Researchers at the University of Waterloo have developed a new way to tackle one of the world’s most persistent forms of pollution: microplastics that slip through wastewater treatment plants and into rivers and lakes, and eventually into the food chain.
The team has engineered bacteria already found in wastewater systems to break down polyethylene terephthalate (PET), a common plastic used in clothing, carpets, and food and beverage containers.
PET plastics can take hundreds of years to degrade in the environment, slowly fragmenting into microplastics (plastic particles smaller than five millimetres total). These plastics are now found abundantly in water, soil, food, and even human blood.
Though tiny, the presence of these microplastics is alarming for several reasons. Organisms easily take up microplastics across the food web and, once ingested, accumulate in tissues in animals across the food chain.
Microplastics have already impacted animals, particularly in aquatic environments. The plastics can potentially block the digestive tracts of fish and invertebrates, reducing nutrient absorption and leading to starvation.
“Think of these bacteria that already exist in water systems to clean up microplastics as biorobots that can be programmed to get the job done,” said Marc Aucoin, a professor in the Department of Chemical Engineering. “Microplastics in water also enhance the spread of antibiotic resistance, so this breakthrough could also address that concern.”
Microplastics are small enough to pass through many wastewater treatment processes unchanged.
The current research suggests that even recycling facilities contribute to the problem: one recent study found that about six per cent of plastic processed at a recycling plant ended up as microplastics in wash water after filtration.
Globally, plastics production has surged since the 1950s. Between 1950 and 2015, roughly 4,900 megatonnes (about 59 per cent of all plastics ever produced) were discarded into landfills or the environment. If current trends continue, annual plastic waste generation is expected to nearly triple by 2060 compared to 2019 levels.
Microplastics are not just an environmental issue. Studies have linked chemicals found in plastics to insulin resistance, cancer, and reduced reproductive health. People who drink bottled water daily have been estimated to ingest tens of thousands more microplastic particles each year than those who do not.
Rather than introducing foreign organisms, the Waterloo researchers used bacteria already native to wastewater treatment plants and gave them a new ability: the capacity to biodegrade PET plastics.
The technique relies on a natural process known as horizontal gene transfer. This is sometimes also referred to as “bacterial sex”, where bacteria exchange genetic material as they multiply.
In the lab, researchers introduced DNA encoding a new plastic-degrading trait into wastewater bacteria using conjugative plasmids, allowing the trait to spread through bacterial populations.
A video released by the University of Waterloo research team visually shows this process, with red- and green-fluorescent strains of bacteria exchanging genetic material until the recipient bacteria acquire new characteristics.
The same gene-transfer mechanism is believed to be one of the main ways antibiotic-resistance genes spread in the environment, making it both powerful and well understood.
“We used this same gene-exchange technique to enable wastewater bacteria to degrade plastics,” Aucoin said.
Before the approach can be deployed outside the lab, the team is focusing on modelling how efficiently the bacteria pass along the new genetic information under different conditions.
“As next steps, we will use modelling to understand how well the bacteria transfer the new genetic information under different environmental conditions and thus how effectively they can break down the plastics,” said Brian Ingalls, a professor in the school’s Department of Applied Mathematics. “The long-term vision is to break down microplastics in wastewater treatment plants at scale.”
Wastewater facilities are the initial target, in part because of built-in safety measures.
“We will assess the risks of using engineered, plastic-eating bacteria in the natural environment,” said Aaron Yip, a PhD candidate in chemical engineering. “Right now, microplastic degradation in wastewater treatment plants is a safer application to target. Many of these facilities are already designed to neutralize bacteria in wastewater, which would kill any engineered bacteria before discharging water back into the environment.”
For communities across the region, the research shows how upstream innovation can reduce downstream pollution – protecting rivers, farmland, and drinking-water sources before plastics reach them.
While the initial focus is on wastewater treatment plants, the researchers say the long-term goal is to adapt the approach to help clean up plastic pollution in oceans and other natural environments, once safety and effectiveness are fully understood.
As plastic waste continues to rise worldwide, the researchers argue that biological solutions, which work with natural systems rather than against them, may be one of the few scalable ways to address pollution that conventional filtration and cleanup methods cannot capture.
