A new report suggests that people around the world are consuming an average five grams of plastic each week - or the weight of an Eftpos card. Photo / File
Scientists have just offered another grim comparison to the amount of plastic that humans could be unknowingly ingesting: the equivalent of a credit card, each week.
Herald science reporter Jamie Morton looks at five of the most alarming figures that have come out of recent research into the global scourge that is marine plastic pollution.
Take your bank card out of your wallet and imagine putting that inside you, each week.
A new report suggests that people are consuming about 2000 tiny pieces of plastic every week – that's equal to 21 grams a month, just over 250 grams a year, and five grams, or the weight of an Eftpos card.
Based on analysis from Australia's University of Newcastle, the WWF-commissioned report drew on data from more than 50 studies on the ingestion of microplastics by people.
The research found the single largest source of plastic ingestion was through water, both bottled and tap, all over the world.
Large regional variations were reported, with twice as much plastic found in the US or India than in European or Indonesian water.
Of the consumables studied, those with the highest recorded plastic levels included shellfish, salt - and beer.
What did that mean for human health?
The long-term effects weren't yet well documented, but studies have shown that beyond a certain exposure level, inhalation of plastic fibres seems to produce mild inflammation of the respiratory tract.
In marine animals, higher concentrations of microplastics in their digestive and respiratory system could lead to early death.
Research studies have demonstrated toxicity in vitro to lung cells, the liver, and brain cells, while some types of plastic carried chemicals and additives with potential effects on our health.
Scientists have singled out production process residues, additives, dyes and pigments found in plastic, some of which have been shown to have an influence on sexual function, fertility and even an increased occurrence of mutations and cancers.
The report pointed out that it was hard to narrow down the risk, given the overwhelming presence of plastic in our daily life.
Nonetheless, the findings were a wake-up call to governments, WWF International Director General Marco Lambertini said.
"Not only are plastics polluting our oceans and waterways and killing marine life - it's in all of us and we can't escape consuming plastics. Global action is urgent and essential to tackling this crisis."
As of today, a third of plastic waste ended up in nature, accounting for an astonishing 100 million metric tonnes of plastic waste in 2016.
Plastic was used as a disposable material to such an extent that more than three quarters of all plastic ever produced was chucked away.
And of that waste, about 87 per cent was leaked into nature and became plastic pollution.
In the ocean, plastic has been found at the bottom of the Mariana Trench, in Arctic sea ice, and, most recently, around Antarctica.
Here and overseas, more than 270 species, including mammals, reptiles, birds and fish, have been reported being entangled in plastic, something which often led to a slow and painful death.
Eight million tonnes of plastic is estimated to enter the ocean each year: that's roughly the equivalent weight of 24 jumbo jets, or Eden Park stadium stacked with plastic more than a kilometre high.
It was important to clarify that the estimate of eight million tonnes was a mean projection from 2015 – and the upper estimate was 12.7 million tonnes.
Plastic production has increased from 322 in 2015 - to 335 million tonnes in 2016, the latest data available shows.
If we assumed plastic production was increasing 4 per cent annually, that's around 348 million tonnes produced in 2017 – an extra 26 million tonnes since 2015, with a proportion of that ending up as waste in the ocean on top of that estimated eight million tonnes.
Without a complete dataset, it was hard to say accurately how much plastic there really was.
But, as Auckland University of Technology marine biologist Steph Borrelle told the Herald last year, we'd likely be underestimating, rather than overestimating the problem.
"While the metaphors of 'there will be more plastic in the ocean than fish by 2050' are not necessarily numerically accurate, they are a useful way of illustrating the scale of the problem and it also can help relate how plastic pollution could affect human food security."
There's a glaring lack of data about the scale of plastic pollution in New Zealand waters, particularly – but a range of new studies is trying to close that research gap.
What data we do have tells us that our coastal waters aren't immune to the global scourge.
One recent survey, carried out last year during the Pollution Use Resistance Education (PURE) Tour and Waka Odyssey Festival, collected samples between Hawke's Bay and Wellington, with further surveys on the city's Oriental Bay beach.
Microplastics are generally described as small particles, less than 5mm in diameter, that are either manufactured at that size or result from the physical breakdown of larger plastic pieces.
While there's now plenty of evidence around the impact on animals and ecosystems from large plastic items, notably single-use bags, less is known about damage wrought by this much smaller scourge.
The trawls recovered 21 microplastic fragments - mainly polyethylene and polypropylene, which, along with PET, polystyrene and PVC, also comprised the nearly 300 pieces found on the beach.
Most of the samples also came in the form of multi-coloured nurdles, which have been found on our beaches since the 1970s, and may have entered the environment through poor transport or handling.
As the survey wasn't a comprehensive one, it was difficult to extrapolate the results elsewhere to centres such as Auckland.
Auckland, along with Nelson, was meanwhile being used as a test site for a five-year, $12.5m project trying to understand the national picture.
Plastic pollution is also linked to another monster threat facing the planet: climate change.
Globally, overall CO2 emissions from the plastic life cycle are expected to increase by 50 per cent, while the CO2 increase from plastic incineration is set to triple by 2030, due to wrong waste management choices.
Plastics have surprisingly carbon-intense life cycles.
The overwhelming majority of plastic resins come from petroleum, which requires extraction and distillation. Then the resins are formed into products and transported to market.
All of these processes emit greenhouse gases, either directly or via the energy required to accomplish them – and the carbon footprint of plastics continues even after we've disposed of them.
Dumping, incinerating, recycling and composting (for certain plastics) all release carbon dioxide.
All told, the emissions from plastics in 2015 were equivalent to nearly 1.8 billion metric tonnes of CO2.
And researchers expect this number to grow.
They project the global demand for plastics will increase by some 22 per cent over the next five years.
This means we'll need to reduce emissions by 18 per cent just to break even.
On the current course, emissions from plastics will reach 17 per cent of the global carbon budget by 2050, according to a US study published in April.
The budget estimates the maximum amount of greenhouse gasses we can emit while still keeping global temperatures from rising more than 1.5C.
"If we truly want to limit global mean temperature rise from the pre-industrial era below 1.5C, there is no room for increasing greenhouse gas emissions, not to mention substantially increasing greenhouse gas emissions like what we have projected for the life cycle of plastics," said one of that study's authors, Professor Sangwon Suh of the University of California at Santa Barbara.
The 19-year-old disappeared without her wallet or mobile phone.