All of us are eating a lot of plastic without knowing it – maybe as much as a credit card amount each week, one recent report found – but now authorities have allayed some of the fears around what that means for our health.

At the same time, however, the World Health Organisation (WHO) also today found that there is a worrying amount we do not know about the growing scourge of broken down plastics, or microplastics.

"We urgently need to know more about the health impact of microplastics because they are everywhere - including in our drinking-water," said Dr Maria Neira, director of the WHO's Department of Public Health, Environment and Social Determinants of Health.

"Based on the limited information we have, microplastics in drinking water don't appear to pose a health risk at current levels. But we need to find out more. We also need to stop the rise in plastic pollution worldwide."


According to the 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.

Absorption and distribution of very small microplastic particles including in the nano size range may, however, be higher, although the data is extremely limited.

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.

Wastewater treatment could strip out more than 90 per cent of microplastics from wastewater, with the highest removal coming from tertiary treatment such as filtration, while conventional drinking-water treatment could remove particles smaller than a micrometre.

One report in June suggested people around the world were consuming about 2000 tiny pieces of plastic, 5g or the weight of a credit card, every week – that's equal to 21g a month, just over 250g a year.

But 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.

"We know from a recent New Zealand study that treated wastewater effluent also contains large amounts of microplastics, in line with international studies, which represents a direct source of microplastics to terrestrial, marine and freshwater environments," ESR senior scientist Dr Olga Pantos said.


"Although we do not know what the levels of microplastics are in New Zealand drinking water, based on international studies we may expect that the treatments used for the removal of microbiological contamination and turbidity of municipal supplies in New Zealand will be effective in also removing microplastics."

Associate Professor Duncan McGillivray, from the University of Auckland's School of Chemical Sciences, said Kiwis were more exposed to microplastics than we think.

"There are studies that have shown the presence of as much as 1000 particles per litre of bottled water."

Yet he said the main message from the WHO report was not to panic.

"Any potential health risk appears to be much less than other potential contaminants in drinking water such as bacteria and pollutant chemicals, and treatment systems that reduce those contaminants can do a good job of dealing with microplastics as well," he said.

"But we should not relax either - there are too many unknowns about how microplastics impact health, and the WHO report strongly encourages further research in the area.


"Even the definition of microplastics is not clearly agreed on, and the biological effect of a microplastic depends on complex combinations of factors including what it's made of, how big it is, and whatever it may have picked up as a surface coating.

"And overall, we just need to reduce the amount of plastic waste we are creating."