Walk along a beach pretty much anywhere in the world and you'll find seashells, seaweed - and plastic.

From bottles and bags, to flip-flops, polystyrene boxes and old fishing nets, the world is dumping millions of tonnes of plastic into the world's oceans, and the amount is growing every year. Plastic waste clogs reefs and beaches and kills marine life that gets entangled or eats plastic, thinking it is food.

This is the dark side of disposable lifestyles where plastic packaging is discarded instead of being reused.

As more waste pours into the oceans and as more breaks down into smaller and smaller pieces, we are turning the seas into a toxic soup, scientists say, risking marine life and human livelihoods that depend on fishing and tourism.

Worse, the seafood people eat, such as mussels and oysters, can contain tiny plastic particles, studies have found.

"It shocks me how little people understand about the issue," said Australian Greens Senator Peter Whish-Wilson. "I think it's the biggest global pollution problem that we face that we talk so little about and do so little about," he told The Straits Times from Canberra.

Mr Whish-Wilson initiated a Senate inquiry into marine plastic pollution that is holding public hearings. The inquiry has stirred a lot of interest, with 190 submissions from government agencies, scientists, companies and green groups. The next hearing is on Thursday in Brisbane.

"This problem has been creeping up on us and it is going to get so much worse if we don't do something about the quantity of plastic getting into the oceans," he said.

Increasingly, Asia is the major source of plastic pollution, a lot of it dumped in rivers and then washed out to sea. A study published last year in the journal Science estimated about eight million tonnes of plastic, much of it bags and food and drinks containers, reach the world's oceans.

The authors said eight of the top 10 plastic polluting nations were in Asia. China, Indonesia and the Philippines were the worst, highlighting the urgent need for better waste management, recycling and public education.

While some of the plastic is washed up on beaches, other waste sinks to the sea floor or is swept up in giant ocean currents called gyres.

"Just one plastic bottle can break down into thousands and thousands of tiny pieces, which become smaller and smaller and are then accessible to different organisms up the food chain," leading marine debris scientist Denise Hardesty told The Straits Times.

She said no one really knows where all the plastic goes. A lot ends up on coastlines and some is eaten by marine life, she said, adding that about 40 per cent of litter along coastlines was related to the beverage industry, such as bottles, straws and lids.

Studies have shown plastic is eaten by even the tiniest sea creatures, such as zooplankton, as well as fish, birds, turtles and even whales. Once eaten, the plastic - anything from bags to cigarette lighters and plastic fragments - gets stuck in the gut and many animals starve to death.

A study by researchers from the University of California, Davis, and Hasanuddin University in Indonesia published last year found that a quarter of the fish from markets in California and Indonesia contained plastic debris and textile fibres.

Globally, about half of all seabird species are likely to eat plastic debris, everything from balloons to glow sticks, according to Australia's state-backed research body, the Commonwealth Scientific and Industrial Research Organisation (CSIRO), which recently completed a three-year study of marine debris around Australia.

Dr Hardesty of the CSIRO's Oceans and Atmosphere Flagship in Hobart, Tasmania, travels extensively to study plastic pollution, as well as conduct autopsies on birds. In some cases, plastic waste removed from the guts of dead birds totalled 8 per cent of body weight.

The CSIRO predicts plastics ingestion in seabirds may reach 95 per cent of all species by 2050 as plastic production grows.

That paints a bleak picture for the future of the world's oceans, already under threat from over-fishing, warming seas from climate change and other types of pollution.

A growing threat comes from the plastics many consumers do not see, scientists say. Tiny plastic microbeads used in cosmetics and toothpaste are not captured by most sewerage systems and wash out to sea. Even smaller nanoplastics, such as paint flakes, tyre dust and microfibres from clothes washing, are also polluting oceans and being found in marine life.

Mr Dave West, national policy director for the Boomerang Alliance, an Australian waste and recycling NGO coalition, told The Straits Times that, in addition to the estimated eight million tonnes of plastic waste, another two million to three million tonnes of tiny plastic particles are clogging the oceans.

A study released in January by the Ellen MacArthur Foundation during the World Economic Forum in Davos said unless we radically reduce the amount of plastic waste, there could be as much plastic in the sea by 2050 as fish by weight.

World plastic production has grown from 15 million tonnes in 1964 to 311 million tonnes in 2014, and is expected to double again over the next 20 years. Plastics can last from decades to centuries in the sea.

Globally, only a small percentage of plastic is recycled.

The Australian Senate inquiry heard that bans on microbeads and thin plastic bags, and con- tainer deposit recycling schemes for bottles can slash the amount of waste. For example, container deposit schemes in South Australia and the Northern Territory have raised plastic recycling rates to 85 per cent.

In Germany, China, the United States and other countries, vending machines pay customers who return their plastic bottles to be reused. In places where plastic bags are banned, people have adapted. It is all part of changing people's behaviour, said Mr Whish-Wilson.

"If you put a value on something, it's no longer rubbish," he said.