Scientists are learning about how broken down plastics affect fish – by feeding it to them.
Microplastics, one of the world's most pervasive pollutants, have now been found in the planet's most pristine ocean waters – and even rainwater.
But there's much that scientists still have to understand about the microscopic scourge – especially its impacts on our health and that of marine species.
In a two-part experiment, University of Auckland masters student Veronica Rotman has been feeding microplastics to snapper at Niwa's aquaculture research facility near Whangarei.
"It's critical to find out what's going on with plastic in our ecosystems," she said.
"I want to see whether the plastic is egested, remains in the gut or migrates to other parts of the fish, including the flesh we eat."
Rotman was using coloured polystyrene – one of the ocean's top five plastic polluters - and a blender to generate microplastics between 50 microns and 2mm in size.
She then soaked some samples in the Waitemata Harbour for just over a month to mimic similar conditions fishes experience in the environment.
"Plastic acts a sponge for pollutants, soaking up harbour waste - industrial chemicals, pesticides, heavy metals and bacteria, so I wanted a relevant environmental treatment."
Lastly, the polystyrene was being fed in varying amounts to 160 juvenile snapper held in 20 aquaculture tanks at Niwa's Northland Marine Research Centre at Bream Bay, along with their regular diet.
After 10 weeks of treatment the snapper would be dissected to determine how much the fish had retained.
She'd also be looking for any effects on growth or condition, whether it had done any damage to their gastrointestinal tract, and whether the microplastics translocated into the liver and muscular tissue.
"What I'm really interested in is the levels of toxicity caused by microplastics accumulating in the digestive tract," she said.
"The snapper experiment should shed some light on whether microplastics can translocate into the flesh we eat and how exposure may impact their physiology, reprodction and fitness."
The second part of the experiment will see the focus shift to hoki – New Zealand's most commercially valuable finfish species.
"It will be very interesting to see whether hoki are consuming microplastics and if there are any variations between the different sample locations due to proximity to human settlement and sources of pollution."
Her work came as the World Health Organisation somewhat allayed fears around the human consumption of microplastics.
According to its recent analysis, which summarised the latest knowledge on microplastics in drinking water, microplastics larger than 150 micrometres were not likely to be absorbed in the human body and uptake of smaller particles is expected to be limited.
But further research was needed to obtain a more accurate assessment of exposure to microplastics and their potential impacts on human health.
These included developing standard methods for measuring microplastic particles in water; more studies on the sources and occurrence of microplastics in fresh water; and the efficacy of different treatment processes.
Here in New Zealand, where groundwater and surface water are the major sources of drinking water, authorities didn't have good information on the burden of microplastics in our environments, or how they were getting there.
Plastics are also the focus of a renowned US scientist giving a talk at the University of Auckland next Tuesday evening.
Dr Pete Myers, chief executive and chief scientist of US organisation Environmental Health Sciences, has been at the forefront of research into how human health is affected by toxic pollutants - especially those that disrupt or interfere with our endocrine system.