How do you clear 1.8 trillion pieces of plastic, weighing 80,000 tonnes, from the surface of the Pacific Ocean?

Key points: The cleaning vessel launched from San Francisco and is undergoing a two-week trial

The cleaning vessel launched from San Francisco and is undergoing a two-week trial Ingestion and ensnaring are the main threats that plastic pollution poses to ocean life

Ingestion and ensnaring are the main threats that plastic pollution poses to ocean life The Ocean Cleanup hopes to scale up to about 60 systems if System 001 goes well

That's the challenge Dutch not-for-profit The Ocean Cleanup is facing as it attempts to clean a vast area between the coasts of California and Hawaii, using a unique 600-metre-long floating boom and a three-metre impenetrable skirt that hangs in the water beneath it to collect the plastic.

The group believes that with their cleaning vessels, or "systems" as they call them, they can halve the notorious Great Pacific Garbage Patch in just five years.

But despite the optimism from the group, many in the science community are not sold on the idea.

Environmental scientist and founder of the 5 Gyres Institute, Dr Marcus Eriksen, said The Ocean Cleanup did not understand the problem or how to tackle it effectively.

"I think people still perceive that there are islands of trash out there and it's just the opposite … it's mostly small particles," he told Pacific Beat.

"I think the better analogy, instead of islands, would be a smog. Like the way we have smog over our cities, we have a smog of plastic over our oceans."

The barrier will scoop up floating fishing nets, plastic bottles, laundry baskets and other plastic refuse. ( AP: The Ocean Cleanup, file photo )

Addressing the tiny plastics the real key to solving issue

Dr Eriksen explained that rather than forming islands, microplastics mix with chemicals that have also found their way into the water, posing potential harm to the ocean life that ingest them, and humans who consume them.

"The frontline of research right now is understanding what are the population-level effects of microplastics on marine life, including close to 50 species that we consume and harvest from the sea," Dr Eriksen said.

"The net array that they've deployed, it's not going to capture the microplastics, and that's where I would argue the majority of the harm is coming from."

The headline grabbing tactics of Ocean Cleanup have attracted critics, who say it won't solve the plastic problem. ( Supplied: Dr Marcus Eriksen )

Lead Oceanographer at The Ocean Cleanup, Laurent Lebreton, agreed that microplastics were the problem, but said there was still value in retrieving larger pieces of plastic.

"We still have to deal with the legacy of plastic accumulated in the last 60 years," Mr Lebreton said.

"The idea is to try to collect this from the natural environment before it breaks down into microplastic particles."

Scientists say that it is microplastics, rather than large items, that pose the bigger threat to marine ecosystems. ( Supplied: Dr Marcus Eriksen )

But Dr Eriksen argued that oceans already had natural mechanisms to sink or beach bulky debris at a similar rate to what The Ocean Cleanup planned to operate.

Citing a recently published paper by the International Pacific Research Centre's Nikolai Maximenko looking at debris from the 2011 Japan tsunami, he said of the estimated 1,000 boats that were lost at sea, it was projected that less than 10 per cent remained.

"That's because of sinking and stranding, the boats getting beached, the ocean is moving things and kicking things out. It doesn't want that trash on the sea surface," he said.

This, Dr Eriksen argued, made prevention a more viable solution to reducing plastic pollution, and he believed that The Ocean Cleanup's systems could play a role on that front.

"If they want to build these structures, at the very least, the last place you put them is the mouth of rivers," Dr Eriksen said.

"Even better, go further upstream and work on prevention to stop the problem in the first place. That's what's sorely needed, and that's where the conversation is today."

Sorry, this video has expired The U-shaped barrier is designed to trap plastic on the surface while allowing marine life to swim safely beneath it.

Danger of giving public a 'magic solution'

Beyond the debate over The Ocean Cleanup's effectiveness, Jen Kennedy, executive director of the Blue Ocean Society for Marine Conservation, suggested they should also be mindful of their message to the public.

"I think this happens in a lot of situations where people just want this magic solution, which means they don't have to change their behaviour or do anything more difficult with their lives," she said.

"This big clean up thing is going to happen, and you can keep putting plastic in the ocean, and they're going to clean it up, and we don't have to worry about it anymore."

Scientists have urged people to focus on changing behaviour so plastic doesn't end up in the oceans at all. ( Supplied: Jen Kennedy )

But Mr Lebreton disagreed, saying that by showing the huge quantity of plastic retrieved by the project, the public can visualise the magnitude of the crisis.

"I don't think that's a valuable argument … no-one is saying, 'Let's keep putting plastic in the ocean because someone is going to clean it up for them'," he said.

"The whole idea is to bring it back to land and put it in front of people … it's really bringing that visibility there and helping people understand that we need to do something about it."

Dr Christian Schmidt — a hydrogeologist from the Helmholtz Centre for Environmental Research in Leipzig, who co-authored a 2017 study that found that nearly a quarter of ocean plastics came from 10 rivers in Asia and Africa — said that multiple strategies are needed.

"I think there's probably no one-size-fits-all strategy," Dr Schmidt said.

"Developing countries have very different problems and pathways for plastics entering the environment than industrial countries."

According to Dr Schmidt, the complexities of the issue and cultural differences in each national context means that while a prevention strategy will work in one instance, visual proof from groups like The Ocean Cleanup will be more successful in another.

But all the debate around their approach is not getting to The Ocean Cleanup, who are confident that if their current two-week trial of prototype "System 001" is successful, the group will be ready to tackle the Great Pacific Garbage Patch.

"The idea is, if everything goes well with System One, to scale up to about 60 systems, and by 2020 … hopefully start a clean up of the Great Pacific Garbage Patch," Mr Lebreton said.