Researchers at Washington State University have shown the fundamental mechanisms that allow tiny pieces of nanoscale plastic bags and foam packaging to move around in the environment.
Researchers have found that a silica surface such as sand has little effect in slowing the movement of plastics, but that natural organic matter resulting from the decomposition of plant and animal remains can temporarily or permanently trap the particles of nanoscale plastic, depending on the type. plastics.
The work, published in the journal Water research, could help researchers develop better ways to filter and clean ubiquitous plastics from the environment. Researchers include Indranil Chowdhury, assistant professor in the Department of Civil and Environmental Engineering at WSU, as well as Mehnaz Shams and Iftaykhairul Alam, recent graduates of the Civil Engineering program.
“We are looking to develop a filter that can be more efficient at removing these plastics,” Chowdhury said. “People have seen these plastics leaking into our drinking water, and our current drinking water system is not adequate enough to remove these micro and nanoscale plastics. This work is the first fundamental way to examine these mechanisms. “
By the 1950s, plastics had properties that made them useful in modern society. They are water resistant, inexpensive, easy to manufacture, and useful for a wide variety of uses. However, the build-up of plastics is becoming a growing concern around the world with giant patches of plastic waste floating in the oceans and plastic waste appearing in the most remote parts of the world.
“Plastics are a great invention and so easy to use, but they are so persistent in the environment,” Chowdhury said.
Once used, plastics degrade through chemical, mechanical and biological processes into micro and nanometric particles smaller than 100 nanometers. Despite their disposal in some wastewater treatment plants, large amounts of micro and nanoscale plastics are still found in the environment. More than 90% of tap water in the United States contains nanoscale plastics, Chowdhury said, and a 2019 study found that people eat about five grams of plastic per week or the amount of plastic in a card. credit. The health effects of such environmental pollution are not well understood.
“We don’t know the health effects and the toxicity is still unknown, but we continue to drink these plastics every day,” Chowdhury said.
As part of the new study, the researchers investigated the interactions with the environment of the smallest particles of the two most common types of plastics, polyethylene and polystyrene, to find out what could impede their movement. Polyethylene is used in plastic bags, milk cartons and food packaging, while polystyrene is a plastic foam used in foam cups and packaging materials.
In their work, the researchers found that polyethylene particles in plastic bags move easily in the environment – whether through a silica surface like sand or through natural organic matter. Sand and plastic particles repel each other in the same way as the poles of a magnet, so the plastic does not stick to the sand particles. The plastic particles glomerate on the natural organic matter which is ubiquitous in the natural aquatic environment, but only temporarily. They can be easily washed off with a change of chemistry in the water.
“This is bad news for polyethylene in the environment,” Chowdhury said. “It doesn’t stick much to the surface of silica and if it sticks to the surface of natural organic matter, it can be remobilized. Based on these results, this indicates that nanoscale polyethylene plastics can leak out. our drinking water treatment processes, in particular filtration. “
In the case of polystyrene particles, researchers have found better news. While a silica surface could not stop its movement, organic matter did. Once the polystyrene particles stuck to the organic material, they stayed in place.
The researchers hope the research will eventually help them develop filtration systems for water treatment facilities to remove plastic nanoparticles.
The work was funded by the State of Washington Water Research Center.