Plastic oceans: far beyond the visible

Just over four years ago, New Zealand researcher Laurent Lebreton showed in a study that the area of ​​maximum plastic accumulation in the Pacific Ocean is equal to the area of ​​France, Spain and Germany combined.

This soup of garbage in the sea contains mostly macroplastics, i.e. large-sized plastics such as bottles, nets and bags, among other examples.

The total extent of this massive plastic patch was 1.6 million km² in 2018, four to sixteen times the 2014 estimate.

Predictive models, even the most optimistic ones, show that this value will increase rapidly from year to year. Between 8 and 12 million tons of plastic are dumped into the oceans every year, and there is no short-term forecast for a decrease in this figure, quite the contrary.

However, when comparing the plastic to be dumped into the oceans with experimental measurements, the numbers don’t add up. As early as 2004, at the start of all this research, Richard Thompson, the father of the term “microplastic”, raised this question: where is the plastic being lost in the ocean?

Plastic invisible to the human eye

Microplastic is any piece of plastic or fiber less than 5mm in length. It could have been made directly in this size, or it could have arisen from macroplastic fragmentation. And let’s think: how many fragments of 5 mm (or less) can a plastic bottle be divided into? Perhaps in the thousands. This means that when we focus on studying the existing microplastics in the ocean, its zones of abundance and accumulation, the problem also multiplies in the same way.

Macroplastics basically have two zones of accumulation: either it floats on the surface, drifting with the current and accumulating in the great oceanic gyres (as happens in the Pacific), or it sinks into the ocean depths on the seafloor, with the Mediterranean Sea in the foreground. . example.

There are several projects around the world, such as Ocean Clean Up, that are trying to clean up this macroplastic, albeit at a very high cost per ton removed from the ocean ($5,000 per ton), far exceeding the cost of this material.

Problems associated with microplastics

Macroplastics in the ocean is a serious problem, but perhaps (only may be) solvable. But what about microplastics? Why does this turn us scientists upside down? What are his additional problems?

1. Cleaning up the entire ocean is impossible.

If large plastic is broken into smaller pieces, and we know that there are trillions of large particles in the ocean, then how many pieces of microplastic are there? This is unknown. But multiply the amount of macroplastic by at least a few thousand, because this process of fragmentation in the ocean has been going on since time immemorial. boom plastic from the 70s.

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

2. Seriously affects the ecosystem

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

In smaller organisms, not just birds or fish, but organisms as small as a few centimeters or millimeters (depending on the species), such as zooplankton, they can cause suffocation or starvation by filling the digestive tract with plastic.

On the other hand, marine microplastics contain a mixture of chemical compounds, some of which can be harmful to the environment and the living creatures that inhabit it.

3. Accumulates other chemical compounds

The plastic itself is a basic chemical compound (such as polyethylene) plus a number of additives, some of which have harmful effects on certain organisms (such as mammals), such as bisphenol A and phthalates.

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

5. Transported far and deep

Microplastic is transported by the oceans: it is a passive object carried along by ocean currents. But there are not only surface currents in the sea. The ocean moves in different layers, each at a different depth, even several thousand meters, carrying the microplastics that are present.

For example, in the Canary Islands, we have evidence of the arrival of a large amount of plastic on the coast. Due to the location of the islands, the sea brings plastic from very remote regions, even from the other side of the Atlantic.

6. We don’t know where he is “hiding”

Like macroplastics, microplastics can accumulate on the surface (if they float) as well as on the seafloor (if they sink, if they are denser than sea water). But this happens mainly for microplastics ranging in size from 1 to 5 mm.

Microplastics smaller than 1 mm can be “hidden” in the ocean depths, at any depth and in any place. They are so small that their density does not affect whether they float or sink. They sway under the influence of the current, obeying it, like a feather driven by the wind. If there is 1,332 million km³ of water in the ocean, then there are plenty of places 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 don’t know yet.

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

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

We recommend you METADATA, an RPP technology podcast. News, analytics, reviews, recommendations and everything you need to know about the world of technology.