Plastic and how it affects our oceans

Plastic is woven into the fabric of our lives.

"No-one in their daily life within a period of 10 minutes isn't touching something that is made of plastic," said Professor Andrew Holmes, an emeritus professor at the University of Melbourne and a polymer chemist who has developed special plastics for flat screen TVs and solar cells.

It's used in everything from the keyboard or pen you are using, to your glasses or contact lenses, the Teflon on your frying pan, and the banknotes in your wallet. It's in your clothes, phone, car, mattress, and TV screen.

"Plastic can be flexible or rigid, and its lightness also makes it very appealing," said Professor Holmes.

But for all the benefits plastic has given us, disposing of products — particularly those designed to be used only once, such as packaging — has become a major environmental issue.

"The ocean is full of waste because humans have disposed of it carelessly," said Professor Holmes.

So how big is the problem, what happens once plastic goes into the ocean, and what can we do about it?

How much plastic goes into the ocean?

Around 8 million tonnes of plastic went into the ocean in 2010, according to the most comprehensive study of plastic pollution so far.

The international study calculated that 192 nations produced a total of 275 million tonnes of plastic waste.

The largest amount of this waste was produced by China, at 1.32 to 3.52 million tonnes. This was followed by Indonesia, the Philippines, Sri Lanka and Vietnam.

Australia — which didn't rate in the top 20 polluters — contributed less than 0.01 million tonnes.

But that still added up to 13,888 tonnes of litter per year, a quarter of which finds its way into waterways, according to study co-author Dr Chris Wilcox of CSIRO's Oceans and Atmosphere Flagship.

With global production of plastic increasing exponentially, the amount of plastic finding its way into the ocean is likely to get much bigger.

"About every 11 years the amount of plastic produced doubles," said Dr Wilcox.

"To put that in other words, between now and 2028 we will produce as much plastic as we produced [from the 1950s] until now."

How long does plastic last in the ocean?

Plastic is made to be strong and durable, so it can take a long time to break down.

"Plastics are very hard materials so they are hard to break down unless you can burn them," said Professor Holmes.

"There are some you can get back to original building blocks, but not many."

These include the newer plant-based bioplastics made out of polylactic acid (PLA). But much like traditional petrochemical plastics such as Perspex, PLA-based plastics only break down under very high temperatures.

In the natural environment, the main things that break down plastics are sunlight, oxygen and water.

"The problem is that normal degradation leaves particles that can still be harmful to living things — nanoparticles and microparticles," said Professor Holmes.

"That includes so-called degradable polymers used in some plastic bags, which have starch added to help them fall apart."

The rate at which plastic breaks down depends upon the conditions and the type of plastic.

It breaks down faster if exposed to physical abrasion and sunlight — so it will break down faster in surf zones than if it is buried under sediment in an estuary, Dr Wilcox explained.

"Then there's a lot to do with how thick the plastic is, how dense the plastic is, and does it have UV stabilisers."

For example, dense monofilament fishing line could last for up to 600 years, whereas a thin plastic bag getting bashed around in the surf could last just months.

"But even if that bag breaks down over the course of six months or a year, it might well have had a lot of environmental impact before that," he said.

Where does the plastic go?

It is really hard to quantify just how much plastic is in the ocean, but the latest figures estimate there are up to 51 trillion particles or 236,000 tonnes.

That may sound like a lot, but in fact it is nowhere near the estimated 8 billion tonnes that went into the oceans in 2010 alone.

Precisely what happens to the "missing" plastic is a puzzle for researchers like Dr Wilcox.

"That says around 40 times the plastic that's in the ocean is going in every year. So there's a whole bunch that has to be going somewhere else."

Plastic is widespread in the open ocean, but is particularly concentrated in the five major ocean gyres — rotating currents of water — in the Pacific, Atlantic and Indian Oceans.

The largest and best known of these is the Great Garbage Patch in the north Pacific — a concentrated soup of microplastics, or tiny fragments less than 5 millimetres across.

There are two types of plastics that float: polyethelene, which is used to make milk jugs and plastic bags, and polypropolene, which is used for things like bottle caps, straws and dairy containers.

As they travel out to sea plastics get ground down into small, hard cubes, which can be eaten by marine animals.

Plastics are also home to microbes in a phenomenon dubbed the "plastisphere". These microbes may be simply using the plastic to float around the ocean, but there is some evidence they may play a role breaking down the plastic.

Plastics should become more abundant as they break down in size, but recent research found the concentration of the smallest particles, between a few microns and a few millimetres, was much lower than expected.

"It's not clear what's going on — whether there's some kind of sampling problem, or if those things are settling to the bottom of the ocean," Dr Wilcox said.

Scientists have found evidence of microplastics in deep-sea sediments from the Atlantic Ocean, Mediterranean Sea and Indian Ocean.

Some of the missing plastic could also be in coastal regions.

"I think that that is something that people really don't appreciate. The gyres may have a fair bit of plastic in them, but the coastal margin probably has much more," said Dr Wilcox.

"Even in Australia, you can tell how far away you are from a city by how much plastic is on the beach and in the water near the beach."

An analysis of waters around Australia found on average there were around 4,000 microplastic fragments per square kilometre, although some hotspots had concentrations of around 15,000 to 23,000.

The vast majority of the microplastic fragments came from plastic packaging such as cups, bottles, bags, as well as fragments of fishing gear.

Dr Wilcox said coastal pollution was an even greater problem for biodiversity than in the open ocean.

"The number of species in the coastal margin is much higher than out in the gyres."

What impact does plastic have on marine animals?

Research shows getting entangled in plastic was the biggest issue, said Dr Wilcox.

Animals get wrapped up in monofilament fishing line nets, plastic bags, balloons, and straps.

His research has estimated that between 5,000 and 15,000 sea turtles are entangled each year by derelict fishing gear washing ashore in northern Australia alone.

"Anything that is long or flexible or sheet-like is the worst."

The second biggest issue is the impact of eating plastic — it is estimated around 90 per cent of seabirds are doing so.

These plastics can cause blockages of the gut or perforation of the intestines.

Ingestion of plastic can also cause toxic chemicals such as phthalates — a plasticiser that effects the hormone system — to leach into the animal.

"In our research, we can predict how much plastic is in a seabird's stomach by measuring how much phthalate is in its fat," said Dr Wilcox.

So what can we do about it?

"The solution to all this stuff is on land and it has to do with changing our supply chains around packaging, how we use packaging, and how we take care of packaging," said Dr Wilcox.

The main problem, he added, was how cheap plastic was.

"If plastic had a fee or deposit associated with it we would produce and consume less."

He said one way of doing this was to introduce container deposit schemes, which had been shown to reduce the amount of drink containers in the environment by 60 per cent.

"That is a big deal, as beverage containers make up 40 per cent of the waste in the environment."

Consumers could also press retailers to use less plastic packaging, Dr Wilcox said.

"In many cases individuals have been able to drive significant local change by governments and businesses."

According to Professor Holmes, the world may have to move to fully biodegradable plastics, made out of plants. But these have drawbacks.

"The challenge is, is there enough arable land to produce the building blocks of plastic when we also need to produce food?"

In the meantime, he said, we must recycle anything we can.

"Ideally all plastics should be recyclable, but at present that is not the case."

Professor Holmes said plastics that cannot be recycled — such as those used in plastic bags, or expanded polystyrene foam used in coffee cups and packaging around electronic goods — must be responsibly disposed into landfill or by burning.

"The plastic waste in the oceans is disastrous for marine and bird life, and the human race has to avoid disposal of this waste in a way that enables it to enter drains, rivers, and eventually the ocean," he said.

What is plastic made from?

  • Plastics is the name we give to a group of substances mostly made from carbon-based molecules arranged in many repeat units (n) in a long chain known as a polymer.
  • There are many different types of plastics depending upon what is attached to the carbon
  • Plastic shopping bags, for example, are made from a type of polymer called polyethylene (C2H4n) — where each unit in the chain is made up of two hydrogen atoms joined to one carbon atom.
  • Most plastics are derived from petroleum, although some newer ones, known as bioplastics, are derived from building blocks produced by microbial fermentation or from corn syrup.
  • Chemicals including colourants, foaming agents, plasticisers, antioxidants and flame retardants can be added to different types of plastics to give them specific qualities such as colour, texture, flexibility and durability.