It’s enough to make you cry over your moules frites. Scientists at Ghent University in Belgium recently calculated that shellfish lovers are eating up to 11,000 plastic fragments in their seafood each year. We absorb fewer than 1%, but they will still accumulate in the body over time. The findings affect all Europeans, but, as the most voracious consumers of mussels, the Belgians were deemed to be most exposed. Britons should sympathise – last August, the results of a study by Plymouth University caused a stir when it was reported that plastic was found in a third of UK-caught fish, including cod, haddock, mackerel and shellfish. Now, UK supermarkets are being lobbied to create plastic-free aisles by the campaign group A Plastic Planet, as a feature-length documentary, A Plastic Ocean, is released in Britain this week.

We are finally paying attention to the pollution that has plagued our seas for years – the government is considering a refundable deposit on plastic bottles, and pharmaceutical company Johnson & Johnson recently switched from plastic to paper stems on its cotton buds. Evidently, there’s nothing like serving plastic up on a dinner plate to focus the mind.

Whether your national obsession is moules frites or fish and chips, this problem goes way beyond Britain and Belgium. Contaminated fish and shellfish have been found everywhere from Europe, Canada and Brazil to the coast of mainland China – and plastic-eating fish are now showing up in supermarkets. The question is no longer: are we eating plastic in our seafood? What scientists are urgently trying to establish is just how bad for us that is. Another question we might ask: how did we get here?

More than a century ago, in 1907, another Belgian, Leo Baekeland, a graduate of Ghent University, invented bakelite. It was, he later admitted, something of an accident, but this welcome development ushered in a colourful new age of plastics. Until then, we had, at great cost and effort, been manipulating products out of natural materials such as shellac, derived from beetle shells. (Charles Mackintosh’s first “mac” – which used derivatives of tar and rubber – must have been pretty pungent in a downpour.) Baekeland, who had moved to the US, saw commercial potential in an entirely synthetic replacement for shellac that would be suitable for mass production. Bakelite was lightweight, affordable, malleable and safe, but perhaps the greatest thing about the plastic Baekeland created, and those that followed, was its durability.

Throughout the first half of the 20th century, innovations came thick (and thin) and fast – polystyrene, polyester, PVC, nylon. Soon, they were an inextricable part of everyday life. And then, in 1950, that scourge of the sea arrived: the throwaway polythene bag. In that decade, annual global plastic production reached 5m tonnes; by 2014, it stood at 311m tonnes – shockingly, over 40% of it for single-use packing. Now, plastic’s durability looks less of a boon than it once did. A study in Science Magazine in 2015 estimated that around 8m tonnes of plastic go into the sea each year. And, last year, a report for the Ellen MacArthur Foundation (launched in 2010 by the former round-the-world sailor to promote a more circular economy) estimated that, by 2050, the volume of accumulated plastics in the oceans will be greater than that of fish.

Evidently a keen sailor, Baekeland retired in 1939, to spend time on his 70ft yacht, the Ion. Ninety years after his plastics breakthrough, in 1997, another sailor (since turned oceanographer and campaigner), Charles Moore, was traversing the ocean between Hawaii and California when he came across the now infamous Great Pacific Garbage Patch, one of the five main subtropical gyres (circulating systems of ocean currents that draw floating debris into a kind of massive junk vortex). Ever since its discovery, there has been vigorous debate over the size of the patch, with descriptions ranging from the size of Texas to twice that of France. It is, in fact, impossible to definitively measure, because its size – and litter visible on the surface – changes with currents and winds, but its heart is thought to be around 1m sq km, with the periphery spanning a further 3.5m sq km, stretching roughly from the west coast of North America to Japan. An aerial survey last year by Dutch foundation The Ocean Cleanup found it is far bigger than previously estimated, while the UN’s environmental programme warns it is growing so fast that it is now visible from space.

In 1997, Moore saw bottles, bags and bits of polystyrene. But what really worried him, and has occupied campaigners and scientists ever since, was the vast soup of tiny plastic particles swirling around below the junk. Moore returned in 1999 to measure the weight of these “microplastics”. “We found six times more plastic than plankton,” he said, sparking a flurry of worldwide research that has not let up since. Researchers from around the world pooled data over six years to 2013, and reached the conclusion that there are already more than five trillion pieces of plastic in the world’s oceans, most of them microplastics.

Microplastics – which range in size from 5mm to 10 nanometres – come from a number of sources. One culprit is “nurdles”, the raw plastic pellets shipped around the world for manufacturing, easily lost during transportation (in 2012 a typhoon spilled millions from a ship in Hong Kong). Recently, the spotlight has been on so-called microbeads, tiny plastic balls found in some cosmetic facial scrubs and toothpaste (many governments, including the UK’s, have moved to ban them). Like microfibres – the threads from synthetic clothes lost during laundry, and rubber debris from vehicle tyres – these tiny pieces of plastic are too small to be filtered out of our wastewater systems, and huge quantities end up in the sea. But it’s the single-use plastics for packaging, more than a third of everything we produce, that present the greatest problem. While many plastics don’t biodegrade, they do photodegrade – UV exposure eventually breaks all those plastic bottles and bags down into tiny pieces, which, in common with microbeads and fibres, potentially leach toxic chemical additives – PCBs, pesticides, flame retardants – put there by manufacturers. These tiny particles look like food to some species, and, last November, new research showed that common plastics attract a thin layer of marine algae, making them smell like nutritious food.

In July 2015, a team at the Plymouth Marine Laboratory released film they had captured under a microscope showing zooplankton eating microplastic. Given that these tiny organisms form a crucial part of the food chain, the implications were immediately shocking. But a huge variety of the fish and shellfish we eat are consuming plastics directly too. Research published last year in the journal Science found that juvenile perch actively preferred polystyrene particles to the plankton they would normally eat. While most plastic has been found in the guts of fish, and would therefore be removed before eating, some studies have warned that microplastics, particularly at the nanoscale, could transfer from the guts to the meat (and, of course, we eat some species of small fish and shellfish whole). There is growing concern about toxins leaching – laboratory tests have shown that chemicals associated with microplastics can concentrate in the tissues of marine animals. Some commercially important species have seen the majority of their population affected. In 2011 in the Clyde in Scotland, 83% of Dublin Bay prawns, the tails of which are used in scampi, had ingested microplastics; so had 63% of brown shrimp tested across the Channel and southern part of the North Sea.

A fortnight ago, Gesamp, a joint group of experts on the scientific aspects of marine environmental protection, published the second part of its global assessment on microplastics. It confirmed that contamination has been recorded in tens of thousands of organisms and more than 100 species. Last year, the European Food Safety Authority called for urgent research, citing increasing concern for human health and food safety “given the potential for microplastic pollution in edible tissues of commercial fish”. In the face of such widespread contamination, the outlook seems bleak.

Yet Professor Richard Thompson, a leading international expert on microplastics and marine debris, is upbeat. He has been working in this field for 20 years. In 2004, his team at Plymouth University released the first research on marine microplastics, were the first to show microplastics were retained by organisms such as mussels, and it was their research that found plastic in a third of UK-caught fish. He is reassuringly unfazed about the recent headlines. “You would have to eat well over 10,000 mussels a year to reach the quantities of plastics the Belgian studies suggest,” he says. Even for Belgians, that seems excessive. And, crucially, there is no evidence of harm to humans from those quantities. He agrees contamination is widespread – and concerning – but it is “not yet a cause for alarm. Quantities are low, and at current levels human exposure is likely to be greater in the home or office than via food or drink.” But, he adds: “It’s only going to increase. If we carry on with business as usual, it will be a different story down the line, in 10, 20 years.”

It’s important not to overstate the risks before they’re fully understood. The UN’s Food and Agriculture Organisation pointed out in 2014 just how reliant we have become on seafood as a source of protein – an estimated 10-12% of the global population relies on fisheries and aquaculture for their livelihood. Per capita fish consumption has risen from 10kg in the 1960s to more than 19kg in 2012, and seafood production is annually increasing at a rate of 3.2%, twice the world population growth rate. In other words, demand for seafood is increasing, just as its future viability is at risk. Something has to give – and it is increasingly clear that has to be our reliance on throwaway plastics.

When you’re alone in the middle of the Southern Ocean, the nearest land is Antarctica and the closest people are manning the space station above, there’s time to think. If you’re Dame Ellen MacArthur, it sets you to thinking about the flaws of our global economy. As she tells it: “Your boat is your entire world and what you take with you when you leave is all you have, to the last drop of diesel and last package of food. There is no more.” Our economy, she realised, is no different: “It’s entirely dependent on finite materials we have only once in the history of humanity.” To MacArthur, the solution is simple – instead of using these resources up, we should design the waste element out of products in the first place. MacArthur, through her foundation, is working with industry leaders and others to approach design with end of life in mind. She has found one particularly strong ally in the Prince of Wales, whose International Sustainability Unit (ISU) is also working on how innovation and design can reduce the impact of plastic production on the environment.

Two weeks ago, the ISU organised a working group, which included MacArthur, to look at plastic waste in the oceans. This is how Professor Thompson found himself on the banks of Rainham Marshes in Essex, collecting plastic debris with senior executives from Coca-Cola, PepsiCo, Adidas, Dell and Marks & Spencer. Of what they picked up, about 80% was plastic bottles – those executives probably saw their own products spat back at them from the Thames. They were shocked, apparently, at the scale of it, which Thompson pointed out “was not inconsistent with beaches worldwide”. Then they all went to the recycling plant. Only a third of the UK’s annual 1.5m tonnes of recyclable plastic waste is recycled. While many drinks bottles are made of easily recyclable PET, some brands add plastic sleeves or colour the bottles, reducing their recyclability. The execs watched those bottles picked out, simply due to a lack of thought at the design stage.

The idea of the circular economy is taking hold; there is now broad agreement that industry needs to move towards products that maximise recycling and re-use. As the Prince of Wales put it: “We do need to consider, from the very beginning, the second, third and, indeed, fourth life of the products we use in everyday life.” Thompson is heartened. “This growing recognition,” he says, “was not the case 10 years ago when industry pointed at consumers saying they were responsible … now it’s much clearer there’s responsibility on both sides.” And in what he describes as an exciting step forward, we might see the formation of a stewardship council for plastics, which will connect industries from manufacture through to recycling, and, as the Marine Stewardship Council does for fishing, accredit responsible practice. After all, plastic is not the enemy, it’s incredibly useful, not least in reducing food waste. What’s so positive about recent progress, Thompson points out, is that “unlike other environmental problems, this isn’t a case of us having to do without, we just have to do it differently”.

Perhaps the shock of finding plastics returning to us on our dinner plates will help to bring that message home. “We’re on the edge of a major ecological disaster,” Thompson says. “Microplastics in seafood is an illustration of that. There are things we can do, but we need to do them now.”