Plastic waste – more than just unsightly debris!

Nic Slocum, The Southern Star 30 May 08

Since Methuselah’s grandfather was a small boy, sailors have used the oceans as a dumping ground for waste products. Local pollution incidents, largely reversible, would undoubtedly have occurred during these earlier times caused by those living on the seashore or waterways flowing to the coast.

During the last 60 years the nature and amount of waste we dump into the oceans, either directly or inadvertently, has changed dramatically causing possibly irreversible damage to marine ecosystems on a scale proving difficult to measure. Damage that may have far-reaching effects, not only on marine life but ultimately on human health.

Polluting marine debris originates from a variety of sources. Items discarded or lost by those who live, work or play next to the ocean, waste deliberately discarded from ships and offshore drilling platforms and material that originates further inland but is carried to the sea via rivers and estuarine outflows. Of the staggering array of beverage cans, styrofoam cups, polystyrene packaging, discarded polypropylene fish netting and line, plastic carrier bags, disposable lighters, balloons, bottles, bottle caps, oil drums and cartons ending up in the ocean, plastic items and their derivatives pose the greatest threat to creatures both large and small.

What happens to plastic in the ocean?

Of an annual global production of 100 million tonnes of plastic, a tiny 5% gets recycled. Much of the remainder ends up in landfills but an estimated 20 million tonnes end up in our oceans. The visible evidence of this plastic debris, some of which washes up on our shores, belies a more sinister and potentially larger problem. Plastic is valued for its resistance to degradation, which gives it a lifespan of hundreds of years in the marine environment. The bigger plastic items, when subjected to sunlight, wave action and mechanical abrasion simply break down into increasingly smaller, but no less indestructible particles that disperse over an ever-widening area of ocean. It is calculated that a single 1 litre plastic bottle could break down in this way to produce enough smaller fragments to put one particle per mile on every beach across the globe!

These smaller fragments of plastic debris combine with small pellets, the form in which many new plastics are marketed and distributed around the world. These degraded particles and pelleted plastic join with the plethora of other plastic debris to form ‘rafts’ of floating debris. Much attention has been given to these floating islands of discarded plastic; not so much because of the vast tonnage that finds its way ashore but more because they have been found to preferentially accumulate in parts of the ocean where wind is light, currents are circular and there are few land masses for this debris to be washed up on.

The North Pacific sub tropical gyre

Just such an area exists off the western seaboard of the USA. The North Pacific sub-tropical gyre is a large body of water that turns in a clockwise slow spiral. The winds are light in this area of the ocean and the nature of the current tends to cause plastic material to accumulate towards the centre of the gyre in enormous quantities. Studies have shown the volume of plastic in this gyre is so great that for every kilo of naturally produced plankton there are 6 kilos of plastic debris currently covering an area of ocean the size of Texas! This slow moving spiral of micro and macro plastic debris has been nicknamed the ‘Asian Trash Trail’ or, in deference to the increasingly galactic proportions of rubbish accumulating, the ‘Trash Vortex’. This North Pacific Ocean gyre is one of five oceanic gyres around the globe, which may exhibit similar vortices of discarded plastic. A slow circulation area in the Atlantic that has been studied is the Sargasso Sea. Unsurprisingly, large amounts of particulate plastic have been recorded in the water there.

Death and destruction

Unsightly as these oceanic gyres of plastic debris are, the damage occurs when wildlife interacts with them. From marine mammals to the smaller bird species, these items are mistaken for prey items and ingested, frequently causing death through poisoning, blockage or simply subduing the hunger reflex. Conservative estimates put the number of birds killed annually around the globe as a result of ingesting plastic items or becoming entangled in plastic bags or twine at one million. Additionally, over one hundred thousand marine mammals and sea turtles are estimated to die annually as a result of entanglement or ingestion. Over a thousand pieces of plastic were found in the stomach and intestines of a large pacific leatherback turtle washed ashore dead on the Hawaiian islands recently. Closer to home, a study published in 2005 looked at the pelagic seabird, the fulmar, so familiar to us here along the Cork coastline. Over 95% of birds washed up dead in countries surrounding the North Sea had fragments of plastic in their stomachs. One bird recovered from Denmark had a staggering 20 grams of plastic in its stomach; in human terms this is equivalent to around 2 kilograms. Fulmars, like many other pelagic species, feed on floating offal, much of it discarded from fishing vessels and frequently mistake floating plastic debris for food. The latest findings of this ongoing study found that those fulmars most contaminated were recovered alongside the busiest shipping lanes, which, according to the marine biologist leading the project, strongly suggests illegal dumping of waste at sea by fishing boats, other commercial shipping and offshore installations. The presence of fragments of balloons, plastic bags and bottles and other packaging suggests that some of this contaminating plastic originated from the land.

A sinister sting in the tail

Unexpectedly, a group of Japanese scientists found that these plastic fragments can concentrate some of the most harmful chemical pollutants present in the ocean, the persistent organic pollutants (POPs), and act as a chemical sponge concentrating these harmful compounds to as much as a million times the concentration than in the surrounding seawater. Additionally, plastics themselves are capable of leaching out endocrine disrupting chemicals, a byproduct of their manufacture. Marine organisms that consume this contaminated plastic debris imbibe a lethal cocktail of harmful, long-lived man-made chemicals capable of disrupting breeding patterns and reducing immune capability.

Many of the larger pieces of floating plastic that contaminate our oceans affect marine ecosystems in surprising ways. Plants and animals colonising floating plastic debris may be transported by currents far outside their normal habitat ranges, ultimately colonising areas they would not traditionally be found in. These introduced species may become ‘nuisance’ colonisers upsetting the balance of an ecosystem to the detriment of rarer, potentially economically more important species.

Not all plastic floats

Not all plastic debris that finds its way to the sea floats. Nearly 70% sinks and can – and does – smother bottom-dwelling organisms. A recent study of the North Sea by Dutch scientists found 110 pieces of plastic refuse for every square kilometre leading to estimates that the North Sea alone harbours a staggering 600,000 tonnes of litter on its polluted bottom. Following ratification of annex five of the MARPOL convention designed to prevent pollution by garbage from ships, the amount of marine debris, including plastics, declined. Recent years have seen an increase again with beaches both locally and worldwide bearing witness to the vast amounts of plastic debris continuing to find its way into our oceans.

Most marine scientists agree that over-fishing and habitat destruction through trawling is the most important issue facing marine ecosystems today – pollution by plastic debris lines up as a close second, alongside persistent organic chemicals and noise, as long-term pollutants – the effects of which we have yet to fully comprehend.