Washing machine filters failing to stop microplastic pollutants ending up on Kiwi beaches

Alarming new microplastics research has sparked calls for better filters in household washing machines and water treatment plants.

Masters research scholarship student Anita du Plessis Lewis will present New Zealand's latest microplastics research on Thursday at the country's biggest-ever marine science gathering at Waikato University's Tauranga campus.

She took sediment and shellfish samples along 180 kilometres of Bay of Plenty coastline from Waihi Beach to Opotiki and found up to 11,000 tiny plastic particles per square metre. 

"People do have the perception they can't see it and it's not there but once you start sampling and look at the bivalve and sediment you realise we do have a massive problem," says du Plessis Lewis.

Particularly high levels were found in kaimoana like tuatua, wedge shells and cockles close to municipal outfalls and popular areas like Papamoa.

"Seafood gathering is a common practice and this research shows microplastics and nano-plastics are now bioaccumulating in our food chain."

Plastic beads, hundreds of tonnes of oil and containers decimated the Bay of Plenty's ecosystem in 2011 when the cargo ship Rena grounded on the Astrolabe reef.

Canterbury University's marine ecology research group head professor David Schiel was heavily involved in the cleanup operation. 

"All the logic in the world is not going to change how we ship food around, how we preserve it, pelletise it and make it available in shops. It's a huge problem."

Just last week the Government announced a ban on a raft of plastic products by 2025. 

Single-use plastics such as bags, plates, cutlery, drinking straws, fruit labels, PVC and polystyrene packaging will be phased out in three stages between 2022 and 2025.

Marine scientists believe more work to improve filters in the humble washing machine could help.

"We are all wearing plastic. If it's nylon, rayon, anything that's not 100 percent natural is spitting out microplastic pollutants. With no filter small enough to catch those particles it will end up in the marine environment," says du Plessis Lewis, who received a $23,000 Waikato University scholarship to fund her study.

She's not alone in calling for membranes in wastewater treatment plants to improve too.

They act like abrasives, breaking down microplastics into even smaller nano-plastics.

The country's biggest wastewater player Watercare says while work's underway in Europe there's no requirement here yet under New Zealand law to filter out nano-plastics.

It would require significant investment in ultrafiltration membranes.

"Any future development in this area will have to trade-off against the significant costs of treatment which are prohibitive… as well as a significant increase in the carbon footprint, power to run, and consumption of cleaning chemicals."

A trade-off we're unlikely to see for a while, no matter how loud the science is.