Sunlight makes plastic in the oceans “invisible”.
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Our planet’s oceans are home to over 150 million tons of plasticto which we add an amount between 5 and 13 tons: a full-blown emergency, in short, which creates problems for marine life, the economy, human health and the climate. Given all its implications, the question is much studied by scientists: a new work, conducted by a group of experts from the Royal Netherlands Institute for Sea Research and published on Marine Pollution Bulletinshowed that the sun also plays a role in plastic pollution.
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In particular, the scientists say, the ultraviolet part of solar radiation is capable of shredding plastic and microplastic into even smaller fragments – the so-called nanoplastic – which are distributed along the entire height of the water column, thus “disappearing” from the surface.
“About two percent of visible plastic, the one that floats,” he explains Annalisa Delreone of the authors of the paper, “disappears from the surface of the sea every year due to the effect of sunlight. It may seem small, but over the years the amount begins to become substantial. The data we have examined show that sunlight could have degraded a considerable amount of all the floating plastic that has been dumped into the oceans since the 1950s.”
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The findings of Delre and colleagues’ study could help resolve the so-called “missing plastic paradox”: from the development of plastics to today it is estimated that around 9 billion tons have been produced, and of this enormous quantity only a minimal fraction has been recycled or incinerated; most of it ended up in landfills or in rivers and seas, where natural agents – including, to be precise, also solar radiation – have broken it up into ever smaller fragments. This continuous process of crushing and dispersion means that much of the plastic poured into the water is difficult to trace and even seems to “disappear”.
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Of course – nothing is created and nothing is destroyed – this is not the case: a scientific expedition conducted in 2016 by a team of experts who scoured the depths of theAtlantic Ocean on board the British ship RRS James Clark has revealed that microplastics, unlike larger debris which tend to accumulate on the surface and in more or less delimited areas, are distributed more homogeneously, both geographically and in depth of the ‘water, and therefore effectively they are all therealthough harder to see.
Delre’s group, in fact, tried to understand if and how much sunlight played a role in this apparent disappearance of plastic. To do this, he placed small plastic fragments in containers filled with sea water, and then exposed them to artificial lighting similar to sunlight, finally analyzing the gases and compounds dissolved in the water. From their measurements, the researchers deduced that at least 1.7% of visible microplastics degrades each year due to the effect of sunlight: most of it fragments into smaller pieces, the nanoplastics; a smaller portion of the nanoplastics is then attacked and further degraded by bacteria, an even smaller portion is converted into carbon dioxide.
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Putting it all together, the scientists estimated that sunlight might have transformed about one-fifth of all floating plastic released into the ocean: “With our calculations,” says Helge Niemann, another of the authors of the study, “we have added an important piece to the complex puzzle of the missing plastic paradox. But there is still much to study: we don’t know, for example, what exactly is theeffect of these nanoplastics on the life cycle of algae, fish and other life forms that inhabit the ocean. We still have to continue to study the matter; and in the meantime we should also stop throwing plastic away, to avoid making the problem even worse”.
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