UBC researchers Dr. Tianyu Guo (front) and Marina Mehling
Researchers at the University of British Columbia have developed a filter that traps virtually all micro and nano plastics from water using bark and sawdust. The sawdust acts as a scaffold, drawing water through its aligned cellulosic fibres, while bark-derived tannic acid, which is immobilized on the scaffold, captures microplastics.
The magic ingredient is tannic acid, says Orlando Rojas, a professor in the departments of wood science, chemical and biological engineering, and chemistry. While unmodified sawdust filters less than 10% of microplastics from water, his team discovered adding tannic acid can remove 95.2% to 99.9% of plastic particles, including the very small ones that are harder to capture.
This is important because the smallest microplastics (110 nm or less) have a higher surface area and are more likely to get through the blood-to-brain barrier. This means they can accumulate in organs.
Tannic acid is a common and naturally occurring plant polyphenol – the same compound that makes your mouth pucker when you bite into unripe fruit. But the UBC researchers were more interested in its Swiss Army Knife-like properties.
It forms different types of bonds with a wide range of compounds. Rojas’s previous work used tannins to bind proteins, antibiotics and other drugs from poultry farm wastewater.
“Basically, we’ve been working with a universal biomolecule that has a special ability to bind with different compounds,” says Rojas. “This is how the idea came about.”
The team used scanning electron microscopy, flow cytometry and other techniques to show tannic acid removed a wide range of microplastics, including polystyrene, polymethyl methacrylate, polypropylene, polyvinyl chloride, polyethylene terephthalate, and polyethylene.
They also examined the organs of two groups of mice which were fed either the filtered or unfiltered water for one week. Those that drank the filtered water had fewer plastic particles in their organs.
What’s at stake
Microplastics are the result of the breakdown of water bottles, plastic bags or other things that started out larger. Clothing made of fleece or nylon can also shed microplastic fibres when washed, and those go down the drain and into the environment. Some companies add tiny plastic beads to toothpastes and skin-care products to help scrub away tooth plaque and dead skin cells. Then they, too, wash down the drain.
Ingredients in some plastics, such as polyvinyl chloride, can cause cancer, and phthalates — used to soften some types of plastics — can mimic the activity of hormones. These false hormones can cause unexpected changes in how cells grow and develop, leading to disease.
Plastic also can soak up pollution like a sponge. The pesticide DDT and PCBs are two types of toxic pollution found in plastics floating in the ocean.
Different types of wood waste can be used to create the water filter
The problem is that microplastics have been found just about everywhere in our water, air and soil. One study found that virtually all tap water is contaminated by microplastics, and other research states that more than 10 billion tons of mismanaged plastic waste will be released into the environment by 2025.
While we eliminate plastics from our bodies when we defecate, no one knows how long it takes for them to completely leave our system.
There are commercially available microplastic filters, such as those used to capture plastic fibres from washing machines. But unlike the UBC filter, which the team calls Biocap, they don’t capture the smallest particles, says Rojas.
Microplastics researcher Lisa Erdle agrees, calling the UBC team’s filter promising.
“Many commercial filters, like the filters used to capture microfibres from laundry, are capturing particles with a 100 micron mesh,” says Erdle, director of science and innovation at the 5 Gyres Institute. “Researchers in this study captured particles that were 0.1 micron in size, which is really small. If this technology were to scale up, to use commercially in filtering drinking water, or laundry effluent, it would be a natural replacement to many synthetic filters.”
While Biocap is still in the experimental stage, Rojas says it can be scaled up easily and inexpensively once they find the right industry partner.