Samples collected from 39 spots around the region were now being analysed at Scion's labs in Rotorua.
This work would reveal what types of microplastics, and in what amounts, were present at which sites, so scientists could trace the pollution back to the source.
"The goal here is to qualify and quantify – we really have to know what we are dealing with," said Dr Florian Graichen, Scion's science leader for biopolymers and chemicals.
While there wasn't a single fix, part of the solution lay in the design of plastic products, he said.
"The next stage will be coming up with a plan to remove the dominant sources of these microplastics before they enter the New Zealand environment, and ideally introducing alternative options, such as biodegradable plastics, into manufacturing applications," he said.
"Traditionally, these have never been designed with end-of-life in mind – so we really need to open the minds of brand owners and consumers, because this needs to change."
The project, a collaboration between Scion and the University of Canterbury supported through the Government's Waste Minimisation Fund, was designed so its results could be shared and compared with other sites around the country and overseas.
It was one of several new projects trying to shed more light on the scale of the problem in New Zealand.
One major study just awarded a five-year $12.5m Government grant aimed to take a rigorous assessment, using Auckland and Nelson as test sites.
"Research into this area is fairly new to New Zealand and we need to do a lot more testing on a larger scale to see how much plastic is out there, not only in the marine but also freshwater and terrestrial ecosystems, and understand the risks they pose to ecosystems, animals and potentially humans," the study's leader, ESR scientist Dr Olga Pantos said.
While New Zealand has moved to ban microbeads, the wider problem of microplastics couldn't be tackled in the same way.
Current legislation encouraged product stewardship and environmental responsibility at the beginning of a product's life cycle.
Globally, microplastic pollution has become so invasive and ubiquitous that the United Nations recently likened its impacts to climate change.
This year, environmentalists were alarmed to discover microplastic pollution had reached the pristine waters of Antarctica.
It was estimated eight million tonnes of plastics now entered the sea each year - and with plastic production having ramped up 20-fold over the past 50 years, its volume in our oceans could outweigh that of even fish by the middle of this century.
