is downright dangerous for marine fauna. The first direct impact is the risk of entrapment, strangulation or obstruction of the respiratory tracts of marine animals by macroplastics. We all remember the images of turtles struggling with plastic bags! There is also the 'raft' effect for an opportunistic population of bacteria, some of which are potentially pathogenic, viruses and fungi that live on pieces of plastic floating for long-distance crossings. Species have been seen to travel from Japan to the USA using this mode of 'transport'. These arrivals are likely to upset the balance of communities, sometimes to the point of becoming invasive species. 

Even in the brains of fish  

‘Another indirect consequence of ingesting plastic is that it alters the feeling of satiety in animals, resulting in delayed growth and reduced immune defences. When ingested by living organisms, plastic releases chemical substances such as phthalates and bisphenol, which are endocrine disruptors,’ explains Arnaud Huvet. In the case of our study model, the oyster, we were able to observe experimentally the effects on reproduction, which are then passed on to the next generation. We have also been able to show that ‘new’ plastic has more harmful effects than used plastic due to the release of chemical molecules. Finally, laboratory studies have shown the presence of nanoplastics in the circulatory system of shellfish or fish brains, leading to changes in their behaviour, which is important for feeding, but also in their strategy for escaping predators’.  

Ocean racing allows data collection 

Aware of this largely invisible pollution, many Vendée Globe skippers have been helping  scientists to draw up a sad inventory of plastic contamination at sea, taking advantage of their passage through little-frequented areas. ‘Since the Vendée Globe 2020, we have formed a partnership with yachtsman Fabrice Amédéo, who has installed a multi-sensor oceanographic instrument on board his IMOCA yacht, capable of taking samples of microplastics of different sizes (300, 100 and 30 microns) every 24 hours,’ explains Enora Prado, a researcher in analytical chemistry at Ifremer's Detection, Sensors and Measurements laboratory. ‘This type of association with ocean racing skippers is very interesting from a scientific point of view because, in the case of the Vendée Globe, the sailors are carrying out a complete circumnavigation of the oceans, whereas oceanographic campaigns have a much more limited field of exploration, for reasons of cost. Unlike other types of vessel, there is no risk of contamination from dirty water being discharged from the yachts, so we can be sure of taking high-quality samples. What's more, each edition offers the possibility of regular monitoring every four years. Lastly, the competitors are taking less-travelled routes, enabling us to collect data in less-studied areas such as the Indian Ocean. Another benefit of this collaboration is that we have greatly improved and automated our methodology. There are three scientists involved in the laboratory and we are now analysing 30 particles per hour, compared with 80 measurements per day in 2020. It's taken time to standardise our process, but we've become much more efficient’.  

In the wake of the ocean races, there are spin-offs other than sporting ones, with scientific knowledge accelerating as the miles are covered.