Auckland's coastal environment has been found to be teeming with plastic particles – as one expert warns this week's bag ban won't be nearly enough to curb the problem.
Scion researchers surveyed 29 beaches and waterways around the city to find plastic microparticles were present in all of them.
These tiny traces, typically smaller than 5mm, are notorious for the threat they pose to marine life – and scientists are working to understand how they enter the foodchain and harm our own health.
At Manukau Harbour, the researchers found an average 1200 of the particles in every square metre, compared with 500 pieces per square metre in Waitemata Harbour.
The bulk of them were fibres – mostly plant-based ones like cellulose, but also polyethylene and polypropylene.
Such microfibres made up the overwhelming majority of microparticles found on shorelines around the world – and if they originated from textiles, washing machines and laundering facilities might be able to be targeted.
Some items of clothing had been reported to shed nearly two grams of fibre every time they were washed, Scion's packaging solutions research leader Kate Parker said.
Yet, because amounts found on west coast beaches were much higher than those on the east, it wasn't clear whether the microfibres had come from New Zealand, or been carried here by ocean currents.
In any case, the levels of plastic microparticles found in Auckland were similar to those found in an earlier study looking at waterways and beaches around the Christchurch region.
Scientists regarded Auckland, with its mix of different industrial, commercial and residential areas so close to the ocean, as an ideal laboratory to investigate the impact of plastic pollution on marine life.
The study also offered a baseline that New Zealand could work off to reduce this impact, partly through bringing in alternative options like marine degradable plastics.
There's a glaring lack of data about the scale of plastic pollution in New Zealand waters, and the new study, funded by the Ministry for the Environment, was among those trying to close the gap.
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.
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.
"While there is limited data for Aotearoa New Zealand, the available data indicates that microplastics are an issue for New Zealand's marine environment and urban waterways," said Associate Professor Sally Gaw, of the University of Canterbury.
"Microplastics have been found in beach sediments in Auckland and Christchurch, in urban waterways in Auckland and in green-lipped mussels from around the country.
"The ban on single-use plastic bags is a great start but on its own will not be enough to reduce the volumes of plastics entering the wider environment.
"New Zealanders will need to decide what appropriate uses of plastics are, and when it would be preferable to use less permanent alternatives."
Globally, 8 million tonnes of plastic was 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.