What are microplastics? How do they get into our food and drink - and what impact do they have?

• Watch Bob Cruwys' report here.

Twenty years ago in a laboratory in Plymouth, researchers discovered what had for a long time been an invisible threat - microplastics.

Professor Richard Thompson OBE and his team at University of Plymouth were the first in the world to publish a scientific paper on microplastics in 2004.

Their work showed that tiny pieces and particles of plastic - measuring 5mm or less - have been accumulating in the world's oceans since the 1960s.

Professor Thompson specialises in marine biology, he is the director of University of Plymouth's Marine Institute and founded and heads up is International Marine Litter Research Unit.

He and his team have charted the global distribution of microplastics from the Arctic sea ice to the deep seas.

"We'll find bits of plastic now in and amongst the grains of sand on the beach itself," he told ITV News.

He said many of these microplastics are so small they are not visible to the naked eye, but if you were to look at them under a microscope you will see things like clothing fibres made of plastic.

"It's only when you take a much closer look, back at the lab, that you really start to see what actually makes up that handful of sand," he said.

"We can confirm the identity of the polymer and we find a range of everyday polymers that are used in plastic packaging and other applications."

But what are microplastics? Where does it come from? And how is it making its way into our food chain - and into the human body?

Below, Professor Thompson answers some of the most common questions on microplastics, the threat they pose to the environment and what we can do to reduce the amount of plastic entering the ecosystem.

What are microplastics?

Microplastics are pieces of plastic smaller than 5mm.

They originate from multiple sources but are broadly subdivided as primary microplastics, which have been manufactured to be less than 5mm - this includes microbeads in cosmetics and pigments in paint - and secondary microplastics, which have been generated by wear or fragmentation of larger items, such as car tyres.

Recent estimates suggest emissions of 12.7 million tonnes of microplastics enter to the environment annually.

Research at the University of Plymouth in 2004 was the first to describe these pieces as microplastics and to demonstrate they had been accumulating in the oceans since the 1960s.

Microplastics are persistent and once in the environment cannot effectively be removed. They now contaminate the planet from the deepest oceans to the highest mountains, and have been detected in a wide range of organisms with numerous studies demonstrating harmful effects.

Interventions to address this issue must focus on reducing emissions and be applied at global scale.

How long does it take plastics to fragment into a microplastic?

The rate at which plastic items fragment into microplastics plastic depends on the type of plastic item and the surrounding environment it conditions. For example, each time you put on the brakes in your car or wear synthetic clothing you will rapidly generate microplastics.

Plastic litter will fragment into microplastic in the environment. The rate this happens at will be faster on sunny beach where ultraviolet light and elevated temperature will make the plastic brittle and physical action from wind and waves will help break up the plastic. By contrast, the same plastic item deep down on the seabed with little light or physical energy would take much longer to fragment.

It is important to realise fragmentation into microplastics is very different to biodegradation; polymer scientists suggest that, unless it has been incinerated, all of the conventional plastic ever produced is still present on the planet in a form too big to biodegrade.

What impact do microplastics have on marine life?

Hundreds of species are known to eat microplastics, some do so inadvertently while others mistake it for their normal food.

A study at the University of Plymouth looked at 500 fish from the English Channel and found that a third of those fish had microplastics in their gut.

Laboratory studies have shown that plastics particles and associated chemicals have the potential to cause harm to organisms in a variety of ways.

In some locations the amount of microplastics in the environment is already causing harm. Unless changes are made in how humans produce, use and dispose of plastics to reduce the release of microplastics it is estimated that there will be wide scale environmental harm within around 100 years.

Since it is almost impossible to remove microplastics form the environment it is essential that we find way to reduce emissions.

How do microplastics enter our food chain?

Microplastics are widely documented in food and drink including seafood, honey, sugar, beer and tea, as well as in the air we breathe.

This can occur because the animals we are eating have consumed microplastics or because contamination has occurred during processing and packaging of the food.

This will also occur in the home - we have shown the amount of microplastics you might eat from a fish supper will mostly come from plastic particles settling on the food in your home while you prepare and eat the food.

Are microplastics in our drinking water?

Microplastics are present in bottle and tap water. Quantities will vary according to the level of water treatment and a recent study indicated that the quantities of microplastics in UK tap water were very low.

The World Health Organisation recently concluded that 'based on the limited evidence available, chemicals and microbial pathogens associated with microplastics in drinking-water pose a low concern for human health'.

How can we stop ourselves from consuming microplastics?

It is almost inevitable that in day to day life you will eat and also breath in microplastic particles. They have been detected in the human gut and in poo, as well as in several organs in the human body.

What impact do microplastics have on humans?

It is not clear whether day to day exposure to microplastics is sufficient to cause harmful effects on humans. Researchers, including those in my team at the University of Plymouth, have started to examine the potential links between microplastic exposure and harmful effects.

Given the evidence from laboratory experiments on animals there is a clear indication of the potential for harm and consequently we need to start using plastics more responsibly in order reduce the quantity of plastics in entering the environment.

What are the solutions to reduce emissions of microplastics to the environment?

Once microplastics have entered the environment, it would be extremely challenging to remove them. Hence prevention at source is key. Reduction in plastic production will reduce the potential for microplastics to be released.

Legislation on intentionally added microplastics, such as microbeads in cosmetics, has successfully been implemented in multiple countries.

Improved product design could dramatically reduce the release of microplastics fibres from textiles and it is likely that this approach could also be used to reduce the rate at which particles are released from vehicle tyres.

Substantial quantities of microplastic pellets, powders and flakes - out of which most larger items are made - are spilled into the environment every year. Classifying these materials as hazardous could help promote better industrial practice.

Evidence from the University of Plymouth directly informed the UK ban on microplastics in cosmetics.

Want a quick and expert briefing on the biggest news stories? Listen to our latest podcasts to find out What You Need To Know...