Microplastics have turned up inside green-lipped mussels - and researchers say we still don't understand what that means for people consuming the popular kaimoana species. Photo / File
Microplastics have turned up inside green-lipped mussels - and researchers say we still don't understand what that means for people consuming the popular kaimoana species. Photo / File
Microplastics have turned up inside green-lipped mussels – and researchers say we still don't understand what that means for people consuming the popular kaimoana species.
So small that they're typically invisible to the naked eye, microplastics nonetheless pose a goliath threat to our oceans.
These particles of broken-down plastic products are now being found within rainwater, sea salt, air and even us, entering the food chain through a range of species like tuna and mackerel.
University of Canterbury scientists set out to check the species after earlier studies indicated microplastics were widespread across New Zealand beaches.
Being filter feeders that siphon large volumes of water, and much larger than other mussel species used in studies overseas, made them important to assess.
Nine sampling sites were used so the team could get a clear idea of how concentrations varied around the country.
After the mussels were collected and shucked, the scientists physically extracted the microplastics and then counted each particle under microscopes.
They found microplastics were found in mussels at six out of the nine sites, at abundances ranging from zero to 1.5 particles per mussel.
The particles themselves varied in size from 50 to 700 micrometres, with a median diameter of 100 micrometres.
The most common plastic type found was polyethylene, which didn't surprise the team as it was the most commonly-used polymer in New Zealand.
So small that they're typically invisible to the naked eye, microplastics nonetheless pose a goliath threat to our oceans. Photo / File
Environmental chemist Associate Professor Sally Gaw said the concentrations were at the lower end of what had been reported for mussels in the Northern Hemisphere.
"We were surprised that the concentrations found did not correlate with population density as has been found overseas," said Gaw, who, with Professor Islay Marsden, supervised student Samantha Webb on the project.
"This may be due to New Zealand's overall lower population density."
But Gaw noted the research was a small pilot study that only aimed to determine if there was an issue – which meant the team could only draw on a limited number of mussels from a small number of sites.
They also found that microplastic contamination among mussels was "very variable".
"This is because we are literally looking for small bits of plastic and the number, types, colour and size can be very different for mussels collected from the same site at the same time, she said.
The findings prompted further questions that needed addressing.
"We need to determine the types and concentrations of microplastics in shellfish with different feeding mechanisms," Gaw said.
"Mussels are filter feeders so they take up microplastics from the water whereas other species like paua graze on algae.
"It would also be interesting to look at sediment dwelling organisms like polychaete worms to see if they have higher concentrations of microplastics."
And ultimately, we needed to know what eating polluted seafood meant for us.
"We don't yet know if there are human health implications for people consuming shellfish containing microplastics."
The scourge is the focus of several major studies now underway – one based at Auckland and Nelson, and another which has suggested fibres from washing clothes are the biggest part of the problem.
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 – it's estimated eight million tonnes of plastics now enter the sea each year – that the United Nations has likened its impacts to climate change.
