Of the 9 billion or so tonnes of plastics ever produced, only 9 per cent has ever been recycled, and of that only 10 per cent has been recycled a second time. "I find it horrifying," Ms Prince-Ruiz says.

'So angry'

In Mr Dee's case, coaxing positive environmental action had been his life for three decades.

It took a 2012 trip to Lord Howe Island - 600 kilometres off the NSW coast - to prompt "a real wake-up call" to target plastics.

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In an otherwise pristine rainforest, the founder of the DoSomething Foundation spied tiny mounds of plastic on the forest floor - detritus left after passing through chicks' bodies.

"It made me so angry," Mr Dee says. "We are literally trashing our environment."

Not that Mr Dee hadn't seen it coming. He co-organised Australia’s first plastic bag ban in the Tasmanian town of Coles Bay in 2003, and helped front South Australia's statewide ban in 2009.

Mr Dee has since worked closely with several states on their bag bans - including NSW - and continues to help nudge corporation and consumer behaviour towards conserving resources and recycling.

'Weak' evidence?

While plastic bag bans are spreading across the world, some Australian opponents have lately pointed to a 2006 Productivity Commission report that dismissed such an approach.

“Governments should ensure that any such regulation is likely to deliver a greater net benefit to the community - including impacts on the environment - than other policy options,” it said, adding that it deemed the evidence for backing a phase-out of plastic bags “appears particularly weak”.

Moreover, “the true extent to which plastic-bag litter injures populations of marine wildlife, as opposed to individual animals, is likely to remain very uncertain because it is extremely difficult to measure”, it said.

Supporters of the ban, though, say the Commission’s report is out of date, not least because there are likely hundreds of millions of plastic bags littered in the 12 years since in Australia alone.

'Our doors blown open'

Science is also getting a better grip on what plastic is doing in the oceans, not least forming five huge rubbish gyres, such as the Great Pacific Garbage Path between Hawaii and California.

“[P]lastic bags pose one of the greatest impacts to ocean wildlife,” a 2016 CSIRO-led paper in Marine Policy journal found. "[F]rom an environmental impact perspective, plastic bags warrant the specific attention they have received from governments and advocates to address their use."

Not only do animals get entangled in plastic, some such as turtles mistake them for jellyfish prey. Plastics also disintegrate in micro- or nano-sized fragments, some of which get injested along the foodchain.

"Plastics don’t break down, they break up," Jennifer Lavers, a marine biologist at the University of Tasmania, says, adding “they have the potential to cause tremendous damage”.

With about 10,000 man-made chemicals in play, "science can’t keep pace", Ms Lavers said.

Research is also targeting the chemicals the plastics themselves attract, and what happens when they get into the bloodstream of animals large and small, including humans.

"We’ll have our eyes opened and our doors blown open as we learn more and more," she says.

'Spurious' claims

Vaughan Levitzke, head of South Australia’s waste management, says he’s “constantly amazed” other states have taken so long to follow his state’s 2009 plastic bag ban.

Mr Levitzke, chief executive of Green Industries SA, dismisses as “spurious” recent claims in some tabloid media that re-using bags led to illness, adding that support for the single-use ban in his state continues to hover around 80 per cent.

Bans also force suppliers to look for alternative materials, such as compostable bags – which can replace those given at the grocers. “The early signs are really good,” he says.

Both Ms Prince-Ruis and Mr Dee attribute programs such as the ABC’s War on Waste and the BBC’s Blue Planet for boosting support to curb bags and other plastics, such as drinking straws.

"I'm really excited," Ms Prince-Ruis said. The anti-plastics movement "is much more mainstream, it's not just a fringe".