A new study from the University of Canterbury has found that not even our humble compost is safe from the scourge of microplastics. 

At first, you could be looking at a beautiful piece of abstract art, or a collection of precious gemstones extracted from a distant planet. There’s what appears to be giant chunk of hot fuchsia-coloured quartz, toffee-coloured spidery clusters of alien DNA, and even a tiny electric blue replica of a human heart. But the reality is far bleaker: these are all tiny microplastic fragments that have been discovered in organic waste collected from across Aotearoa. 

University of Canterbury PhD student Helena Ruffell has spent the last two years looking for microplastics, aka the “needle in a haystack” nestled within our compost and other nutrient-rich biosolids (like the leftover sludge collected from wastewater plants). “Microplastics are basically really small pieces of plastic that either purposefully produced to be that small, for use in micro beads or glitter, or they’re broken down and fragmented into the environment,” she explained. 

The term microplastics was first coined in 2004 by professor Richard Thompson to describe fragments of plastic measuring as small as a millionth of a metre. Since then, microplastics have been found in places of increasing concern, be it the depths of the Mariana Trench, frozen into Arctic Sea ice, inside commercially caught fish off the New Zealand coast or, even closer to home, inside our hearts, blood and brain tissue. Now it is confirmed to be in our compost too. 

Collecting samples from council wastewater and composting facilities, private and community composting facilities, and commercial bagged compost from various garden centres, Ruffell’s study detected an average of between 1,100 and 2,700 microplastic particles per kilogram of local organic waste. “The thing that did surprise me the most was finding glitter, kitchen sponge, and all this multi-coloured rainbow film in the compost,” she said.

Although undetectable to the naked eye, these microplastics can have a huge impact. “The smaller they get, the more like toxic they can be, because they’re more available to a wider range of organisms,” Ruffell explained. “It can effect the soil, the microorganisms and the plants, which raises a few scary questions for food production security.” A 2022 study found that microplastics can cause “physiological toxicities” in plants, including inhibiting photosynthesis.  

“It kind of cuts out the food chain from the bottom,” Ruffell explained. “We know that plastic and its chemical additives are toxic. And with such a diverse range of plastics we’re all using, it turns into this big chemical cocktail getting put into our soil.” 

Also concerning for Ruffell was that some of the microplastics found in mature compost from commercial composting facilities were allegedly “biodegradable” packaging. “This was their one chance to biodegrade, because these facilities are supposed to provide the right conditions, but they have not biodegraded in 12 weeks,” she said. “So instead, it’s gonna be applied onto soil, and there’s no evidence that biodegradable plastics will actually biodegrade in soil.”

Although the findings are bleak, Ruffell doesn’t want people to get despondent, but instead take action. “We don’t want everyone to give up and start sending everything to landfill,” she said. “Organic waste and compost is still such a good source of carbon, nitrogen and other nutrients, and means we are not reliant on synthetic fertilisers or importing fertilisers which are potentially contaminated with other heavy metals, and it’s also promoting the circular economy.”

So for the average person, the biggest impact you can have – outside of not pouring glitter into your household green bin – is to be extremely intentional with your day-to-day purchasing. “Everyone just needs to be a bit more aware that every plastic product, no matter how robust it is, is contributing to this problem. Try and prioritise looking at reusable, refillable options. And please do not use a kitchen sponge, use a bamboo dish brush or a cloth instead.”

And in more positive news, Ruffell has even managed to find a creative byproduct during her grim hunt for nasty microplastics. “Everyone uses plastic and has a personal connection to it, and so I want to eventually do an art exhibition, because no one else in the world has pictures like this,” she said. “I’ve spent two years of my life on the end of the microscope, and it is really beautiful to look at all the unique rainbow colours and irregular shapes.”

“It’s just a shame,” she adds, “that what you’re really looking at is a tangible contaminant.”