Plastic oceans: far beyond what is visible

A little over four years ago, New Zealand researcher Laurent Lebreton revealed in a study.

the area of ​​maximum plastic accumulation in the Pacific was the size of France, Spain and Germany combined.

A little over four years ago, New Zealand researcher Laurent Lebreton revealed in a study that the area of ​​maximum plastic accumulation in the Pacific was the size of France, Spain and Germany combined.

This soup of garbage in the sea contains mainly macroplastic, that is, large-sized plastics, such as bottles, nets and bags, among other examples.

The total extension of this great plastic stain was 1.6 million km² in 2018, a value between four and sixteen times higher than the estimate in 2014 .

Prediction models, even the most optimistic ones, indicate that this value will increase rapidly year by year . Between 8 and 12 million tons of plastic are dumped into the oceans annually , and there is no short-term forecast that this value will decrease, quite the opposite.

However, when comparing the plastic that should be in the oceans as dumped against experimental measurements, the values ​​do not add up. Already in 2004, at the beginning of all these studies, Richard Thompson, father of the term microplastic, raised this question: where is the plastic lost in the ocean?

Plastic invisible to the human eye

microplastic is any plastic fragment or fiber smaller than 5mm at its longest. It may have been manufactured directly in that size or come from the fragmentation of the macroplastic. And let’s think: into how many fragments of 5 mm (or less) can a plastic bottle be divided? Possibly in thousands. This implies that when we focus on studying the existing microplastic in the ocean, its abundance and accumulation zones, the problem also multiplies in the same way.

Macroplastic basically has two accumulation zones: either it floats on the surface, drifting with the currents and accumulating in the great oceanic gyres (as occurs in the Pacific), or it sinks towards the oceanic depths on the seabed, with the Mediterranean Sea as prominent example.

There are some projects worldwide, such as the Ocean Clean Up , that try to clean this macroplastic, although at a very high cost per ton removed from the ocean (5,000 dollars per ton), much higher than the production cost of this material.

The challenges posed by microplastics

Macroplastic in the ocean is a serious problem, but maybe (just maybe) addressable. But what about microplastic? Why does it bring us scientists upside down? What additional problems does it have?

1. It is impossible to clean the entire ocean.

If large plastic is broken into smaller pieces, and we know that there are trillions of large particles in the ocean, how many pieces of microplastic are there? It is not known. But multiply the amount of macroplastic by at least several thousand, as this fragmentation process in the ocean has been going on since the plastic boom in the 1970s.

And another bad news: once they are in the ocean, removing them effectively is not feasible, they are too small and too numerous. You can catch the biggest plastic, but you can’t filter the entire ocean to remove the smallest.

2. It causes serious effects on the ecosystem

The damage that plastic bags or fishing nets cause to marine fauna is well known, but what impact can such small fragments have?

In smaller organisms, not only birds or fish, but also organisms of several centimeters or millimeters (depending on the type) such as zooplankton, they can cause choking or death by starvation by filling the digestive tract with plastic.

On the other hand, marine microplastic has a mixture of chemical compounds and some of them can be harmful to the environment and the living beings that inhabit it.

3. Accumulates Other Chemical Compounds

Plastic itself is a basic chemical compound (such as polyethylene, among others) plus a series of additives, some of which have a detrimental effect on certain organisms (such as mammals), such as bisphenol A and phthalates .

In addition, since the microplastic is in the middle, a lot of extra chemical compounds adhere to its surface , such as pesticides, PCBs and hydrocarbons, which, being hydrophobic and having no affinity for water, feel “more comfortable” next to plastic. .

5. It is transported far and deep

Microplastic is transported in the oceans: it is a passive object that is dragged along by ocean currents. But in the sea there are not only surface currents. The ocean moves in different layers, each one at a different depth, even some thousands of meters deep, transporting the microplastic present.

In the Canary Islands, for example, we have evidence of the arrival of a large amount of plastic on the coasts . Due to the position of the islands, the sea brings plastic from very remote regions, even from the other side of the Atlantic.

6. We do not know where it is “hiding”

Like macroplastics, microplastics can accumulate on the surface (if they float) and also on the seabed (if they sink if they are denser than seawater). But this happens mainly for the microplastic that measures between 1 and 5 mm.

Microplastics smaller than 1mm can “hide” in the deep ocean, at any depth, anywhere . They are so small that their density does not influence whether they float or sink. They move rocked by the current, dominated by it, like a feather displaced by the wind. If there is 1,332 million km³ of water in the ocean, there is plenty of space to hide. And they’ve been playing hide-and-seek for 50 years.

How much microplastic is hidden? Is this the fraction that R. Thompson has been looking for for almost 20 years? We do not know yet.The Conversation

Daura Vega Moreno , Associate Professor PhD, University of Las Palmas de Gran Canaria

This article was originally published on The Conversation . Read the original .