New study reveals how plastic particles travel

Plastic particles have now invaded natural spaces all over the globe, including the most remote regions of Antarctica and some of the deepest parts of the ocean. A new study from Princeton University describes how these particles move and accumulate in various types of environments worldwide. 

While it is known that microplastics are carried over long distances, the methods of transport have remained somewhat of a mystery. The researchers report that plastic particles get stuck as they travel through porous materials such as soil and sediment, and then break free and continue to travel. 

Professor Sujit Datta said that this is the first time this stop-and-restart process and the conditions that control it have been identified. Prior to this study, experts assumed that when microparticles got stuck, they generally stayed put.

According to the researchers, the microparticles are pushed free when the rate of fluid flowing through the soil, groundwater, or other repository remains persistent. The Princeton team showed that the process of deposition – the formation of clogs and their breakup – runs in cycles. Clogs are broken up by fluid pressure over time and distance, pushing particles further through the pore space until clogs reform.

“Not only did we find these cool dynamics of particles getting stuck, clogged, building up deposits and then getting pushed through, but that process enables particles to get spread out over much larger distances than we would have thought otherwise,” said Professor Datta.

Polystyrene is a plastic microparticle that makes up styrofoam, which is often dumped into soils and waterways through shipping materials and fast food containers. 

The researchers pumped fluorescent polystyrene microparticles and fluid through a transparent porous media created in Professor Datta’s lab. The transparency allowed them to watch the microparticles move under a microscope. 

“We figured out tricks to make the media transparent. Then, by using fluorescent microparticles, we can watch their dynamics in real time using a microscope,” said Professor Datta. “The nice thing is that we can actually see what individual particles are doing under different experimental conditions.”

Professor Philippe Coussot said the study authors took a remarkable approach that “opened the black box” to reveal how plastic particles move through natural environments. 

The ultimate goal is to use the findings to improve parameters for larger scale models to predict the amount and location of contamination. The research can inform mathematical models to predict the likelihood of a particle moving over a certain distance and reaching a vulnerable destination, such as a nearby farmland or river. This would help prevent the spread and accumulation of contaminants in food and water sources.

Professor Datta said this experiment is the tip of the iceberg in terms of particles and applications that researchers can now study. “Now that we found something so surprising in a system so simple, we’re excited to see what the implications are for more complex systems.”

The study is published in the journal Science Advances.

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By Chrissy Sexton, Earth.com Staff Writer