It is estimated that between 52,000 and 184,000 tons of plastic pellets are dumped into the ocean each year due to poor management in its production and transportation chain. These small spheres, which these days are reaching the Galician coasts, are between 2 and 5 mm in diameter and are generally composed of a high percentage of polymer (polyethylene, polypropylene, etc.) and a lower percentage of additives (stabilizers UV, flame retardants, etc.).
Pellets are solid, persistent, non-soluble, non-emulsifying, non-biodegradable and most are floating.
These particles are generally used as raw materials in the manufacturing of plastic items. In this process, two main phases are differentiated: in the first, the polymer is made (already containing different proportions of additives) and presented in the form of pellets and in the second, starting from these pellets and through different industrial processes (molding, injection, etc.), they are given the final form for use.
In 2019, 460 million tons of plastic pellets were produced and it is estimated that 540 million tons will be produced in 2040 if there are no actions to reduce their production.
The specific composition of the pellet will determine its density and this is what determines its behavior once in the water. If they are less dense than seawater (about 1.025 g/ml), they will float in it, and if they are more dense, they will sink.
In the case of the pellets that have been dumped near the Galician coast, they are polyethylene. This material has a lower density than seawater (around 0.9 g/ml) and, therefore, floats in water and is dragged by currents and tides and can travel long distances in the marine environment.
When they reach the coast, these particles are dragged ashore by tides and waves. The most common thing is to find them mixed with other waste left in the highest area reached by the tide.
Due to their physicochemical characteristics, the pellets can be transported by the wind onto the beach or return to the water with the next tide. It is also possible that due to the effects of the waves or people's own footsteps they could be buried in the sand.
One of the characteristics of plastic material is its high durability. They are materials that resist the passage of time well and are difficult to degradable. If, in addition, as seems to be the case in the case of the material dumped these days, the pellet is treated to prevent degradation by UV rays, it is to be expected that its degradation will be slower.
What usually happens is that they degrade and break down into smaller particles. In this case it is expected that smaller microplastics and finally nanoplastics will form from the pellets.
Any substance, particle or energy that reaches the environment as a consequence of human activity is considered pollution and is, in principle, an environmental problem.
Furthermore, depending on the composition of the specific substance we may have a toxicity problem.
Polymers, in general, are inert materials in principle and hence their low degradability. But the fact that the polymer is inert does not free it from possible harmful effects such as obstruction of the digestive system of animals that ingest them.
On the other hand, in a plastic, in addition to polymers, we have one or more additives that can be more or less harmful depending on its composition. That is why it is important to know the composition of the specific additives in the poured pellets.
Pellets can have several impacts on the marine environment:
But beyond the impact of this specific discharge, which will depend on the quantity of pellets as well as their composition, the important thing would be that we become aware of the environmental impact of microplastics and nanoplastics and begin to take measures to prevent their reaching the environment.
This article was originally published on The Conversation.
Lucía Viñas Diéguez and Jesús Gago are researchers at the Spanish Institute of Oceanography (IEO - CSIC).
