The rise in the use of plastics has created a substantial increase in plastic waste. Of the 8.4 billion tonnes of plastic produced since the 1950s, around 6.3 billion tonnes have already become waste. With only nine per cent of plastic waste having been recycled, it raises the question – where did it all go? Unfortunately, much of this waste is finding its way into the environment where it breaks down into very small particles – and there are frightening amounts of it.

We do not yet know the full implications of that, but we do know small particles of anything can be harmful to human and ecosystem health. Such environmental plastic not only contains many harmful chemicals, it also picks up anything it comes in contact with such as DDT, heavy metals, mercury and many other pollutants.

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As keen paraglider pilots and offshore sailors, we spend a lot of time in places that should be pristine. But having witnessed plastic litter in the middle of the Pacific Ocean, 1,500 nautical miles from land and in the air when flying, we could see that plastic was becoming a problem. Being pilots, we have a good understanding of weather and how air moves.

We thought that if plastic pollution is in the air in cities, it is very likely that it will be blown to other areas. So, we began our research into microplastic pollution in the French Pyrenees, choosing a sampling site as far away from towns and cities as possible. We used an existing weather station that was already catching rain and snow for mercury and other chemical pollutant research. During the sampling period, the area, 1,400 metres above sea level, was uninhabited and blanketed in snow.

It should have been pristine. The rain and snow samples we captured were filtered, leaving just the solid material, which was rinsed off into test tubes with mild acid to remove any organic material. We then took our samples to the lab in the University of Strathclyde in Scotland. There we used a technique called Raman spectroscopy, named after Indian Nobel Laureate CV Raman, to identify any plastic particles.

We fully expected to find microplastics in our samples but being more than 100 kms away from any towns, which we thought might be a source, we did not expect to find much – an average of 365 particles, per square metre, per day. It was our first proof of atmospheric transport of microplastic. The next logical objective was to look at where it was coming from. Recent research has shown that up to 30 million metric tonnes of plastic is entering the oceans via rivers each year.

We should naturally be concerned with what effect that will have on marine life which we rely on for our food but also our oxygen production. The ocean has traditionally been seen as a resting place for plastic pollution. Once it goes in, it was thought that it would stay trapped in the ocean currents or sink into the ocean’s bottom.

However, the ocean ejects seven giga tonnes of material each year in the form of salt and algae, so we decided to research whether plastic could also be ejected into the atmosphere through a mechanism known as “bubble burst ejection”. “Bubble burst ejection” has been well studied since about the 1980s and is known to eject a great deal of material. When a wave breaks, it pushes air into the water.

The air forms bubbles and rises to the surface. As it does so it collects hydrophobic material on its surface. Once the bubble reaches air, it shatters ejecting nano-sized spray. That still leaves a hollow in the water, which fills rapidly. When the sides come together, it forms a jet of water, which ejects micro-sized matter up to 30 cm into the air where the wind can pick up the material along with the water. Like when you drink soda water, the bubble ejection lifts the liquid up to your nose.

You can see this on a beach in the form of sea spray or mist. Now imagine that on a global scale, on every beach with an onshore wind. For this study we chose a research site on the French Atlantic coast, a location well known for large waves and violent storms. As this research was completely new, we employed two different but well-established atmospheric sampling techniques.

The first being a simple vacuum pump with a glass fibre filter to extract any particles at about the same rate as human respiration during exercise (50 litres/minute). We wanted to measure what a human on the beach would be exposed to under normal conditions, like going for a run. The second technique used a machine commonly known among scientists as a “cloud catcher”, which uses a large fan to draw air over layers of Teflon filaments.

The water droplets stick to the filaments and drain into a glass bottle. We found onshore and offshore winds carrying microplastics but on the last day of sampling, the wind dropped to zero and a sea mist from the surf covered the beach. During that sampling time we found 19 microplastic particles per cubic metre of air. Considering a human breathes around 16 cubic metres of air every eight hours, we are inhaling a lot of microplastics in what we normally think is pure sea breeze.

By taking the estimated marine boundary layer, air mass and a five kms length of beach, we found 136,000 metric tonnes could be blowing ashore every year. Not an insignificant amount and probably a conservative estimate. It is clear that plastic pollution is becoming a serious issue. As yet, we do not have a lot of evidence that it will cause harm, but more research is being published every day pointing to worrisome human and ecosystem health problems. Might there be a threshold where it causes an irreversible effect? If so, will we reach that threshold before we know what level that is?

(The writers are respectively, lecturer and Leverhulme Trust Research Fellow in civil and environmental engineering, University of Strathclyde, Glasgow, UK)