If you're concerned about microplastic pollution and are one of the majority of Australian households who use a dishwasher, you may not realise you are contributing to the problem.
Recent studies show washing plastic objects in dishwashers at high temperatures causes those items to shed micro and nano-sized particles, which can end up in wastewater and on our dinner plates.
We asked two experts about the impact washing plastic containers can have on the environment, the possible health implications and ways to help minimise the release of microplastics from our kitchens.
What happens to plastic containers and kitchenware in your dishwasher?
Elvis Okoffo is a research fellow at the Queensland Alliance for Environmental Health Sciences at the University of Queensland in Brisbane/Meanjin, and has been studying the volume of particles that are released from plastics when they are washed in a typical household dishwasher.
"We know there are a lot of plastics released from laundries, but one of the things people had not looked at was dishwashers," Dr Okoffo says.
His team's research involved placing containers made from common household plastics — polypropylene (PP), polyethylene (PE), polystyrene (PS), nylon, and polyethylene terephthalate (PET) — into a dishwasher and subjecting them to "chemical, thermal, and abrasive processes", including exposing them to water temperatures up to 70 degrees Celsius, detergents and repeated rinse cycles.
"These containers were all 'dishwasher safe'," Dr Okoffo adds, and says, "because of the temperature and the detergent, we [thought] these sorts of conditions would cause these plastics to release or shed particles from the dishwasher".
"Basically, that was what we found … in a washing cycle, you release about 920,000 micro and nanoparticles, and about 33 million particles per year."
What are microplastics and nanoplastics?
Microplastics are small fibres or fragments of plastic that range in size from a micrometre (one millionth of a metre) to 5 millimetres, and nanoplastics are even smaller particles.
As Dr Jordi Nelis, a laboratory manager and researcher at James Cook University, explains, "a nanometre is 1,000 times smaller than a micrometre".
Are plastic particles likely to go into your food?
Dr Nelis, who is based in Cairns, on the traditional lands of the Yirrganydji people, previously led studies into the pervasiveness of plastic in Australia's food supply at CSIRO, and says heating plastics can lead to the release of micro and nanoplastics, as well as plasticisers, which are substances added to increase the material's flexibility.
He says this is especially the case for less durable containers commonly used for takeaway foods and also advises against microwaving these types of containers, "especially if the food that's in there is a bit oily".
"What you end up doing is, you're just extracting compounds from the plastic into your food."
Dr Okoffo says his research also concluded "polypropylene containers, the takeaway containers that we all use, release more plastic particles than all the others, in terms of microplastics and nanoplastics".
Government statutory body Food Standards Australia New Zealand's website says its "current view is that plastic contamination of the food chain is unlikely to result in immediate health risks to consumers".
Dr Okoffo acknowledges that "we don't know the impacts [on human health] yet," but recommends exercising caution.
"Basically, we have seen plastics in drinking water and we've had a lot of reports of plastics ending up in the food chain, so if it goes into wastewater, goes into the treatment plants and then gets into the rivers and ocean, those particles could be consumed by marine organisms, which will end up on our plates in the grand scheme of things.
"I'm very cautious of what I use and very aware of the impact that I'm causing to the environment if I use plastics; I'm trying to help in my own daily activities."
Is it safer to wash plastic containers by hand?
Dr Okoffo says although tests showed washing containers in hot water in a dishwasher led them to release more particles, they still shed some particles when washed in cold water.
"So, washing the containers just by hand without using the dishwasher doesn't solve the problem," he says.
"It still releases particles, just in a lower number compared to when higher-temperature water is involved."
What can you use instead of plastic containers?
Dr Nelis suggests people "try to avoid using single plastic and plastic use as much as we can".
"I would advise anyone to not heat up food in a plastic container, use ceramic or glass or something instead."
It's a sentiment echoed by Dr Okoffo, who says he has phased out his use of plastics.
"I come to the office with a glass food container, I don't use plastic [containers] anymore, and I don't use plastic bottles anymore, I use stainless steel."
