plastic pollution
General information on plastic
Global plastic production
Since the appearance of plastics in the 1950s, global production has continued to increase. More than half of the world's production was carried out during the 21st century, and it is estimated that this production could increase by another 40% by 2030.
In 2020, global plastic production was estimated at 367 million tonnes, of which 32% was produced by China, 19% by North America, and 17% by the rest of Asia. Europe contributes 15% to this production with 55 million tonnes produced in 2020.
Making plastic from petroleum
Plastic is most often made from petroleum. The oil comes from the sedimentation of plankton which has undergone a transformation during its burial, and finds itself trapped in an underground reserve under a layer of impermeable rock.
To extract the oil, it is necessary to drill a hole and pump the liquid to the surface. So-called “unconventional” oils require more costly extraction techniques and have a heavy environmental impact . The oil is then processed in a refinery and, by distillation, various products are obtained, such as naphtha. The naphtha will then undergo cracking with the aim of "breaking" the large hydrocarbon molecules into small molecules that are easier to work with, such as ethylene. These small molecules will then undergo a polymerization that is to say an assembly in a long repeated carbon chain.
Plastic therefore poses a problem from its manufacture : not only is oil a non-renewable energy (it takes millions of years to reconstitute it), but its process of extraction and transformation into plastic releases CO2 into the atmosphere, contributing to global warming.
The plastic material
Plastic is a very strong, light and inexpensive material to produce, which is why it has been so successful! It is made of carbon polymers whose composition varies between types of plastics, giving them different properties. Chemicals are also added, such as dyes or flame retardants for example. It is thus possible to obtain, from the same raw material, a multitude of different plastics for a multitude of uses.
Note: the chemicals used in their composition are often toxic to ecosystems.
There are 3 main families of plastics:
Thermoplastics which take their shape on cooling but which can be deformed and shaped again under the effect of heat. This property makes them mostly recyclable . Among the thermoplastics, we find in particular the polyolefins which are used in the composition of many bags, toys and packaging (polyethylene (PE) is the most common polymer in this family in the world). There are also polyvinyls (such as PVC) which, for example, make up the synthetic fibers used in the manufacture of clothing.
Thermosets which have a geometrically fixed three-dimensional structure when cooled. They are rigid, brittle, insoluble and infusible, which makes them non-recyclable. Among these plastics are the polyimides used for the manufacture of printed circuits or cables. There are also unsaturated polyesters which are used in the composition of lacquers, varnishes and glues.
Elastomers are able to withstand large deformations before breaking. Elastomers include tire rubber and shoe soles.
The sectors that use the most plastic are the packaging , construction and textile industries .
The main polymers produced are polyolefins : polypropylene (PP) and polyethylene (PE).
Plastic waste treatment
In Europe, of the 29 million tonnes of plastic waste collected in 2020, only 35% was recycled . But of the share of recycled waste, half is exported outside the EU for treatment. The remaining part is either buried (23%) or incinerated (42%), allowing the recovery of energy but which also releases CO2. In 2019, globally, researchers estimated that plastic production and incineration pushed more than 850 million tonnes of greenhouse gases into the atmosphere. By 2050, these emissions could reach 2.8 billion tonnes.
Whether burned or transported to the other side of the world for recycling, the treatment of plastics contributes to global warming.
ocean pollution
The journey of plastic from its use to the ocean
The majority of plastic pollution found at sea comes from land, and it is estimated that ⅓ of plastic waste ends up in nature . Of the cumulative global production of plastic between 1950 and 2017, estimated at 9,200 million tonnes, around 7,000 million tonnes became plastic waste. Of this waste, 1,000 million tonnes was incinerated (14%) and 5,300 million tonnes (76%) ended up in landfills or in uncontrolled waste streams.
2,900 million metric tons are still in use, of which 700 million metric tons (8%) have been recycled. Throughout the life cycle of plastics, the greatest environmental losses occur during use and end of life.
The sources of terrestrial plastic pollution are agricultural soils , the building and construction sector, the transport sector (abrasion of tires on the pavement or painting of road markings), cosmetics and pharmaceuticals and of course the sector of the industry. packaging , of which an estimated 85% globally ends up in landfills or uncontrolled waste streams.
This is where some of the microplastics are generated: these are the primary microplastics , the main sources of which are the washing of synthetic fiber clothing by machine, the abrasion of car tires on the roadway, urban dust. Some cosmetic products also contain microplastics.
Unfortunately, the microplastics found in wastewater are not currently treated in wastewater treatment plants, and end up in the outgoing water, or in the sludge spread on agricultural soils._cc781905-5cde- 3194-bb3b-136bad5cf58d_
Macro-waste and primary microplastics then reach waterways and rivers, and end up in the seas and oceans.
Plastic pollution is not only of terrestrial origin.
Sources of marine plastic pollution include aquaculture , fishing , shipping , and tourism .
The fate of plastics in the ocean
Plastic never completely degrades. Once at sea, under the mechanical action of currents , tides and winds , the action of the sun (photolysis) and bacteria present on their surface, plastic macro-waste will fragment into smaller particles, smaller than 5 mm: microplastics . We then speak of secondary microplastics . There are also even smaller particles, smaller than 1 micrometer, nanoplastics._cc781905-5cde -3194-bb3b-136bad5cf58d_
Plastics accumulate on beaches, in sediments along coasts, or continue to float on the surface of the oceans. It is estimated that out of the approximately 400 million tonnes of plastic produced each year, nearly ⅔ of the synthetic polymers created have a density lower than that of seawater.
We observe areas of privileged accumulation of microplastics at the level of the 5 oceanic gyres , or on certain islands in the middle of the Pacific Ocean. Plastics are also transported via thermohaline circulation currents, for some as far as Antarctica.
With a stock of plastic currently estimated at 1.2 million tonnes , the Mediterranean Sea is also an area of significant accumulation of plastics due to its closed nature and its large watershed.
A significant amount of plastic ends up at the bottom of the oceans, in deep marine sediments or even in ocean trenches . Finally, one of the largest estimated reservoir of plastics is that of the marine biosphere , which consumes microplastics.
Plastics and the ocean, what is the problem?
Plastic pollution, and microplastic in particular, is a major problem for the marine environment and its biodiversity.
Macro-plastics mainly affect macro-fauna. They are responsible for phenomena of obstruction of the respiratory and digestive tracts but also for strangulation , trapping and injuries that can lead to the death of animals. Ghost fishing , caused by abandoned nets or traps, is also a cause of fish mortality.
But the major threat comes from microplastics , since they are easily ingested by organisms and can penetrate tissues. Physical interactions due to the presence of particles in the animal's digestive tract can cause internal injuries and disrupt nutrition and respiration. It has also now been demonstrated that microplastics can transport chemical pollutants (either because they were part of the composition of the plastic originally, or because they are attached to it once in the water) as well as only microorganisms which can be pathogenic (and which we call the “plastisphere”). Once in organisms, certain chemical pollutants can disrupt their functioning (endocrine disruptors, neurotoxic effects, effects on reproduction, on development, etc.)
Microplastics are not completely eliminated by marine organisms, but will partly accumulate in the tissues of the animal throughout its life (kidney, liver for example). When a predator feeds on fish, it will also swallow the microplastics and pollutants that the latter will have accumulated. Thus, at the top of the food chain, among the top predators, the accumulation of microplastics and chemical pollutants is greatest. This phenomenon is called bioaccumulation .
Humans, who eat at all levels of the food chain, also consume microplastics and chemical pollutants accumulated in fish. It is estimated that we consume up to 5 g of microplastic per week , the equivalent of a credit card!
Finally, by disrupting marine ecosystems and in particular phytoplankton, microplastics could also disrupt the carbon sequestration role of the oceans, and thus aggravate global warming!
Sources:
Thompson, RC, Olsen, Y., Mitchell, RP, Davis, A., Rowland, SJ, John, AWG, et al., 2004. Lost at sea: where is all the plastic? Science 304, 838. https://doi.org/10.1126/science.1094559 .
Barnes, DK, Galgani, F., Thompson, RC, Barlaz, M., 2009. Accumulation and fragmentation of plastic debris in global environments. Philos. Trans. R. Soc. London. Ser. B Biol. Science. 364, 1985–1998. https://doi.org/10.1098/rstb.2008.0205 .
Plastics Europe Annual report of Plastics Europe. “Plastics: the facts 2019”. Available from: http://www.plasticseurope.org (Internet, cited April 2020).
United Nations Environment Program (2021). From Pollution to Solution: A global assessment of marine litter and plastic pollution. Nairobi.
WWF. World Wildlife Fund (2019). Plastic pollution: whose fault is it?
Boucher, J. & Bilard, G. (2020). The Mediterranean: Mare plasticum. Gland, Switzerland: IUCN. x+62pp
