The origin of plastic
Plastic first appeared 60 years ago. What makes this material so unique?
Plastic is a very strong material, made of carbon polymers whose composition varies between different types of plastic, giving them different properties.
There are 3 families of plastics:
Thermoplastics which are capable of being deformed and shaped into different forms when they cool after being subjected to heat. This property makes these types of plastic polymers recyclable. Among the thermoplastics are the synthetic fibres used, for example, in synthetic clothing.
Thermosetting plastics which have a geometrically fixed structure. They are therefore rigid, brittle, insoluble and infusible, making these types of plastics non-recyclable.
Elastomers are capable of withstanding large deformations before breaking. Elastomers include the rubber of tyres and the soles of shoes.
Global plastics production
Since their appearance, plastic production has continued to increase. The latest data from 2018 quantify global plastics production at 360 million tons. Europe contributes 17% of this production with 62 million tonnes produced in 2018.
The largest contributor is China, which alone produces 30% of the world's plastics.
Of all the debris currently recorded, plastic debris are systematically the most abundant (1).
In order to better understand plastic debris in the sea, their location in relation to sea currents and their impact on living organisms, several scientific expeditions have carried out field studies.
Water samples are generally taken from areas of interest,
which are determined in advance by computer models
predicting, among other things, the direction of sea currents.
A recent study has shown a correlation between the quantity of
plastics on the surface, and the presence of anticyclonic and
depressionary currents (2).
We use these studies as basis for our sampling.
Depending on its density, it is usually assumed that the plastic will either float on the surface of the water or sink and settle to the bottom. As a result, very few studies have focused on mapping the plastic in the water column, i.e. the vertical distribution of the plastic in the sea. This is why one of our research areas is focused on the study of the vertical distribution of plastic.
Sampling in the shallow and deep water
Expedition 2021 has teamed up with Sandra DOMENEK, researcher at AgroParisTech, in the Food and Bioproduct Engineering.
Sandra's research focuses on the development of new methods for the identification and quantification of microplastics in seawater. The aim is to enable the development of high-speed methods and research into analytical methods for nano-plastics.
Once these methods have been set up, the aim is to describe the chemical composition of the plastics found on the surface (measured with a manta net) and in the water column (measured with a fermenting net). The main research concerns the composition: does it change according to the sampling location? Does it change with depth?
Finally, an additional part of the project focuses on the degradation of plastic in seawater. How does a macroscopic waste decompose into millions of microplastics?
Surface sampling of the microplastics is carried out using a Manta net (mesh 125 μm) pulled behind the boat for 15 minutes at a speed of 2 knots. A current meter attached to the net will allow us to know the quantity of water filtered by the net. The microplastic recovered measures between 125 μm and 5 mm.
The protocol for the use of the WP2 closing net has been validated by the 2017, 2018 and 2019 oceanographic expeditions. Expedition 2020 is using this protocol to sample the microplastic between 30 m and 80 m depth.
The microplastics recovered measure between 100 μm and 5 mm.
Zettler et Al., 2013 : Life in the “Plastisphere”: Microbial Communities on Plastic Marine Debris
Brach et Al., 2017 : Anticyclonic eddies increase accumulation of micoplastic in the North Atlantic subtropical gyre
Gall et Al., 2015 : The impact of debris on marine life
Galgani et Al., 2014 : Monitoring the impact of litter in large vertebrates in the Mediterranean Sea within the European Marine Strategy Framework Directive (MSFD) : Constraints, specificities and recommendations