Analysis: we are putting about 8 million tonnes of plastic waste into the ocean but only 1% of this actually resurfaces

Every year, over 300 million tonnes of plastic products are produced globally, and the amount of plastic waste generated is even higher as it accumulates year after year. Around 3% of the global plastic waste generated annually enters the ocean via various channels, including rivers, wastewater systems, fishing activities, and landfill seepage.

Although a significant proportion of plastic waste ends up in landfills, incinerated or illegally dumped, approximately 8 million tons of plastic waste still go into the ocean annually. This number continues to grow every year with economic growth. Plastic is essential and evidentially it saved millions of lives during the recent pandemic through protective measures.

The plastic waste is designed to be virtually indestructible and will persist indefinitely. The world's oceans currently contain five developing garbage patches where all types of plastic, including single-use items, accumulate. The Great Pacific Garbage Patch (GPGP) is the largest of these garbage patches, which contains an astonishing ten times more plastic pieces than stars in our Milky Way galaxy. Despite its name, the GPGP is not a solid mass of garbage, but a vast ocean filled with scattered plastic debris of varying colours, shapes, sizes, and types. In addition to the GPGP, there are four other expanding garbage patches in the world's oceans.

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From RTÉ Radio 1's Today with Claire Byrne, Physicist from the UCD School of Education Shane Bergin on the chemistry and recycling of plastic

Despite our understanding that roughly 8 million tonnes of plastic waste enter the oceans annually, only a small fraction of that waste - a few hundred thousand tonnes - has been located on the ocean surface by researchers. Although this little quantity of plastic is still sufficient to have adverse effects on wildlife, ecosystems, and public health, it represents just 1% of the total amount that scientists estimate is being deposited into the ocean each year. Consequently, the whereabouts of the remaining 99% of plastic debris is a mystery. The missing plastic problem has led scientists to investigate where this unaccounted-for plastic waste may be going. Some potential explanations include:

Imprecise Measurement

Quantifying and monitoring the amount of plastic that enters the ocean and the amount of plastic floating on the ocean surface are both highly challenging endeavours. As a result, it is conceivable that scientists could be miscalculating one or even both of these figures. But the degree of uncertainty in the calculation is much less than the several orders of magnitude to match the missing plastic mystery.

Combined Degeneration

Plastic can be fragmented into smaller pieces called microplastics through photo-degradation, mechanical degradation, and thermal degradation. The "missing" microplastics could have been incorporated into sediments, consumed by organisms, or submerged after fouling. But the plastic in the water degrades at much slower rates than on land due to lower temperature, lower light exposure, lower Oxygen levels, and significant chances of fouling which makes the degradation process much slower and difficult.

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Deep-sea sediments

It is also possible that plastics sink into the deep-sea sediments. Evidence suggests that microplastics are up to four orders of magnitude more prevalent (per unit volume) in deep-sea sediments than in plastic-polluted water surfaces. Furthermore, microplastics have been discovered in the Mariana Trench, which is the deepest part of the ocean. But macro plastics persist on the ocean's surface for decades without being broken down. Scientists have found large plastic objects dating back to the 1950s and 1960s.

Suppose the disparity between the amount of plastic waste estimated to enter the ocean and the quantity that has been identified is not due to calculation uncertainty, and the plastics are not degrading more quickly than anticipated. In that case, the question remains: where is the missing 99% of waste going?

Read more: How plastics get made

Recent findings have shown that the new plastic is much closer than previously thought, as evidenced by the production date of plastic debris discovered on shorelines. However, it is uncertain whether the amount found is proportional to the missing plastic equation. Although we know the amount of plastic introduced into the ocean, we have no idea where it is going or where it is ultimately being deposited. One thing is for sure: plastic never truly disappears, and it poses a significant risk to wildlife and human health through entanglement and ingestion, as well as its potential to infiltrate our food chain. This is highly concerning. Although some parts of the world contribute more than others, the interconnectedness of the ocean makes marine plastic pollution a common global problem.

It is imperative to solve the enigma of missing plastic since understanding the scope of the problem is crucial before devising a solution. Even if we were to locate the missing plastic, cleaning up the widespread and scattered plastic debris in the oceans would be daunting.

The views expressed here are those of the author and do not represent or reflect the views of RTÉ